From b54afb6046e08e4877319b91d56ca75b16980483 Mon Sep 17 00:00:00 2001
From: Light <VerodiciaTheNatureGoddess@gmail.com>
Date: Sat, 24 Jul 2021 13:54:50 +0430
Subject: [PATCH] Added EnTT

- Added EnTT
- Minor maintenance and fixes
---
 BuildScripts/build.lua                        |     1 +
 Dependencies/entt/build.lua                   |    36 +
 Dependencies/entt/entt.cpp                    |     1 +
 Dependencies/entt/entt.hpp                    | 48909 ++++++++++++++++
 Dependencies/stb_image/build.lua              |     4 +-
 Engine/build.lua                              |     4 +-
 Engine/src/Engine/Base.h                      |     1 -
 Engine/src/Engine/Debug/Logger.h              |     1 -
 Engine/src/Engine/Utility/ResourceManager.cpp |    18 +-
 .../GraphicsAPI/DirectX/dxGraphicsContext.cpp |     4 +-
 .../Platform/GraphicsAPI/OpenGL/glShader.cpp  |     2 -
 Mirror/build.lua                              |     1 +
 Sandbox/build.lua                             |     1 +
 13 files changed, 48965 insertions(+), 18 deletions(-)
 create mode 100644 Dependencies/entt/build.lua
 create mode 100644 Dependencies/entt/entt.cpp
 create mode 100644 Dependencies/entt/entt.hpp

diff --git a/BuildScripts/build.lua b/BuildScripts/build.lua
index 2499380..9a6b29a 100644
--- a/BuildScripts/build.lua
+++ b/BuildScripts/build.lua
@@ -26,3 +26,4 @@ include "../Dependencies/GLFW/build.lua"
 include "../Dependencies/GLAD/build.lua"
 include "../Dependencies/imgui/build.lua"
 include "../Dependencies/stb_image/build.lua"
+include "../Dependencies/entt/build.lua"
diff --git a/Dependencies/entt/build.lua b/Dependencies/entt/build.lua
new file mode 100644
index 0000000..bc10c38
--- /dev/null
+++ b/Dependencies/entt/build.lua
@@ -0,0 +1,36 @@
+project "entt"
+
+	location "%{wks.location}/Dependencies/entt"
+
+	-- Output Directories --
+	targetdir ("%{wks.location}/bin/"     .. outputdir)
+	objdir    ("%{wks.location}/bin-int/" .. outputdir)
+
+	-- Compiler --
+	kind "StaticLib"
+	language "C++"
+	cppdialect "C++17"
+	
+	optimize "on"
+
+	-- Project Files ---
+	files
+	{
+		"entt.cpp",
+		"entt.hpp",
+
+		"build.lua"
+	}
+	
+	--- Filters ---
+	-- windows
+	filter "system:windows"
+		systemversion "latest"
+		staticruntime "On"
+
+		defines 
+		{ 
+			"_CRT_SECURE_NO_WARNINGS",
+		}
+
+		flags { "MultiProcessorCompile" }
\ No newline at end of file
diff --git a/Dependencies/entt/entt.cpp b/Dependencies/entt/entt.cpp
new file mode 100644
index 0000000..d4a77e7
--- /dev/null
+++ b/Dependencies/entt/entt.cpp
@@ -0,0 +1 @@
+#include "entt.hpp"
\ No newline at end of file
diff --git a/Dependencies/entt/entt.hpp b/Dependencies/entt/entt.hpp
new file mode 100644
index 0000000..80a7790
--- /dev/null
+++ b/Dependencies/entt/entt.hpp
@@ -0,0 +1,48909 @@
+// #include "config/version.h"
+#ifndef ENTT_CONFIG_VERSION_H
+#define ENTT_CONFIG_VERSION_H
+
+
+#define ENTT_VERSION_MAJOR 3
+#define ENTT_VERSION_MINOR 8
+#define ENTT_VERSION_PATCH 0
+
+
+#endif
+
+// #include "core/algorithm.hpp"
+#ifndef ENTT_CORE_ALGORITHM_HPP
+#define ENTT_CORE_ALGORITHM_HPP
+
+
+#include <vector>
+#include <utility>
+#include <iterator>
+#include <algorithm>
+#include <functional>
+// #include "utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Function object to wrap `std::sort` in a class type.
+     *
+     * Unfortunately, `std::sort` cannot be passed as template argument to a class
+     * template or a function template.<br/>
+     * This class fills the gap by wrapping some flavors of `std::sort` in a
+     * function object.
+     */
+    struct std_sort {
+        /**
+         * @brief Sorts the elements in a range.
+         *
+         * Sorts the elements in a range using the given binary comparison function.
+         *
+         * @tparam It Type of random access iterator.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Args Types of arguments to forward to the sort function.
+         * @param first An iterator to the first element of the range to sort.
+         * @param last An iterator past the last element of the range to sort.
+         * @param compare A valid comparison function object.
+         * @param args Arguments to forward to the sort function, if any.
+         */
+        template<typename It, typename Compare = std::less<>, typename... Args>
+        void operator()(It first, It last, Compare compare = Compare{}, Args &&... args) const {
+            std::sort(std::forward<Args>(args)..., std::move(first), std::move(last), std::move(compare));
+        }
+    };
+
+
+    /*! @brief Function object for performing insertion sort. */
+    struct insertion_sort {
+        /**
+         * @brief Sorts the elements in a range.
+         *
+         * Sorts the elements in a range using the given binary comparison function.
+         *
+         * @tparam It Type of random access iterator.
+         * @tparam Compare Type of comparison function object.
+         * @param first An iterator to the first element of the range to sort.
+         * @param last An iterator past the last element of the range to sort.
+         * @param compare A valid comparison function object.
+         */
+        template<typename It, typename Compare = std::less<>>
+        void operator()(It first, It last, Compare compare = Compare{}) const {
+            if (first < last) {
+                for (auto it = first + 1; it < last; ++it) {
+                    auto value = std::move(*it);
+                    auto pre = it;
+
+                    for (; pre > first && compare(value, *(pre - 1)); --pre) {
+                        *pre = std::move(*(pre - 1));
+                    }
+
+                    *pre = std::move(value);
+                }
+            }
+        }
+    };
+
+
+    /**
+     * @brief Function object for performing LSD radix sort.
+     * @tparam Bit Number of bits processed per pass.
+     * @tparam N Maximum number of bits to sort.
+     */
+    template<std::size_t Bit, std::size_t N>
+    struct radix_sort {
+        static_assert((N% Bit) == 0, "The maximum number of bits to sort must be a multiple of the number of bits processed per pass");
+
+        /**
+         * @brief Sorts the elements in a range.
+         *
+         * Sorts the elements in a range using the given _getter_ to access the
+         * actual data to be sorted.
+         *
+         * This implementation is inspired by the online book
+         * [Physically Based Rendering](http://www.pbr-book.org/3ed-2018/Primitives_and_Intersection_Acceleration/Bounding_Volume_Hierarchies.html#RadixSort).
+         *
+         * @tparam It Type of random access iterator.
+         * @tparam Getter Type of _getter_ function object.
+         * @param first An iterator to the first element of the range to sort.
+         * @param last An iterator past the last element of the range to sort.
+         * @param getter A valid _getter_ function object.
+         */
+        template<typename It, typename Getter = identity>
+        void operator()(It first, It last, Getter getter = Getter{}) const {
+            if (first < last) {
+                static constexpr auto mask = (1 << Bit) - 1;
+                static constexpr auto buckets = 1 << Bit;
+                static constexpr auto passes = N / Bit;
+
+                using value_type = typename std::iterator_traits<It>::value_type;
+                std::vector<value_type> aux(std::distance(first, last));
+
+                auto part = [getter = std::move(getter)](auto from, auto to, auto out, auto start) {
+                    std::size_t index[buckets]{};
+                    std::size_t count[buckets]{};
+
+                    for (auto it = from; it != to; ++it) {
+                        ++count[(getter(*it) >> start) & mask];
+                    }
+
+                    for (std::size_t pos{}, end = buckets - 1u; pos < end; ++pos) {
+                        index[pos + 1u] = index[pos] + count[pos];
+                    }
+
+                    for (auto it = from; it != to; ++it) {
+                        out[index[(getter(*it) >> start) & mask]++] = std::move(*it);
+                    }
+                };
+
+                for (std::size_t pass = 0; pass < (passes & ~1); pass += 2) {
+                    part(first, last, aux.begin(), pass * Bit);
+                    part(aux.begin(), aux.end(), first, (pass + 1) * Bit);
+                }
+
+                if constexpr (passes & 1) {
+                    part(first, last, aux.begin(), (passes - 1) * Bit);
+                    std::move(aux.begin(), aux.end(), first);
+                }
+            }
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "core/any.hpp"
+#ifndef ENTT_CORE_ANY_HPP
+#define ENTT_CORE_ANY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+// #include "type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief A SBO friendly, type-safe container for single values of any type.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<std::size_t Len, std::size_t Align>
+    class basic_any {
+        enum class operation : std::uint8_t { COPY, MOVE, DTOR, COMP, ADDR, CADDR, TYPE };
+        enum class policy : std::uint8_t { OWNER, REF, CREF };
+
+        using storage_type = std::aligned_storage_t<Len + !Len, Align>;
+        using vtable_type = const void* (const operation, const basic_any&, void*);
+
+        template<typename Type>
+        static constexpr bool in_situ = Len && alignof(Type) <= alignof(storage_type) && sizeof(Type) <= sizeof(storage_type) && std::is_nothrow_move_constructible_v<Type>;
+
+        template<typename Type>
+        [[nodiscard]] static constexpr policy type_to_policy() {
+            if constexpr (std::is_lvalue_reference_v<Type>) {
+                if constexpr (std::is_const_v<std::remove_reference_t<Type>>) {
+                    return policy::CREF;
+                }
+                else {
+                    return policy::REF;
+                }
+            }
+            else {
+                return policy::OWNER;
+            }
+        }
+
+        template<typename Type>
+        [[nodiscard]] static bool compare(const void* lhs, const void* rhs) {
+            if constexpr (!std::is_function_v<Type> && is_equality_comparable_v<Type>) {
+                return *static_cast<const Type*>(lhs) == *static_cast<const Type*>(rhs);
+            }
+            else {
+                return lhs == rhs;
+            }
+        }
+
+        template<typename Type>
+        static const void* basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const basic_any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                const Type* instance = (in_situ<Type> && from.mode == policy::OWNER)
+                    ? ENTT_LAUNDER(reinterpret_cast<const Type*>(&from.storage))
+                    : static_cast<const Type*>(from.instance);
+
+                switch (op) {
+                case operation::COPY:
+                    if constexpr (std::is_copy_constructible_v<Type>) {
+                        static_cast<basic_any*>(to)->emplace<Type>(*instance);
+                    }
+                    break;
+                case operation::MOVE:
+                    if constexpr (in_situ<Type>) {
+                        if (from.mode == policy::OWNER) {
+                            return new (&static_cast<basic_any*>(to)->storage) Type{ std::move(*const_cast<Type*>(instance)) };
+                        }
+                    }
+
+                    return (static_cast<basic_any*>(to)->instance = std::exchange(const_cast<basic_any&>(from).instance, nullptr));
+                case operation::DTOR:
+                    if (from.mode == policy::OWNER) {
+                        if constexpr (in_situ<Type>) {
+                            instance->~Type();
+                        }
+                        else if constexpr (std::is_array_v<Type>) {
+                            delete[] instance;
+                        }
+                        else {
+                            delete instance;
+                        }
+                    }
+                    break;
+                case operation::COMP:
+                    return compare<Type>(instance, (*static_cast<const basic_any**>(to))->data()) ? to : nullptr;
+                case operation::ADDR:
+                    if (from.mode == policy::CREF) {
+                        return nullptr;
+                    }
+                    [[fallthrough]];
+                case operation::CADDR:
+                    return instance;
+                case operation::TYPE:
+                    *static_cast<type_info*>(to) = type_id<Type>();
+                    break;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<typename Type, typename... Args>
+        void initialize([[maybe_unused]] Args &&... args) {
+            if constexpr (!std::is_void_v<Type>) {
+                if constexpr (std::is_lvalue_reference_v<Type>) {
+                    static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
+                    instance = (std::addressof(args), ...);
+                }
+                else if constexpr (in_situ<Type>) {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        new (&storage) Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        new (&storage) Type(std::forward<Args>(args)...);
+                    }
+                }
+                else {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        instance = new Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        instance = new Type(std::forward<Args>(args)...);
+                    }
+                }
+            }
+        }
+
+        basic_any(const basic_any& other, const policy pol) ENTT_NOEXCEPT
+            : instance{ other.data() },
+            vtable{ other.vtable },
+            mode{ pol }
+        {}
+
+    public:
+        /*! @brief Size of the internal storage. */
+        static constexpr auto length = Len;
+        /*! @brief Alignment requirement. */
+        static constexpr auto alignment = Align;
+
+        /*! @brief Default constructor. */
+        basic_any() ENTT_NOEXCEPT
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_any(std::in_place_type_t<Type>, Args &&... args)
+            : instance{},
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> },
+            mode{ type_to_policy<Type>() }
+        {
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        basic_any(std::reference_wrapper<Type> value) ENTT_NOEXCEPT
+            : basic_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
+        basic_any(Type&& value)
+            : instance{},
+            vtable{ &basic_vtable<std::decay_t<Type>> },
+            mode{ policy::OWNER }
+        {
+            initialize<std::decay_t<Type>>(std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_any(const basic_any& other)
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {
+            other.vtable(operation::COPY, other, this);
+        }
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_any(basic_any&& other) ENTT_NOEXCEPT
+            : instance{},
+            vtable{ other.vtable },
+            mode{ other.mode }
+        {
+            vtable(operation::MOVE, other, this);
+        }
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~basic_any() {
+            vtable(operation::DTOR, *this, nullptr);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This any object.
+         */
+        basic_any& operator=(const basic_any& other) {
+            reset();
+            other.vtable(operation::COPY, other, this);
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This any object.
+         */
+        basic_any& operator=(basic_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, other.vtable)(operation::DTOR, *this, nullptr);
+            other.vtable(operation::MOVE, other, this);
+            mode = other.mode;
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_any<T &>, emplace<Type &> or forward_as_any instead")]]
+        basic_any& operator=(std::reference_wrapper<Type> value) ENTT_NOEXCEPT {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            type_info info{};
+            vtable(operation::TYPE, *this, &info);
+            return info;
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return vtable(operation::CADDR, *this, nullptr);
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return const_cast<void*>(vtable(operation::ADDR, *this, nullptr));
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, *this, nullptr);
+            mode = type_to_policy<Type>();
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, *this, nullptr);
+            mode = policy::OWNER;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is empty, true otherwise.
+         * @return False if the wrapper is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable(operation::CADDR, *this, nullptr) == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        bool operator==(const basic_any& other) const ENTT_NOEXCEPT {
+            const basic_any* trampoline = &other;
+            return type() == other.type() && (vtable(operation::COMP, *this, &trampoline) || !other.data());
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_any as_ref() ENTT_NOEXCEPT {
+            return basic_any{ *this, (mode == policy::CREF ? policy::CREF : policy::REF) };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_any as_ref() const ENTT_NOEXCEPT {
+            return basic_any{ *this, policy::CREF };
+        }
+
+        /**
+         * @brief Returns true if a wrapper owns its object, false otherwise.
+         * @return True if the wrapper owns its object, false otherwise.
+         */
+        [[nodiscard]] bool owner() const ENTT_NOEXCEPT {
+            return (mode == policy::OWNER);
+        }
+
+    private:
+        union { const void* instance; storage_type storage; };
+        vtable_type* vtable;
+        policy mode;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    template<std::size_t Len, std::size_t Align>
+    [[nodiscard]] inline bool operator!=(const basic_any<Len, Align>& lhs, const basic_any<Len, Align>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Performs type-safe access to the contained object.
+     * @tparam Type Type to which conversion is required.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param data Target any object.
+     * @return The element converted to the requested type.
+     */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(const basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        const auto* const instance = any_cast<std::remove_reference_t<Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>&& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(std::move(*instance));
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    const Type* any_cast(const basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        return (data->type() == type_id<Type>() ? static_cast<const Type*>(data->data()) : nullptr);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type* any_cast(basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        // last attempt to make wrappers for const references return their values
+        return (data->type() == type_id<Type>() ? static_cast<Type*>(static_cast<constness_as_t<basic_any<Len, Align>, Type> *>(data)->data()) : nullptr);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
+    basic_any<Len, Align> make_any(Args &&... args) {
+        return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
+    basic_any<Len, Align> forward_as_any(Type&& value) {
+        return basic_any<Len, Align>{std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value)};
+    }
+
+
+}
+
+
+#endif
+
+// #include "core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "core/family.hpp"
+#ifndef ENTT_CORE_FAMILY_HPP
+#define ENTT_CORE_FAMILY_HPP
+
+
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Dynamic identifier generator.
+     *
+     * Utility class template that can be used to assign unique identifiers to types
+     * at runtime. Use different specializations to create separate sets of
+     * identifiers.
+     */
+    template<typename...>
+    class family {
+        inline static ENTT_MAYBE_ATOMIC(id_type) identifier {};
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using family_type = id_type;
+
+        /*! @brief Statically generated unique identifier for the given type. */
+        template<typename... Type>
+        // at the time I'm writing, clang crashes during compilation if auto is used instead of family_type
+        inline static const family_type type = identifier++;
+    };
+
+
+}
+
+
+#endif
+
+// #include "core/hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "core/ident.hpp"
+#ifndef ENTT_CORE_IDENT_HPP
+#define ENTT_CORE_IDENT_HPP
+
+
+#include <cstddef>
+#include <utility>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+// #include "type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Types identifiers.
+     *
+     * Variable template used to generate identifiers at compile-time for the given
+     * types. Use the `get` member function to know what's the identifier associated
+     * to the specific type.
+     *
+     * @note
+     * Identifiers are constant expression and can be used in any context where such
+     * an expression is required. As an example:
+     * @code{.cpp}
+     * using id = entt::identifier<a_type, another_type>;
+     *
+     * switch(a_type_identifier) {
+     * case id::type<a_type>:
+     *     // ...
+     *     break;
+     * case id::type<another_type>:
+     *     // ...
+     *     break;
+     * default:
+     *     // ...
+     * }
+     * @endcode
+     *
+     * @tparam Types List of types for which to generate identifiers.
+     */
+    template<typename... Types>
+    class identifier {
+        template<typename Type, std::size_t... Index>
+        [[nodiscard]] static constexpr id_type get(std::index_sequence<Index...>) {
+            static_assert(std::disjunction_v<std::is_same<Type, Types>...>, "Invalid type");
+            return (0 + ... + (std::is_same_v<Type, type_list_element_t<Index, type_list<std::decay_t<Types>...>>> ? id_type{ Index } : id_type{}));
+        }
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using identifier_type = id_type;
+
+        /*! @brief Statically generated unique identifier for the given type. */
+        template<typename Type>
+        static constexpr identifier_type type = get<std::decay_t<Type>>(std::index_sequence_for<Types...>{});
+    };
+
+
+}
+
+
+#endif
+
+// #include "core/monostate.hpp"
+#ifndef ENTT_CORE_MONOSTATE_HPP
+#define ENTT_CORE_MONOSTATE_HPP
+
+
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Minimal implementation of the monostate pattern.
+     *
+     * A minimal, yet complete configuration system built on top of the monostate
+     * pattern. Thread safe by design, it works only with basic types like `int`s or
+     * `bool`s.<br/>
+     * Multiple types and therefore more than one value can be associated with a
+     * single key. Because of this, users must pay attention to use the same type
+     * both during an assignment and when they try to read back their data.
+     * Otherwise, they can incur in unexpected results.
+     */
+    template<id_type>
+    struct monostate {
+        /**
+         * @brief Assigns a value of a specific type to a given key.
+         * @tparam Type Type of the value to assign.
+         * @param val User data to assign to the given key.
+         */
+        template<typename Type>
+        void operator=(Type val) const ENTT_NOEXCEPT {
+            value<Type> = val;
+        }
+
+        /**
+         * @brief Gets a value of a specific type for a given key.
+         * @tparam Type Type of the value to get.
+         * @return Stored value, if any.
+         */
+        template<typename Type>
+        operator Type() const ENTT_NOEXCEPT {
+            return value<Type>;
+        }
+
+    private:
+        template<typename Type>
+        inline static ENTT_MAYBE_ATOMIC(Type) value {};
+    };
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Value Value used to differentiate between different variables.
+     */
+    template<id_type Value>
+    inline monostate<Value> monostate_v = {};
+
+
+}
+
+
+#endif
+
+// #include "core/type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "hashed_string.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/component.hpp"
+#ifndef ENTT_ENTITY_COMPONENT_HPP
+#define ENTT_ENTITY_COMPONENT_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Commonly used default traits for all types. */
+    struct basic_component_traits {
+        /*! @brief Pointer stability, default is `std::false_type`. */
+        using in_place_delete = std::false_type;
+        /*! @brief Empty type optimization, default is `ENTT_IGNORE_IF_EMPTY`. */
+        using ignore_if_empty = ENTT_IGNORE_IF_EMPTY;
+    };
+
+
+    /**
+     * @brief Common way to access various properties of components.
+     * @tparam Type Type of component.
+     */
+    template<typename Type, typename = void>
+    struct component_traits : basic_component_traits {
+        static_assert(std::is_same_v<std::decay_t<Type>, Type>, "Unsupported type");
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/entity.hpp"
+#ifndef ENTT_ENTITY_ENTITY_HPP
+#define ENTT_ENTITY_ENTITY_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename, typename = void>
+        struct entt_traits;
+
+
+        template<typename Type>
+        struct entt_traits<Type, std::enable_if_t<std::is_enum_v<Type>>>
+            : entt_traits<std::underlying_type_t<Type>>
+        {};
+
+
+        template<typename Type>
+        struct entt_traits<Type, std::enable_if_t<std::is_class_v<Type>>>
+            : entt_traits<typename Type::entity_type>
+        {};
+
+
+        template<>
+        struct entt_traits<std::uint32_t> {
+            using entity_type = std::uint32_t;
+            using version_type = std::uint16_t;
+            using difference_type = std::int64_t;
+
+            static constexpr entity_type entity_mask = 0xFFFFF;
+            static constexpr entity_type version_mask = 0xFFF;
+            static constexpr std::size_t entity_shift = 20u;
+        };
+
+
+        template<>
+        struct entt_traits<std::uint64_t> {
+            using entity_type = std::uint64_t;
+            using version_type = std::uint32_t;
+            using difference_type = std::int64_t;
+
+            static constexpr entity_type entity_mask = 0xFFFFFFFF;
+            static constexpr entity_type version_mask = 0xFFFFFFFF;
+            static constexpr std::size_t entity_shift = 32u;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Entity traits.
+      * @tparam Type Type of identifier.
+      */
+    template<typename Type>
+    class entt_traits : private internal::entt_traits<Type> {
+        using traits_type = internal::entt_traits<Type>;
+
+    public:
+        /*! @brief Value type. */
+        using value_type = Type;
+        /*! @brief Underlying entity type. */
+        using entity_type = typename traits_type::entity_type;
+        /*! @brief Underlying version type. */
+        using version_type = typename traits_type::version_type;
+        /*! @brief Difference type. */
+        using difference_type = typename traits_type::difference_type;
+
+        /**
+         * @brief Converts an entity to its underlying type.
+         * @param value The value to convert.
+         * @return The integral representation of the given value.
+         */
+        [[nodiscard]] static constexpr entity_type to_integral(const value_type value) ENTT_NOEXCEPT {
+            return static_cast<entity_type>(value);
+        }
+
+        /**
+         * @brief Returns the entity part once converted to the underlying type.
+         * @param value The value to convert.
+         * @return The integral representation of the entity part.
+         */
+        [[nodiscard]] static constexpr entity_type to_entity(const value_type value) ENTT_NOEXCEPT {
+            return (to_integral(value) & traits_type::entity_mask);
+        }
+
+        /**
+         * @brief Returns the version part once converted to the underlying type.
+         * @param value The value to convert.
+         * @return The integral representation of the version part.
+         */
+        [[nodiscard]] static constexpr version_type to_version(const value_type value) ENTT_NOEXCEPT {
+            constexpr auto mask = (traits_type::version_mask << traits_type::entity_shift);
+            return ((to_integral(value) & mask) >> traits_type::entity_shift);
+        }
+
+        /**
+         * @brief Constructs an identifier from its parts.
+         *
+         * If the version part is not provided, a tombstone is returned.<br/>
+         * If the entity part is not provided, a null identifier is returned.
+         *
+         * @param entity The entity part of the identifier.
+         * @param version The version part of the identifier.
+         * @return A properly constructed identifier.
+         */
+        [[nodiscard]] static constexpr value_type construct(const entity_type entity = traits_type::entity_mask, const version_type version = traits_type::version_mask) ENTT_NOEXCEPT {
+            return value_type{ (entity & traits_type::entity_mask) | (version << traits_type::entity_shift) };
+        }
+    };
+
+
+    /**
+     * @brief Converts an entity to its underlying type.
+     * @tparam Entity The value type.
+     * @param entity The value to convert.
+     * @return The integral representation of the given value.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr auto to_integral(const Entity entity) ENTT_NOEXCEPT {
+        return entt_traits<Entity>::to_integral(entity);
+    }
+
+
+    /*! @brief Null object for all entity identifiers.  */
+    struct null_t {
+        /**
+         * @brief Converts the null object to identifiers of any type.
+         * @tparam Entity Type of entity identifier.
+         * @return The null representation for the given type.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct();
+        }
+
+        /**
+         * @brief Compares two null objects.
+         * @param other A null object.
+         * @return True in all cases.
+         */
+        [[nodiscard]] constexpr bool operator==([[maybe_unused]] const null_t other) const ENTT_NOEXCEPT {
+            return true;
+        }
+
+        /**
+         * @brief Compares two null objects.
+         * @param other A null object.
+         * @return False in all cases.
+         */
+        [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const null_t other) const ENTT_NOEXCEPT {
+            return false;
+        }
+
+        /**
+         * @brief Compares a null object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return False if the two elements differ, true otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::to_entity(entity) == entt_traits<Entity>::to_entity(*this);
+        }
+
+        /**
+         * @brief Compares a null object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return True if the two elements differ, false otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator!=(const Entity entity) const ENTT_NOEXCEPT {
+            return !(entity == *this);
+        }
+
+        /**
+         * @brief Creates a null object from an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier to turn into a null object.
+         * @return The null representation for the given identifier.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr Entity operator|(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct(entt_traits<Entity>::to_entity(*this), entt_traits<Entity>::to_version(entity));
+        }
+    };
+
+
+    /**
+     * @brief Compares a null object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A null object yet to be converted.
+     * @return False if the two elements differ, true otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator==(const Entity entity, const null_t other) ENTT_NOEXCEPT {
+        return other.operator==(entity);
+    }
+
+
+    /**
+     * @brief Compares a null object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A null object yet to be converted.
+     * @return True if the two elements differ, false otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator!=(const Entity entity, const null_t other) ENTT_NOEXCEPT {
+        return !(other == entity);
+    }
+
+
+    /*! @brief Tombstone object for all entity identifiers.  */
+    struct tombstone_t {
+        /**
+         * @brief Converts the tombstone object to identifiers of any type.
+         * @tparam Entity Type of entity identifier.
+         * @return The tombstone representation for the given type.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct();
+        }
+
+        /**
+         * @brief Compares two tombstone objects.
+         * @param other A tombstone object.
+         * @return True in all cases.
+         */
+        [[nodiscard]] constexpr bool operator==([[maybe_unused]] const tombstone_t other) const ENTT_NOEXCEPT {
+            return true;
+        }
+
+        /**
+         * @brief Compares two tombstone objects.
+         * @param other A tombstone object.
+         * @return False in all cases.
+         */
+        [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const tombstone_t other) const ENTT_NOEXCEPT {
+            return false;
+        }
+
+        /**
+         * @brief Compares a tombstone object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return False if the two elements differ, true otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::to_version(entity) == entt_traits<Entity>::to_version(*this);
+        }
+
+        /**
+         * @brief Compares a tombstone object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return True if the two elements differ, false otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator!=(const Entity entity) const ENTT_NOEXCEPT {
+            return !(entity == *this);
+        }
+
+        /**
+         * @brief Creates a tombstone object from an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier to turn into a tombstone object.
+         * @return The tombstone representation for the given identifier.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr Entity operator|(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct(entt_traits<Entity>::to_entity(entity));
+        }
+    };
+
+
+    /**
+     * @brief Compares a tombstone object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A tombstone object yet to be converted.
+     * @return False if the two elements differ, true otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator==(const Entity entity, const tombstone_t other) ENTT_NOEXCEPT {
+        return other.operator==(entity);
+    }
+
+
+    /**
+     * @brief Compares a tombstone object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A tombstone object yet to be converted.
+     * @return True if the two elements differ, false otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator!=(const Entity entity, const tombstone_t other) ENTT_NOEXCEPT {
+        return !(other == entity);
+    }
+
+
+    /**
+     * @brief Compile-time constant for null entities.
+     *
+     * There exist implicit conversions from this variable to entity identifiers of
+     * any allowed type. Similarly, there exist comparision operators between the
+     * null entity and any other entity identifier.
+     */
+    inline constexpr null_t null{};
+
+
+    /**
+     * @brief Compile-time constant for tombstone entities.
+     *
+     * There exist implicit conversions from this variable to entity identifiers of
+     * any allowed type. Similarly, there exist comparision operators between the
+     * tombstone entity and any other entity identifier.
+     */
+    inline constexpr tombstone_t tombstone{};
+
+
+}
+
+
+#endif
+
+// #include "entity/group.hpp"
+#ifndef ENTT_ENTITY_GROUP_HPP
+#define ENTT_ENTITY_GROUP_HPP
+
+
+#include <tuple>
+#include <utility>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "entity.hpp"
+#ifndef ENTT_ENTITY_ENTITY_HPP
+#define ENTT_ENTITY_ENTITY_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename, typename = void>
+        struct entt_traits;
+
+
+        template<typename Type>
+        struct entt_traits<Type, std::enable_if_t<std::is_enum_v<Type>>>
+            : entt_traits<std::underlying_type_t<Type>>
+        {};
+
+
+        template<typename Type>
+        struct entt_traits<Type, std::enable_if_t<std::is_class_v<Type>>>
+            : entt_traits<typename Type::entity_type>
+        {};
+
+
+        template<>
+        struct entt_traits<std::uint32_t> {
+            using entity_type = std::uint32_t;
+            using version_type = std::uint16_t;
+            using difference_type = std::int64_t;
+
+            static constexpr entity_type entity_mask = 0xFFFFF;
+            static constexpr entity_type version_mask = 0xFFF;
+            static constexpr std::size_t entity_shift = 20u;
+        };
+
+
+        template<>
+        struct entt_traits<std::uint64_t> {
+            using entity_type = std::uint64_t;
+            using version_type = std::uint32_t;
+            using difference_type = std::int64_t;
+
+            static constexpr entity_type entity_mask = 0xFFFFFFFF;
+            static constexpr entity_type version_mask = 0xFFFFFFFF;
+            static constexpr std::size_t entity_shift = 32u;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Entity traits.
+      * @tparam Type Type of identifier.
+      */
+    template<typename Type>
+    class entt_traits : private internal::entt_traits<Type> {
+        using traits_type = internal::entt_traits<Type>;
+
+    public:
+        /*! @brief Value type. */
+        using value_type = Type;
+        /*! @brief Underlying entity type. */
+        using entity_type = typename traits_type::entity_type;
+        /*! @brief Underlying version type. */
+        using version_type = typename traits_type::version_type;
+        /*! @brief Difference type. */
+        using difference_type = typename traits_type::difference_type;
+
+        /**
+         * @brief Converts an entity to its underlying type.
+         * @param value The value to convert.
+         * @return The integral representation of the given value.
+         */
+        [[nodiscard]] static constexpr entity_type to_integral(const value_type value) ENTT_NOEXCEPT {
+            return static_cast<entity_type>(value);
+        }
+
+        /**
+         * @brief Returns the entity part once converted to the underlying type.
+         * @param value The value to convert.
+         * @return The integral representation of the entity part.
+         */
+        [[nodiscard]] static constexpr entity_type to_entity(const value_type value) ENTT_NOEXCEPT {
+            return (to_integral(value) & traits_type::entity_mask);
+        }
+
+        /**
+         * @brief Returns the version part once converted to the underlying type.
+         * @param value The value to convert.
+         * @return The integral representation of the version part.
+         */
+        [[nodiscard]] static constexpr version_type to_version(const value_type value) ENTT_NOEXCEPT {
+            constexpr auto mask = (traits_type::version_mask << traits_type::entity_shift);
+            return ((to_integral(value) & mask) >> traits_type::entity_shift);
+        }
+
+        /**
+         * @brief Constructs an identifier from its parts.
+         *
+         * If the version part is not provided, a tombstone is returned.<br/>
+         * If the entity part is not provided, a null identifier is returned.
+         *
+         * @param entity The entity part of the identifier.
+         * @param version The version part of the identifier.
+         * @return A properly constructed identifier.
+         */
+        [[nodiscard]] static constexpr value_type construct(const entity_type entity = traits_type::entity_mask, const version_type version = traits_type::version_mask) ENTT_NOEXCEPT {
+            return value_type{ (entity & traits_type::entity_mask) | (version << traits_type::entity_shift) };
+        }
+    };
+
+
+    /**
+     * @brief Converts an entity to its underlying type.
+     * @tparam Entity The value type.
+     * @param entity The value to convert.
+     * @return The integral representation of the given value.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr auto to_integral(const Entity entity) ENTT_NOEXCEPT {
+        return entt_traits<Entity>::to_integral(entity);
+    }
+
+
+    /*! @brief Null object for all entity identifiers.  */
+    struct null_t {
+        /**
+         * @brief Converts the null object to identifiers of any type.
+         * @tparam Entity Type of entity identifier.
+         * @return The null representation for the given type.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct();
+        }
+
+        /**
+         * @brief Compares two null objects.
+         * @param other A null object.
+         * @return True in all cases.
+         */
+        [[nodiscard]] constexpr bool operator==([[maybe_unused]] const null_t other) const ENTT_NOEXCEPT {
+            return true;
+        }
+
+        /**
+         * @brief Compares two null objects.
+         * @param other A null object.
+         * @return False in all cases.
+         */
+        [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const null_t other) const ENTT_NOEXCEPT {
+            return false;
+        }
+
+        /**
+         * @brief Compares a null object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return False if the two elements differ, true otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::to_entity(entity) == entt_traits<Entity>::to_entity(*this);
+        }
+
+        /**
+         * @brief Compares a null object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return True if the two elements differ, false otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator!=(const Entity entity) const ENTT_NOEXCEPT {
+            return !(entity == *this);
+        }
+
+        /**
+         * @brief Creates a null object from an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier to turn into a null object.
+         * @return The null representation for the given identifier.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr Entity operator|(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct(entt_traits<Entity>::to_entity(*this), entt_traits<Entity>::to_version(entity));
+        }
+    };
+
+
+    /**
+     * @brief Compares a null object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A null object yet to be converted.
+     * @return False if the two elements differ, true otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator==(const Entity entity, const null_t other) ENTT_NOEXCEPT {
+        return other.operator==(entity);
+    }
+
+
+    /**
+     * @brief Compares a null object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A null object yet to be converted.
+     * @return True if the two elements differ, false otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator!=(const Entity entity, const null_t other) ENTT_NOEXCEPT {
+        return !(other == entity);
+    }
+
+
+    /*! @brief Tombstone object for all entity identifiers.  */
+    struct tombstone_t {
+        /**
+         * @brief Converts the tombstone object to identifiers of any type.
+         * @tparam Entity Type of entity identifier.
+         * @return The tombstone representation for the given type.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct();
+        }
+
+        /**
+         * @brief Compares two tombstone objects.
+         * @param other A tombstone object.
+         * @return True in all cases.
+         */
+        [[nodiscard]] constexpr bool operator==([[maybe_unused]] const tombstone_t other) const ENTT_NOEXCEPT {
+            return true;
+        }
+
+        /**
+         * @brief Compares two tombstone objects.
+         * @param other A tombstone object.
+         * @return False in all cases.
+         */
+        [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const tombstone_t other) const ENTT_NOEXCEPT {
+            return false;
+        }
+
+        /**
+         * @brief Compares a tombstone object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return False if the two elements differ, true otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::to_version(entity) == entt_traits<Entity>::to_version(*this);
+        }
+
+        /**
+         * @brief Compares a tombstone object and an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier with which to compare.
+         * @return True if the two elements differ, false otherwise.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr bool operator!=(const Entity entity) const ENTT_NOEXCEPT {
+            return !(entity == *this);
+        }
+
+        /**
+         * @brief Creates a tombstone object from an entity identifier of any type.
+         * @tparam Entity Type of entity identifier.
+         * @param entity Entity identifier to turn into a tombstone object.
+         * @return The tombstone representation for the given identifier.
+         */
+        template<typename Entity>
+        [[nodiscard]] constexpr Entity operator|(const Entity entity) const ENTT_NOEXCEPT {
+            return entt_traits<Entity>::construct(entt_traits<Entity>::to_entity(entity));
+        }
+    };
+
+
+    /**
+     * @brief Compares a tombstone object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A tombstone object yet to be converted.
+     * @return False if the two elements differ, true otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator==(const Entity entity, const tombstone_t other) ENTT_NOEXCEPT {
+        return other.operator==(entity);
+    }
+
+
+    /**
+     * @brief Compares a tombstone object and an entity identifier of any type.
+     * @tparam Entity Type of entity identifier.
+     * @param entity Entity identifier with which to compare.
+     * @param other A tombstone object yet to be converted.
+     * @return True if the two elements differ, false otherwise.
+     */
+    template<typename Entity>
+    [[nodiscard]] constexpr bool operator!=(const Entity entity, const tombstone_t other) ENTT_NOEXCEPT {
+        return !(other == entity);
+    }
+
+
+    /**
+     * @brief Compile-time constant for null entities.
+     *
+     * There exist implicit conversions from this variable to entity identifiers of
+     * any allowed type. Similarly, there exist comparision operators between the
+     * null entity and any other entity identifier.
+     */
+    inline constexpr null_t null{};
+
+
+    /**
+     * @brief Compile-time constant for tombstone entities.
+     *
+     * There exist implicit conversions from this variable to entity identifiers of
+     * any allowed type. Similarly, there exist comparision operators between the
+     * tombstone entity and any other entity identifier.
+     */
+    inline constexpr tombstone_t tombstone{};
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_ENTITY_FWD_HPP
+#define ENTT_ENTITY_FWD_HPP
+
+
+#include <memory>
+// #include "../core/fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    template<typename Entity, typename = std::allocator<Entity>>
+    class basic_sparse_set;
+
+
+    template<typename, typename Type, typename = std::allocator<Type>>
+    struct basic_storage;
+
+
+    template<typename>
+    class basic_registry;
+
+
+    template<typename...>
+    struct basic_view;
+
+
+    template<typename>
+    class basic_runtime_view;
+
+
+    template<typename...>
+    class basic_group;
+
+
+    template<typename>
+    class basic_observer;
+
+
+    template<typename>
+    class basic_organizer;
+
+
+    template<typename, typename...>
+    struct basic_handle;
+
+
+    template<typename>
+    class basic_snapshot;
+
+
+    template<typename>
+    class basic_snapshot_loader;
+
+
+    template<typename>
+    class basic_continuous_loader;
+
+
+    /*! @brief Default entity identifier. */
+    enum class entity : id_type {};
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using sparse_set = basic_sparse_set<entity>;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Args Other template parameters.
+     */
+    template<typename... Args>
+    using storage = basic_storage<entity, Args...>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using registry = basic_registry<entity>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using observer = basic_observer<entity>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using organizer = basic_organizer<entity>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using handle = basic_handle<entity>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using const_handle = basic_handle<const entity>;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Args Other template parameters.
+     */
+    template<typename... Args>
+    using handle_view = basic_handle<entity, Args...>;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Args Other template parameters.
+     */
+    template<typename... Args>
+    using const_handle_view = basic_handle<const entity, Args...>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using snapshot = basic_snapshot<entity>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using snapshot_loader = basic_snapshot_loader<entity>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using continuous_loader = basic_continuous_loader<entity>;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Args Other template parameters.
+     */
+    template<typename... Args>
+    using view = basic_view<entity, Args...>;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using runtime_view = basic_runtime_view<entity>;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Args Other template parameters.
+     */
+    template<typename... Args>
+    using group = basic_group<entity, Args...>;
+
+
+}
+
+
+#endif
+
+// #include "sparse_set.hpp"
+#ifndef ENTT_ENTITY_SPARSE_SET_HPP
+#define ENTT_ENTITY_SPARSE_SET_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/algorithm.hpp"
+#ifndef ENTT_CORE_ALGORITHM_HPP
+#define ENTT_CORE_ALGORITHM_HPP
+
+
+#include <vector>
+#include <utility>
+#include <iterator>
+#include <algorithm>
+#include <functional>
+// #include "utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Function object to wrap `std::sort` in a class type.
+     *
+     * Unfortunately, `std::sort` cannot be passed as template argument to a class
+     * template or a function template.<br/>
+     * This class fills the gap by wrapping some flavors of `std::sort` in a
+     * function object.
+     */
+    struct std_sort {
+        /**
+         * @brief Sorts the elements in a range.
+         *
+         * Sorts the elements in a range using the given binary comparison function.
+         *
+         * @tparam It Type of random access iterator.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Args Types of arguments to forward to the sort function.
+         * @param first An iterator to the first element of the range to sort.
+         * @param last An iterator past the last element of the range to sort.
+         * @param compare A valid comparison function object.
+         * @param args Arguments to forward to the sort function, if any.
+         */
+        template<typename It, typename Compare = std::less<>, typename... Args>
+        void operator()(It first, It last, Compare compare = Compare{}, Args &&... args) const {
+            std::sort(std::forward<Args>(args)..., std::move(first), std::move(last), std::move(compare));
+        }
+    };
+
+
+    /*! @brief Function object for performing insertion sort. */
+    struct insertion_sort {
+        /**
+         * @brief Sorts the elements in a range.
+         *
+         * Sorts the elements in a range using the given binary comparison function.
+         *
+         * @tparam It Type of random access iterator.
+         * @tparam Compare Type of comparison function object.
+         * @param first An iterator to the first element of the range to sort.
+         * @param last An iterator past the last element of the range to sort.
+         * @param compare A valid comparison function object.
+         */
+        template<typename It, typename Compare = std::less<>>
+        void operator()(It first, It last, Compare compare = Compare{}) const {
+            if (first < last) {
+                for (auto it = first + 1; it < last; ++it) {
+                    auto value = std::move(*it);
+                    auto pre = it;
+
+                    for (; pre > first && compare(value, *(pre - 1)); --pre) {
+                        *pre = std::move(*(pre - 1));
+                    }
+
+                    *pre = std::move(value);
+                }
+            }
+        }
+    };
+
+
+    /**
+     * @brief Function object for performing LSD radix sort.
+     * @tparam Bit Number of bits processed per pass.
+     * @tparam N Maximum number of bits to sort.
+     */
+    template<std::size_t Bit, std::size_t N>
+    struct radix_sort {
+        static_assert((N% Bit) == 0, "The maximum number of bits to sort must be a multiple of the number of bits processed per pass");
+
+        /**
+         * @brief Sorts the elements in a range.
+         *
+         * Sorts the elements in a range using the given _getter_ to access the
+         * actual data to be sorted.
+         *
+         * This implementation is inspired by the online book
+         * [Physically Based Rendering](http://www.pbr-book.org/3ed-2018/Primitives_and_Intersection_Acceleration/Bounding_Volume_Hierarchies.html#RadixSort).
+         *
+         * @tparam It Type of random access iterator.
+         * @tparam Getter Type of _getter_ function object.
+         * @param first An iterator to the first element of the range to sort.
+         * @param last An iterator past the last element of the range to sort.
+         * @param getter A valid _getter_ function object.
+         */
+        template<typename It, typename Getter = identity>
+        void operator()(It first, It last, Getter getter = Getter{}) const {
+            if (first < last) {
+                static constexpr auto mask = (1 << Bit) - 1;
+                static constexpr auto buckets = 1 << Bit;
+                static constexpr auto passes = N / Bit;
+
+                using value_type = typename std::iterator_traits<It>::value_type;
+                std::vector<value_type> aux(std::distance(first, last));
+
+                auto part = [getter = std::move(getter)](auto from, auto to, auto out, auto start) {
+                    std::size_t index[buckets]{};
+                    std::size_t count[buckets]{};
+
+                    for (auto it = from; it != to; ++it) {
+                        ++count[(getter(*it) >> start) & mask];
+                    }
+
+                    for (std::size_t pos{}, end = buckets - 1u; pos < end; ++pos) {
+                        index[pos + 1u] = index[pos] + count[pos];
+                    }
+
+                    for (auto it = from; it != to; ++it) {
+                        out[index[(getter(*it) >> start) & mask]++] = std::move(*it);
+                    }
+                };
+
+                for (std::size_t pass = 0; pass < (passes & ~1); pass += 2) {
+                    part(first, last, aux.begin(), pass * Bit);
+                    part(aux.begin(), aux.end(), first, (pass + 1) * Bit);
+                }
+
+                if constexpr (passes & 1) {
+                    part(first, last, aux.begin(), (passes - 1) * Bit);
+                    std::move(aux.begin(), aux.end(), first);
+                }
+            }
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "../core/fwd.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /*! @brief Sparse set deletion policy. */
+    enum class deletion_policy : std::uint8_t {
+        /*! @brief Swap-and-pop deletion policy. */
+        swap_and_pop = 0u,
+        /*! @brief In-place deletion policy. */
+        in_place = 1u
+    };
+
+
+    /**
+     * @brief Basic sparse set implementation.
+     *
+     * Sparse set or packed array or whatever is the name users give it.<br/>
+     * Two arrays: an _external_ one and an _internal_ one; a _sparse_ one and a
+     * _packed_ one; one used for direct access through contiguous memory, the other
+     * one used to get the data through an extra level of indirection.<br/>
+     * This is largely used by the registry to offer users the fastest access ever
+     * to the components. Views and groups in general are almost entirely designed
+     * around sparse sets.
+     *
+     * This type of data structure is widely documented in the literature and on the
+     * web. This is nothing more than a customized implementation suitable for the
+     * purpose of the framework.
+     *
+     * @note
+     * Internal data structures arrange elements to maximize performance. There are
+     * no guarantees that entities are returned in the insertion order when iterate
+     * a sparse set. Do not make assumption on the order in any case.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Allocator Type of allocator used to manage memory and elements.
+     */
+    template<typename Entity, typename Allocator>
+    class basic_sparse_set {
+        static constexpr auto growth_factor = 1.5;
+        static constexpr auto sparse_page = ENTT_SPARSE_PAGE;
+
+        using traits_type = entt_traits<Entity>;
+
+        using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Entity>;
+        using alloc_pointer = typename alloc_traits::pointer;
+        using alloc_const_pointer = typename alloc_traits::const_pointer;
+
+        using bucket_alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<alloc_pointer>;
+        using bucket_alloc_pointer = typename bucket_alloc_traits::pointer;
+
+        static_assert(alloc_traits::propagate_on_container_move_assignment::value);
+        static_assert(bucket_alloc_traits::propagate_on_container_move_assignment::value);
+
+        struct sparse_set_iterator final {
+            using difference_type = typename traits_type::difference_type;
+            using value_type = Entity;
+            using pointer = const value_type*;
+            using reference = const value_type&;
+            using iterator_category = std::random_access_iterator_tag;
+
+            sparse_set_iterator() ENTT_NOEXCEPT = default;
+
+            sparse_set_iterator(const alloc_const_pointer* ref, const difference_type idx) ENTT_NOEXCEPT
+                : packed{ ref },
+                index{ idx }
+            {}
+
+            sparse_set_iterator& operator++() ENTT_NOEXCEPT {
+                return --index, * this;
+            }
+
+            sparse_set_iterator operator++(int) ENTT_NOEXCEPT {
+                iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            sparse_set_iterator& operator--() ENTT_NOEXCEPT {
+                return ++index, * this;
+            }
+
+            sparse_set_iterator operator--(int) ENTT_NOEXCEPT {
+                sparse_set_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            sparse_set_iterator& operator+=(const difference_type value) ENTT_NOEXCEPT {
+                index -= value;
+                return *this;
+            }
+
+            sparse_set_iterator operator+(const difference_type value) const ENTT_NOEXCEPT {
+                sparse_set_iterator copy = *this;
+                return (copy += value);
+            }
+
+            sparse_set_iterator& operator-=(const difference_type value) ENTT_NOEXCEPT {
+                return (*this += -value);
+            }
+
+            sparse_set_iterator operator-(const difference_type value) const ENTT_NOEXCEPT {
+                return (*this + -value);
+            }
+
+            difference_type operator-(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return other.index - index;
+            }
+
+            [[nodiscard]] reference operator[](const difference_type value) const {
+                const auto pos = size_type(index - value - 1u);
+                return (*packed)[pos];
+            }
+
+            [[nodiscard]] bool operator==(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return other.index == index;
+            }
+
+            [[nodiscard]] bool operator!=(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] bool operator<(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return index > other.index;
+            }
+
+            [[nodiscard]] bool operator>(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return index < other.index;
+            }
+
+            [[nodiscard]] bool operator<=(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this > other);
+            }
+
+            [[nodiscard]] bool operator>=(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this < other);
+            }
+
+            [[nodiscard]] pointer operator->() const {
+                const auto pos = size_type(index - 1u);
+                return std::addressof((*packed)[pos]);
+            }
+
+            [[nodiscard]] reference operator*() const {
+                return *operator->();
+            }
+
+        private:
+            const alloc_const_pointer* packed;
+            difference_type index;
+        };
+
+        [[nodiscard]] static auto page(const Entity entt) ENTT_NOEXCEPT {
+            return size_type{ traits_type::to_entity(entt) / sparse_page };
+        }
+
+        [[nodiscard]] static auto offset(const Entity entt) ENTT_NOEXCEPT {
+            return size_type{ traits_type::to_entity(entt) & (sparse_page - 1) };
+        }
+
+        [[nodiscard]] auto assure_page(const std::size_t idx) {
+            if (!(idx < bucket)) {
+                const size_type sz = idx + 1u;
+                const auto mem = bucket_alloc_traits::allocate(bucket_allocator, sz);
+
+                std::uninitialized_value_construct(mem + bucket, mem + sz);
+                std::uninitialized_copy(sparse, sparse + bucket, mem);
+
+                std::destroy(sparse, sparse + bucket);
+                bucket_alloc_traits::deallocate(bucket_allocator, sparse, bucket);
+
+                sparse = mem;
+                bucket = sz;
+            }
+
+            if (!sparse[idx]) {
+                sparse[idx] = alloc_traits::allocate(allocator, sparse_page);
+                std::uninitialized_fill(sparse[idx], sparse[idx] + sparse_page, null);
+            }
+
+            return sparse[idx];
+        }
+
+        void resize_packed(const std::size_t req) {
+            ENTT_ASSERT((req != reserved) && !(req < count), "Invalid request");
+            const auto mem = alloc_traits::allocate(allocator, req);
+
+            std::uninitialized_copy(packed, packed + count, mem);
+            std::uninitialized_fill(mem + count, mem + req, tombstone);
+
+            std::destroy(packed, packed + reserved);
+            alloc_traits::deallocate(allocator, packed, reserved);
+
+            packed = mem;
+            reserved = req;
+        }
+
+        void release_memory() {
+            if (packed) {
+                for (size_type pos{}; pos < bucket; ++pos) {
+                    if (sparse[pos]) {
+                        std::destroy(sparse[pos], sparse[pos] + sparse_page);
+                        alloc_traits::deallocate(allocator, sparse[pos], sparse_page);
+                    }
+                }
+
+                std::destroy(packed, packed + reserved);
+                std::destroy(sparse, sparse + bucket);
+                alloc_traits::deallocate(allocator, packed, reserved);
+                bucket_alloc_traits::deallocate(bucket_allocator, sparse, bucket);
+            }
+        }
+
+    protected:
+        /**
+         * @brief Swaps two entities in the internal packed array.
+         * @param lhs A valid position of an entity within storage.
+         * @param rhs A valid position of an entity within storage.
+         */
+        virtual void swap_at([[maybe_unused]] const std::size_t lhs, [[maybe_unused]] const std::size_t rhs) {}
+
+        /**
+         * @brief Moves an entity in the internal packed array.
+         * @param from A valid position of an entity within storage.
+         * @param to A valid position of an entity within storage.
+         */
+        virtual void move_and_pop([[maybe_unused]] const std::size_t from, [[maybe_unused]] const std::size_t to) {}
+
+        /**
+         * @brief Attempts to erase an entity from the internal packed array.
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        virtual void swap_and_pop(const Entity entt, [[maybe_unused]] void* ud) {
+            auto& ref = sparse[page(entt)][offset(entt)];
+            const auto pos = size_type{ traits_type::to_entity(ref) };
+            ENTT_ASSERT(packed[pos] == entt, "Invalid entity identifier");
+            auto& last = packed[--count];
+
+            packed[pos] = last;
+            sparse[page(last)][offset(last)] = ref;
+            // lazy self-assignment guard
+            ref = null;
+            // unnecessary but it helps to detect nasty bugs
+            ENTT_ASSERT((last = tombstone, true), "");
+        }
+
+        /**
+         * @brief Attempts to erase an entity from the internal packed array.
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        virtual void in_place_pop(const Entity entt, [[maybe_unused]] void* ud) {
+            auto& ref = sparse[page(entt)][offset(entt)];
+            const auto pos = size_type{ traits_type::to_entity(ref) };
+            ENTT_ASSERT(packed[pos] == entt, "Invalid entity identifier");
+
+            packed[pos] = std::exchange(free_list, traits_type::construct(static_cast<typename traits_type::entity_type>(pos)));
+            // lazy self-assignment guard
+            ref = null;
+        }
+
+    public:
+        /*! @brief Allocator type. */
+        using allocator_type = typename alloc_traits::allocator_type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Pointer type to contained entities. */
+        using pointer = alloc_const_pointer;
+        /*! @brief Random access iterator type. */
+        using iterator = sparse_set_iterator;
+        /*! @brief Reverse iterator type. */
+        using reverse_iterator = std::reverse_iterator<iterator>;
+
+        /**
+         * @brief Constructs an empty container with the given policy and allocator.
+         * @param pol Type of deletion policy.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_sparse_set(deletion_policy pol, const allocator_type& alloc = {})
+            : allocator{ alloc },
+            bucket_allocator{ alloc },
+            sparse{ bucket_alloc_traits::allocate(bucket_allocator, 0u) },
+            packed{ alloc_traits::allocate(allocator, 0u) },
+            bucket{ 0u },
+            count{ 0u },
+            reserved{ 0u },
+            free_list{ tombstone },
+            mode{ pol }
+        {}
+
+        /**
+         * @brief Constructs an empty container with the given allocator.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_sparse_set(const allocator_type& alloc = {})
+            : basic_sparse_set{ deletion_policy::swap_and_pop, alloc }
+        {}
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_sparse_set(basic_sparse_set&& other) ENTT_NOEXCEPT
+            : allocator{ std::move(other.allocator) },
+            bucket_allocator{ std::move(other.bucket_allocator) },
+            sparse{ std::exchange(other.sparse, bucket_alloc_pointer{}) },
+            packed{ std::exchange(other.packed, alloc_pointer{}) },
+            bucket{ std::exchange(other.bucket, 0u) },
+            count{ std::exchange(other.count, 0u) },
+            reserved{ std::exchange(other.reserved, 0u) },
+            free_list{ std::exchange(other.free_list, tombstone) },
+            mode{ other.mode }
+        {}
+
+        /*! @brief Default destructor. */
+        virtual ~basic_sparse_set() {
+            release_memory();
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This sparse set.
+         */
+        basic_sparse_set& operator=(basic_sparse_set&& other) ENTT_NOEXCEPT {
+            release_memory();
+
+            allocator = std::move(other.allocator);
+            bucket_allocator = std::move(other.bucket_allocator);
+            sparse = std::exchange(other.sparse, bucket_alloc_pointer{});
+            packed = std::exchange(other.packed, alloc_pointer{});
+            bucket = std::exchange(other.bucket, 0u);
+            count = std::exchange(other.count, 0u);
+            reserved = std::exchange(other.reserved, 0u);
+            free_list = std::exchange(other.free_list, tombstone);
+            mode = other.mode;
+
+            return *this;
+        }
+
+        /**
+         * @brief Returns the deletion policy of a sparse set.
+         * @return The deletion policy of the sparse set.
+         */
+        [[nodiscard]] deletion_policy policy() const ENTT_NOEXCEPT {
+            return mode;
+        }
+
+        /**
+         * @brief Returns the next slot available for insertion.
+         * @return The next slot available for insertion.
+         */
+        [[nodiscard]] size_type slot() const ENTT_NOEXCEPT {
+            return free_list == null ? count : size_type{ traits_type::to_entity(free_list) };
+        }
+
+        /**
+         * @brief Increases the capacity of a sparse set.
+         *
+         * If the new capacity is greater than the current capacity, new storage is
+         * allocated, otherwise the method does nothing.
+         *
+         * @param cap Desired capacity.
+         */
+        void reserve(const size_type cap) {
+            if (cap > reserved) {
+                resize_packed(cap);
+            }
+        }
+
+        /**
+         * @brief Returns the number of elements that a sparse set has currently
+         * allocated space for.
+         * @return Capacity of the sparse set.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return reserved;
+        }
+
+        /*! @brief Requests the removal of unused capacity. */
+        void shrink_to_fit() {
+            if (count < reserved) {
+                resize_packed(count);
+            }
+        }
+
+        /**
+         * @brief Returns the extent of a sparse set.
+         *
+         * The extent of a sparse set is also the size of the internal sparse array.
+         * There is no guarantee that the internal packed array has the same size.
+         * Usually the size of the internal sparse array is equal or greater than
+         * the one of the internal packed array.
+         *
+         * @return Extent of the sparse set.
+         */
+        [[nodiscard]] size_type extent() const ENTT_NOEXCEPT {
+            return bucket * sparse_page;
+        }
+
+        /**
+         * @brief Returns the number of elements in a sparse set.
+         *
+         * The number of elements is also the size of the internal packed array.
+         * There is no guarantee that the internal sparse array has the same size.
+         * Usually the size of the internal sparse array is equal or greater than
+         * the one of the internal packed array.
+         *
+         * @return Number of elements.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return count;
+        }
+
+        /**
+         * @brief Checks whether a sparse set is empty.
+         * @return True if the sparse set is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return (count == size_type{});
+        }
+
+        /**
+         * @brief Direct access to the internal packed array.
+         * @return A pointer to the internal packed array.
+         */
+        [[nodiscard]] pointer data() const ENTT_NOEXCEPT {
+            return packed;
+        }
+
+        /**
+         * @brief Returns an iterator to the beginning.
+         *
+         * The returned iterator points to the first entity of the internal packed
+         * array. If the sparse set is empty, the returned iterator will be equal to
+         * `end()`.
+         *
+         * @return An iterator to the first entity of the internal packed array.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return iterator{ std::addressof(packed), static_cast<typename traits_type::difference_type>(count) };
+        }
+
+        /**
+         * @brief Returns an iterator to the end.
+         *
+         * The returned iterator points to the element following the last entity in
+         * the internal packed array. Attempting to dereference the returned
+         * iterator results in undefined behavior.
+         *
+         * @return An iterator to the element following the last entity of the
+         * internal packed array.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return iterator{ std::addressof(packed), {} };
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the beginning.
+         *
+         * The returned iterator points to the first entity of the reversed internal
+         * packed array. If the sparse set is empty, the returned iterator will be
+         * equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed internal packed
+         * array.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(end());
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the end.
+         *
+         * The returned iterator points to the element following the last entity in
+         * the reversed internal packed array. Attempting to dereference the
+         * returned iterator results in undefined behavior.
+         *
+         * @return An iterator to the element following the last entity of the
+         * reversed internal packed array.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(begin());
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const ENTT_NOEXCEPT {
+            return contains(entt) ? --(end() - index(entt)) : end();
+        }
+
+        /**
+         * @brief Checks if a sparse set contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the sparse set contains the entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(entt != tombstone && entt != null, "Invalid entity");
+            const auto curr = page(entt);
+            // testing versions permits to avoid accessing the packed array
+            return (curr < bucket&& sparse[curr] && sparse[curr][offset(entt)] != null);
+        }
+
+        /**
+         * @brief Returns the position of an entity in a sparse set.
+         *
+         * @warning
+         * Attempting to get the position of an entity that doesn't belong to the
+         * sparse set results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The position of the entity in the sparse set.
+         */
+        [[nodiscard]] size_type index(const entity_type entt) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(contains(entt), "Set does not contain entity");
+            return size_type{ traits_type::to_entity(sparse[page(entt)][offset(entt)]) };
+        }
+
+        /**
+         * @brief Returns the entity at specified location, with bounds checking.
+         * @param pos The position for which to return the entity.
+         * @return The entity at specified location if any, a null entity otherwise.
+         */
+        [[nodiscard]] entity_type at(const size_type pos) const ENTT_NOEXCEPT {
+            return pos < count ? packed[pos] : null;
+        }
+
+        /**
+         * @brief Returns the entity at specified location, without bounds checking.
+         * @param pos The position for which to return the entity.
+         * @return The entity at specified location.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(pos < count, "Position is out of bounds");
+            return packed[pos];
+        }
+
+        /**
+         * @brief Appends an entity to a sparse set.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the sparse set
+         * results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The slot used for insertion.
+         */
+        size_type emplace_back(const entity_type entt) {
+            ENTT_ASSERT(!contains(entt), "Set already contains entity");
+
+            if (count == reserved) {
+                const size_type sz = static_cast<size_type>(reserved * growth_factor);
+                resize_packed(sz + !(sz > reserved));
+            }
+
+            assure_page(page(entt))[offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(count));
+            packed[count] = entt;
+            return count++;
+        }
+
+        /**
+         * @brief Assigns an entity to a sparse set.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the sparse set
+         * results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The slot used for insertion.
+         */
+        size_type emplace(const entity_type entt) {
+            if (free_list == null) {
+                return emplace_back(entt);
+            }
+            else {
+                ENTT_ASSERT(!contains(entt), "Set already contains entity");
+                const auto pos = size_type{ traits_type::to_entity(free_list) };
+                sparse[page(entt)][offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(pos));
+                free_list = std::exchange(packed[pos], entt);
+                return pos;
+            }
+        }
+
+        /**
+         * @brief Assigns one or more entities to a sparse set.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the sparse set
+         * results in undefined behavior.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void insert(It first, It last) {
+            reserve(count + std::distance(first, last));
+
+            for (; first != last; ++first) {
+                const auto entt = *first;
+                ENTT_ASSERT(!contains(entt), "Set already contains entity");
+                assure_page(page(entt))[offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(count));
+                packed[count++] = entt;
+            }
+        }
+
+        /**
+         * @brief Erases an entity from a sparse set.
+         *
+         * @warning
+         * Attempting to erase an entity that doesn't belong to the sparse set
+         * results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        void erase(const entity_type entt, void* ud = nullptr) {
+            ENTT_ASSERT(contains(entt), "Set does not contain entity");
+            (mode == deletion_policy::in_place) ? in_place_pop(entt, ud) : swap_and_pop(entt, ud);
+        }
+
+        /**
+         * @brief Erases entities from a set.
+         *
+         * @sa erase
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        template<typename It>
+        void erase(It first, It last, void* ud = nullptr) {
+            for (; first != last; ++first) {
+                erase(*first, ud);
+            }
+        }
+
+        /**
+         * @brief Removes an entity from a sparse set if it exists.
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         * @return True if the entity is actually removed, false otherwise.
+         */
+        bool remove(const entity_type entt, void* ud = nullptr) {
+            return contains(entt) && (erase(entt, ud), true);
+        }
+
+        /**
+         * @brief Removes entities from a sparse set if they exist.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         * @return The number of entities actually removed.
+         */
+        template<typename It>
+        size_type remove(It first, It last, void* ud = nullptr) {
+            size_type found{};
+
+            for (; first != last; ++first) {
+                found += remove(*first, ud);
+            }
+
+            return found;
+        }
+
+        /*! @brief Removes all tombstones from the packed array of a sparse set. */
+        void compact() {
+            size_type next = count;
+            for (; next && packed[next - 1u] == tombstone; --next);
+
+            for (auto* it = &free_list; *it != null && next; it = std::addressof(packed[traits_type::to_entity(*it)])) {
+                if (const size_type pos = traits_type::to_entity(*it); pos < next) {
+                    --next;
+                    move_and_pop(next, pos);
+                    std::swap(packed[next], packed[pos]);
+                    sparse[page(packed[pos])][offset(packed[pos])] = traits_type::construct(static_cast<const typename traits_type::entity_type>(pos));
+                    *it = traits_type::construct(static_cast<typename traits_type::entity_type>(next));
+                    for (; next && packed[next - 1u] == tombstone; --next);
+                }
+            }
+
+            free_list = tombstone;
+            count = next;
+        }
+
+        /**
+         * @copybrief swap_at
+         *
+         * For what it's worth, this function affects both the internal sparse array
+         * and the internal packed array. Users should not care of that anyway.
+         *
+         * @warning
+         * Attempting to swap entities that don't belong to the sparse set results
+         * in undefined behavior.
+         *
+         * @param lhs A valid entity identifier.
+         * @param rhs A valid entity identifier.
+         */
+        void swap(const entity_type lhs, const entity_type rhs) {
+            ENTT_ASSERT(contains(lhs), "Set does not contain entity");
+            ENTT_ASSERT(contains(rhs), "Set does not contain entity");
+
+            auto& entt = sparse[page(lhs)][offset(lhs)];
+            auto& other = sparse[page(rhs)][offset(rhs)];
+
+            const auto from = size_type{ traits_type::to_entity(entt) };
+            const auto to = size_type{ traits_type::to_entity(other) };
+
+            // basic no-leak guarantee (with invalid state) if swapping throws
+            swap_at(from, to);
+            std::swap(entt, other);
+            std::swap(packed[from], packed[to]);
+        }
+
+        /**
+         * @brief Sort the first count elements according to the given comparison
+         * function.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * bool(const Entity, const Entity);
+         * @endcode
+         *
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function object must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param length Number of elements to sort.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort_n(const size_type length, Compare compare, Sort algo = Sort{}, Args &&... args) {
+            // basic no-leak guarantee (with invalid state) if sorting throws
+            ENTT_ASSERT(!(length > count), "Length exceeds the number of elements");
+            compact();
+
+            algo(std::make_reverse_iterator(packed + length), std::make_reverse_iterator(packed), std::move(compare), std::forward<Args>(args)...);
+
+            for (size_type pos{}; pos < length; ++pos) {
+                auto curr = pos;
+                auto next = index(packed[curr]);
+
+                while (curr != next) {
+                    const auto idx = index(packed[next]);
+                    const auto entt = packed[curr];
+
+                    swap_at(next, idx);
+                    sparse[page(entt)][offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(curr));
+                    curr = std::exchange(next, idx);
+                }
+            }
+        }
+
+        /**
+         * @brief Sort all elements according to the given comparison function.
+         *
+         * @sa sort_n
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            sort_n(count, std::move(compare), std::move(algo), std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Sort entities according to their order in another sparse set.
+         *
+         * Entities that are part of both the sparse sets are ordered internally
+         * according to the order they have in `other`. All the other entities goes
+         * to the end of the list and there are no guarantees on their order.<br/>
+         * In other terms, this function can be used to impose the same order on two
+         * sets by using one of them as a master and the other one as a slave.
+         *
+         * Iterating the sparse set with a couple of iterators returns elements in
+         * the expected order after a call to `respect`. See `begin` and `end` for
+         * more details.
+         *
+         * @param other The sparse sets that imposes the order of the entities.
+         */
+        void respect(const basic_sparse_set& other) {
+            compact();
+
+            const auto to = other.end();
+            auto from = other.begin();
+
+            for (size_type pos = count - 1; pos && from != to; ++from) {
+                if (contains(*from)) {
+                    if (*from != packed[pos]) {
+                        // basic no-leak guarantee (with invalid state) if swapping throws
+                        swap(packed[pos], *from);
+                    }
+
+                    --pos;
+                }
+            }
+        }
+
+        /**
+         * @brief Clears a sparse set.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        void clear(void* ud = nullptr) {
+            for (auto&& entity : *this) {
+                if (entity != tombstone) {
+                    in_place_pop(entity, ud);
+                }
+            }
+
+            free_list = tombstone;
+            count = 0u;
+        }
+
+    private:
+        typename alloc_traits::allocator_type allocator;
+        typename bucket_alloc_traits::allocator_type bucket_allocator;
+        bucket_alloc_pointer sparse;
+        alloc_pointer packed;
+        std::size_t bucket;
+        std::size_t count;
+        std::size_t reserved;
+        entity_type free_list;
+        deletion_policy mode;
+    };
+
+
+}
+
+
+#endif
+
+// #include "storage.hpp"
+#ifndef ENTT_ENTITY_STORAGE_HPP
+#define ENTT_ENTITY_STORAGE_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/algorithm.hpp"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../signal/sigh.hpp"
+#ifndef ENTT_SIGNAL_SIGH_HPP
+#define ENTT_SIGNAL_SIGH_HPP
+
+
+#include <vector>
+#include <utility>
+#include <iterator>
+#include <algorithm>
+#include <functional>
+#include <type_traits>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "delegate.hpp"
+#ifndef ENTT_SIGNAL_DELEGATE_HPP
+#define ENTT_SIGNAL_DELEGATE_HPP
+
+
+#include <tuple>
+#include <cstddef>
+#include <utility>
+#include <functional>
+#include <type_traits>
+// #include "../core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Ret, typename... Args>
+        auto function_pointer(Ret(*)(Args...))->Ret(*)(Args...);
+
+
+        template<typename Ret, typename Type, typename... Args, typename Other>
+        auto function_pointer(Ret(*)(Type, Args...), Other&&)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...), Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...) const, Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Type, typename... Other>
+        auto function_pointer(Type Class::*, Other &&...)->Type(*)();
+
+
+        template<typename... Type>
+        using function_pointer_t = decltype(internal::function_pointer(std::declval<Type>()...));
+
+
+        template<typename... Class, typename Ret, typename... Args>
+        [[nodiscard]] constexpr auto index_sequence_for(Ret(*)(Args...)) {
+            return std::index_sequence_for<Class..., Args...>{};
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Used to wrap a function or a member of a specified type. */
+    template<auto>
+    struct connect_arg_t {};
+
+
+    /*! @brief Constant of type connect_arg_t used to disambiguate calls. */
+    template<auto Func>
+    inline constexpr connect_arg_t<Func> connect_arg{};
+
+
+    /**
+     * @brief Basic delegate implementation.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     */
+    template<typename>
+    class delegate;
+
+
+    /**
+     * @brief Utility class to use to send around functions and members.
+     *
+     * Unmanaged delegate for function pointers and members. Users of this class are
+     * in charge of disconnecting instances before deleting them.
+     *
+     * A delegate can be used as a general purpose invoker without memory overhead
+     * for free functions possibly with payloads and bound or unbound members.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class delegate<Ret(Args...)> {
+        template<auto Candidate, std::size_t... Index>
+        [[nodiscard]] auto wrap(std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void*, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type&, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type*, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+    public:
+        /*! @brief Function type of the contained target. */
+        using function_type = Ret(const void*, Args...);
+        /*! @brief Function type of the delegate. */
+        using type = Ret(Args...);
+        /*! @brief Return type of the delegate. */
+        using result_type = Ret;
+
+        /*! @brief Default constructor. */
+        delegate() ENTT_NOEXCEPT
+            : fn{ nullptr }, data{ nullptr }
+        {}
+
+        /**
+         * @brief Constructs a delegate and connects a free function or an unbound
+         * member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        delegate(connect_arg_t<Candidate>) ENTT_NOEXCEPT {
+            connect<Candidate>();
+        }
+
+        /**
+         * @brief Constructs a delegate and connects a free function with payload or
+         * a bound member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        delegate(connect_arg_t<Candidate>, Type&& value_or_instance) ENTT_NOEXCEPT {
+            connect<Candidate>(std::forward<Type>(value_or_instance));
+        }
+
+        /**
+         * @brief Constructs a delegate and connects an user defined function with
+         * optional payload.
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        delegate(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            connect(function, payload);
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a delegate.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        void connect() ENTT_NOEXCEPT {
+            data = nullptr;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
+                fn = [](const void*, Args... args) -> Ret {
+                    return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
+                };
+            }
+            else if constexpr (std::is_member_pointer_v<decltype(Candidate)>) {
+                fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+            else {
+                fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the delegate.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the delegate itself.
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid reference that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type& value_or_instance) ENTT_NOEXCEPT {
+            data = &value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type&, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * @sa connect(Type &)
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type* value_or_instance) ENTT_NOEXCEPT {
+            data = value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type*, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects an user defined function with optional payload to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of an instance overcomes
+         * the one of the delegate.<br/>
+         * The payload is returned as the first argument to the target function in
+         * all cases.
+         *
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        void connect(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            fn = function;
+            data = payload;
+        }
+
+        /**
+         * @brief Resets a delegate.
+         *
+         * After a reset, a delegate cannot be invoked anymore.
+         */
+        void reset() ENTT_NOEXCEPT {
+            fn = nullptr;
+            data = nullptr;
+        }
+
+        /**
+         * @brief Returns the instance or the payload linked to a delegate, if any.
+         * @return An opaque pointer to the underlying data.
+         */
+        [[nodiscard]] const void* instance() const ENTT_NOEXCEPT {
+            return data;
+        }
+
+        /**
+         * @brief Triggers a delegate.
+         *
+         * The delegate invokes the underlying function and returns the result.
+         *
+         * @warning
+         * Attempting to trigger an invalid delegate results in undefined
+         * behavior.
+         *
+         * @param args Arguments to use to invoke the underlying function.
+         * @return The value returned by the underlying function.
+         */
+        Ret operator()(Args... args) const {
+            ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
+            return fn(data, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Checks whether a delegate actually stores a listener.
+         * @return False if the delegate is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            // no need to test also data
+            return !(fn == nullptr);
+        }
+
+        /**
+         * @brief Compares the contents of two delegates.
+         * @param other Delegate with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const delegate<Ret(Args...)>& other) const ENTT_NOEXCEPT {
+            return fn == other.fn && data == other.data;
+        }
+
+    private:
+        function_type* fn;
+        const void* data;
+    };
+
+
+    /**
+     * @brief Compares the contents of two delegates.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     * @param lhs A valid delegate object.
+     * @param rhs A valid delegate object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    template<typename Ret, typename... Args>
+    [[nodiscard]] bool operator!=(const delegate<Ret(Args...)>& lhs, const delegate<Ret(Args...)>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     */
+    template<auto Candidate>
+    delegate(connect_arg_t<Candidate>)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     * @tparam Type Type of class or type of payload.
+     */
+    template<auto Candidate, typename Type>
+    delegate(connect_arg_t<Candidate>, Type&&)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    delegate(Ret(*)(const void*, Args...), const void* = nullptr)
+        ->delegate<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_SIGNAL_FWD_HPP
+#define ENTT_SIGNAL_FWD_HPP
+
+
+namespace entt {
+
+
+    template<typename>
+    class delegate;
+
+
+    class dispatcher;
+
+
+    template<typename>
+    class emitter;
+
+
+    class connection;
+
+
+    struct scoped_connection;
+
+
+    template<typename>
+    class sink;
+
+
+    template<typename>
+    class sigh;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Sink class.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     *
+     * @tparam Function A valid function type.
+     */
+    template<typename Function>
+    class sink;
+
+
+    /**
+     * @brief Unmanaged signal handler.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     *
+     * @tparam Function A valid function type.
+     */
+    template<typename Function>
+    class sigh;
+
+
+    /**
+     * @brief Unmanaged signal handler.
+     *
+     * It works directly with references to classes and pointers to member functions
+     * as well as pointers to free functions. Users of this class are in charge of
+     * disconnecting instances before deleting them.
+     *
+     * This class serves mainly two purposes:
+     *
+     * * Creating signals to use later to notify a bunch of listeners.
+     * * Collecting results from a set of functions like in a voting system.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class sigh<Ret(Args...)> {
+        /*! @brief A sink is allowed to modify a signal. */
+        friend class sink<Ret(Args...)>;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Sink type. */
+        using sink_type = sink<Ret(Args...)>;
+
+        /**
+         * @brief Instance type when it comes to connecting member functions.
+         * @tparam Class Type of class to which the member function belongs.
+         */
+        template<typename Class>
+        using instance_type = Class*;
+
+        /**
+         * @brief Number of listeners connected to the signal.
+         * @return Number of listeners currently connected.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return calls.size();
+        }
+
+        /**
+         * @brief Returns false if at least a listener is connected to the signal.
+         * @return True if the signal has no listeners connected, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return calls.empty();
+        }
+
+        /**
+         * @brief Triggers a signal.
+         *
+         * All the listeners are notified. Order isn't guaranteed.
+         *
+         * @param args Arguments to use to invoke listeners.
+         */
+        void publish(Args... args) const {
+            for (auto&& call : std::as_const(calls)) {
+                call(args...);
+            }
+        }
+
+        /**
+         * @brief Collects return values from the listeners.
+         *
+         * The collector must expose a call operator with the following properties:
+         *
+         * * The return type is either `void` or such that it's convertible to
+         *   `bool`. In the second case, a true value will stop the iteration.
+         * * The list of parameters is empty if `Ret` is `void`, otherwise it
+         *   contains a single element such that `Ret` is convertible to it.
+         *
+         * @tparam Func Type of collector to use, if any.
+         * @param func A valid function object.
+         * @param args Arguments to use to invoke listeners.
+         */
+        template<typename Func>
+        void collect(Func func, Args... args) const {
+            for (auto&& call : calls) {
+                if constexpr (std::is_void_v<Ret>) {
+                    if constexpr (std::is_invocable_r_v<bool, Func>) {
+                        call(args...);
+                        if (func()) { break; }
+                    }
+                    else {
+                        call(args...);
+                        func();
+                    }
+                }
+                else {
+                    if constexpr (std::is_invocable_r_v<bool, Func, Ret>) {
+                        if (func(call(args...))) { break; }
+                    }
+                    else {
+                        func(call(args...));
+                    }
+                }
+            }
+        }
+
+    private:
+        std::vector<delegate<Ret(Args...)>> calls;
+    };
+
+
+    /**
+     * @brief Connection class.
+     *
+     * Opaque object the aim of which is to allow users to release an already
+     * estabilished connection without having to keep a reference to the signal or
+     * the sink that generated it.
+     */
+    class connection {
+        /*! @brief A sink is allowed to create connection objects. */
+        template<typename>
+        friend class sink;
+
+        connection(delegate<void(void*)> fn, void* ref)
+            : disconnect{ fn }, signal{ ref }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        connection() = default;
+
+        /**
+         * @brief Checks whether a connection is properly initialized.
+         * @return True if the connection is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(disconnect);
+        }
+
+        /*! @brief Breaks the connection. */
+        void release() {
+            if (disconnect) {
+                disconnect(signal);
+                disconnect.reset();
+            }
+        }
+
+    private:
+        delegate<void(void*)> disconnect;
+        void* signal{};
+    };
+
+
+    /**
+     * @brief Scoped connection class.
+     *
+     * Opaque object the aim of which is to allow users to release an already
+     * estabilished connection without having to keep a reference to the signal or
+     * the sink that generated it.<br/>
+     * A scoped connection automatically breaks the link between the two objects
+     * when it goes out of scope.
+     */
+    struct scoped_connection {
+        /*! @brief Default constructor. */
+        scoped_connection() = default;
+
+        /**
+         * @brief Constructs a scoped connection from a basic connection.
+         * @param other A valid connection object.
+         */
+        scoped_connection(const connection& other)
+            : conn{ other }
+        {}
+
+        /*! @brief Default copy constructor, deleted on purpose. */
+        scoped_connection(const scoped_connection&) = delete;
+
+        /*! @brief Automatically breaks the link on destruction. */
+        ~scoped_connection() {
+            conn.release();
+        }
+
+        /**
+         * @brief Default copy assignment operator, deleted on purpose.
+         * @return This scoped connection.
+         */
+        scoped_connection& operator=(const scoped_connection&) = delete;
+
+        /**
+         * @brief Acquires a connection.
+         * @param other The connection object to acquire.
+         * @return This scoped connection.
+         */
+        scoped_connection& operator=(connection other) {
+            conn = std::move(other);
+            return *this;
+        }
+
+        /**
+         * @brief Checks whether a scoped connection is properly initialized.
+         * @return True if the connection is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(conn);
+        }
+
+        /*! @brief Breaks the connection. */
+        void release() {
+            conn.release();
+        }
+
+    private:
+        connection conn;
+    };
+
+
+    /**
+     * @brief Sink class.
+     *
+     * A sink is used to connect listeners to signals and to disconnect them.<br/>
+     * The function type for a listener is the one of the signal to which it
+     * belongs.
+     *
+     * The clear separation between a signal and a sink permits to store the former
+     * as private data member without exposing the publish functionality to the
+     * users of the class.
+     *
+     * @warning
+     * Lifetime of a sink must not overcome that of the signal to which it refers.
+     * In any other case, attempting to use a sink results in undefined behavior.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class sink<Ret(Args...)> {
+        using signal_type = sigh<Ret(Args...)>;
+        using difference_type = typename std::iterator_traits<typename decltype(signal_type::calls)::iterator>::difference_type;
+
+        template<auto Candidate, typename Type>
+        static void release(Type value_or_instance, void* signal) {
+            sink{ *static_cast<signal_type*>(signal) }.disconnect<Candidate>(value_or_instance);
+        }
+
+        template<auto Candidate>
+        static void release(void* signal) {
+            sink{ *static_cast<signal_type*>(signal) }.disconnect<Candidate>();
+        }
+
+    public:
+        /**
+         * @brief Constructs a sink that is allowed to modify a given signal.
+         * @param ref A valid reference to a signal object.
+         */
+        sink(sigh<Ret(Args...)>& ref) ENTT_NOEXCEPT
+            : offset{},
+            signal{ &ref }
+        {}
+
+        /**
+         * @brief Returns false if at least a listener is connected to the sink.
+         * @return True if the sink has no listeners connected, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return signal->calls.empty();
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given free function or an
+         * unbound member.
+         * @tparam Function A valid free function pointer.
+         * @return A properly initialized sink object.
+         */
+        template<auto Function>
+        [[nodiscard]] sink before() {
+            delegate<Ret(Args...)> call{};
+            call.template connect<Function>();
+
+            const auto& calls = signal->calls;
+            const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));
+
+            sink other{ *this };
+            other.offset = std::distance(it, calls.cend());
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before a free function with payload
+         * or a bound member.
+         * @tparam Candidate Member or free function to look for.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<auto Candidate, typename Type>
+        [[nodiscard]] sink before(Type&& value_or_instance) {
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+
+            const auto& calls = signal->calls;
+            const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));
+
+            sink other{ *this };
+            other.offset = std::distance(it, calls.cend());
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given instance or specific
+         * payload.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<typename Type>
+        [[nodiscard]] sink before(Type& value_or_instance) {
+            return before(&value_or_instance);
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given instance or specific
+         * payload.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<typename Type>
+        [[nodiscard]] sink before(Type* value_or_instance) {
+            sink other{ *this };
+
+            if (value_or_instance) {
+                const auto& calls = signal->calls;
+                const auto it = std::find_if(calls.cbegin(), calls.cend(), [value_or_instance](const auto& delegate) {
+                    return delegate.instance() == value_or_instance;
+                    });
+
+                other.offset = std::distance(it, calls.cend());
+            }
+
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before anything else.
+         * @return A properly initialized sink object.
+         */
+        [[nodiscard]] sink before() {
+            sink other{ *this };
+            other.offset = signal->calls.size();
+            return other;
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a signal.
+         *
+         * The signal handler performs checks to avoid multiple connections for the
+         * same function.
+         *
+         * @tparam Candidate Function or member to connect to the signal.
+         * @return A properly initialized connection object.
+         */
+        template<auto Candidate>
+        connection connect() {
+            disconnect<Candidate>();
+
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>();
+            signal->calls.insert(signal->calls.end() - offset, std::move(call));
+
+            delegate<void(void*)> conn{};
+            conn.template connect<&release<Candidate>>();
+            return { std::move(conn), signal };
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * signal.
+         *
+         * The signal isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the signal. On the other side, the signal handler performs
+         * checks to avoid multiple connections for the same function.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the signal itself.
+         *
+         * @tparam Candidate Function or member to connect to the signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized connection object.
+         */
+        template<auto Candidate, typename Type>
+        connection connect(Type&& value_or_instance) {
+            disconnect<Candidate>(value_or_instance);
+
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+            signal->calls.insert(signal->calls.end() - offset, std::move(call));
+
+            delegate<void(void*)> conn{};
+            conn.template connect<&release<Candidate, Type>>(value_or_instance);
+            return { std::move(conn), signal };
+        }
+
+        /**
+         * @brief Disconnects a free function or an unbound member from a signal.
+         * @tparam Candidate Function or member to disconnect from the signal.
+         */
+        template<auto Candidate>
+        void disconnect() {
+            auto& calls = signal->calls;
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>();
+            calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
+        }
+
+        /**
+         * @brief Disconnects a free function with payload or a bound member from a
+         * signal.
+         * @tparam Candidate Function or member to disconnect from the signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void disconnect(Type&& value_or_instance) {
+            auto& calls = signal->calls;
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+            calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
+        }
+
+        /**
+         * @brief Disconnects free functions with payload or bound members from a
+         * signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type& value_or_instance) {
+            disconnect(&value_or_instance);
+        }
+
+        /**
+         * @brief Disconnects free functions with payload or bound members from a
+         * signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type* value_or_instance) {
+            if (value_or_instance) {
+                auto& calls = signal->calls;
+                calls.erase(std::remove_if(calls.begin(), calls.end(), [value_or_instance](const auto& delegate) {
+                    return delegate.instance() == value_or_instance;
+                    }), calls.end());
+            }
+        }
+
+        /*! @brief Disconnects all the listeners from a signal. */
+        void disconnect() {
+            signal->calls.clear();
+        }
+
+    private:
+        difference_type offset;
+        signal_type* signal;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the function type of a sink directly from the signal it
+     * refers to.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    sink(sigh<Ret(Args...)>&)
+        ->sink<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
+// #include "component.hpp"
+#ifndef ENTT_ENTITY_COMPONENT_HPP
+#define ENTT_ENTITY_COMPONENT_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /*! @brief Commonly used default traits for all types. */
+    struct basic_component_traits {
+        /*! @brief Pointer stability, default is `std::false_type`. */
+        using in_place_delete = std::false_type;
+        /*! @brief Empty type optimization, default is `ENTT_IGNORE_IF_EMPTY`. */
+        using ignore_if_empty = ENTT_IGNORE_IF_EMPTY;
+    };
+
+
+    /**
+     * @brief Common way to access various properties of components.
+     * @tparam Type Type of component.
+     */
+    template<typename Type, typename = void>
+    struct component_traits : basic_component_traits {
+        static_assert(std::is_same_v<std::decay_t<Type>, Type>, "Unsupported type");
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "sparse_set.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Basic storage implementation.
+     *
+     * This class is a refinement of a sparse set that associates an object to an
+     * entity. The main purpose of this class is to extend sparse sets to store
+     * components in a registry. It guarantees fast access both to the elements and
+     * to the entities.
+     *
+     * @note
+     * Entities and objects have the same order.
+     *
+     * @note
+     * Internal data structures arrange elements to maximize performance. There are
+     * no guarantees that objects are returned in the insertion order when iterate
+     * a storage. Do not make assumption on the order in any case.
+     *
+     * @warning
+     * Empty types aren't explicitly instantiated. Therefore, many of the functions
+     * normally available for non-empty types will not be available for empty ones.
+     *
+     * @sa sparse_set<Entity>
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Type of objects assigned to the entities.
+     * @tparam Allocator Type of allocator used to manage memory and elements.
+     */
+    template<typename Entity, typename Type, typename Allocator, typename = void>
+    class basic_storage_impl : public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>> {
+        static constexpr auto packed_page = ENTT_PACKED_PAGE;
+
+        using comp_traits = component_traits<Type>;
+
+        using underlying_type = basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>>;
+        using difference_type = typename entt_traits<Entity>::difference_type;
+
+        using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
+        using alloc_pointer = typename alloc_traits::pointer;
+        using alloc_const_pointer = typename alloc_traits::const_pointer;
+
+        using bucket_alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<alloc_pointer>;
+        using bucket_alloc_pointer = typename bucket_alloc_traits::pointer;
+
+        using bucket_alloc_const_type = typename std::allocator_traits<Allocator>::template rebind_alloc<alloc_const_pointer>;
+        using bucket_alloc_const_pointer = typename std::allocator_traits<bucket_alloc_const_type>::const_pointer;
+
+        static_assert(alloc_traits::propagate_on_container_move_assignment::value);
+        static_assert(bucket_alloc_traits::propagate_on_container_move_assignment::value);
+
+        template<typename Value>
+        struct storage_iterator final {
+            using difference_type = typename basic_storage_impl::difference_type;
+            using value_type = Value;
+            using pointer = value_type*;
+            using reference = value_type&;
+            using iterator_category = std::random_access_iterator_tag;
+
+            storage_iterator() ENTT_NOEXCEPT = default;
+
+            storage_iterator(bucket_alloc_pointer const* ref, const typename basic_storage_impl::difference_type idx) ENTT_NOEXCEPT
+                : packed{ ref },
+                index{ idx }
+            {}
+
+            storage_iterator& operator++() ENTT_NOEXCEPT {
+                return --index, * this;
+            }
+
+            storage_iterator operator++(int) ENTT_NOEXCEPT {
+                storage_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            storage_iterator& operator--() ENTT_NOEXCEPT {
+                return ++index, * this;
+            }
+
+            storage_iterator operator--(int) ENTT_NOEXCEPT {
+                storage_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            storage_iterator& operator+=(const difference_type value) ENTT_NOEXCEPT {
+                index -= value;
+                return *this;
+            }
+
+            storage_iterator operator+(const difference_type value) const ENTT_NOEXCEPT {
+                storage_iterator copy = *this;
+                return (copy += value);
+            }
+
+            storage_iterator& operator-=(const difference_type value) ENTT_NOEXCEPT {
+                return (*this += -value);
+            }
+
+            storage_iterator operator-(const difference_type value) const ENTT_NOEXCEPT {
+                return (*this + -value);
+            }
+
+            difference_type operator-(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return other.index - index;
+            }
+
+            [[nodiscard]] reference operator[](const difference_type value) const ENTT_NOEXCEPT {
+                const auto pos = size_type(index - value - 1);
+                return (*packed)[page(pos)][offset(pos)];
+            }
+
+            [[nodiscard]] bool operator==(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return other.index == index;
+            }
+
+            [[nodiscard]] bool operator!=(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] bool operator<(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return index > other.index;
+            }
+
+            [[nodiscard]] bool operator>(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return index < other.index;
+            }
+
+            [[nodiscard]] bool operator<=(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this > other);
+            }
+
+            [[nodiscard]] bool operator>=(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this < other);
+            }
+
+            [[nodiscard]] pointer operator->() const ENTT_NOEXCEPT {
+                const auto pos = size_type(index - 1u);
+                return std::addressof((*packed)[page(pos)][offset(pos)]);
+            }
+
+            [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                return *operator->();
+            }
+
+        private:
+            bucket_alloc_pointer const* packed;
+            difference_type index;
+        };
+
+        [[nodiscard]] static auto page(const std::size_t pos) ENTT_NOEXCEPT {
+            return pos / packed_page;
+        }
+
+        [[nodiscard]] static auto offset(const std::size_t pos) ENTT_NOEXCEPT {
+            return pos & (packed_page - 1);
+        }
+
+        void release_memory() {
+            if (packed) {
+                // no-throw stable erase iteration
+                underlying_type::clear();
+
+                for (size_type pos{}; pos < bucket; ++pos) {
+                    alloc_traits::deallocate(allocator, packed[pos], packed_page);
+                    bucket_alloc_traits::destroy(bucket_allocator, std::addressof(packed[pos]));
+                }
+
+                bucket_alloc_traits::deallocate(bucket_allocator, packed, bucket);
+            }
+        }
+
+        void assure_at_least(const std::size_t last) {
+            if (const auto idx = page(last - 1u); !(idx < bucket)) {
+                const size_type sz = idx + 1u;
+                const auto mem = bucket_alloc_traits::allocate(bucket_allocator, sz);
+                std::uninitialized_copy(packed, packed + bucket, mem);
+                size_type pos{};
+
+                ENTT_TRY{
+                    for (pos = bucket; pos < sz; ++pos) {
+                        auto pg = alloc_traits::allocate(allocator, packed_page);
+                        bucket_alloc_traits::construct(bucket_allocator, std::addressof(mem[pos]), pg);
+                    }
+                } ENTT_CATCH{
+                    for (auto next = bucket; next < pos; ++next) {
+                        alloc_traits::deallocate(allocator, mem[next], packed_page);
+                    }
+
+                    std::destroy(mem, mem + pos);
+                    bucket_alloc_traits::deallocate(bucket_allocator, mem, sz);
+                    ENTT_THROW;
+                }
+
+                std::destroy(packed, packed + bucket);
+                bucket_alloc_traits::deallocate(bucket_allocator, packed, bucket);
+
+                packed = mem;
+                bucket = sz;
+            }
+        }
+
+        void release_unused_pages() {
+            if (const auto length = underlying_type::size() / packed_page; length < bucket) {
+                const auto mem = bucket_alloc_traits::allocate(bucket_allocator, length);
+                std::uninitialized_copy(packed, packed + length, mem);
+
+                for (auto pos = length; pos < bucket; ++pos) {
+                    alloc_traits::deallocate(allocator, packed[pos], packed_page);
+                    bucket_alloc_traits::destroy(bucket_allocator, std::addressof(packed[pos]));
+                }
+
+                bucket_alloc_traits::deallocate(bucket_allocator, packed, bucket);
+
+                packed = mem;
+                bucket = length;
+            }
+        }
+
+        template<typename... Args>
+        auto& push_at(const std::size_t pos, Args &&... args) {
+            ENTT_ASSERT(pos < (bucket* packed_page), "Out of bounds index");
+            auto* instance = std::addressof(packed[page(pos)][offset(pos)]);
+
+            if constexpr (std::is_aggregate_v<value_type>) {
+                alloc_traits::construct(allocator, instance, Type{ std::forward<Args>(args)... });
+            }
+            else {
+                alloc_traits::construct(allocator, instance, std::forward<Args>(args)...);
+            }
+
+            return *instance;
+        }
+
+        void pop_at(const std::size_t pos) {
+            alloc_traits::destroy(allocator, std::addressof(packed[page(pos)][offset(pos)]));
+        }
+
+    protected:
+        /*! @copydoc basic_sparse_set::swap_at */
+        void swap_at(const std::size_t lhs, const std::size_t rhs) final {
+            std::swap(packed[page(lhs)][offset(lhs)], packed[page(rhs)][offset(rhs)]);
+        }
+
+        /*! @copydoc basic_sparse_set::move_and_pop */
+        void move_and_pop(const std::size_t from, const std::size_t to) final {
+            push_at(to, std::move(packed[page(from)][offset(from)]));
+            pop_at(from);
+        }
+
+        /*! @copydoc basic_sparse_set::swap_and_pop */
+        void swap_and_pop(const Entity entt, void* ud) override {
+            const auto pos = underlying_type::index(entt);
+            const auto last = underlying_type::size() - 1u;
+            auto&& elem = packed[page(pos)][offset(pos)];
+
+            // support for nosy destructors
+            [[maybe_unused]] auto unused = std::move(elem);
+            elem = std::move(packed[page(last)][offset(last)]);
+            pop_at(last);
+
+            underlying_type::swap_and_pop(entt, ud);
+        }
+
+        /*! @copydoc basic_sparse_set::in_place_pop */
+        void in_place_pop(const Entity entt, void* ud) override {
+            const auto pos = underlying_type::index(entt);
+            underlying_type::in_place_pop(entt, ud);
+            // support for nosy destructors
+            pop_at(pos);
+        }
+
+    public:
+        /*! @brief Allocator type. */
+        using allocator_type = typename alloc_traits::allocator_type;
+        /*! @brief Type of the objects assigned to entities. */
+        using value_type = Type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Pointer type to contained elements. */
+        using pointer = bucket_alloc_pointer;
+        /*! @brief Constant pointer type to contained elements. */
+        using const_pointer = bucket_alloc_const_pointer;
+        /*! @brief Random access iterator type. */
+        using iterator = storage_iterator<value_type>;
+        /*! @brief Constant random access iterator type. */
+        using const_iterator = storage_iterator<const value_type>;
+        /*! @brief Reverse iterator type. */
+        using reverse_iterator = std::reverse_iterator<iterator>;
+        /*! @brief Constant reverse iterator type. */
+        using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+        /**
+         * @brief Default constructor.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_storage_impl(const allocator_type& alloc = {})
+            : underlying_type{ deletion_policy{comp_traits::in_place_delete::value}, alloc },
+            allocator{ alloc },
+            bucket_allocator{ alloc },
+            packed{ bucket_alloc_traits::allocate(bucket_allocator, 0u) },
+            bucket{}
+        {}
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_storage_impl(basic_storage_impl&& other) ENTT_NOEXCEPT
+            : underlying_type{ std::move(other) },
+            allocator{ std::move(other.allocator) },
+            bucket_allocator{ std::move(other.bucket_allocator) },
+            packed{ std::exchange(other.packed, bucket_alloc_pointer{}) },
+            bucket{ std::exchange(other.bucket, 0u) }
+        {}
+
+        /*! @brief Default destructor. */
+        ~basic_storage_impl() override {
+            release_memory();
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This sparse set.
+         */
+        basic_storage_impl& operator=(basic_storage_impl&& other) ENTT_NOEXCEPT {
+            release_memory();
+
+            underlying_type::operator=(std::move(other));
+
+            allocator = std::move(other.allocator);
+            bucket_allocator = std::move(other.bucket_allocator);
+            packed = std::exchange(other.packed, bucket_alloc_pointer{});
+            bucket = std::exchange(other.bucket, 0u);
+
+            return *this;
+        }
+
+        /**
+         * @brief Increases the capacity of a storage.
+         *
+         * If the new capacity is greater than the current capacity, new storage is
+         * allocated, otherwise the method does nothing.
+         *
+         * @param cap Desired capacity.
+         */
+        void reserve(const size_type cap) {
+            underlying_type::reserve(cap);
+
+            if (cap > underlying_type::size()) {
+                assure_at_least(cap);
+            }
+        }
+
+        /**
+         * @brief Returns the number of elements that a storage has currently
+         * allocated space for.
+         * @return Capacity of the storage.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return bucket * packed_page;
+        }
+
+        /*! @brief Requests the removal of unused capacity. */
+        void shrink_to_fit() {
+            underlying_type::shrink_to_fit();
+            release_unused_pages();
+        }
+
+        /**
+         * @brief Direct access to the array of objects.
+         * @return A pointer to the array of objects.
+         */
+        [[nodiscard]] const_pointer raw() const ENTT_NOEXCEPT {
+            return packed;
+        }
+
+        /*! @copydoc raw */
+        [[nodiscard]] pointer raw() ENTT_NOEXCEPT {
+            return packed;
+        }
+
+        /**
+         * @brief Returns an iterator to the beginning.
+         *
+         * The returned iterator points to the first instance of the internal array.
+         * If the storage is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first instance of the internal array.
+         */
+        [[nodiscard]] const_iterator cbegin() const ENTT_NOEXCEPT {
+            const difference_type pos = underlying_type::size();
+            return const_iterator{ std::addressof(packed), pos };
+        }
+
+        /*! @copydoc cbegin */
+        [[nodiscard]] const_iterator begin() const ENTT_NOEXCEPT {
+            return cbegin();
+        }
+
+        /*! @copydoc begin */
+        [[nodiscard]] iterator begin() ENTT_NOEXCEPT {
+            const difference_type pos = underlying_type::size();
+            return iterator{ std::addressof(packed), pos };
+        }
+
+        /**
+         * @brief Returns an iterator to the end.
+         *
+         * The returned iterator points to the element following the last instance
+         * of the internal array. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the element following the last instance of the
+         * internal array.
+         */
+        [[nodiscard]] const_iterator cend() const ENTT_NOEXCEPT {
+            return const_iterator{ std::addressof(packed), {} };
+        }
+
+        /*! @copydoc cend */
+        [[nodiscard]] const_iterator end() const ENTT_NOEXCEPT {
+            return cend();
+        }
+
+        /*! @copydoc end */
+        [[nodiscard]] iterator end() ENTT_NOEXCEPT {
+            return iterator{ std::addressof(packed), {} };
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the beginning.
+         *
+         * The returned iterator points to the first instance of the reversed
+         * internal array. If the storage is empty, the returned iterator will be
+         * equal to `rend()`.
+         *
+         * @return An iterator to the first instance of the reversed internal array.
+         */
+        [[nodiscard]] const_reverse_iterator crbegin() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(cend());
+        }
+
+        /*! @copydoc crbegin */
+        [[nodiscard]] const_reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return crbegin();
+        }
+
+        /*! @copydoc rbegin */
+        [[nodiscard]] reverse_iterator rbegin() ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(end());
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the end.
+         *
+         * The returned iterator points to the element following the last instance
+         * of the reversed internal array. Attempting to dereference the returned
+         * iterator results in undefined behavior.
+         *
+         * @return An iterator to the element following the last instance of the
+         * reversed internal array.
+         */
+        [[nodiscard]] const_reverse_iterator crend() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(cbegin());
+        }
+
+        /*! @copydoc crend */
+        [[nodiscard]] const_reverse_iterator rend() const ENTT_NOEXCEPT {
+            return crend();
+        }
+
+        /*! @copydoc rend */
+        [[nodiscard]] reverse_iterator rend() ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(begin());
+        }
+
+        /**
+         * @brief Returns the object assigned to an entity.
+         *
+         * @warning
+         * Attempting to use an entity that doesn't belong to the storage results in
+         * undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The object assigned to the entity.
+         */
+        [[nodiscard]] const value_type& get(const entity_type entt) const ENTT_NOEXCEPT {
+            const auto idx = underlying_type::index(entt);
+            return packed[page(idx)][offset(idx)];
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] value_type& get(const entity_type entt) ENTT_NOEXCEPT {
+            return const_cast<value_type&>(std::as_const(*this).get(entt));
+        }
+
+        /**
+         * @brief Assigns an entity to a storage and constructs its object.
+         *
+         * This version accept both types that can be constructed in place directly
+         * and types like aggregates that do not work well with a placement new as
+         * performed usually under the hood during an _emplace back_.
+         *
+         * @warning
+         * Attempting to use an entity that already belongs to the storage results
+         * in undefined behavior.
+         *
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to construct an object for the entity.
+         * @return A reference to the newly created object.
+         */
+        template<typename... Args>
+        value_type& emplace(const entity_type entt, Args &&... args) {
+            const auto pos = underlying_type::slot();
+            assure_at_least(pos + 1u);
+
+            auto& value = push_at(pos, std::forward<Args>(args)...);
+
+            ENTT_TRY{
+                [[maybe_unused]] const auto curr = underlying_type::emplace(entt);
+                ENTT_ASSERT(pos == curr, "Misplaced component");
+            } ENTT_CATCH{
+                pop_at(pos);
+                ENTT_THROW;
+            }
+
+            return value;
+        }
+
+        /**
+         * @brief Updates the instance assigned to a given entity in-place.
+         * @tparam Func Types of the function objects to invoke.
+         * @param entt A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the updated instance.
+         */
+        template<typename... Func>
+        decltype(auto) patch(const entity_type entt, Func &&... func) {
+            const auto idx = underlying_type::index(entt);
+            auto&& elem = packed[page(idx)][offset(idx)];
+            (std::forward<Func>(func)(elem), ...);
+            return elem;
+        }
+
+        /**
+         * @brief Assigns one or more entities to a storage and constructs their
+         * objects from a given instance.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the storage
+         * results in undefined behavior.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param value An instance of the object to construct.
+         */
+        template<typename It>
+        void insert(It first, It last, const value_type& value = {}) {
+            const auto cap = underlying_type::size() + std::distance(first, last);
+            underlying_type::reserve(cap);
+            assure_at_least(cap);
+
+            for (; first != last; ++first) {
+                push_at(underlying_type::size(), value);
+
+                ENTT_TRY{
+                    underlying_type::emplace_back(*first);
+                } ENTT_CATCH{
+                    pop_at(underlying_type::size());
+                    ENTT_THROW;
+                }
+            }
+        }
+
+        /**
+         * @brief Assigns one or more entities to a storage and constructs their
+         * objects from a given range.
+         *
+         * @sa construct
+         *
+         * @tparam EIt Type of input iterator.
+         * @tparam CIt Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param from An iterator to the first element of the range of objects.
+         */
+        template<typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<std::decay_t<typename std::iterator_traits<CIt>::value_type>, value_type>>>
+        void insert(EIt first, EIt last, CIt from) {
+            const auto cap = underlying_type::size() + std::distance(first, last);
+            underlying_type::reserve(cap);
+            assure_at_least(cap);
+
+            for (; first != last; ++first, ++from) {
+                push_at(underlying_type::size(), *from);
+
+                ENTT_TRY{
+                    underlying_type::emplace_back(*first);
+                } ENTT_CATCH{
+                    pop_at(underlying_type::size());
+                    ENTT_THROW;
+                }
+            }
+        }
+
+        /**
+         * @brief Sort elements according to the given comparison function.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(const Entity, const Entity);
+         * bool(const Type &, const Type &);
+         * @endcode
+         *
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @warning
+         * Empty types are never instantiated. Therefore, only comparison function
+         * objects that require to return entities rather than components are
+         * accepted.
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param length Number of elements to sort.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort_n(const size_type length, Compare compare, Sort algo = Sort{}, Args &&... args) {
+            if constexpr (std::is_invocable_v<Compare, const value_type&, const value_type&>) {
+                underlying_type::sort_n(length, [this, compare = std::move(compare)](const auto lhs, const auto rhs) {
+                    const auto ilhs = underlying_type::index(lhs), irhs = underlying_type::index(rhs);
+                    return compare(std::as_const(packed[page(ilhs)][offset(ilhs)]), std::as_const(packed[page(irhs)][offset(irhs)]));
+                }, std::move(algo), std::forward<Args>(args)...);
+            }
+            else {
+                underlying_type::sort_n(length, std::move(compare), std::move(algo), std::forward<Args>(args)...);
+            }
+        }
+
+        /**
+         * @brief Sort all elements according to the given comparison function.
+         *
+         * @sa sort_n
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            sort_n(underlying_type::size(), std::move(compare), std::move(algo), std::forward<Args>(args)...);
+        }
+
+    private:
+        typename alloc_traits::allocator_type allocator;
+        typename bucket_alloc_traits::allocator_type bucket_allocator;
+        bucket_alloc_pointer packed;
+        size_type bucket;
+    };
+
+
+    /*! @copydoc basic_storage_impl */
+    template<typename Entity, typename Type, typename Allocator>
+    class basic_storage_impl<Entity, Type, Allocator, std::enable_if_t<component_traits<Type>::ignore_if_empty::value&& std::is_empty_v<Type>>>
+        : public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>>
+    {
+        using comp_traits = component_traits<Type>;
+        using underlying_type = basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>>;
+        using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
+
+    public:
+        /*! @brief Allocator type. */
+        using allocator_type = typename alloc_traits::allocator_type;
+        /*! @brief Type of the objects assigned to entities. */
+        using value_type = Type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+
+        /**
+         * @brief Default constructor.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_storage_impl(const allocator_type& alloc = {})
+            : underlying_type{ deletion_policy{comp_traits::in_place_delete::value}, alloc }
+        {}
+
+        /**
+         * @brief Fake get function.
+         *
+         * @warning
+         * Attempting to use an entity that doesn't belong to the storage results in
+         * undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         */
+        void get([[maybe_unused]] const entity_type entt) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(underlying_type::contains(entt), "Storage does not contain entity");
+        }
+
+        /**
+         * @brief Assigns an entity to a storage and constructs its object.
+         *
+         * @warning
+         * Attempting to use an entity that already belongs to the storage results
+         * in undefined behavior.
+         *
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to construct an object for the entity.
+         */
+        template<typename... Args>
+        void emplace(const entity_type entt, Args &&... args) {
+            [[maybe_unused]] value_type instance{ std::forward<Args>(args)... };
+            underlying_type::emplace(entt);
+        }
+
+        /**
+        * @brief Updates the instance assigned to a given entity in-place.
+        * @tparam Func Types of the function objects to invoke.
+        * @param entt A valid entity identifier.
+        * @param func Valid function objects.
+        */
+        template<typename... Func>
+        void patch([[maybe_unused]] const entity_type entt, Func &&... func) {
+            ENTT_ASSERT(underlying_type::contains(entt), "Storage does not contain entity");
+            (std::forward<Func>(func)(), ...);
+        }
+
+        /**
+         * @brief Assigns one or more entities to a storage.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the storage
+         * results in undefined behavior.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void insert(It first, It last, const value_type & = {}) {
+            underlying_type::insert(first, last);
+        }
+    };
+
+
+    /**
+     * @brief Mixin type to use to wrap basic storage classes.
+     * @tparam Type The type of the underlying storage.
+     */
+    template<typename Type>
+    struct storage_adapter_mixin : Type {
+        static_assert(std::is_same_v<typename Type::value_type, std::decay_t<typename Type::value_type>>, "Invalid object type");
+
+        /*! @brief Type of the objects assigned to entities. */
+        using value_type = typename Type::value_type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = typename Type::entity_type;
+
+        /*! @brief Inherited constructors. */
+        using Type::Type;
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to initialize the object.
+         * @return A reference to the newly created object.
+         */
+        template<typename... Args>
+        decltype(auto) emplace(basic_registry<entity_type>&, const entity_type entt, Args &&... args) {
+            return Type::emplace(entt, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam It Type of input iterator.
+         * @tparam Args Types of arguments to use to construct the objects assigned
+         * to the entities.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param args Parameters to use to initialize the objects assigned to the
+         * entities.
+         */
+        template<typename It, typename... Args>
+        void insert(basic_registry<entity_type>&, It first, It last, Args &&... args) {
+            Type::insert(first, last, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Patches the given instance for an entity.
+         * @tparam Func Types of the function objects to invoke.
+         * @param entt A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the patched instance.
+         */
+        template<typename... Func>
+        decltype(auto) patch(basic_registry<entity_type>&, const entity_type entt, Func &&... func) {
+            return Type::patch(entt, std::forward<Func>(func)...);
+        }
+    };
+
+
+    /**
+     * @brief Mixin type to use to add signal support to storage types.
+     * @tparam Type The type of the underlying storage.
+     */
+    template<typename Type>
+    class sigh_storage_mixin final : public Type {
+        /*! @copydoc basic_sparse_set::swap_and_pop */
+        void swap_and_pop(const typename Type::entity_type entt, void* ud) final {
+            ENTT_ASSERT(ud != nullptr, "Invalid pointer to registry");
+            destruction.publish(*static_cast<basic_registry<typename Type::entity_type> *>(ud), entt);
+            Type::swap_and_pop(entt, ud);
+        }
+
+        /*! @copydoc basic_sparse_set::in_place_pop */
+        void in_place_pop(const typename Type::entity_type entt, void* ud) final {
+            ENTT_ASSERT(ud != nullptr, "Invalid pointer to registry");
+            destruction.publish(*static_cast<basic_registry<typename Type::entity_type> *>(ud), entt);
+            Type::in_place_pop(entt, ud);
+        }
+
+    public:
+        /*! @brief Underlying value type. */
+        using value_type = typename Type::value_type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = typename Type::entity_type;
+
+        /*! @brief Inherited constructors. */
+        using Type::Type;
+
+        /**
+         * @brief Returns a sink object.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever a new instance is created and assigned to an entity.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<entity_type> &, entity_type);
+         * @endcode
+         *
+         * Listeners are invoked **after** the object has been assigned to the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @return A temporary sink object.
+         */
+        [[nodiscard]] auto on_construct() ENTT_NOEXCEPT {
+            return sink{ construction };
+        }
+
+        /**
+         * @brief Returns a sink object.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance is explicitly updated.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<entity_type> &, entity_type);
+         * @endcode
+         *
+         * Listeners are invoked **after** the object has been updated.
+         *
+         * @sa sink
+         *
+         * @return A temporary sink object.
+         */
+        [[nodiscard]] auto on_update() ENTT_NOEXCEPT {
+            return sink{ update };
+        }
+
+        /**
+         * @brief Returns a sink object.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance is removed from an entity and thus destroyed.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<entity_type> &, entity_type);
+         * @endcode
+         *
+         * Listeners are invoked **before** the object has been removed from the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @return A temporary sink object.
+         */
+        [[nodiscard]] auto on_destroy() ENTT_NOEXCEPT {
+            return sink{ destruction };
+        }
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param owner The registry that issued the request.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to initialize the object.
+         * @return A reference to the newly created object.
+         */
+        template<typename... Args>
+        decltype(auto) emplace(basic_registry<entity_type>& owner, const entity_type entt, Args &&... args) {
+            Type::emplace(entt, std::forward<Args>(args)...);
+            construction.publish(owner, entt);
+            return this->get(entt);
+        }
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam It Type of input iterator.
+         * @tparam Args Types of arguments to use to construct the objects assigned
+         * to the entities.
+         * @param owner The registry that issued the request.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param args Parameters to use to initialize the objects assigned to the
+         * entities.
+         */
+        template<typename It, typename... Args>
+        void insert(basic_registry<entity_type>& owner, It first, It last, Args &&... args) {
+            Type::insert(first, last, std::forward<Args>(args)...);
+
+            if (!construction.empty()) {
+                for (; first != last; ++first) {
+                    construction.publish(owner, *first);
+                }
+            }
+        }
+
+        /**
+         * @brief Patches the given instance for an entity.
+         * @tparam Func Types of the function objects to invoke.
+         * @param owner The registry that issued the request.
+         * @param entt A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the patched instance.
+         */
+        template<typename... Func>
+        decltype(auto) patch(basic_registry<entity_type>& owner, const entity_type entt, Func &&... func) {
+            Type::patch(entt, std::forward<Func>(func)...);
+            update.publish(owner, entt);
+            return this->get(entt);
+        }
+
+    private:
+        sigh<void(basic_registry<entity_type>&, const entity_type)> construction{};
+        sigh<void(basic_registry<entity_type>&, const entity_type)> destruction{};
+        sigh<void(basic_registry<entity_type>&, const entity_type)> update{};
+    };
+
+
+    /**
+     * @brief Storage implementation dispatcher.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Type of objects assigned to the entities.
+     * @tparam Allocator Type of allocator used to manage memory and elements.
+     */
+    template<typename Entity, typename Type, typename Allocator>
+    struct basic_storage : basic_storage_impl<Entity, Type, Allocator> {
+        using basic_storage_impl<Entity, Type, Allocator>::basic_storage_impl;
+    };
+
+
+    /**
+     * @brief Provides a common way to access certain properties of storage types.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Type of objects managed by the storage class.
+     */
+    template<typename Entity, typename Type, typename = void>
+    struct storage_traits {
+        /*! @brief Resulting type after component-to-storage conversion. */
+        using storage_type = sigh_storage_mixin<basic_storage<Entity, Type>>;
+    };
+
+
+    /**
+     * @brief Gets the element assigned to an entity from a storage, if any.
+     * @tparam Type Storage type.
+     * @param container A valid instance of a storage class.
+     * @param entt A valid entity identifier.
+     * @return A possibly empty tuple containing the requested element.
+     */
+    template<typename Type>
+    [[nodiscard]] auto get_as_tuple([[maybe_unused]] Type& container, [[maybe_unused]] const typename Type::entity_type entt) {
+        static_assert(std::is_same_v<std::remove_const_t<Type>, typename storage_traits<typename Type::entity_type, typename Type::value_type>::storage_type>, "Invalid storage");
+
+        if constexpr (std::is_void_v<decltype(container.get({})) > ) {
+            return std::make_tuple();
+        }
+        else {
+            return std::forward_as_tuple(container.get(entt));
+        }
+    }
+
+
+}
+
+
+#endif
+
+// #include "utility.hpp"
+#ifndef ENTT_ENTITY_UTILITY_HPP
+#define ENTT_ENTITY_UTILITY_HPP
+
+
+// #include "../core/type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Alias for exclusion lists.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    struct exclude_t : type_list<Type...> {};
+
+
+    /**
+     * @brief Variable template for exclusion lists.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    inline constexpr exclude_t<Type...> exclude{};
+
+
+    /**
+     * @brief Alias for lists of observed components.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    struct get_t : type_list<Type...> {};
+
+
+    /**
+     * @brief Variable template for lists of observed components.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    inline constexpr get_t<Type...> get{};
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Group.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error, but for a few reasonable cases.
+     */
+    template<typename...>
+    class basic_group;
+
+
+    /**
+     * @brief Non-owning group.
+     *
+     * A non-owning group returns all entities and only the entities that have at
+     * least the given components. Moreover, it's guaranteed that the entity list
+     * is tightly packed in memory for fast iterations.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pools iterated by the group in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Groups share references to the underlying data structures of the registry
+     * that generated them. Therefore any change to the entities and to the
+     * components made by means of the registry are immediately reflected by all the
+     * groups.<br/>
+     * Moreover, sorting a non-owning group affects all the instances of the same
+     * group (it means that users don't have to call `sort` on each instance to sort
+     * all of them because they _share_ entities and components).
+     *
+     * @warning
+     * Lifetime of a group must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a group results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the group.
+     * @tparam Get Type of components observed by the group.
+     */
+    template<typename Entity, typename... Exclude, typename... Get>
+    class basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>> final {
+        /*! @brief A registry is allowed to create groups. */
+        friend class basic_registry<Entity>;
+
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Component>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        class iterable final {
+            template<typename It>
+            struct iterable_iterator final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_group>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                template<typename... Args>
+                iterable_iterator(It from, const std::tuple<storage_type<Get> *...>& args) ENTT_NOEXCEPT
+                    : it{ from },
+                    pools{ args }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return ++it, * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    const auto entt = *it;
+                    return std::tuple_cat(std::make_tuple(entt), get_as_tuple(*std::get<storage_type<Get>*>(pools), entt)...);
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return other.it == it;
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                It it;
+                std::tuple<storage_type<Get> *...> pools;
+            };
+
+        public:
+            using iterator = iterable_iterator<typename basic_common_type::iterator>;
+            using reverse_iterator = iterable_iterator<typename basic_common_type::reverse_iterator>;
+
+            iterable(basic_common_type* const ref, const std::tuple<storage_type<Get> *...>& cpools)
+                : handler{ ref },
+                pools{ cpools }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return handler ? iterator{ handler->begin(), pools } : iterator{ {}, pools };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return handler ? iterator{ handler->end(), pools } : iterator{ {}, pools };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return handler ? reverse_iterator{ handler->rbegin(), pools } : reverse_iterator{ {}, pools };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return handler ? reverse_iterator{ handler->rend(), pools } : reverse_iterator{ {}, pools };
+            }
+
+        private:
+            basic_common_type* const handler;
+            const std::tuple<storage_type<Get> *...> pools;
+        };
+
+        basic_group(basic_common_type& ref, storage_type<Get> &... gpool) ENTT_NOEXCEPT
+            : handler{ &ref },
+            pools{ &gpool... }
+        {}
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_common_type::iterator;
+        /*! @brief Reversed iterator type. */
+        using reverse_iterator = typename basic_common_type::reverse_iterator;
+        /*! @brief Iterable group type. */
+        using iterable_group = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid groups. */
+        basic_group() ENTT_NOEXCEPT
+            : handler{}
+        {}
+
+        /**
+         * @brief Returns the number of entities that have the given components.
+         * @return Number of entities that have the given components.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return *this ? handler->size() : size_type{};
+        }
+
+        /**
+         * @brief Returns the number of elements that a group has currently
+         * allocated space for.
+         * @return Capacity of the group.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return *this ? handler->capacity() : size_type{};
+        }
+
+        /*! @brief Requests the removal of unused capacity. */
+        void shrink_to_fit() {
+            if (*this) {
+                handler->shrink_to_fit();
+            }
+        }
+
+        /**
+         * @brief Checks whether a group is empty.
+         * @return True if the group is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return !*this || handler->empty();
+        }
+
+        /**
+         * @brief Direct access to the list of entities.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] auto data() const ENTT_NOEXCEPT {
+            return *this ? handler->data() : nullptr;
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the group.
+         *
+         * The returned iterator points to the first entity of the group. If the
+         * group is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the group.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return *this ? handler->begin() : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the group. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * group.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return *this ? handler->end() : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed group.
+         *
+         * The returned iterator points to the first entity of the reversed group.
+         * If the group is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed group.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return *this ? handler->rbegin() : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed group. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed group.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return *this ? handler->rend() : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns the first entity of the group, if any.
+         * @return The first entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the group, if any.
+         * @return The last entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = *this ? handler->find(entt) : iterator{};
+            return it != end() && *it == entt ? it : end();
+        }
+
+        /**
+         * @brief Returns the identifier that occupies the given position.
+         * @param pos Position of the element to return.
+         * @return The identifier that occupies the given position.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const {
+            return begin()[pos];
+        }
+
+        /**
+         * @brief Checks if a group is properly initialized.
+         * @return True if the group is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return handler != nullptr;
+        }
+
+        /**
+         * @brief Checks if a group contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the group contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return *this && handler->contains(entt);
+        }
+
+        /**
+         * @brief Returns the components assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the group
+         * results in undefined behavior.
+         *
+         * @tparam Component Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The components assigned to the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get(const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "Group does not contain entity");
+
+            if constexpr (sizeof...(Component) == 0) {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Get>*>(pools), entt)...);
+            }
+            else if constexpr (sizeof...(Component) == 1) {
+                return (std::get<storage_type<Component>*>(pools)->get(entt), ...);
+            }
+            else {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Component>*>(pools), entt)...);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a set of references to non-empty components. The
+         * _constness_ of the components is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Type &...);
+         * void(Type &...);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (const auto entt : *this) {
+                if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({}))) > ) {
+                    std::apply(func, std::tuple_cat(std::make_tuple(entt), get(entt)));
+                }
+                else {
+                    std::apply(func, get(entt));
+                }
+            }
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the group.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * set of references to its non-empty components. The _constness_ of the
+         * components is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the group.
+         */
+        [[nodiscard]] iterable_group each() const ENTT_NOEXCEPT {
+            return iterable_group{ handler, pools };
+        }
+
+        /**
+         * @brief Sort a group according to the given comparison function.
+         *
+         * Sort the group so that iterating it with a couple of iterators returns
+         * entities and components in the expected order. See `begin` and `end` for
+         * more details.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(std::tuple<Component &...>, std::tuple<Component &...>);
+         * bool(const Component &..., const Component &...);
+         * bool(const Entity, const Entity);
+         * @endcode
+         *
+         * Where `Component` are such that they are iterated by the group.<br/>
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @tparam Component Optional types of components to compare.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename... Component, typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            if (*this) {
+                if constexpr (sizeof...(Component) == 0) {
+                    static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
+                    handler->sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
+                }
+                else if constexpr (sizeof...(Component) == 1) {
+                    handler->sort([this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                        return compare((std::get<storage_type<Component>*>(pools)->get(lhs), ...), (std::get<storage_type<Component>*>(pools)->get(rhs), ...));
+                    }, std::move(algo), std::forward<Args>(args)...);
+                }
+                else {
+                    handler->sort([this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                        return compare(std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(lhs)...), std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(rhs)...));
+                    }, std::move(algo), std::forward<Args>(args)...);
+                }
+            }
+        }
+
+        /**
+         * @brief Sort the shared pool of entities according to the given component.
+         *
+         * Non-owning groups of the same type share with the registry a pool of
+         * entities with its own order that doesn't depend on the order of any pool
+         * of components. Users can order the underlying data structure so that it
+         * respects the order of the pool of the given component.
+         *
+         * @note
+         * The shared pool of entities and thus its order is affected by the changes
+         * to each and every pool that it tracks. Therefore changes to those pools
+         * can quickly ruin the order imposed to the pool of entities shared between
+         * the non-owning groups.
+         *
+         * @tparam Component Type of component to use to impose the order.
+         */
+        template<typename Component>
+        void sort() const {
+            if (*this) {
+                handler->respect(*std::get<storage_type<Component>*>(pools));
+            }
+        }
+
+    private:
+        basic_common_type* const handler;
+        const std::tuple<storage_type<Get> *...> pools;
+    };
+
+
+    /**
+     * @brief Owning group.
+     *
+     * Owning groups return all entities and only the entities that have at least
+     * the given components. Moreover:
+     *
+     * * It's guaranteed that the entity list is tightly packed in memory for fast
+     *   iterations.
+     * * It's guaranteed that the lists of owned components are tightly packed in
+     *   memory for even faster iterations and to allow direct access.
+     * * They stay true to the order of the owned components and all instances have
+     *   the same order in memory.
+     *
+     * The more types of components are owned by a group, the faster it is to
+     * iterate them.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pools iterated by the group in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Groups share references to the underlying data structures of the registry
+     * that generated them. Therefore any change to the entities and to the
+     * components made by means of the registry are immediately reflected by all the
+     * groups.
+     * Moreover, sorting an owning group affects all the instance of the same group
+     * (it means that users don't have to call `sort` on each instance to sort all
+     * of them because they share the underlying data structure).
+     *
+     * @warning
+     * Lifetime of a group must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a group results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the group.
+     * @tparam Get Types of components observed by the group.
+     * @tparam Owned Types of components owned by the group.
+     */
+    template<typename Entity, typename... Exclude, typename... Get, typename... Owned>
+    class basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> final {
+        /*! @brief A registry is allowed to create groups. */
+        friend class basic_registry<Entity>;
+
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Component>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        class iterable final {
+            template<typename, typename>
+            struct iterable_iterator;
+
+            template<typename It, typename... OIt>
+            struct iterable_iterator<It, type_list<OIt...>> final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_group>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                template<typename... Other>
+                iterable_iterator(It from, const std::tuple<Other...>& other, const std::tuple<storage_type<Get> *...>& cpools) ENTT_NOEXCEPT
+                    : it{ from },
+                    owned{ std::get<OIt>(other)... },
+                    get{ cpools }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return ++it, (++std::get<OIt>(owned), ...), * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    return std::tuple_cat(
+                        std::make_tuple(*it),
+                        std::forward_as_tuple(*std::get<OIt>(owned)...),
+                        get_as_tuple(*std::get<storage_type<Get>*>(get), *it)...
+                    );
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return other.it == it;
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                It it;
+                std::tuple<OIt...> owned;
+                std::tuple<storage_type<Get> *...> get;
+            };
+
+        public:
+            using iterator = iterable_iterator<
+                typename basic_common_type::iterator,
+                type_list_cat_t < std::conditional_t < std::is_void_v<decltype(std::declval<storage_type<Owned>>().get({})) > , type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().end()) >> ... >
+                > ;
+            using reverse_iterator = iterable_iterator<
+                typename basic_common_type::reverse_iterator,
+                type_list_cat_t < std::conditional_t < std::is_void_v<decltype(std::declval<storage_type<Owned>>().get({})) > , type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().rbegin()) >> ... >
+                > ;
+
+            iterable(std::tuple<storage_type<Owned> *..., storage_type<Get> *...> cpools, const std::size_t* const extent)
+                : pools{ cpools },
+                length{ extent }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return length ? iterator{
+                    std::get<0>(pools)->basic_common_type::end() - *length,
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->end() - *length)...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->end()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return length ? iterator{
+                    std::get<0>(pools)->basic_common_type::end(),
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->end())...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->end()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return length ? reverse_iterator{
+                    std::get<0>(pools)->basic_common_type::rbegin(),
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->rbegin())...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : reverse_iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->rbegin()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return length ? reverse_iterator{
+                    std::get<0>(pools)->basic_common_type::rbegin() + *length,
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->rbegin() + *length)...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : reverse_iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->rbegin()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+        private:
+            const std::tuple<storage_type<Owned> *..., storage_type<Get> *...> pools;
+            const std::size_t* const length;
+        };
+
+        basic_group(const std::size_t& extent, storage_type<Owned> &... opool, storage_type<Get> &... gpool) ENTT_NOEXCEPT
+            : pools{ &opool..., &gpool... },
+            length{ &extent }
+        {}
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_common_type::iterator;
+        /*! @brief Reversed iterator type. */
+        using reverse_iterator = typename basic_common_type::reverse_iterator;
+        /*! @brief Iterable group type. */
+        using iterable_group = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid groups. */
+        basic_group() ENTT_NOEXCEPT
+            : length{}
+        {}
+
+        /**
+         * @brief Returns the number of entities that have the given components.
+         * @return Number of entities that have the given components.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return *this ? *length : size_type{};
+        }
+
+        /**
+         * @brief Checks whether a group is empty.
+         * @return True if the group is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return !*this || !*length;
+        }
+
+        /**
+         * @brief Direct access to the raw representation offered by the storage.
+         *
+         * @warning
+         * This function is only available for owned types.
+         *
+         * @tparam Component Type of component in which one is interested.
+         * @return A pointer to the array of components.
+         */
+        template<typename Component>
+        [[nodiscard]] auto raw() const ENTT_NOEXCEPT {
+            static_assert((std::is_same_v<Component, Owned> || ...), "Non-owned type");
+            auto* cpool = std::get<storage_type<Component>*>(pools);
+            return cpool ? cpool->raw() : decltype(cpool->raw()){};
+        }
+
+        /**
+         * @brief Direct access to the list of entities.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] auto data() const ENTT_NOEXCEPT {
+            return *this ? std::get<0>(pools)->data() : nullptr;
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the group.
+         *
+         * The returned iterator points to the first entity of the group. If the
+         * group is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the group.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return *this ? (std::get<0>(pools)->basic_common_type::end() - *length) : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the group. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * group.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return *this ? std::get<0>(pools)->basic_common_type::end() : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed group.
+         *
+         * The returned iterator points to the first entity of the reversed group.
+         * If the group is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed group.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return *this ? std::get<0>(pools)->basic_common_type::rbegin() : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed group. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed group.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return *this ? (std::get<0>(pools)->basic_common_type::rbegin() + *length) : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns the first entity of the group, if any.
+         * @return The first entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the group, if any.
+         * @return The last entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = *this ? std::get<0>(pools)->find(entt) : iterator{};
+            return it != end() && it >= begin() && *it == entt ? it : end();
+        }
+
+        /**
+         * @brief Returns the identifier that occupies the given position.
+         * @param pos Position of the element to return.
+         * @return The identifier that occupies the given position.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const {
+            return begin()[pos];
+        }
+
+        /**
+         * @brief Checks if a group is properly initialized.
+         * @return True if the group is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return length != nullptr;
+        }
+
+        /**
+         * @brief Checks if a group contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the group contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return *this && std::get<0>(pools)->contains(entt) && (std::get<0>(pools)->index(entt) < (*length));
+        }
+
+        /**
+         * @brief Returns the components assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the group
+         * results in undefined behavior.
+         *
+         * @tparam Component Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The components assigned to the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get(const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "Group does not contain entity");
+
+            if constexpr (sizeof...(Component) == 0) {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Owned>*>(pools), entt)..., get_as_tuple(*std::get<storage_type<Get>*>(pools), entt)...);
+            }
+            else if constexpr (sizeof...(Component) == 1) {
+                return (std::get<storage_type<Component>*>(pools)->get(entt), ...);
+            }
+            else {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Component>*>(pools), entt)...);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a set of references to non-empty components. The
+         * _constness_ of the components is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Type &...);
+         * void(Type &...);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (auto args : each()) {
+                if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({}))) > ) {
+                    std::apply(func, args);
+                }
+                else {
+                    std::apply([&func](auto, auto &&... less) { func(std::forward<decltype(less)>(less)...); }, args);
+                }
+            }
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the group.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * set of references to its non-empty components. The _constness_ of the
+         * components is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the group.
+         */
+        [[nodiscard]] iterable_group each() const ENTT_NOEXCEPT {
+            return iterable_group{ pools, length };
+        }
+
+        /**
+         * @brief Sort a group according to the given comparison function.
+         *
+         * Sort the group so that iterating it with a couple of iterators returns
+         * entities and components in the expected order. See `begin` and `end` for
+         * more details.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(std::tuple<Component &...>, std::tuple<Component &...>);
+         * bool(const Component &, const Component &);
+         * bool(const Entity, const Entity);
+         * @endcode
+         *
+         * Where `Component` are either owned types or not but still such that they
+         * are iterated by the group.<br/>
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @tparam Component Optional types of components to compare.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename... Component, typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) const {
+            auto* cpool = std::get<0>(pools);
+
+            if constexpr (sizeof...(Component) == 0) {
+                static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
+                cpool->sort_n(*length, std::move(compare), std::move(algo), std::forward<Args>(args)...);
+            }
+            else if constexpr (sizeof...(Component) == 1) {
+                cpool->sort_n(*length, [this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                    return compare((std::get<storage_type<Component>*>(pools)->get(lhs), ...), (std::get<storage_type<Component>*>(pools)->get(rhs), ...));
+                }, std::move(algo), std::forward<Args>(args)...);
+            }
+            else {
+                cpool->sort_n(*length, [this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                    return compare(std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(lhs)...), std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(rhs)...));
+                }, std::move(algo), std::forward<Args>(args)...);
+            }
+
+            [this](auto* head, auto *... other) {
+                for (auto next = *length; next; --next) {
+                    const auto pos = next - 1;
+                    [[maybe_unused]] const auto entt = head->data()[pos];
+                    (other->swap(other->data()[pos], entt), ...);
+                }
+            }(std::get<storage_type<Owned>*>(pools)...);
+        }
+
+    private:
+        const std::tuple<storage_type<Owned> *..., storage_type<Get> *...> pools;
+        const size_type* const length;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/handle.hpp"
+#ifndef ENTT_ENTITY_HANDLE_HPP
+#define ENTT_ENTITY_HANDLE_HPP
+
+
+#include <tuple>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "fwd.hpp"
+
+// #include "registry.hpp"
+#ifndef ENTT_ENTITY_REGISTRY_HPP
+#define ENTT_ENTITY_REGISTRY_HPP
+
+
+#include <algorithm>
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+#include <vector>
+// #include "../config/config.h"
+
+// #include "../core/algorithm.hpp"
+
+// #include "../core/any.hpp"
+#ifndef ENTT_CORE_ANY_HPP
+#define ENTT_CORE_ANY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+// #include "type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief A SBO friendly, type-safe container for single values of any type.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<std::size_t Len, std::size_t Align>
+    class basic_any {
+        enum class operation : std::uint8_t { COPY, MOVE, DTOR, COMP, ADDR, CADDR, TYPE };
+        enum class policy : std::uint8_t { OWNER, REF, CREF };
+
+        using storage_type = std::aligned_storage_t<Len + !Len, Align>;
+        using vtable_type = const void* (const operation, const basic_any&, void*);
+
+        template<typename Type>
+        static constexpr bool in_situ = Len && alignof(Type) <= alignof(storage_type) && sizeof(Type) <= sizeof(storage_type) && std::is_nothrow_move_constructible_v<Type>;
+
+        template<typename Type>
+        [[nodiscard]] static constexpr policy type_to_policy() {
+            if constexpr (std::is_lvalue_reference_v<Type>) {
+                if constexpr (std::is_const_v<std::remove_reference_t<Type>>) {
+                    return policy::CREF;
+                }
+                else {
+                    return policy::REF;
+                }
+            }
+            else {
+                return policy::OWNER;
+            }
+        }
+
+        template<typename Type>
+        [[nodiscard]] static bool compare(const void* lhs, const void* rhs) {
+            if constexpr (!std::is_function_v<Type> && is_equality_comparable_v<Type>) {
+                return *static_cast<const Type*>(lhs) == *static_cast<const Type*>(rhs);
+            }
+            else {
+                return lhs == rhs;
+            }
+        }
+
+        template<typename Type>
+        static const void* basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const basic_any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                const Type* instance = (in_situ<Type> && from.mode == policy::OWNER)
+                    ? ENTT_LAUNDER(reinterpret_cast<const Type*>(&from.storage))
+                    : static_cast<const Type*>(from.instance);
+
+                switch (op) {
+                case operation::COPY:
+                    if constexpr (std::is_copy_constructible_v<Type>) {
+                        static_cast<basic_any*>(to)->emplace<Type>(*instance);
+                    }
+                    break;
+                case operation::MOVE:
+                    if constexpr (in_situ<Type>) {
+                        if (from.mode == policy::OWNER) {
+                            return new (&static_cast<basic_any*>(to)->storage) Type{ std::move(*const_cast<Type*>(instance)) };
+                        }
+                    }
+
+                    return (static_cast<basic_any*>(to)->instance = std::exchange(const_cast<basic_any&>(from).instance, nullptr));
+                case operation::DTOR:
+                    if (from.mode == policy::OWNER) {
+                        if constexpr (in_situ<Type>) {
+                            instance->~Type();
+                        }
+                        else if constexpr (std::is_array_v<Type>) {
+                            delete[] instance;
+                        }
+                        else {
+                            delete instance;
+                        }
+                    }
+                    break;
+                case operation::COMP:
+                    return compare<Type>(instance, (*static_cast<const basic_any**>(to))->data()) ? to : nullptr;
+                case operation::ADDR:
+                    if (from.mode == policy::CREF) {
+                        return nullptr;
+                    }
+                    [[fallthrough]];
+                case operation::CADDR:
+                    return instance;
+                case operation::TYPE:
+                    *static_cast<type_info*>(to) = type_id<Type>();
+                    break;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<typename Type, typename... Args>
+        void initialize([[maybe_unused]] Args &&... args) {
+            if constexpr (!std::is_void_v<Type>) {
+                if constexpr (std::is_lvalue_reference_v<Type>) {
+                    static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
+                    instance = (std::addressof(args), ...);
+                }
+                else if constexpr (in_situ<Type>) {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        new (&storage) Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        new (&storage) Type(std::forward<Args>(args)...);
+                    }
+                }
+                else {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        instance = new Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        instance = new Type(std::forward<Args>(args)...);
+                    }
+                }
+            }
+        }
+
+        basic_any(const basic_any& other, const policy pol) ENTT_NOEXCEPT
+            : instance{ other.data() },
+            vtable{ other.vtable },
+            mode{ pol }
+        {}
+
+    public:
+        /*! @brief Size of the internal storage. */
+        static constexpr auto length = Len;
+        /*! @brief Alignment requirement. */
+        static constexpr auto alignment = Align;
+
+        /*! @brief Default constructor. */
+        basic_any() ENTT_NOEXCEPT
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_any(std::in_place_type_t<Type>, Args &&... args)
+            : instance{},
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> },
+            mode{ type_to_policy<Type>() }
+        {
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        basic_any(std::reference_wrapper<Type> value) ENTT_NOEXCEPT
+            : basic_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
+        basic_any(Type&& value)
+            : instance{},
+            vtable{ &basic_vtable<std::decay_t<Type>> },
+            mode{ policy::OWNER }
+        {
+            initialize<std::decay_t<Type>>(std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_any(const basic_any& other)
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {
+            other.vtable(operation::COPY, other, this);
+        }
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_any(basic_any&& other) ENTT_NOEXCEPT
+            : instance{},
+            vtable{ other.vtable },
+            mode{ other.mode }
+        {
+            vtable(operation::MOVE, other, this);
+        }
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~basic_any() {
+            vtable(operation::DTOR, *this, nullptr);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This any object.
+         */
+        basic_any& operator=(const basic_any& other) {
+            reset();
+            other.vtable(operation::COPY, other, this);
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This any object.
+         */
+        basic_any& operator=(basic_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, other.vtable)(operation::DTOR, *this, nullptr);
+            other.vtable(operation::MOVE, other, this);
+            mode = other.mode;
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_any<T &>, emplace<Type &> or forward_as_any instead")]]
+        basic_any& operator=(std::reference_wrapper<Type> value) ENTT_NOEXCEPT {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            type_info info{};
+            vtable(operation::TYPE, *this, &info);
+            return info;
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return vtable(operation::CADDR, *this, nullptr);
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return const_cast<void*>(vtable(operation::ADDR, *this, nullptr));
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, *this, nullptr);
+            mode = type_to_policy<Type>();
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, *this, nullptr);
+            mode = policy::OWNER;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is empty, true otherwise.
+         * @return False if the wrapper is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable(operation::CADDR, *this, nullptr) == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        bool operator==(const basic_any& other) const ENTT_NOEXCEPT {
+            const basic_any* trampoline = &other;
+            return type() == other.type() && (vtable(operation::COMP, *this, &trampoline) || !other.data());
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_any as_ref() ENTT_NOEXCEPT {
+            return basic_any{ *this, (mode == policy::CREF ? policy::CREF : policy::REF) };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_any as_ref() const ENTT_NOEXCEPT {
+            return basic_any{ *this, policy::CREF };
+        }
+
+        /**
+         * @brief Returns true if a wrapper owns its object, false otherwise.
+         * @return True if the wrapper owns its object, false otherwise.
+         */
+        [[nodiscard]] bool owner() const ENTT_NOEXCEPT {
+            return (mode == policy::OWNER);
+        }
+
+    private:
+        union { const void* instance; storage_type storage; };
+        vtable_type* vtable;
+        policy mode;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    template<std::size_t Len, std::size_t Align>
+    [[nodiscard]] inline bool operator!=(const basic_any<Len, Align>& lhs, const basic_any<Len, Align>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Performs type-safe access to the contained object.
+     * @tparam Type Type to which conversion is required.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param data Target any object.
+     * @return The element converted to the requested type.
+     */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(const basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        const auto* const instance = any_cast<std::remove_reference_t<Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>&& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(std::move(*instance));
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    const Type* any_cast(const basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        return (data->type() == type_id<Type>() ? static_cast<const Type*>(data->data()) : nullptr);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type* any_cast(basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        // last attempt to make wrappers for const references return their values
+        return (data->type() == type_id<Type>() ? static_cast<Type*>(static_cast<constness_as_t<basic_any<Len, Align>, Type> *>(data)->data()) : nullptr);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
+    basic_any<Len, Align> make_any(Args &&... args) {
+        return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
+    basic_any<Len, Align> forward_as_any(Type&& value) {
+        return basic_any<Len, Align>{std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value)};
+    }
+
+
+}
+
+
+#endif
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "hashed_string.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "../core/type_traits.hpp"
+
+// #include "component.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "group.hpp"
+#ifndef ENTT_ENTITY_GROUP_HPP
+#define ENTT_ENTITY_GROUP_HPP
+
+
+#include <tuple>
+#include <utility>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "sparse_set.hpp"
+
+// #include "storage.hpp"
+
+// #include "utility.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Group.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error, but for a few reasonable cases.
+     */
+    template<typename...>
+    class basic_group;
+
+
+    /**
+     * @brief Non-owning group.
+     *
+     * A non-owning group returns all entities and only the entities that have at
+     * least the given components. Moreover, it's guaranteed that the entity list
+     * is tightly packed in memory for fast iterations.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pools iterated by the group in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Groups share references to the underlying data structures of the registry
+     * that generated them. Therefore any change to the entities and to the
+     * components made by means of the registry are immediately reflected by all the
+     * groups.<br/>
+     * Moreover, sorting a non-owning group affects all the instances of the same
+     * group (it means that users don't have to call `sort` on each instance to sort
+     * all of them because they _share_ entities and components).
+     *
+     * @warning
+     * Lifetime of a group must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a group results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the group.
+     * @tparam Get Type of components observed by the group.
+     */
+    template<typename Entity, typename... Exclude, typename... Get>
+    class basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>> final {
+        /*! @brief A registry is allowed to create groups. */
+        friend class basic_registry<Entity>;
+
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Component>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        class iterable final {
+            template<typename It>
+            struct iterable_iterator final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_group>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                template<typename... Args>
+                iterable_iterator(It from, const std::tuple<storage_type<Get> *...>& args) ENTT_NOEXCEPT
+                    : it{ from },
+                    pools{ args }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return ++it, * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    const auto entt = *it;
+                    return std::tuple_cat(std::make_tuple(entt), get_as_tuple(*std::get<storage_type<Get>*>(pools), entt)...);
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return other.it == it;
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                It it;
+                std::tuple<storage_type<Get> *...> pools;
+            };
+
+        public:
+            using iterator = iterable_iterator<typename basic_common_type::iterator>;
+            using reverse_iterator = iterable_iterator<typename basic_common_type::reverse_iterator>;
+
+            iterable(basic_common_type* const ref, const std::tuple<storage_type<Get> *...>& cpools)
+                : handler{ ref },
+                pools{ cpools }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return handler ? iterator{ handler->begin(), pools } : iterator{ {}, pools };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return handler ? iterator{ handler->end(), pools } : iterator{ {}, pools };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return handler ? reverse_iterator{ handler->rbegin(), pools } : reverse_iterator{ {}, pools };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return handler ? reverse_iterator{ handler->rend(), pools } : reverse_iterator{ {}, pools };
+            }
+
+        private:
+            basic_common_type* const handler;
+            const std::tuple<storage_type<Get> *...> pools;
+        };
+
+        basic_group(basic_common_type& ref, storage_type<Get> &... gpool) ENTT_NOEXCEPT
+            : handler{ &ref },
+            pools{ &gpool... }
+        {}
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_common_type::iterator;
+        /*! @brief Reversed iterator type. */
+        using reverse_iterator = typename basic_common_type::reverse_iterator;
+        /*! @brief Iterable group type. */
+        using iterable_group = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid groups. */
+        basic_group() ENTT_NOEXCEPT
+            : handler{}
+        {}
+
+        /**
+         * @brief Returns the number of entities that have the given components.
+         * @return Number of entities that have the given components.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return *this ? handler->size() : size_type{};
+        }
+
+        /**
+         * @brief Returns the number of elements that a group has currently
+         * allocated space for.
+         * @return Capacity of the group.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return *this ? handler->capacity() : size_type{};
+        }
+
+        /*! @brief Requests the removal of unused capacity. */
+        void shrink_to_fit() {
+            if (*this) {
+                handler->shrink_to_fit();
+            }
+        }
+
+        /**
+         * @brief Checks whether a group is empty.
+         * @return True if the group is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return !*this || handler->empty();
+        }
+
+        /**
+         * @brief Direct access to the list of entities.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] auto data() const ENTT_NOEXCEPT {
+            return *this ? handler->data() : nullptr;
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the group.
+         *
+         * The returned iterator points to the first entity of the group. If the
+         * group is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the group.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return *this ? handler->begin() : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the group. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * group.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return *this ? handler->end() : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed group.
+         *
+         * The returned iterator points to the first entity of the reversed group.
+         * If the group is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed group.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return *this ? handler->rbegin() : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed group. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed group.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return *this ? handler->rend() : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns the first entity of the group, if any.
+         * @return The first entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the group, if any.
+         * @return The last entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = *this ? handler->find(entt) : iterator{};
+            return it != end() && *it == entt ? it : end();
+        }
+
+        /**
+         * @brief Returns the identifier that occupies the given position.
+         * @param pos Position of the element to return.
+         * @return The identifier that occupies the given position.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const {
+            return begin()[pos];
+        }
+
+        /**
+         * @brief Checks if a group is properly initialized.
+         * @return True if the group is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return handler != nullptr;
+        }
+
+        /**
+         * @brief Checks if a group contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the group contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return *this && handler->contains(entt);
+        }
+
+        /**
+         * @brief Returns the components assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the group
+         * results in undefined behavior.
+         *
+         * @tparam Component Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The components assigned to the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get(const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "Group does not contain entity");
+
+            if constexpr (sizeof...(Component) == 0) {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Get>*>(pools), entt)...);
+            }
+            else if constexpr (sizeof...(Component) == 1) {
+                return (std::get<storage_type<Component>*>(pools)->get(entt), ...);
+            }
+            else {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Component>*>(pools), entt)...);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a set of references to non-empty components. The
+         * _constness_ of the components is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Type &...);
+         * void(Type &...);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (const auto entt : *this) {
+                if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({}))) > ) {
+                    std::apply(func, std::tuple_cat(std::make_tuple(entt), get(entt)));
+                }
+                else {
+                    std::apply(func, get(entt));
+                }
+            }
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the group.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * set of references to its non-empty components. The _constness_ of the
+         * components is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the group.
+         */
+        [[nodiscard]] iterable_group each() const ENTT_NOEXCEPT {
+            return iterable_group{ handler, pools };
+        }
+
+        /**
+         * @brief Sort a group according to the given comparison function.
+         *
+         * Sort the group so that iterating it with a couple of iterators returns
+         * entities and components in the expected order. See `begin` and `end` for
+         * more details.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(std::tuple<Component &...>, std::tuple<Component &...>);
+         * bool(const Component &..., const Component &...);
+         * bool(const Entity, const Entity);
+         * @endcode
+         *
+         * Where `Component` are such that they are iterated by the group.<br/>
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @tparam Component Optional types of components to compare.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename... Component, typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            if (*this) {
+                if constexpr (sizeof...(Component) == 0) {
+                    static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
+                    handler->sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
+                }
+                else if constexpr (sizeof...(Component) == 1) {
+                    handler->sort([this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                        return compare((std::get<storage_type<Component>*>(pools)->get(lhs), ...), (std::get<storage_type<Component>*>(pools)->get(rhs), ...));
+                    }, std::move(algo), std::forward<Args>(args)...);
+                }
+                else {
+                    handler->sort([this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                        return compare(std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(lhs)...), std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(rhs)...));
+                    }, std::move(algo), std::forward<Args>(args)...);
+                }
+            }
+        }
+
+        /**
+         * @brief Sort the shared pool of entities according to the given component.
+         *
+         * Non-owning groups of the same type share with the registry a pool of
+         * entities with its own order that doesn't depend on the order of any pool
+         * of components. Users can order the underlying data structure so that it
+         * respects the order of the pool of the given component.
+         *
+         * @note
+         * The shared pool of entities and thus its order is affected by the changes
+         * to each and every pool that it tracks. Therefore changes to those pools
+         * can quickly ruin the order imposed to the pool of entities shared between
+         * the non-owning groups.
+         *
+         * @tparam Component Type of component to use to impose the order.
+         */
+        template<typename Component>
+        void sort() const {
+            if (*this) {
+                handler->respect(*std::get<storage_type<Component>*>(pools));
+            }
+        }
+
+    private:
+        basic_common_type* const handler;
+        const std::tuple<storage_type<Get> *...> pools;
+    };
+
+
+    /**
+     * @brief Owning group.
+     *
+     * Owning groups return all entities and only the entities that have at least
+     * the given components. Moreover:
+     *
+     * * It's guaranteed that the entity list is tightly packed in memory for fast
+     *   iterations.
+     * * It's guaranteed that the lists of owned components are tightly packed in
+     *   memory for even faster iterations and to allow direct access.
+     * * They stay true to the order of the owned components and all instances have
+     *   the same order in memory.
+     *
+     * The more types of components are owned by a group, the faster it is to
+     * iterate them.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pools iterated by the group in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Groups share references to the underlying data structures of the registry
+     * that generated them. Therefore any change to the entities and to the
+     * components made by means of the registry are immediately reflected by all the
+     * groups.
+     * Moreover, sorting an owning group affects all the instance of the same group
+     * (it means that users don't have to call `sort` on each instance to sort all
+     * of them because they share the underlying data structure).
+     *
+     * @warning
+     * Lifetime of a group must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a group results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the group.
+     * @tparam Get Types of components observed by the group.
+     * @tparam Owned Types of components owned by the group.
+     */
+    template<typename Entity, typename... Exclude, typename... Get, typename... Owned>
+    class basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> final {
+        /*! @brief A registry is allowed to create groups. */
+        friend class basic_registry<Entity>;
+
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Component>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        class iterable final {
+            template<typename, typename>
+            struct iterable_iterator;
+
+            template<typename It, typename... OIt>
+            struct iterable_iterator<It, type_list<OIt...>> final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_group>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                template<typename... Other>
+                iterable_iterator(It from, const std::tuple<Other...>& other, const std::tuple<storage_type<Get> *...>& cpools) ENTT_NOEXCEPT
+                    : it{ from },
+                    owned{ std::get<OIt>(other)... },
+                    get{ cpools }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return ++it, (++std::get<OIt>(owned), ...), * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    return std::tuple_cat(
+                        std::make_tuple(*it),
+                        std::forward_as_tuple(*std::get<OIt>(owned)...),
+                        get_as_tuple(*std::get<storage_type<Get>*>(get), *it)...
+                    );
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return other.it == it;
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                It it;
+                std::tuple<OIt...> owned;
+                std::tuple<storage_type<Get> *...> get;
+            };
+
+        public:
+            using iterator = iterable_iterator<
+                typename basic_common_type::iterator,
+                type_list_cat_t < std::conditional_t < std::is_void_v<decltype(std::declval<storage_type<Owned>>().get({})) > , type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().end()) >> ... >
+                > ;
+            using reverse_iterator = iterable_iterator<
+                typename basic_common_type::reverse_iterator,
+                type_list_cat_t < std::conditional_t < std::is_void_v<decltype(std::declval<storage_type<Owned>>().get({})) > , type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().rbegin()) >> ... >
+                > ;
+
+            iterable(std::tuple<storage_type<Owned> *..., storage_type<Get> *...> cpools, const std::size_t* const extent)
+                : pools{ cpools },
+                length{ extent }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return length ? iterator{
+                    std::get<0>(pools)->basic_common_type::end() - *length,
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->end() - *length)...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->end()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return length ? iterator{
+                    std::get<0>(pools)->basic_common_type::end(),
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->end())...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->end()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return length ? reverse_iterator{
+                    std::get<0>(pools)->basic_common_type::rbegin(),
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->rbegin())...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : reverse_iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->rbegin()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return length ? reverse_iterator{
+                    std::get<0>(pools)->basic_common_type::rbegin() + *length,
+                    std::make_tuple((std::get<storage_type<Owned>*>(pools)->rbegin() + *length)...),
+                    std::make_tuple(std::get<storage_type<Get>*>(pools)...)
+                } : reverse_iterator{ {}, std::make_tuple(decltype(std::get<storage_type<Owned>*>(pools)->rbegin()){}...), std::make_tuple(std::get<storage_type<Get>*>(pools)...) };
+            }
+
+        private:
+            const std::tuple<storage_type<Owned> *..., storage_type<Get> *...> pools;
+            const std::size_t* const length;
+        };
+
+        basic_group(const std::size_t& extent, storage_type<Owned> &... opool, storage_type<Get> &... gpool) ENTT_NOEXCEPT
+            : pools{ &opool..., &gpool... },
+            length{ &extent }
+        {}
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_common_type::iterator;
+        /*! @brief Reversed iterator type. */
+        using reverse_iterator = typename basic_common_type::reverse_iterator;
+        /*! @brief Iterable group type. */
+        using iterable_group = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid groups. */
+        basic_group() ENTT_NOEXCEPT
+            : length{}
+        {}
+
+        /**
+         * @brief Returns the number of entities that have the given components.
+         * @return Number of entities that have the given components.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return *this ? *length : size_type{};
+        }
+
+        /**
+         * @brief Checks whether a group is empty.
+         * @return True if the group is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return !*this || !*length;
+        }
+
+        /**
+         * @brief Direct access to the raw representation offered by the storage.
+         *
+         * @warning
+         * This function is only available for owned types.
+         *
+         * @tparam Component Type of component in which one is interested.
+         * @return A pointer to the array of components.
+         */
+        template<typename Component>
+        [[nodiscard]] auto raw() const ENTT_NOEXCEPT {
+            static_assert((std::is_same_v<Component, Owned> || ...), "Non-owned type");
+            auto* cpool = std::get<storage_type<Component>*>(pools);
+            return cpool ? cpool->raw() : decltype(cpool->raw()){};
+        }
+
+        /**
+         * @brief Direct access to the list of entities.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] auto data() const ENTT_NOEXCEPT {
+            return *this ? std::get<0>(pools)->data() : nullptr;
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the group.
+         *
+         * The returned iterator points to the first entity of the group. If the
+         * group is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the group.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return *this ? (std::get<0>(pools)->basic_common_type::end() - *length) : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the group. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * group.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return *this ? std::get<0>(pools)->basic_common_type::end() : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed group.
+         *
+         * The returned iterator points to the first entity of the reversed group.
+         * If the group is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed group.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return *this ? std::get<0>(pools)->basic_common_type::rbegin() : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * group.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed group. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed group.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return *this ? (std::get<0>(pools)->basic_common_type::rbegin() + *length) : reverse_iterator{};
+        }
+
+        /**
+         * @brief Returns the first entity of the group, if any.
+         * @return The first entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the group, if any.
+         * @return The last entity of the group if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = *this ? std::get<0>(pools)->find(entt) : iterator{};
+            return it != end() && it >= begin() && *it == entt ? it : end();
+        }
+
+        /**
+         * @brief Returns the identifier that occupies the given position.
+         * @param pos Position of the element to return.
+         * @return The identifier that occupies the given position.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const {
+            return begin()[pos];
+        }
+
+        /**
+         * @brief Checks if a group is properly initialized.
+         * @return True if the group is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return length != nullptr;
+        }
+
+        /**
+         * @brief Checks if a group contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the group contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return *this && std::get<0>(pools)->contains(entt) && (std::get<0>(pools)->index(entt) < (*length));
+        }
+
+        /**
+         * @brief Returns the components assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the group
+         * results in undefined behavior.
+         *
+         * @tparam Component Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The components assigned to the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get(const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "Group does not contain entity");
+
+            if constexpr (sizeof...(Component) == 0) {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Owned>*>(pools), entt)..., get_as_tuple(*std::get<storage_type<Get>*>(pools), entt)...);
+            }
+            else if constexpr (sizeof...(Component) == 1) {
+                return (std::get<storage_type<Component>*>(pools)->get(entt), ...);
+            }
+            else {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Component>*>(pools), entt)...);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a set of references to non-empty components. The
+         * _constness_ of the components is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Type &...);
+         * void(Type &...);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (auto args : each()) {
+                if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({}))) > ) {
+                    std::apply(func, args);
+                }
+                else {
+                    std::apply([&func](auto, auto &&... less) { func(std::forward<decltype(less)>(less)...); }, args);
+                }
+            }
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the group.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * set of references to its non-empty components. The _constness_ of the
+         * components is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the group.
+         */
+        [[nodiscard]] iterable_group each() const ENTT_NOEXCEPT {
+            return iterable_group{ pools, length };
+        }
+
+        /**
+         * @brief Sort a group according to the given comparison function.
+         *
+         * Sort the group so that iterating it with a couple of iterators returns
+         * entities and components in the expected order. See `begin` and `end` for
+         * more details.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(std::tuple<Component &...>, std::tuple<Component &...>);
+         * bool(const Component &, const Component &);
+         * bool(const Entity, const Entity);
+         * @endcode
+         *
+         * Where `Component` are either owned types or not but still such that they
+         * are iterated by the group.<br/>
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @tparam Component Optional types of components to compare.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename... Component, typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) const {
+            auto* cpool = std::get<0>(pools);
+
+            if constexpr (sizeof...(Component) == 0) {
+                static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
+                cpool->sort_n(*length, std::move(compare), std::move(algo), std::forward<Args>(args)...);
+            }
+            else if constexpr (sizeof...(Component) == 1) {
+                cpool->sort_n(*length, [this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                    return compare((std::get<storage_type<Component>*>(pools)->get(lhs), ...), (std::get<storage_type<Component>*>(pools)->get(rhs), ...));
+                }, std::move(algo), std::forward<Args>(args)...);
+            }
+            else {
+                cpool->sort_n(*length, [this, compare = std::move(compare)](const entity_type lhs, const entity_type rhs) {
+                    return compare(std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(lhs)...), std::forward_as_tuple(std::get<storage_type<Component>*>(pools)->get(rhs)...));
+                }, std::move(algo), std::forward<Args>(args)...);
+            }
+
+            [this](auto* head, auto *... other) {
+                for (auto next = *length; next; --next) {
+                    const auto pos = next - 1;
+                    [[maybe_unused]] const auto entt = head->data()[pos];
+                    (other->swap(other->data()[pos], entt), ...);
+                }
+            }(std::get<storage_type<Owned>*>(pools)...);
+        }
+
+    private:
+        const std::tuple<storage_type<Owned> *..., storage_type<Get> *...> pools;
+        const size_type* const length;
+    };
+
+
+}
+
+
+#endif
+
+// #include "poly_storage.hpp"
+#ifndef ENTT_ENTITY_POLY_STORAGE_HPP
+#define ENTT_ENTITY_POLY_STORAGE_HPP
+
+
+#include <cstddef>
+#include <tuple>
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../poly/poly.hpp"
+#ifndef ENTT_POLY_POLY_HPP
+#define ENTT_POLY_POLY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "../core/any.hpp"
+#ifndef ENTT_CORE_ANY_HPP
+#define ENTT_CORE_ANY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "../core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+// #include "type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief A SBO friendly, type-safe container for single values of any type.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<std::size_t Len, std::size_t Align>
+    class basic_any {
+        enum class operation : std::uint8_t { COPY, MOVE, DTOR, COMP, ADDR, CADDR, TYPE };
+        enum class policy : std::uint8_t { OWNER, REF, CREF };
+
+        using storage_type = std::aligned_storage_t<Len + !Len, Align>;
+        using vtable_type = const void* (const operation, const basic_any&, void*);
+
+        template<typename Type>
+        static constexpr bool in_situ = Len && alignof(Type) <= alignof(storage_type) && sizeof(Type) <= sizeof(storage_type) && std::is_nothrow_move_constructible_v<Type>;
+
+        template<typename Type>
+        [[nodiscard]] static constexpr policy type_to_policy() {
+            if constexpr (std::is_lvalue_reference_v<Type>) {
+                if constexpr (std::is_const_v<std::remove_reference_t<Type>>) {
+                    return policy::CREF;
+                }
+                else {
+                    return policy::REF;
+                }
+            }
+            else {
+                return policy::OWNER;
+            }
+        }
+
+        template<typename Type>
+        [[nodiscard]] static bool compare(const void* lhs, const void* rhs) {
+            if constexpr (!std::is_function_v<Type> && is_equality_comparable_v<Type>) {
+                return *static_cast<const Type*>(lhs) == *static_cast<const Type*>(rhs);
+            }
+            else {
+                return lhs == rhs;
+            }
+        }
+
+        template<typename Type>
+        static const void* basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const basic_any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                const Type* instance = (in_situ<Type> && from.mode == policy::OWNER)
+                    ? ENTT_LAUNDER(reinterpret_cast<const Type*>(&from.storage))
+                    : static_cast<const Type*>(from.instance);
+
+                switch (op) {
+                case operation::COPY:
+                    if constexpr (std::is_copy_constructible_v<Type>) {
+                        static_cast<basic_any*>(to)->emplace<Type>(*instance);
+                    }
+                    break;
+                case operation::MOVE:
+                    if constexpr (in_situ<Type>) {
+                        if (from.mode == policy::OWNER) {
+                            return new (&static_cast<basic_any*>(to)->storage) Type{ std::move(*const_cast<Type*>(instance)) };
+                        }
+                    }
+
+                    return (static_cast<basic_any*>(to)->instance = std::exchange(const_cast<basic_any&>(from).instance, nullptr));
+                case operation::DTOR:
+                    if (from.mode == policy::OWNER) {
+                        if constexpr (in_situ<Type>) {
+                            instance->~Type();
+                        }
+                        else if constexpr (std::is_array_v<Type>) {
+                            delete[] instance;
+                        }
+                        else {
+                            delete instance;
+                        }
+                    }
+                    break;
+                case operation::COMP:
+                    return compare<Type>(instance, (*static_cast<const basic_any**>(to))->data()) ? to : nullptr;
+                case operation::ADDR:
+                    if (from.mode == policy::CREF) {
+                        return nullptr;
+                    }
+                    [[fallthrough]];
+                case operation::CADDR:
+                    return instance;
+                case operation::TYPE:
+                    *static_cast<type_info*>(to) = type_id<Type>();
+                    break;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<typename Type, typename... Args>
+        void initialize([[maybe_unused]] Args &&... args) {
+            if constexpr (!std::is_void_v<Type>) {
+                if constexpr (std::is_lvalue_reference_v<Type>) {
+                    static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
+                    instance = (std::addressof(args), ...);
+                }
+                else if constexpr (in_situ<Type>) {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        new (&storage) Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        new (&storage) Type(std::forward<Args>(args)...);
+                    }
+                }
+                else {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        instance = new Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        instance = new Type(std::forward<Args>(args)...);
+                    }
+                }
+            }
+        }
+
+        basic_any(const basic_any& other, const policy pol) ENTT_NOEXCEPT
+            : instance{ other.data() },
+            vtable{ other.vtable },
+            mode{ pol }
+        {}
+
+    public:
+        /*! @brief Size of the internal storage. */
+        static constexpr auto length = Len;
+        /*! @brief Alignment requirement. */
+        static constexpr auto alignment = Align;
+
+        /*! @brief Default constructor. */
+        basic_any() ENTT_NOEXCEPT
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_any(std::in_place_type_t<Type>, Args &&... args)
+            : instance{},
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> },
+            mode{ type_to_policy<Type>() }
+        {
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        basic_any(std::reference_wrapper<Type> value) ENTT_NOEXCEPT
+            : basic_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
+        basic_any(Type&& value)
+            : instance{},
+            vtable{ &basic_vtable<std::decay_t<Type>> },
+            mode{ policy::OWNER }
+        {
+            initialize<std::decay_t<Type>>(std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_any(const basic_any& other)
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {
+            other.vtable(operation::COPY, other, this);
+        }
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_any(basic_any&& other) ENTT_NOEXCEPT
+            : instance{},
+            vtable{ other.vtable },
+            mode{ other.mode }
+        {
+            vtable(operation::MOVE, other, this);
+        }
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~basic_any() {
+            vtable(operation::DTOR, *this, nullptr);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This any object.
+         */
+        basic_any& operator=(const basic_any& other) {
+            reset();
+            other.vtable(operation::COPY, other, this);
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This any object.
+         */
+        basic_any& operator=(basic_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, other.vtable)(operation::DTOR, *this, nullptr);
+            other.vtable(operation::MOVE, other, this);
+            mode = other.mode;
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_any<T &>, emplace<Type &> or forward_as_any instead")]]
+        basic_any& operator=(std::reference_wrapper<Type> value) ENTT_NOEXCEPT {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            type_info info{};
+            vtable(operation::TYPE, *this, &info);
+            return info;
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return vtable(operation::CADDR, *this, nullptr);
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return const_cast<void*>(vtable(operation::ADDR, *this, nullptr));
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, *this, nullptr);
+            mode = type_to_policy<Type>();
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, *this, nullptr);
+            mode = policy::OWNER;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is empty, true otherwise.
+         * @return False if the wrapper is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable(operation::CADDR, *this, nullptr) == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        bool operator==(const basic_any& other) const ENTT_NOEXCEPT {
+            const basic_any* trampoline = &other;
+            return type() == other.type() && (vtable(operation::COMP, *this, &trampoline) || !other.data());
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_any as_ref() ENTT_NOEXCEPT {
+            return basic_any{ *this, (mode == policy::CREF ? policy::CREF : policy::REF) };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_any as_ref() const ENTT_NOEXCEPT {
+            return basic_any{ *this, policy::CREF };
+        }
+
+        /**
+         * @brief Returns true if a wrapper owns its object, false otherwise.
+         * @return True if the wrapper owns its object, false otherwise.
+         */
+        [[nodiscard]] bool owner() const ENTT_NOEXCEPT {
+            return (mode == policy::OWNER);
+        }
+
+    private:
+        union { const void* instance; storage_type storage; };
+        vtable_type* vtable;
+        policy mode;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    template<std::size_t Len, std::size_t Align>
+    [[nodiscard]] inline bool operator!=(const basic_any<Len, Align>& lhs, const basic_any<Len, Align>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Performs type-safe access to the contained object.
+     * @tparam Type Type to which conversion is required.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param data Target any object.
+     * @return The element converted to the requested type.
+     */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(const basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        const auto* const instance = any_cast<std::remove_reference_t<Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>&& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(std::move(*instance));
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    const Type* any_cast(const basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        return (data->type() == type_id<Type>() ? static_cast<const Type*>(data->data()) : nullptr);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type* any_cast(basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        // last attempt to make wrappers for const references return their values
+        return (data->type() == type_id<Type>() ? static_cast<Type*>(static_cast<constness_as_t<basic_any<Len, Align>, Type> *>(data)->data()) : nullptr);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
+    basic_any<Len, Align> make_any(Args &&... args) {
+        return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
+    basic_any<Len, Align> forward_as_any(Type&& value) {
+        return basic_any<Len, Align>{std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value)};
+    }
+
+
+}
+
+
+#endif
+
+// #include "../core/type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "hashed_string.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "../core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_POLY_FWD_HPP
+#define ENTT_POLY_FWD_HPP
+
+
+#include <type_traits>
+
+
+namespace entt {
+
+
+    template<typename, std::size_t Len, std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_poly;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Concept Concept descriptor.
+     */
+    template<typename Concept>
+    using poly = basic_poly<Concept, sizeof(double[2])>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Inspector class used to infer the type of the virtual table. */
+    struct poly_inspector {
+        /**
+         * @brief Generic conversion operator (definition only).
+         * @tparam Type Type to which conversion is requested.
+         */
+        template <class Type>
+        operator Type && () const;
+
+        /**
+         * @brief Dummy invocation function (definition only).
+         * @tparam Member Index of the function to invoke.
+         * @tparam Args Types of arguments to pass to the function.
+         * @param args The arguments to pass to the function.
+         * @return A poly inspector convertible to any type.
+         */
+        template<auto Member, typename... Args>
+        poly_inspector invoke(Args &&... args) const;
+
+        /*! @copydoc invoke */
+        template<auto Member, typename... Args>
+        poly_inspector invoke(Args &&... args);
+    };
+
+
+    /**
+     * @brief Static virtual table factory.
+     * @tparam Concept Concept descriptor.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     */
+    template<typename Concept, std::size_t Len, std::size_t Align>
+    class poly_vtable {
+        using inspector = typename Concept::template type<poly_inspector>;
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(*)(inspector&, Args...))->Ret(*)(basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(*)(const inspector&, Args...))->Ret(*)(const basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(*)(Args...))->Ret(*)(const basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(inspector::*)(Args...))->Ret(*)(basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(inspector::*)(Args...) const)->Ret(*)(const basic_any<Len, Align>&, Args...);
+
+        template<auto... Candidate>
+        static auto make_vtable(value_list<Candidate...>)
+            -> decltype(std::make_tuple(vtable_entry(Candidate)...));
+
+        template<typename... Func>
+        [[nodiscard]] static constexpr auto make_vtable(type_list<Func...>) {
+            if constexpr (sizeof...(Func) == 0) {
+                return decltype(make_vtable(typename Concept::template impl<inspector>{})){};
+            }
+            else if constexpr ((std::is_function_v<Func> && ...)) {
+                return decltype(std::make_tuple(vtable_entry(std::declval<Func inspector::*>())...)){};
+            }
+        }
+
+        template<typename Type, auto Candidate, typename Ret, typename Any, typename... Args>
+        static void fill_vtable_entry(Ret(*&entry)(Any&, Args...)) {
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
+                entry = +[](Any&, Args... args) -> Ret {
+                    return std::invoke(Candidate, std::forward<Args>(args)...);
+                };
+            }
+            else {
+                entry = +[](Any& instance, Args... args) -> Ret {
+                    return static_cast<Ret>(std::invoke(Candidate, any_cast<constness_as_t<Type, Any>&>(instance), std::forward<Args>(args)...));
+                };
+            }
+        }
+
+        template<typename Type, auto... Index>
+        [[nodiscard]] static auto fill_vtable(std::index_sequence<Index...>) {
+            type impl{};
+            (fill_vtable_entry<Type, value_list_element_v<Index, typename Concept::template impl<Type>>>(std::get<Index>(impl)), ...);
+            return impl;
+        }
+
+    public:
+        /*! @brief Virtual table type. */
+        using type = decltype(make_vtable(Concept{}));
+
+        /**
+         * @brief Returns a static virtual table for a specific concept and type.
+         * @tparam Type The type for which to generate the virtual table.
+         * @return A static virtual table for the given concept and type.
+         */
+        template<typename Type>
+        [[nodiscard]] static const auto* instance() {
+            static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Type differs from its decayed form");
+            static const auto vtable = fill_vtable<Type>(std::make_index_sequence<Concept::template impl<Type>::size>{});
+            return &vtable;
+        }
+    };
+
+
+    /**
+     * @brief Poly base class used to inject functionalities into concepts.
+     * @tparam Poly The outermost poly class.
+     */
+    template<typename Poly>
+    struct poly_base {
+        /**
+         * @brief Invokes a function from the static virtual table.
+         * @tparam Member Index of the function to invoke.
+         * @tparam Args Types of arguments to pass to the function.
+         * @param self A reference to the poly object that made the call.
+         * @param args The arguments to pass to the function.
+         * @return The return value of the invoked function, if any.
+         */
+        template<auto Member, typename... Args>
+        [[nodiscard]] decltype(auto) invoke(const poly_base& self, Args &&... args) const {
+            const auto& poly = static_cast<const Poly&>(self);
+            return std::get<Member>(*poly.vtable)(poly.storage, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc invoke */
+        template<auto Member, typename... Args>
+        [[nodiscard]] decltype(auto) invoke(poly_base& self, Args &&... args) {
+            auto& poly = static_cast<Poly&>(self);
+            return std::get<Member>(*poly.vtable)(poly.storage, std::forward<Args>(args)...);
+        }
+    };
+
+
+    /**
+     * @brief Shortcut for calling `poly_base<Type>::invoke`.
+     * @tparam Member Index of the function to invoke.
+     * @tparam Poly A fully defined poly object.
+     * @tparam Args Types of arguments to pass to the function.
+     * @param self A reference to the poly object that made the call.
+     * @param args The arguments to pass to the function.
+     * @return The return value of the invoked function, if any.
+     */
+    template<auto Member, typename Poly, typename... Args>
+    decltype(auto) poly_call(Poly&& self, Args &&... args) {
+        return std::forward<Poly>(self).template invoke<Member>(self, std::forward<Args>(args)...);
+    }
+
+
+    /**
+     * @brief Static polymorphism made simple and within everyone's reach.
+     *
+     * Static polymorphism is a very powerful tool in C++, albeit sometimes
+     * cumbersome to obtain.<br/>
+     * This class aims to make it simple and easy to use.
+     *
+     * @note
+     * Both deduced and defined static virtual tables are supported.<br/>
+     * Moreover, the `poly` class template also works with unmanaged objects.
+     *
+     * @tparam Concept Concept descriptor.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<typename Concept, std::size_t Len, std::size_t Align>
+    class basic_poly : private Concept::template type<poly_base<basic_poly<Concept, Len, Align>>> {
+        /*! @brief A poly base is allowed to snoop into a poly object. */
+        friend struct poly_base<basic_poly>;
+
+        using vtable_type = typename poly_vtable<Concept, Len, Align>::type;
+
+    public:
+        /*! @brief Concept type. */
+        using concept_type = typename Concept::template type<poly_base<basic_poly>>;
+
+        /*! @brief Default constructor. */
+        basic_poly() ENTT_NOEXCEPT
+            : storage{},
+            vtable{}
+        {}
+
+        /**
+         * @brief Constructs a poly by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the poly.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_poly(std::in_place_type_t<Type>, Args &&... args)
+            : storage{ std::in_place_type<Type>, std::forward<Args>(args)... },
+            vtable{ poly_vtable<Concept, Len, Align>::template instance<std::remove_const_t<std::remove_reference_t<Type>>>() }
+        {}
+
+        /**
+         * @brief Constructs a poly from a given value.
+         * @tparam Type Type of object to use to initialize the poly.
+         * @param value An instance of an object to use to initialize the poly.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, basic_poly>>>
+        basic_poly(Type&& value) ENTT_NOEXCEPT
+            : basic_poly{ std::in_place_type<std::remove_cv_t<std::remove_reference_t<Type>>>, std::forward<Type>(value) }
+        {}
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_poly(const basic_poly& other) = default;
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_poly(basic_poly&& other) ENTT_NOEXCEPT
+            : basic_poly{}
+        {
+            swap(*this, other);
+        }
+
+        /**
+         * @brief Assignment operator.
+         * @param other The instance to assign from.
+         * @return This poly object.
+         */
+        basic_poly& operator=(basic_poly other) {
+            swap(other, *this);
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            return storage.type();
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the poly.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            *this = basic_poly{ std::in_place_type<Type>, std::forward<Args>(args)... };
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            *this = basic_poly{};
+        }
+
+        /**
+         * @brief Returns false if a poly is empty, true otherwise.
+         * @return False if the poly is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable == nullptr);
+        }
+
+        /**
+         * @brief Returns a pointer to the underlying concept.
+         * @return A pointer to the underlying concept.
+         */
+        [[nodiscard]] concept_type* operator->() ENTT_NOEXCEPT {
+            return this;
+        }
+
+        /*! @copydoc operator-> */
+        [[nodiscard]] const concept_type* operator->() const ENTT_NOEXCEPT {
+            return this;
+        }
+
+        /**
+         * @brief Swaps two poly objects.
+         * @param lhs A valid poly object.
+         * @param rhs A valid poly object.
+         */
+        friend void swap(basic_poly& lhs, basic_poly& rhs) {
+            using std::swap;
+            swap(lhs.storage, rhs.storage);
+            swap(lhs.vtable, rhs.vtable);
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A poly that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_poly as_ref() ENTT_NOEXCEPT {
+            basic_poly ref = std::as_const(*this).as_ref();
+            ref.storage = storage.as_ref();
+            return ref;
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_poly as_ref() const ENTT_NOEXCEPT {
+            basic_poly ref{};
+            ref.storage = storage.as_ref();
+            ref.vtable = vtable;
+            return ref;
+        }
+
+    private:
+        basic_any<Len, Align> storage;
+        const vtable_type* vtable;
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Basic poly storage implementation.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    struct Storage : type_list<type_info() const ENTT_NOEXCEPT> {
+        /**
+         * @brief Concept definition.
+         * @tparam Base Opaque base class from which to inherit.
+         */
+        template<typename Base>
+        struct type : Base {
+            /**
+             * @brief Returns a type info for the contained objects.
+             * @return The type info for the contained objects.
+             */
+            type_info value_type() const ENTT_NOEXCEPT {
+                return poly_call<0>(*this);
+            }
+        };
+
+        /**
+         * @brief Concept implementation.
+         * @tparam Type Type for which to generate an implementation.
+         */
+        template<typename Type>
+        using impl = value_list<&type_id<typename Type::value_type>>;
+    };
+
+
+    /**
+     * @brief Defines the poly storage type associate with a given entity type.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity, typename = void>
+    struct poly_storage_traits {
+        /*! @brief Poly storage type for the given entity type. */
+        using storage_type = poly<Storage<Entity>>;
+    };
+
+
+}
+
+
+#endif
+
+// #include "runtime_view.hpp"
+#ifndef ENTT_ENTITY_RUNTIME_VIEW_HPP
+#define ENTT_ENTITY_RUNTIME_VIEW_HPP
+
+
+#include <iterator>
+#include <vector>
+#include <utility>
+#include <algorithm>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "entity.hpp"
+
+// #include "sparse_set.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Runtime view.
+     *
+     * Runtime views iterate over those entities that have at least all the given
+     * components in their bags. During initialization, a runtime view looks at the
+     * number of entities available for each component and picks up a reference to
+     * the smallest set of candidate entities in order to get a performance boost
+     * when iterate.<br/>
+     * Order of elements during iterations are highly dependent on the order of the
+     * underlying data structures. See sparse_set and its specializations for more
+     * details.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all the other cases, modifying the pools of the given components in any
+     * way invalidates all the iterators and using them results in undefined
+     * behavior.
+     *
+     * @note
+     * Views share references to the underlying data structures of the registry that
+     * generated them. Therefore any change to the entities and to the components
+     * made by means of the registry are immediately reflected by the views, unless
+     * a pool was missing when the view was built (in this case, the view won't
+     * have a valid reference and won't be updated accordingly).
+     *
+     * @warning
+     * Lifetime of a view must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a view results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_runtime_view final {
+        using basic_common_type = basic_sparse_set<Entity>;
+        using underlying_iterator = typename basic_common_type::iterator;
+
+        class view_iterator final {
+            [[nodiscard]] bool valid() const {
+                const auto entt = *it;
+
+                return (!stable_storage || (entt != tombstone))
+                    && std::all_of(pools->begin()++, pools->end(), [entt](const auto* curr) { return curr->contains(entt); })
+                    && std::none_of(filter->cbegin(), filter->cend(), [entt](const auto* curr) { return curr && curr->contains(entt); });
+            }
+
+        public:
+            using difference_type = typename underlying_iterator::difference_type;
+            using value_type = typename underlying_iterator::value_type;
+            using pointer = typename underlying_iterator::pointer;
+            using reference = typename underlying_iterator::reference;
+            using iterator_category = std::bidirectional_iterator_tag;
+
+            view_iterator() ENTT_NOEXCEPT = default;
+
+            view_iterator(const std::vector<const basic_common_type*>& cpools, const std::vector<const basic_common_type*>& ignore, underlying_iterator curr) ENTT_NOEXCEPT
+                : pools{ &cpools },
+                filter{ &ignore },
+                it{ curr },
+                stable_storage{ std::any_of(pools->cbegin(), pools->cend(), [](const basic_common_type* cpool) { return (cpool->policy() == deletion_policy::in_place); }) }
+            {
+                if (it != (*pools)[0]->end() && !valid()) {
+                    ++(*this);
+                }
+            }
+
+            view_iterator& operator++() {
+                while (++it != (*pools)[0]->end() && !valid());
+                return *this;
+            }
+
+            view_iterator operator++(int) {
+                view_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            view_iterator& operator--() ENTT_NOEXCEPT {
+                while (--it != (*pools)[0]->begin() && !valid());
+                return *this;
+            }
+
+            view_iterator operator--(int) ENTT_NOEXCEPT {
+                view_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            [[nodiscard]] bool operator==(const view_iterator& other) const ENTT_NOEXCEPT {
+                return other.it == it;
+            }
+
+            [[nodiscard]] bool operator!=(const view_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] pointer operator->() const {
+                return it.operator->();
+            }
+
+            [[nodiscard]] reference operator*() const {
+                return *operator->();
+            }
+
+        private:
+            const std::vector<const basic_common_type*>* pools;
+            const std::vector<const basic_common_type*>* filter;
+            underlying_iterator it;
+            bool stable_storage;
+        };
+
+        [[nodiscard]] bool valid() const {
+            return !pools.empty() && pools.front();
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Bidirectional iterator type. */
+        using iterator = view_iterator;
+
+        /*! @brief Default constructor to use to create empty, invalid views. */
+        basic_runtime_view() ENTT_NOEXCEPT
+            : pools{},
+            filter{}
+        {}
+
+        /**
+         * @brief Constructs a runtime view from a set of storage classes.
+         * @param cpools The storage for the types to iterate.
+         * @param epools The storage for the types used to filter the view.
+         */
+        basic_runtime_view(std::vector<const basic_common_type*> cpools, std::vector<const basic_common_type*> epools) ENTT_NOEXCEPT
+            : pools{ std::move(cpools) },
+            filter{ std::move(epools) }
+        {
+            // brings the best candidate (if any) on front of the vector
+            std::rotate(pools.begin(), std::min_element(pools.begin(), pools.end(), [](const auto* lhs, const auto* rhs) {
+                return (!lhs && rhs) || (lhs && rhs && lhs->size() < rhs->size());
+                }), pools.end());
+        }
+
+        /**
+         * @brief Estimates the number of entities iterated by the view.
+         * @return Estimated number of entities iterated by the view.
+         */
+        [[nodiscard]] size_type size_hint() const {
+            return valid() ? pools.front()->size() : size_type{};
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity that has the given
+         * components.
+         *
+         * The returned iterator points to the first entity that has the given
+         * components. If the view is empty, the returned iterator will be equal to
+         * `end()`.
+         *
+         * @return An iterator to the first entity that has the given components.
+         */
+        [[nodiscard]] iterator begin() const {
+            return valid() ? iterator{ pools, filter, pools[0]->begin() } : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity that has the
+         * given components.
+         *
+         * The returned iterator points to the entity following the last entity that
+         * has the given components. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity that has the
+         * given components.
+         */
+        [[nodiscard]] iterator end() const {
+            return valid() ? iterator{ pools, filter, pools[0]->end() } : iterator{};
+        }
+
+        /**
+         * @brief Checks if a view contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the view contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return valid() && std::all_of(pools.cbegin(), pools.cend(), [entt](const auto* curr) { return curr->contains(entt); })
+                && std::none_of(filter.cbegin(), filter.cend(), [entt](const auto* curr) { return curr && curr->contains(entt); });
+        }
+
+        /**
+         * @brief Iterates entities and applies the given function object to them.
+         *
+         * The function object is invoked for each entity. It is provided only with
+         * the entity itself. To get the components, users can use the registry with
+         * which the view was built.<br/>
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const entity_type);
+         * @endcode
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (const auto entity : *this) {
+                func(entity);
+            }
+        }
+
+    private:
+        std::vector<const basic_common_type*> pools;
+        std::vector<const basic_common_type*> filter;
+    };
+
+
+}
+
+
+#endif
+
+// #include "sparse_set.hpp"
+
+// #include "storage.hpp"
+
+// #include "utility.hpp"
+
+// #include "view.hpp"
+#ifndef ENTT_ENTITY_VIEW_HPP
+#define ENTT_ENTITY_VIEW_HPP
+
+
+#include <iterator>
+#include <array>
+#include <tuple>
+#include <utility>
+#include <algorithm>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "component.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "sparse_set.hpp"
+
+// #include "storage.hpp"
+
+// #include "utility.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Policy, typename It, std::size_t AllOf, std::size_t NoneOf>
+        class view_iterator final {
+            using basic_common_type = basic_sparse_set<typename std::iterator_traits<It>::value_type>;
+
+            [[nodiscard]] bool valid() const {
+                const auto entt = *it;
+                return Policy::accept(entt)
+                    && std::apply([entt](const auto *... curr) { return (curr->contains(entt) && ...); }, pools)
+                    && std::apply([entt](const auto *... curr) { return (!curr->contains(entt) && ...); }, filter);
+            }
+
+        public:
+            using iterator_type = It;
+            using difference_type = typename std::iterator_traits<It>::difference_type;
+            using value_type = typename std::iterator_traits<It>::value_type;
+            using pointer = typename std::iterator_traits<It>::pointer;
+            using reference = typename std::iterator_traits<It>::reference;
+            using iterator_category = std::bidirectional_iterator_tag;
+
+            view_iterator() ENTT_NOEXCEPT
+                : first{},
+                last{},
+                it{},
+                pools{},
+                filter{}
+            {}
+
+            view_iterator(It from, It to, It curr, std::array<const basic_common_type*, AllOf> all_of, std::array<const basic_common_type*, NoneOf> none_of) ENTT_NOEXCEPT
+                : first{ from },
+                last{ to },
+                it{ curr },
+                pools{ all_of },
+                filter{ none_of }
+            {
+                if (it != last && !valid()) {
+                    ++(*this);
+                }
+            }
+
+            view_iterator& operator++() ENTT_NOEXCEPT {
+                while (++it != last && !valid());
+                return *this;
+            }
+
+            view_iterator operator++(int) ENTT_NOEXCEPT {
+                view_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            view_iterator& operator--() ENTT_NOEXCEPT {
+                while (--it != first && !valid());
+                return *this;
+            }
+
+            view_iterator operator--(int) ENTT_NOEXCEPT {
+                view_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            [[nodiscard]] bool operator==(const view_iterator& other) const ENTT_NOEXCEPT {
+                return other.it == it;
+            }
+
+            [[nodiscard]] bool operator!=(const view_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] pointer operator->() const {
+                return &*it;
+            }
+
+            [[nodiscard]] reference operator*() const {
+                return *operator->();
+            }
+
+        private:
+            It first;
+            It last;
+            It it;
+            std::array<const basic_common_type*, AllOf> pools;
+            std::array<const basic_common_type*, NoneOf> filter;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Stable storage policy, aimed at pointer stability. */
+    struct stable_storage_policy {
+        /**
+        * @cond TURN_OFF_DOXYGEN
+        * Internal details not to be documented.
+        */
+        template<typename Entity>
+        [[nodiscard]] static constexpr bool accept(const Entity entity) ENTT_NOEXCEPT {
+            return entity != tombstone;
+        }
+        /**
+        * Internal details not to be documented.
+        * @endcond
+        */
+    };
+
+
+    /*! @brief Packed storage policy, aimed at faster linear iteration. */
+    struct packed_storage_policy {
+        /**
+        * @cond TURN_OFF_DOXYGEN
+        * Internal details not to be documented.
+        */
+        template<typename Entity>
+        [[nodiscard]] static constexpr bool accept(const Entity) ENTT_NOEXCEPT {
+            return true;
+        }
+        /**
+        * Internal details not to be documented.
+        * @endcond
+        */
+    };
+
+
+    /**
+     * @brief View implementation.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error, but for a few reasonable cases.
+     */
+    template<typename...>
+    class basic_view_impl;
+
+
+    /*! @brief View implementation dispatcher. */
+    template<typename...>
+    struct basic_view;
+
+
+    /**
+     * @brief Multi component view.
+     *
+     * Multi component views iterate over those entities that have at least all the
+     * given components in their bags. During initialization, a multi component view
+     * looks at the number of entities available for each component and uses the
+     * smallest set in order to get a performance boost when iterate.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pools iterated by the view in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Views share references to the underlying data structures of the registry that
+     * generated them. Therefore any change to the entities and to the components
+     * made by means of the registry are immediately reflected by views.
+     *
+     * @warning
+     * Lifetime of a view must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a view results in undefined behavior.
+     *
+     * @tparam Policy Common (stricter) storage policy.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the view.
+     * @tparam Component Types of components iterated by the view.
+     */
+    template<typename Policy, typename Entity, typename... Exclude, typename... Component>
+    class basic_view_impl<Policy, Entity, exclude_t<Exclude...>, Component...> {
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Comp>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Comp>>::storage_type, Comp>;
+
+        class iterable final {
+            template<typename It>
+            struct iterable_iterator final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_view_impl>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                iterable_iterator(It from, const basic_view_impl* parent) ENTT_NOEXCEPT
+                    : it{ from },
+                    view{ parent }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return ++it, * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    return std::tuple_cat(std::make_tuple(*it), view->get(*it));
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return other.it == it;
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                It it;
+                const basic_view_impl* view;
+            };
+
+        public:
+            using iterator = iterable_iterator<internal::view_iterator<Policy, typename basic_common_type::iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>>;
+            using reverse_iterator = iterable_iterator<internal::view_iterator<Policy, typename basic_common_type::reverse_iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>>;
+
+            iterable(const basic_view_impl& parent)
+                : view{ parent }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return { view.begin(), &view };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return { view.end(), &view };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return { view.rbegin(), &view };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return { view.rend(), &view };
+            }
+
+        private:
+            const basic_view_impl view;
+        };
+
+        [[nodiscard]] const auto* candidate() const ENTT_NOEXCEPT {
+            return (std::min)({ static_cast<const basic_common_type*>(std::get<storage_type<Component>*>(pools))... }, [](const auto* lhs, const auto* rhs) {
+                return lhs->size() < rhs->size();
+                });
+        }
+
+        [[nodiscard]] auto pools_to_unchecked_array() const ENTT_NOEXCEPT {
+            std::size_t pos{};
+            std::array<const basic_common_type*, sizeof...(Component) - 1u> other{};
+            (static_cast<void>(std::get<storage_type<Component>*>(pools) == view ? void() : void(other[pos++] = std::get<storage_type<Component>*>(pools))), ...);
+            return other;
+        }
+
+        [[nodiscard]] auto filter_to_array() const ENTT_NOEXCEPT {
+            return std::array<const basic_common_type*, sizeof...(Exclude)>{std::get<const storage_type<Exclude>*>(filter)...};
+        }
+
+        template<typename Comp, typename It>
+        [[nodiscard]] auto dispatch_get([[maybe_unused]] It& it, [[maybe_unused]] const Entity entt) const {
+            if constexpr (std::is_same_v<typename std::iterator_traits<It>::value_type, typename storage_type<Comp>::value_type>) {
+                return std::forward_as_tuple(*it);
+            }
+            else {
+                return get_as_tuple(*std::get<storage_type<Comp>*>(pools), entt);
+            }
+        }
+
+        template<typename Comp, typename Func>
+        void traverse(Func func) const {
+            if constexpr (std::is_void_v<decltype(std::get<storage_type<Comp> *>(pools)->get({})) > ) {
+                for (const auto entt : static_cast<const basic_common_type&>(*std::get<storage_type<Comp>*>(pools))) {
+                    if (Policy::accept(entt) && ((std::is_same_v<Comp, Component> || std::get<storage_type<Component> *>(pools)->contains(entt)) && ...)
+                        && (!std::get<const storage_type<Exclude> *>(filter)->contains(entt) && ...))
+                    {
+                        if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view_impl>().get({}))) > ) {
+                            std::apply(func, std::tuple_cat(std::make_tuple(entt), get(entt)));
+                        }
+                        else {
+                            std::apply(func, get(entt));
+                        }
+                    }
+                }
+            }
+            else {
+                auto it = std::get<storage_type<Comp>*>(pools)->begin();
+
+                for (const auto entt : static_cast<const basic_common_type&>(*std::get<storage_type<Comp>*>(pools))) {
+                    if (Policy::accept(entt) && ((std::is_same_v<Comp, Component> || std::get<storage_type<Component> *>(pools)->contains(entt)) && ...)
+                        && (!std::get<const storage_type<Exclude> *>(filter)->contains(entt) && ...))
+                    {
+                        if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view_impl>().get({}))) > ) {
+                            std::apply(func, std::tuple_cat(std::make_tuple(entt), dispatch_get<Component>(it, entt)...));
+                        }
+                        else {
+                            std::apply(func, std::tuple_cat(dispatch_get<Component>(it, entt)...));
+                        }
+                    }
+
+                    ++it;
+                }
+            }
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Bidirectional iterator type. */
+        using iterator = internal::view_iterator<Policy, typename basic_common_type::iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>;
+        /*! @brief Reverse iterator type. */
+        using reverse_iterator = internal::view_iterator<Policy, typename basic_common_type::reverse_iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>;
+        /*! @brief Iterable view type. */
+        using iterable_view = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid views. */
+        basic_view_impl() ENTT_NOEXCEPT
+            : view{}
+        {}
+
+        /**
+         * @brief Constructs a multi-type view from a set of storage classes.
+         * @param component The storage for the types to iterate.
+         * @param epool The storage for the types used to filter the view.
+         */
+        basic_view_impl(storage_type<Component> &... component, const storage_type<Exclude> &... epool) ENTT_NOEXCEPT
+            : pools{ &component... },
+            filter{ &epool... },
+            view{ candidate() }
+        {}
+
+        /**
+         * @brief Forces the type to use to drive iterations.
+         * @tparam Comp Type of component to use to drive the iteration.
+         */
+        template<typename Comp>
+        void use() const ENTT_NOEXCEPT {
+            view = std::get<storage_type<Comp>*>(pools);
+        }
+
+        /**
+         * @brief Estimates the number of entities iterated by the view.
+         * @return Estimated number of entities iterated by the view.
+         */
+        [[nodiscard]] size_type size_hint() const ENTT_NOEXCEPT {
+            return view->size();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the view.
+         *
+         * The returned iterator points to the first entity of the view. If the view
+         * is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the view.
+         */
+        [[nodiscard]] iterator begin() const {
+            return iterator{ view->begin(), view->end(), view->begin(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the view. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the view.
+         */
+        [[nodiscard]] iterator end() const {
+            return iterator{ view->begin(), view->end(), view->end(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed view.
+         *
+         * The returned iterator points to the first entity of the reversed view. If
+         * the view is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed view.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const {
+            return reverse_iterator{ view->rbegin(), view->rend(), view->rbegin(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed view. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed view.
+         */
+        [[nodiscard]] reverse_iterator rend() const {
+            return reverse_iterator{ view->rbegin(), view->rend(), view->rend(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns the first entity of the view, if any.
+         * @return The first entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the view, if any.
+         * @return The last entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = iterator{ view->begin(), view->end(), view->find(entt), pools_to_unchecked_array(), filter_to_array() };
+            return (it != end() && *it == entt) ? it : end();
+        }
+
+        /**
+         * @brief Checks if a view is properly initialized.
+         * @return True if the view is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return view != nullptr;
+        }
+
+        /**
+         * @brief Checks if a view contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the view contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return (std::get<storage_type<Component>*>(pools)->contains(entt) && ...) && (!std::get<const storage_type<Exclude>*>(filter)->contains(entt) && ...);
+        }
+
+        /**
+         * @brief Returns the components assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the view
+         * results in undefined behavior.
+         *
+         * @tparam Comp Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The components assigned to the entity.
+         */
+        template<typename... Comp>
+        [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "View does not contain entity");
+
+            if constexpr (sizeof...(Comp) == 0) {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Component>*>(pools), entt)...);
+            }
+            else if constexpr (sizeof...(Comp) == 1) {
+                return (std::get<storage_type<Comp>*>(pools)->get(entt), ...);
+            }
+            else {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Comp>*>(pools), entt)...);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a set of references to non-empty components. The
+         * _constness_ of the components is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Type &...);
+         * void(Type &...);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            ((std::get<storage_type<Component>*>(pools) == view ? traverse<Component>(std::move(func)) : void()), ...);
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The pool of the suggested component is used to lead the iterations. The
+         * returned entities will therefore respect the order of the pool associated
+         * with that type.
+         *
+         * @sa each
+         *
+         * @tparam Comp Type of component to use to drive the iteration.
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Comp, typename Func>
+        void each(Func func) const {
+            use<Comp>();
+            traverse<Comp>(std::move(func));
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the view.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * set of references to its non-empty components. The _constness_ of the
+         * components is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the view.
+         */
+        [[nodiscard]] iterable_view each() const ENTT_NOEXCEPT {
+            return iterable_view{ *this };
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the view.
+         *
+         * The pool of the suggested component is used to lead the iterations. The
+         * returned elements will therefore respect the order of the pool associated
+         * with that type.
+         *
+         * @sa each
+         *
+         * @tparam Comp Type of component to use to drive the iteration.
+         * @return An iterable object to use to _visit_ the view.
+         */
+        template<typename Comp>
+        [[nodiscard]] iterable_view each() const ENTT_NOEXCEPT {
+            use<Comp>();
+            return iterable_view{ *this };
+        }
+
+        /**
+         * @brief Combines two views in a _more specific_ one (friend function).
+         * @tparam Id A valid entity type (see entt_traits for more details).
+         * @tparam ELhs Filter list of the first view.
+         * @tparam CLhs Component list of the first view.
+         * @tparam ERhs Filter list of the second view.
+         * @tparam CRhs Component list of the second view.
+         * @return A more specific view.
+         */
+        template<typename Id, typename... ELhs, typename... CLhs, typename... ERhs, typename... CRhs>
+        friend auto operator|(const basic_view<Id, exclude_t<ELhs...>, CLhs...>&, const basic_view<Id, exclude_t<ERhs...>, CRhs...>&);
+
+    private:
+        const std::tuple<storage_type<Component> *...> pools;
+        const std::tuple<const storage_type<Exclude> *...> filter;
+        mutable const basic_common_type* view;
+    };
+
+
+    /**
+     * @brief Single component view specialization.
+     *
+     * Single component views are specialized in order to get a boost in terms of
+     * performance. This kind of views can access the underlying data structure
+     * directly and avoid superfluous checks.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given component are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, the given
+     *   component is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pool iterated by the view in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Views share a reference to the underlying data structure of the registry that
+     * generated them. Therefore any change to the entities and to the components
+     * made by means of the registry are immediately reflected by views.
+     *
+     * @warning
+     * Lifetime of a view must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a view results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Component Type of component iterated by the view.
+     */
+    template<typename Entity, typename Component>
+    class basic_view_impl<packed_storage_policy, Entity, exclude_t<>, Component> {
+        using basic_common_type = basic_sparse_set<Entity>;
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        class iterable final {
+            template<typename... It>
+            struct iterable_iterator final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_view_impl>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                template<typename... Discard>
+                iterable_iterator(It... from, Discard...) ENTT_NOEXCEPT
+                    : it{ from... }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return (++std::get<It>(it), ...), * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    return { *std::get<It>(it)... };
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return std::get<0>(other.it) == std::get<0>(it);
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                std::tuple<It...> it;
+            };
+
+        public:
+            using iterator = std::conditional_t <
+                std::is_void_v<decltype(std::declval<storage_type>().get({})) > ,
+                iterable_iterator<typename basic_common_type::iterator>,
+                iterable_iterator<typename basic_common_type::iterator, decltype(std::declval<storage_type>().begin())>
+            > ;
+            using reverse_iterator = std::conditional_t <
+                std::is_void_v<decltype(std::declval<storage_type>().get({})) > ,
+                iterable_iterator<typename basic_common_type::reverse_iterator>,
+                iterable_iterator<typename basic_common_type::reverse_iterator, decltype(std::declval<storage_type>().rbegin())>
+            > ;
+
+            iterable(storage_type& ref)
+                : pool{ &ref }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return iterator{ pool->basic_common_type::begin(), pool->begin() };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return iterator{ pool->basic_common_type::end(), pool->end() };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return reverse_iterator{ pool->basic_common_type::rbegin(), pool->rbegin() };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return reverse_iterator{ pool->basic_common_type::rend(), pool->rend() };
+            }
+
+        private:
+            storage_type* const pool;
+        };
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_common_type::iterator;
+        /*! @brief Reversed iterator type. */
+        using reverse_iterator = typename basic_common_type::reverse_iterator;
+        /*! @brief Iterable view type. */
+        using iterable_view = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid views. */
+        basic_view_impl() ENTT_NOEXCEPT
+            : pools{},
+            filter{}
+        {}
+
+        /**
+         * @brief Constructs a single-type view from a storage class.
+         * @param ref The storage for the type to iterate.
+         */
+        basic_view_impl(storage_type& ref) ENTT_NOEXCEPT
+            : pools{ &ref },
+            filter{}
+        {}
+
+        /**
+         * @brief Returns the number of entities that have the given component.
+         * @return Number of entities that have the given component.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->size();
+        }
+
+        /**
+         * @brief Checks whether a view is empty.
+         * @return True if the view is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->empty();
+        }
+
+        /**
+         * @brief Direct access to the raw representation offered by the storage.
+         * @return A pointer to the array of components.
+         */
+        [[nodiscard]] auto raw() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->raw();
+        }
+
+        /**
+         * @brief Direct access to the list of entities.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] auto data() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->data();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the view.
+         *
+         * The returned iterator points to the first entity of the view. If the view
+         * is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the view.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::begin();
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the view. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the view.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::end();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed view.
+         *
+         * The returned iterator points to the first entity of the reversed view. If
+         * the view is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed view.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::rbegin();
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed view. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed view.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::rend();
+        }
+
+        /**
+         * @brief Returns the first entity of the view, if any.
+         * @return The first entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the view, if any.
+         * @return The last entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = std::get<0>(pools)->find(entt);
+            return it != end() && *it == entt ? it : end();
+        }
+
+        /**
+         * @brief Returns the identifier that occupies the given position.
+         * @param pos Position of the element to return.
+         * @return The identifier that occupies the given position.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const {
+            return begin()[pos];
+        }
+
+        /**
+         * @brief Checks if a view is properly initialized.
+         * @return True if the view is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return std::get<0>(pools) != nullptr;
+        }
+
+        /**
+         * @brief Checks if a view contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the view contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return std::get<0>(pools)->contains(entt);
+        }
+
+        /**
+         * @brief Returns the component assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the view
+         * results in undefined behavior.
+         *
+         * @tparam Comp Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The component assigned to the entity.
+         */
+        template<typename... Comp>
+        [[nodiscard]] decltype(auto) get(const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "View does not contain entity");
+
+            if constexpr (sizeof...(Comp) == 0) {
+                return get_as_tuple(*std::get<0>(pools), entt);
+            }
+            else {
+                static_assert(std::is_same_v<Comp..., Component>, "Invalid component type");
+                return std::get<0>(pools)->get(entt);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a reference to the component if it's a non-empty one.
+         * The _constness_ of the component is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Component &);
+         * void(Component &);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            if constexpr (std::is_void_v<decltype(std::get<0>(pools)->get({})) > ) {
+                if constexpr (std::is_invocable_v<Func>) {
+                    for (auto pos = size(); pos; --pos) {
+                        func();
+                    }
+                }
+                else {
+                    for (auto entity : *this) {
+                        func(entity);
+                    }
+                }
+            }
+            else {
+                if constexpr (is_applicable_v<Func, decltype(*each().begin())>) {
+                    for (const auto pack : each()) {
+                        std::apply(func, pack);
+                    }
+                }
+                else {
+                    for (auto&& component : *std::get<0>(pools)) {
+                        func(component);
+                    }
+                }
+            }
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the view.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * reference to its component if it's a non-empty one. The _constness_ of
+         * the component is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the view.
+         */
+        [[nodiscard]] iterable_view each() const ENTT_NOEXCEPT {
+            return iterable_view{ *std::get<0>(pools) };
+        }
+
+        /**
+         * @brief Combines two views in a _more specific_ one (friend function).
+         * @tparam Id A valid entity type (see entt_traits for more details).
+         * @tparam ELhs Filter list of the first view.
+         * @tparam CLhs Component list of the first view.
+         * @tparam ERhs Filter list of the second view.
+         * @tparam CRhs Component list of the second view.
+         * @return A more specific view.
+         */
+        template<typename Id, typename... ELhs, typename... CLhs, typename... ERhs, typename... CRhs>
+        friend auto operator|(const basic_view<Id, exclude_t<ELhs...>, CLhs...>&, const basic_view<Id, exclude_t<ERhs...>, CRhs...>&);
+
+    private:
+        const std::tuple<storage_type*> pools;
+        const std::tuple<> filter;
+    };
+
+
+    /**
+     * @brief View implementation dispatcher.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the view.
+     * @tparam Component Types of components iterated by the view.
+     */
+    template<typename Entity, typename... Exclude, typename... Component>
+    struct basic_view<Entity, exclude_t<Exclude...>, Component...>
+        : basic_view_impl<std::conditional_t<std::disjunction_v<typename component_traits<std::remove_const_t<Component>>::in_place_delete...>, stable_storage_policy, packed_storage_policy>, Entity, exclude_t<Exclude...>, Component...>
+    {
+        /*! @brief Most restrictive storage policy of all component types. */
+        using storage_policy = std::conditional_t<std::disjunction_v<typename component_traits<std::remove_const_t<Component>>::in_place_delete...>, stable_storage_policy, packed_storage_policy>;
+        using basic_view_impl<storage_policy, Entity, exclude_t<Exclude...>, Component...>::basic_view_impl;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Storage Type of storage classes used to create the view.
+     * @param storage The storage for the types to iterate.
+     */
+    template<typename... Storage>
+    basic_view(Storage &... storage)
+        ->basic_view<std::common_type_t<typename Storage::entity_type...>, entt::exclude_t<>, constness_as_t<typename Storage::value_type, Storage>...>;
+
+
+    /**
+     * @brief Combines two views in a _more specific_ one.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam ELhs Filter list of the first view.
+     * @tparam CLhs Component list of the first view.
+     * @tparam ERhs Filter list of the second view.
+     * @tparam CRhs Component list of the second view.
+     * @param lhs A valid reference to the first view.
+     * @param rhs A valid reference to the second view.
+     * @return A more specific view.
+     */
+    template<typename Entity, typename... ELhs, typename... CLhs, typename... ERhs, typename... CRhs>
+    [[nodiscard]] auto operator|(const basic_view<Entity, exclude_t<ELhs...>, CLhs...>& lhs, const basic_view<Entity, exclude_t<ERhs...>, CRhs...>& rhs) {
+        using view_type = basic_view<Entity, exclude_t<ELhs..., ERhs...>, CLhs..., CRhs...>;
+        return std::apply([](auto *... storage) { return view_type{ *storage... }; }, std::tuple_cat(lhs.pools, rhs.pools, lhs.filter, rhs.filter));
+    }
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Fast and reliable entity-component system.
+     *
+     * The registry is the core class of the entity-component framework.<br/>
+     * It stores entities and arranges pools of components on a per request basis.
+     * By means of a registry, users can manage entities and components, then create
+     * views or groups to iterate them.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_registry {
+        using traits_type = entt_traits<Entity>;
+        using poly_storage_type = typename poly_storage_traits<Entity>::storage_type;
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Component>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        struct pool_data {
+            poly_storage_type poly;
+            std::unique_ptr<basic_common_type> pool{};
+        };
+
+        template<typename...>
+        struct group_handler;
+
+        template<typename... Exclude, typename... Get, typename... Owned>
+        struct group_handler<exclude_t<Exclude...>, get_t<Get...>, Owned...> {
+            static_assert(!std::disjunction_v<typename component_traits<Owned>::in_place_delete...>, "Groups do not support in-place delete");
+            static_assert(std::conjunction_v<std::is_same<Owned, std::remove_const_t<Owned>>..., std::is_same<Get, std::remove_const_t<Get>>..., std::is_same<Exclude, std::remove_const_t<Exclude>>...>, "One or more component types are invalid");
+            std::conditional_t<sizeof...(Owned) == 0, basic_common_type, std::size_t> current{};
+
+            template<typename Component>
+            void maybe_valid_if(basic_registry& owner, const Entity entt) {
+                [[maybe_unused]] const auto cpools = std::make_tuple(owner.assure<Owned>()...);
+
+                const auto is_valid = ((std::is_same_v<Component, Owned> || std::get<storage_type<Owned>*>(cpools)->contains(entt)) && ...)
+                    && ((std::is_same_v<Component, Get> || owner.assure<Get>()->contains(entt)) && ...)
+                    && ((std::is_same_v<Component, Exclude> || !owner.assure<Exclude>()->contains(entt)) && ...);
+
+                if constexpr (sizeof...(Owned) == 0) {
+                    if (is_valid && !current.contains(entt)) {
+                        current.emplace(entt);
+                    }
+                }
+                else {
+                    if (is_valid && !(std::get<0>(cpools)->index(entt) < current)) {
+                        const auto pos = current++;
+                        (std::get<storage_type<Owned>*>(cpools)->swap(std::get<storage_type<Owned>*>(cpools)->data()[pos], entt), ...);
+                    }
+                }
+            }
+
+            void discard_if([[maybe_unused]] basic_registry& owner, const Entity entt) {
+                if constexpr (sizeof...(Owned) == 0) {
+                    current.remove(entt);
+                }
+                else {
+                    if (const auto cpools = std::make_tuple(owner.assure<Owned>()...); std::get<0>(cpools)->contains(entt) && (std::get<0>(cpools)->index(entt) < current)) {
+                        const auto pos = --current;
+                        (std::get<storage_type<Owned>*>(cpools)->swap(std::get<storage_type<Owned>*>(cpools)->data()[pos], entt), ...);
+                    }
+                }
+            }
+        };
+
+        struct group_data {
+            std::size_t size;
+            std::unique_ptr<void, void(*)(void*)> group;
+            bool (*owned)(const id_type) ENTT_NOEXCEPT;
+            bool (*get)(const id_type) ENTT_NOEXCEPT;
+            bool (*exclude)(const id_type) ENTT_NOEXCEPT;
+        };
+
+        template<typename Component>
+        [[nodiscard]] storage_type<Component>* assure() const {
+            static_assert(std::is_same_v<Component, std::decay_t<Component>>, "Non-decayed types not allowed");
+            const auto index = type_seq<Component>::value();
+
+            if (!(index < pools.size())) {
+                pools.resize(size_type(index) + 1u);
+            }
+
+            if (auto&& pdata = pools[index]; !pdata.pool) {
+                pdata.pool.reset(new storage_type<Component>());
+                pdata.poly.template emplace<storage_type<Component>&>(*static_cast<storage_type<Component> *>(pdata.pool.get()));
+            }
+
+            return static_cast<storage_type<Component> *>(pools[index].pool.get());
+        }
+
+        template<typename Component>
+        [[nodiscard]] const storage_type<Component>* pool_if_exists() const ENTT_NOEXCEPT {
+            static_assert(std::is_same_v<Component, std::decay_t<Component>>, "Non-decayed types not allowed");
+            const auto index = type_seq<Component>::value();
+            return (!(index < pools.size()) || !pools[index].pool) ? nullptr : static_cast<const storage_type<Component> *>(pools[index].pool.get());
+        }
+
+        auto generate_identifier(const std::size_t pos) ENTT_NOEXCEPT {
+            ENTT_ASSERT(pos < traits_type::to_integral(null), "No entities available");
+            return traits_type::construct(static_cast<typename traits_type::entity_type>(pos), {});
+        }
+
+        auto recycle_identifier() ENTT_NOEXCEPT {
+            ENTT_ASSERT(free_list != null, "No entities available");
+            const auto curr = traits_type::to_entity(free_list);
+            free_list = (tombstone | entities[curr]);
+            return (entities[curr] = traits_type::construct(curr, traits_type::to_version(entities[curr])));
+        }
+
+        auto release_entity(const Entity entity, const typename traits_type::version_type version) {
+            const typename traits_type::version_type vers = version + (version == traits_type::to_version(tombstone));
+            entities[traits_type::to_entity(entity)] = traits_type::construct(traits_type::to_entity(free_list), vers);
+            free_list = (tombstone | entity);
+            return vers;
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Underlying version type. */
+        using version_type = typename traits_type::version_type;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Poly storage type. */
+        using poly_storage = typename poly_storage_traits<Entity>::storage_type;
+
+        /**
+         * @brief Returns the entity identifier without the version.
+         * @param entity An entity identifier, either valid or not.
+         * @return The entity identifier without the version.
+         */
+        [[nodiscard]] static entity_type entity(const entity_type entity) ENTT_NOEXCEPT {
+            return traits_type::construct(traits_type::to_entity(entity), {});
+        }
+
+        /**
+         * @brief Returns the version stored along with an entity identifier.
+         * @param entity An entity identifier, either valid or not.
+         * @return The version stored along with the given entity identifier.
+         */
+        [[nodiscard]] static version_type version(const entity_type entity) ENTT_NOEXCEPT {
+            return traits_type::to_version(entity);
+        }
+
+        /*! @brief Default constructor. */
+        basic_registry() = default;
+
+        /*! @brief Default move constructor. */
+        basic_registry(basic_registry&&) = default;
+
+        /*! @brief Default move assignment operator. @return This registry. */
+        basic_registry& operator=(basic_registry&&) = default;
+
+        /**
+         * @brief Prepares a pool for the given type if required.
+         * @tparam Component Type of component for which to prepare a pool.
+         */
+        template<typename Component>
+        void prepare() {
+            // suppress the warning due to the [[nodiscard]] attribute
+            static_cast<void>(assure<Component>());
+        }
+
+        /**
+         * @brief Returns a poly storage for a given type.
+         * @param info The type for which to return a poly storage.
+         * @return A valid poly storage if a pool for the given type exists, an
+         * empty and thus invalid element otherwise.
+         */
+        poly_storage& storage(const type_info info) {
+            ENTT_ASSERT(info.seq() < pools.size() && pools[info.seq()].poly, "Storage not available");
+            return pools[info.seq()].poly;
+        }
+
+        /*! @copydoc storage */
+        const poly_storage& storage(const type_info info) const {
+            ENTT_ASSERT(info.seq() < pools.size() && pools[info.seq()].poly, "Storage not available");
+            return pools[info.seq()].poly;
+        }
+
+        /**
+         * @brief Returns the number of existing components of the given type.
+         * @tparam Component Type of component of which to return the size.
+         * @return Number of existing components of the given type.
+         */
+        template<typename Component>
+        [[nodiscard]] size_type size() const {
+            const auto* cpool = pool_if_exists<Component>();
+            return cpool ? cpool->size() : size_type{};
+        }
+
+        /**
+         * @brief Returns the number of entities created so far.
+         * @return Number of entities created so far.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return entities.size();
+        }
+
+        /**
+         * @brief Returns the number of entities still in use.
+         * @return Number of entities still in use.
+         */
+        [[nodiscard]] size_type alive() const {
+            auto sz = entities.size();
+
+            for (auto curr = free_list; curr != null; --sz) {
+                curr = entities[traits_type::to_entity(curr)];
+            }
+
+            return sz;
+        }
+
+        /**
+         * @brief Increases the capacity of the registry or of the pools for the
+         * given components.
+         *
+         * If no components are specified, the capacity of the registry is
+         * increased, that is the number of entities it contains. Otherwise the
+         * capacity of the pools for the given components is increased.<br/>
+         * In both cases, if the new capacity is greater than the current capacity,
+         * new storage is allocated, otherwise the method does nothing.
+         *
+         * @tparam Component Types of components for which to reserve storage.
+         * @param cap Desired capacity.
+         */
+        template<typename... Component>
+        void reserve(const size_type cap) {
+            if constexpr (sizeof...(Component) == 0) {
+                entities.reserve(cap);
+            }
+            else {
+                (assure<Component>()->reserve(cap), ...);
+            }
+        }
+
+        /**
+         * @brief Reserves enough space to store `count` pools.
+         * @param count Number of pools to reserve space for.
+         */
+        [[deprecated("No longer supported")]]
+        void reserve_pools(const size_t count) {
+            pools.reserve(count);
+        }
+
+        /**
+         * @brief Returns the capacity of the pool for the given component.
+         * @tparam Component Type of component in which one is interested.
+         * @return Capacity of the pool of the given component.
+         */
+        template<typename Component>
+        [[nodiscard]] size_type capacity() const {
+            const auto* cpool = pool_if_exists<Component>();
+            return cpool ? cpool->capacity() : size_type{};
+        }
+
+        /**
+         * @brief Returns the number of entities that a registry has currently
+         * allocated space for.
+         * @return Capacity of the registry.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return entities.capacity();
+        }
+
+        /**
+         * @brief Requests the removal of unused capacity for the given components.
+         * @tparam Component Types of components for which to reclaim unused
+         * capacity.
+         */
+        template<typename... Component>
+        void shrink_to_fit() {
+            (assure<Component>()->shrink_to_fit(), ...);
+        }
+
+        /**
+         * @brief Checks whether the registry or the pools of the given components
+         * are empty.
+         *
+         * A registry is considered empty when it doesn't contain entities that are
+         * still in use.
+         *
+         * @tparam Component Types of components in which one is interested.
+         * @return True if the registry or the pools of the given components are
+         * empty, false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool empty() const {
+            if constexpr (sizeof...(Component) == 0) {
+                return !alive();
+            }
+            else {
+                return [](const auto *... cpool) { return ((!cpool || cpool->empty()) && ...); }(pool_if_exists<Component>()...);
+            }
+        }
+
+        /**
+         * @brief Direct access to the list of entities of a registry.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @warning
+         * This list contains both valid and destroyed entities and isn't suitable
+         * for direct use.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] const entity_type* data() const ENTT_NOEXCEPT {
+            return entities.data();
+        }
+
+        /**
+         * @brief Returns the head of the list of released entities.
+         *
+         * This function is intended for use in conjunction with `assign`.<br/>
+         * The returned entity has an invalid identifier in all cases.
+         *
+         * @return The head of the list of released entities.
+         */
+        [[nodiscard]] entity_type released() const ENTT_NOEXCEPT {
+            return free_list;
+        }
+
+        /*! @copydoc released */
+        [[deprecated("Use ::released instead")]]
+        [[nodiscard]] entity_type destroyed() const ENTT_NOEXCEPT {
+            return released();
+        }
+
+        /**
+         * @brief Checks if an entity identifier refers to a valid entity.
+         * @param entity An entity identifier, either valid or not.
+         * @return True if the identifier is valid, false otherwise.
+         */
+        [[nodiscard]] bool valid(const entity_type entity) const {
+            const auto pos = size_type(traits_type::to_entity(entity));
+            return (pos < entities.size() && entities[pos] == entity);
+        }
+
+        /**
+         * @brief Returns the actual version for an entity identifier.
+         *
+         * @warning
+         * Attempting to use an entity that doesn't belong to the registry results
+         * in undefined behavior. An entity belongs to the registry even if it has
+         * been previously destroyed and/or recycled.
+         *
+         * @param entity A valid entity identifier.
+         * @return Actual version for the given entity identifier.
+         */
+        [[nodiscard]] version_type current(const entity_type entity) const {
+            const auto pos = size_type(traits_type::to_entity(entity));
+            ENTT_ASSERT(pos < entities.size(), "Entity does not exist");
+            return version(entities[pos]);
+        }
+
+        /**
+         * @brief Creates a new entity and returns it.
+         *
+         * There are two kinds of possible entity identifiers:
+         *
+         * * Newly created ones in case no entities have been previously destroyed.
+         * * Recycled ones with updated versions.
+         *
+         * @return A valid entity identifier.
+         */
+        [[nodiscard]] entity_type create() {
+            return (free_list == null) ? entities.emplace_back(generate_identifier(entities.size())) : recycle_identifier();
+        }
+
+        /**
+         * @brief Creates a new entity and returns it.
+         *
+         * @sa create
+         *
+         * If the requested entity isn't in use, the suggested identifier is created
+         * and returned. Otherwise, a new identifier is generated.
+         *
+         * @param hint Required entity identifier.
+         * @return A valid entity identifier.
+         */
+        [[nodiscard]] entity_type create(const entity_type hint) {
+            const auto length = entities.size();
+
+            if (hint == null || hint == tombstone) {
+                return create();
+            }
+            else if (const auto req = traits_type::to_entity(hint); !(req < length)) {
+                entities.resize(size_type(req) + 1u, null);
+
+                for (auto pos = length; pos < req; ++pos) {
+                    release_entity(generate_identifier(pos), {});
+                }
+
+                return (entities[req] = hint);
+            }
+            else if (const auto curr = traits_type::to_entity(entities[req]); req == curr) {
+                return create();
+            }
+            else {
+                auto* it = &free_list;
+                for (; traits_type::to_entity(*it) != req; it = &entities[traits_type::to_entity(*it)]);
+                *it = traits_type::construct(curr, traits_type::to_version(*it));
+                return (entities[req] = hint);
+            }
+        }
+
+        /**
+         * @brief Assigns each element in a range an entity.
+         *
+         * @sa create
+         *
+         * @tparam It Type of forward iterator.
+         * @param first An iterator to the first element of the range to generate.
+         * @param last An iterator past the last element of the range to generate.
+         */
+        template<typename It>
+        void create(It first, It last) {
+            for (; free_list != null && first != last; ++first) {
+                *first = recycle_identifier();
+            }
+
+            const auto length = entities.size();
+            entities.resize(length + std::distance(first, last), null);
+
+            for (auto pos = length; first != last; ++first, ++pos) {
+                *first = entities[pos] = generate_identifier(pos);
+            }
+        }
+
+        /**
+         * @brief Assigns entities to an empty registry.
+         *
+         * This function is intended for use in conjunction with `data`, `size` and
+         * `destroyed`.<br/>
+         * Don't try to inject ranges of randomly generated entities nor the _wrong_
+         * head for the list of destroyed entities. There is no guarantee that a
+         * registry will continue to work properly in this case.
+         *
+         * @warning
+         * There must be no entities still alive for this to work properly.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param destroyed The head of the list of destroyed entities.
+         */
+        template<typename It>
+        void assign(It first, It last, const entity_type destroyed) {
+            ENTT_ASSERT(!alive(), "Entities still alive");
+            entities.assign(first, last);
+            free_list = destroyed;
+        }
+
+        /**
+         * @brief Releases an entity identifier.
+         *
+         * The version is updated and the identifier can be recycled at any time.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @param entity A valid entity identifier.
+         * @return The version of the recycled entity.
+         */
+        version_type release(const entity_type entity) {
+            return release(entity, version(entity) + 1u);
+        }
+
+        /**
+         * @brief Releases an entity identifier.
+         *
+         * The suggested version or the valid version closest to the suggested one
+         * is used instead of the implicitly generated version.
+         *
+         * @sa release
+         *
+         * @param entity A valid entity identifier.
+         * @param version A desired version upon destruction.
+         * @return The version actually assigned to the entity.
+         */
+        version_type release(const entity_type entity, const version_type version) {
+            ENTT_ASSERT(orphan(entity), "Non-orphan entity");
+            return release_entity(entity, version);
+        }
+
+        /**
+         * @brief Releases all entity identifiers in a range.
+         *
+         * @sa release
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void release(It first, It last) {
+            for (; first != last; ++first) {
+                release(*first, version(*first) + 1u);
+            }
+        }
+
+        /**
+         * @brief Destroys an entity and releases its identifier.
+         *
+         * The version is updated and the identifier can be recycled at any time.
+         *
+         * @warning
+         * Adding or removing components to an entity that is being destroyed can
+         * result in undefined behavior.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @param entity A valid entity identifier.
+         * @return The version of the recycled entity.
+         */
+        version_type destroy(const entity_type entity) {
+            return destroy(entity, version(entity) + 1u);
+        }
+
+        /**
+         * @brief Destroys an entity and releases its identifier.
+         *
+         * The suggested version or the valid version closest to the suggested one
+         * is used instead of the implicitly generated version.
+         *
+         * @sa destroy
+         *
+         * @param entity A valid entity identifier.
+         * @param version A desired version upon destruction.
+         * @return The version actually assigned to the entity.
+         */
+        version_type destroy(const entity_type entity, const version_type version) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            for (auto&& pdata : pools) {
+                pdata.pool&& pdata.pool->remove(entity, this);
+            }
+
+            return release_entity(entity, version);
+        }
+
+        /**
+         * @brief Destroys all entities in a range and releases their identifiers.
+         *
+         * @sa destroy
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void destroy(It first, It last) {
+            if constexpr (is_iterator_type_v<typename basic_common_type::iterator, It>) {
+                for (; first != last; ++first) {
+                    destroy(*first, version(*first) + 1u);
+                }
+            }
+            else {
+                for (auto&& pdata : pools) {
+                    pdata.pool&& pdata.pool->remove(first, last, this);
+                }
+
+                release(first, last);
+            }
+        }
+
+        /**
+         * @brief Assigns the given component to an entity.
+         *
+         * A new instance of the given component is created and initialized with the
+         * arguments provided (the component must have a proper constructor or be of
+         * aggregate type). Then the component is assigned to the given entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to assign a component to an entity
+         * that already owns it results in undefined behavior.
+         *
+         * @tparam Component Type of component to create.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the newly created component.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) emplace(const entity_type entity, Args &&... args) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return assure<Component>()->emplace(*this, entity, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Assigns each entity in a range the given component.
+         *
+         * @sa emplace
+         *
+         * @tparam Component Type of component to create.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param value An instance of the component to assign.
+         */
+        template<typename Component, typename It>
+        void insert(It first, It last, const Component& value = {}) {
+            ENTT_ASSERT(std::all_of(first, last, [this](const auto entity) { return valid(entity); }), "Invalid entity");
+            assure<Component>()->insert(*this, first, last, value);
+        }
+
+        /**
+         * @brief Assigns each entity in a range the given components.
+         *
+         * @sa emplace
+         *
+         * @tparam Component Type of component to create.
+         * @tparam EIt Type of input iterator.
+         * @tparam CIt Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param from An iterator to the first element of the range of components.
+         */
+        template<typename Component, typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<std::decay_t<typename std::iterator_traits<CIt>::value_type>, Component>>>
+        void insert(EIt first, EIt last, CIt from) {
+            static_assert(std::is_constructible_v<Component, typename std::iterator_traits<CIt>::value_type>, "Invalid value type");
+            ENTT_ASSERT(std::all_of(first, last, [this](const auto entity) { return valid(entity); }), "Invalid entity");
+            assure<Component>()->insert(*this, first, last, from);
+        }
+
+        /**
+         * @brief Assigns or replaces the given component for an entity.
+         *
+         * Equivalent to the following snippet (pseudocode):
+         *
+         * @code{.cpp}
+         * auto &component = registry.all_of<Component>(entity) ? registry.replace<Component>(entity, args...) : registry.emplace<Component>(entity, args...);
+         * @endcode
+         *
+         * Prefer this function anyway because it has slightly better performance.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Type of component to assign or replace.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the newly created component.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) emplace_or_replace(const entity_type entity, Args &&... args) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            auto* cpool = assure<Component>();
+
+            return cpool->contains(entity)
+                ? cpool->patch(*this, entity, [&args...](auto &... curr) { ((curr = Component{ std::forward<Args>(args)... }), ...); })
+                : cpool->emplace(*this, entity, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Patches the given component for an entity.
+         *
+         * The signature of the functions should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(Component &);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned. However, this function can be used to trigger an update signal
+         * for them.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to patch a component of an entity
+         * that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Type of component to patch.
+         * @tparam Func Types of the function objects to invoke.
+         * @param entity A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the patched component.
+         */
+        template<typename Component, typename... Func>
+        decltype(auto) patch(const entity_type entity, Func &&... func) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return assure<Component>()->patch(*this, entity, std::forward<Func>(func)...);
+        }
+
+        /**
+         * @brief Replaces the given component for an entity.
+         *
+         * A new instance of the given component is created and initialized with the
+         * arguments provided (the component must have a proper constructor or be of
+         * aggregate type). Then the component is assigned to the given entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to replace a component of an
+         * entity that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Type of component to replace.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the component being replaced.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) replace(const entity_type entity, Args &&... args) {
+            return assure<Component>()->patch(*this, entity, [&args...](auto &... curr) { ((curr = Component{ std::forward<Args>(args)... }), ...); });
+        }
+
+        /**
+         * @brief Removes the given components from an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Types of components to remove.
+         * @param entity A valid entity identifier.
+         * @return The number of components actually removed.
+         */
+        template<typename... Component>
+        size_type remove(const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            return (assure<Component>()->remove(entity, this) + ... + size_type{});
+        }
+
+        /**
+         * @brief Removes the given components from all the entities in a range.
+         *
+         * @sa remove
+         *
+         * @tparam Component Types of components to remove.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @return The number of components actually removed.
+         */
+        template<typename... Component, typename It>
+        size_type remove(It first, It last) {
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            const auto cpools = std::make_tuple(assure<Component>()...);
+            size_type count{};
+
+            for (; first != last; ++first) {
+                const auto entity = *first;
+                ENTT_ASSERT(valid(entity), "Invalid entity");
+                count += (std::get<storage_type<Component>*>(cpools)->remove(entity, this) + ...);
+            }
+
+            return count;
+        }
+
+        /**
+         * @brief Erases the given components from an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to erase a component from an
+         * entity that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Types of components to erase.
+         * @param entity A valid entity identifier.
+         */
+        template<typename... Component>
+        void erase(const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            (assure<Component>()->erase(entity, this), ...);
+        }
+
+        /**
+         * @brief Erases the given components from all the entities in a range.
+         *
+         * @sa erase
+         *
+         * @tparam Component Types of components to erase.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename... Component, typename It>
+        void erase(It first, It last) {
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            const auto cpools = std::make_tuple(assure<Component>()...);
+
+            for (; first != last; ++first) {
+                const auto entity = *first;
+                ENTT_ASSERT(valid(entity), "Invalid entity");
+                (std::get<storage_type<Component>*>(cpools)->erase(entity, this), ...);
+            }
+        }
+
+        /**
+         * @brief Removes all tombstones from a registry or only the pools for the
+         * given components.
+         * @tparam Component Types of components for which to clear all tombstones.
+         */
+        template<typename... Component>
+        void compact() {
+            if constexpr (sizeof...(Component) == 0) {
+                for (auto&& pdata : pools) {
+                    pdata.pool && (pdata.pool->compact(), true);
+                }
+            }
+            else {
+                (assure<Component>()->compact(), ...);
+            }
+        }
+
+        /*! @copydoc remove */
+        template<typename... Component>
+        [[deprecated("Use ::remove instead")]]
+        size_type remove_if_exists(const entity_type entity) {
+            return remove<Component...>(entity);
+        }
+
+        /**
+         * @brief Removes all the components from an entity and makes it orphaned.
+         *
+         * @warning
+         * In case there are listeners that observe the destruction of components
+         * and assign other components to the entity in their bodies, the result of
+         * invoking this function may not be as expected. In the worst case, it
+         * could lead to undefined behavior.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @param entity A valid entity identifier.
+         */
+        [[deprecated("Use ::destroy(entity)/::create(entity) instead")]]
+        void remove_all(const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            for (auto&& pdata : pools) {
+                pdata.pool&& pdata.pool->remove(entity, this);
+            }
+        }
+
+        /**
+         * @brief Checks if an entity has all the given components.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Components for which to perform the check.
+         * @param entity A valid entity identifier.
+         * @return True if the entity has all the components, false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool all_of(const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return [entity](const auto *... cpool) { return ((cpool && cpool->contains(entity)) && ...); }(pool_if_exists<Component>()...);
+        }
+
+        /**
+         * @brief Checks if an entity has at least one of the given components.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Components for which to perform the check.
+         * @param entity A valid entity identifier.
+         * @return True if the entity has at least one of the given components,
+         * false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool any_of(const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return [entity](const auto *... cpool) { return !((!cpool || !cpool->contains(entity)) && ...); }(pool_if_exists<Component>()...);
+        }
+
+        /**
+         * @brief Returns references to the given components for an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to get a component from an entity
+         * that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Types of components to get.
+         * @param entity A valid entity identifier.
+         * @return References to the components owned by the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                const auto* cpool = pool_if_exists<std::remove_const_t<Component>...>();
+                ENTT_ASSERT(cpool, "Storage not available");
+                return cpool->get(entity);
+            }
+            else {
+                return std::forward_as_tuple(get<Component>(entity)...);
+            }
+        }
+
+        /*! @copydoc get */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                return (const_cast<Component&>(assure<std::remove_const_t<Component>>()->get(entity)), ...);
+            }
+            else {
+                return std::forward_as_tuple(get<Component>(entity)...);
+            }
+        }
+
+        /**
+         * @brief Returns a reference to the given component for an entity.
+         *
+         * In case the entity doesn't own the component, the parameters provided are
+         * used to construct it.<br/>
+         * Equivalent to the following snippet (pseudocode):
+         *
+         * @code{.cpp}
+         * auto &component = registry.all_of<Component>(entity) ? registry.get<Component>(entity) : registry.emplace<Component>(entity, args...);
+         * @endcode
+         *
+         * Prefer this function anyway because it has slightly better performance.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Type of component to get.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return Reference to the component owned by the entity.
+         */
+        template<typename Component, typename... Args>
+        [[nodiscard]] decltype(auto) get_or_emplace(const entity_type entity, Args &&... args) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            auto* cpool = assure<Component>();
+            return cpool->contains(entity) ? cpool->get(entity) : cpool->emplace(*this, entity, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Returns pointers to the given components for an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @note
+         * The registry retains ownership of the pointed-to components.
+         *
+         * @tparam Component Types of components to get.
+         * @param entity A valid entity identifier.
+         * @return Pointers to the components owned by the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] auto try_get([[maybe_unused]] const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                const auto* cpool = pool_if_exists<std::remove_const_t<Component>...>();
+                return (cpool && cpool->contains(entity)) ? &cpool->get(entity) : nullptr;
+            }
+            else {
+                return std::make_tuple(try_get<Component>(entity)...);
+            }
+        }
+
+        /*! @copydoc try_get */
+        template<typename... Component>
+        [[nodiscard]] auto try_get([[maybe_unused]] const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                return (const_cast<Component*>(std::as_const(*this).template try_get<Component>(entity)), ...);
+            }
+            else {
+                return std::make_tuple(try_get<Component>(entity)...);
+            }
+        }
+
+        /**
+         * @brief Clears a whole registry or the pools for the given components.
+         * @tparam Component Types of components to remove from their entities.
+         */
+        template<typename... Component>
+        void clear() {
+            if constexpr (sizeof...(Component) == 0) {
+                for (auto&& pdata : pools) {
+                    pdata.pool && (pdata.pool->clear(this), true);
+                }
+
+                each([this](const auto entity) { release_entity(entity, version(entity) + 1u); });
+            }
+            else {
+                (assure<Component>()->clear(this), ...);
+            }
+        }
+
+        /**
+         * @brief Iterates all the entities that are still in use.
+         *
+         * The function object is invoked for each entity that is still in use.<br/>
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const Entity);
+         * @endcode
+         *
+         * This function is fairly slow and should not be used frequently. However,
+         * it's useful for iterating all the entities still in use, regardless of
+         * their components.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            if (free_list == null) {
+                for (auto pos = entities.size(); pos; --pos) {
+                    func(entities[pos - 1]);
+                }
+            }
+            else {
+                for (auto pos = entities.size(); pos; --pos) {
+                    if (const auto entity = entities[pos - 1]; traits_type::to_entity(entity) == (pos - 1)) {
+                        func(entity);
+                    }
+                }
+            }
+        }
+
+        /**
+         * @brief Checks if an entity has components assigned.
+         * @param entity A valid entity identifier.
+         * @return True if the entity has no components assigned, false otherwise.
+         */
+        [[nodiscard]] bool orphan(const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return std::none_of(pools.cbegin(), pools.cend(), [entity](auto&& pdata) { return pdata.pool && pdata.pool->contains(entity); });
+        }
+
+        /**
+         * @brief Iterates orphans and applies them the given function object.
+         *
+         * The function object is invoked for each entity that is still in use and
+         * has no components assigned.<br/>
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const Entity);
+         * @endcode
+         *
+         * This function can be very slow and should not be used frequently.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void orphans(Func func) const {
+            each([this, &func](const auto entity) {
+                if (orphan(entity)) {
+                    func(entity);
+                }
+                });
+        }
+
+        /**
+         * @brief Returns a sink object for the given component.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever a new instance of the given component is created and assigned to
+         * an entity.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<Entity> &, Entity);
+         * @endcode
+         *
+         * Listeners are invoked **after** the component has been assigned to the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @tparam Component Type of component of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Component>
+        [[nodiscard]] auto on_construct() {
+            return assure<Component>()->on_construct();
+        }
+
+        /**
+         * @brief Returns a sink object for the given component.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance of the given component is explicitly updated.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<Entity> &, Entity);
+         * @endcode
+         *
+         * Listeners are invoked **after** the component has been updated.
+         *
+         * @sa sink
+         *
+         * @tparam Component Type of component of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Component>
+        [[nodiscard]] auto on_update() {
+            return assure<Component>()->on_update();
+        }
+
+        /**
+         * @brief Returns a sink object for the given component.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance of the given component is removed from an entity and
+         * thus destroyed.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<Entity> &, Entity);
+         * @endcode
+         *
+         * Listeners are invoked **before** the component has been removed from the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @tparam Component Type of component of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Component>
+        [[nodiscard]] auto on_destroy() {
+            return assure<Component>()->on_destroy();
+        }
+
+        /**
+         * @brief Returns a view for the given components.
+         *
+         * This kind of objects are created on the fly and share with the registry
+         * its internal data structures.<br/>
+         * Feel free to discard a view after the use. Creating and destroying a view
+         * is an incredibly cheap operation because they do not require any type of
+         * initialization.<br/>
+         * As a rule of thumb, storing a view should never be an option.
+         *
+         * Views do their best to iterate the smallest set of candidate entities.
+         * In particular:
+         *
+         * * Single component views are incredibly fast and iterate a packed array
+         *   of entities, all of which has the given component.
+         * * Multi component views look at the number of entities available for each
+         *   component and pick up a reference to the smallest set of candidates to
+         *   test for the given components.
+         *
+         * Views in no way affect the functionalities of the registry nor those of
+         * the underlying pools.
+         *
+         * @note
+         * Multi component views are pretty fast. However their performance tend to
+         * degenerate when the number of components to iterate grows up and the most
+         * of the entities have all the given components.<br/>
+         * To get a performance boost, consider using a group instead.
+         *
+         * @tparam Component Type of components used to construct the view.
+         * @tparam Exclude Types of components used to filter the view.
+         * @return A newly created view.
+         */
+        template<typename... Component, typename... Exclude>
+        [[nodiscard]] basic_view<Entity, exclude_t<Exclude...>, std::add_const_t<Component>...> view(exclude_t<Exclude...> = {}) const {
+            static_assert(sizeof...(Component) > 0, "Exclusion-only views are not supported");
+            return { *assure<std::remove_const_t<Component>>()..., *assure<Exclude>()... };
+        }
+
+        /*! @copydoc view */
+        template<typename... Component, typename... Exclude>
+        [[nodiscard]] basic_view<Entity, exclude_t<Exclude...>, Component...> view(exclude_t<Exclude...> = {}) {
+            static_assert(sizeof...(Component) > 0, "Exclusion-only views are not supported");
+            return { *assure<std::remove_const_t<Component>>()..., *assure<Exclude>()... };
+        }
+
+        /**
+         * @brief Returns a runtime view for the given components.
+         *
+         * This kind of objects are created on the fly and share with the registry
+         * its internal data structures.<br/>
+         * Users should throw away the view after use. Fortunately, creating and
+         * destroying a runtime view is an incredibly cheap operation because they
+         * do not require any type of initialization.<br/>
+         * As a rule of thumb, storing a view should never be an option.
+         *
+         * Runtime views are to be used when users want to construct a view from
+         * some external inputs and don't know at compile-time what are the required
+         * components.
+         *
+         * @tparam ItComp Type of input iterator for the components to use to
+         * construct the view.
+         * @tparam ItExcl Type of input iterator for the components to use to filter
+         * the view.
+         * @param first An iterator to the first element of the range of components
+         * to use to construct the view.
+         * @param last An iterator past the last element of the range of components
+         * to use to construct the view.
+         * @param from An iterator to the first element of the range of components
+         * to use to filter the view.
+         * @param to An iterator past the last element of the range of components to
+         * use to filter the view.
+         * @return A newly created runtime view.
+         */
+        template<typename ItComp, typename ItExcl = id_type*>
+        [[nodiscard]] basic_runtime_view<Entity> runtime_view(ItComp first, ItComp last, ItExcl from = {}, ItExcl to = {}) const {
+            std::vector<const basic_common_type*> component(std::distance(first, last));
+            std::vector<const basic_common_type*> filter(std::distance(from, to));
+
+            std::transform(first, last, component.begin(), [this](const auto ctype) {
+                const auto it = std::find_if(pools.cbegin(), pools.cend(), [ctype](auto&& pdata) { return pdata.poly && pdata.poly->value_type().hash() == ctype; });
+                return it == pools.cend() ? nullptr : it->pool.get();
+                });
+
+            std::transform(from, to, filter.begin(), [this](const auto ctype) {
+                const auto it = std::find_if(pools.cbegin(), pools.cend(), [ctype](auto&& pdata) { return pdata.poly && pdata.poly->value_type().hash() == ctype; });
+                return it == pools.cend() ? nullptr : it->pool.get();
+                });
+
+            return { std::move(component), std::move(filter) };
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * This kind of objects are created on the fly and share with the registry
+         * its internal data structures.<br/>
+         * Feel free to discard a group after the use. Creating and destroying a
+         * group is an incredibly cheap operation because they do not require any
+         * type of initialization, but for the first time they are requested.<br/>
+         * As a rule of thumb, storing a group should never be an option.
+         *
+         * Groups support exclusion lists and can own types of components. The more
+         * types are owned by a group, the faster it is to iterate entities and
+         * components.<br/>
+         * However, groups also affect some features of the registry such as the
+         * creation and destruction of components, which will consequently be
+         * slightly slower (nothing that can be noticed in most cases).
+         *
+         * @note
+         * Pools of components that are owned by a group cannot be sorted anymore.
+         * The group takes the ownership of the pools and arrange components so as
+         * to iterate them as fast as possible.
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Get, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> group(get_t<Get...>, exclude_t<Exclude...> = {}) {
+            static_assert(sizeof...(Owned) + sizeof...(Get) > 0, "Exclusion-only groups are not supported");
+            static_assert(sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude) > 1, "Single component groups are not allowed");
+
+            using handler_type = group_handler<exclude_t<Exclude...>, get_t<std::remove_const_t<Get>...>, std::remove_const_t<Owned>...>;
+
+            const auto cpools = std::make_tuple(assure<std::remove_const_t<Owned>>()..., assure<std::remove_const_t<Get>>()...);
+            constexpr auto size = sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude);
+            handler_type* handler = nullptr;
+
+            if (auto it = std::find_if(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                return gdata.size == size
+                    && (gdata.owned(type_hash<std::remove_const_t<Owned>>::value()) && ...)
+                    && (gdata.get(type_hash<std::remove_const_t<Get>>::value()) && ...)
+                    && (gdata.exclude(type_hash<Exclude>::value()) && ...);
+                }); it != groups.cend())
+            {
+                handler = static_cast<handler_type*>(it->group.get());
+            }
+
+                if (!handler) {
+                    group_data candidate = {
+                        size,
+                        { new handler_type{}, [](void* instance) { delete static_cast<handler_type*>(instance); } },
+                        []([[maybe_unused]] const id_type ctype) ENTT_NOEXCEPT { return ((ctype == type_hash<std::remove_const_t<Owned>>::value()) || ...); },
+                        []([[maybe_unused]] const id_type ctype) ENTT_NOEXCEPT { return ((ctype == type_hash<std::remove_const_t<Get>>::value()) || ...); },
+                        []([[maybe_unused]] const id_type ctype) ENTT_NOEXCEPT { return ((ctype == type_hash<Exclude>::value()) || ...); },
+                    };
+
+                    handler = static_cast<handler_type*>(candidate.group.get());
+
+                    const void* maybe_valid_if = nullptr;
+                    const void* discard_if = nullptr;
+
+                    if constexpr (sizeof...(Owned) == 0) {
+                        groups.push_back(std::move(candidate));
+                    }
+                    else {
+                        ENTT_ASSERT(std::all_of(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                            const auto overlapping = (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value()));
+                            const auto sz = overlapping + (0u + ... + gdata.get(type_hash<std::remove_const_t<Get>>::value())) + (0u + ... + gdata.exclude(type_hash<Exclude>::value()));
+                            return !overlapping || ((sz == size) || (sz == gdata.size));
+                            }), "Conflicting groups");
+
+                        const auto next = std::find_if_not(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                            return !(0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value())) || (size > gdata.size);
+                            });
+
+                        const auto prev = std::find_if(std::make_reverse_iterator(next), groups.crend(), [](const auto& gdata) {
+                            return (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value()));
+                            });
+
+                        maybe_valid_if = (next == groups.cend() ? maybe_valid_if : next->group.get());
+                        discard_if = (prev == groups.crend() ? discard_if : prev->group.get());
+                        groups.insert(next, std::move(candidate));
+                    }
+
+                    (on_construct<std::remove_const_t<Owned>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Owned>>>(*handler), ...);
+                    (on_construct<std::remove_const_t<Get>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Get>>>(*handler), ...);
+                    (on_destroy<Exclude>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<Exclude>>(*handler), ...);
+
+                    (on_destroy<std::remove_const_t<Owned>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
+                    (on_destroy<std::remove_const_t<Get>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
+                    (on_construct<Exclude>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
+
+                    if constexpr (sizeof...(Owned) == 0) {
+                        for (const auto entity : view<Owned..., Get...>(exclude<Exclude...>)) {
+                            handler->current.emplace(entity);
+                        }
+                    }
+                    else {
+                        // we cannot iterate backwards because we want to leave behind valid entities in case of owned types
+                        for (auto* first = std::get<0>(cpools)->data(), *last = first + std::get<0>(cpools)->size(); first != last; ++first) {
+                            handler->template maybe_valid_if<type_list_element_t<0, type_list<std::remove_const_t<Owned>...>>>(*this, *first);
+                        }
+                    }
+                }
+
+                return { handler->current, *std::get<storage_type<std::remove_const_t<Owned>>*>(cpools)..., *std::get<storage_type<std::remove_const_t<Get>>*>(cpools)... };
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * @sa group
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Get, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<std::add_const_t<Get>...>, std::add_const_t<Owned>...> group_if_exists(get_t<Get...>, exclude_t<Exclude...> = {}) const {
+            if (auto it = std::find_if(groups.cbegin(), groups.cend(), [](const auto& gdata) {
+                return gdata.size == (sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude))
+                    && (gdata.owned(type_hash<std::remove_const_t<Owned>>::value()) && ...)
+                    && (gdata.get(type_hash<std::remove_const_t<Get>>::value()) && ...)
+                    && (gdata.exclude(type_hash<Exclude>::value()) && ...);
+                }); it == groups.cend())
+            {
+                return {};
+            }
+            else {
+                using handler_type = group_handler<exclude_t<Exclude...>, get_t<std::remove_const_t<Get>...>, std::remove_const_t<Owned>...>;
+                return { static_cast<handler_type*>(it->group.get())->current, *pool_if_exists<std::remove_const_t<Owned>>()... , *pool_if_exists<std::remove_const_t<Get>>()... };
+            }
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * @sa group
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<>, Owned...> group(exclude_t<Exclude...> = {}) {
+            return group<Owned...>(get_t<>{}, exclude<Exclude...>);
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * @sa group_if_exists
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<>, std::add_const_t<Owned>...> group_if_exists(exclude_t<Exclude...> = {}) const {
+            return group_if_exists<std::add_const_t<Owned>...>(get_t<>{}, exclude<Exclude...>);
+        }
+
+        /**
+         * @brief Checks whether the given components belong to any group.
+         * @tparam Component Types of components in which one is interested.
+         * @return True if the pools of the given components are sortable, false
+         * otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool sortable() const {
+            return std::none_of(groups.cbegin(), groups.cend(), [](auto&& gdata) { return (gdata.owned(type_hash<std::remove_const_t<Component>>::value()) || ...); });
+        }
+
+        /**
+         * @brief Checks whether a group can be sorted.
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return True if the group can be sorted, false otherwise.
+         */
+        template<typename... Owned, typename... Get, typename... Exclude>
+        [[nodiscard]] bool sortable(const basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...>&) ENTT_NOEXCEPT {
+            constexpr auto size = sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude);
+            return std::find_if(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                return (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value())) && (size < gdata.size);
+                }) == groups.cend();
+        }
+
+        /**
+         * @brief Sorts the pool of entities for the given component.
+         *
+         * The order of the elements in a pool is highly affected by assignments
+         * of components to entities and deletions. Components are arranged to
+         * maximize the performance during iterations and users should not make any
+         * assumption on the order.<br/>
+         * This function can be used to impose an order to the elements in the pool
+         * of the given component. The order is kept valid until a component of the
+         * given type is assigned or removed from an entity.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(const Entity, const Entity);
+         * bool(const Component &, const Component &);
+         * @endcode
+         *
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * The comparison funtion object received by the sort function object hasn't
+         * necessarily the type of the one passed along with the other parameters to
+         * this member function.
+         *
+         * @warning
+         * Pools of components owned by a group cannot be sorted.
+         *
+         * @tparam Component Type of components to sort.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Component, typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            ENTT_ASSERT(sortable<Component>(), "Cannot sort owned storage");
+            assure<Component>()->sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Sorts two pools of components in the same way.
+         *
+         * The order of the elements in a pool is highly affected by assignments
+         * of components to entities and deletions. Components are arranged to
+         * maximize the performance during iterations and users should not make any
+         * assumption on the order.
+         *
+         * It happens that different pools of components must be sorted the same way
+         * because of runtime and/or performance constraints. This function can be
+         * used to order a pool of components according to the order between the
+         * entities in another pool of components.
+         *
+         * @b How @b it @b works
+         *
+         * Being `A` and `B` the two sets where `B` is the master (the one the order
+         * of which rules) and `A` is the slave (the one to sort), after a call to
+         * this function an iterator for `A` will return the entities according to
+         * the following rules:
+         *
+         * * All the entities in `A` that are also in `B` are returned first
+         *   according to the order they have in `B`.
+         * * All the entities in `A` that are not in `B` are returned in no
+         *   particular order after all the other entities.
+         *
+         * Any subsequent change to `B` won't affect the order in `A`.
+         *
+         * @warning
+         * Pools of components owned by a group cannot be sorted.
+         *
+         * @tparam To Type of components to sort.
+         * @tparam From Type of components to use to sort.
+         */
+        template<typename To, typename From>
+        void sort() {
+            ENTT_ASSERT(sortable<To>(), "Cannot sort owned storage");
+            assure<To>()->respect(*assure<From>());
+        }
+
+        /**
+         * @brief Visits an entity and returns the type info for its components.
+         *
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const type_info);
+         * @endcode
+         *
+         * Returned identifiers are those of the components owned by the entity.
+         *
+         * @sa type_info
+         *
+         * @warning
+         * It's not specified whether a component attached to or removed from the
+         * given entity during the visit is returned or not to the caller.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param entity A valid entity identifier.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void visit(entity_type entity, Func func) const {
+            for (auto pos = pools.size(); pos; --pos) {
+                if (const auto& pdata = pools[pos - 1]; pdata.pool && pdata.pool->contains(entity)) {
+                    func(pdata.poly->value_type());
+                }
+            }
+        }
+
+        /**
+         * @brief Visits a registry and returns the type info for its components.
+         *
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const type_info);
+         * @endcode
+         *
+         * Returned identifiers are those of the components managed by the registry.
+         *
+         * @sa type_info
+         *
+         * @warning
+         * It's not specified whether a component for which a pool is created during
+         * the visit is returned or not to the caller.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void visit(Func func) const {
+            for (auto pos = pools.size(); pos; --pos) {
+                if (const auto& pdata = pools[pos - 1]; pdata.pool) {
+                    func(pdata.poly->value_type());
+                }
+            }
+        }
+
+        /**
+         * @brief Binds an object to the context of the registry.
+         *
+         * If the value already exists it is overwritten, otherwise a new instance
+         * of the given type is created and initialized with the arguments provided.
+         *
+         * @tparam Type Type of object to set.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param args Parameters to use to initialize the value.
+         * @return A reference to the newly created object.
+         */
+        template<typename Type, typename... Args>
+        Type& set(Args &&... args) {
+            unset<Type>();
+            vars.emplace_back(std::in_place_type<Type>, std::forward<Args>(args)...);
+            return any_cast<Type&>(vars.back());
+        }
+
+        /**
+         * @brief Unsets a context variable if it exists.
+         * @tparam Type Type of object to set.
+         */
+        template<typename Type>
+        void unset() {
+            vars.erase(std::remove_if(vars.begin(), vars.end(), [type = type_id<Type>()](auto&& var) { return var.type() == type; }), vars.end());
+        }
+
+        /**
+         * @brief Binds an object to the context of the registry.
+         *
+         * In case the context doesn't contain the given object, the parameters
+         * provided are used to construct it.
+         *
+         * @tparam Type Type of object to set.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param args Parameters to use to initialize the object.
+         * @return A reference to the object in the context of the registry.
+         */
+        template<typename Type, typename... Args>
+        [[nodiscard]] Type& ctx_or_set(Args &&... args) {
+            auto* value = try_ctx<Type>();
+            return value ? *value : set<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Returns a pointer to an object in the context of the registry.
+         * @tparam Type Type of object to get.
+         * @return A pointer to the object if it exists in the context of the
+         * registry, a null pointer otherwise.
+         */
+        template<typename Type>
+        [[nodiscard]] std::add_const_t<Type>* try_ctx() const {
+            auto it = std::find_if(vars.cbegin(), vars.cend(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            return it == vars.cend() ? nullptr : any_cast<std::add_const_t<Type>>(&*it);
+        }
+
+        /*! @copydoc try_ctx */
+        template<typename Type>
+        [[nodiscard]] Type* try_ctx() {
+            auto it = std::find_if(vars.begin(), vars.end(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            return it == vars.end() ? nullptr : any_cast<Type>(&*it);
+        }
+
+        /**
+         * @brief Returns a reference to an object in the context of the registry.
+         *
+         * @warning
+         * Attempting to get a context variable that doesn't exist results in
+         * undefined behavior.
+         *
+         * @tparam Type Type of object to get.
+         * @return A valid reference to the object in the context of the registry.
+         */
+        template<typename Type>
+        [[nodiscard]] std::add_const_t<Type>& ctx() const {
+            auto it = std::find_if(vars.cbegin(), vars.cend(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            ENTT_ASSERT(it != vars.cend(), "Invalid instance");
+            return any_cast<std::add_const_t<Type>&>(*it);
+        }
+
+        /*! @copydoc ctx */
+        template<typename Type>
+        [[nodiscard]] Type& ctx() {
+            auto it = std::find_if(vars.begin(), vars.end(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            ENTT_ASSERT(it != vars.end(), "Invalid instance");
+            return any_cast<Type&>(*it);
+        }
+
+        /**
+         * @brief Visits a registry and returns the type info for its context
+         * variables.
+         *
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const type_info);
+         * @endcode
+         *
+         * Returned identifiers are those of the context variables currently set.
+         *
+         * @sa type_info
+         *
+         * @warning
+         * It's not specified whether a context variable created during the visit is
+         * returned or not to the caller.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void ctx(Func func) const {
+            for (auto pos = vars.size(); pos; --pos) {
+                func(vars[pos - 1].type());
+            }
+        }
+
+    private:
+        std::vector<basic_any<0u>> vars{};
+        mutable std::vector<pool_data> pools{};
+        std::vector<group_data> groups{};
+        std::vector<entity_type> entities{};
+        entity_type free_list{ tombstone };
+    };
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Non-owning handle to an entity.
+     *
+     * Tiny wrapper around a registry and an entity.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Types to which to restrict the scope of a handle.
+     */
+    template<typename Entity, typename... Type>
+    struct basic_handle {
+        /*! @brief Type of registry accepted by the handle. */
+        using registry_type = constness_as_t<basic_registry<std::remove_const_t<Entity>>, Entity>;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = typename registry_type::entity_type;
+        /*! @brief Underlying version type. */
+        using version_type = typename registry_type::version_type;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename registry_type::size_type;
+
+        /*! @brief Constructs an invalid handle. */
+        basic_handle() ENTT_NOEXCEPT
+            : reg{}, entt{ null }
+        {}
+
+        /**
+         * @brief Constructs a handle from a given registry and entity.
+         * @param ref An instance of the registry class.
+         * @param value An entity identifier.
+         */
+        basic_handle(registry_type& ref, entity_type value) ENTT_NOEXCEPT
+            : reg{ &ref }, entt{ value }
+        {}
+
+        /**
+         * @brief Compares two handles.
+         * @tparam Args Template parameters of the handle with which to compare.
+         * @param other Handle with which to compare.
+         * @return True if both handles refer to the same registry and the same
+         * entity, false otherwise.
+         */
+        template<typename... Args>
+        [[nodiscard]] bool operator==(const basic_handle<Args...>& other) const ENTT_NOEXCEPT {
+            return reg == other.registry() && entt == other.entity();
+        }
+
+        /**
+         * @brief Constructs a const handle from a non-const one.
+         * @tparam Other A valid entity type (see entt_traits for more details).
+         * @tparam Args Scope of the handle to construct.
+         * @return A const handle referring to the same registry and the same
+         * entity.
+         */
+        template<typename Other, typename... Args>
+        operator basic_handle<Other, Args...>() const ENTT_NOEXCEPT {
+            static_assert(
+                (std::is_same_v<Other, Entity> || std::is_same_v<std::remove_const_t<Other>, Entity>)
+                && (sizeof...(Type) == 0 || ((sizeof...(Args) != 0 && sizeof...(Args) <= sizeof...(Type)) && ... && (type_list_contains_v<type_list<Type...>, Args>))),
+                "Invalid conversion between different handles"
+                );
+
+            return reg ? basic_handle<Other, Args...>{*reg, entt} : basic_handle<Other, Args...>{};
+        }
+
+        /**
+         * @brief Converts a handle to its underlying entity.
+         * @return An entity identifier.
+         */
+        [[nodiscard]] operator entity_type() const ENTT_NOEXCEPT {
+            return entity();
+        }
+
+        /**
+         * @brief Checks if a handle refers to non-null registry pointer and entity.
+         * @return True if the handle refers to non-null registry and entity, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return reg && reg->valid(entt);
+        }
+
+        /**
+         * @brief Checks if a handle refers to a valid entity or not.
+         * @return True if the handle refers to a valid entity, false otherwise.
+         */
+        [[nodiscard]] bool valid() const {
+            return reg->valid(entt);
+        }
+
+        /**
+         * @brief Returns a pointer to the underlying registry, if any.
+         * @return A pointer to the underlying registry, if any.
+         */
+        [[nodiscard]] registry_type* registry() const ENTT_NOEXCEPT {
+            return reg;
+        }
+
+        /**
+         * @brief Returns the entity associated with a handle.
+         * @return The entity associated with the handle.
+         */
+        [[nodiscard]] entity_type entity() const ENTT_NOEXCEPT {
+            return entt;
+        }
+
+        /**
+         * @brief Destroys the entity associated with a handle.
+         * @sa basic_registry::destroy
+         */
+        void destroy() {
+            reg->destroy(entt);
+        }
+
+        /**
+         * @brief Destroys the entity associated with a handle.
+         * @sa basic_registry::destroy
+         * @param version A desired version upon destruction.
+         */
+        void destroy(const version_type version) {
+            reg->destroy(entt, version);
+        }
+
+        /**
+         * @brief Assigns the given component to a handle.
+         * @sa basic_registry::emplace
+         * @tparam Component Type of component to create.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the newly created component.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) emplace(Args &&... args) const {
+            static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
+            return reg->template emplace<Component>(entt, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Assigns or replaces the given component for a handle.
+         * @sa basic_registry::emplace_or_replace
+         * @tparam Component Type of component to assign or replace.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the newly created component.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) emplace_or_replace(Args &&... args) const {
+            static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
+            return reg->template emplace_or_replace<Component>(entt, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Patches the given component for a handle.
+         * @sa basic_registry::patch
+         * @tparam Component Type of component to patch.
+         * @tparam Func Types of the function objects to invoke.
+         * @param func Valid function objects.
+         * @return A reference to the patched component.
+         */
+        template<typename Component, typename... Func>
+        decltype(auto) patch(Func &&... func) const {
+            static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
+            return reg->template patch<Component>(entt, std::forward<Func>(func)...);
+        }
+
+        /**
+         * @brief Replaces the given component for a handle.
+         * @sa basic_registry::replace
+         * @tparam Component Type of component to replace.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the component being replaced.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) replace(Args &&... args) const {
+            static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
+            return reg->template replace<Component>(entt, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Removes the given components from a handle.
+         * @sa basic_registry::remove
+         * @tparam Component Types of components to remove.
+         * @return The number of components actually removed.
+         */
+        template<typename... Component>
+        size_type remove() const {
+            static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
+            return reg->template remove<Component...>(entt);
+        }
+
+        /**
+         * @brief Erases the given components from a handle.
+         * @sa basic_registry::erase
+         * @tparam Component Types of components to erase.
+         */
+        template<typename... Component>
+        void erase() const {
+            static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
+            reg->template erase<Component...>(entt);
+        }
+
+        /*! @copydoc remove */
+        template<typename... Component>
+        [[deprecated("Use ::remove instead")]]
+        size_type remove_if_exists() const {
+            return remove<Component...>();
+        }
+
+        /**
+         * @brief Removes all the components from a handle and makes it orphaned.
+         * @sa basic_registry::remove_all
+         */
+        [[deprecated("No longer supported")]]
+        void remove_all() const {
+            static_assert(sizeof...(Type) == 0, "Invalid operation");
+            reg->remove_all(entt);
+        }
+
+        /**
+         * @brief Checks if a handle has all the given components.
+         * @sa basic_registry::all_of
+         * @tparam Component Components for which to perform the check.
+         * @return True if the handle has all the components, false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) all_of() const {
+            return reg->template all_of<Component...>(entt);
+        }
+
+        /**
+         * @brief Checks if a handle has at least one of the given components.
+         * @sa basic_registry::any_of
+         * @tparam Component Components for which to perform the check.
+         * @return True if the handle has at least one of the given components,
+         * false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) any_of() const {
+            return reg->template any_of<Component...>(entt);
+        }
+
+        /**
+         * @brief Returns references to the given components for a handle.
+         * @sa basic_registry::get
+         * @tparam Component Types of components to get.
+         * @return References to the components owned by the handle.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get() const {
+            static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
+            return reg->template get<Component...>(entt);
+        }
+
+        /**
+         * @brief Returns a reference to the given component for a handle.
+         * @sa basic_registry::get_or_emplace
+         * @tparam Component Type of component to get.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param args Parameters to use to initialize the component.
+         * @return Reference to the component owned by the handle.
+         */
+        template<typename Component, typename... Args>
+        [[nodiscard]] decltype(auto) get_or_emplace(Args &&... args) const {
+            static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
+            return reg->template get_or_emplace<Component>(entt, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Returns pointers to the given components for a handle.
+         * @sa basic_registry::try_get
+         * @tparam Component Types of components to get.
+         * @return Pointers to the components owned by the handle.
+         */
+        template<typename... Component>
+        [[nodiscard]] auto try_get() const {
+            static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
+            return reg->template try_get<Component...>(entt);
+        }
+
+        /**
+         * @brief Checks if a handle has components assigned.
+         * @return True if the handle has no components assigned, false otherwise.
+         */
+        [[nodiscard]] bool orphan() const {
+            return reg->orphan(entt);
+        }
+
+        /**
+         * @brief Visits a handle and returns the types for its components.
+         * @sa basic_registry::visit
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void visit(Func&& func) const {
+            reg->visit(entt, std::forward<Func>(func));
+        }
+
+    private:
+        registry_type* reg;
+        entity_type entt;
+    };
+
+
+    /**
+     * @brief Compares two handles.
+     * @tparam Type A valid entity type (see entt_traits for more details).
+     * @tparam Other A valid entity type (see entt_traits for more details).
+     * @param lhs A valid handle.
+     * @param rhs A valid handle.
+     * @return False if both handles refer to the same registry and the same
+     * entity, true otherwise.
+     */
+    template<typename Type, typename Other>
+    bool operator!=(const basic_handle<Type>& lhs, const basic_handle<Other>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    basic_handle(basic_registry<Entity>&, Entity)
+        ->basic_handle<Entity>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    basic_handle(const basic_registry<Entity>&, Entity)
+        ->basic_handle<const Entity>;
+
+
+}
+
+
+#endif
+
+// #include "entity/helper.hpp"
+#ifndef ENTT_ENTITY_HELPER_HPP
+#define ENTT_ENTITY_HELPER_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../signal/delegate.hpp"
+#ifndef ENTT_SIGNAL_DELEGATE_HPP
+#define ENTT_SIGNAL_DELEGATE_HPP
+
+
+#include <tuple>
+#include <cstddef>
+#include <utility>
+#include <functional>
+#include <type_traits>
+// #include "../core/type_traits.hpp"
+
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Ret, typename... Args>
+        auto function_pointer(Ret(*)(Args...))->Ret(*)(Args...);
+
+
+        template<typename Ret, typename Type, typename... Args, typename Other>
+        auto function_pointer(Ret(*)(Type, Args...), Other&&)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...), Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...) const, Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Type, typename... Other>
+        auto function_pointer(Type Class::*, Other &&...)->Type(*)();
+
+
+        template<typename... Type>
+        using function_pointer_t = decltype(internal::function_pointer(std::declval<Type>()...));
+
+
+        template<typename... Class, typename Ret, typename... Args>
+        [[nodiscard]] constexpr auto index_sequence_for(Ret(*)(Args...)) {
+            return std::index_sequence_for<Class..., Args...>{};
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Used to wrap a function or a member of a specified type. */
+    template<auto>
+    struct connect_arg_t {};
+
+
+    /*! @brief Constant of type connect_arg_t used to disambiguate calls. */
+    template<auto Func>
+    inline constexpr connect_arg_t<Func> connect_arg{};
+
+
+    /**
+     * @brief Basic delegate implementation.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     */
+    template<typename>
+    class delegate;
+
+
+    /**
+     * @brief Utility class to use to send around functions and members.
+     *
+     * Unmanaged delegate for function pointers and members. Users of this class are
+     * in charge of disconnecting instances before deleting them.
+     *
+     * A delegate can be used as a general purpose invoker without memory overhead
+     * for free functions possibly with payloads and bound or unbound members.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class delegate<Ret(Args...)> {
+        template<auto Candidate, std::size_t... Index>
+        [[nodiscard]] auto wrap(std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void*, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type&, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type*, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+    public:
+        /*! @brief Function type of the contained target. */
+        using function_type = Ret(const void*, Args...);
+        /*! @brief Function type of the delegate. */
+        using type = Ret(Args...);
+        /*! @brief Return type of the delegate. */
+        using result_type = Ret;
+
+        /*! @brief Default constructor. */
+        delegate() ENTT_NOEXCEPT
+            : fn{ nullptr }, data{ nullptr }
+        {}
+
+        /**
+         * @brief Constructs a delegate and connects a free function or an unbound
+         * member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        delegate(connect_arg_t<Candidate>) ENTT_NOEXCEPT {
+            connect<Candidate>();
+        }
+
+        /**
+         * @brief Constructs a delegate and connects a free function with payload or
+         * a bound member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        delegate(connect_arg_t<Candidate>, Type&& value_or_instance) ENTT_NOEXCEPT {
+            connect<Candidate>(std::forward<Type>(value_or_instance));
+        }
+
+        /**
+         * @brief Constructs a delegate and connects an user defined function with
+         * optional payload.
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        delegate(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            connect(function, payload);
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a delegate.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        void connect() ENTT_NOEXCEPT {
+            data = nullptr;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
+                fn = [](const void*, Args... args) -> Ret {
+                    return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
+                };
+            }
+            else if constexpr (std::is_member_pointer_v<decltype(Candidate)>) {
+                fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+            else {
+                fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the delegate.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the delegate itself.
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid reference that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type& value_or_instance) ENTT_NOEXCEPT {
+            data = &value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type&, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * @sa connect(Type &)
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type* value_or_instance) ENTT_NOEXCEPT {
+            data = value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type*, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects an user defined function with optional payload to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of an instance overcomes
+         * the one of the delegate.<br/>
+         * The payload is returned as the first argument to the target function in
+         * all cases.
+         *
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        void connect(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            fn = function;
+            data = payload;
+        }
+
+        /**
+         * @brief Resets a delegate.
+         *
+         * After a reset, a delegate cannot be invoked anymore.
+         */
+        void reset() ENTT_NOEXCEPT {
+            fn = nullptr;
+            data = nullptr;
+        }
+
+        /**
+         * @brief Returns the instance or the payload linked to a delegate, if any.
+         * @return An opaque pointer to the underlying data.
+         */
+        [[nodiscard]] const void* instance() const ENTT_NOEXCEPT {
+            return data;
+        }
+
+        /**
+         * @brief Triggers a delegate.
+         *
+         * The delegate invokes the underlying function and returns the result.
+         *
+         * @warning
+         * Attempting to trigger an invalid delegate results in undefined
+         * behavior.
+         *
+         * @param args Arguments to use to invoke the underlying function.
+         * @return The value returned by the underlying function.
+         */
+        Ret operator()(Args... args) const {
+            ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
+            return fn(data, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Checks whether a delegate actually stores a listener.
+         * @return False if the delegate is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            // no need to test also data
+            return !(fn == nullptr);
+        }
+
+        /**
+         * @brief Compares the contents of two delegates.
+         * @param other Delegate with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const delegate<Ret(Args...)>& other) const ENTT_NOEXCEPT {
+            return fn == other.fn && data == other.data;
+        }
+
+    private:
+        function_type* fn;
+        const void* data;
+    };
+
+
+    /**
+     * @brief Compares the contents of two delegates.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     * @param lhs A valid delegate object.
+     * @param rhs A valid delegate object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    template<typename Ret, typename... Args>
+    [[nodiscard]] bool operator!=(const delegate<Ret(Args...)>& lhs, const delegate<Ret(Args...)>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     */
+    template<auto Candidate>
+    delegate(connect_arg_t<Candidate>)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     * @tparam Type Type of class or type of payload.
+     */
+    template<auto Candidate, typename Type>
+    delegate(connect_arg_t<Candidate>, Type&&)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    delegate(Ret(*)(const void*, Args...), const void* = nullptr)
+        ->delegate<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
+// #include "registry.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Converts a registry to a view.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    struct as_view {
+        /*! @brief Underlying entity identifier. */
+        using entity_type = std::remove_const_t<Entity>;
+        /*! @brief Type of registry to convert. */
+        using registry_type = constness_as_t<basic_registry<entity_type>, Entity>;
+
+        /**
+         * @brief Constructs a converter for a given registry.
+         * @param source A valid reference to a registry.
+         */
+        as_view(registry_type& source) ENTT_NOEXCEPT: reg{ source } {}
+
+        /**
+         * @brief Conversion function from a registry to a view.
+         * @tparam Exclude Types of components used to filter the view.
+         * @tparam Component Type of components used to construct the view.
+         * @return A newly created view.
+         */
+        template<typename Exclude, typename... Component>
+        operator basic_view<entity_type, Exclude, Component...>() const {
+            return reg.template view<Component...>(Exclude{});
+        }
+
+    private:
+        registry_type& reg;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_view(basic_registry<Entity>&)->as_view<Entity>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_view(const basic_registry<Entity>&)->as_view<const Entity>;
+
+
+    /**
+     * @brief Converts a registry to a group.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    struct as_group {
+        /*! @brief Underlying entity identifier. */
+        using entity_type = std::remove_const_t<Entity>;
+        /*! @brief Type of registry to convert. */
+        using registry_type = constness_as_t<basic_registry<entity_type>, Entity>;
+
+        /**
+         * @brief Constructs a converter for a given registry.
+         * @param source A valid reference to a registry.
+         */
+        as_group(registry_type& source) ENTT_NOEXCEPT: reg{ source } {}
+
+        /**
+         * @brief Conversion function from a registry to a group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Owned Types of components owned by the group.
+         * @return A newly created group.
+         */
+        template<typename Exclude, typename Get, typename... Owned>
+        operator basic_group<entity_type, Exclude, Get, Owned...>() const {
+            if constexpr (std::is_const_v<registry_type>) {
+                return reg.template group_if_exists<Owned...>(Get{}, Exclude{});
+            }
+            else {
+                return reg.template group<Owned...>(Get{}, Exclude{});
+            }
+        }
+
+    private:
+        registry_type& reg;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_group(basic_registry<Entity>&)->as_group<Entity>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_group(const basic_registry<Entity>&)->as_group<const Entity>;
+
+
+
+    /**
+     * @brief Helper to create a listener that directly invokes a member function.
+     * @tparam Member Member function to invoke on a component of the given type.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @param reg A registry that contains the given entity and its components.
+     * @param entt Entity from which to get the component.
+     */
+    template<auto Member, typename Entity = entity>
+    void invoke(basic_registry<Entity>& reg, const Entity entt) {
+        static_assert(std::is_member_function_pointer_v<decltype(Member)>, "Invalid pointer to non-static member function");
+        delegate<void(basic_registry<Entity>&, const Entity)> func;
+        func.template connect<Member>(reg.template get<member_class_t<decltype(Member)>>(entt));
+        func(reg, entt);
+    }
+
+
+    /**
+     * @brief Returns the entity associated with a given component.
+     *
+     * @warning
+     * Currently, this function only works correctly with the default pool as it
+     * makes assumptions about how the components are laid out.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Component Type of component.
+     * @param reg A registry that contains the given entity and its components.
+     * @param instance A valid component instance.
+     * @return The entity associated with the given component.
+     */
+    template<typename Entity, typename Component>
+    Entity to_entity(const basic_registry<Entity>& reg, const Component& instance) {
+        const auto view = reg.template view<const Component>();
+        const auto* addr = std::addressof(instance);
+
+        for (auto it = view.rbegin(), last = view.rend(); it < last; it += ENTT_PACKED_PAGE) {
+            if (const auto dist = (addr - std::addressof(view.template get<const Component>(*it))); dist >= 0 && dist < ENTT_PACKED_PAGE) {
+                return *(it + dist);
+            }
+        }
+
+        return entt::null;
+    }
+
+
+}
+
+
+#endif
+
+// #include "entity/observer.hpp"
+#ifndef ENTT_ENTITY_OBSERVER_HPP
+#define ENTT_ENTITY_OBSERVER_HPP
+
+
+#include <limits>
+#include <cstddef>
+#include <cstdint>
+#include <utility>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../signal/delegate.hpp"
+
+// #include "registry.hpp"
+
+// #include "storage.hpp"
+
+// #include "utility.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /*! @brief Grouping matcher. */
+    template<typename...>
+    struct matcher {};
+
+
+    /**
+     * @brief Collector.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error, but for a few reasonable cases.
+     */
+    template<typename...>
+    struct basic_collector;
+
+
+    /**
+     * @brief Collector.
+     *
+     * A collector contains a set of rules (literally, matchers) to use to track
+     * entities.<br/>
+     * Its main purpose is to generate a descriptor that allows an observer to know
+     * how to connect to a registry.
+     */
+    template<>
+    struct basic_collector<> {
+        /**
+         * @brief Adds a grouping matcher to the collector.
+         * @tparam AllOf Types of components tracked by the matcher.
+         * @tparam NoneOf Types of components used to filter out entities.
+         * @return The updated collector.
+         */
+        template<typename... AllOf, typename... NoneOf>
+        static constexpr auto group(exclude_t<NoneOf...> = {}) ENTT_NOEXCEPT {
+            return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>>{};
+        }
+
+        /**
+         * @brief Adds an observing matcher to the collector.
+         * @tparam AnyOf Type of component for which changes should be detected.
+         * @return The updated collector.
+         */
+        template<typename AnyOf>
+        static constexpr auto update() ENTT_NOEXCEPT {
+            return basic_collector<matcher<type_list<>, type_list<>, AnyOf>>{};
+        }
+    };
+
+    /**
+     * @brief Collector.
+     * @copydetails basic_collector<>
+     * @tparam Reject Untracked types used to filter out entities.
+     * @tparam Require Untracked types required by the matcher.
+     * @tparam Rule Specific details of the current matcher.
+     * @tparam Other Other matchers.
+     */
+    template<typename... Reject, typename... Require, typename... Rule, typename... Other>
+    struct basic_collector<matcher<type_list<Reject...>, type_list<Require...>, Rule...>, Other...> {
+        /*! @brief Current matcher. */
+        using current_type = matcher<type_list<Reject...>, type_list<Require...>, Rule...>;
+
+        /**
+         * @brief Adds a grouping matcher to the collector.
+         * @tparam AllOf Types of components tracked by the matcher.
+         * @tparam NoneOf Types of components used to filter out entities.
+         * @return The updated collector.
+         */
+        template<typename... AllOf, typename... NoneOf>
+        static constexpr auto group(exclude_t<NoneOf...> = {}) ENTT_NOEXCEPT {
+            return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>, current_type, Other...>{};
+        }
+
+        /**
+         * @brief Adds an observing matcher to the collector.
+         * @tparam AnyOf Type of component for which changes should be detected.
+         * @return The updated collector.
+         */
+        template<typename AnyOf>
+        static constexpr auto update() ENTT_NOEXCEPT {
+            return basic_collector<matcher<type_list<>, type_list<>, AnyOf>, current_type, Other...>{};
+        }
+
+        /**
+         * @brief Updates the filter of the last added matcher.
+         * @tparam AllOf Types of components required by the matcher.
+         * @tparam NoneOf Types of components used to filter out entities.
+         * @return The updated collector.
+         */
+        template<typename... AllOf, typename... NoneOf>
+        static constexpr auto where(exclude_t<NoneOf...> = {}) ENTT_NOEXCEPT {
+            using extended_type = matcher<type_list<Reject..., NoneOf...>, type_list<Require..., AllOf...>, Rule...>;
+            return basic_collector<extended_type, Other...>{};
+        }
+    };
+
+
+    /*! @brief Variable template used to ease the definition of collectors. */
+    inline constexpr basic_collector<> collector{};
+
+
+    /**
+     * @brief Observer.
+     *
+     * An observer returns all the entities and only the entities that fit the
+     * requirements of at least one matcher. Moreover, it's guaranteed that the
+     * entity list is tightly packed in memory for fast iterations.<br/>
+     * In general, observers don't stay true to the order of any set of components.
+     *
+     * Observers work mainly with two types of matchers, provided through a
+     * collector:
+     *
+     * * Observing matcher: an observer will return at least all the living entities
+     *   for which one or more of the given components have been updated and not yet
+     *   destroyed.
+     * * Grouping matcher: an observer will return at least all the living entities
+     *   that would have entered the given group if it existed and that would have
+     *   not yet left it.
+     *
+     * If an entity respects the requirements of multiple matchers, it will be
+     * returned once and only once by the observer in any case.
+     *
+     * Matchers support also filtering by means of a _where_ clause that accepts
+     * both a list of types and an exclusion list.<br/>
+     * Whenever a matcher finds that an entity matches its requirements, the
+     * condition of the filter is verified before to register the entity itself.
+     * Moreover, a registered entity isn't returned by the observer if the condition
+     * set by the filter is broken in the meantime.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all the other cases, modifying the pools of the given components in any
+     * way invalidates all the iterators and using them results in undefined
+     * behavior.
+     *
+     * @warning
+     * Lifetime of an observer doesn't necessarily have to overcome that of the
+     * registry to which it is connected. However, the observer must be disconnected
+     * from the registry before being destroyed to avoid crashes due to dangling
+     * pointers.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_observer {
+        using payload_type = std::uint32_t;
+
+        template<typename>
+        struct matcher_handler;
+
+        template<typename... Reject, typename... Require, typename AnyOf>
+        struct matcher_handler<matcher<type_list<Reject...>, type_list<Require...>, AnyOf>> {
+            template<std::size_t Index>
+            static void maybe_valid_if(basic_observer& obs, basic_registry<Entity>& reg, const Entity entt) {
+                if (reg.template all_of<Require...>(entt) && !reg.template any_of<Reject...>(entt)) {
+                    if (!obs.storage.contains(entt)) {
+                        obs.storage.emplace(entt);
+                    }
+
+                    obs.storage.get(entt) |= (1 << Index);
+                }
+            }
+
+            template<std::size_t Index>
+            static void discard_if(basic_observer& obs, basic_registry<Entity>&, const Entity entt) {
+                if (obs.storage.contains(entt) && !(obs.storage.get(entt) &= (~(1 << Index)))) {
+                    obs.storage.erase(entt);
+                }
+            }
+
+            template<std::size_t Index>
+            static void connect(basic_observer& obs, basic_registry<Entity>& reg) {
+                (reg.template on_destroy<Require>().template connect<&discard_if<Index>>(obs), ...);
+                (reg.template on_construct<Reject>().template connect<&discard_if<Index>>(obs), ...);
+                reg.template on_update<AnyOf>().template connect<&maybe_valid_if<Index>>(obs);
+                reg.template on_destroy<AnyOf>().template connect<&discard_if<Index>>(obs);
+            }
+
+            static void disconnect(basic_observer& obs, basic_registry<Entity>& reg) {
+                (reg.template on_destroy<Require>().disconnect(obs), ...);
+                (reg.template on_construct<Reject>().disconnect(obs), ...);
+                reg.template on_update<AnyOf>().disconnect(obs);
+                reg.template on_destroy<AnyOf>().disconnect(obs);
+            }
+        };
+
+        template<typename... Reject, typename... Require, typename... NoneOf, typename... AllOf>
+        struct matcher_handler<matcher<type_list<Reject...>, type_list<Require...>, type_list<NoneOf...>, AllOf...>> {
+            template<std::size_t Index, typename... Ignore>
+            static void maybe_valid_if(basic_observer& obs, basic_registry<Entity>& reg, const Entity entt) {
+                if ([&reg, entt]() {
+                    if constexpr (sizeof...(Ignore) == 0) {
+                        return reg.template all_of<AllOf..., Require...>(entt) && !reg.template any_of<NoneOf..., Reject...>(entt);
+                    }
+                    else {
+                        return reg.template all_of<AllOf..., Require...>(entt) && ((std::is_same_v<Ignore..., NoneOf> || !reg.template any_of<NoneOf>(entt)) && ...) && !reg.template any_of<Reject...>(entt);
+                    }
+                    }())
+                {
+                    if (!obs.storage.contains(entt)) {
+                        obs.storage.emplace(entt);
+                    }
+
+                    obs.storage.get(entt) |= (1 << Index);
+                }
+            }
+
+            template<std::size_t Index>
+            static void discard_if(basic_observer& obs, basic_registry<Entity>&, const Entity entt) {
+                if (obs.storage.contains(entt) && !(obs.storage.get(entt) &= (~(1 << Index)))) {
+                    obs.storage.erase(entt);
+                }
+            }
+
+            template<std::size_t Index>
+            static void connect(basic_observer& obs, basic_registry<Entity>& reg) {
+                (reg.template on_destroy<Require>().template connect<&discard_if<Index>>(obs), ...);
+                (reg.template on_construct<Reject>().template connect<&discard_if<Index>>(obs), ...);
+                (reg.template on_construct<AllOf>().template connect<&maybe_valid_if<Index>>(obs), ...);
+                (reg.template on_destroy<NoneOf>().template connect<&maybe_valid_if<Index, NoneOf>>(obs), ...);
+                (reg.template on_destroy<AllOf>().template connect<&discard_if<Index>>(obs), ...);
+                (reg.template on_construct<NoneOf>().template connect<&discard_if<Index>>(obs), ...);
+            }
+
+            static void disconnect(basic_observer& obs, basic_registry<Entity>& reg) {
+                (reg.template on_destroy<Require>().disconnect(obs), ...);
+                (reg.template on_construct<Reject>().disconnect(obs), ...);
+                (reg.template on_construct<AllOf>().disconnect(obs), ...);
+                (reg.template on_destroy<NoneOf>().disconnect(obs), ...);
+                (reg.template on_destroy<AllOf>().disconnect(obs), ...);
+                (reg.template on_construct<NoneOf>().disconnect(obs), ...);
+            }
+        };
+
+        template<typename... Matcher>
+        static void disconnect(basic_registry<Entity>& reg, basic_observer& obs) {
+            (matcher_handler<Matcher>::disconnect(obs, reg), ...);
+        }
+
+        template<typename... Matcher, std::size_t... Index>
+        void connect(basic_registry<Entity>& reg, std::index_sequence<Index...>) {
+            static_assert(sizeof...(Matcher) < std::numeric_limits<payload_type>::digits, "Too many matchers");
+            (matcher_handler<Matcher>::template connect<Index>(*this, reg), ...);
+            release.template connect<&basic_observer::disconnect<Matcher...>>(reg);
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_sparse_set<Entity>::iterator;
+
+        /*! @brief Default constructor. */
+        basic_observer()
+            : release{},
+            storage{}
+        {}
+
+        /*! @brief Default copy constructor, deleted on purpose. */
+        basic_observer(const basic_observer&) = delete;
+        /*! @brief Default move constructor, deleted on purpose. */
+        basic_observer(basic_observer&&) = delete;
+
+        /**
+         * @brief Creates an observer and connects it to a given registry.
+         * @tparam Matcher Types of matchers to use to initialize the observer.
+         * @param reg A valid reference to a registry.
+         */
+        template<typename... Matcher>
+        basic_observer(basic_registry<entity_type>& reg, basic_collector<Matcher...>)
+            : basic_observer{}
+        {
+            connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
+        }
+
+        /*! @brief Default destructor. */
+        ~basic_observer() = default;
+
+        /**
+         * @brief Default copy assignment operator, deleted on purpose.
+         * @return This observer.
+         */
+        basic_observer& operator=(const basic_observer&) = delete;
+
+        /**
+         * @brief Default move assignment operator, deleted on purpose.
+         * @return This observer.
+         */
+        basic_observer& operator=(basic_observer&&) = delete;
+
+        /**
+         * @brief Connects an observer to a given registry.
+         * @tparam Matcher Types of matchers to use to initialize the observer.
+         * @param reg A valid reference to a registry.
+         */
+        template<typename... Matcher>
+        void connect(basic_registry<entity_type>& reg, basic_collector<Matcher...>) {
+            disconnect();
+            connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
+            storage.clear();
+        }
+
+        /*! @brief Disconnects an observer from the registry it keeps track of. */
+        void disconnect() {
+            if (release) {
+                release(*this);
+                release.reset();
+            }
+        }
+
+        /**
+         * @brief Returns the number of elements in an observer.
+         * @return Number of elements.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return storage.size();
+        }
+
+        /**
+         * @brief Checks whether an observer is empty.
+         * @return True if the observer is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return storage.empty();
+        }
+
+        /**
+         * @brief Direct access to the list of entities of the observer.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @note
+         * Entities are in the reverse order as returned by the `begin`/`end`
+         * iterators.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] const entity_type* data() const ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the observer.
+         *
+         * The returned iterator points to the first entity of the observer. If the
+         * container is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the observer.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return storage.basic_sparse_set<entity_type>::begin();
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the observer.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the observer. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * observer.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return storage.basic_sparse_set<entity_type>::end();
+        }
+
+        /*! @brief Clears the underlying container. */
+        void clear() ENTT_NOEXCEPT {
+            storage.clear();
+        }
+
+        /**
+         * @brief Iterates entities and applies the given function object to them.
+         *
+         * The function object is invoked for each entity.<br/>
+         * The signature of the function must be equivalent to the following form:
+         *
+         * @code{.cpp}
+         * void(const entity_type);
+         * @endcode
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (const auto entity : *this) {
+                func(entity);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and applies the given function object to them,
+         * then clears the observer.
+         *
+         * @sa each
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) {
+            std::as_const(*this).each(std::move(func));
+            clear();
+        }
+
+    private:
+        delegate<void(basic_observer&)> release;
+        basic_storage<entity_type, payload_type> storage;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/organizer.hpp"
+#ifndef ENTT_ENTITY_ORGANIZER_HPP
+#define ENTT_ENTITY_ORGANIZER_HPP
+
+
+#include <cstddef>
+#include <algorithm>
+#include <type_traits>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "fwd.hpp"
+
+// #include "helper.hpp"
+#ifndef ENTT_ENTITY_HELPER_HPP
+#define ENTT_ENTITY_HELPER_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../signal/delegate.hpp"
+
+// #include "registry.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Converts a registry to a view.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    struct as_view {
+        /*! @brief Underlying entity identifier. */
+        using entity_type = std::remove_const_t<Entity>;
+        /*! @brief Type of registry to convert. */
+        using registry_type = constness_as_t<basic_registry<entity_type>, Entity>;
+
+        /**
+         * @brief Constructs a converter for a given registry.
+         * @param source A valid reference to a registry.
+         */
+        as_view(registry_type& source) ENTT_NOEXCEPT: reg{ source } {}
+
+        /**
+         * @brief Conversion function from a registry to a view.
+         * @tparam Exclude Types of components used to filter the view.
+         * @tparam Component Type of components used to construct the view.
+         * @return A newly created view.
+         */
+        template<typename Exclude, typename... Component>
+        operator basic_view<entity_type, Exclude, Component...>() const {
+            return reg.template view<Component...>(Exclude{});
+        }
+
+    private:
+        registry_type& reg;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_view(basic_registry<Entity>&)->as_view<Entity>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_view(const basic_registry<Entity>&)->as_view<const Entity>;
+
+
+    /**
+     * @brief Converts a registry to a group.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    struct as_group {
+        /*! @brief Underlying entity identifier. */
+        using entity_type = std::remove_const_t<Entity>;
+        /*! @brief Type of registry to convert. */
+        using registry_type = constness_as_t<basic_registry<entity_type>, Entity>;
+
+        /**
+         * @brief Constructs a converter for a given registry.
+         * @param source A valid reference to a registry.
+         */
+        as_group(registry_type& source) ENTT_NOEXCEPT: reg{ source } {}
+
+        /**
+         * @brief Conversion function from a registry to a group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Owned Types of components owned by the group.
+         * @return A newly created group.
+         */
+        template<typename Exclude, typename Get, typename... Owned>
+        operator basic_group<entity_type, Exclude, Get, Owned...>() const {
+            if constexpr (std::is_const_v<registry_type>) {
+                return reg.template group_if_exists<Owned...>(Get{}, Exclude{});
+            }
+            else {
+                return reg.template group<Owned...>(Get{}, Exclude{});
+            }
+        }
+
+    private:
+        registry_type& reg;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_group(basic_registry<Entity>&)->as_group<Entity>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    as_group(const basic_registry<Entity>&)->as_group<const Entity>;
+
+
+
+    /**
+     * @brief Helper to create a listener that directly invokes a member function.
+     * @tparam Member Member function to invoke on a component of the given type.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @param reg A registry that contains the given entity and its components.
+     * @param entt Entity from which to get the component.
+     */
+    template<auto Member, typename Entity = entity>
+    void invoke(basic_registry<Entity>& reg, const Entity entt) {
+        static_assert(std::is_member_function_pointer_v<decltype(Member)>, "Invalid pointer to non-static member function");
+        delegate<void(basic_registry<Entity>&, const Entity)> func;
+        func.template connect<Member>(reg.template get<member_class_t<decltype(Member)>>(entt));
+        func(reg, entt);
+    }
+
+
+    /**
+     * @brief Returns the entity associated with a given component.
+     *
+     * @warning
+     * Currently, this function only works correctly with the default pool as it
+     * makes assumptions about how the components are laid out.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Component Type of component.
+     * @param reg A registry that contains the given entity and its components.
+     * @param instance A valid component instance.
+     * @return The entity associated with the given component.
+     */
+    template<typename Entity, typename Component>
+    Entity to_entity(const basic_registry<Entity>& reg, const Component& instance) {
+        const auto view = reg.template view<const Component>();
+        const auto* addr = std::addressof(instance);
+
+        for (auto it = view.rbegin(), last = view.rend(); it < last; it += ENTT_PACKED_PAGE) {
+            if (const auto dist = (addr - std::addressof(view.template get<const Component>(*it))); dist >= 0 && dist < ENTT_PACKED_PAGE) {
+                return *(it + dist);
+            }
+        }
+
+        return entt::null;
+    }
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct is_view : std::false_type {};
+
+        template<typename Entity, typename... Exclude, typename... Component>
+        struct is_view<basic_view<Entity, exclude_t<Exclude...>, Component...>> : std::true_type {};
+
+        template<typename Type>
+        inline constexpr bool is_view_v = is_view<Type>::value;
+
+
+        template<typename Type, typename Override>
+        struct unpack_type {
+            using ro = std::conditional_t<
+                type_list_contains_v<Override, std::add_const_t<Type>> || (std::is_const_v<Type> && !type_list_contains_v<Override, std::remove_const_t<Type>>),
+                type_list<std::remove_const_t<Type>>,
+                type_list<>
+            >;
+
+            using rw = std::conditional_t<
+                type_list_contains_v<Override, std::remove_const_t<Type>> || (!std::is_const_v<Type> && !type_list_contains_v<Override, std::add_const_t<Type>>),
+                type_list<Type>,
+                type_list<>
+            >;
+        };
+
+        template<typename Entity, typename... Override>
+        struct unpack_type<basic_registry<Entity>, type_list<Override...>> {
+            using ro = type_list<>;
+            using rw = type_list<>;
+        };
+
+        template<typename Entity, typename... Override>
+        struct unpack_type<const basic_registry<Entity>, type_list<Override...>>
+            : unpack_type<basic_registry<Entity>, type_list<Override...>>
+        {};
+
+        template<typename Entity, typename... Exclude, typename... Component, typename... Override>
+        struct unpack_type<basic_view<Entity, exclude_t<Exclude...>, Component...>, type_list<Override...>> {
+            using ro = type_list_cat_t<type_list<Exclude...>, typename unpack_type<Component, type_list<Override...>>::ro...>;
+            using rw = type_list_cat_t<typename unpack_type<Component, type_list<Override...>>::rw...>;
+        };
+
+        template<typename Entity, typename... Exclude, typename... Component, typename... Override>
+        struct unpack_type<const basic_view<Entity, exclude_t<Exclude...>, Component...>, type_list<Override...>>
+            : unpack_type<basic_view<Entity, exclude_t<Exclude...>, Component...>, type_list<Override...>>
+        {};
+
+
+        template<typename, typename>
+        struct resource;
+
+        template<typename... Args, typename... Req>
+        struct resource<type_list<Args...>, type_list<Req...>> {
+            using args = type_list<std::remove_const_t<Args>...>;
+            using ro = type_list_cat_t<typename unpack_type<Args, type_list<Req...>>::ro..., typename unpack_type<Req, type_list<>>::ro...>;
+            using rw = type_list_cat_t<typename unpack_type<Args, type_list<Req...>>::rw..., typename unpack_type<Req, type_list<>>::rw...>;
+        };
+
+
+        template<typename... Req, typename Ret, typename... Args>
+        resource<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> free_function_to_resource(Ret(*)(Args...));
+
+        template<typename... Req, typename Ret, typename Type, typename... Args>
+        resource<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> constrained_function_to_resource(Ret(*)(Type&, Args...));
+
+        template<typename... Req, typename Ret, typename Class, typename... Args>
+        resource<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> constrained_function_to_resource(Ret(Class::*)(Args...));
+
+        template<typename... Req, typename Ret, typename Class, typename... Args>
+        resource<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> constrained_function_to_resource(Ret(Class::*)(Args...) const);
+
+        template<typename... Req>
+        resource<type_list<>, type_list<Req...>> to_resource();
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Utility class for creating a static task graph.
+      *
+      * This class offers minimal support (but sufficient in many cases) for creating
+      * an execution graph from functions and their requirements on resources.<br/>
+      * Note that the resulting tasks aren't executed in any case. This isn't the
+      * goal of the tool. Instead, they are returned to the user in the form of a
+      * graph that allows for safe execution.
+      *
+      * @tparam Entity A valid entity type (see entt_traits for more details).
+      */
+    template<typename Entity>
+    class basic_organizer final {
+        using callback_type = void(const void*, entt::basic_registry<Entity>&);
+        using prepare_type = void(entt::basic_registry<Entity>&);
+        using dependency_type = std::size_t(const bool, type_info*, const std::size_t);
+
+        struct vertex_data final {
+            std::size_t ro_count{};
+            std::size_t rw_count{};
+            const char* name{};
+            const void* payload{};
+            callback_type* callback{};
+            dependency_type* dependency;
+            prepare_type* prepare{};
+            type_info info{};
+        };
+
+        template<typename Type>
+        [[nodiscard]] static decltype(auto) extract(basic_registry<Entity>& reg) {
+            if constexpr (std::is_same_v<Type, basic_registry<Entity>>) {
+                return reg;
+            }
+            else if constexpr (internal::is_view_v<Type>) {
+                return as_view{ reg };
+            }
+            else {
+                return reg.template ctx_or_set<std::remove_reference_t<Type>>();
+            }
+        }
+
+        template<typename... Args>
+        [[nodiscard]] static auto to_args(basic_registry<Entity>& reg, type_list<Args...>) {
+            return std::tuple<decltype(extract<Args>(reg))...>(extract<Args>(reg)...);
+        }
+
+        template<typename... Type>
+        static std::size_t fill_dependencies(type_list<Type...>, [[maybe_unused]] type_info* buffer, [[maybe_unused]] const std::size_t count) {
+            if constexpr (sizeof...(Type) == 0u) {
+                return {};
+            }
+            else {
+                type_info info[sizeof...(Type)]{ type_id<Type>()... };
+                const auto length = (std::min)(count, sizeof...(Type));
+                std::copy_n(info, length, buffer);
+                return length;
+            }
+        }
+
+        template<typename... RO, typename... RW>
+        void track_dependencies(std::size_t index, const bool requires_registry, type_list<RO...>, type_list<RW...>) {
+            dependencies[type_hash<basic_registry<Entity>>::value()].emplace_back(index, requires_registry || (sizeof...(RO) + sizeof...(RW) == 0u));
+            (dependencies[type_hash<RO>::value()].emplace_back(index, false), ...);
+            (dependencies[type_hash<RW>::value()].emplace_back(index, true), ...);
+        }
+
+        [[nodiscard]] std::vector<bool> adjacency_matrix() {
+            const auto length = vertices.size();
+            std::vector<bool> edges(length * length, false);
+
+            // creates the ajacency matrix
+            for (const auto& deps : dependencies) {
+                const auto last = deps.second.cend();
+                auto it = deps.second.cbegin();
+
+                while (it != last) {
+                    if (it->second) {
+                        // rw item
+                        if (auto curr = it++; it != last) {
+                            if (it->second) {
+                                edges[curr->first * length + it->first] = true;
+                            }
+                            else {
+                                if (const auto next = std::find_if(it, last, [](const auto& elem) { return elem.second; }); next != last) {
+                                    for (; it != next; ++it) {
+                                        edges[curr->first * length + it->first] = true;
+                                        edges[it->first * length + next->first] = true;
+                                    }
+                                }
+                                else {
+                                    for (; it != next; ++it) {
+                                        edges[curr->first * length + it->first] = true;
+                                    }
+                                }
+                            }
+                        }
+                    }
+                    else {
+                        // ro item, possibly only on first iteration
+                        if (const auto next = std::find_if(it, last, [](const auto& elem) { return elem.second; }); next != last) {
+                            for (; it != next; ++it) {
+                                edges[it->first * length + next->first] = true;
+                            }
+                        }
+                        else {
+                            it = last;
+                        }
+                    }
+                }
+            }
+
+            // computes the transitive closure
+            for (std::size_t vk{}; vk < length; ++vk) {
+                for (std::size_t vi{}; vi < length; ++vi) {
+                    for (std::size_t vj{}; vj < length; ++vj) {
+                        edges[vi * length + vj] = edges[vi * length + vj] || (edges[vi * length + vk] && edges[vk * length + vj]);
+                    }
+                }
+            }
+
+            // applies the transitive reduction
+            for (std::size_t vert{}; vert < length; ++vert) {
+                edges[vert * length + vert] = false;
+            }
+
+            for (std::size_t vj{}; vj < length; ++vj) {
+                for (std::size_t vi{}; vi < length; ++vi) {
+                    if (edges[vi * length + vj]) {
+                        for (std::size_t vk{}; vk < length; ++vk) {
+                            if (edges[vj * length + vk]) {
+                                edges[vi * length + vk] = false;
+                            }
+                        }
+                    }
+                }
+            }
+
+            return edges;
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Raw task function type. */
+        using function_type = callback_type;
+
+        /*! @brief Vertex type of a task graph defined as an adjacency list. */
+        struct vertex {
+            /**
+             * @brief Constructs a vertex of the task graph.
+             * @param vtype True if the vertex is a top-level one, false otherwise.
+             * @param data The data associated with the vertex.
+             * @param edges The indices of the children in the adjacency list.
+             */
+            vertex(const bool vtype, vertex_data data, std::vector<std::size_t> edges)
+                : is_top_level{ vtype },
+                node{ std::move(data) },
+                reachable{ std::move(edges) }
+            {}
+
+            /**
+             * @brief Fills a buffer with the type info objects for the writable
+             * resources of a vertex.
+             * @param buffer A buffer pre-allocated by the user.
+             * @param length The length of the user-supplied buffer.
+             * @return The number of type info objects written to the buffer.
+             */
+            size_type ro_dependency(type_info* buffer, const std::size_t length) const ENTT_NOEXCEPT {
+                return node.dependency(false, buffer, length);
+            }
+
+            /**
+             * @brief Fills a buffer with the type info objects for the read-only
+             * resources of a vertex.
+             * @param buffer A buffer pre-allocated by the user.
+             * @param length The length of the user-supplied buffer.
+             * @return The number of type info objects written to the buffer.
+             */
+            size_type rw_dependency(type_info* buffer, const std::size_t length) const ENTT_NOEXCEPT {
+                return node.dependency(true, buffer, length);
+            }
+
+            /**
+             * @brief Returns the number of read-only resources of a vertex.
+             * @return The number of read-only resources of the vertex.
+             */
+            size_type ro_count() const ENTT_NOEXCEPT {
+                return node.ro_count;
+            }
+
+            /**
+             * @brief Returns the number of writable resources of a vertex.
+             * @return The number of writable resources of the vertex.
+             */
+            size_type rw_count() const ENTT_NOEXCEPT {
+                return node.rw_count;
+            }
+
+            /**
+             * @brief Checks if a vertex is also a top-level one.
+             * @return True if the vertex is a top-level one, false otherwise.
+             */
+            bool top_level() const ENTT_NOEXCEPT {
+                return is_top_level;
+            }
+
+            /**
+             * @brief Returns a type info object associated with a vertex.
+             * @return A properly initialized type info object.
+             */
+            type_info info() const ENTT_NOEXCEPT {
+                return node.info;
+            }
+
+            /**
+             * @brief Returns a user defined name associated with a vertex, if any.
+             * @return The user defined name associated with the vertex, if any.
+             */
+            const char* name() const ENTT_NOEXCEPT {
+                return node.name;
+            }
+
+            /**
+             * @brief Returns the function associated with a vertex.
+             * @return The function associated with the vertex.
+             */
+            function_type* callback() const ENTT_NOEXCEPT {
+                return node.callback;
+            }
+
+            /**
+             * @brief Returns the payload associated with a vertex, if any.
+             * @return The payload associated with the vertex, if any.
+             */
+            const void* data() const ENTT_NOEXCEPT {
+                return node.payload;
+            }
+
+            /**
+             * @brief Returns the list of nodes reachable from a given vertex.
+             * @return The list of nodes reachable from the vertex.
+             */
+            const std::vector<std::size_t>& children() const ENTT_NOEXCEPT {
+                return reachable;
+            }
+
+            /**
+             * @brief Prepares a registry and assures that all required resources
+             * are properly instantiated before using them.
+             * @param reg A valid registry.
+             */
+            void prepare(basic_registry<entity_type>& reg) const {
+                node.prepare ? node.prepare(reg) : void();
+            }
+
+        private:
+            bool is_top_level;
+            vertex_data node;
+            std::vector<std::size_t> reachable;
+        };
+
+        /**
+         * @brief Adds a free function to the task list.
+         * @tparam Candidate Function to add to the task list.
+         * @tparam Req Additional requirements and/or override resource access mode.
+         * @param name Optional name to associate with the task.
+         */
+        template<auto Candidate, typename... Req>
+        void emplace(const char* name = nullptr) {
+            using resource_type = decltype(internal::free_function_to_resource<Req...>(Candidate));
+            constexpr auto requires_registry = type_list_contains_v<typename resource_type::args, basic_registry<entity_type>>;
+
+            callback_type* callback = +[](const void*, basic_registry<entity_type>& reg) {
+                std::apply(Candidate, to_args(reg, typename resource_type::args{}));
+            };
+
+            track_dependencies(vertices.size(), requires_registry, typename resource_type::ro{}, typename resource_type::rw{});
+
+            vertices.push_back({
+                resource_type::ro::size,
+                resource_type::rw::size,
+                name,
+                nullptr,
+                callback,
+                +[](const bool rw, type_info* buffer, const std::size_t length) { return rw ? fill_dependencies(typename resource_type::rw{}, buffer, length) : fill_dependencies(typename resource_type::ro{}, buffer, length); },
+                +[](basic_registry<entity_type>& reg) { void(to_args(reg, typename resource_type::args{})); },
+                type_id<std::integral_constant<decltype(Candidate), Candidate>>()
+                });
+        }
+
+        /**
+         * @brief Adds a free function with payload or a member function with an
+         * instance to the task list.
+         * @tparam Candidate Function or member to add to the task list.
+         * @tparam Req Additional requirements and/or override resource access mode.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @param name Optional name to associate with the task.
+         */
+        template<auto Candidate, typename... Req, typename Type>
+        void emplace(Type& value_or_instance, const char* name = nullptr) {
+            using resource_type = decltype(internal::constrained_function_to_resource<Req...>(Candidate));
+            constexpr auto requires_registry = type_list_contains_v<typename resource_type::args, basic_registry<entity_type>>;
+
+            callback_type* callback = +[](const void* payload, basic_registry<entity_type>& reg) {
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                std::apply(Candidate, std::tuple_cat(std::forward_as_tuple(*curr), to_args(reg, typename resource_type::args{})));
+            };
+
+            track_dependencies(vertices.size(), requires_registry, typename resource_type::ro{}, typename resource_type::rw{});
+
+            vertices.push_back({
+                resource_type::ro::size,
+                resource_type::rw::size,
+                name,
+                &value_or_instance,
+                callback,
+                +[](const bool rw, type_info* buffer, const std::size_t length) {
+                    return rw ? fill_dependencies(typename resource_type::rw{}, buffer, length) : fill_dependencies(typename resource_type::ro{}, buffer, length);
+                },
+                +[](basic_registry<entity_type>& reg) {
+                    void(to_args(reg, typename resource_type::args{}));
+                },
+                type_id<std::integral_constant<decltype(Candidate), Candidate>>()
+                });
+        }
+
+        /**
+         * @brief Adds an user defined function with optional payload to the task
+         * list.
+         * @tparam Req Additional requirements and/or override resource access mode.
+         * @param func Function to add to the task list.
+         * @param payload User defined arbitrary data.
+         * @param name Optional name to associate with the task.
+         */
+        template<typename... Req>
+        void emplace(function_type* func, const void* payload = nullptr, const char* name = nullptr) {
+            using resource_type = internal::resource<type_list<>, type_list<Req...>>;
+            track_dependencies(vertices.size(), true, typename resource_type::ro{}, typename resource_type::rw{});
+
+            vertices.push_back({
+                resource_type::ro::size,
+                resource_type::rw::size,
+                name,
+                payload,
+                func,
+                +[](const bool rw, type_info* buffer, const std::size_t length) {
+                    return rw ? fill_dependencies(typename resource_type::rw{}, buffer, length) : fill_dependencies(typename resource_type::ro{}, buffer, length);
+                },
+                nullptr,
+                type_info{}
+                });
+        }
+
+        /**
+         * @brief Generates a task graph for the current content.
+         * @return The adjacency list of the task graph.
+         */
+        std::vector<vertex> graph() {
+            const auto edges = adjacency_matrix();
+
+            // creates the adjacency list
+            std::vector<vertex> adjacency_list{};
+            adjacency_list.reserve(vertices.size());
+
+            for (std::size_t col{}, length = vertices.size(); col < length; ++col) {
+                std::vector<std::size_t> reachable{};
+                const auto row = col * length;
+                bool is_top_level = true;
+
+                for (std::size_t next{}; next < length; ++next) {
+                    if (edges[row + next]) {
+                        reachable.push_back(next);
+                    }
+                }
+
+                for (std::size_t next{}; next < length && is_top_level; ++next) {
+                    is_top_level = !edges[next * length + col];
+                }
+
+                adjacency_list.emplace_back(is_top_level, vertices[col], std::move(reachable));
+            }
+
+            return adjacency_list;
+        }
+
+        /*! @brief Erases all elements from a container. */
+        void clear() {
+            dependencies.clear();
+            vertices.clear();
+        }
+
+    private:
+        std::unordered_map<entt::id_type, std::vector<std::pair<std::size_t, bool>>> dependencies;
+        std::vector<vertex_data> vertices;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/poly_storage.hpp"
+#ifndef ENTT_ENTITY_POLY_STORAGE_HPP
+#define ENTT_ENTITY_POLY_STORAGE_HPP
+
+
+#include <cstddef>
+#include <tuple>
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../poly/poly.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Basic poly storage implementation.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    struct Storage : type_list<type_info() const ENTT_NOEXCEPT> {
+        /**
+         * @brief Concept definition.
+         * @tparam Base Opaque base class from which to inherit.
+         */
+        template<typename Base>
+        struct type : Base {
+            /**
+             * @brief Returns a type info for the contained objects.
+             * @return The type info for the contained objects.
+             */
+            type_info value_type() const ENTT_NOEXCEPT {
+                return poly_call<0>(*this);
+            }
+        };
+
+        /**
+         * @brief Concept implementation.
+         * @tparam Type Type for which to generate an implementation.
+         */
+        template<typename Type>
+        using impl = value_list<&type_id<typename Type::value_type>>;
+    };
+
+
+    /**
+     * @brief Defines the poly storage type associate with a given entity type.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity, typename = void>
+    struct poly_storage_traits {
+        /*! @brief Poly storage type for the given entity type. */
+        using storage_type = poly<Storage<Entity>>;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/registry.hpp"
+#ifndef ENTT_ENTITY_REGISTRY_HPP
+#define ENTT_ENTITY_REGISTRY_HPP
+
+
+#include <algorithm>
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+#include <vector>
+// #include "../config/config.h"
+
+// #include "../core/algorithm.hpp"
+
+// #include "../core/any.hpp"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "component.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "group.hpp"
+
+// #include "poly_storage.hpp"
+
+// #include "runtime_view.hpp"
+
+// #include "sparse_set.hpp"
+
+// #include "storage.hpp"
+
+// #include "utility.hpp"
+
+// #include "view.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Fast and reliable entity-component system.
+     *
+     * The registry is the core class of the entity-component framework.<br/>
+     * It stores entities and arranges pools of components on a per request basis.
+     * By means of a registry, users can manage entities and components, then create
+     * views or groups to iterate them.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_registry {
+        using traits_type = entt_traits<Entity>;
+        using poly_storage_type = typename poly_storage_traits<Entity>::storage_type;
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Component>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        struct pool_data {
+            poly_storage_type poly;
+            std::unique_ptr<basic_common_type> pool{};
+        };
+
+        template<typename...>
+        struct group_handler;
+
+        template<typename... Exclude, typename... Get, typename... Owned>
+        struct group_handler<exclude_t<Exclude...>, get_t<Get...>, Owned...> {
+            static_assert(!std::disjunction_v<typename component_traits<Owned>::in_place_delete...>, "Groups do not support in-place delete");
+            static_assert(std::conjunction_v<std::is_same<Owned, std::remove_const_t<Owned>>..., std::is_same<Get, std::remove_const_t<Get>>..., std::is_same<Exclude, std::remove_const_t<Exclude>>...>, "One or more component types are invalid");
+            std::conditional_t<sizeof...(Owned) == 0, basic_common_type, std::size_t> current{};
+
+            template<typename Component>
+            void maybe_valid_if(basic_registry& owner, const Entity entt) {
+                [[maybe_unused]] const auto cpools = std::make_tuple(owner.assure<Owned>()...);
+
+                const auto is_valid = ((std::is_same_v<Component, Owned> || std::get<storage_type<Owned>*>(cpools)->contains(entt)) && ...)
+                    && ((std::is_same_v<Component, Get> || owner.assure<Get>()->contains(entt)) && ...)
+                    && ((std::is_same_v<Component, Exclude> || !owner.assure<Exclude>()->contains(entt)) && ...);
+
+                if constexpr (sizeof...(Owned) == 0) {
+                    if (is_valid && !current.contains(entt)) {
+                        current.emplace(entt);
+                    }
+                }
+                else {
+                    if (is_valid && !(std::get<0>(cpools)->index(entt) < current)) {
+                        const auto pos = current++;
+                        (std::get<storage_type<Owned>*>(cpools)->swap(std::get<storage_type<Owned>*>(cpools)->data()[pos], entt), ...);
+                    }
+                }
+            }
+
+            void discard_if([[maybe_unused]] basic_registry& owner, const Entity entt) {
+                if constexpr (sizeof...(Owned) == 0) {
+                    current.remove(entt);
+                }
+                else {
+                    if (const auto cpools = std::make_tuple(owner.assure<Owned>()...); std::get<0>(cpools)->contains(entt) && (std::get<0>(cpools)->index(entt) < current)) {
+                        const auto pos = --current;
+                        (std::get<storage_type<Owned>*>(cpools)->swap(std::get<storage_type<Owned>*>(cpools)->data()[pos], entt), ...);
+                    }
+                }
+            }
+        };
+
+        struct group_data {
+            std::size_t size;
+            std::unique_ptr<void, void(*)(void*)> group;
+            bool (*owned)(const id_type) ENTT_NOEXCEPT;
+            bool (*get)(const id_type) ENTT_NOEXCEPT;
+            bool (*exclude)(const id_type) ENTT_NOEXCEPT;
+        };
+
+        template<typename Component>
+        [[nodiscard]] storage_type<Component>* assure() const {
+            static_assert(std::is_same_v<Component, std::decay_t<Component>>, "Non-decayed types not allowed");
+            const auto index = type_seq<Component>::value();
+
+            if (!(index < pools.size())) {
+                pools.resize(size_type(index) + 1u);
+            }
+
+            if (auto&& pdata = pools[index]; !pdata.pool) {
+                pdata.pool.reset(new storage_type<Component>());
+                pdata.poly.template emplace<storage_type<Component>&>(*static_cast<storage_type<Component> *>(pdata.pool.get()));
+            }
+
+            return static_cast<storage_type<Component> *>(pools[index].pool.get());
+        }
+
+        template<typename Component>
+        [[nodiscard]] const storage_type<Component>* pool_if_exists() const ENTT_NOEXCEPT {
+            static_assert(std::is_same_v<Component, std::decay_t<Component>>, "Non-decayed types not allowed");
+            const auto index = type_seq<Component>::value();
+            return (!(index < pools.size()) || !pools[index].pool) ? nullptr : static_cast<const storage_type<Component> *>(pools[index].pool.get());
+        }
+
+        auto generate_identifier(const std::size_t pos) ENTT_NOEXCEPT {
+            ENTT_ASSERT(pos < traits_type::to_integral(null), "No entities available");
+            return traits_type::construct(static_cast<typename traits_type::entity_type>(pos), {});
+        }
+
+        auto recycle_identifier() ENTT_NOEXCEPT {
+            ENTT_ASSERT(free_list != null, "No entities available");
+            const auto curr = traits_type::to_entity(free_list);
+            free_list = (tombstone | entities[curr]);
+            return (entities[curr] = traits_type::construct(curr, traits_type::to_version(entities[curr])));
+        }
+
+        auto release_entity(const Entity entity, const typename traits_type::version_type version) {
+            const typename traits_type::version_type vers = version + (version == traits_type::to_version(tombstone));
+            entities[traits_type::to_entity(entity)] = traits_type::construct(traits_type::to_entity(free_list), vers);
+            free_list = (tombstone | entity);
+            return vers;
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Underlying version type. */
+        using version_type = typename traits_type::version_type;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Poly storage type. */
+        using poly_storage = typename poly_storage_traits<Entity>::storage_type;
+
+        /**
+         * @brief Returns the entity identifier without the version.
+         * @param entity An entity identifier, either valid or not.
+         * @return The entity identifier without the version.
+         */
+        [[nodiscard]] static entity_type entity(const entity_type entity) ENTT_NOEXCEPT {
+            return traits_type::construct(traits_type::to_entity(entity), {});
+        }
+
+        /**
+         * @brief Returns the version stored along with an entity identifier.
+         * @param entity An entity identifier, either valid or not.
+         * @return The version stored along with the given entity identifier.
+         */
+        [[nodiscard]] static version_type version(const entity_type entity) ENTT_NOEXCEPT {
+            return traits_type::to_version(entity);
+        }
+
+        /*! @brief Default constructor. */
+        basic_registry() = default;
+
+        /*! @brief Default move constructor. */
+        basic_registry(basic_registry&&) = default;
+
+        /*! @brief Default move assignment operator. @return This registry. */
+        basic_registry& operator=(basic_registry&&) = default;
+
+        /**
+         * @brief Prepares a pool for the given type if required.
+         * @tparam Component Type of component for which to prepare a pool.
+         */
+        template<typename Component>
+        void prepare() {
+            // suppress the warning due to the [[nodiscard]] attribute
+            static_cast<void>(assure<Component>());
+        }
+
+        /**
+         * @brief Returns a poly storage for a given type.
+         * @param info The type for which to return a poly storage.
+         * @return A valid poly storage if a pool for the given type exists, an
+         * empty and thus invalid element otherwise.
+         */
+        poly_storage& storage(const type_info info) {
+            ENTT_ASSERT(info.seq() < pools.size() && pools[info.seq()].poly, "Storage not available");
+            return pools[info.seq()].poly;
+        }
+
+        /*! @copydoc storage */
+        const poly_storage& storage(const type_info info) const {
+            ENTT_ASSERT(info.seq() < pools.size() && pools[info.seq()].poly, "Storage not available");
+            return pools[info.seq()].poly;
+        }
+
+        /**
+         * @brief Returns the number of existing components of the given type.
+         * @tparam Component Type of component of which to return the size.
+         * @return Number of existing components of the given type.
+         */
+        template<typename Component>
+        [[nodiscard]] size_type size() const {
+            const auto* cpool = pool_if_exists<Component>();
+            return cpool ? cpool->size() : size_type{};
+        }
+
+        /**
+         * @brief Returns the number of entities created so far.
+         * @return Number of entities created so far.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return entities.size();
+        }
+
+        /**
+         * @brief Returns the number of entities still in use.
+         * @return Number of entities still in use.
+         */
+        [[nodiscard]] size_type alive() const {
+            auto sz = entities.size();
+
+            for (auto curr = free_list; curr != null; --sz) {
+                curr = entities[traits_type::to_entity(curr)];
+            }
+
+            return sz;
+        }
+
+        /**
+         * @brief Increases the capacity of the registry or of the pools for the
+         * given components.
+         *
+         * If no components are specified, the capacity of the registry is
+         * increased, that is the number of entities it contains. Otherwise the
+         * capacity of the pools for the given components is increased.<br/>
+         * In both cases, if the new capacity is greater than the current capacity,
+         * new storage is allocated, otherwise the method does nothing.
+         *
+         * @tparam Component Types of components for which to reserve storage.
+         * @param cap Desired capacity.
+         */
+        template<typename... Component>
+        void reserve(const size_type cap) {
+            if constexpr (sizeof...(Component) == 0) {
+                entities.reserve(cap);
+            }
+            else {
+                (assure<Component>()->reserve(cap), ...);
+            }
+        }
+
+        /**
+         * @brief Reserves enough space to store `count` pools.
+         * @param count Number of pools to reserve space for.
+         */
+        [[deprecated("No longer supported")]]
+        void reserve_pools(const size_t count) {
+            pools.reserve(count);
+        }
+
+        /**
+         * @brief Returns the capacity of the pool for the given component.
+         * @tparam Component Type of component in which one is interested.
+         * @return Capacity of the pool of the given component.
+         */
+        template<typename Component>
+        [[nodiscard]] size_type capacity() const {
+            const auto* cpool = pool_if_exists<Component>();
+            return cpool ? cpool->capacity() : size_type{};
+        }
+
+        /**
+         * @brief Returns the number of entities that a registry has currently
+         * allocated space for.
+         * @return Capacity of the registry.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return entities.capacity();
+        }
+
+        /**
+         * @brief Requests the removal of unused capacity for the given components.
+         * @tparam Component Types of components for which to reclaim unused
+         * capacity.
+         */
+        template<typename... Component>
+        void shrink_to_fit() {
+            (assure<Component>()->shrink_to_fit(), ...);
+        }
+
+        /**
+         * @brief Checks whether the registry or the pools of the given components
+         * are empty.
+         *
+         * A registry is considered empty when it doesn't contain entities that are
+         * still in use.
+         *
+         * @tparam Component Types of components in which one is interested.
+         * @return True if the registry or the pools of the given components are
+         * empty, false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool empty() const {
+            if constexpr (sizeof...(Component) == 0) {
+                return !alive();
+            }
+            else {
+                return [](const auto *... cpool) { return ((!cpool || cpool->empty()) && ...); }(pool_if_exists<Component>()...);
+            }
+        }
+
+        /**
+         * @brief Direct access to the list of entities of a registry.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @warning
+         * This list contains both valid and destroyed entities and isn't suitable
+         * for direct use.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] const entity_type* data() const ENTT_NOEXCEPT {
+            return entities.data();
+        }
+
+        /**
+         * @brief Returns the head of the list of released entities.
+         *
+         * This function is intended for use in conjunction with `assign`.<br/>
+         * The returned entity has an invalid identifier in all cases.
+         *
+         * @return The head of the list of released entities.
+         */
+        [[nodiscard]] entity_type released() const ENTT_NOEXCEPT {
+            return free_list;
+        }
+
+        /*! @copydoc released */
+        [[deprecated("Use ::released instead")]]
+        [[nodiscard]] entity_type destroyed() const ENTT_NOEXCEPT {
+            return released();
+        }
+
+        /**
+         * @brief Checks if an entity identifier refers to a valid entity.
+         * @param entity An entity identifier, either valid or not.
+         * @return True if the identifier is valid, false otherwise.
+         */
+        [[nodiscard]] bool valid(const entity_type entity) const {
+            const auto pos = size_type(traits_type::to_entity(entity));
+            return (pos < entities.size() && entities[pos] == entity);
+        }
+
+        /**
+         * @brief Returns the actual version for an entity identifier.
+         *
+         * @warning
+         * Attempting to use an entity that doesn't belong to the registry results
+         * in undefined behavior. An entity belongs to the registry even if it has
+         * been previously destroyed and/or recycled.
+         *
+         * @param entity A valid entity identifier.
+         * @return Actual version for the given entity identifier.
+         */
+        [[nodiscard]] version_type current(const entity_type entity) const {
+            const auto pos = size_type(traits_type::to_entity(entity));
+            ENTT_ASSERT(pos < entities.size(), "Entity does not exist");
+            return version(entities[pos]);
+        }
+
+        /**
+         * @brief Creates a new entity and returns it.
+         *
+         * There are two kinds of possible entity identifiers:
+         *
+         * * Newly created ones in case no entities have been previously destroyed.
+         * * Recycled ones with updated versions.
+         *
+         * @return A valid entity identifier.
+         */
+        [[nodiscard]] entity_type create() {
+            return (free_list == null) ? entities.emplace_back(generate_identifier(entities.size())) : recycle_identifier();
+        }
+
+        /**
+         * @brief Creates a new entity and returns it.
+         *
+         * @sa create
+         *
+         * If the requested entity isn't in use, the suggested identifier is created
+         * and returned. Otherwise, a new identifier is generated.
+         *
+         * @param hint Required entity identifier.
+         * @return A valid entity identifier.
+         */
+        [[nodiscard]] entity_type create(const entity_type hint) {
+            const auto length = entities.size();
+
+            if (hint == null || hint == tombstone) {
+                return create();
+            }
+            else if (const auto req = traits_type::to_entity(hint); !(req < length)) {
+                entities.resize(size_type(req) + 1u, null);
+
+                for (auto pos = length; pos < req; ++pos) {
+                    release_entity(generate_identifier(pos), {});
+                }
+
+                return (entities[req] = hint);
+            }
+            else if (const auto curr = traits_type::to_entity(entities[req]); req == curr) {
+                return create();
+            }
+            else {
+                auto* it = &free_list;
+                for (; traits_type::to_entity(*it) != req; it = &entities[traits_type::to_entity(*it)]);
+                *it = traits_type::construct(curr, traits_type::to_version(*it));
+                return (entities[req] = hint);
+            }
+        }
+
+        /**
+         * @brief Assigns each element in a range an entity.
+         *
+         * @sa create
+         *
+         * @tparam It Type of forward iterator.
+         * @param first An iterator to the first element of the range to generate.
+         * @param last An iterator past the last element of the range to generate.
+         */
+        template<typename It>
+        void create(It first, It last) {
+            for (; free_list != null && first != last; ++first) {
+                *first = recycle_identifier();
+            }
+
+            const auto length = entities.size();
+            entities.resize(length + std::distance(first, last), null);
+
+            for (auto pos = length; first != last; ++first, ++pos) {
+                *first = entities[pos] = generate_identifier(pos);
+            }
+        }
+
+        /**
+         * @brief Assigns entities to an empty registry.
+         *
+         * This function is intended for use in conjunction with `data`, `size` and
+         * `destroyed`.<br/>
+         * Don't try to inject ranges of randomly generated entities nor the _wrong_
+         * head for the list of destroyed entities. There is no guarantee that a
+         * registry will continue to work properly in this case.
+         *
+         * @warning
+         * There must be no entities still alive for this to work properly.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param destroyed The head of the list of destroyed entities.
+         */
+        template<typename It>
+        void assign(It first, It last, const entity_type destroyed) {
+            ENTT_ASSERT(!alive(), "Entities still alive");
+            entities.assign(first, last);
+            free_list = destroyed;
+        }
+
+        /**
+         * @brief Releases an entity identifier.
+         *
+         * The version is updated and the identifier can be recycled at any time.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @param entity A valid entity identifier.
+         * @return The version of the recycled entity.
+         */
+        version_type release(const entity_type entity) {
+            return release(entity, version(entity) + 1u);
+        }
+
+        /**
+         * @brief Releases an entity identifier.
+         *
+         * The suggested version or the valid version closest to the suggested one
+         * is used instead of the implicitly generated version.
+         *
+         * @sa release
+         *
+         * @param entity A valid entity identifier.
+         * @param version A desired version upon destruction.
+         * @return The version actually assigned to the entity.
+         */
+        version_type release(const entity_type entity, const version_type version) {
+            ENTT_ASSERT(orphan(entity), "Non-orphan entity");
+            return release_entity(entity, version);
+        }
+
+        /**
+         * @brief Releases all entity identifiers in a range.
+         *
+         * @sa release
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void release(It first, It last) {
+            for (; first != last; ++first) {
+                release(*first, version(*first) + 1u);
+            }
+        }
+
+        /**
+         * @brief Destroys an entity and releases its identifier.
+         *
+         * The version is updated and the identifier can be recycled at any time.
+         *
+         * @warning
+         * Adding or removing components to an entity that is being destroyed can
+         * result in undefined behavior.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @param entity A valid entity identifier.
+         * @return The version of the recycled entity.
+         */
+        version_type destroy(const entity_type entity) {
+            return destroy(entity, version(entity) + 1u);
+        }
+
+        /**
+         * @brief Destroys an entity and releases its identifier.
+         *
+         * The suggested version or the valid version closest to the suggested one
+         * is used instead of the implicitly generated version.
+         *
+         * @sa destroy
+         *
+         * @param entity A valid entity identifier.
+         * @param version A desired version upon destruction.
+         * @return The version actually assigned to the entity.
+         */
+        version_type destroy(const entity_type entity, const version_type version) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            for (auto&& pdata : pools) {
+                pdata.pool&& pdata.pool->remove(entity, this);
+            }
+
+            return release_entity(entity, version);
+        }
+
+        /**
+         * @brief Destroys all entities in a range and releases their identifiers.
+         *
+         * @sa destroy
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void destroy(It first, It last) {
+            if constexpr (is_iterator_type_v<typename basic_common_type::iterator, It>) {
+                for (; first != last; ++first) {
+                    destroy(*first, version(*first) + 1u);
+                }
+            }
+            else {
+                for (auto&& pdata : pools) {
+                    pdata.pool&& pdata.pool->remove(first, last, this);
+                }
+
+                release(first, last);
+            }
+        }
+
+        /**
+         * @brief Assigns the given component to an entity.
+         *
+         * A new instance of the given component is created and initialized with the
+         * arguments provided (the component must have a proper constructor or be of
+         * aggregate type). Then the component is assigned to the given entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to assign a component to an entity
+         * that already owns it results in undefined behavior.
+         *
+         * @tparam Component Type of component to create.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the newly created component.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) emplace(const entity_type entity, Args &&... args) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return assure<Component>()->emplace(*this, entity, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Assigns each entity in a range the given component.
+         *
+         * @sa emplace
+         *
+         * @tparam Component Type of component to create.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param value An instance of the component to assign.
+         */
+        template<typename Component, typename It>
+        void insert(It first, It last, const Component& value = {}) {
+            ENTT_ASSERT(std::all_of(first, last, [this](const auto entity) { return valid(entity); }), "Invalid entity");
+            assure<Component>()->insert(*this, first, last, value);
+        }
+
+        /**
+         * @brief Assigns each entity in a range the given components.
+         *
+         * @sa emplace
+         *
+         * @tparam Component Type of component to create.
+         * @tparam EIt Type of input iterator.
+         * @tparam CIt Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param from An iterator to the first element of the range of components.
+         */
+        template<typename Component, typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<std::decay_t<typename std::iterator_traits<CIt>::value_type>, Component>>>
+        void insert(EIt first, EIt last, CIt from) {
+            static_assert(std::is_constructible_v<Component, typename std::iterator_traits<CIt>::value_type>, "Invalid value type");
+            ENTT_ASSERT(std::all_of(first, last, [this](const auto entity) { return valid(entity); }), "Invalid entity");
+            assure<Component>()->insert(*this, first, last, from);
+        }
+
+        /**
+         * @brief Assigns or replaces the given component for an entity.
+         *
+         * Equivalent to the following snippet (pseudocode):
+         *
+         * @code{.cpp}
+         * auto &component = registry.all_of<Component>(entity) ? registry.replace<Component>(entity, args...) : registry.emplace<Component>(entity, args...);
+         * @endcode
+         *
+         * Prefer this function anyway because it has slightly better performance.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Type of component to assign or replace.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the newly created component.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) emplace_or_replace(const entity_type entity, Args &&... args) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            auto* cpool = assure<Component>();
+
+            return cpool->contains(entity)
+                ? cpool->patch(*this, entity, [&args...](auto &... curr) { ((curr = Component{ std::forward<Args>(args)... }), ...); })
+                : cpool->emplace(*this, entity, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Patches the given component for an entity.
+         *
+         * The signature of the functions should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(Component &);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned. However, this function can be used to trigger an update signal
+         * for them.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to patch a component of an entity
+         * that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Type of component to patch.
+         * @tparam Func Types of the function objects to invoke.
+         * @param entity A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the patched component.
+         */
+        template<typename Component, typename... Func>
+        decltype(auto) patch(const entity_type entity, Func &&... func) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return assure<Component>()->patch(*this, entity, std::forward<Func>(func)...);
+        }
+
+        /**
+         * @brief Replaces the given component for an entity.
+         *
+         * A new instance of the given component is created and initialized with the
+         * arguments provided (the component must have a proper constructor or be of
+         * aggregate type). Then the component is assigned to the given entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to replace a component of an
+         * entity that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Type of component to replace.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return A reference to the component being replaced.
+         */
+        template<typename Component, typename... Args>
+        decltype(auto) replace(const entity_type entity, Args &&... args) {
+            return assure<Component>()->patch(*this, entity, [&args...](auto &... curr) { ((curr = Component{ std::forward<Args>(args)... }), ...); });
+        }
+
+        /**
+         * @brief Removes the given components from an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Types of components to remove.
+         * @param entity A valid entity identifier.
+         * @return The number of components actually removed.
+         */
+        template<typename... Component>
+        size_type remove(const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            return (assure<Component>()->remove(entity, this) + ... + size_type{});
+        }
+
+        /**
+         * @brief Removes the given components from all the entities in a range.
+         *
+         * @sa remove
+         *
+         * @tparam Component Types of components to remove.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @return The number of components actually removed.
+         */
+        template<typename... Component, typename It>
+        size_type remove(It first, It last) {
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            const auto cpools = std::make_tuple(assure<Component>()...);
+            size_type count{};
+
+            for (; first != last; ++first) {
+                const auto entity = *first;
+                ENTT_ASSERT(valid(entity), "Invalid entity");
+                count += (std::get<storage_type<Component>*>(cpools)->remove(entity, this) + ...);
+            }
+
+            return count;
+        }
+
+        /**
+         * @brief Erases the given components from an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to erase a component from an
+         * entity that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Types of components to erase.
+         * @param entity A valid entity identifier.
+         */
+        template<typename... Component>
+        void erase(const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            (assure<Component>()->erase(entity, this), ...);
+        }
+
+        /**
+         * @brief Erases the given components from all the entities in a range.
+         *
+         * @sa erase
+         *
+         * @tparam Component Types of components to erase.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename... Component, typename It>
+        void erase(It first, It last) {
+            static_assert(sizeof...(Component) > 0, "Provide one or more component types");
+            const auto cpools = std::make_tuple(assure<Component>()...);
+
+            for (; first != last; ++first) {
+                const auto entity = *first;
+                ENTT_ASSERT(valid(entity), "Invalid entity");
+                (std::get<storage_type<Component>*>(cpools)->erase(entity, this), ...);
+            }
+        }
+
+        /**
+         * @brief Removes all tombstones from a registry or only the pools for the
+         * given components.
+         * @tparam Component Types of components for which to clear all tombstones.
+         */
+        template<typename... Component>
+        void compact() {
+            if constexpr (sizeof...(Component) == 0) {
+                for (auto&& pdata : pools) {
+                    pdata.pool && (pdata.pool->compact(), true);
+                }
+            }
+            else {
+                (assure<Component>()->compact(), ...);
+            }
+        }
+
+        /*! @copydoc remove */
+        template<typename... Component>
+        [[deprecated("Use ::remove instead")]]
+        size_type remove_if_exists(const entity_type entity) {
+            return remove<Component...>(entity);
+        }
+
+        /**
+         * @brief Removes all the components from an entity and makes it orphaned.
+         *
+         * @warning
+         * In case there are listeners that observe the destruction of components
+         * and assign other components to the entity in their bodies, the result of
+         * invoking this function may not be as expected. In the worst case, it
+         * could lead to undefined behavior.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @param entity A valid entity identifier.
+         */
+        [[deprecated("Use ::destroy(entity)/::create(entity) instead")]]
+        void remove_all(const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            for (auto&& pdata : pools) {
+                pdata.pool&& pdata.pool->remove(entity, this);
+            }
+        }
+
+        /**
+         * @brief Checks if an entity has all the given components.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Components for which to perform the check.
+         * @param entity A valid entity identifier.
+         * @return True if the entity has all the components, false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool all_of(const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return [entity](const auto *... cpool) { return ((cpool && cpool->contains(entity)) && ...); }(pool_if_exists<Component>()...);
+        }
+
+        /**
+         * @brief Checks if an entity has at least one of the given components.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Components for which to perform the check.
+         * @param entity A valid entity identifier.
+         * @return True if the entity has at least one of the given components,
+         * false otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool any_of(const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return [entity](const auto *... cpool) { return !((!cpool || !cpool->contains(entity)) && ...); }(pool_if_exists<Component>()...);
+        }
+
+        /**
+         * @brief Returns references to the given components for an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity or to get a component from an entity
+         * that doesn't own it results in undefined behavior.
+         *
+         * @tparam Component Types of components to get.
+         * @param entity A valid entity identifier.
+         * @return References to the components owned by the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                const auto* cpool = pool_if_exists<std::remove_const_t<Component>...>();
+                ENTT_ASSERT(cpool, "Storage not available");
+                return cpool->get(entity);
+            }
+            else {
+                return std::forward_as_tuple(get<Component>(entity)...);
+            }
+        }
+
+        /*! @copydoc get */
+        template<typename... Component>
+        [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                return (const_cast<Component&>(assure<std::remove_const_t<Component>>()->get(entity)), ...);
+            }
+            else {
+                return std::forward_as_tuple(get<Component>(entity)...);
+            }
+        }
+
+        /**
+         * @brief Returns a reference to the given component for an entity.
+         *
+         * In case the entity doesn't own the component, the parameters provided are
+         * used to construct it.<br/>
+         * Equivalent to the following snippet (pseudocode):
+         *
+         * @code{.cpp}
+         * auto &component = registry.all_of<Component>(entity) ? registry.get<Component>(entity) : registry.emplace<Component>(entity, args...);
+         * @endcode
+         *
+         * Prefer this function anyway because it has slightly better performance.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @tparam Component Type of component to get.
+         * @tparam Args Types of arguments to use to construct the component.
+         * @param entity A valid entity identifier.
+         * @param args Parameters to use to initialize the component.
+         * @return Reference to the component owned by the entity.
+         */
+        template<typename Component, typename... Args>
+        [[nodiscard]] decltype(auto) get_or_emplace(const entity_type entity, Args &&... args) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            auto* cpool = assure<Component>();
+            return cpool->contains(entity) ? cpool->get(entity) : cpool->emplace(*this, entity, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Returns pointers to the given components for an entity.
+         *
+         * @warning
+         * Attempting to use an invalid entity results in undefined behavior.
+         *
+         * @note
+         * The registry retains ownership of the pointed-to components.
+         *
+         * @tparam Component Types of components to get.
+         * @param entity A valid entity identifier.
+         * @return Pointers to the components owned by the entity.
+         */
+        template<typename... Component>
+        [[nodiscard]] auto try_get([[maybe_unused]] const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                const auto* cpool = pool_if_exists<std::remove_const_t<Component>...>();
+                return (cpool && cpool->contains(entity)) ? &cpool->get(entity) : nullptr;
+            }
+            else {
+                return std::make_tuple(try_get<Component>(entity)...);
+            }
+        }
+
+        /*! @copydoc try_get */
+        template<typename... Component>
+        [[nodiscard]] auto try_get([[maybe_unused]] const entity_type entity) {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+
+            if constexpr (sizeof...(Component) == 1) {
+                return (const_cast<Component*>(std::as_const(*this).template try_get<Component>(entity)), ...);
+            }
+            else {
+                return std::make_tuple(try_get<Component>(entity)...);
+            }
+        }
+
+        /**
+         * @brief Clears a whole registry or the pools for the given components.
+         * @tparam Component Types of components to remove from their entities.
+         */
+        template<typename... Component>
+        void clear() {
+            if constexpr (sizeof...(Component) == 0) {
+                for (auto&& pdata : pools) {
+                    pdata.pool && (pdata.pool->clear(this), true);
+                }
+
+                each([this](const auto entity) { release_entity(entity, version(entity) + 1u); });
+            }
+            else {
+                (assure<Component>()->clear(this), ...);
+            }
+        }
+
+        /**
+         * @brief Iterates all the entities that are still in use.
+         *
+         * The function object is invoked for each entity that is still in use.<br/>
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const Entity);
+         * @endcode
+         *
+         * This function is fairly slow and should not be used frequently. However,
+         * it's useful for iterating all the entities still in use, regardless of
+         * their components.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            if (free_list == null) {
+                for (auto pos = entities.size(); pos; --pos) {
+                    func(entities[pos - 1]);
+                }
+            }
+            else {
+                for (auto pos = entities.size(); pos; --pos) {
+                    if (const auto entity = entities[pos - 1]; traits_type::to_entity(entity) == (pos - 1)) {
+                        func(entity);
+                    }
+                }
+            }
+        }
+
+        /**
+         * @brief Checks if an entity has components assigned.
+         * @param entity A valid entity identifier.
+         * @return True if the entity has no components assigned, false otherwise.
+         */
+        [[nodiscard]] bool orphan(const entity_type entity) const {
+            ENTT_ASSERT(valid(entity), "Invalid entity");
+            return std::none_of(pools.cbegin(), pools.cend(), [entity](auto&& pdata) { return pdata.pool && pdata.pool->contains(entity); });
+        }
+
+        /**
+         * @brief Iterates orphans and applies them the given function object.
+         *
+         * The function object is invoked for each entity that is still in use and
+         * has no components assigned.<br/>
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const Entity);
+         * @endcode
+         *
+         * This function can be very slow and should not be used frequently.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void orphans(Func func) const {
+            each([this, &func](const auto entity) {
+                if (orphan(entity)) {
+                    func(entity);
+                }
+                });
+        }
+
+        /**
+         * @brief Returns a sink object for the given component.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever a new instance of the given component is created and assigned to
+         * an entity.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<Entity> &, Entity);
+         * @endcode
+         *
+         * Listeners are invoked **after** the component has been assigned to the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @tparam Component Type of component of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Component>
+        [[nodiscard]] auto on_construct() {
+            return assure<Component>()->on_construct();
+        }
+
+        /**
+         * @brief Returns a sink object for the given component.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance of the given component is explicitly updated.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<Entity> &, Entity);
+         * @endcode
+         *
+         * Listeners are invoked **after** the component has been updated.
+         *
+         * @sa sink
+         *
+         * @tparam Component Type of component of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Component>
+        [[nodiscard]] auto on_update() {
+            return assure<Component>()->on_update();
+        }
+
+        /**
+         * @brief Returns a sink object for the given component.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance of the given component is removed from an entity and
+         * thus destroyed.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<Entity> &, Entity);
+         * @endcode
+         *
+         * Listeners are invoked **before** the component has been removed from the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @tparam Component Type of component of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Component>
+        [[nodiscard]] auto on_destroy() {
+            return assure<Component>()->on_destroy();
+        }
+
+        /**
+         * @brief Returns a view for the given components.
+         *
+         * This kind of objects are created on the fly and share with the registry
+         * its internal data structures.<br/>
+         * Feel free to discard a view after the use. Creating and destroying a view
+         * is an incredibly cheap operation because they do not require any type of
+         * initialization.<br/>
+         * As a rule of thumb, storing a view should never be an option.
+         *
+         * Views do their best to iterate the smallest set of candidate entities.
+         * In particular:
+         *
+         * * Single component views are incredibly fast and iterate a packed array
+         *   of entities, all of which has the given component.
+         * * Multi component views look at the number of entities available for each
+         *   component and pick up a reference to the smallest set of candidates to
+         *   test for the given components.
+         *
+         * Views in no way affect the functionalities of the registry nor those of
+         * the underlying pools.
+         *
+         * @note
+         * Multi component views are pretty fast. However their performance tend to
+         * degenerate when the number of components to iterate grows up and the most
+         * of the entities have all the given components.<br/>
+         * To get a performance boost, consider using a group instead.
+         *
+         * @tparam Component Type of components used to construct the view.
+         * @tparam Exclude Types of components used to filter the view.
+         * @return A newly created view.
+         */
+        template<typename... Component, typename... Exclude>
+        [[nodiscard]] basic_view<Entity, exclude_t<Exclude...>, std::add_const_t<Component>...> view(exclude_t<Exclude...> = {}) const {
+            static_assert(sizeof...(Component) > 0, "Exclusion-only views are not supported");
+            return { *assure<std::remove_const_t<Component>>()..., *assure<Exclude>()... };
+        }
+
+        /*! @copydoc view */
+        template<typename... Component, typename... Exclude>
+        [[nodiscard]] basic_view<Entity, exclude_t<Exclude...>, Component...> view(exclude_t<Exclude...> = {}) {
+            static_assert(sizeof...(Component) > 0, "Exclusion-only views are not supported");
+            return { *assure<std::remove_const_t<Component>>()..., *assure<Exclude>()... };
+        }
+
+        /**
+         * @brief Returns a runtime view for the given components.
+         *
+         * This kind of objects are created on the fly and share with the registry
+         * its internal data structures.<br/>
+         * Users should throw away the view after use. Fortunately, creating and
+         * destroying a runtime view is an incredibly cheap operation because they
+         * do not require any type of initialization.<br/>
+         * As a rule of thumb, storing a view should never be an option.
+         *
+         * Runtime views are to be used when users want to construct a view from
+         * some external inputs and don't know at compile-time what are the required
+         * components.
+         *
+         * @tparam ItComp Type of input iterator for the components to use to
+         * construct the view.
+         * @tparam ItExcl Type of input iterator for the components to use to filter
+         * the view.
+         * @param first An iterator to the first element of the range of components
+         * to use to construct the view.
+         * @param last An iterator past the last element of the range of components
+         * to use to construct the view.
+         * @param from An iterator to the first element of the range of components
+         * to use to filter the view.
+         * @param to An iterator past the last element of the range of components to
+         * use to filter the view.
+         * @return A newly created runtime view.
+         */
+        template<typename ItComp, typename ItExcl = id_type*>
+        [[nodiscard]] basic_runtime_view<Entity> runtime_view(ItComp first, ItComp last, ItExcl from = {}, ItExcl to = {}) const {
+            std::vector<const basic_common_type*> component(std::distance(first, last));
+            std::vector<const basic_common_type*> filter(std::distance(from, to));
+
+            std::transform(first, last, component.begin(), [this](const auto ctype) {
+                const auto it = std::find_if(pools.cbegin(), pools.cend(), [ctype](auto&& pdata) { return pdata.poly && pdata.poly->value_type().hash() == ctype; });
+                return it == pools.cend() ? nullptr : it->pool.get();
+                });
+
+            std::transform(from, to, filter.begin(), [this](const auto ctype) {
+                const auto it = std::find_if(pools.cbegin(), pools.cend(), [ctype](auto&& pdata) { return pdata.poly && pdata.poly->value_type().hash() == ctype; });
+                return it == pools.cend() ? nullptr : it->pool.get();
+                });
+
+            return { std::move(component), std::move(filter) };
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * This kind of objects are created on the fly and share with the registry
+         * its internal data structures.<br/>
+         * Feel free to discard a group after the use. Creating and destroying a
+         * group is an incredibly cheap operation because they do not require any
+         * type of initialization, but for the first time they are requested.<br/>
+         * As a rule of thumb, storing a group should never be an option.
+         *
+         * Groups support exclusion lists and can own types of components. The more
+         * types are owned by a group, the faster it is to iterate entities and
+         * components.<br/>
+         * However, groups also affect some features of the registry such as the
+         * creation and destruction of components, which will consequently be
+         * slightly slower (nothing that can be noticed in most cases).
+         *
+         * @note
+         * Pools of components that are owned by a group cannot be sorted anymore.
+         * The group takes the ownership of the pools and arrange components so as
+         * to iterate them as fast as possible.
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Get, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> group(get_t<Get...>, exclude_t<Exclude...> = {}) {
+            static_assert(sizeof...(Owned) + sizeof...(Get) > 0, "Exclusion-only groups are not supported");
+            static_assert(sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude) > 1, "Single component groups are not allowed");
+
+            using handler_type = group_handler<exclude_t<Exclude...>, get_t<std::remove_const_t<Get>...>, std::remove_const_t<Owned>...>;
+
+            const auto cpools = std::make_tuple(assure<std::remove_const_t<Owned>>()..., assure<std::remove_const_t<Get>>()...);
+            constexpr auto size = sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude);
+            handler_type* handler = nullptr;
+
+            if (auto it = std::find_if(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                return gdata.size == size
+                    && (gdata.owned(type_hash<std::remove_const_t<Owned>>::value()) && ...)
+                    && (gdata.get(type_hash<std::remove_const_t<Get>>::value()) && ...)
+                    && (gdata.exclude(type_hash<Exclude>::value()) && ...);
+                }); it != groups.cend())
+            {
+                handler = static_cast<handler_type*>(it->group.get());
+            }
+
+                if (!handler) {
+                    group_data candidate = {
+                        size,
+                        { new handler_type{}, [](void* instance) { delete static_cast<handler_type*>(instance); } },
+                        []([[maybe_unused]] const id_type ctype) ENTT_NOEXCEPT { return ((ctype == type_hash<std::remove_const_t<Owned>>::value()) || ...); },
+                        []([[maybe_unused]] const id_type ctype) ENTT_NOEXCEPT { return ((ctype == type_hash<std::remove_const_t<Get>>::value()) || ...); },
+                        []([[maybe_unused]] const id_type ctype) ENTT_NOEXCEPT { return ((ctype == type_hash<Exclude>::value()) || ...); },
+                    };
+
+                    handler = static_cast<handler_type*>(candidate.group.get());
+
+                    const void* maybe_valid_if = nullptr;
+                    const void* discard_if = nullptr;
+
+                    if constexpr (sizeof...(Owned) == 0) {
+                        groups.push_back(std::move(candidate));
+                    }
+                    else {
+                        ENTT_ASSERT(std::all_of(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                            const auto overlapping = (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value()));
+                            const auto sz = overlapping + (0u + ... + gdata.get(type_hash<std::remove_const_t<Get>>::value())) + (0u + ... + gdata.exclude(type_hash<Exclude>::value()));
+                            return !overlapping || ((sz == size) || (sz == gdata.size));
+                            }), "Conflicting groups");
+
+                        const auto next = std::find_if_not(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                            return !(0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value())) || (size > gdata.size);
+                            });
+
+                        const auto prev = std::find_if(std::make_reverse_iterator(next), groups.crend(), [](const auto& gdata) {
+                            return (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value()));
+                            });
+
+                        maybe_valid_if = (next == groups.cend() ? maybe_valid_if : next->group.get());
+                        discard_if = (prev == groups.crend() ? discard_if : prev->group.get());
+                        groups.insert(next, std::move(candidate));
+                    }
+
+                    (on_construct<std::remove_const_t<Owned>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Owned>>>(*handler), ...);
+                    (on_construct<std::remove_const_t<Get>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Get>>>(*handler), ...);
+                    (on_destroy<Exclude>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<Exclude>>(*handler), ...);
+
+                    (on_destroy<std::remove_const_t<Owned>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
+                    (on_destroy<std::remove_const_t<Get>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
+                    (on_construct<Exclude>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
+
+                    if constexpr (sizeof...(Owned) == 0) {
+                        for (const auto entity : view<Owned..., Get...>(exclude<Exclude...>)) {
+                            handler->current.emplace(entity);
+                        }
+                    }
+                    else {
+                        // we cannot iterate backwards because we want to leave behind valid entities in case of owned types
+                        for (auto* first = std::get<0>(cpools)->data(), *last = first + std::get<0>(cpools)->size(); first != last; ++first) {
+                            handler->template maybe_valid_if<type_list_element_t<0, type_list<std::remove_const_t<Owned>...>>>(*this, *first);
+                        }
+                    }
+                }
+
+                return { handler->current, *std::get<storage_type<std::remove_const_t<Owned>>*>(cpools)..., *std::get<storage_type<std::remove_const_t<Get>>*>(cpools)... };
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * @sa group
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Get, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<std::add_const_t<Get>...>, std::add_const_t<Owned>...> group_if_exists(get_t<Get...>, exclude_t<Exclude...> = {}) const {
+            if (auto it = std::find_if(groups.cbegin(), groups.cend(), [](const auto& gdata) {
+                return gdata.size == (sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude))
+                    && (gdata.owned(type_hash<std::remove_const_t<Owned>>::value()) && ...)
+                    && (gdata.get(type_hash<std::remove_const_t<Get>>::value()) && ...)
+                    && (gdata.exclude(type_hash<Exclude>::value()) && ...);
+                }); it == groups.cend())
+            {
+                return {};
+            }
+            else {
+                using handler_type = group_handler<exclude_t<Exclude...>, get_t<std::remove_const_t<Get>...>, std::remove_const_t<Owned>...>;
+                return { static_cast<handler_type*>(it->group.get())->current, *pool_if_exists<std::remove_const_t<Owned>>()... , *pool_if_exists<std::remove_const_t<Get>>()... };
+            }
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * @sa group
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<>, Owned...> group(exclude_t<Exclude...> = {}) {
+            return group<Owned...>(get_t<>{}, exclude<Exclude...>);
+        }
+
+        /**
+         * @brief Returns a group for the given components.
+         *
+         * @sa group_if_exists
+         *
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return A newly created group.
+         */
+        template<typename... Owned, typename... Exclude>
+        [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<>, std::add_const_t<Owned>...> group_if_exists(exclude_t<Exclude...> = {}) const {
+            return group_if_exists<std::add_const_t<Owned>...>(get_t<>{}, exclude<Exclude...>);
+        }
+
+        /**
+         * @brief Checks whether the given components belong to any group.
+         * @tparam Component Types of components in which one is interested.
+         * @return True if the pools of the given components are sortable, false
+         * otherwise.
+         */
+        template<typename... Component>
+        [[nodiscard]] bool sortable() const {
+            return std::none_of(groups.cbegin(), groups.cend(), [](auto&& gdata) { return (gdata.owned(type_hash<std::remove_const_t<Component>>::value()) || ...); });
+        }
+
+        /**
+         * @brief Checks whether a group can be sorted.
+         * @tparam Owned Types of components owned by the group.
+         * @tparam Get Types of components observed by the group.
+         * @tparam Exclude Types of components used to filter the group.
+         * @return True if the group can be sorted, false otherwise.
+         */
+        template<typename... Owned, typename... Get, typename... Exclude>
+        [[nodiscard]] bool sortable(const basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...>&) ENTT_NOEXCEPT {
+            constexpr auto size = sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude);
+            return std::find_if(groups.cbegin(), groups.cend(), [size](const auto& gdata) {
+                return (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value())) && (size < gdata.size);
+                }) == groups.cend();
+        }
+
+        /**
+         * @brief Sorts the pool of entities for the given component.
+         *
+         * The order of the elements in a pool is highly affected by assignments
+         * of components to entities and deletions. Components are arranged to
+         * maximize the performance during iterations and users should not make any
+         * assumption on the order.<br/>
+         * This function can be used to impose an order to the elements in the pool
+         * of the given component. The order is kept valid until a component of the
+         * given type is assigned or removed from an entity.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(const Entity, const Entity);
+         * bool(const Component &, const Component &);
+         * @endcode
+         *
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * The comparison funtion object received by the sort function object hasn't
+         * necessarily the type of the one passed along with the other parameters to
+         * this member function.
+         *
+         * @warning
+         * Pools of components owned by a group cannot be sorted.
+         *
+         * @tparam Component Type of components to sort.
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Component, typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            ENTT_ASSERT(sortable<Component>(), "Cannot sort owned storage");
+            assure<Component>()->sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Sorts two pools of components in the same way.
+         *
+         * The order of the elements in a pool is highly affected by assignments
+         * of components to entities and deletions. Components are arranged to
+         * maximize the performance during iterations and users should not make any
+         * assumption on the order.
+         *
+         * It happens that different pools of components must be sorted the same way
+         * because of runtime and/or performance constraints. This function can be
+         * used to order a pool of components according to the order between the
+         * entities in another pool of components.
+         *
+         * @b How @b it @b works
+         *
+         * Being `A` and `B` the two sets where `B` is the master (the one the order
+         * of which rules) and `A` is the slave (the one to sort), after a call to
+         * this function an iterator for `A` will return the entities according to
+         * the following rules:
+         *
+         * * All the entities in `A` that are also in `B` are returned first
+         *   according to the order they have in `B`.
+         * * All the entities in `A` that are not in `B` are returned in no
+         *   particular order after all the other entities.
+         *
+         * Any subsequent change to `B` won't affect the order in `A`.
+         *
+         * @warning
+         * Pools of components owned by a group cannot be sorted.
+         *
+         * @tparam To Type of components to sort.
+         * @tparam From Type of components to use to sort.
+         */
+        template<typename To, typename From>
+        void sort() {
+            ENTT_ASSERT(sortable<To>(), "Cannot sort owned storage");
+            assure<To>()->respect(*assure<From>());
+        }
+
+        /**
+         * @brief Visits an entity and returns the type info for its components.
+         *
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const type_info);
+         * @endcode
+         *
+         * Returned identifiers are those of the components owned by the entity.
+         *
+         * @sa type_info
+         *
+         * @warning
+         * It's not specified whether a component attached to or removed from the
+         * given entity during the visit is returned or not to the caller.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param entity A valid entity identifier.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void visit(entity_type entity, Func func) const {
+            for (auto pos = pools.size(); pos; --pos) {
+                if (const auto& pdata = pools[pos - 1]; pdata.pool && pdata.pool->contains(entity)) {
+                    func(pdata.poly->value_type());
+                }
+            }
+        }
+
+        /**
+         * @brief Visits a registry and returns the type info for its components.
+         *
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const type_info);
+         * @endcode
+         *
+         * Returned identifiers are those of the components managed by the registry.
+         *
+         * @sa type_info
+         *
+         * @warning
+         * It's not specified whether a component for which a pool is created during
+         * the visit is returned or not to the caller.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void visit(Func func) const {
+            for (auto pos = pools.size(); pos; --pos) {
+                if (const auto& pdata = pools[pos - 1]; pdata.pool) {
+                    func(pdata.poly->value_type());
+                }
+            }
+        }
+
+        /**
+         * @brief Binds an object to the context of the registry.
+         *
+         * If the value already exists it is overwritten, otherwise a new instance
+         * of the given type is created and initialized with the arguments provided.
+         *
+         * @tparam Type Type of object to set.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param args Parameters to use to initialize the value.
+         * @return A reference to the newly created object.
+         */
+        template<typename Type, typename... Args>
+        Type& set(Args &&... args) {
+            unset<Type>();
+            vars.emplace_back(std::in_place_type<Type>, std::forward<Args>(args)...);
+            return any_cast<Type&>(vars.back());
+        }
+
+        /**
+         * @brief Unsets a context variable if it exists.
+         * @tparam Type Type of object to set.
+         */
+        template<typename Type>
+        void unset() {
+            vars.erase(std::remove_if(vars.begin(), vars.end(), [type = type_id<Type>()](auto&& var) { return var.type() == type; }), vars.end());
+        }
+
+        /**
+         * @brief Binds an object to the context of the registry.
+         *
+         * In case the context doesn't contain the given object, the parameters
+         * provided are used to construct it.
+         *
+         * @tparam Type Type of object to set.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param args Parameters to use to initialize the object.
+         * @return A reference to the object in the context of the registry.
+         */
+        template<typename Type, typename... Args>
+        [[nodiscard]] Type& ctx_or_set(Args &&... args) {
+            auto* value = try_ctx<Type>();
+            return value ? *value : set<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Returns a pointer to an object in the context of the registry.
+         * @tparam Type Type of object to get.
+         * @return A pointer to the object if it exists in the context of the
+         * registry, a null pointer otherwise.
+         */
+        template<typename Type>
+        [[nodiscard]] std::add_const_t<Type>* try_ctx() const {
+            auto it = std::find_if(vars.cbegin(), vars.cend(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            return it == vars.cend() ? nullptr : any_cast<std::add_const_t<Type>>(&*it);
+        }
+
+        /*! @copydoc try_ctx */
+        template<typename Type>
+        [[nodiscard]] Type* try_ctx() {
+            auto it = std::find_if(vars.begin(), vars.end(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            return it == vars.end() ? nullptr : any_cast<Type>(&*it);
+        }
+
+        /**
+         * @brief Returns a reference to an object in the context of the registry.
+         *
+         * @warning
+         * Attempting to get a context variable that doesn't exist results in
+         * undefined behavior.
+         *
+         * @tparam Type Type of object to get.
+         * @return A valid reference to the object in the context of the registry.
+         */
+        template<typename Type>
+        [[nodiscard]] std::add_const_t<Type>& ctx() const {
+            auto it = std::find_if(vars.cbegin(), vars.cend(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            ENTT_ASSERT(it != vars.cend(), "Invalid instance");
+            return any_cast<std::add_const_t<Type>&>(*it);
+        }
+
+        /*! @copydoc ctx */
+        template<typename Type>
+        [[nodiscard]] Type& ctx() {
+            auto it = std::find_if(vars.begin(), vars.end(), [type = type_id<Type>()](auto&& var) { return var.type() == type; });
+            ENTT_ASSERT(it != vars.end(), "Invalid instance");
+            return any_cast<Type&>(*it);
+        }
+
+        /**
+         * @brief Visits a registry and returns the type info for its context
+         * variables.
+         *
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const type_info);
+         * @endcode
+         *
+         * Returned identifiers are those of the context variables currently set.
+         *
+         * @sa type_info
+         *
+         * @warning
+         * It's not specified whether a context variable created during the visit is
+         * returned or not to the caller.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void ctx(Func func) const {
+            for (auto pos = vars.size(); pos; --pos) {
+                func(vars[pos - 1].type());
+            }
+        }
+
+    private:
+        std::vector<basic_any<0u>> vars{};
+        mutable std::vector<pool_data> pools{};
+        std::vector<group_data> groups{};
+        std::vector<entity_type> entities{};
+        entity_type free_list{ tombstone };
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/runtime_view.hpp"
+#ifndef ENTT_ENTITY_RUNTIME_VIEW_HPP
+#define ENTT_ENTITY_RUNTIME_VIEW_HPP
+
+
+#include <iterator>
+#include <vector>
+#include <utility>
+#include <algorithm>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "entity.hpp"
+
+// #include "sparse_set.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Runtime view.
+     *
+     * Runtime views iterate over those entities that have at least all the given
+     * components in their bags. During initialization, a runtime view looks at the
+     * number of entities available for each component and picks up a reference to
+     * the smallest set of candidate entities in order to get a performance boost
+     * when iterate.<br/>
+     * Order of elements during iterations are highly dependent on the order of the
+     * underlying data structures. See sparse_set and its specializations for more
+     * details.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all the other cases, modifying the pools of the given components in any
+     * way invalidates all the iterators and using them results in undefined
+     * behavior.
+     *
+     * @note
+     * Views share references to the underlying data structures of the registry that
+     * generated them. Therefore any change to the entities and to the components
+     * made by means of the registry are immediately reflected by the views, unless
+     * a pool was missing when the view was built (in this case, the view won't
+     * have a valid reference and won't be updated accordingly).
+     *
+     * @warning
+     * Lifetime of a view must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a view results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_runtime_view final {
+        using basic_common_type = basic_sparse_set<Entity>;
+        using underlying_iterator = typename basic_common_type::iterator;
+
+        class view_iterator final {
+            [[nodiscard]] bool valid() const {
+                const auto entt = *it;
+
+                return (!stable_storage || (entt != tombstone))
+                    && std::all_of(pools->begin()++, pools->end(), [entt](const auto* curr) { return curr->contains(entt); })
+                    && std::none_of(filter->cbegin(), filter->cend(), [entt](const auto* curr) { return curr && curr->contains(entt); });
+            }
+
+        public:
+            using difference_type = typename underlying_iterator::difference_type;
+            using value_type = typename underlying_iterator::value_type;
+            using pointer = typename underlying_iterator::pointer;
+            using reference = typename underlying_iterator::reference;
+            using iterator_category = std::bidirectional_iterator_tag;
+
+            view_iterator() ENTT_NOEXCEPT = default;
+
+            view_iterator(const std::vector<const basic_common_type*>& cpools, const std::vector<const basic_common_type*>& ignore, underlying_iterator curr) ENTT_NOEXCEPT
+                : pools{ &cpools },
+                filter{ &ignore },
+                it{ curr },
+                stable_storage{ std::any_of(pools->cbegin(), pools->cend(), [](const basic_common_type* cpool) { return (cpool->policy() == deletion_policy::in_place); }) }
+            {
+                if (it != (*pools)[0]->end() && !valid()) {
+                    ++(*this);
+                }
+            }
+
+            view_iterator& operator++() {
+                while (++it != (*pools)[0]->end() && !valid());
+                return *this;
+            }
+
+            view_iterator operator++(int) {
+                view_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            view_iterator& operator--() ENTT_NOEXCEPT {
+                while (--it != (*pools)[0]->begin() && !valid());
+                return *this;
+            }
+
+            view_iterator operator--(int) ENTT_NOEXCEPT {
+                view_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            [[nodiscard]] bool operator==(const view_iterator& other) const ENTT_NOEXCEPT {
+                return other.it == it;
+            }
+
+            [[nodiscard]] bool operator!=(const view_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] pointer operator->() const {
+                return it.operator->();
+            }
+
+            [[nodiscard]] reference operator*() const {
+                return *operator->();
+            }
+
+        private:
+            const std::vector<const basic_common_type*>* pools;
+            const std::vector<const basic_common_type*>* filter;
+            underlying_iterator it;
+            bool stable_storage;
+        };
+
+        [[nodiscard]] bool valid() const {
+            return !pools.empty() && pools.front();
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Bidirectional iterator type. */
+        using iterator = view_iterator;
+
+        /*! @brief Default constructor to use to create empty, invalid views. */
+        basic_runtime_view() ENTT_NOEXCEPT
+            : pools{},
+            filter{}
+        {}
+
+        /**
+         * @brief Constructs a runtime view from a set of storage classes.
+         * @param cpools The storage for the types to iterate.
+         * @param epools The storage for the types used to filter the view.
+         */
+        basic_runtime_view(std::vector<const basic_common_type*> cpools, std::vector<const basic_common_type*> epools) ENTT_NOEXCEPT
+            : pools{ std::move(cpools) },
+            filter{ std::move(epools) }
+        {
+            // brings the best candidate (if any) on front of the vector
+            std::rotate(pools.begin(), std::min_element(pools.begin(), pools.end(), [](const auto* lhs, const auto* rhs) {
+                return (!lhs && rhs) || (lhs && rhs && lhs->size() < rhs->size());
+                }), pools.end());
+        }
+
+        /**
+         * @brief Estimates the number of entities iterated by the view.
+         * @return Estimated number of entities iterated by the view.
+         */
+        [[nodiscard]] size_type size_hint() const {
+            return valid() ? pools.front()->size() : size_type{};
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity that has the given
+         * components.
+         *
+         * The returned iterator points to the first entity that has the given
+         * components. If the view is empty, the returned iterator will be equal to
+         * `end()`.
+         *
+         * @return An iterator to the first entity that has the given components.
+         */
+        [[nodiscard]] iterator begin() const {
+            return valid() ? iterator{ pools, filter, pools[0]->begin() } : iterator{};
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity that has the
+         * given components.
+         *
+         * The returned iterator points to the entity following the last entity that
+         * has the given components. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity that has the
+         * given components.
+         */
+        [[nodiscard]] iterator end() const {
+            return valid() ? iterator{ pools, filter, pools[0]->end() } : iterator{};
+        }
+
+        /**
+         * @brief Checks if a view contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the view contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return valid() && std::all_of(pools.cbegin(), pools.cend(), [entt](const auto* curr) { return curr->contains(entt); })
+                && std::none_of(filter.cbegin(), filter.cend(), [entt](const auto* curr) { return curr && curr->contains(entt); });
+        }
+
+        /**
+         * @brief Iterates entities and applies the given function object to them.
+         *
+         * The function object is invoked for each entity. It is provided only with
+         * the entity itself. To get the components, users can use the registry with
+         * which the view was built.<br/>
+         * The signature of the function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * void(const entity_type);
+         * @endcode
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            for (const auto entity : *this) {
+                func(entity);
+            }
+        }
+
+    private:
+        std::vector<const basic_common_type*> pools;
+        std::vector<const basic_common_type*> filter;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/snapshot.hpp"
+#ifndef ENTT_ENTITY_SNAPSHOT_HPP
+#define ENTT_ENTITY_SNAPSHOT_HPP
+
+
+#include <array>
+#include <cstddef>
+#include <iterator>
+#include <tuple>
+#include <type_traits>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "registry.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to create snapshots from a registry.
+     *
+     * A _snapshot_ can be either a dump of the entire registry or a narrower
+     * selection of components of interest.<br/>
+     * This type can be used in both cases if provided with a correctly configured
+     * output archive.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_snapshot {
+        using traits_type = entt_traits<Entity>;
+
+        template<typename Component, typename Archive, typename It>
+        void get(Archive& archive, std::size_t sz, It first, It last) const {
+            const auto view = reg->template view<std::add_const_t<Component>>();
+            archive(typename traits_type::entity_type(sz));
+
+            while (first != last) {
+                const auto entt = *(first++);
+
+                if (reg->template all_of<Component>(entt)) {
+                    std::apply(archive, std::tuple_cat(std::make_tuple(entt), view.get(entt)));
+                }
+            }
+        }
+
+        template<typename... Component, typename Archive, typename It, std::size_t... Index>
+        void component(Archive& archive, It first, It last, std::index_sequence<Index...>) const {
+            std::array<std::size_t, sizeof...(Index)> size{};
+            auto begin = first;
+
+            while (begin != last) {
+                const auto entt = *(begin++);
+                ((reg->template all_of<Component>(entt) ? ++size[Index] : size[Index]), ...);
+            }
+
+            (get<Component>(archive, size[Index], first, last), ...);
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+
+        /**
+         * @brief Constructs an instance that is bound to a given registry.
+         * @param source A valid reference to a registry.
+         */
+        basic_snapshot(const basic_registry<entity_type>& source) ENTT_NOEXCEPT
+            : reg{ &source }
+        {}
+
+        /*! @brief Default move constructor. */
+        basic_snapshot(basic_snapshot&&) = default;
+
+        /*! @brief Default move assignment operator. @return This snapshot. */
+        basic_snapshot& operator=(basic_snapshot&&) = default;
+
+        /**
+         * @brief Puts aside all the entities from the underlying registry.
+         *
+         * Entities are serialized along with their versions. Destroyed entities are
+         * taken in consideration as well by this function.
+         *
+         * @tparam Archive Type of output archive.
+         * @param archive A valid reference to an output archive.
+         * @return An object of this type to continue creating the snapshot.
+         */
+        template<typename Archive>
+        const basic_snapshot& entities(Archive& archive) const {
+            const auto sz = reg->size();
+
+            archive(typename traits_type::entity_type(sz));
+
+            for (auto first = reg->data(), last = first + sz; first != last; ++first) {
+                archive(*first);
+            }
+
+            archive(reg->released());
+
+            return *this;
+        }
+
+        /**
+         * @brief Puts aside the given components.
+         *
+         * Each instance is serialized together with the entity to which it belongs.
+         * Entities are serialized along with their versions.
+         *
+         * @tparam Component Types of components to serialize.
+         * @tparam Archive Type of output archive.
+         * @param archive A valid reference to an output archive.
+         * @return An object of this type to continue creating the snapshot.
+         */
+        template<typename... Component, typename Archive>
+        const basic_snapshot& component(Archive& archive) const {
+            if constexpr (sizeof...(Component) == 1u) {
+                const auto view = reg->template view<const Component...>();
+                (component<Component>(archive, view.data(), view.data() + view.size()), ...);
+                return *this;
+            }
+            else {
+                (component<Component>(archive), ...);
+                return *this;
+            }
+        }
+
+        /**
+         * @brief Puts aside the given components for the entities in a range.
+         *
+         * Each instance is serialized together with the entity to which it belongs.
+         * Entities are serialized along with their versions.
+         *
+         * @tparam Component Types of components to serialize.
+         * @tparam Archive Type of output archive.
+         * @tparam It Type of input iterator.
+         * @param archive A valid reference to an output archive.
+         * @param first An iterator to the first element of the range to serialize.
+         * @param last An iterator past the last element of the range to serialize.
+         * @return An object of this type to continue creating the snapshot.
+         */
+        template<typename... Component, typename Archive, typename It>
+        const basic_snapshot& component(Archive& archive, It first, It last) const {
+            component<Component...>(archive, first, last, std::index_sequence_for<Component...>{});
+            return *this;
+        }
+
+    private:
+        const basic_registry<entity_type>* reg;
+    };
+
+
+    /**
+     * @brief Utility class to restore a snapshot as a whole.
+     *
+     * A snapshot loader requires that the destination registry be empty and loads
+     * all the data at once while keeping intact the identifiers that the entities
+     * originally had.<br/>
+     * An example of use is the implementation of a save/restore utility.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_snapshot_loader {
+        using traits_type = entt_traits<Entity>;
+
+        template<typename Type, typename Archive>
+        void assign(Archive& archive) const {
+            typename traits_type::entity_type length{};
+            archive(length);
+
+            entity_type entt{};
+
+            if constexpr (std::tuple_size_v<decltype(reg->template view<Type>().get({})) > == 0) {
+                while (length--) {
+                    archive(entt);
+                    const auto entity = reg->valid(entt) ? entt : reg->create(entt);
+                    ENTT_ASSERT(entity == entt, "Entity not available for use");
+                    reg->template emplace<Type>(entity);
+                }
+            }
+            else {
+                Type instance{};
+
+                while (length--) {
+                    archive(entt, instance);
+                    const auto entity = reg->valid(entt) ? entt : reg->create(entt);
+                    ENTT_ASSERT(entity == entt, "Entity not available for use");
+                    reg->template emplace<Type>(entity, std::move(instance));
+                }
+            }
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+
+        /**
+         * @brief Constructs an instance that is bound to a given registry.
+         * @param source A valid reference to a registry.
+         */
+        basic_snapshot_loader(basic_registry<entity_type>& source) ENTT_NOEXCEPT
+            : reg{ &source }
+        {
+            // restoring a snapshot as a whole requires a clean registry
+            ENTT_ASSERT(reg->empty(), "Registry must be empty");
+        }
+
+        /*! @brief Default move constructor. */
+        basic_snapshot_loader(basic_snapshot_loader&&) = default;
+
+        /*! @brief Default move assignment operator. @return This loader. */
+        basic_snapshot_loader& operator=(basic_snapshot_loader&&) = default;
+
+        /**
+         * @brief Restores entities that were in use during serialization.
+         *
+         * This function restores the entities that were in use during serialization
+         * and gives them the versions they originally had.
+         *
+         * @tparam Archive Type of input archive.
+         * @param archive A valid reference to an input archive.
+         * @return A valid loader to continue restoring data.
+         */
+        template<typename Archive>
+        const basic_snapshot_loader& entities(Archive& archive) const {
+            typename traits_type::entity_type length{};
+
+            archive(length);
+            std::vector<entity_type> all(length);
+
+            for (decltype(length) pos{}; pos < length; ++pos) {
+                archive(all[pos]);
+            }
+
+            entity_type destroyed;
+            archive(destroyed);
+
+            reg->assign(all.cbegin(), all.cend(), destroyed);
+
+            return *this;
+        }
+
+        /**
+         * @brief Restores components and assigns them to the right entities.
+         *
+         * The template parameter list must be exactly the same used during
+         * serialization. In the event that the entity to which the component is
+         * assigned doesn't exist yet, the loader will take care to create it with
+         * the version it originally had.
+         *
+         * @tparam Component Types of components to restore.
+         * @tparam Archive Type of input archive.
+         * @param archive A valid reference to an input archive.
+         * @return A valid loader to continue restoring data.
+         */
+        template<typename... Component, typename Archive>
+        const basic_snapshot_loader& component(Archive& archive) const {
+            (assign<Component>(archive), ...);
+            return *this;
+        }
+
+        /**
+         * @brief Destroys those entities that have no components.
+         *
+         * In case all the entities were serialized but only part of the components
+         * was saved, it could happen that some of the entities have no components
+         * once restored.<br/>
+         * This functions helps to identify and destroy those entities.
+         *
+         * @return A valid loader to continue restoring data.
+         */
+        const basic_snapshot_loader& orphans() const {
+            reg->orphans([this](const auto entt) {
+                reg->release(entt);
+                });
+
+            return *this;
+        }
+
+    private:
+        basic_registry<entity_type>* reg;
+    };
+
+
+    /**
+     * @brief Utility class for _continuous loading_.
+     *
+     * A _continuous loader_ is designed to load data from a source registry to a
+     * (possibly) non-empty destination. The loader can accommodate in a registry
+     * more than one snapshot in a sort of _continuous loading_ that updates the
+     * destination one step at a time.<br/>
+     * Identifiers that entities originally had are not transferred to the target.
+     * Instead, the loader maps remote identifiers to local ones while restoring a
+     * snapshot.<br/>
+     * An example of use is the implementation of a client-server applications with
+     * the requirement of transferring somehow parts of the representation side to
+     * side.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     */
+    template<typename Entity>
+    class basic_continuous_loader {
+        using traits_type = entt_traits<Entity>;
+
+        void destroy(Entity entt) {
+            if (const auto it = remloc.find(entt); it == remloc.cend()) {
+                const auto local = reg->create();
+                remloc.emplace(entt, std::make_pair(local, true));
+                reg->destroy(local);
+            }
+        }
+
+        void restore(Entity entt) {
+            const auto it = remloc.find(entt);
+
+            if (it == remloc.cend()) {
+                const auto local = reg->create();
+                remloc.emplace(entt, std::make_pair(local, true));
+            }
+            else {
+                if (!reg->valid(remloc[entt].first)) {
+                    remloc[entt].first = reg->create();
+                }
+
+                // set the dirty flag
+                remloc[entt].second = true;
+            }
+        }
+
+        template<typename Container>
+        auto update(int, Container& container)
+            -> decltype(typename Container::mapped_type{}, void()) {
+            // map like container
+            Container other;
+
+            for (auto&& pair : container) {
+                using first_type = std::remove_const_t<typename std::decay_t<decltype(pair)>::first_type>;
+                using second_type = typename std::decay_t<decltype(pair)>::second_type;
+
+                if constexpr (std::is_same_v<first_type, entity_type> && std::is_same_v<second_type, entity_type>) {
+                    other.emplace(map(pair.first), map(pair.second));
+                }
+                else if constexpr (std::is_same_v<first_type, entity_type>) {
+                    other.emplace(map(pair.first), std::move(pair.second));
+                }
+                else {
+                    static_assert(std::is_same_v<second_type, entity_type>, "Neither the key nor the value are of entity type");
+                    other.emplace(std::move(pair.first), map(pair.second));
+                }
+            }
+
+            std::swap(container, other);
+        }
+
+        template<typename Container>
+        auto update(char, Container& container)
+            -> decltype(typename Container::value_type{}, void()) {
+            // vector like container
+            static_assert(std::is_same_v<typename Container::value_type, entity_type>, "Invalid value type");
+
+            for (auto&& entt : container) {
+                entt = map(entt);
+            }
+        }
+
+        template<typename Other, typename Type, typename Member>
+        void update([[maybe_unused]] Other& instance, [[maybe_unused]] Member Type::* member) {
+            if constexpr (!std::is_same_v<Other, Type>) {
+                return;
+            }
+            else if constexpr (std::is_same_v<Member, entity_type>) {
+                instance.*member = map(instance.*member);
+            }
+            else {
+                // maybe a container? let's try...
+                update(0, instance.*member);
+            }
+        }
+
+        template<typename Component>
+        void remove_if_exists() {
+            for (auto&& ref : remloc) {
+                const auto local = ref.second.first;
+
+                if (reg->valid(local)) {
+                    reg->template remove<Component>(local);
+                }
+            }
+        }
+
+        template<typename Other, typename Archive, typename... Type, typename... Member>
+        void assign(Archive& archive, [[maybe_unused]] Member Type:: *... member) {
+            typename traits_type::entity_type length{};
+            archive(length);
+
+            entity_type entt{};
+
+            if constexpr (std::tuple_size_v<decltype(reg->template view<Other>().get({})) > == 0) {
+                while (length--) {
+                    archive(entt);
+                    restore(entt);
+                    reg->template emplace_or_replace<Other>(map(entt));
+                }
+            }
+            else {
+                Other instance{};
+
+                while (length--) {
+                    archive(entt, instance);
+                    (update(instance, member), ...);
+                    restore(entt);
+                    reg->template emplace_or_replace<Other>(map(entt), std::move(instance));
+                }
+            }
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+
+        /**
+         * @brief Constructs an instance that is bound to a given registry.
+         * @param source A valid reference to a registry.
+         */
+        basic_continuous_loader(basic_registry<entity_type>& source) ENTT_NOEXCEPT
+            : reg{ &source }
+        {}
+
+        /*! @brief Default move constructor. */
+        basic_continuous_loader(basic_continuous_loader&&) = default;
+
+        /*! @brief Default move assignment operator. @return This loader. */
+        basic_continuous_loader& operator=(basic_continuous_loader&&) = default;
+
+        /**
+         * @brief Restores entities that were in use during serialization.
+         *
+         * This function restores the entities that were in use during serialization
+         * and creates local counterparts for them if required.
+         *
+         * @tparam Archive Type of input archive.
+         * @param archive A valid reference to an input archive.
+         * @return A non-const reference to this loader.
+         */
+        template<typename Archive>
+        basic_continuous_loader& entities(Archive& archive) {
+            typename traits_type::entity_type length{};
+            entity_type entt{};
+
+            archive(length);
+
+            for (decltype(length) pos{}; pos < length; ++pos) {
+                archive(entt);
+
+                if (const auto entity = traits_type::to_entity(entt); entity == pos) {
+                    restore(entt);
+                }
+                else {
+                    destroy(entt);
+                }
+            }
+
+            // discards the head of the list of destroyed entities
+            archive(entt);
+
+            return *this;
+        }
+
+        /**
+         * @brief Restores components and assigns them to the right entities.
+         *
+         * The template parameter list must be exactly the same used during
+         * serialization. In the event that the entity to which the component is
+         * assigned doesn't exist yet, the loader will take care to create a local
+         * counterpart for it.<br/>
+         * Members can be either data members of type entity_type or containers of
+         * entities. In both cases, the loader will visit them and update the
+         * entities by replacing each one with its local counterpart.
+         *
+         * @tparam Component Type of component to restore.
+         * @tparam Archive Type of input archive.
+         * @tparam Type Types of components to update with local counterparts.
+         * @tparam Member Types of members to update with their local counterparts.
+         * @param archive A valid reference to an input archive.
+         * @param member Members to update with their local counterparts.
+         * @return A non-const reference to this loader.
+         */
+        template<typename... Component, typename Archive, typename... Type, typename... Member>
+        basic_continuous_loader& component(Archive& archive, Member Type:: *... member) {
+            (remove_if_exists<Component>(), ...);
+            (assign<Component>(archive, member...), ...);
+            return *this;
+        }
+
+        /**
+         * @brief Helps to purge entities that no longer have a conterpart.
+         *
+         * Users should invoke this member function after restoring each snapshot,
+         * unless they know exactly what they are doing.
+         *
+         * @return A non-const reference to this loader.
+         */
+        basic_continuous_loader& shrink() {
+            auto it = remloc.begin();
+
+            while (it != remloc.cend()) {
+                const auto local = it->second.first;
+                bool& dirty = it->second.second;
+
+                if (dirty) {
+                    dirty = false;
+                    ++it;
+                }
+                else {
+                    if (reg->valid(local)) {
+                        reg->destroy(local);
+                    }
+
+                    it = remloc.erase(it);
+                }
+            }
+
+            return *this;
+        }
+
+        /**
+         * @brief Destroys those entities that have no components.
+         *
+         * In case all the entities were serialized but only part of the components
+         * was saved, it could happen that some of the entities have no components
+         * once restored.<br/>
+         * This functions helps to identify and destroy those entities.
+         *
+         * @return A non-const reference to this loader.
+         */
+        basic_continuous_loader& orphans() {
+            reg->orphans([this](const auto entt) {
+                reg->release(entt);
+                });
+
+            return *this;
+        }
+
+        /**
+         * @brief Tests if a loader knows about a given entity.
+         * @param entt An entity identifier.
+         * @return True if `entity` is managed by the loader, false otherwise.
+         */
+        [[nodiscard]] bool contains(entity_type entt) const ENTT_NOEXCEPT {
+            return (remloc.find(entt) != remloc.cend());
+        }
+
+        /**
+         * @brief Returns the identifier to which an entity refers.
+         * @param entt An entity identifier.
+         * @return The local identifier if any, the null entity otherwise.
+         */
+        [[nodiscard]] entity_type map(entity_type entt) const ENTT_NOEXCEPT {
+            const auto it = remloc.find(entt);
+            entity_type other = null;
+
+            if (it != remloc.cend()) {
+                other = it->second.first;
+            }
+
+            return other;
+        }
+
+    private:
+        std::unordered_map<entity_type, std::pair<entity_type, bool>> remloc;
+        basic_registry<entity_type>* reg;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/sparse_set.hpp"
+#ifndef ENTT_ENTITY_SPARSE_SET_HPP
+#define ENTT_ENTITY_SPARSE_SET_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/algorithm.hpp"
+
+// #include "../core/fwd.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /*! @brief Sparse set deletion policy. */
+    enum class deletion_policy : std::uint8_t {
+        /*! @brief Swap-and-pop deletion policy. */
+        swap_and_pop = 0u,
+        /*! @brief In-place deletion policy. */
+        in_place = 1u
+    };
+
+
+    /**
+     * @brief Basic sparse set implementation.
+     *
+     * Sparse set or packed array or whatever is the name users give it.<br/>
+     * Two arrays: an _external_ one and an _internal_ one; a _sparse_ one and a
+     * _packed_ one; one used for direct access through contiguous memory, the other
+     * one used to get the data through an extra level of indirection.<br/>
+     * This is largely used by the registry to offer users the fastest access ever
+     * to the components. Views and groups in general are almost entirely designed
+     * around sparse sets.
+     *
+     * This type of data structure is widely documented in the literature and on the
+     * web. This is nothing more than a customized implementation suitable for the
+     * purpose of the framework.
+     *
+     * @note
+     * Internal data structures arrange elements to maximize performance. There are
+     * no guarantees that entities are returned in the insertion order when iterate
+     * a sparse set. Do not make assumption on the order in any case.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Allocator Type of allocator used to manage memory and elements.
+     */
+    template<typename Entity, typename Allocator>
+    class basic_sparse_set {
+        static constexpr auto growth_factor = 1.5;
+        static constexpr auto sparse_page = ENTT_SPARSE_PAGE;
+
+        using traits_type = entt_traits<Entity>;
+
+        using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Entity>;
+        using alloc_pointer = typename alloc_traits::pointer;
+        using alloc_const_pointer = typename alloc_traits::const_pointer;
+
+        using bucket_alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<alloc_pointer>;
+        using bucket_alloc_pointer = typename bucket_alloc_traits::pointer;
+
+        static_assert(alloc_traits::propagate_on_container_move_assignment::value);
+        static_assert(bucket_alloc_traits::propagate_on_container_move_assignment::value);
+
+        struct sparse_set_iterator final {
+            using difference_type = typename traits_type::difference_type;
+            using value_type = Entity;
+            using pointer = const value_type*;
+            using reference = const value_type&;
+            using iterator_category = std::random_access_iterator_tag;
+
+            sparse_set_iterator() ENTT_NOEXCEPT = default;
+
+            sparse_set_iterator(const alloc_const_pointer* ref, const difference_type idx) ENTT_NOEXCEPT
+                : packed{ ref },
+                index{ idx }
+            {}
+
+            sparse_set_iterator& operator++() ENTT_NOEXCEPT {
+                return --index, * this;
+            }
+
+            sparse_set_iterator operator++(int) ENTT_NOEXCEPT {
+                iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            sparse_set_iterator& operator--() ENTT_NOEXCEPT {
+                return ++index, * this;
+            }
+
+            sparse_set_iterator operator--(int) ENTT_NOEXCEPT {
+                sparse_set_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            sparse_set_iterator& operator+=(const difference_type value) ENTT_NOEXCEPT {
+                index -= value;
+                return *this;
+            }
+
+            sparse_set_iterator operator+(const difference_type value) const ENTT_NOEXCEPT {
+                sparse_set_iterator copy = *this;
+                return (copy += value);
+            }
+
+            sparse_set_iterator& operator-=(const difference_type value) ENTT_NOEXCEPT {
+                return (*this += -value);
+            }
+
+            sparse_set_iterator operator-(const difference_type value) const ENTT_NOEXCEPT {
+                return (*this + -value);
+            }
+
+            difference_type operator-(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return other.index - index;
+            }
+
+            [[nodiscard]] reference operator[](const difference_type value) const {
+                const auto pos = size_type(index - value - 1u);
+                return (*packed)[pos];
+            }
+
+            [[nodiscard]] bool operator==(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return other.index == index;
+            }
+
+            [[nodiscard]] bool operator!=(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] bool operator<(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return index > other.index;
+            }
+
+            [[nodiscard]] bool operator>(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return index < other.index;
+            }
+
+            [[nodiscard]] bool operator<=(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this > other);
+            }
+
+            [[nodiscard]] bool operator>=(const sparse_set_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this < other);
+            }
+
+            [[nodiscard]] pointer operator->() const {
+                const auto pos = size_type(index - 1u);
+                return std::addressof((*packed)[pos]);
+            }
+
+            [[nodiscard]] reference operator*() const {
+                return *operator->();
+            }
+
+        private:
+            const alloc_const_pointer* packed;
+            difference_type index;
+        };
+
+        [[nodiscard]] static auto page(const Entity entt) ENTT_NOEXCEPT {
+            return size_type{ traits_type::to_entity(entt) / sparse_page };
+        }
+
+        [[nodiscard]] static auto offset(const Entity entt) ENTT_NOEXCEPT {
+            return size_type{ traits_type::to_entity(entt) & (sparse_page - 1) };
+        }
+
+        [[nodiscard]] auto assure_page(const std::size_t idx) {
+            if (!(idx < bucket)) {
+                const size_type sz = idx + 1u;
+                const auto mem = bucket_alloc_traits::allocate(bucket_allocator, sz);
+
+                std::uninitialized_value_construct(mem + bucket, mem + sz);
+                std::uninitialized_copy(sparse, sparse + bucket, mem);
+
+                std::destroy(sparse, sparse + bucket);
+                bucket_alloc_traits::deallocate(bucket_allocator, sparse, bucket);
+
+                sparse = mem;
+                bucket = sz;
+            }
+
+            if (!sparse[idx]) {
+                sparse[idx] = alloc_traits::allocate(allocator, sparse_page);
+                std::uninitialized_fill(sparse[idx], sparse[idx] + sparse_page, null);
+            }
+
+            return sparse[idx];
+        }
+
+        void resize_packed(const std::size_t req) {
+            ENTT_ASSERT((req != reserved) && !(req < count), "Invalid request");
+            const auto mem = alloc_traits::allocate(allocator, req);
+
+            std::uninitialized_copy(packed, packed + count, mem);
+            std::uninitialized_fill(mem + count, mem + req, tombstone);
+
+            std::destroy(packed, packed + reserved);
+            alloc_traits::deallocate(allocator, packed, reserved);
+
+            packed = mem;
+            reserved = req;
+        }
+
+        void release_memory() {
+            if (packed) {
+                for (size_type pos{}; pos < bucket; ++pos) {
+                    if (sparse[pos]) {
+                        std::destroy(sparse[pos], sparse[pos] + sparse_page);
+                        alloc_traits::deallocate(allocator, sparse[pos], sparse_page);
+                    }
+                }
+
+                std::destroy(packed, packed + reserved);
+                std::destroy(sparse, sparse + bucket);
+                alloc_traits::deallocate(allocator, packed, reserved);
+                bucket_alloc_traits::deallocate(bucket_allocator, sparse, bucket);
+            }
+        }
+
+    protected:
+        /**
+         * @brief Swaps two entities in the internal packed array.
+         * @param lhs A valid position of an entity within storage.
+         * @param rhs A valid position of an entity within storage.
+         */
+        virtual void swap_at([[maybe_unused]] const std::size_t lhs, [[maybe_unused]] const std::size_t rhs) {}
+
+        /**
+         * @brief Moves an entity in the internal packed array.
+         * @param from A valid position of an entity within storage.
+         * @param to A valid position of an entity within storage.
+         */
+        virtual void move_and_pop([[maybe_unused]] const std::size_t from, [[maybe_unused]] const std::size_t to) {}
+
+        /**
+         * @brief Attempts to erase an entity from the internal packed array.
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        virtual void swap_and_pop(const Entity entt, [[maybe_unused]] void* ud) {
+            auto& ref = sparse[page(entt)][offset(entt)];
+            const auto pos = size_type{ traits_type::to_entity(ref) };
+            ENTT_ASSERT(packed[pos] == entt, "Invalid entity identifier");
+            auto& last = packed[--count];
+
+            packed[pos] = last;
+            sparse[page(last)][offset(last)] = ref;
+            // lazy self-assignment guard
+            ref = null;
+            // unnecessary but it helps to detect nasty bugs
+            ENTT_ASSERT((last = tombstone, true), "");
+        }
+
+        /**
+         * @brief Attempts to erase an entity from the internal packed array.
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        virtual void in_place_pop(const Entity entt, [[maybe_unused]] void* ud) {
+            auto& ref = sparse[page(entt)][offset(entt)];
+            const auto pos = size_type{ traits_type::to_entity(ref) };
+            ENTT_ASSERT(packed[pos] == entt, "Invalid entity identifier");
+
+            packed[pos] = std::exchange(free_list, traits_type::construct(static_cast<typename traits_type::entity_type>(pos)));
+            // lazy self-assignment guard
+            ref = null;
+        }
+
+    public:
+        /*! @brief Allocator type. */
+        using allocator_type = typename alloc_traits::allocator_type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Pointer type to contained entities. */
+        using pointer = alloc_const_pointer;
+        /*! @brief Random access iterator type. */
+        using iterator = sparse_set_iterator;
+        /*! @brief Reverse iterator type. */
+        using reverse_iterator = std::reverse_iterator<iterator>;
+
+        /**
+         * @brief Constructs an empty container with the given policy and allocator.
+         * @param pol Type of deletion policy.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_sparse_set(deletion_policy pol, const allocator_type& alloc = {})
+            : allocator{ alloc },
+            bucket_allocator{ alloc },
+            sparse{ bucket_alloc_traits::allocate(bucket_allocator, 0u) },
+            packed{ alloc_traits::allocate(allocator, 0u) },
+            bucket{ 0u },
+            count{ 0u },
+            reserved{ 0u },
+            free_list{ tombstone },
+            mode{ pol }
+        {}
+
+        /**
+         * @brief Constructs an empty container with the given allocator.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_sparse_set(const allocator_type& alloc = {})
+            : basic_sparse_set{ deletion_policy::swap_and_pop, alloc }
+        {}
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_sparse_set(basic_sparse_set&& other) ENTT_NOEXCEPT
+            : allocator{ std::move(other.allocator) },
+            bucket_allocator{ std::move(other.bucket_allocator) },
+            sparse{ std::exchange(other.sparse, bucket_alloc_pointer{}) },
+            packed{ std::exchange(other.packed, alloc_pointer{}) },
+            bucket{ std::exchange(other.bucket, 0u) },
+            count{ std::exchange(other.count, 0u) },
+            reserved{ std::exchange(other.reserved, 0u) },
+            free_list{ std::exchange(other.free_list, tombstone) },
+            mode{ other.mode }
+        {}
+
+        /*! @brief Default destructor. */
+        virtual ~basic_sparse_set() {
+            release_memory();
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This sparse set.
+         */
+        basic_sparse_set& operator=(basic_sparse_set&& other) ENTT_NOEXCEPT {
+            release_memory();
+
+            allocator = std::move(other.allocator);
+            bucket_allocator = std::move(other.bucket_allocator);
+            sparse = std::exchange(other.sparse, bucket_alloc_pointer{});
+            packed = std::exchange(other.packed, alloc_pointer{});
+            bucket = std::exchange(other.bucket, 0u);
+            count = std::exchange(other.count, 0u);
+            reserved = std::exchange(other.reserved, 0u);
+            free_list = std::exchange(other.free_list, tombstone);
+            mode = other.mode;
+
+            return *this;
+        }
+
+        /**
+         * @brief Returns the deletion policy of a sparse set.
+         * @return The deletion policy of the sparse set.
+         */
+        [[nodiscard]] deletion_policy policy() const ENTT_NOEXCEPT {
+            return mode;
+        }
+
+        /**
+         * @brief Returns the next slot available for insertion.
+         * @return The next slot available for insertion.
+         */
+        [[nodiscard]] size_type slot() const ENTT_NOEXCEPT {
+            return free_list == null ? count : size_type{ traits_type::to_entity(free_list) };
+        }
+
+        /**
+         * @brief Increases the capacity of a sparse set.
+         *
+         * If the new capacity is greater than the current capacity, new storage is
+         * allocated, otherwise the method does nothing.
+         *
+         * @param cap Desired capacity.
+         */
+        void reserve(const size_type cap) {
+            if (cap > reserved) {
+                resize_packed(cap);
+            }
+        }
+
+        /**
+         * @brief Returns the number of elements that a sparse set has currently
+         * allocated space for.
+         * @return Capacity of the sparse set.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return reserved;
+        }
+
+        /*! @brief Requests the removal of unused capacity. */
+        void shrink_to_fit() {
+            if (count < reserved) {
+                resize_packed(count);
+            }
+        }
+
+        /**
+         * @brief Returns the extent of a sparse set.
+         *
+         * The extent of a sparse set is also the size of the internal sparse array.
+         * There is no guarantee that the internal packed array has the same size.
+         * Usually the size of the internal sparse array is equal or greater than
+         * the one of the internal packed array.
+         *
+         * @return Extent of the sparse set.
+         */
+        [[nodiscard]] size_type extent() const ENTT_NOEXCEPT {
+            return bucket * sparse_page;
+        }
+
+        /**
+         * @brief Returns the number of elements in a sparse set.
+         *
+         * The number of elements is also the size of the internal packed array.
+         * There is no guarantee that the internal sparse array has the same size.
+         * Usually the size of the internal sparse array is equal or greater than
+         * the one of the internal packed array.
+         *
+         * @return Number of elements.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return count;
+        }
+
+        /**
+         * @brief Checks whether a sparse set is empty.
+         * @return True if the sparse set is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return (count == size_type{});
+        }
+
+        /**
+         * @brief Direct access to the internal packed array.
+         * @return A pointer to the internal packed array.
+         */
+        [[nodiscard]] pointer data() const ENTT_NOEXCEPT {
+            return packed;
+        }
+
+        /**
+         * @brief Returns an iterator to the beginning.
+         *
+         * The returned iterator points to the first entity of the internal packed
+         * array. If the sparse set is empty, the returned iterator will be equal to
+         * `end()`.
+         *
+         * @return An iterator to the first entity of the internal packed array.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return iterator{ std::addressof(packed), static_cast<typename traits_type::difference_type>(count) };
+        }
+
+        /**
+         * @brief Returns an iterator to the end.
+         *
+         * The returned iterator points to the element following the last entity in
+         * the internal packed array. Attempting to dereference the returned
+         * iterator results in undefined behavior.
+         *
+         * @return An iterator to the element following the last entity of the
+         * internal packed array.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return iterator{ std::addressof(packed), {} };
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the beginning.
+         *
+         * The returned iterator points to the first entity of the reversed internal
+         * packed array. If the sparse set is empty, the returned iterator will be
+         * equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed internal packed
+         * array.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(end());
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the end.
+         *
+         * The returned iterator points to the element following the last entity in
+         * the reversed internal packed array. Attempting to dereference the
+         * returned iterator results in undefined behavior.
+         *
+         * @return An iterator to the element following the last entity of the
+         * reversed internal packed array.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(begin());
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const ENTT_NOEXCEPT {
+            return contains(entt) ? --(end() - index(entt)) : end();
+        }
+
+        /**
+         * @brief Checks if a sparse set contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the sparse set contains the entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(entt != tombstone && entt != null, "Invalid entity");
+            const auto curr = page(entt);
+            // testing versions permits to avoid accessing the packed array
+            return (curr < bucket&& sparse[curr] && sparse[curr][offset(entt)] != null);
+        }
+
+        /**
+         * @brief Returns the position of an entity in a sparse set.
+         *
+         * @warning
+         * Attempting to get the position of an entity that doesn't belong to the
+         * sparse set results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The position of the entity in the sparse set.
+         */
+        [[nodiscard]] size_type index(const entity_type entt) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(contains(entt), "Set does not contain entity");
+            return size_type{ traits_type::to_entity(sparse[page(entt)][offset(entt)]) };
+        }
+
+        /**
+         * @brief Returns the entity at specified location, with bounds checking.
+         * @param pos The position for which to return the entity.
+         * @return The entity at specified location if any, a null entity otherwise.
+         */
+        [[nodiscard]] entity_type at(const size_type pos) const ENTT_NOEXCEPT {
+            return pos < count ? packed[pos] : null;
+        }
+
+        /**
+         * @brief Returns the entity at specified location, without bounds checking.
+         * @param pos The position for which to return the entity.
+         * @return The entity at specified location.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(pos < count, "Position is out of bounds");
+            return packed[pos];
+        }
+
+        /**
+         * @brief Appends an entity to a sparse set.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the sparse set
+         * results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The slot used for insertion.
+         */
+        size_type emplace_back(const entity_type entt) {
+            ENTT_ASSERT(!contains(entt), "Set already contains entity");
+
+            if (count == reserved) {
+                const size_type sz = static_cast<size_type>(reserved * growth_factor);
+                resize_packed(sz + !(sz > reserved));
+            }
+
+            assure_page(page(entt))[offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(count));
+            packed[count] = entt;
+            return count++;
+        }
+
+        /**
+         * @brief Assigns an entity to a sparse set.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the sparse set
+         * results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The slot used for insertion.
+         */
+        size_type emplace(const entity_type entt) {
+            if (free_list == null) {
+                return emplace_back(entt);
+            }
+            else {
+                ENTT_ASSERT(!contains(entt), "Set already contains entity");
+                const auto pos = size_type{ traits_type::to_entity(free_list) };
+                sparse[page(entt)][offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(pos));
+                free_list = std::exchange(packed[pos], entt);
+                return pos;
+            }
+        }
+
+        /**
+         * @brief Assigns one or more entities to a sparse set.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the sparse set
+         * results in undefined behavior.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void insert(It first, It last) {
+            reserve(count + std::distance(first, last));
+
+            for (; first != last; ++first) {
+                const auto entt = *first;
+                ENTT_ASSERT(!contains(entt), "Set already contains entity");
+                assure_page(page(entt))[offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(count));
+                packed[count++] = entt;
+            }
+        }
+
+        /**
+         * @brief Erases an entity from a sparse set.
+         *
+         * @warning
+         * Attempting to erase an entity that doesn't belong to the sparse set
+         * results in undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        void erase(const entity_type entt, void* ud = nullptr) {
+            ENTT_ASSERT(contains(entt), "Set does not contain entity");
+            (mode == deletion_policy::in_place) ? in_place_pop(entt, ud) : swap_and_pop(entt, ud);
+        }
+
+        /**
+         * @brief Erases entities from a set.
+         *
+         * @sa erase
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        template<typename It>
+        void erase(It first, It last, void* ud = nullptr) {
+            for (; first != last; ++first) {
+                erase(*first, ud);
+            }
+        }
+
+        /**
+         * @brief Removes an entity from a sparse set if it exists.
+         * @param entt A valid entity identifier.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         * @return True if the entity is actually removed, false otherwise.
+         */
+        bool remove(const entity_type entt, void* ud = nullptr) {
+            return contains(entt) && (erase(entt, ud), true);
+        }
+
+        /**
+         * @brief Removes entities from a sparse set if they exist.
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         * @return The number of entities actually removed.
+         */
+        template<typename It>
+        size_type remove(It first, It last, void* ud = nullptr) {
+            size_type found{};
+
+            for (; first != last; ++first) {
+                found += remove(*first, ud);
+            }
+
+            return found;
+        }
+
+        /*! @brief Removes all tombstones from the packed array of a sparse set. */
+        void compact() {
+            size_type next = count;
+            for (; next && packed[next - 1u] == tombstone; --next);
+
+            for (auto* it = &free_list; *it != null && next; it = std::addressof(packed[traits_type::to_entity(*it)])) {
+                if (const size_type pos = traits_type::to_entity(*it); pos < next) {
+                    --next;
+                    move_and_pop(next, pos);
+                    std::swap(packed[next], packed[pos]);
+                    sparse[page(packed[pos])][offset(packed[pos])] = traits_type::construct(static_cast<const typename traits_type::entity_type>(pos));
+                    *it = traits_type::construct(static_cast<typename traits_type::entity_type>(next));
+                    for (; next && packed[next - 1u] == tombstone; --next);
+                }
+            }
+
+            free_list = tombstone;
+            count = next;
+        }
+
+        /**
+         * @copybrief swap_at
+         *
+         * For what it's worth, this function affects both the internal sparse array
+         * and the internal packed array. Users should not care of that anyway.
+         *
+         * @warning
+         * Attempting to swap entities that don't belong to the sparse set results
+         * in undefined behavior.
+         *
+         * @param lhs A valid entity identifier.
+         * @param rhs A valid entity identifier.
+         */
+        void swap(const entity_type lhs, const entity_type rhs) {
+            ENTT_ASSERT(contains(lhs), "Set does not contain entity");
+            ENTT_ASSERT(contains(rhs), "Set does not contain entity");
+
+            auto& entt = sparse[page(lhs)][offset(lhs)];
+            auto& other = sparse[page(rhs)][offset(rhs)];
+
+            const auto from = size_type{ traits_type::to_entity(entt) };
+            const auto to = size_type{ traits_type::to_entity(other) };
+
+            // basic no-leak guarantee (with invalid state) if swapping throws
+            swap_at(from, to);
+            std::swap(entt, other);
+            std::swap(packed[from], packed[to]);
+        }
+
+        /**
+         * @brief Sort the first count elements according to the given comparison
+         * function.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to the following:
+         *
+         * @code{.cpp}
+         * bool(const Entity, const Entity);
+         * @endcode
+         *
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function object must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param length Number of elements to sort.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort_n(const size_type length, Compare compare, Sort algo = Sort{}, Args &&... args) {
+            // basic no-leak guarantee (with invalid state) if sorting throws
+            ENTT_ASSERT(!(length > count), "Length exceeds the number of elements");
+            compact();
+
+            algo(std::make_reverse_iterator(packed + length), std::make_reverse_iterator(packed), std::move(compare), std::forward<Args>(args)...);
+
+            for (size_type pos{}; pos < length; ++pos) {
+                auto curr = pos;
+                auto next = index(packed[curr]);
+
+                while (curr != next) {
+                    const auto idx = index(packed[next]);
+                    const auto entt = packed[curr];
+
+                    swap_at(next, idx);
+                    sparse[page(entt)][offset(entt)] = traits_type::construct(static_cast<typename traits_type::entity_type>(curr));
+                    curr = std::exchange(next, idx);
+                }
+            }
+        }
+
+        /**
+         * @brief Sort all elements according to the given comparison function.
+         *
+         * @sa sort_n
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            sort_n(count, std::move(compare), std::move(algo), std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Sort entities according to their order in another sparse set.
+         *
+         * Entities that are part of both the sparse sets are ordered internally
+         * according to the order they have in `other`. All the other entities goes
+         * to the end of the list and there are no guarantees on their order.<br/>
+         * In other terms, this function can be used to impose the same order on two
+         * sets by using one of them as a master and the other one as a slave.
+         *
+         * Iterating the sparse set with a couple of iterators returns elements in
+         * the expected order after a call to `respect`. See `begin` and `end` for
+         * more details.
+         *
+         * @param other The sparse sets that imposes the order of the entities.
+         */
+        void respect(const basic_sparse_set& other) {
+            compact();
+
+            const auto to = other.end();
+            auto from = other.begin();
+
+            for (size_type pos = count - 1; pos && from != to; ++from) {
+                if (contains(*from)) {
+                    if (*from != packed[pos]) {
+                        // basic no-leak guarantee (with invalid state) if swapping throws
+                        swap(packed[pos], *from);
+                    }
+
+                    --pos;
+                }
+            }
+        }
+
+        /**
+         * @brief Clears a sparse set.
+         * @param ud Optional user data that are forwarded as-is to derived classes.
+         */
+        void clear(void* ud = nullptr) {
+            for (auto&& entity : *this) {
+                if (entity != tombstone) {
+                    in_place_pop(entity, ud);
+                }
+            }
+
+            free_list = tombstone;
+            count = 0u;
+        }
+
+    private:
+        typename alloc_traits::allocator_type allocator;
+        typename bucket_alloc_traits::allocator_type bucket_allocator;
+        bucket_alloc_pointer sparse;
+        alloc_pointer packed;
+        std::size_t bucket;
+        std::size_t count;
+        std::size_t reserved;
+        entity_type free_list;
+        deletion_policy mode;
+    };
+
+
+}
+
+
+#endif
+
+// #include "entity/storage.hpp"
+#ifndef ENTT_ENTITY_STORAGE_HPP
+#define ENTT_ENTITY_STORAGE_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/algorithm.hpp"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "../signal/sigh.hpp"
+
+// #include "component.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "sparse_set.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Basic storage implementation.
+     *
+     * This class is a refinement of a sparse set that associates an object to an
+     * entity. The main purpose of this class is to extend sparse sets to store
+     * components in a registry. It guarantees fast access both to the elements and
+     * to the entities.
+     *
+     * @note
+     * Entities and objects have the same order.
+     *
+     * @note
+     * Internal data structures arrange elements to maximize performance. There are
+     * no guarantees that objects are returned in the insertion order when iterate
+     * a storage. Do not make assumption on the order in any case.
+     *
+     * @warning
+     * Empty types aren't explicitly instantiated. Therefore, many of the functions
+     * normally available for non-empty types will not be available for empty ones.
+     *
+     * @sa sparse_set<Entity>
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Type of objects assigned to the entities.
+     * @tparam Allocator Type of allocator used to manage memory and elements.
+     */
+    template<typename Entity, typename Type, typename Allocator, typename = void>
+    class basic_storage_impl : public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>> {
+        static constexpr auto packed_page = ENTT_PACKED_PAGE;
+
+        using comp_traits = component_traits<Type>;
+
+        using underlying_type = basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>>;
+        using difference_type = typename entt_traits<Entity>::difference_type;
+
+        using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
+        using alloc_pointer = typename alloc_traits::pointer;
+        using alloc_const_pointer = typename alloc_traits::const_pointer;
+
+        using bucket_alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<alloc_pointer>;
+        using bucket_alloc_pointer = typename bucket_alloc_traits::pointer;
+
+        using bucket_alloc_const_type = typename std::allocator_traits<Allocator>::template rebind_alloc<alloc_const_pointer>;
+        using bucket_alloc_const_pointer = typename std::allocator_traits<bucket_alloc_const_type>::const_pointer;
+
+        static_assert(alloc_traits::propagate_on_container_move_assignment::value);
+        static_assert(bucket_alloc_traits::propagate_on_container_move_assignment::value);
+
+        template<typename Value>
+        struct storage_iterator final {
+            using difference_type = typename basic_storage_impl::difference_type;
+            using value_type = Value;
+            using pointer = value_type*;
+            using reference = value_type&;
+            using iterator_category = std::random_access_iterator_tag;
+
+            storage_iterator() ENTT_NOEXCEPT = default;
+
+            storage_iterator(bucket_alloc_pointer const* ref, const typename basic_storage_impl::difference_type idx) ENTT_NOEXCEPT
+                : packed{ ref },
+                index{ idx }
+            {}
+
+            storage_iterator& operator++() ENTT_NOEXCEPT {
+                return --index, * this;
+            }
+
+            storage_iterator operator++(int) ENTT_NOEXCEPT {
+                storage_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            storage_iterator& operator--() ENTT_NOEXCEPT {
+                return ++index, * this;
+            }
+
+            storage_iterator operator--(int) ENTT_NOEXCEPT {
+                storage_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            storage_iterator& operator+=(const difference_type value) ENTT_NOEXCEPT {
+                index -= value;
+                return *this;
+            }
+
+            storage_iterator operator+(const difference_type value) const ENTT_NOEXCEPT {
+                storage_iterator copy = *this;
+                return (copy += value);
+            }
+
+            storage_iterator& operator-=(const difference_type value) ENTT_NOEXCEPT {
+                return (*this += -value);
+            }
+
+            storage_iterator operator-(const difference_type value) const ENTT_NOEXCEPT {
+                return (*this + -value);
+            }
+
+            difference_type operator-(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return other.index - index;
+            }
+
+            [[nodiscard]] reference operator[](const difference_type value) const ENTT_NOEXCEPT {
+                const auto pos = size_type(index - value - 1);
+                return (*packed)[page(pos)][offset(pos)];
+            }
+
+            [[nodiscard]] bool operator==(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return other.index == index;
+            }
+
+            [[nodiscard]] bool operator!=(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] bool operator<(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return index > other.index;
+            }
+
+            [[nodiscard]] bool operator>(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return index < other.index;
+            }
+
+            [[nodiscard]] bool operator<=(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this > other);
+            }
+
+            [[nodiscard]] bool operator>=(const storage_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this < other);
+            }
+
+            [[nodiscard]] pointer operator->() const ENTT_NOEXCEPT {
+                const auto pos = size_type(index - 1u);
+                return std::addressof((*packed)[page(pos)][offset(pos)]);
+            }
+
+            [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                return *operator->();
+            }
+
+        private:
+            bucket_alloc_pointer const* packed;
+            difference_type index;
+        };
+
+        [[nodiscard]] static auto page(const std::size_t pos) ENTT_NOEXCEPT {
+            return pos / packed_page;
+        }
+
+        [[nodiscard]] static auto offset(const std::size_t pos) ENTT_NOEXCEPT {
+            return pos & (packed_page - 1);
+        }
+
+        void release_memory() {
+            if (packed) {
+                // no-throw stable erase iteration
+                underlying_type::clear();
+
+                for (size_type pos{}; pos < bucket; ++pos) {
+                    alloc_traits::deallocate(allocator, packed[pos], packed_page);
+                    bucket_alloc_traits::destroy(bucket_allocator, std::addressof(packed[pos]));
+                }
+
+                bucket_alloc_traits::deallocate(bucket_allocator, packed, bucket);
+            }
+        }
+
+        void assure_at_least(const std::size_t last) {
+            if (const auto idx = page(last - 1u); !(idx < bucket)) {
+                const size_type sz = idx + 1u;
+                const auto mem = bucket_alloc_traits::allocate(bucket_allocator, sz);
+                std::uninitialized_copy(packed, packed + bucket, mem);
+                size_type pos{};
+
+                ENTT_TRY{
+                    for (pos = bucket; pos < sz; ++pos) {
+                        auto pg = alloc_traits::allocate(allocator, packed_page);
+                        bucket_alloc_traits::construct(bucket_allocator, std::addressof(mem[pos]), pg);
+                    }
+                } ENTT_CATCH{
+                    for (auto next = bucket; next < pos; ++next) {
+                        alloc_traits::deallocate(allocator, mem[next], packed_page);
+                    }
+
+                    std::destroy(mem, mem + pos);
+                    bucket_alloc_traits::deallocate(bucket_allocator, mem, sz);
+                    ENTT_THROW;
+                }
+
+                std::destroy(packed, packed + bucket);
+                bucket_alloc_traits::deallocate(bucket_allocator, packed, bucket);
+
+                packed = mem;
+                bucket = sz;
+            }
+        }
+
+        void release_unused_pages() {
+            if (const auto length = underlying_type::size() / packed_page; length < bucket) {
+                const auto mem = bucket_alloc_traits::allocate(bucket_allocator, length);
+                std::uninitialized_copy(packed, packed + length, mem);
+
+                for (auto pos = length; pos < bucket; ++pos) {
+                    alloc_traits::deallocate(allocator, packed[pos], packed_page);
+                    bucket_alloc_traits::destroy(bucket_allocator, std::addressof(packed[pos]));
+                }
+
+                bucket_alloc_traits::deallocate(bucket_allocator, packed, bucket);
+
+                packed = mem;
+                bucket = length;
+            }
+        }
+
+        template<typename... Args>
+        auto& push_at(const std::size_t pos, Args &&... args) {
+            ENTT_ASSERT(pos < (bucket* packed_page), "Out of bounds index");
+            auto* instance = std::addressof(packed[page(pos)][offset(pos)]);
+
+            if constexpr (std::is_aggregate_v<value_type>) {
+                alloc_traits::construct(allocator, instance, Type{ std::forward<Args>(args)... });
+            }
+            else {
+                alloc_traits::construct(allocator, instance, std::forward<Args>(args)...);
+            }
+
+            return *instance;
+        }
+
+        void pop_at(const std::size_t pos) {
+            alloc_traits::destroy(allocator, std::addressof(packed[page(pos)][offset(pos)]));
+        }
+
+    protected:
+        /*! @copydoc basic_sparse_set::swap_at */
+        void swap_at(const std::size_t lhs, const std::size_t rhs) final {
+            std::swap(packed[page(lhs)][offset(lhs)], packed[page(rhs)][offset(rhs)]);
+        }
+
+        /*! @copydoc basic_sparse_set::move_and_pop */
+        void move_and_pop(const std::size_t from, const std::size_t to) final {
+            push_at(to, std::move(packed[page(from)][offset(from)]));
+            pop_at(from);
+        }
+
+        /*! @copydoc basic_sparse_set::swap_and_pop */
+        void swap_and_pop(const Entity entt, void* ud) override {
+            const auto pos = underlying_type::index(entt);
+            const auto last = underlying_type::size() - 1u;
+            auto&& elem = packed[page(pos)][offset(pos)];
+
+            // support for nosy destructors
+            [[maybe_unused]] auto unused = std::move(elem);
+            elem = std::move(packed[page(last)][offset(last)]);
+            pop_at(last);
+
+            underlying_type::swap_and_pop(entt, ud);
+        }
+
+        /*! @copydoc basic_sparse_set::in_place_pop */
+        void in_place_pop(const Entity entt, void* ud) override {
+            const auto pos = underlying_type::index(entt);
+            underlying_type::in_place_pop(entt, ud);
+            // support for nosy destructors
+            pop_at(pos);
+        }
+
+    public:
+        /*! @brief Allocator type. */
+        using allocator_type = typename alloc_traits::allocator_type;
+        /*! @brief Type of the objects assigned to entities. */
+        using value_type = Type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Pointer type to contained elements. */
+        using pointer = bucket_alloc_pointer;
+        /*! @brief Constant pointer type to contained elements. */
+        using const_pointer = bucket_alloc_const_pointer;
+        /*! @brief Random access iterator type. */
+        using iterator = storage_iterator<value_type>;
+        /*! @brief Constant random access iterator type. */
+        using const_iterator = storage_iterator<const value_type>;
+        /*! @brief Reverse iterator type. */
+        using reverse_iterator = std::reverse_iterator<iterator>;
+        /*! @brief Constant reverse iterator type. */
+        using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+        /**
+         * @brief Default constructor.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_storage_impl(const allocator_type& alloc = {})
+            : underlying_type{ deletion_policy{comp_traits::in_place_delete::value}, alloc },
+            allocator{ alloc },
+            bucket_allocator{ alloc },
+            packed{ bucket_alloc_traits::allocate(bucket_allocator, 0u) },
+            bucket{}
+        {}
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_storage_impl(basic_storage_impl&& other) ENTT_NOEXCEPT
+            : underlying_type{ std::move(other) },
+            allocator{ std::move(other.allocator) },
+            bucket_allocator{ std::move(other.bucket_allocator) },
+            packed{ std::exchange(other.packed, bucket_alloc_pointer{}) },
+            bucket{ std::exchange(other.bucket, 0u) }
+        {}
+
+        /*! @brief Default destructor. */
+        ~basic_storage_impl() override {
+            release_memory();
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This sparse set.
+         */
+        basic_storage_impl& operator=(basic_storage_impl&& other) ENTT_NOEXCEPT {
+            release_memory();
+
+            underlying_type::operator=(std::move(other));
+
+            allocator = std::move(other.allocator);
+            bucket_allocator = std::move(other.bucket_allocator);
+            packed = std::exchange(other.packed, bucket_alloc_pointer{});
+            bucket = std::exchange(other.bucket, 0u);
+
+            return *this;
+        }
+
+        /**
+         * @brief Increases the capacity of a storage.
+         *
+         * If the new capacity is greater than the current capacity, new storage is
+         * allocated, otherwise the method does nothing.
+         *
+         * @param cap Desired capacity.
+         */
+        void reserve(const size_type cap) {
+            underlying_type::reserve(cap);
+
+            if (cap > underlying_type::size()) {
+                assure_at_least(cap);
+            }
+        }
+
+        /**
+         * @brief Returns the number of elements that a storage has currently
+         * allocated space for.
+         * @return Capacity of the storage.
+         */
+        [[nodiscard]] size_type capacity() const ENTT_NOEXCEPT {
+            return bucket * packed_page;
+        }
+
+        /*! @brief Requests the removal of unused capacity. */
+        void shrink_to_fit() {
+            underlying_type::shrink_to_fit();
+            release_unused_pages();
+        }
+
+        /**
+         * @brief Direct access to the array of objects.
+         * @return A pointer to the array of objects.
+         */
+        [[nodiscard]] const_pointer raw() const ENTT_NOEXCEPT {
+            return packed;
+        }
+
+        /*! @copydoc raw */
+        [[nodiscard]] pointer raw() ENTT_NOEXCEPT {
+            return packed;
+        }
+
+        /**
+         * @brief Returns an iterator to the beginning.
+         *
+         * The returned iterator points to the first instance of the internal array.
+         * If the storage is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first instance of the internal array.
+         */
+        [[nodiscard]] const_iterator cbegin() const ENTT_NOEXCEPT {
+            const difference_type pos = underlying_type::size();
+            return const_iterator{ std::addressof(packed), pos };
+        }
+
+        /*! @copydoc cbegin */
+        [[nodiscard]] const_iterator begin() const ENTT_NOEXCEPT {
+            return cbegin();
+        }
+
+        /*! @copydoc begin */
+        [[nodiscard]] iterator begin() ENTT_NOEXCEPT {
+            const difference_type pos = underlying_type::size();
+            return iterator{ std::addressof(packed), pos };
+        }
+
+        /**
+         * @brief Returns an iterator to the end.
+         *
+         * The returned iterator points to the element following the last instance
+         * of the internal array. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the element following the last instance of the
+         * internal array.
+         */
+        [[nodiscard]] const_iterator cend() const ENTT_NOEXCEPT {
+            return const_iterator{ std::addressof(packed), {} };
+        }
+
+        /*! @copydoc cend */
+        [[nodiscard]] const_iterator end() const ENTT_NOEXCEPT {
+            return cend();
+        }
+
+        /*! @copydoc end */
+        [[nodiscard]] iterator end() ENTT_NOEXCEPT {
+            return iterator{ std::addressof(packed), {} };
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the beginning.
+         *
+         * The returned iterator points to the first instance of the reversed
+         * internal array. If the storage is empty, the returned iterator will be
+         * equal to `rend()`.
+         *
+         * @return An iterator to the first instance of the reversed internal array.
+         */
+        [[nodiscard]] const_reverse_iterator crbegin() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(cend());
+        }
+
+        /*! @copydoc crbegin */
+        [[nodiscard]] const_reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return crbegin();
+        }
+
+        /*! @copydoc rbegin */
+        [[nodiscard]] reverse_iterator rbegin() ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(end());
+        }
+
+        /**
+         * @brief Returns a reverse iterator to the end.
+         *
+         * The returned iterator points to the element following the last instance
+         * of the reversed internal array. Attempting to dereference the returned
+         * iterator results in undefined behavior.
+         *
+         * @return An iterator to the element following the last instance of the
+         * reversed internal array.
+         */
+        [[nodiscard]] const_reverse_iterator crend() const ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(cbegin());
+        }
+
+        /*! @copydoc crend */
+        [[nodiscard]] const_reverse_iterator rend() const ENTT_NOEXCEPT {
+            return crend();
+        }
+
+        /*! @copydoc rend */
+        [[nodiscard]] reverse_iterator rend() ENTT_NOEXCEPT {
+            return std::make_reverse_iterator(begin());
+        }
+
+        /**
+         * @brief Returns the object assigned to an entity.
+         *
+         * @warning
+         * Attempting to use an entity that doesn't belong to the storage results in
+         * undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         * @return The object assigned to the entity.
+         */
+        [[nodiscard]] const value_type& get(const entity_type entt) const ENTT_NOEXCEPT {
+            const auto idx = underlying_type::index(entt);
+            return packed[page(idx)][offset(idx)];
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] value_type& get(const entity_type entt) ENTT_NOEXCEPT {
+            return const_cast<value_type&>(std::as_const(*this).get(entt));
+        }
+
+        /**
+         * @brief Assigns an entity to a storage and constructs its object.
+         *
+         * This version accept both types that can be constructed in place directly
+         * and types like aggregates that do not work well with a placement new as
+         * performed usually under the hood during an _emplace back_.
+         *
+         * @warning
+         * Attempting to use an entity that already belongs to the storage results
+         * in undefined behavior.
+         *
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to construct an object for the entity.
+         * @return A reference to the newly created object.
+         */
+        template<typename... Args>
+        value_type& emplace(const entity_type entt, Args &&... args) {
+            const auto pos = underlying_type::slot();
+            assure_at_least(pos + 1u);
+
+            auto& value = push_at(pos, std::forward<Args>(args)...);
+
+            ENTT_TRY{
+                [[maybe_unused]] const auto curr = underlying_type::emplace(entt);
+                ENTT_ASSERT(pos == curr, "Misplaced component");
+            } ENTT_CATCH{
+                pop_at(pos);
+                ENTT_THROW;
+            }
+
+            return value;
+        }
+
+        /**
+         * @brief Updates the instance assigned to a given entity in-place.
+         * @tparam Func Types of the function objects to invoke.
+         * @param entt A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the updated instance.
+         */
+        template<typename... Func>
+        decltype(auto) patch(const entity_type entt, Func &&... func) {
+            const auto idx = underlying_type::index(entt);
+            auto&& elem = packed[page(idx)][offset(idx)];
+            (std::forward<Func>(func)(elem), ...);
+            return elem;
+        }
+
+        /**
+         * @brief Assigns one or more entities to a storage and constructs their
+         * objects from a given instance.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the storage
+         * results in undefined behavior.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param value An instance of the object to construct.
+         */
+        template<typename It>
+        void insert(It first, It last, const value_type& value = {}) {
+            const auto cap = underlying_type::size() + std::distance(first, last);
+            underlying_type::reserve(cap);
+            assure_at_least(cap);
+
+            for (; first != last; ++first) {
+                push_at(underlying_type::size(), value);
+
+                ENTT_TRY{
+                    underlying_type::emplace_back(*first);
+                } ENTT_CATCH{
+                    pop_at(underlying_type::size());
+                    ENTT_THROW;
+                }
+            }
+        }
+
+        /**
+         * @brief Assigns one or more entities to a storage and constructs their
+         * objects from a given range.
+         *
+         * @sa construct
+         *
+         * @tparam EIt Type of input iterator.
+         * @tparam CIt Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param from An iterator to the first element of the range of objects.
+         */
+        template<typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<std::decay_t<typename std::iterator_traits<CIt>::value_type>, value_type>>>
+        void insert(EIt first, EIt last, CIt from) {
+            const auto cap = underlying_type::size() + std::distance(first, last);
+            underlying_type::reserve(cap);
+            assure_at_least(cap);
+
+            for (; first != last; ++first, ++from) {
+                push_at(underlying_type::size(), *from);
+
+                ENTT_TRY{
+                    underlying_type::emplace_back(*first);
+                } ENTT_CATCH{
+                    pop_at(underlying_type::size());
+                    ENTT_THROW;
+                }
+            }
+        }
+
+        /**
+         * @brief Sort elements according to the given comparison function.
+         *
+         * The comparison function object must return `true` if the first element
+         * is _less_ than the second one, `false` otherwise. The signature of the
+         * comparison function should be equivalent to one of the following:
+         *
+         * @code{.cpp}
+         * bool(const Entity, const Entity);
+         * bool(const Type &, const Type &);
+         * @endcode
+         *
+         * Moreover, the comparison function object shall induce a
+         * _strict weak ordering_ on the values.
+         *
+         * The sort function oject must offer a member function template
+         * `operator()` that accepts three arguments:
+         *
+         * * An iterator to the first element of the range to sort.
+         * * An iterator past the last element of the range to sort.
+         * * A comparison function to use to compare the elements.
+         *
+         * @warning
+         * Empty types are never instantiated. Therefore, only comparison function
+         * objects that require to return entities rather than components are
+         * accepted.
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param length Number of elements to sort.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort_n(const size_type length, Compare compare, Sort algo = Sort{}, Args &&... args) {
+            if constexpr (std::is_invocable_v<Compare, const value_type&, const value_type&>) {
+                underlying_type::sort_n(length, [this, compare = std::move(compare)](const auto lhs, const auto rhs) {
+                    const auto ilhs = underlying_type::index(lhs), irhs = underlying_type::index(rhs);
+                    return compare(std::as_const(packed[page(ilhs)][offset(ilhs)]), std::as_const(packed[page(irhs)][offset(irhs)]));
+                }, std::move(algo), std::forward<Args>(args)...);
+            }
+            else {
+                underlying_type::sort_n(length, std::move(compare), std::move(algo), std::forward<Args>(args)...);
+            }
+        }
+
+        /**
+         * @brief Sort all elements according to the given comparison function.
+         *
+         * @sa sort_n
+         *
+         * @tparam Compare Type of comparison function object.
+         * @tparam Sort Type of sort function object.
+         * @tparam Args Types of arguments to forward to the sort function object.
+         * @param compare A valid comparison function object.
+         * @param algo A valid sort function object.
+         * @param args Arguments to forward to the sort function object, if any.
+         */
+        template<typename Compare, typename Sort = std_sort, typename... Args>
+        void sort(Compare compare, Sort algo = Sort{}, Args &&... args) {
+            sort_n(underlying_type::size(), std::move(compare), std::move(algo), std::forward<Args>(args)...);
+        }
+
+    private:
+        typename alloc_traits::allocator_type allocator;
+        typename bucket_alloc_traits::allocator_type bucket_allocator;
+        bucket_alloc_pointer packed;
+        size_type bucket;
+    };
+
+
+    /*! @copydoc basic_storage_impl */
+    template<typename Entity, typename Type, typename Allocator>
+    class basic_storage_impl<Entity, Type, Allocator, std::enable_if_t<component_traits<Type>::ignore_if_empty::value&& std::is_empty_v<Type>>>
+        : public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>>
+    {
+        using comp_traits = component_traits<Type>;
+        using underlying_type = basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>>;
+        using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
+
+    public:
+        /*! @brief Allocator type. */
+        using allocator_type = typename alloc_traits::allocator_type;
+        /*! @brief Type of the objects assigned to entities. */
+        using value_type = Type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+
+        /**
+         * @brief Default constructor.
+         * @param alloc Allocator to use (possibly default-constructed).
+         */
+        explicit basic_storage_impl(const allocator_type& alloc = {})
+            : underlying_type{ deletion_policy{comp_traits::in_place_delete::value}, alloc }
+        {}
+
+        /**
+         * @brief Fake get function.
+         *
+         * @warning
+         * Attempting to use an entity that doesn't belong to the storage results in
+         * undefined behavior.
+         *
+         * @param entt A valid entity identifier.
+         */
+        void get([[maybe_unused]] const entity_type entt) const ENTT_NOEXCEPT {
+            ENTT_ASSERT(underlying_type::contains(entt), "Storage does not contain entity");
+        }
+
+        /**
+         * @brief Assigns an entity to a storage and constructs its object.
+         *
+         * @warning
+         * Attempting to use an entity that already belongs to the storage results
+         * in undefined behavior.
+         *
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to construct an object for the entity.
+         */
+        template<typename... Args>
+        void emplace(const entity_type entt, Args &&... args) {
+            [[maybe_unused]] value_type instance{ std::forward<Args>(args)... };
+            underlying_type::emplace(entt);
+        }
+
+        /**
+        * @brief Updates the instance assigned to a given entity in-place.
+        * @tparam Func Types of the function objects to invoke.
+        * @param entt A valid entity identifier.
+        * @param func Valid function objects.
+        */
+        template<typename... Func>
+        void patch([[maybe_unused]] const entity_type entt, Func &&... func) {
+            ENTT_ASSERT(underlying_type::contains(entt), "Storage does not contain entity");
+            (std::forward<Func>(func)(), ...);
+        }
+
+        /**
+         * @brief Assigns one or more entities to a storage.
+         *
+         * @warning
+         * Attempting to assign an entity that already belongs to the storage
+         * results in undefined behavior.
+         *
+         * @tparam It Type of input iterator.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         */
+        template<typename It>
+        void insert(It first, It last, const value_type & = {}) {
+            underlying_type::insert(first, last);
+        }
+    };
+
+
+    /**
+     * @brief Mixin type to use to wrap basic storage classes.
+     * @tparam Type The type of the underlying storage.
+     */
+    template<typename Type>
+    struct storage_adapter_mixin : Type {
+        static_assert(std::is_same_v<typename Type::value_type, std::decay_t<typename Type::value_type>>, "Invalid object type");
+
+        /*! @brief Type of the objects assigned to entities. */
+        using value_type = typename Type::value_type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = typename Type::entity_type;
+
+        /*! @brief Inherited constructors. */
+        using Type::Type;
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to initialize the object.
+         * @return A reference to the newly created object.
+         */
+        template<typename... Args>
+        decltype(auto) emplace(basic_registry<entity_type>&, const entity_type entt, Args &&... args) {
+            return Type::emplace(entt, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam It Type of input iterator.
+         * @tparam Args Types of arguments to use to construct the objects assigned
+         * to the entities.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param args Parameters to use to initialize the objects assigned to the
+         * entities.
+         */
+        template<typename It, typename... Args>
+        void insert(basic_registry<entity_type>&, It first, It last, Args &&... args) {
+            Type::insert(first, last, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Patches the given instance for an entity.
+         * @tparam Func Types of the function objects to invoke.
+         * @param entt A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the patched instance.
+         */
+        template<typename... Func>
+        decltype(auto) patch(basic_registry<entity_type>&, const entity_type entt, Func &&... func) {
+            return Type::patch(entt, std::forward<Func>(func)...);
+        }
+    };
+
+
+    /**
+     * @brief Mixin type to use to add signal support to storage types.
+     * @tparam Type The type of the underlying storage.
+     */
+    template<typename Type>
+    class sigh_storage_mixin final : public Type {
+        /*! @copydoc basic_sparse_set::swap_and_pop */
+        void swap_and_pop(const typename Type::entity_type entt, void* ud) final {
+            ENTT_ASSERT(ud != nullptr, "Invalid pointer to registry");
+            destruction.publish(*static_cast<basic_registry<typename Type::entity_type> *>(ud), entt);
+            Type::swap_and_pop(entt, ud);
+        }
+
+        /*! @copydoc basic_sparse_set::in_place_pop */
+        void in_place_pop(const typename Type::entity_type entt, void* ud) final {
+            ENTT_ASSERT(ud != nullptr, "Invalid pointer to registry");
+            destruction.publish(*static_cast<basic_registry<typename Type::entity_type> *>(ud), entt);
+            Type::in_place_pop(entt, ud);
+        }
+
+    public:
+        /*! @brief Underlying value type. */
+        using value_type = typename Type::value_type;
+        /*! @brief Underlying entity identifier. */
+        using entity_type = typename Type::entity_type;
+
+        /*! @brief Inherited constructors. */
+        using Type::Type;
+
+        /**
+         * @brief Returns a sink object.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever a new instance is created and assigned to an entity.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<entity_type> &, entity_type);
+         * @endcode
+         *
+         * Listeners are invoked **after** the object has been assigned to the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @return A temporary sink object.
+         */
+        [[nodiscard]] auto on_construct() ENTT_NOEXCEPT {
+            return sink{ construction };
+        }
+
+        /**
+         * @brief Returns a sink object.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance is explicitly updated.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<entity_type> &, entity_type);
+         * @endcode
+         *
+         * Listeners are invoked **after** the object has been updated.
+         *
+         * @sa sink
+         *
+         * @return A temporary sink object.
+         */
+        [[nodiscard]] auto on_update() ENTT_NOEXCEPT {
+            return sink{ update };
+        }
+
+        /**
+         * @brief Returns a sink object.
+         *
+         * The sink returned by this function can be used to receive notifications
+         * whenever an instance is removed from an entity and thus destroyed.<br/>
+         * The function type for a listener is equivalent to:
+         *
+         * @code{.cpp}
+         * void(basic_registry<entity_type> &, entity_type);
+         * @endcode
+         *
+         * Listeners are invoked **before** the object has been removed from the
+         * entity.
+         *
+         * @sa sink
+         *
+         * @return A temporary sink object.
+         */
+        [[nodiscard]] auto on_destroy() ENTT_NOEXCEPT {
+            return sink{ destruction };
+        }
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam Args Types of arguments to use to construct the object.
+         * @param owner The registry that issued the request.
+         * @param entt A valid entity identifier.
+         * @param args Parameters to use to initialize the object.
+         * @return A reference to the newly created object.
+         */
+        template<typename... Args>
+        decltype(auto) emplace(basic_registry<entity_type>& owner, const entity_type entt, Args &&... args) {
+            Type::emplace(entt, std::forward<Args>(args)...);
+            construction.publish(owner, entt);
+            return this->get(entt);
+        }
+
+        /**
+         * @brief Assigns entities to a storage.
+         * @tparam It Type of input iterator.
+         * @tparam Args Types of arguments to use to construct the objects assigned
+         * to the entities.
+         * @param owner The registry that issued the request.
+         * @param first An iterator to the first element of the range of entities.
+         * @param last An iterator past the last element of the range of entities.
+         * @param args Parameters to use to initialize the objects assigned to the
+         * entities.
+         */
+        template<typename It, typename... Args>
+        void insert(basic_registry<entity_type>& owner, It first, It last, Args &&... args) {
+            Type::insert(first, last, std::forward<Args>(args)...);
+
+            if (!construction.empty()) {
+                for (; first != last; ++first) {
+                    construction.publish(owner, *first);
+                }
+            }
+        }
+
+        /**
+         * @brief Patches the given instance for an entity.
+         * @tparam Func Types of the function objects to invoke.
+         * @param owner The registry that issued the request.
+         * @param entt A valid entity identifier.
+         * @param func Valid function objects.
+         * @return A reference to the patched instance.
+         */
+        template<typename... Func>
+        decltype(auto) patch(basic_registry<entity_type>& owner, const entity_type entt, Func &&... func) {
+            Type::patch(entt, std::forward<Func>(func)...);
+            update.publish(owner, entt);
+            return this->get(entt);
+        }
+
+    private:
+        sigh<void(basic_registry<entity_type>&, const entity_type)> construction{};
+        sigh<void(basic_registry<entity_type>&, const entity_type)> destruction{};
+        sigh<void(basic_registry<entity_type>&, const entity_type)> update{};
+    };
+
+
+    /**
+     * @brief Storage implementation dispatcher.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Type of objects assigned to the entities.
+     * @tparam Allocator Type of allocator used to manage memory and elements.
+     */
+    template<typename Entity, typename Type, typename Allocator>
+    struct basic_storage : basic_storage_impl<Entity, Type, Allocator> {
+        using basic_storage_impl<Entity, Type, Allocator>::basic_storage_impl;
+    };
+
+
+    /**
+     * @brief Provides a common way to access certain properties of storage types.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Type Type of objects managed by the storage class.
+     */
+    template<typename Entity, typename Type, typename = void>
+    struct storage_traits {
+        /*! @brief Resulting type after component-to-storage conversion. */
+        using storage_type = sigh_storage_mixin<basic_storage<Entity, Type>>;
+    };
+
+
+    /**
+     * @brief Gets the element assigned to an entity from a storage, if any.
+     * @tparam Type Storage type.
+     * @param container A valid instance of a storage class.
+     * @param entt A valid entity identifier.
+     * @return A possibly empty tuple containing the requested element.
+     */
+    template<typename Type>
+    [[nodiscard]] auto get_as_tuple([[maybe_unused]] Type& container, [[maybe_unused]] const typename Type::entity_type entt) {
+        static_assert(std::is_same_v<std::remove_const_t<Type>, typename storage_traits<typename Type::entity_type, typename Type::value_type>::storage_type>, "Invalid storage");
+
+        if constexpr (std::is_void_v<decltype(container.get({})) > ) {
+            return std::make_tuple();
+        }
+        else {
+            return std::forward_as_tuple(container.get(entt));
+        }
+    }
+
+
+}
+
+
+#endif
+
+// #include "entity/utility.hpp"
+#ifndef ENTT_ENTITY_UTILITY_HPP
+#define ENTT_ENTITY_UTILITY_HPP
+
+
+// #include "../core/type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Alias for exclusion lists.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    struct exclude_t : type_list<Type...> {};
+
+
+    /**
+     * @brief Variable template for exclusion lists.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    inline constexpr exclude_t<Type...> exclude{};
+
+
+    /**
+     * @brief Alias for lists of observed components.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    struct get_t : type_list<Type...> {};
+
+
+    /**
+     * @brief Variable template for lists of observed components.
+     * @tparam Type List of types.
+     */
+    template<typename... Type>
+    inline constexpr get_t<Type...> get{};
+
+
+}
+
+
+#endif
+
+// #include "entity/view.hpp"
+#ifndef ENTT_ENTITY_VIEW_HPP
+#define ENTT_ENTITY_VIEW_HPP
+
+
+#include <iterator>
+#include <array>
+#include <tuple>
+#include <utility>
+#include <algorithm>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "component.hpp"
+
+// #include "entity.hpp"
+
+// #include "fwd.hpp"
+
+// #include "sparse_set.hpp"
+
+// #include "storage.hpp"
+
+// #include "utility.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Policy, typename It, std::size_t AllOf, std::size_t NoneOf>
+        class view_iterator final {
+            using basic_common_type = basic_sparse_set<typename std::iterator_traits<It>::value_type>;
+
+            [[nodiscard]] bool valid() const {
+                const auto entt = *it;
+                return Policy::accept(entt)
+                    && std::apply([entt](const auto *... curr) { return (curr->contains(entt) && ...); }, pools)
+                    && std::apply([entt](const auto *... curr) { return (!curr->contains(entt) && ...); }, filter);
+            }
+
+        public:
+            using iterator_type = It;
+            using difference_type = typename std::iterator_traits<It>::difference_type;
+            using value_type = typename std::iterator_traits<It>::value_type;
+            using pointer = typename std::iterator_traits<It>::pointer;
+            using reference = typename std::iterator_traits<It>::reference;
+            using iterator_category = std::bidirectional_iterator_tag;
+
+            view_iterator() ENTT_NOEXCEPT
+                : first{},
+                last{},
+                it{},
+                pools{},
+                filter{}
+            {}
+
+            view_iterator(It from, It to, It curr, std::array<const basic_common_type*, AllOf> all_of, std::array<const basic_common_type*, NoneOf> none_of) ENTT_NOEXCEPT
+                : first{ from },
+                last{ to },
+                it{ curr },
+                pools{ all_of },
+                filter{ none_of }
+            {
+                if (it != last && !valid()) {
+                    ++(*this);
+                }
+            }
+
+            view_iterator& operator++() ENTT_NOEXCEPT {
+                while (++it != last && !valid());
+                return *this;
+            }
+
+            view_iterator operator++(int) ENTT_NOEXCEPT {
+                view_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            view_iterator& operator--() ENTT_NOEXCEPT {
+                while (--it != first && !valid());
+                return *this;
+            }
+
+            view_iterator operator--(int) ENTT_NOEXCEPT {
+                view_iterator orig = *this;
+                return operator--(), orig;
+            }
+
+            [[nodiscard]] bool operator==(const view_iterator& other) const ENTT_NOEXCEPT {
+                return other.it == it;
+            }
+
+            [[nodiscard]] bool operator!=(const view_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+            [[nodiscard]] pointer operator->() const {
+                return &*it;
+            }
+
+            [[nodiscard]] reference operator*() const {
+                return *operator->();
+            }
+
+        private:
+            It first;
+            It last;
+            It it;
+            std::array<const basic_common_type*, AllOf> pools;
+            std::array<const basic_common_type*, NoneOf> filter;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Stable storage policy, aimed at pointer stability. */
+    struct stable_storage_policy {
+        /**
+        * @cond TURN_OFF_DOXYGEN
+        * Internal details not to be documented.
+        */
+        template<typename Entity>
+        [[nodiscard]] static constexpr bool accept(const Entity entity) ENTT_NOEXCEPT {
+            return entity != tombstone;
+        }
+        /**
+        * Internal details not to be documented.
+        * @endcond
+        */
+    };
+
+
+    /*! @brief Packed storage policy, aimed at faster linear iteration. */
+    struct packed_storage_policy {
+        /**
+        * @cond TURN_OFF_DOXYGEN
+        * Internal details not to be documented.
+        */
+        template<typename Entity>
+        [[nodiscard]] static constexpr bool accept(const Entity) ENTT_NOEXCEPT {
+            return true;
+        }
+        /**
+        * Internal details not to be documented.
+        * @endcond
+        */
+    };
+
+
+    /**
+     * @brief View implementation.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error, but for a few reasonable cases.
+     */
+    template<typename...>
+    class basic_view_impl;
+
+
+    /*! @brief View implementation dispatcher. */
+    template<typename...>
+    struct basic_view;
+
+
+    /**
+     * @brief Multi component view.
+     *
+     * Multi component views iterate over those entities that have at least all the
+     * given components in their bags. During initialization, a multi component view
+     * looks at the number of entities available for each component and uses the
+     * smallest set in order to get a performance boost when iterate.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given components are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, if one of the
+     *   given components is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pools iterated by the view in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Views share references to the underlying data structures of the registry that
+     * generated them. Therefore any change to the entities and to the components
+     * made by means of the registry are immediately reflected by views.
+     *
+     * @warning
+     * Lifetime of a view must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a view results in undefined behavior.
+     *
+     * @tparam Policy Common (stricter) storage policy.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the view.
+     * @tparam Component Types of components iterated by the view.
+     */
+    template<typename Policy, typename Entity, typename... Exclude, typename... Component>
+    class basic_view_impl<Policy, Entity, exclude_t<Exclude...>, Component...> {
+        using basic_common_type = basic_sparse_set<Entity>;
+
+        template<typename Comp>
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Comp>>::storage_type, Comp>;
+
+        class iterable final {
+            template<typename It>
+            struct iterable_iterator final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_view_impl>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                iterable_iterator(It from, const basic_view_impl* parent) ENTT_NOEXCEPT
+                    : it{ from },
+                    view{ parent }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return ++it, * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    return std::tuple_cat(std::make_tuple(*it), view->get(*it));
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return other.it == it;
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                It it;
+                const basic_view_impl* view;
+            };
+
+        public:
+            using iterator = iterable_iterator<internal::view_iterator<Policy, typename basic_common_type::iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>>;
+            using reverse_iterator = iterable_iterator<internal::view_iterator<Policy, typename basic_common_type::reverse_iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>>;
+
+            iterable(const basic_view_impl& parent)
+                : view{ parent }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return { view.begin(), &view };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return { view.end(), &view };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return { view.rbegin(), &view };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return { view.rend(), &view };
+            }
+
+        private:
+            const basic_view_impl view;
+        };
+
+        [[nodiscard]] const auto* candidate() const ENTT_NOEXCEPT {
+            return (std::min)({ static_cast<const basic_common_type*>(std::get<storage_type<Component>*>(pools))... }, [](const auto* lhs, const auto* rhs) {
+                return lhs->size() < rhs->size();
+                });
+        }
+
+        [[nodiscard]] auto pools_to_unchecked_array() const ENTT_NOEXCEPT {
+            std::size_t pos{};
+            std::array<const basic_common_type*, sizeof...(Component) - 1u> other{};
+            (static_cast<void>(std::get<storage_type<Component>*>(pools) == view ? void() : void(other[pos++] = std::get<storage_type<Component>*>(pools))), ...);
+            return other;
+        }
+
+        [[nodiscard]] auto filter_to_array() const ENTT_NOEXCEPT {
+            return std::array<const basic_common_type*, sizeof...(Exclude)>{std::get<const storage_type<Exclude>*>(filter)...};
+        }
+
+        template<typename Comp, typename It>
+        [[nodiscard]] auto dispatch_get([[maybe_unused]] It& it, [[maybe_unused]] const Entity entt) const {
+            if constexpr (std::is_same_v<typename std::iterator_traits<It>::value_type, typename storage_type<Comp>::value_type>) {
+                return std::forward_as_tuple(*it);
+            }
+            else {
+                return get_as_tuple(*std::get<storage_type<Comp>*>(pools), entt);
+            }
+        }
+
+        template<typename Comp, typename Func>
+        void traverse(Func func) const {
+            if constexpr (std::is_void_v<decltype(std::get<storage_type<Comp> *>(pools)->get({})) > ) {
+                for (const auto entt : static_cast<const basic_common_type&>(*std::get<storage_type<Comp>*>(pools))) {
+                    if (Policy::accept(entt) && ((std::is_same_v<Comp, Component> || std::get<storage_type<Component> *>(pools)->contains(entt)) && ...)
+                        && (!std::get<const storage_type<Exclude> *>(filter)->contains(entt) && ...))
+                    {
+                        if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view_impl>().get({}))) > ) {
+                            std::apply(func, std::tuple_cat(std::make_tuple(entt), get(entt)));
+                        }
+                        else {
+                            std::apply(func, get(entt));
+                        }
+                    }
+                }
+            }
+            else {
+                auto it = std::get<storage_type<Comp>*>(pools)->begin();
+
+                for (const auto entt : static_cast<const basic_common_type&>(*std::get<storage_type<Comp>*>(pools))) {
+                    if (Policy::accept(entt) && ((std::is_same_v<Comp, Component> || std::get<storage_type<Component> *>(pools)->contains(entt)) && ...)
+                        && (!std::get<const storage_type<Exclude> *>(filter)->contains(entt) && ...))
+                    {
+                        if constexpr (is_applicable_v < Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view_impl>().get({}))) > ) {
+                            std::apply(func, std::tuple_cat(std::make_tuple(entt), dispatch_get<Component>(it, entt)...));
+                        }
+                        else {
+                            std::apply(func, std::tuple_cat(dispatch_get<Component>(it, entt)...));
+                        }
+                    }
+
+                    ++it;
+                }
+            }
+        }
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Bidirectional iterator type. */
+        using iterator = internal::view_iterator<Policy, typename basic_common_type::iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>;
+        /*! @brief Reverse iterator type. */
+        using reverse_iterator = internal::view_iterator<Policy, typename basic_common_type::reverse_iterator, sizeof...(Component) - 1u, sizeof...(Exclude)>;
+        /*! @brief Iterable view type. */
+        using iterable_view = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid views. */
+        basic_view_impl() ENTT_NOEXCEPT
+            : view{}
+        {}
+
+        /**
+         * @brief Constructs a multi-type view from a set of storage classes.
+         * @param component The storage for the types to iterate.
+         * @param epool The storage for the types used to filter the view.
+         */
+        basic_view_impl(storage_type<Component> &... component, const storage_type<Exclude> &... epool) ENTT_NOEXCEPT
+            : pools{ &component... },
+            filter{ &epool... },
+            view{ candidate() }
+        {}
+
+        /**
+         * @brief Forces the type to use to drive iterations.
+         * @tparam Comp Type of component to use to drive the iteration.
+         */
+        template<typename Comp>
+        void use() const ENTT_NOEXCEPT {
+            view = std::get<storage_type<Comp>*>(pools);
+        }
+
+        /**
+         * @brief Estimates the number of entities iterated by the view.
+         * @return Estimated number of entities iterated by the view.
+         */
+        [[nodiscard]] size_type size_hint() const ENTT_NOEXCEPT {
+            return view->size();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the view.
+         *
+         * The returned iterator points to the first entity of the view. If the view
+         * is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the view.
+         */
+        [[nodiscard]] iterator begin() const {
+            return iterator{ view->begin(), view->end(), view->begin(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the view. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the view.
+         */
+        [[nodiscard]] iterator end() const {
+            return iterator{ view->begin(), view->end(), view->end(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed view.
+         *
+         * The returned iterator points to the first entity of the reversed view. If
+         * the view is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed view.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const {
+            return reverse_iterator{ view->rbegin(), view->rend(), view->rbegin(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed view. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed view.
+         */
+        [[nodiscard]] reverse_iterator rend() const {
+            return reverse_iterator{ view->rbegin(), view->rend(), view->rend(), pools_to_unchecked_array(), filter_to_array() };
+        }
+
+        /**
+         * @brief Returns the first entity of the view, if any.
+         * @return The first entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the view, if any.
+         * @return The last entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = iterator{ view->begin(), view->end(), view->find(entt), pools_to_unchecked_array(), filter_to_array() };
+            return (it != end() && *it == entt) ? it : end();
+        }
+
+        /**
+         * @brief Checks if a view is properly initialized.
+         * @return True if the view is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return view != nullptr;
+        }
+
+        /**
+         * @brief Checks if a view contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the view contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return (std::get<storage_type<Component>*>(pools)->contains(entt) && ...) && (!std::get<const storage_type<Exclude>*>(filter)->contains(entt) && ...);
+        }
+
+        /**
+         * @brief Returns the components assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the view
+         * results in undefined behavior.
+         *
+         * @tparam Comp Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The components assigned to the entity.
+         */
+        template<typename... Comp>
+        [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "View does not contain entity");
+
+            if constexpr (sizeof...(Comp) == 0) {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Component>*>(pools), entt)...);
+            }
+            else if constexpr (sizeof...(Comp) == 1) {
+                return (std::get<storage_type<Comp>*>(pools)->get(entt), ...);
+            }
+            else {
+                return std::tuple_cat(get_as_tuple(*std::get<storage_type<Comp>*>(pools), entt)...);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a set of references to non-empty components. The
+         * _constness_ of the components is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Type &...);
+         * void(Type &...);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            ((std::get<storage_type<Component>*>(pools) == view ? traverse<Component>(std::move(func)) : void()), ...);
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The pool of the suggested component is used to lead the iterations. The
+         * returned entities will therefore respect the order of the pool associated
+         * with that type.
+         *
+         * @sa each
+         *
+         * @tparam Comp Type of component to use to drive the iteration.
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Comp, typename Func>
+        void each(Func func) const {
+            use<Comp>();
+            traverse<Comp>(std::move(func));
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the view.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * set of references to its non-empty components. The _constness_ of the
+         * components is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the view.
+         */
+        [[nodiscard]] iterable_view each() const ENTT_NOEXCEPT {
+            return iterable_view{ *this };
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the view.
+         *
+         * The pool of the suggested component is used to lead the iterations. The
+         * returned elements will therefore respect the order of the pool associated
+         * with that type.
+         *
+         * @sa each
+         *
+         * @tparam Comp Type of component to use to drive the iteration.
+         * @return An iterable object to use to _visit_ the view.
+         */
+        template<typename Comp>
+        [[nodiscard]] iterable_view each() const ENTT_NOEXCEPT {
+            use<Comp>();
+            return iterable_view{ *this };
+        }
+
+        /**
+         * @brief Combines two views in a _more specific_ one (friend function).
+         * @tparam Id A valid entity type (see entt_traits for more details).
+         * @tparam ELhs Filter list of the first view.
+         * @tparam CLhs Component list of the first view.
+         * @tparam ERhs Filter list of the second view.
+         * @tparam CRhs Component list of the second view.
+         * @return A more specific view.
+         */
+        template<typename Id, typename... ELhs, typename... CLhs, typename... ERhs, typename... CRhs>
+        friend auto operator|(const basic_view<Id, exclude_t<ELhs...>, CLhs...>&, const basic_view<Id, exclude_t<ERhs...>, CRhs...>&);
+
+    private:
+        const std::tuple<storage_type<Component> *...> pools;
+        const std::tuple<const storage_type<Exclude> *...> filter;
+        mutable const basic_common_type* view;
+    };
+
+
+    /**
+     * @brief Single component view specialization.
+     *
+     * Single component views are specialized in order to get a boost in terms of
+     * performance. This kind of views can access the underlying data structure
+     * directly and avoid superfluous checks.
+     *
+     * @b Important
+     *
+     * Iterators aren't invalidated if:
+     *
+     * * New instances of the given component are created and assigned to entities.
+     * * The entity currently pointed is modified (as an example, the given
+     *   component is removed from the entity to which the iterator points).
+     * * The entity currently pointed is destroyed.
+     *
+     * In all other cases, modifying the pool iterated by the view in any way
+     * invalidates all the iterators and using them results in undefined behavior.
+     *
+     * @note
+     * Views share a reference to the underlying data structure of the registry that
+     * generated them. Therefore any change to the entities and to the components
+     * made by means of the registry are immediately reflected by views.
+     *
+     * @warning
+     * Lifetime of a view must not overcome that of the registry that generated it.
+     * In any other case, attempting to use a view results in undefined behavior.
+     *
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Component Type of component iterated by the view.
+     */
+    template<typename Entity, typename Component>
+    class basic_view_impl<packed_storage_policy, Entity, exclude_t<>, Component> {
+        using basic_common_type = basic_sparse_set<Entity>;
+        using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
+
+        class iterable final {
+            template<typename... It>
+            struct iterable_iterator final {
+                using difference_type = std::ptrdiff_t;
+                using value_type = decltype(std::tuple_cat(std::tuple<Entity>{}, std::declval<basic_view_impl>().get({})));
+                using pointer = void;
+                using reference = value_type;
+                using iterator_category = std::input_iterator_tag;
+
+                template<typename... Discard>
+                iterable_iterator(It... from, Discard...) ENTT_NOEXCEPT
+                    : it{ from... }
+                {}
+
+                iterable_iterator& operator++() ENTT_NOEXCEPT {
+                    return (++std::get<It>(it), ...), * this;
+                }
+
+                iterable_iterator operator++(int) ENTT_NOEXCEPT {
+                    iterable_iterator orig = *this;
+                    return ++(*this), orig;
+                }
+
+                [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                    return { *std::get<It>(it)... };
+                }
+
+                [[nodiscard]] bool operator==(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return std::get<0>(other.it) == std::get<0>(it);
+                }
+
+                [[nodiscard]] bool operator!=(const iterable_iterator& other) const ENTT_NOEXCEPT {
+                    return !(*this == other);
+                }
+
+            private:
+                std::tuple<It...> it;
+            };
+
+        public:
+            using iterator = std::conditional_t <
+                std::is_void_v<decltype(std::declval<storage_type>().get({})) > ,
+                iterable_iterator<typename basic_common_type::iterator>,
+                iterable_iterator<typename basic_common_type::iterator, decltype(std::declval<storage_type>().begin())>
+            > ;
+            using reverse_iterator = std::conditional_t <
+                std::is_void_v<decltype(std::declval<storage_type>().get({})) > ,
+                iterable_iterator<typename basic_common_type::reverse_iterator>,
+                iterable_iterator<typename basic_common_type::reverse_iterator, decltype(std::declval<storage_type>().rbegin())>
+            > ;
+
+            iterable(storage_type& ref)
+                : pool{ &ref }
+            {}
+
+            [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+                return iterator{ pool->basic_common_type::begin(), pool->begin() };
+            }
+
+            [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+                return iterator{ pool->basic_common_type::end(), pool->end() };
+            }
+
+            [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+                return reverse_iterator{ pool->basic_common_type::rbegin(), pool->rbegin() };
+            }
+
+            [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+                return reverse_iterator{ pool->basic_common_type::rend(), pool->rend() };
+            }
+
+        private:
+            storage_type* const pool;
+        };
+
+    public:
+        /*! @brief Underlying entity identifier. */
+        using entity_type = Entity;
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Random access iterator type. */
+        using iterator = typename basic_common_type::iterator;
+        /*! @brief Reversed iterator type. */
+        using reverse_iterator = typename basic_common_type::reverse_iterator;
+        /*! @brief Iterable view type. */
+        using iterable_view = iterable;
+
+        /*! @brief Default constructor to use to create empty, invalid views. */
+        basic_view_impl() ENTT_NOEXCEPT
+            : pools{},
+            filter{}
+        {}
+
+        /**
+         * @brief Constructs a single-type view from a storage class.
+         * @param ref The storage for the type to iterate.
+         */
+        basic_view_impl(storage_type& ref) ENTT_NOEXCEPT
+            : pools{ &ref },
+            filter{}
+        {}
+
+        /**
+         * @brief Returns the number of entities that have the given component.
+         * @return Number of entities that have the given component.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->size();
+        }
+
+        /**
+         * @brief Checks whether a view is empty.
+         * @return True if the view is empty, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->empty();
+        }
+
+        /**
+         * @brief Direct access to the raw representation offered by the storage.
+         * @return A pointer to the array of components.
+         */
+        [[nodiscard]] auto raw() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->raw();
+        }
+
+        /**
+         * @brief Direct access to the list of entities.
+         *
+         * The returned pointer is such that range `[data(), data() + size())` is
+         * always a valid range, even if the container is empty.
+         *
+         * @return A pointer to the array of entities.
+         */
+        [[nodiscard]] auto data() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->data();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the view.
+         *
+         * The returned iterator points to the first entity of the view. If the view
+         * is empty, the returned iterator will be equal to `end()`.
+         *
+         * @return An iterator to the first entity of the view.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::begin();
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the view. Attempting to dereference the returned iterator results in
+         * undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the view.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::end();
+        }
+
+        /**
+         * @brief Returns an iterator to the first entity of the reversed view.
+         *
+         * The returned iterator points to the first entity of the reversed view. If
+         * the view is empty, the returned iterator will be equal to `rend()`.
+         *
+         * @return An iterator to the first entity of the reversed view.
+         */
+        [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::rbegin();
+        }
+
+        /**
+         * @brief Returns an iterator that is past the last entity of the reversed
+         * view.
+         *
+         * The returned iterator points to the entity following the last entity of
+         * the reversed view. Attempting to dereference the returned iterator
+         * results in undefined behavior.
+         *
+         * @return An iterator to the entity following the last entity of the
+         * reversed view.
+         */
+        [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
+            return std::get<0>(pools)->basic_common_type::rend();
+        }
+
+        /**
+         * @brief Returns the first entity of the view, if any.
+         * @return The first entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type front() const {
+            const auto it = begin();
+            return it != end() ? *it : null;
+        }
+
+        /**
+         * @brief Returns the last entity of the view, if any.
+         * @return The last entity of the view if one exists, the null entity
+         * otherwise.
+         */
+        [[nodiscard]] entity_type back() const {
+            const auto it = rbegin();
+            return it != rend() ? *it : null;
+        }
+
+        /**
+         * @brief Finds an entity.
+         * @param entt A valid entity identifier.
+         * @return An iterator to the given entity if it's found, past the end
+         * iterator otherwise.
+         */
+        [[nodiscard]] iterator find(const entity_type entt) const {
+            const auto it = std::get<0>(pools)->find(entt);
+            return it != end() && *it == entt ? it : end();
+        }
+
+        /**
+         * @brief Returns the identifier that occupies the given position.
+         * @param pos Position of the element to return.
+         * @return The identifier that occupies the given position.
+         */
+        [[nodiscard]] entity_type operator[](const size_type pos) const {
+            return begin()[pos];
+        }
+
+        /**
+         * @brief Checks if a view is properly initialized.
+         * @return True if the view is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return std::get<0>(pools) != nullptr;
+        }
+
+        /**
+         * @brief Checks if a view contains an entity.
+         * @param entt A valid entity identifier.
+         * @return True if the view contains the given entity, false otherwise.
+         */
+        [[nodiscard]] bool contains(const entity_type entt) const {
+            return std::get<0>(pools)->contains(entt);
+        }
+
+        /**
+         * @brief Returns the component assigned to the given entity.
+         *
+         * Prefer this function instead of `registry::get` during iterations. It has
+         * far better performance than its counterpart.
+         *
+         * @warning
+         * Attempting to use an invalid component type results in a compilation
+         * error. Attempting to use an entity that doesn't belong to the view
+         * results in undefined behavior.
+         *
+         * @tparam Comp Types of components to get.
+         * @param entt A valid entity identifier.
+         * @return The component assigned to the entity.
+         */
+        template<typename... Comp>
+        [[nodiscard]] decltype(auto) get(const entity_type entt) const {
+            ENTT_ASSERT(contains(entt), "View does not contain entity");
+
+            if constexpr (sizeof...(Comp) == 0) {
+                return get_as_tuple(*std::get<0>(pools), entt);
+            }
+            else {
+                static_assert(std::is_same_v<Comp..., Component>, "Invalid component type");
+                return std::get<0>(pools)->get(entt);
+            }
+        }
+
+        /**
+         * @brief Iterates entities and components and applies the given function
+         * object to them.
+         *
+         * The function object is invoked for each entity. It is provided with the
+         * entity itself and a reference to the component if it's a non-empty one.
+         * The _constness_ of the component is as requested.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entity_type, Component &);
+         * void(Component &);
+         * @endcode
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template<typename Func>
+        void each(Func func) const {
+            if constexpr (std::is_void_v<decltype(std::get<0>(pools)->get({})) > ) {
+                if constexpr (std::is_invocable_v<Func>) {
+                    for (auto pos = size(); pos; --pos) {
+                        func();
+                    }
+                }
+                else {
+                    for (auto entity : *this) {
+                        func(entity);
+                    }
+                }
+            }
+            else {
+                if constexpr (is_applicable_v<Func, decltype(*each().begin())>) {
+                    for (const auto pack : each()) {
+                        std::apply(func, pack);
+                    }
+                }
+                else {
+                    for (auto&& component : *std::get<0>(pools)) {
+                        func(component);
+                    }
+                }
+            }
+        }
+
+        /**
+         * @brief Returns an iterable object to use to _visit_ the view.
+         *
+         * The iterable object returns tuples that contain the current entity and a
+         * reference to its component if it's a non-empty one. The _constness_ of
+         * the component is as requested.
+         *
+         * @note
+         * Empty types aren't explicitly instantiated and therefore they are never
+         * returned during iterations.
+         *
+         * @return An iterable object to use to _visit_ the view.
+         */
+        [[nodiscard]] iterable_view each() const ENTT_NOEXCEPT {
+            return iterable_view{ *std::get<0>(pools) };
+        }
+
+        /**
+         * @brief Combines two views in a _more specific_ one (friend function).
+         * @tparam Id A valid entity type (see entt_traits for more details).
+         * @tparam ELhs Filter list of the first view.
+         * @tparam CLhs Component list of the first view.
+         * @tparam ERhs Filter list of the second view.
+         * @tparam CRhs Component list of the second view.
+         * @return A more specific view.
+         */
+        template<typename Id, typename... ELhs, typename... CLhs, typename... ERhs, typename... CRhs>
+        friend auto operator|(const basic_view<Id, exclude_t<ELhs...>, CLhs...>&, const basic_view<Id, exclude_t<ERhs...>, CRhs...>&);
+
+    private:
+        const std::tuple<storage_type*> pools;
+        const std::tuple<> filter;
+    };
+
+
+    /**
+     * @brief View implementation dispatcher.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam Exclude Types of components used to filter the view.
+     * @tparam Component Types of components iterated by the view.
+     */
+    template<typename Entity, typename... Exclude, typename... Component>
+    struct basic_view<Entity, exclude_t<Exclude...>, Component...>
+        : basic_view_impl<std::conditional_t<std::disjunction_v<typename component_traits<std::remove_const_t<Component>>::in_place_delete...>, stable_storage_policy, packed_storage_policy>, Entity, exclude_t<Exclude...>, Component...>
+    {
+        /*! @brief Most restrictive storage policy of all component types. */
+        using storage_policy = std::conditional_t<std::disjunction_v<typename component_traits<std::remove_const_t<Component>>::in_place_delete...>, stable_storage_policy, packed_storage_policy>;
+        using basic_view_impl<storage_policy, Entity, exclude_t<Exclude...>, Component...>::basic_view_impl;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Storage Type of storage classes used to create the view.
+     * @param storage The storage for the types to iterate.
+     */
+    template<typename... Storage>
+    basic_view(Storage &... storage)
+        ->basic_view<std::common_type_t<typename Storage::entity_type...>, entt::exclude_t<>, constness_as_t<typename Storage::value_type, Storage>...>;
+
+
+    /**
+     * @brief Combines two views in a _more specific_ one.
+     * @tparam Entity A valid entity type (see entt_traits for more details).
+     * @tparam ELhs Filter list of the first view.
+     * @tparam CLhs Component list of the first view.
+     * @tparam ERhs Filter list of the second view.
+     * @tparam CRhs Component list of the second view.
+     * @param lhs A valid reference to the first view.
+     * @param rhs A valid reference to the second view.
+     * @return A more specific view.
+     */
+    template<typename Entity, typename... ELhs, typename... CLhs, typename... ERhs, typename... CRhs>
+    [[nodiscard]] auto operator|(const basic_view<Entity, exclude_t<ELhs...>, CLhs...>& lhs, const basic_view<Entity, exclude_t<ERhs...>, CRhs...>& rhs) {
+        using view_type = basic_view<Entity, exclude_t<ELhs..., ERhs...>, CLhs..., CRhs...>;
+        return std::apply([](auto *... storage) { return view_type{ *storage... }; }, std::tuple_cat(lhs.pools, rhs.pools, lhs.filter, rhs.filter));
+    }
+
+
+}
+
+
+#endif
+
+// #include "locator/locator.hpp"
+#ifndef ENTT_LOCATOR_LOCATOR_HPP
+#define ENTT_LOCATOR_LOCATOR_HPP
+
+
+#include <memory>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Service locator, nothing more.
+     *
+     * A service locator can be used to do what it promises: locate services.<br/>
+     * Usually service locators are tightly bound to the services they expose and
+     * thus it's hard to define a general purpose class to do that. This template
+     * based implementation tries to fill the gap and to get rid of the burden of
+     * defining a different specific locator for each application.
+     *
+     * @tparam Service Type of service managed by the locator.
+     */
+    template<typename Service>
+    struct service_locator {
+        /*! @brief Type of service offered. */
+        using service_type = Service;
+
+        /*! @brief Default constructor, deleted on purpose. */
+        service_locator() = delete;
+        /*! @brief Default destructor, deleted on purpose. */
+        ~service_locator() = delete;
+
+        /**
+         * @brief Tests if a valid service implementation is set.
+         * @return True if the service is set, false otherwise.
+         */
+        [[nodiscard]] static bool empty() ENTT_NOEXCEPT {
+            return !static_cast<bool>(service);
+        }
+
+        /**
+         * @brief Returns a weak pointer to a service implementation, if any.
+         *
+         * Clients of a service shouldn't retain references to it. The recommended
+         * way is to retrieve the service implementation currently set each and
+         * every time the need of using it arises. Otherwise users can incur in
+         * unexpected behaviors.
+         *
+         * @return A reference to the service implementation currently set, if any.
+         */
+        [[nodiscard]] static std::weak_ptr<Service> get() ENTT_NOEXCEPT {
+            return service;
+        }
+
+        /**
+         * @brief Returns a weak reference to a service implementation, if any.
+         *
+         * Clients of a service shouldn't retain references to it. The recommended
+         * way is to retrieve the service implementation currently set each and
+         * every time the need of using it arises. Otherwise users can incur in
+         * unexpected behaviors.
+         *
+         * @warning
+         * In case no service implementation has been set, a call to this function
+         * results in undefined behavior.
+         *
+         * @return A reference to the service implementation currently set, if any.
+         */
+        [[nodiscard]] static Service& ref() ENTT_NOEXCEPT {
+            return *service;
+        }
+
+        /**
+         * @brief Sets or replaces a service.
+         * @tparam Impl Type of the new service to use.
+         * @tparam Args Types of arguments to use to construct the service.
+         * @param args Parameters to use to construct the service.
+         */
+        template<typename Impl = Service, typename... Args>
+        static void set(Args &&... args) {
+            service = std::make_shared<Impl>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Sets or replaces a service.
+         * @param ptr Service to use to replace the current one.
+         */
+        static void set(std::shared_ptr<Service> ptr) {
+            ENTT_ASSERT(static_cast<bool>(ptr), "Null service not allowed");
+            service = std::move(ptr);
+        }
+
+        /**
+         * @brief Resets a service.
+         *
+         * The service is no longer valid after a reset.
+         */
+        static void reset() {
+            service.reset();
+        }
+
+    private:
+        inline static std::shared_ptr<Service> service = nullptr;
+    };
+
+
+}
+
+
+#endif
+
+// #include "meta/adl_pointer.hpp"
+#ifndef ENTT_META_ADL_POINTER_HPP
+#define ENTT_META_ADL_POINTER_HPP
+
+
+namespace entt {
+
+
+    /**
+     * @brief ADL based lookup function for dereferencing meta pointer-like types.
+     * @tparam Type Element type.
+     * @param value A pointer-like object.
+     * @return The value returned from the dereferenced pointer.
+     */
+    template<typename Type>
+    decltype(auto) dereference_meta_pointer_like(const Type& value) {
+        return *value;
+    }
+
+
+    /**
+     * @brief Fake ADL based lookup function for meta pointer-like types.
+     * @tparam Type Element type.
+     */
+    template<typename Type>
+    struct adl_meta_pointer_like {
+        /**
+         * @brief Uses the default ADL based lookup method to resolve the call.
+         * @param value A pointer-like object.
+         * @return The value returned from the dereferenced pointer.
+         */
+        static decltype(auto) dereference(const Type& value) {
+            return dereference_meta_pointer_like(value);
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "meta/container.hpp"
+#ifndef ENTT_META_CONTAINER_HPP
+#define ENTT_META_CONTAINER_HPP
+
+
+#include <array>
+#include <map>
+#include <set>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+#include <vector>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "../core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "type_traits.hpp"
+#ifndef ENTT_META_TYPE_TRAITS_HPP
+#define ENTT_META_TYPE_TRAITS_HPP
+
+
+#include <type_traits>
+
+
+namespace entt {
+
+
+    /**
+     * @brief Traits class template to be specialized to enable support for meta
+     * template information.
+     */
+    template<typename>
+    struct meta_template_traits;
+
+
+    /**
+     * @brief Traits class template to be specialized to enable support for meta
+     * sequence containers.
+     */
+    template<typename>
+    struct meta_sequence_container_traits;
+
+
+    /**
+     * @brief Traits class template to be specialized to enable support for meta
+     * associative containers.
+     */
+    template<typename>
+    struct meta_associative_container_traits;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a meta associative
+     * container claims to wrap a key-only type, false otherwise.
+     * @tparam Type Potentially key-only meta associative container type.
+     */
+    template<typename, typename = void>
+    struct is_key_only_meta_associative_container : std::true_type {};
+
+
+    /*! @copydoc is_key_only_meta_associative_container */
+    template<typename Type>
+    struct is_key_only_meta_associative_container<Type, std::void_t<typename meta_associative_container_traits<Type>::type::mapped_type>>
+        : std::false_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type Potentially key-only meta associative container type.
+     */
+    template<typename Type>
+    inline constexpr auto is_key_only_meta_associative_container_v = is_key_only_meta_associative_container<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is a
+     * pointer-like type from the point of view of the meta system, false otherwise.
+     * @tparam Type Potentially pointer-like type.
+     */
+    template<typename>
+    struct is_meta_pointer_like : std::false_type {};
+
+
+    /**
+     * @brief Partial specialization to ensure that const pointer-like types are
+     * also accepted.
+     * @tparam Type Potentially pointer-like type.
+     */
+    template<typename Type>
+    struct is_meta_pointer_like<const Type> : is_meta_pointer_like<Type> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type Potentially pointer-like type.
+     */
+    template<typename Type>
+    inline constexpr auto is_meta_pointer_like_v = is_meta_pointer_like<Type>::value;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Container traits.
+     * @tparam Container Type of the underlying container.
+     * @tparam Trait Traits associated with the underlying container.
+     */
+    template<typename Container, template<typename> class... Trait>
+    struct meta_container_traits : public Trait<Container>... {
+        /*! @brief Type of container. */
+        using type = Container;
+    };
+
+
+    /**
+     * @brief Basic STL-compatible container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct basic_container {
+        /**
+         * @brief Returns the size of the given container.
+         * @param cont The container for which to return the size.
+         * @return The size of the given container.
+         */
+        [[nodiscard]] static typename Container::size_type size(const Container& cont) ENTT_NOEXCEPT {
+            return cont.size();
+        }
+
+        /**
+         * @brief Returns an iterator to the first element of the given container.
+         * @param cont The container for which to return the iterator.
+         * @return An iterator to the first element of the given container.
+         */
+        [[nodiscard]] static typename Container::iterator begin(Container& cont) {
+            return cont.begin();
+        }
+
+        /**
+         * @brief Returns an iterator to the first element of the given container.
+         * @param cont The container for which to return the iterator.
+         * @return An iterator to the first element of the given container.
+         */
+        [[nodiscard]] static typename Container::const_iterator cbegin(const Container& cont) {
+            return cont.begin();
+        }
+
+        /**
+         * @brief Returns an iterator past the last element of the given container.
+         * @param cont The container for which to return the iterator.
+         * @return An iterator past the last element of the given container.
+         */
+        [[nodiscard]] static typename Container::iterator end(Container& cont) {
+            return cont.end();
+        }
+
+        /**
+         * @brief Returns an iterator past the last element of the given container.
+         * @param cont The container for which to return the iterator.
+         * @return An iterator past the last element of the given container.
+         */
+        [[nodiscard]] static typename Container::const_iterator cend(const Container& cont) {
+            return cont.end();
+        }
+    };
+
+
+    /**
+     * @brief Basic STL-compatible associative container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct basic_associative_container {
+        /**
+         * @brief Returns an iterator to the element with key equivalent to the
+         * given one, if any.
+         * @param cont The container in which to search for the element.
+         * @param key The key of the element to search.
+         * @return An iterator to the element with the given key, if any.
+         */
+        [[nodiscard]] static typename Container::iterator find(Container& cont, const typename Container::key_type& key) {
+            return cont.find(key);
+        }
+
+        /*! @copydoc find */
+        [[nodiscard]] static typename Container::const_iterator cfind(const Container& cont, const typename Container::key_type& key) {
+            return cont.find(key);
+        }
+    };
+
+
+    /**
+     * @brief Basic STL-compatible dynamic container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct basic_dynamic_container {
+        /**
+         * @brief Clears the content of the given container.
+         * @param cont The container for which to clear the content.
+         * @return True in case of success, false otherwise.
+         */
+        [[nodiscard]] static bool clear([[maybe_unused]] Container& cont) {
+            return cont.clear(), true;
+        }
+    };
+
+
+    /**
+     * @brief Basic STL-compatible dynamic associative container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct basic_dynamic_associative_container {
+        /**
+         * @brief Removes the specified element from the given container.
+         * @param cont The container from which to remove the element.
+         * @param key The element to remove.
+         * @return A bool denoting whether the removal took place.
+         */
+        [[nodiscard]] static bool erase([[maybe_unused]] Container& cont, [[maybe_unused]] const typename Container::key_type& key) {
+            const auto sz = cont.size();
+            return cont.erase(key) != sz;
+        }
+    };
+
+
+    /**
+     * @brief Basic STL-compatible sequence container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct basic_sequence_container {
+        /**
+         * @brief Returns a reference to the element at the specified location of
+         * the given container (no bounds checking is performed).
+         * @param cont The container from which to get the element.
+         * @param pos The position of the element to return.
+         * @return A reference to the requested element.
+         */
+        [[nodiscard]] static typename Container::reference get(Container& cont, typename Container::size_type pos) {
+            return cont[pos];
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] static typename Container::const_reference cget(const Container& cont, typename Container::size_type pos) {
+            return cont[pos];
+        }
+    };
+
+
+    /**
+     * @brief STL-compatible dynamic associative key-only container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct dynamic_associative_key_only_container {
+        /**
+         * @brief Inserts an element into the given container.
+         * @param cont The container in which to insert the element.
+         * @param key The element to insert.
+         * @return A bool denoting whether the insertion took place.
+         */
+        [[nodiscard]] static bool insert([[maybe_unused]] Container& cont, [[maybe_unused]] const typename Container::key_type& key) {
+            return cont.insert(key).second;
+        }
+    };
+
+
+    /**
+     * @brief STL-compatible dynamic key-value associative container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct dynamic_associative_key_value_container {
+        /**
+         * @brief Inserts an element (a key/value pair) into the given container.
+         * @param cont The container in which to insert the element.
+         * @param key The key of the element to insert.
+         * @param value The value of the element to insert.
+         * @return A bool denoting whether the insertion took place.
+         */
+        [[nodiscard]] static bool insert([[maybe_unused]] Container& cont, [[maybe_unused]] const typename Container::key_type& key, [[maybe_unused]] const typename Container::mapped_type& value) {
+            return cont.insert(std::make_pair(key, value)).second;
+        }
+    };
+
+
+    /**
+     * @brief STL-compatible dynamic sequence container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct dynamic_sequence_container {
+        /**
+         * @brief Resizes the given container to contain the given number of
+         * elements.
+         * @param cont The container to resize.
+         * @param sz The new size of the container.
+         * @return True in case of success, false otherwise.
+         */
+        [[nodiscard]] static bool resize([[maybe_unused]] Container& cont, [[maybe_unused]] typename Container::size_type sz) {
+            return cont.resize(sz), true;
+        }
+
+        /**
+         * @brief Inserts an element at the specified location of the given
+         * container.
+         * @param cont The container into which to insert the element.
+         * @param it Iterator before which the element will be inserted.
+         * @param value Element value to insert.
+         * @return A pair consisting of an iterator to the inserted element (in case
+         * of success) and a bool denoting whether the insertion took place.
+         */
+        [[nodiscard]] static std::pair<typename Container::iterator, bool> insert([[maybe_unused]] Container& cont, [[maybe_unused]] typename Container::const_iterator it, [[maybe_unused]] const typename Container::value_type& value) {
+            return { cont.insert(it, value), true };
+        }
+
+        /**
+         * @brief Removes the element at the specified location from the given
+         * container.
+         * @param cont The container from which to remove the element.
+         * @param it Iterator to the element to remove.
+         * @return A pair consisting of an iterator following the last removed
+         * element (in case of success) and a bool denoting whether the insertion
+         * took place.
+         */
+        [[nodiscard]] static std::pair<typename Container::iterator, bool> erase([[maybe_unused]] Container& cont, [[maybe_unused]] typename Container::const_iterator it) {
+            return { cont.erase(it), true };
+        }
+    };
+
+
+    /**
+     * @brief STL-compatible fixed sequence container traits
+     * @tparam Container The type of the container.
+     */
+    template<typename Container>
+    struct fixed_sequence_container {
+        /**
+         * @brief Does nothing.
+         * @return False to indicate failure in all cases.
+         */
+        [[nodiscard]] static bool resize(const Container&, typename Container::size_type) {
+            return false;
+        }
+
+        /**
+         * @brief Does nothing.
+         * @return False to indicate failure in all cases.
+         */
+        [[nodiscard]] static bool clear(const Container&) {
+            return false;
+        }
+
+        /**
+         * @brief Does nothing.
+         * @return A pair consisting of an invalid iterator and a false value to
+         * indicate failure in all cases.
+         */
+        [[nodiscard]] static std::pair<typename Container::iterator, bool> insert(const Container&, typename Container::const_iterator, const typename Container::value_type&) {
+            return { {}, false };
+        }
+
+        /**
+         * @brief Does nothing.
+         * @return A pair consisting of an invalid iterator and a false value to
+         * indicate failure in all cases.
+         */
+        [[nodiscard]] static std::pair<typename Container::iterator, bool> erase(const Container&, typename Container::const_iterator) {
+            return { {}, false };
+        }
+    };
+
+
+    /**
+     * @brief Meta sequence container traits for `std::vector`s of any type.
+     * @tparam Type The type of elements.
+     * @tparam Args Other arguments.
+     */
+    template<typename Type, typename... Args>
+    struct meta_sequence_container_traits<std::vector<Type, Args...>>
+        : meta_container_traits<
+        std::vector<Type, Args...>,
+        basic_container,
+        basic_dynamic_container,
+        basic_sequence_container,
+        dynamic_sequence_container
+        >
+    {};
+
+
+    /**
+     * @brief Meta sequence container traits for `std::array`s of any type.
+     * @tparam Type The type of elements.
+     * @tparam N The number of elements.
+     */
+    template<typename Type, auto N>
+    struct meta_sequence_container_traits<std::array<Type, N>>
+        : meta_container_traits<
+        std::array<Type, N>,
+        basic_container,
+        basic_sequence_container,
+        fixed_sequence_container
+        >
+    {};
+
+
+    /**
+     * @brief Meta associative container traits for `std::map`s of any type.
+     * @tparam Key The key type of elements.
+     * @tparam Value The value type of elements.
+     * @tparam Args Other arguments.
+     */
+    template<typename Key, typename Value, typename... Args>
+    struct meta_associative_container_traits<std::map<Key, Value, Args...>>
+        : meta_container_traits<
+        std::map<Key, Value, Args...>,
+        basic_container,
+        basic_associative_container,
+        basic_dynamic_container,
+        basic_dynamic_associative_container,
+        dynamic_associative_key_value_container
+        >
+    {};
+
+
+    /**
+     * @brief Meta associative container traits for `std::unordered_map`s of any
+     * type.
+     * @tparam Key The key type of elements.
+     * @tparam Value The value type of elements.
+     * @tparam Args Other arguments.
+     */
+    template<typename Key, typename Value, typename... Args>
+    struct meta_associative_container_traits<std::unordered_map<Key, Value, Args...>>
+        : meta_container_traits<
+        std::unordered_map<Key, Value, Args...>,
+        basic_container,
+        basic_associative_container,
+        basic_dynamic_container,
+        basic_dynamic_associative_container,
+        dynamic_associative_key_value_container
+        >
+    {};
+
+
+    /**
+     * @brief Meta associative container traits for `std::set`s of any type.
+     * @tparam Key The type of elements.
+     * @tparam Args Other arguments.
+     */
+    template<typename Key, typename... Args>
+    struct meta_associative_container_traits<std::set<Key, Args...>>
+        : meta_container_traits<
+        std::set<Key, Args...>,
+        basic_container,
+        basic_associative_container,
+        basic_dynamic_container,
+        basic_dynamic_associative_container,
+        dynamic_associative_key_only_container
+        >
+    {};
+
+
+    /**
+     * @brief Meta associative container traits for `std::unordered_set`s of any
+     * type.
+     * @tparam Key The type of elements.
+     * @tparam Args Other arguments.
+     */
+    template<typename Key, typename... Args>
+    struct meta_associative_container_traits<std::unordered_set<Key, Args...>>
+        : meta_container_traits<
+        std::unordered_set<Key, Args...>,
+        basic_container,
+        basic_associative_container,
+        basic_dynamic_container,
+        basic_dynamic_associative_container,
+        dynamic_associative_key_only_container
+        >
+    {};
+
+
+}
+
+
+#endif
+
+// #include "meta/ctx.hpp"
+#ifndef ENTT_META_CTX_HPP
+#define ENTT_META_CTX_HPP
+
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct meta_type_node;
+
+
+        struct ENTT_API meta_context {
+            // we could use the lines below but VS2017 returns with an ICE if combined with ENTT_API despite the code being valid C++
+            //     inline static meta_type_node *local = nullptr;
+            //     inline static meta_type_node **global = &local;
+
+            [[nodiscard]] static meta_type_node*& local() ENTT_NOEXCEPT {
+                static meta_type_node* chain = nullptr;
+                return chain;
+            }
+
+            [[nodiscard]] static meta_type_node**& global() ENTT_NOEXCEPT {
+                static meta_type_node** chain = &local();
+                return chain;
+            }
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Opaque container for a meta context. */
+    struct meta_ctx {
+        /**
+         * @brief Binds the meta system to a given context.
+         * @param other A valid context to which to bind.
+         */
+        static void bind(meta_ctx other) ENTT_NOEXCEPT {
+            internal::meta_context::global() = other.ctx;
+        }
+
+    private:
+        internal::meta_type_node** ctx{ &internal::meta_context::local() };
+    };
+
+
+}
+
+
+#endif
+
+// #include "meta/factory.hpp"
+#ifndef ENTT_META_FACTORY_HPP
+#define ENTT_META_FACTORY_HPP
+
+
+#include <cstddef>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+// #include "../core/type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "../core/type_traits.hpp"
+
+// #include "meta.hpp"
+#ifndef ENTT_META_META_HPP
+#define ENTT_META_META_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/any.hpp"
+#ifndef ENTT_CORE_ANY_HPP
+#define ENTT_CORE_ANY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+// #include "type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "hashed_string.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief A SBO friendly, type-safe container for single values of any type.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<std::size_t Len, std::size_t Align>
+    class basic_any {
+        enum class operation : std::uint8_t { COPY, MOVE, DTOR, COMP, ADDR, CADDR, TYPE };
+        enum class policy : std::uint8_t { OWNER, REF, CREF };
+
+        using storage_type = std::aligned_storage_t<Len + !Len, Align>;
+        using vtable_type = const void* (const operation, const basic_any&, void*);
+
+        template<typename Type>
+        static constexpr bool in_situ = Len && alignof(Type) <= alignof(storage_type) && sizeof(Type) <= sizeof(storage_type) && std::is_nothrow_move_constructible_v<Type>;
+
+        template<typename Type>
+        [[nodiscard]] static constexpr policy type_to_policy() {
+            if constexpr (std::is_lvalue_reference_v<Type>) {
+                if constexpr (std::is_const_v<std::remove_reference_t<Type>>) {
+                    return policy::CREF;
+                }
+                else {
+                    return policy::REF;
+                }
+            }
+            else {
+                return policy::OWNER;
+            }
+        }
+
+        template<typename Type>
+        [[nodiscard]] static bool compare(const void* lhs, const void* rhs) {
+            if constexpr (!std::is_function_v<Type> && is_equality_comparable_v<Type>) {
+                return *static_cast<const Type*>(lhs) == *static_cast<const Type*>(rhs);
+            }
+            else {
+                return lhs == rhs;
+            }
+        }
+
+        template<typename Type>
+        static const void* basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const basic_any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                const Type* instance = (in_situ<Type> && from.mode == policy::OWNER)
+                    ? ENTT_LAUNDER(reinterpret_cast<const Type*>(&from.storage))
+                    : static_cast<const Type*>(from.instance);
+
+                switch (op) {
+                case operation::COPY:
+                    if constexpr (std::is_copy_constructible_v<Type>) {
+                        static_cast<basic_any*>(to)->emplace<Type>(*instance);
+                    }
+                    break;
+                case operation::MOVE:
+                    if constexpr (in_situ<Type>) {
+                        if (from.mode == policy::OWNER) {
+                            return new (&static_cast<basic_any*>(to)->storage) Type{ std::move(*const_cast<Type*>(instance)) };
+                        }
+                    }
+
+                    return (static_cast<basic_any*>(to)->instance = std::exchange(const_cast<basic_any&>(from).instance, nullptr));
+                case operation::DTOR:
+                    if (from.mode == policy::OWNER) {
+                        if constexpr (in_situ<Type>) {
+                            instance->~Type();
+                        }
+                        else if constexpr (std::is_array_v<Type>) {
+                            delete[] instance;
+                        }
+                        else {
+                            delete instance;
+                        }
+                    }
+                    break;
+                case operation::COMP:
+                    return compare<Type>(instance, (*static_cast<const basic_any**>(to))->data()) ? to : nullptr;
+                case operation::ADDR:
+                    if (from.mode == policy::CREF) {
+                        return nullptr;
+                    }
+                    [[fallthrough]];
+                case operation::CADDR:
+                    return instance;
+                case operation::TYPE:
+                    *static_cast<type_info*>(to) = type_id<Type>();
+                    break;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<typename Type, typename... Args>
+        void initialize([[maybe_unused]] Args &&... args) {
+            if constexpr (!std::is_void_v<Type>) {
+                if constexpr (std::is_lvalue_reference_v<Type>) {
+                    static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
+                    instance = (std::addressof(args), ...);
+                }
+                else if constexpr (in_situ<Type>) {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        new (&storage) Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        new (&storage) Type(std::forward<Args>(args)...);
+                    }
+                }
+                else {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        instance = new Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        instance = new Type(std::forward<Args>(args)...);
+                    }
+                }
+            }
+        }
+
+        basic_any(const basic_any& other, const policy pol) ENTT_NOEXCEPT
+            : instance{ other.data() },
+            vtable{ other.vtable },
+            mode{ pol }
+        {}
+
+    public:
+        /*! @brief Size of the internal storage. */
+        static constexpr auto length = Len;
+        /*! @brief Alignment requirement. */
+        static constexpr auto alignment = Align;
+
+        /*! @brief Default constructor. */
+        basic_any() ENTT_NOEXCEPT
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_any(std::in_place_type_t<Type>, Args &&... args)
+            : instance{},
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> },
+            mode{ type_to_policy<Type>() }
+        {
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        basic_any(std::reference_wrapper<Type> value) ENTT_NOEXCEPT
+            : basic_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
+        basic_any(Type&& value)
+            : instance{},
+            vtable{ &basic_vtable<std::decay_t<Type>> },
+            mode{ policy::OWNER }
+        {
+            initialize<std::decay_t<Type>>(std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_any(const basic_any& other)
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {
+            other.vtable(operation::COPY, other, this);
+        }
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_any(basic_any&& other) ENTT_NOEXCEPT
+            : instance{},
+            vtable{ other.vtable },
+            mode{ other.mode }
+        {
+            vtable(operation::MOVE, other, this);
+        }
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~basic_any() {
+            vtable(operation::DTOR, *this, nullptr);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This any object.
+         */
+        basic_any& operator=(const basic_any& other) {
+            reset();
+            other.vtable(operation::COPY, other, this);
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This any object.
+         */
+        basic_any& operator=(basic_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, other.vtable)(operation::DTOR, *this, nullptr);
+            other.vtable(operation::MOVE, other, this);
+            mode = other.mode;
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_any<T &>, emplace<Type &> or forward_as_any instead")]]
+        basic_any& operator=(std::reference_wrapper<Type> value) ENTT_NOEXCEPT {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            type_info info{};
+            vtable(operation::TYPE, *this, &info);
+            return info;
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return vtable(operation::CADDR, *this, nullptr);
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return const_cast<void*>(vtable(operation::ADDR, *this, nullptr));
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, *this, nullptr);
+            mode = type_to_policy<Type>();
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, *this, nullptr);
+            mode = policy::OWNER;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is empty, true otherwise.
+         * @return False if the wrapper is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable(operation::CADDR, *this, nullptr) == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        bool operator==(const basic_any& other) const ENTT_NOEXCEPT {
+            const basic_any* trampoline = &other;
+            return type() == other.type() && (vtable(operation::COMP, *this, &trampoline) || !other.data());
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_any as_ref() ENTT_NOEXCEPT {
+            return basic_any{ *this, (mode == policy::CREF ? policy::CREF : policy::REF) };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_any as_ref() const ENTT_NOEXCEPT {
+            return basic_any{ *this, policy::CREF };
+        }
+
+        /**
+         * @brief Returns true if a wrapper owns its object, false otherwise.
+         * @return True if the wrapper owns its object, false otherwise.
+         */
+        [[nodiscard]] bool owner() const ENTT_NOEXCEPT {
+            return (mode == policy::OWNER);
+        }
+
+    private:
+        union { const void* instance; storage_type storage; };
+        vtable_type* vtable;
+        policy mode;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    template<std::size_t Len, std::size_t Align>
+    [[nodiscard]] inline bool operator!=(const basic_any<Len, Align>& lhs, const basic_any<Len, Align>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Performs type-safe access to the contained object.
+     * @tparam Type Type to which conversion is required.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param data Target any object.
+     * @return The element converted to the requested type.
+     */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(const basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        const auto* const instance = any_cast<std::remove_reference_t<Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>&& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(std::move(*instance));
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    const Type* any_cast(const basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        return (data->type() == type_id<Type>() ? static_cast<const Type*>(data->data()) : nullptr);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type* any_cast(basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        // last attempt to make wrappers for const references return their values
+        return (data->type() == type_id<Type>() ? static_cast<Type*>(static_cast<constness_as_t<basic_any<Len, Align>, Type> *>(data)->data()) : nullptr);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
+    basic_any<Len, Align> make_any(Args &&... args) {
+        return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
+    basic_any<Len, Align> forward_as_any(Type&& value) {
+        return basic_any<Len, Align>{std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value)};
+    }
+
+
+}
+
+
+#endif
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "adl_pointer.hpp"
+#ifndef ENTT_META_ADL_POINTER_HPP
+#define ENTT_META_ADL_POINTER_HPP
+
+
+namespace entt {
+
+
+    /**
+     * @brief ADL based lookup function for dereferencing meta pointer-like types.
+     * @tparam Type Element type.
+     * @param value A pointer-like object.
+     * @return The value returned from the dereferenced pointer.
+     */
+    template<typename Type>
+    decltype(auto) dereference_meta_pointer_like(const Type& value) {
+        return *value;
+    }
+
+
+    /**
+     * @brief Fake ADL based lookup function for meta pointer-like types.
+     * @tparam Type Element type.
+     */
+    template<typename Type>
+    struct adl_meta_pointer_like {
+        /**
+         * @brief Uses the default ADL based lookup method to resolve the call.
+         * @param value A pointer-like object.
+         * @return The value returned from the dereferenced pointer.
+         */
+        static decltype(auto) dereference(const Type& value) {
+            return dereference_meta_pointer_like(value);
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "ctx.hpp"
+#ifndef ENTT_META_CTX_HPP
+#define ENTT_META_CTX_HPP
+
+
+// #include "../core/attribute.h"
+
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct meta_type_node;
+
+
+        struct ENTT_API meta_context {
+            // we could use the lines below but VS2017 returns with an ICE if combined with ENTT_API despite the code being valid C++
+            //     inline static meta_type_node *local = nullptr;
+            //     inline static meta_type_node **global = &local;
+
+            [[nodiscard]] static meta_type_node*& local() ENTT_NOEXCEPT {
+                static meta_type_node* chain = nullptr;
+                return chain;
+            }
+
+            [[nodiscard]] static meta_type_node**& global() ENTT_NOEXCEPT {
+                static meta_type_node** chain = &local();
+                return chain;
+            }
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Opaque container for a meta context. */
+    struct meta_ctx {
+        /**
+         * @brief Binds the meta system to a given context.
+         * @param other A valid context to which to bind.
+         */
+        static void bind(meta_ctx other) ENTT_NOEXCEPT {
+            internal::meta_context::global() = other.ctx;
+        }
+
+    private:
+        internal::meta_type_node** ctx{ &internal::meta_context::local() };
+    };
+
+
+}
+
+
+#endif
+
+// #include "node.hpp"
+#ifndef ENTT_META_NODE_HPP
+#define ENTT_META_NODE_HPP
+
+
+#include <cstddef>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    class meta_any;
+    class meta_type;
+    struct meta_handle;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct meta_type_node;
+
+
+        struct meta_prop_node {
+            meta_prop_node* next;
+            const meta_any& id;
+            meta_any& value;
+        };
+
+
+        struct meta_base_node {
+            meta_type_node* const parent;
+            meta_base_node* next;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            const void* (* const cast)(const void*) ENTT_NOEXCEPT;
+        };
+
+
+        struct meta_conv_node {
+            meta_type_node* const parent;
+            meta_conv_node* next;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            meta_any(* const conv)(const void*);
+        };
+
+
+        struct meta_ctor_node {
+            using size_type = std::size_t;
+            meta_type_node* const parent;
+            meta_ctor_node* next;
+            meta_prop_node* prop;
+            const size_type arity;
+            meta_type(* const arg)(const size_type) ENTT_NOEXCEPT;
+            meta_any(* const invoke)(meta_any* const);
+        };
+
+
+        struct meta_data_node {
+            id_type id;
+            meta_type_node* const parent;
+            meta_data_node* next;
+            meta_prop_node* prop;
+            const bool is_const;
+            const bool is_static;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            bool(* const set)(meta_handle, meta_any);
+            meta_any(* const get)(meta_handle);
+        };
+
+
+        struct meta_func_node {
+            using size_type = std::size_t;
+            id_type id;
+            meta_type_node* const parent;
+            meta_func_node* next;
+            meta_prop_node* prop;
+            const size_type arity;
+            const bool is_const;
+            const bool is_static;
+            meta_type_node* (* const ret)() ENTT_NOEXCEPT;
+            meta_type(* const arg)(const size_type) ENTT_NOEXCEPT;
+            meta_any(* const invoke)(meta_handle, meta_any*);
+        };
+
+
+        struct meta_template_info {
+            using size_type = std::size_t;
+            const bool is_template_specialization;
+            const size_type arity;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            meta_type_node* (* const arg)(const size_type) ENTT_NOEXCEPT;
+        };
+
+
+        struct meta_type_node {
+            using size_type = std::size_t;
+            const type_info info;
+            id_type id;
+            meta_type_node* next;
+            meta_prop_node* prop;
+            const size_type size_of;
+            const bool is_void;
+            const bool is_integral;
+            const bool is_floating_point;
+            const bool is_array;
+            const bool is_enum;
+            const bool is_union;
+            const bool is_class;
+            const bool is_pointer;
+            const bool is_function_pointer;
+            const bool is_member_object_pointer;
+            const bool is_member_function_pointer;
+            const bool is_pointer_like;
+            const bool is_sequence_container;
+            const bool is_associative_container;
+            const meta_template_info template_info;
+            const size_type rank;
+            size_type(* const extent)(const size_type) ENTT_NOEXCEPT;
+            meta_type_node* (* const remove_pointer)() ENTT_NOEXCEPT;
+            meta_type_node* (* const remove_extent)() ENTT_NOEXCEPT;
+            meta_ctor_node* const def_ctor;
+            meta_ctor_node* ctor{ nullptr };
+            meta_base_node* base{ nullptr };
+            meta_conv_node* conv{ nullptr };
+            meta_data_node* data{ nullptr };
+            meta_func_node* func{ nullptr };
+            void(*dtor)(void*) { nullptr };
+        };
+
+
+        template<auto Member, typename Op, typename Node>
+        auto meta_visit(const Op& op, const Node* node)
+            -> std::decay_t<decltype(node->*Member)> {
+            for (auto* curr = node->*Member; curr; curr = curr->next) {
+                if (op(curr)) {
+                    return curr;
+                }
+            }
+
+            if constexpr (std::is_same_v<Node, meta_type_node>) {
+                for (auto* curr = node->base; curr; curr = curr->next) {
+                    if (auto* ret = meta_visit<Member>(op, curr->type()); ret) {
+                        return ret;
+                    }
+                }
+            }
+
+            return nullptr;
+        }
+
+
+        template<typename... Args>
+        meta_type_node* meta_arg_node(type_list<Args...>, const std::size_t index) ENTT_NOEXCEPT;
+
+
+        template<typename Type>
+        class ENTT_API meta_node {
+            static_assert(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>, "Invalid type");
+
+            template<std::size_t... Index>
+            [[nodiscard]] static auto extent(const meta_type_node::size_type dim, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+                meta_type_node::size_type ext{};
+                ((ext = (dim == Index ? std::extent_v<Type, Index> : ext)), ...);
+                return ext;
+            }
+
+            [[nodiscard]] static meta_ctor_node* meta_default_constructor([[maybe_unused]] meta_type_node* type) ENTT_NOEXCEPT {
+                if constexpr (std::is_default_constructible_v<Type>) {
+                    static meta_ctor_node node{
+                        type,
+                        nullptr,
+                        nullptr,
+                        0u,
+                        nullptr,
+                        [](meta_any* const) { return meta_any{std::in_place_type<Type>}; }
+                    };
+
+                    return &node;
+                }
+                else {
+                    return nullptr;
+                }
+            }
+
+            [[nodiscard]] static meta_template_info meta_template_descriptor() ENTT_NOEXCEPT {
+                if constexpr (is_complete_v<meta_template_traits<Type>>) {
+                    return {
+                        true,
+                        meta_template_traits<Type>::args_type::size,
+                        &meta_node<typename meta_template_traits<Type>::class_type>::resolve,
+                        [](const std::size_t index) ENTT_NOEXCEPT {
+                            return meta_arg_node(typename meta_template_traits<Type>::args_type{}, index);
+                        }
+                    };
+                }
+                else {
+                    return { false, 0u, nullptr, nullptr };
+                }
+            }
+
+        public:
+            [[nodiscard]] static meta_type_node* resolve() ENTT_NOEXCEPT {
+                static meta_type_node node{
+                    type_id<Type>(),
+                    {},
+                    nullptr,
+                    nullptr,
+                    size_of_v<Type>,
+                    std::is_void_v<Type>,
+                    std::is_integral_v<Type>,
+                    std::is_floating_point_v<Type>,
+                    std::is_array_v<Type>,
+                    std::is_enum_v<Type>,
+                    std::is_union_v<Type>,
+                    std::is_class_v<Type>,
+                    std::is_pointer_v<Type>,
+                    std::is_pointer_v<Type> && std::is_function_v<std::remove_pointer_t<Type>>,
+                    std::is_member_object_pointer_v<Type>,
+                    std::is_member_function_pointer_v<Type>,
+                    is_meta_pointer_like_v<Type>,
+                    is_complete_v<meta_sequence_container_traits<Type>>,
+                    is_complete_v<meta_associative_container_traits<Type>>,
+                    meta_template_descriptor(),
+                    std::rank_v<Type>,
+                    [](meta_type_node::size_type dim) ENTT_NOEXCEPT { return extent(dim, std::make_index_sequence<std::rank_v<Type>>{}); },
+                    & meta_node<std::remove_cv_t<std::remove_reference_t<std::remove_pointer_t<Type>>>>::resolve,
+                    & meta_node<std::remove_cv_t<std::remove_reference_t<std::remove_extent_t<Type>>>>::resolve,
+                    meta_default_constructor(&node),
+                    meta_default_constructor(&node)
+                };
+
+                return &node;
+            }
+        };
+
+
+        template<typename Type>
+        struct meta_info : meta_node<std::remove_cv_t<std::remove_reference_t<Type>>> {};
+
+
+        template<typename... Args>
+        meta_type_node* meta_arg_node(type_list<Args...>, const std::size_t index) ENTT_NOEXCEPT {
+            meta_type_node* args[sizeof...(Args) + 1u]{ nullptr, internal::meta_info<Args>::resolve()... };
+            return args[index + 1u];
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+}
+
+
+#endif
+
+// #include "range.hpp"
+#ifndef ENTT_META_RANGE_HPP
+#define ENTT_META_RANGE_HPP
+
+
+#include <cstddef>
+#include <iterator>
+
+
+namespace entt {
+
+
+    /**
+     * @brief Iterable range to use to iterate all types of meta objects.
+     * @tparam Type Type of meta objects returned.
+     * @tparam Node Type of meta nodes iterated.
+     */
+    template<typename Type, typename Node = typename Type::node_type>
+    class meta_range {
+        struct range_iterator {
+            using difference_type = std::ptrdiff_t;
+            using value_type = Type;
+            using pointer = void;
+            using reference = value_type;
+            using iterator_category = std::input_iterator_tag;
+            using node_type = Node;
+
+            range_iterator() ENTT_NOEXCEPT = default;
+
+            range_iterator(node_type* head) ENTT_NOEXCEPT
+                : it{ head }
+            {}
+
+            range_iterator& operator++() ENTT_NOEXCEPT {
+                return (it = it->next), * this;
+            }
+
+            range_iterator operator++(int) ENTT_NOEXCEPT {
+                range_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                return it;
+            }
+
+            [[nodiscard]] bool operator==(const range_iterator& other) const ENTT_NOEXCEPT {
+                return other.it == it;
+            }
+
+            [[nodiscard]] bool operator!=(const range_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+        private:
+            node_type* it{};
+        };
+
+    public:
+        /*! @brief Node type. */
+        using node_type = Node;
+        /*! @brief Input iterator type. */
+        using iterator = range_iterator;
+
+        /*! @brief Default constructor. */
+        meta_range() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Constructs a meta range from a given node.
+         * @param head The underlying node with which to construct the range.
+         */
+        meta_range(node_type* head)
+            : node{ head }
+        {}
+
+        /**
+         * @brief Returns an iterator to the beginning.
+         * @return An iterator to the first meta object of the range.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return iterator{ node };
+        }
+
+        /**
+         * @brief Returns an iterator to the end.
+         * @return An iterator to the element following the last meta object of the
+         * range.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return iterator{};
+        }
+
+    private:
+        node_type* node{ nullptr };
+    };
+
+
+}
+
+
+#endif
+
+// #include "type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    class meta_any;
+    class meta_type;
+
+
+    /*! @brief Proxy object for sequence containers. */
+    class meta_sequence_container {
+        template<typename>
+        struct meta_sequence_container_proxy;
+
+        class meta_iterator;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Meta iterator type. */
+        using iterator = meta_iterator;
+
+        /*! @brief Default constructor. */
+        meta_sequence_container() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Construct a proxy object for sequence containers.
+         * @tparam Type Type of container to wrap.
+         * @param instance The container to wrap.
+         */
+        template<typename Type>
+        meta_sequence_container(std::in_place_type_t<Type>, any instance) ENTT_NOEXCEPT
+            : value_type_fn{ &meta_sequence_container_proxy<Type>::value_type },
+            size_fn{ &meta_sequence_container_proxy<Type>::size },
+            resize_fn{ &meta_sequence_container_proxy<Type>::resize },
+            clear_fn{ &meta_sequence_container_proxy<Type>::clear },
+            begin_fn{ &meta_sequence_container_proxy<Type>::begin },
+            end_fn{ &meta_sequence_container_proxy<Type>::end },
+            insert_fn{ &meta_sequence_container_proxy<Type>::insert },
+            erase_fn{ &meta_sequence_container_proxy<Type>::erase },
+            get_fn{ &meta_sequence_container_proxy<Type>::get },
+            storage{ std::move(instance) }
+        {}
+
+        [[nodiscard]] inline meta_type value_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline size_type size() const ENTT_NOEXCEPT;
+        inline bool resize(size_type);
+        inline bool clear();
+        [[nodiscard]] inline iterator begin();
+        [[nodiscard]] inline iterator end();
+        inline std::pair<iterator, bool> insert(iterator, meta_any);
+        inline std::pair<iterator, bool> erase(iterator);
+        [[nodiscard]] inline meta_any operator[](size_type);
+        [[nodiscard]] inline explicit operator bool() const ENTT_NOEXCEPT;
+
+    private:
+        meta_type(*value_type_fn)() ENTT_NOEXCEPT = nullptr;
+        size_type(*size_fn)(const any&) ENTT_NOEXCEPT = nullptr;
+        bool(*resize_fn)(any&, size_type) = nullptr;
+        bool(*clear_fn)(any&) = nullptr;
+        iterator(*begin_fn)(any&) = nullptr;
+        iterator(*end_fn)(any&) = nullptr;
+        std::pair<iterator, bool>(*insert_fn)(any&, iterator, meta_any&) = nullptr;
+        std::pair<iterator, bool>(*erase_fn)(any&, iterator) = nullptr;
+        meta_any(*get_fn)(any&, size_type) = nullptr;
+        any storage{};
+    };
+
+
+    /*! @brief Proxy object for associative containers. */
+    class meta_associative_container {
+        template<typename>
+        struct meta_associative_container_proxy;
+
+        class meta_iterator;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Meta iterator type. */
+        using iterator = meta_iterator;
+
+        /*! @brief Default constructor. */
+        meta_associative_container() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Construct a proxy object for associative containers.
+         * @tparam Type Type of container to wrap.
+         * @param instance The container to wrap.
+         */
+        template<typename Type>
+        meta_associative_container(std::in_place_type_t<Type>, any instance) ENTT_NOEXCEPT
+            : key_only_container{ is_key_only_meta_associative_container_v<Type> },
+            key_type_fn{ &meta_associative_container_proxy<Type>::key_type },
+            mapped_type_fn{ &meta_associative_container_proxy<Type>::mapped_type },
+            value_type_fn{ &meta_associative_container_proxy<Type>::value_type },
+            size_fn{ &meta_associative_container_proxy<Type>::size },
+            clear_fn{ &meta_associative_container_proxy<Type>::clear },
+            begin_fn{ &meta_associative_container_proxy<Type>::begin },
+            end_fn{ &meta_associative_container_proxy<Type>::end },
+            insert_fn{ &meta_associative_container_proxy<Type>::insert },
+            erase_fn{ &meta_associative_container_proxy<Type>::erase },
+            find_fn{ &meta_associative_container_proxy<Type>::find },
+            storage{ std::move(instance) }
+        {}
+
+        [[nodiscard]] inline bool key_only() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline meta_type key_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline meta_type mapped_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline meta_type value_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline size_type size() const ENTT_NOEXCEPT;
+        inline bool clear();
+        [[nodiscard]] inline iterator begin();
+        [[nodiscard]] inline iterator end();
+        inline bool insert(meta_any, meta_any);
+        inline bool erase(meta_any);
+        [[nodiscard]] inline iterator find(meta_any);
+        [[nodiscard]] inline explicit operator bool() const ENTT_NOEXCEPT;
+
+    private:
+        bool key_only_container{};
+        meta_type(*key_type_fn)() ENTT_NOEXCEPT = nullptr;
+        meta_type(*mapped_type_fn)() ENTT_NOEXCEPT = nullptr;
+        meta_type(*value_type_fn)() ENTT_NOEXCEPT = nullptr;
+        size_type(*size_fn)(const any&) ENTT_NOEXCEPT = nullptr;
+        bool(*clear_fn)(any&) = nullptr;
+        iterator(*begin_fn)(any&) = nullptr;
+        iterator(*end_fn)(any&) = nullptr;
+        bool(*insert_fn)(any&, meta_any&, meta_any&) = nullptr;
+        bool(*erase_fn)(any&, meta_any&) = nullptr;
+        iterator(*find_fn)(any&, meta_any&) = nullptr;
+        any storage{};
+    };
+
+
+    /*! @brief Opaque wrapper for values of any type. */
+    class meta_any {
+        enum class operation { DTOR, DEREF, SEQ, ASSOC };
+
+        using vtable_type = void(const operation, const any&, void*);
+
+        template<typename Type>
+        static void basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                switch (op) {
+                case operation::DTOR:
+                    if (auto* curr = static_cast<internal::meta_type_node*>(to); curr->dtor && from.owner()) {
+                        curr->dtor(const_cast<any&>(from).data());
+                    }
+                    break;
+                case operation::DEREF:
+                    if constexpr (is_meta_pointer_like_v<Type>) {
+                        using element_type = std::remove_const_t<typename std::pointer_traits<Type>::element_type>;
+
+                        if constexpr (std::is_function_v<element_type>) {
+                            *static_cast<meta_any*>(to) = any_cast<Type>(from);
+                        }
+                        else if constexpr (!std::is_same_v<std::remove_const_t<typename std::pointer_traits<Type>::element_type>, void>) {
+                            using in_place_type = decltype(adl_meta_pointer_like<Type>::dereference(any_cast<const Type&>(from)));
+                            static_cast<meta_any*>(to)->emplace<in_place_type>(adl_meta_pointer_like<Type>::dereference(any_cast<const Type&>(from)));
+                        }
+                    }
+                case operation::SEQ:
+                    if constexpr (is_complete_v<meta_sequence_container_traits<Type>>) {
+                        *static_cast<meta_sequence_container*>(to) = { std::in_place_type<Type>, std::move(const_cast<any&>(from)) };
+                    }
+                    break;
+                case operation::ASSOC:
+                    if constexpr (is_complete_v<meta_associative_container_traits<Type>>) {
+                        *static_cast<meta_associative_container*>(to) = { std::in_place_type<Type>, std::move(const_cast<any&>(from)) };
+                    }
+                    break;
+                }
+            }
+        }
+
+        meta_any(const meta_any& other, any ref) ENTT_NOEXCEPT
+            : storage{ std::move(ref) },
+            node{ storage ? other.node : nullptr },
+            vtable{ storage ? other.vtable : &basic_vtable<void> }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        meta_any() ENTT_NOEXCEPT
+            : storage{},
+            node{},
+            vtable{ &basic_vtable<void> }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit meta_any(std::in_place_type_t<Type>, Args &&... args)
+            : storage{ std::in_place_type<Type>, std::forward<Args>(args)... },
+            node{ internal::meta_info<Type>::resolve() },
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> }
+        {}
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        meta_any(std::reference_wrapper<Type> value)
+            : meta_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>>>
+        meta_any(Type&& value)
+            : storage{ std::forward<Type>(value) },
+            node{ internal::meta_info<std::decay_t<Type>>::resolve() },
+            vtable{ &basic_vtable<std::decay_t<Type>> }
+        {}
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        meta_any(const meta_any& other) = default;
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        meta_any(meta_any&& other) ENTT_NOEXCEPT
+            : storage{ std::move(other.storage) },
+            node{ std::exchange(other.node, nullptr) },
+            vtable{ std::exchange(other.vtable, &basic_vtable<void>) }
+        {}
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~meta_any() {
+            vtable(operation::DTOR, storage, node);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This meta any object.
+         */
+        meta_any& operator=(const meta_any& other) {
+            std::exchange(vtable, other.vtable)(operation::DTOR, storage, node);
+            storage = other.storage;
+            node = other.node;
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This meta any object.
+         */
+        meta_any& operator=(meta_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, std::exchange(other.vtable, &basic_vtable<void>))(operation::DTOR, storage, node);
+            storage = std::move(other.storage);
+            node = std::exchange(other.node, nullptr);
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This meta any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_meta<T &>, emplace<Type &> or forward_as_meta instead")]]
+        meta_any& operator=(std::reference_wrapper<Type> value) {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This meta any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>, meta_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the underlying object.
+         * @return The type of the underlying object, if any.
+         */
+        [[nodiscard]] inline meta_type type() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /**
+         * @brief Invokes the underlying function, if possible.
+         *
+         * @sa meta_func::invoke
+         *
+         * @tparam Args Types of arguments to use to invoke the function.
+         * @param id Unique identifier.
+         * @param args Parameters to use to invoke the function.
+         * @return A wrapper containing the returned value, if any.
+         */
+        template<typename... Args>
+        meta_any invoke(const id_type id, Args &&... args) const;
+
+        /*! @copydoc invoke */
+        template<typename... Args>
+        meta_any invoke(const id_type id, Args &&... args);
+
+        /**
+         * @brief Sets the value of a given variable.
+         *
+         * The type of the value must be such that a cast or conversion to the type
+         * of the variable is possible. Otherwise, invoking the setter does nothing.
+         *
+         * @tparam Type Type of value to assign.
+         * @param id Unique identifier.
+         * @param value Parameter to use to set the underlying variable.
+         * @return True in case of success, false otherwise.
+         */
+        template<typename Type>
+        bool set(const id_type id, Type&& value);
+
+        /**
+         * @brief Gets the value of a given variable.
+         * @param id Unique identifier.
+         * @return A wrapper containing the value of the underlying variable.
+         */
+        [[nodiscard]] meta_any get(const id_type id) const;
+
+        /*! @copydoc get */
+        [[nodiscard]] meta_any get(const id_type id);
+
+        /**
+         * @brief Tries to cast an instance to a given type.
+         * @tparam Type Type to which to cast the instance.
+         * @return A (possibly null) pointer to the contained instance.
+         */
+        template<typename Type>
+        [[nodiscard]] const Type* try_cast() const {
+            if (node) {
+                if (const auto info = type_id<Type>(); node->info == info) {
+                    return any_cast<Type>(&storage);
+                }
+                else if (const auto* base = internal::meta_visit<&internal::meta_type_node::base>([info](const auto* curr) { return curr->type()->info == info; }, node); base) {
+                    return static_cast<const Type*>(base->cast(storage.data()));
+                }
+            }
+
+            return nullptr;
+        }
+
+        /*! @copydoc try_cast */
+        template<typename Type>
+        [[nodiscard]] Type* try_cast() {
+            if (node) {
+                if (const auto info = type_id<Type>(); node->info == info) {
+                    return any_cast<Type>(&storage);
+                }
+                else if (const auto* base = internal::meta_visit<&internal::meta_type_node::base>([info](const auto* curr) { return curr->type()->info == info; }, node); base) {
+                    return static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(base->cast(static_cast<constness_as_t<any, Type> &>(storage).data())));
+                }
+            }
+
+            return nullptr;
+        }
+
+        /**
+         * @brief Tries to cast an instance to a given type.
+         *
+         * The type of the instance must be such that the cast is possible.
+         *
+         * @warning
+         * Attempting to perform an invalid cast results in undefined behavior.
+         *
+         * @tparam Type Type to which to cast the instance.
+         * @return A reference to the contained instance.
+         */
+        template<typename Type>
+        [[nodiscard]] Type cast() const {
+            auto* const instance = try_cast<std::remove_reference_t<Type>>();
+            ENTT_ASSERT(instance, "Invalid instance");
+            return static_cast<Type>(*instance);
+        }
+
+        /*! @copydoc cast */
+        template<typename Type>
+        [[nodiscard]] Type cast() {
+            // forces const on non-reference types to make them work also with wrappers for const references
+            auto* const instance = try_cast<std::remove_reference_t<const Type>>();
+            ENTT_ASSERT(instance, "Invalid instance");
+            return static_cast<Type>(*instance);
+        }
+
+        /**
+         * @brief Converts an object in such a way that a given cast becomes viable.
+         * @tparam Type Type to which the cast is requested.
+         * @return A valid meta any object if there exists a viable conversion, an
+         * invalid one otherwise.
+         */
+        template<typename Type>
+        [[nodiscard]] meta_any allow_cast() const {
+            if (try_cast<std::remove_reference_t<Type>>() != nullptr) {
+                return as_ref();
+            }
+            else if (node) {
+                if (const auto* const conv = internal::meta_visit<&internal::meta_type_node::conv>([info = type_id<Type>()](const auto* curr) { return curr->type()->info == info; }, node); conv) {
+                    return conv->conv(storage.data());
+                }
+            }
+
+            return {};
+        }
+
+        /**
+         * @brief Converts an object in such a way that a given cast becomes viable.
+         * @tparam Type Type to which the cast is requested.
+         * @return True if there exists a viable conversion, false otherwise.
+         */
+        template<typename Type>
+        bool allow_cast() {
+            // forces const on non-reference types to make them work also with wrappers for const references
+            if (try_cast<std::remove_reference_t<const Type>>() != nullptr) {
+                return true;
+            }
+            else if (node) {
+                if (const auto* const conv = internal::meta_visit<&internal::meta_type_node::conv>([info = type_id<Type>()](const auto* curr) { return curr->type()->info == info; }, node); conv) {
+                    *this = conv->conv(std::as_const(storage).data());
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, storage, node);
+            storage.emplace<Type>(std::forward<Args>(args)...);
+            node = internal::meta_info<Type>::resolve();
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, storage, node);
+            storage.reset();
+            node = nullptr;
+        }
+
+        /**
+         * @brief Returns a sequence container proxy.
+         * @return A sequence container proxy for the underlying object.
+         */
+        [[nodiscard]] meta_sequence_container as_sequence_container() ENTT_NOEXCEPT {
+            meta_sequence_container proxy;
+            vtable(operation::SEQ, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /*! @copydoc as_sequence_container */
+        [[nodiscard]] meta_sequence_container as_sequence_container() const ENTT_NOEXCEPT {
+            meta_sequence_container proxy;
+            vtable(operation::SEQ, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /**
+         * @brief Returns an associative container proxy.
+         * @return An associative container proxy for the underlying object.
+         */
+        [[nodiscard]] meta_associative_container as_associative_container() ENTT_NOEXCEPT {
+            meta_associative_container proxy;
+            vtable(operation::ASSOC, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /*! @copydoc as_associative_container */
+        [[nodiscard]] meta_associative_container as_associative_container() const ENTT_NOEXCEPT {
+            meta_associative_container proxy;
+            vtable(operation::ASSOC, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /**
+         * @brief Indirection operator for dereferencing opaque objects.
+         * @return A wrapper that shares a reference to an unmanaged object if the
+         * wrapped element is dereferenceable, an invalid meta any otherwise.
+         */
+        [[nodiscard]] meta_any operator*() const ENTT_NOEXCEPT {
+            meta_any ret{};
+            vtable(operation::DEREF, storage, &ret);
+            return ret;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is invalid, true otherwise.
+         * @return False if the wrapper is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_any& other) const {
+            return (!node && !other.node) || (node && other.node && node->info == other.node->info && storage == other.storage);
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] meta_any as_ref() ENTT_NOEXCEPT {
+            return meta_any{ *this, storage.as_ref() };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] meta_any as_ref() const ENTT_NOEXCEPT {
+            return meta_any{ *this, storage.as_ref() };
+        }
+
+    private:
+        any storage;
+        internal::meta_type_node* node;
+        vtable_type* vtable;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const meta_any& lhs, const meta_any& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, typename... Args>
+    meta_any make_meta(Args &&... args) {
+        return meta_any{ std::in_place_type<Type>, std::forward<Args>(args)... };
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<typename Type>
+    meta_any forward_as_meta(Type&& value) {
+        return meta_any{ std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value) };
+    }
+
+
+    /**
+     * @brief Opaque pointers to instances of any type.
+     *
+     * A handle doesn't perform copies and isn't responsible for the contained
+     * object. It doesn't prolong the lifetime of the pointed instance.<br/>
+     * Handles are used to generate references to actual objects when needed.
+     */
+    struct meta_handle {
+        /*! @brief Default constructor. */
+        meta_handle() = default;
+
+
+        /*! @brief Default copy constructor, deleted on purpose. */
+        meta_handle(const meta_handle&) = delete;
+
+        /*! @brief Default move constructor. */
+        meta_handle(meta_handle&&) = default;
+
+        /**
+         * @brief Default copy assignment operator, deleted on purpose.
+         * @return This meta handle.
+         */
+        meta_handle& operator=(const meta_handle&) = delete;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This meta handle.
+         */
+        meta_handle& operator=(meta_handle&&) = default;
+
+        /**
+         * @brief Creates a handle that points to an unmanaged object.
+         * @tparam Type Type of object to use to initialize the handle.
+         * @param value An instance of an object to use to initialize the handle.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_handle>>>
+        meta_handle(Type& value) ENTT_NOEXCEPT
+            : meta_handle{}
+        {
+            if constexpr (std::is_same_v<std::decay_t<Type>, meta_any>) {
+                any = value.as_ref();
+            }
+            else {
+                any.emplace<Type&>(value);
+            }
+        }
+
+        /**
+         * @brief Returns false if a handle is invalid, true otherwise.
+         * @return False if the handle is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(any);
+        }
+
+        /**
+         * @brief Access operator for accessing the contained opaque object.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] meta_any* operator->() {
+            return &any;
+        }
+
+        /*! @copydoc operator-> */
+        [[nodiscard]] const meta_any* operator->() const {
+            return &any;
+        }
+
+    private:
+        meta_any any;
+    };
+
+
+    /*! @brief Opaque wrapper for properties of any type. */
+    struct meta_prop {
+        /*! @brief Node type. */
+        using node_type = internal::meta_prop_node;
+
+        /**
+         * @brief Constructs an instance from a given node.
+         * @param curr The underlying node with which to construct the instance.
+         */
+        meta_prop(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /**
+         * @brief Returns the stored key as a const reference.
+         * @return A wrapper containing the key stored with the property.
+         */
+        [[nodiscard]] meta_any key() const {
+            return node->id.as_ref();
+        }
+
+        /**
+         * @brief Returns the stored value by copy.
+         * @return A wrapper containing the value stored with the property.
+         */
+        [[nodiscard]] meta_any value() const {
+            return node->value;
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for constructors. */
+    struct meta_ctor {
+        /*! @brief Node type. */
+        using node_type = internal::meta_ctor_node;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename node_type::size_type;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_ctor(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /**
+         * @brief Returns the type to which an object belongs.
+         * @return The type to which the object belongs.
+         */
+        [[nodiscard]] inline meta_type parent() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns the number of arguments accepted by a constructor.
+         * @return The number of arguments accepted by the constructor.
+         */
+        [[nodiscard]] size_type arity() const ENTT_NOEXCEPT {
+            return node->arity;
+        }
+
+        /**
+         * @brief Returns the type of the i-th argument of a constructor.
+         * @param index Index of the argument of which to return the type.
+         * @return The type of the i-th argument of a constructor.
+         */
+        [[nodiscard]] meta_type arg(size_type index) const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Creates an instance of the underlying type, if possible.
+         *
+         * Parameters must be such that a cast or conversion to the required types
+         * is possible. Otherwise, an empty and thus invalid wrapper is returned.
+         *
+         * @param args Parameters to use to construct the instance.
+         * @param sz Number of parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        [[nodiscard]] meta_any invoke(meta_any* const args, const size_type sz) const {
+            return sz == arity() ? node->invoke(args) : meta_any{};
+        }
+
+        /**
+         * @copybrief invoke
+         *
+         * @sa invoke
+         *
+         * @tparam Args Types of arguments to use to construct the instance.
+         * @param args Parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        [[nodiscard]] meta_any invoke([[maybe_unused]] Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return invoke(arguments, sizeof...(Args));
+        }
+
+        /**
+         * @brief Returns a range to use to visit all properties.
+         * @return An iterable range to use to visit all properties.
+         */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for data members. */
+    struct meta_data {
+        /*! @brief Node type. */
+        using node_type = internal::meta_data_node;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_data(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /*! @copydoc meta_type::id */
+        [[nodiscard]] id_type id() const ENTT_NOEXCEPT {
+            return node->id;
+        }
+
+        /*! @copydoc meta_ctor::parent */
+        [[nodiscard]] inline meta_type parent() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Indicates whether a data member is constant or not.
+         * @return True if the data member is constant, false otherwise.
+         */
+        [[nodiscard]] bool is_const() const ENTT_NOEXCEPT {
+            return node->is_const;
+        }
+
+        /**
+         * @brief Indicates whether a data member is static or not.
+         * @return True if the data member is static, false otherwise.
+         */
+        [[nodiscard]] bool is_static() const ENTT_NOEXCEPT {
+            return node->is_static;
+        }
+
+        /*! @copydoc meta_any::type */
+        [[nodiscard]] inline meta_type type() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Sets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the setter results in an undefined
+         * behavior.<br/>
+         * The type of the value must be such that a cast or conversion to the type
+         * of the variable is possible. Otherwise, invoking the setter does nothing.
+         *
+         * @tparam Type Type of value to assign.
+         * @param instance An opaque instance of the underlying type.
+         * @param value Parameter to use to set the underlying variable.
+         * @return True in case of success, false otherwise.
+         */
+        template<typename Type>
+        bool set(meta_handle instance, Type&& value) const {
+            return node->set && node->set(std::move(instance), std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Gets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the getter results in an undefined behavior.
+         *
+         * @param instance An opaque instance of the underlying type.
+         * @return A wrapper containing the value of the underlying variable.
+         */
+        [[nodiscard]] meta_any get(meta_handle instance) const {
+            return node->get(std::move(instance));
+        }
+
+        /*! @copydoc meta_ctor::prop */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for member functions. */
+    struct meta_func {
+        /*! @brief Node type. */
+        using node_type = internal::meta_func_node;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename node_type::size_type;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_func(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /*! @copydoc meta_type::id */
+        [[nodiscard]] id_type id() const ENTT_NOEXCEPT {
+            return node->id;
+        }
+
+        /*! @copydoc meta_ctor::parent */
+        [[nodiscard]] inline meta_type parent() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns the number of arguments accepted by a member function.
+         * @return The number of arguments accepted by the member function.
+         */
+        [[nodiscard]] size_type arity() const ENTT_NOEXCEPT {
+            return node->arity;
+        }
+
+        /**
+         * @brief Indicates whether a member function is constant or not.
+         * @return True if the member function is constant, false otherwise.
+         */
+        [[nodiscard]] bool is_const() const ENTT_NOEXCEPT {
+            return node->is_const;
+        }
+
+        /**
+         * @brief Indicates whether a member function is static or not.
+         * @return True if the member function is static, false otherwise.
+         */
+        [[nodiscard]] bool is_static() const ENTT_NOEXCEPT {
+            return node->is_static;
+        }
+
+        /**
+         * @brief Returns the return type of a member function.
+         * @return The return type of the member function.
+         */
+        [[nodiscard]] inline meta_type ret() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns the type of the i-th argument of a member function.
+         * @param index Index of the argument of which to return the type.
+         * @return The type of the i-th argument of a member function.
+         */
+        [[nodiscard]] inline meta_type arg(size_type index) const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Invokes the underlying function, if possible.
+         *
+         * To invoke a member function, the parameters must be such that a cast or
+         * conversion to the required types is possible. Otherwise, an empty and
+         * thus invalid wrapper is returned.<br/>
+         * It must be possible to cast the instance to the parent type of the member
+         * function. Otherwise, invoking the underlying function results in an
+         * undefined behavior.
+         *
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @param sz Number of parameters to use to invoke the function.
+         * @return A wrapper containing the returned value, if any.
+         */
+        meta_any invoke(meta_handle instance, meta_any* const args, const size_type sz) const {
+            return sz == arity() ? node->invoke(std::move(instance), args) : meta_any{};
+        }
+
+        /**
+         * @copybrief invoke
+         *
+         * @sa invoke
+         *
+         * @tparam Args Types of arguments to use to invoke the function.
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        meta_any invoke(meta_handle instance, Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return invoke(std::move(instance), arguments, sizeof...(Args));
+        }
+
+        /*! @copydoc meta_ctor::prop */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for types. */
+    class meta_type {
+        static bool can_cast_or_convert(const internal::meta_type_node* type, const type_info info) ENTT_NOEXCEPT {
+            if (type->info == info) {
+                return true;
+            }
+
+            for (const auto* curr = type->conv; curr; curr = curr->next) {
+                if (curr->type()->info == info) {
+                    return true;
+                }
+            }
+
+            for (const auto* curr = type->base; curr; curr = curr->next) {
+                if (auto* target = curr->type(); can_cast_or_convert(target, info)) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        template<typename... Args, auto... Index>
+        [[nodiscard]] static const internal::meta_ctor_node* ctor(const internal::meta_ctor_node* curr, std::index_sequence<Index...>) {
+            for (; curr; curr = curr->next) {
+                if (curr->arity == sizeof...(Args) && (can_cast_or_convert(internal::meta_info<Args>::resolve(), curr->arg(Index).info()) && ...)) {
+                    return curr;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<auto... Member, typename Node>
+        void unregister_all(Node** curr) {
+            while (*curr) {
+                (unregister_all(&((*curr)->*Member)), ...);
+                *curr = std::exchange((*curr)->next, nullptr);
+            }
+        }
+
+    public:
+        /*! @brief Node type. */
+        using node_type = internal::meta_type_node;
+        /*! @brief Node type. */
+        using base_node_type = internal::meta_base_node;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename node_type::size_type;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_type(node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /**
+         * @brief Constructs an instance from a given base node.
+         * @param curr The base node with which to construct the instance.
+         */
+        meta_type(base_node_type* curr) ENTT_NOEXCEPT
+            : node{ curr ? curr->type() : nullptr }
+        {}
+
+        /**
+         * @brief Returns the type info object of the underlying type.
+         * @return The type info object of the underlying type.
+         */
+        [[nodiscard]] type_info info() const ENTT_NOEXCEPT {
+            return node->info;
+        }
+
+        /**
+         * @brief Returns the identifier assigned to a type.
+         * @return The identifier assigned to the type.
+         */
+        [[nodiscard]] id_type id() const ENTT_NOEXCEPT {
+            return node->id;
+        }
+
+        /**
+         * @brief Returns the size of the underlying type if known.
+         * @return The size of the underlying type if known, 0 otherwise.
+         */
+        [[nodiscard]] size_type size_of() const ENTT_NOEXCEPT {
+            return node->size_of;
+        }
+
+        /**
+         * @brief Checks whether a type refers to void or not.
+         * @return True if the underlying type is void, false otherwise.
+         */
+        [[nodiscard]] bool is_void() const ENTT_NOEXCEPT {
+            return node->is_void;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an integral type or not.
+         * @return True if the underlying type is an integral type, false otherwise.
+         */
+        [[nodiscard]] bool is_integral() const ENTT_NOEXCEPT {
+            return node->is_integral;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a floating-point type or not.
+         * @return True if the underlying type is a floating-point type, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_floating_point() const ENTT_NOEXCEPT {
+            return node->is_floating_point;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an array type or not.
+         * @return True if the underlying type is an array type, false otherwise.
+         */
+        [[nodiscard]] bool is_array() const ENTT_NOEXCEPT {
+            return node->is_array;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an enum or not.
+         * @return True if the underlying type is an enum, false otherwise.
+         */
+        [[nodiscard]] bool is_enum() const ENTT_NOEXCEPT {
+            return node->is_enum;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an union or not.
+         * @return True if the underlying type is an union, false otherwise.
+         */
+        [[nodiscard]] bool is_union() const ENTT_NOEXCEPT {
+            return node->is_union;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a class or not.
+         * @return True if the underlying type is a class, false otherwise.
+         */
+        [[nodiscard]] bool is_class() const ENTT_NOEXCEPT {
+            return node->is_class;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a pointer or not.
+         * @return True if the underlying type is a pointer, false otherwise.
+         */
+        [[nodiscard]] bool is_pointer() const ENTT_NOEXCEPT {
+            return node->is_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a function pointer or not.
+         * @return True if the underlying type is a function pointer, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_function_pointer() const ENTT_NOEXCEPT {
+            return node->is_function_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a pointer to data member or not.
+         * @return True if the underlying type is a pointer to data member, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_member_object_pointer() const ENTT_NOEXCEPT {
+            return node->is_member_object_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a pointer to member function or
+         * not.
+         * @return True if the underlying type is a pointer to member function,
+         * false otherwise.
+         */
+        [[nodiscard]] bool is_member_function_pointer() const ENTT_NOEXCEPT {
+            return node->is_member_function_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type is a pointer-like type or not.
+         * @return True if the underlying type is a pointer-like one, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_pointer_like() const ENTT_NOEXCEPT {
+            return node->is_pointer_like;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a sequence container or not.
+         * @return True if the type is a sequence container, false otherwise.
+         */
+        [[nodiscard]] bool is_sequence_container() const ENTT_NOEXCEPT {
+            return node->is_sequence_container;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an associative container or not.
+         * @return True if the type is an associative container, false otherwise.
+         */
+        [[nodiscard]] bool is_associative_container() const ENTT_NOEXCEPT {
+            return node->is_associative_container;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a recognized class template
+         * specialization or not.
+         * @return True if the type is a recognized class template specialization,
+         * false otherwise.
+         */
+        [[nodiscard]] bool is_template_specialization() const ENTT_NOEXCEPT {
+            return node->template_info.is_template_specialization;
+        }
+
+        /**
+         * @brief Returns the number of template arguments, if any.
+         * @return The number of template arguments, if any.
+         */
+        [[nodiscard]] size_type template_arity() const ENTT_NOEXCEPT {
+            return node->template_info.arity;
+        }
+
+        /**
+         * @brief Returns a tag for the class template of the underlying type.
+         *
+         * @sa meta_class_template_tag
+         *
+         * @return The tag for the class template of the underlying type.
+         */
+        [[nodiscard]] inline meta_type template_type() const ENTT_NOEXCEPT {
+            return is_template_specialization() ? node->template_info.type() : meta_type{};
+        }
+
+        /**
+         * @brief Returns the type of the i-th template argument of a type.
+         * @param index Index of the template argument of which to return the type.
+         * @return The type of the i-th template argument of a type.
+         */
+        [[nodiscard]] inline meta_type template_arg(size_type index) const ENTT_NOEXCEPT {
+            return index < template_arity() ? node->template_info.arg(index) : meta_type{};
+        }
+
+        /**
+         * @brief Provides the number of dimensions of an array type.
+         * @return The number of dimensions in case of array types, 0 otherwise.
+         */
+        [[nodiscard]] size_type rank() const ENTT_NOEXCEPT {
+            return node->rank;
+        }
+
+        /**
+         * @brief The number of elements along the given dimension of an array type.
+         * @param dim The dimension of which to return the number of elements.
+         * @return The number of elements along the given dimension in case of array
+         * types, 0 otherwise.
+         */
+        [[nodiscard]] size_type extent(size_type dim = {}) const ENTT_NOEXCEPT {
+            return node->extent(dim);
+        }
+
+        /**
+         * @brief Provides the type for which the pointer is defined.
+         * @return The type for which the pointer is defined or this type if it
+         * doesn't refer to a pointer type.
+         */
+        [[nodiscard]] meta_type remove_pointer() const ENTT_NOEXCEPT {
+            return node->remove_pointer();
+        }
+
+        /**
+         * @brief Provides the type for which the array is defined.
+         * @return The type for which the array is defined or this type if it
+         * doesn't refer to an array type.
+         */
+        [[nodiscard]] meta_type remove_extent() const ENTT_NOEXCEPT {
+            return node->remove_extent();
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level base meta types.
+         * @return An iterable range to use to visit top-level base meta types.
+         */
+        [[nodiscard]] meta_range<meta_type, internal::meta_base_node> base() const ENTT_NOEXCEPT {
+            return node->base;
+        }
+
+        /**
+         * @brief Returns the base meta type associated with a given identifier.
+         * @param id Unique identifier.
+         * @return The base meta type associated with the given identifier, if any.
+         */
+        [[nodiscard]] meta_type base(const id_type id) const {
+            return internal::meta_visit<&node_type::base>([id](const auto* curr) { return curr->type()->id == id; }, node);
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level constructors.
+         * @return An iterable range to use to visit top-level constructors.
+         */
+        [[nodiscard]] meta_range<meta_ctor> ctor() const ENTT_NOEXCEPT {
+            return node->ctor;
+        }
+
+        /**
+         * @brief Returns a constructor for a given list of types of arguments.
+         * @tparam Args Constructor arguments.
+         * @return The requested constructor, if any.
+         */
+        template<typename... Args>
+        [[nodiscard]] meta_ctor ctor() const {
+            return ctor<Args...>(node->ctor, std::make_index_sequence<sizeof...(Args)>{});
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level data.
+         * @return An iterable range to use to visit top-level data.
+         */
+        [[nodiscard]] meta_range<meta_data> data() const ENTT_NOEXCEPT {
+            return node->data;
+        }
+
+        /**
+         * @brief Returns the data associated with a given identifier.
+         *
+         * The data of the base classes will also be visited, if any.
+         *
+         * @param id Unique identifier.
+         * @return The data associated with the given identifier, if any.
+         */
+        [[nodiscard]] meta_data data(const id_type id) const {
+            return internal::meta_visit<&node_type::data>([id](const auto* curr) { return curr->id == id; }, node);
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level functions.
+         * @return An iterable range to use to visit top-level functions.
+         */
+        [[nodiscard]] meta_range<meta_func> func() const ENTT_NOEXCEPT {
+            return node->func;
+        }
+
+        /**
+         * @brief Returns the function associated with a given identifier.
+         *
+         * The functions of the base classes will also be visited, if any.<br/>
+         * In the case of overloaded functions, the first one with the required
+         * identifier will be returned.
+         *
+         * @param id Unique identifier.
+         * @return The function associated with the given identifier, if any.
+         */
+        [[nodiscard]] meta_func func(const id_type id) const {
+            return internal::meta_visit<&node_type::func>([id](const auto* curr) { return curr->id == id; }, node);
+        }
+
+        /**
+         * @brief Creates an instance of the underlying type, if possible.
+         *
+         * Parameters must be such that a cast or conversion to the required types
+         * is possible. Otherwise, an empty and thus invalid wrapper is returned.
+         *
+         * @param args Parameters to use to construct the instance.
+         * @param sz Number of parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        [[nodiscard]] meta_any construct(meta_any* const args, const size_type sz) const {
+            meta_any ret{};
+            internal::meta_visit<&node_type::ctor>([args, sz, &ret](const auto* curr) { return (curr->arity == sz) && (ret = curr->invoke(args)); }, node);
+            return ret;
+        }
+
+        /**
+         * @copybrief construct
+         *
+         * @sa construct
+         *
+         * @tparam Args Types of arguments to use to construct the instance.
+         * @param args Parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        [[nodiscard]] meta_any construct(Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return construct(arguments, sizeof...(Args));
+        }
+
+        /**
+         * @brief Invokes a function given an identifier, if possible.
+         *
+         * It must be possible to cast the instance to the parent type of the member
+         * function. Otherwise, invoking the underlying function results in an
+         * undefined behavior.
+         *
+         * @sa meta_func::invoke
+         *
+         * @param id Unique identifier.
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @param sz Number of parameters to use to invoke the function.
+         * @return A wrapper containing the returned value, if any.
+         */
+        meta_any invoke(const id_type id, meta_handle instance, meta_any* const args, const size_type sz) const {
+            const internal::meta_func_node* candidate{};
+            size_type extent{ sz + 1u };
+            bool ambiguous{};
+
+            for (auto* it = internal::meta_visit<&node_type::func>([id, sz](const auto* curr) { return curr->id == id && curr->arity == sz; }, node); it && it->id == id && it->arity == sz; it = it->next) {
+                size_type direct{};
+                size_type ext{};
+
+                for (size_type next{}; next < sz && next == (direct + ext); ++next) {
+                    const auto type = args[next].type();
+                    const auto req = it->arg(next).info();
+                    type.info() == req ? ++direct : (ext += can_cast_or_convert(type.node, req));
+                }
+
+                if ((direct + ext) == sz) {
+                    if (ext < extent) {
+                        candidate = it;
+                        extent = ext;
+                        ambiguous = false;
+                    }
+                    else if (ext == extent) {
+                        ambiguous = true;
+                    }
+                }
+            }
+
+            return (candidate && !ambiguous) ? candidate->invoke(std::move(instance), args) : meta_any{};
+        }
+
+        /**
+         * @copybrief invoke
+         *
+         * @sa invoke
+         *
+         * @param id Unique identifier.
+         * @tparam Args Types of arguments to use to invoke the function.
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        meta_any invoke(const id_type id, meta_handle instance, Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return invoke(id, std::move(instance), arguments, sizeof...(Args));
+        }
+
+        /**
+         * @brief Sets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the setter results in an undefined
+         * behavior.<br/>
+         * The type of the value must be such that a cast or conversion to the type
+         * of the variable is possible. Otherwise, invoking the setter does nothing.
+         *
+         * @tparam Type Type of value to assign.
+         * @param id Unique identifier.
+         * @param instance An opaque instance of the underlying type.
+         * @param value Parameter to use to set the underlying variable.
+         * @return True in case of success, false otherwise.
+         */
+        template<typename Type>
+        bool set(const id_type id, meta_handle instance, Type&& value) const {
+            const auto candidate = data(id);
+            return candidate && candidate.set(std::move(instance), std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Gets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the getter results in an undefined behavior.
+         *
+         * @param id Unique identifier.
+         * @param instance An opaque instance of the underlying type.
+         * @return A wrapper containing the value of the underlying variable.
+         */
+        [[nodiscard]] meta_any get(const id_type id, meta_handle instance) const {
+            const auto candidate = data(id);
+            return candidate ? candidate.get(std::move(instance)) : meta_any{};
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level properties.
+         * @return An iterable range to use to visit top-level properties.
+         */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         *
+         * Properties of the base classes will also be visited, if any.
+         *
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+        /**
+         * @brief Checks if two objects refer to the same type.
+         * @param other The object with which to compare.
+         * @return True if the objects refer to the same type, false otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_type& other) const ENTT_NOEXCEPT {
+            return (!node && !other.node) || (node && other.node && node->info == other.node->info);
+        }
+
+        /**
+         * @brief Resets a type and all its parts.
+         *
+         * This function resets a type and all its data members, member functions
+         * and properties, as well as its constructors, destructors and conversion
+         * functions if any.<br/>
+         * Base classes aren't reset but the link between the two types is removed.
+         *
+         * The type is also removed from the list of searchable types.
+         */
+        void reset() ENTT_NOEXCEPT {
+            for (auto** it = internal::meta_context::global(); *it; it = &(*it)->next) {
+                if (*it == node) {
+                    *it = (*it)->next;
+                    break;
+                }
+            }
+
+            unregister_all(&node->prop);
+            unregister_all(&node->base);
+            unregister_all(&node->conv);
+            unregister_all<&internal::meta_ctor_node::prop>(&node->ctor);
+            unregister_all<&internal::meta_data_node::prop>(&node->data);
+            unregister_all<&internal::meta_func_node::prop>(&node->func);
+
+            node->id = {};
+            node->ctor = node->def_ctor;
+            node->dtor = nullptr;
+        }
+
+    private:
+        node_type* node;
+    };
+
+
+    /**
+     * @brief Checks if two objects refer to the same type.
+     * @param lhs An object, either valid or not.
+     * @param rhs An object, either valid or not.
+     * @return False if the objects refer to the same node, true otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const meta_type& lhs, const meta_type& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    [[nodiscard]] inline meta_type meta_any::type() const ENTT_NOEXCEPT {
+        return node;
+    }
+
+
+    template<typename... Args>
+    meta_any meta_any::invoke(const id_type id, Args &&... args) const {
+        return type().invoke(id, *this, std::forward<Args>(args)...);
+    }
+
+
+    template<typename... Args>
+    meta_any meta_any::invoke(const id_type id, Args &&... args) {
+        return type().invoke(id, *this, std::forward<Args>(args)...);
+    }
+
+
+    template<typename Type>
+    bool meta_any::set(const id_type id, Type&& value) {
+        return type().set(id, *this, std::forward<Type>(value));
+    }
+
+
+    [[nodiscard]] inline meta_any meta_any::get(const id_type id) const {
+        return type().get(id, *this);
+    }
+
+
+    [[nodiscard]] inline meta_any meta_any::get(const id_type id) {
+        return type().get(id, *this);
+    }
+
+
+    [[nodiscard]] inline meta_type meta_ctor::parent() const ENTT_NOEXCEPT {
+        return node->parent;
+    }
+
+
+    [[nodiscard]] inline meta_type meta_ctor::arg(size_type index) const ENTT_NOEXCEPT {
+        return index < arity() ? node->arg(index) : meta_type{};
+    }
+
+
+    [[nodiscard]] inline meta_type meta_data::parent() const ENTT_NOEXCEPT {
+        return node->parent;
+    }
+
+
+    [[nodiscard]] inline meta_type meta_data::type() const ENTT_NOEXCEPT {
+        return node->type();
+    }
+
+
+    [[nodiscard]] inline meta_type meta_func::parent() const ENTT_NOEXCEPT {
+        return node->parent;
+    }
+
+
+    [[nodiscard]] inline meta_type meta_func::ret() const ENTT_NOEXCEPT {
+        return node->ret();
+    }
+
+
+    [[nodiscard]] inline meta_type meta_func::arg(size_type index) const ENTT_NOEXCEPT {
+        return index < arity() ? node->arg(index) : meta_type{};
+    }
+
+
+    /*! @brief Opaque iterator for sequence containers. */
+    class meta_sequence_container::meta_iterator {
+        /*! @brief A sequence container can access the underlying iterator. */
+        friend class meta_sequence_container;
+
+        enum class operation { INCR, DEREF };
+
+        using vtable_type = void(const operation, const any&, void*);
+
+        template<typename It>
+        static void basic_vtable(const operation op, const any& from, void* to) {
+            switch (op) {
+            case operation::INCR:
+                ++any_cast<It&>(const_cast<any&>(from));
+                break;
+            case operation::DEREF:
+                static_cast<meta_any*>(to)->emplace<typename std::iterator_traits<It>::reference>(*any_cast<const It&>(from));
+                break;
+            }
+        }
+
+    public:
+        /*! @brief Signed integer type. */
+        using difference_type = std::ptrdiff_t;
+        /*! @brief Type of elements returned by the iterator. */
+        using value_type = meta_any;
+        /*! @brief Pointer type, `void` on purpose. */
+        using pointer = void;
+        /*! @brief Reference type, it is **not** an actual reference. */
+        using reference = value_type;
+        /*! @brief Iterator category. */
+        using iterator_category = std::input_iterator_tag;
+
+        /*! @brief Default constructor. */
+        meta_iterator() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Constructs a meta iterator from a given iterator.
+         * @tparam It Type of actual iterator with which to build the meta iterator.
+         * @param iter The actual iterator with which to build the meta iterator.
+         */
+        template<typename It>
+        meta_iterator(It iter)
+            : vtable{ &basic_vtable<It> },
+            handle{ std::move(iter) }
+        {}
+
+        /*! @brief Pre-increment operator. @return This iterator. */
+        meta_iterator& operator++() ENTT_NOEXCEPT {
+            return vtable(operation::INCR, handle, nullptr), * this;
+        }
+
+        /*! @brief Post-increment operator. @return This iterator. */
+        meta_iterator operator++(int) ENTT_NOEXCEPT {
+            meta_iterator orig = *this;
+            return ++(*this), orig;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return True if the iterators refer to the same element, false otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return handle == other.handle;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return False if the iterators refer to the same element, true otherwise.
+         */
+        [[nodiscard]] bool operator!=(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return !(*this == other);
+        }
+
+        /**
+         * @brief Indirection operator.
+         * @return The element to which the iterator points.
+         */
+        [[nodiscard]] reference operator*() const {
+            meta_any other;
+            vtable(operation::DEREF, handle, &other);
+            return other;
+        }
+
+        /**
+         * @brief Returns false if an iterator is invalid, true otherwise.
+         * @return False if the iterator is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(handle);
+        }
+
+    private:
+        vtable_type* vtable{};
+        any handle{};
+    };
+
+
+    template<typename Type>
+    struct meta_sequence_container::meta_sequence_container_proxy {
+        using traits_type = meta_sequence_container_traits<Type>;
+
+        [[nodiscard]] static meta_type value_type() ENTT_NOEXCEPT {
+            return internal::meta_info<typename Type::value_type>::resolve();
+        }
+
+        [[nodiscard]] static size_type size(const any& container) ENTT_NOEXCEPT {
+            return traits_type::size(any_cast<const Type&>(container));
+        }
+
+        [[nodiscard]] static bool resize(any& container, size_type sz) {
+            auto* const cont = any_cast<Type>(&container);
+            return cont && traits_type::resize(*cont, sz);
+        }
+
+        [[nodiscard]] static bool clear(any& container) {
+            auto* const cont = any_cast<Type>(&container);
+            return cont && traits_type::clear(*cont);
+        }
+
+        [[nodiscard]] static iterator begin(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ traits_type::begin(*cont) };
+            }
+
+            return iterator{ traits_type::cbegin(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static iterator end(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ traits_type::end(*cont) };
+            }
+
+            return iterator{ traits_type::cend(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static std::pair<iterator, bool> insert(any& container, iterator it, meta_any& value) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                // this abomination is necessary because only on macos value_type and const_reference are different types for std::vector<bool>
+                if (value.allow_cast<typename Type::const_reference>() || value.allow_cast<typename Type::value_type>()) {
+                    const auto* element = value.try_cast<std::remove_reference_t<typename Type::const_reference>>();
+                    auto ret = traits_type::insert(*cont, any_cast<const typename Type::iterator&>(it.handle), element ? *element : value.cast<typename Type::value_type>());
+                    return { iterator{std::move(ret.first)}, ret.second };
+                }
+            }
+
+            return {};
+        }
+
+        [[nodiscard]] static std::pair<iterator, bool> erase(any& container, iterator it) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                auto ret = traits_type::erase(*cont, any_cast<const typename Type::iterator&>(it.handle));
+                return { iterator{std::move(ret.first)}, ret.second };
+            }
+
+            return {};
+        }
+
+        [[nodiscard]] static meta_any get(any& container, size_type pos) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return meta_any{ std::in_place_type<typename Type::reference>, traits_type::get(*cont, pos) };
+            }
+
+            return meta_any{ std::in_place_type<typename Type::const_reference>, traits_type::cget(any_cast<const Type&>(container), pos) };
+        }
+    };
+
+
+    /**
+     * @brief Returns the meta value type of a container.
+     * @return The meta value type of the container.
+     */
+    [[nodiscard]] inline meta_type meta_sequence_container::value_type() const ENTT_NOEXCEPT {
+        return value_type_fn();
+    }
+
+
+    /**
+     * @brief Returns the size of a container.
+     * @return The size of the container.
+     */
+    [[nodiscard]] inline meta_sequence_container::size_type meta_sequence_container::size() const ENTT_NOEXCEPT {
+        return size_fn(storage);
+    }
+
+
+    /**
+     * @brief Resizes a container to contain a given number of elements.
+     * @param sz The new size of the container.
+     * @return True in case of success, false otherwise.
+     */
+    inline bool meta_sequence_container::resize(size_type sz) {
+        return resize_fn(storage, sz);
+    }
+
+
+    /**
+     * @brief Clears the content of a container.
+     * @return True in case of success, false otherwise.
+     */
+    inline bool meta_sequence_container::clear() {
+        return clear_fn(storage);
+    }
+
+
+    /**
+     * @brief Returns an iterator to the first element of a container.
+     * @return An iterator to the first element of the container.
+     */
+    [[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::begin() {
+        return begin_fn(storage);
+    }
+
+
+    /**
+     * @brief Returns an iterator that is past the last element of a container.
+     * @return An iterator that is past the last element of the container.
+     */
+    [[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::end() {
+        return end_fn(storage);
+    }
+
+
+    /**
+     * @brief Inserts an element at a specified location of a container.
+     * @param it Iterator before which the element will be inserted.
+     * @param value Element value to insert.
+     * @return A pair consisting of an iterator to the inserted element (in case of
+     * success) and a bool denoting whether the insertion took place.
+     */
+    inline std::pair<meta_sequence_container::iterator, bool> meta_sequence_container::insert(iterator it, meta_any value) {
+        return insert_fn(storage, it, value);
+    }
+
+
+    /**
+     * @brief Removes a given element from a container.
+     * @param it Iterator to the element to remove.
+     * @return A pair consisting of an iterator following the last removed element
+     * (in case of success) and a bool denoting whether the insertion took place.
+     */
+    inline std::pair<meta_sequence_container::iterator, bool> meta_sequence_container::erase(iterator it) {
+        return erase_fn(storage, it);
+    }
+
+
+    /**
+     * @brief Returns a reference to the element at a given location of a container
+     * (no bounds checking is performed).
+     * @param pos The position of the element to return.
+     * @return A reference to the requested element properly wrapped.
+     */
+    [[nodiscard]] inline meta_any meta_sequence_container::operator[](size_type pos) {
+        return get_fn(storage, pos);
+    }
+
+
+    /**
+     * @brief Returns false if a proxy is invalid, true otherwise.
+     * @return False if the proxy is invalid, true otherwise.
+     */
+    [[nodiscard]] inline meta_sequence_container::operator bool() const ENTT_NOEXCEPT {
+        return static_cast<bool>(storage);
+    }
+
+
+    /*! @brief Opaque iterator for associative containers. */
+    class meta_associative_container::meta_iterator {
+        enum operation { INCR, DEREF };
+
+        using vtable_type = void(const operation, const any&, void*);
+
+        template<bool KeyOnly, typename It>
+        static void basic_vtable(const operation op, const any& from, void* to) {
+            switch (op) {
+            case operation::INCR:
+                ++any_cast<It&>(const_cast<any&>(from));
+                break;
+            case operation::DEREF:
+                const auto& it = any_cast<const It&>(from);
+                if constexpr (KeyOnly) {
+                    static_cast<std::pair<meta_any, meta_any>*>(to)->first.emplace<decltype(*it)>(*it);
+                }
+                else {
+                    static_cast<std::pair<meta_any, meta_any>*>(to)->first.emplace<decltype((it->first))>(it->first);
+                    static_cast<std::pair<meta_any, meta_any>*>(to)->second.emplace<decltype((it->second))>(it->second);
+                }
+                break;
+            }
+        }
+
+    public:
+        /*! @brief Signed integer type. */
+        using difference_type = std::ptrdiff_t;
+        /*! @brief Type of elements returned by the iterator. */
+        using value_type = std::pair<meta_any, meta_any>;
+        /*! @brief Pointer type, `void` on purpose. */
+        using pointer = void;
+        /*! @brief Reference type, it is **not** an actual reference. */
+        using reference = value_type;
+        /*! @brief Iterator category. */
+        using iterator_category = std::input_iterator_tag;
+
+        /*! @brief Default constructor. */
+        meta_iterator() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Constructs an meta iterator from a given iterator.
+         * @tparam KeyOnly True if the container is also key-only, false otherwise.
+         * @tparam It Type of actual iterator with which to build the meta iterator.
+         * @param iter The actual iterator with which to build the meta iterator.
+         */
+        template<bool KeyOnly, typename It>
+        meta_iterator(std::integral_constant<bool, KeyOnly>, It iter)
+            : vtable{ &basic_vtable<KeyOnly, It> },
+            handle{ std::move(iter) }
+        {}
+
+        /*! @brief Pre-increment operator. @return This iterator. */
+        meta_iterator& operator++() ENTT_NOEXCEPT {
+            return vtable(operation::INCR, handle, nullptr), * this;
+        }
+
+        /*! @brief Post-increment operator. @return This iterator. */
+        meta_iterator operator++(int) ENTT_NOEXCEPT {
+            meta_iterator orig = *this;
+            return ++(*this), orig;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return True if the iterators refer to the same element, false otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return handle == other.handle;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return False if the iterators refer to the same element, true otherwise.
+         */
+        [[nodiscard]] bool operator!=(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return !(*this == other);
+        }
+
+        /**
+         * @brief Indirection operator.
+         * @return The element to which the iterator points.
+         */
+        [[nodiscard]] reference operator*() const {
+            reference other;
+            vtable(operation::DEREF, handle, &other);
+            return other;
+        }
+
+        /**
+         * @brief Returns false if an iterator is invalid, true otherwise.
+         * @return False if the iterator is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(handle);
+        }
+
+    private:
+        vtable_type* vtable{};
+        any handle{};
+    };
+
+
+    template<typename Type>
+    struct meta_associative_container::meta_associative_container_proxy {
+        using traits_type = meta_associative_container_traits<Type>;
+
+        [[nodiscard]] static meta_type key_type() ENTT_NOEXCEPT {
+            return internal::meta_info<typename Type::key_type>::resolve();
+        }
+
+        [[nodiscard]] static meta_type mapped_type() ENTT_NOEXCEPT {
+            if constexpr (is_key_only_meta_associative_container_v<Type>) {
+                return meta_type{};
+            }
+            else {
+                return internal::meta_info<typename Type::mapped_type>::resolve();
+            }
+        }
+
+        [[nodiscard]] static meta_type value_type() ENTT_NOEXCEPT {
+            return internal::meta_info<typename Type::value_type>::resolve();
+        }
+
+        [[nodiscard]] static size_type size(const any& container) ENTT_NOEXCEPT {
+            return traits_type::size(any_cast<const Type&>(container));
+        }
+
+        [[nodiscard]] static bool clear(any& container) {
+            auto* const cont = any_cast<Type>(&container);
+            return cont && traits_type::clear(*cont);
+        }
+
+        [[nodiscard]] static iterator begin(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::begin(*cont) };
+            }
+
+            return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::cbegin(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static iterator end(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::end(*cont) };
+            }
+
+            return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::cend(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static bool insert(any& container, meta_any& key, meta_any& value) {
+            if (auto* const cont = any_cast<Type>(&container); cont && key.allow_cast<const typename Type::key_type&>()) {
+                if constexpr (is_key_only_meta_associative_container_v<Type>) {
+                    return traits_type::insert(*cont, key.cast<const typename Type::key_type&>());
+                }
+                else {
+                    return value.allow_cast<const typename Type::mapped_type&>()
+                        && traits_type::insert(*cont, key.cast<const typename Type::key_type&>(), value.cast<const typename Type::mapped_type&>());
+                }
+            }
+
+            return false;
+        }
+
+        [[nodiscard]] static bool erase(any& container, meta_any& key) {
+            if (auto* const cont = any_cast<Type>(&container); cont && key.allow_cast<const typename Type::key_type&>()) {
+                return traits_type::erase(*cont, key.cast<const typename Type::key_type&>());
+            }
+
+            return false;
+        }
+
+        [[nodiscard]] static iterator find(any& container, meta_any& key) {
+            if (key.allow_cast<const typename Type::key_type&>()) {
+                if (auto* const cont = any_cast<Type>(&container); cont) {
+                    return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::find(*cont, key.cast<const typename Type::key_type&>()) };
+                }
+
+                return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::cfind(any_cast<const Type&>(container), key.cast<const typename Type::key_type&>()) };
+            }
+
+            return {};
+        }
+    };
+
+
+    /**
+     * @brief Returns true if a container is also key-only, false otherwise.
+     * @return True if the associative container is also key-only, false otherwise.
+     */
+    [[nodiscard]] inline bool meta_associative_container::key_only() const ENTT_NOEXCEPT {
+        return key_only_container;
+    }
+
+
+    /**
+     * @brief Returns the meta key type of a container.
+     * @return The meta key type of the a container.
+     */
+    [[nodiscard]] inline meta_type meta_associative_container::key_type() const ENTT_NOEXCEPT {
+        return key_type_fn();
+    }
+
+
+    /**
+     * @brief Returns the meta mapped type of a container.
+     * @return The meta mapped type of the a container.
+     */
+    [[nodiscard]] inline meta_type meta_associative_container::mapped_type() const ENTT_NOEXCEPT {
+        return mapped_type_fn();
+    }
+
+
+    /*! @copydoc meta_sequence_container::value_type */
+    [[nodiscard]] inline meta_type meta_associative_container::value_type() const ENTT_NOEXCEPT {
+        return value_type_fn();
+    }
+
+
+    /*! @copydoc meta_sequence_container::size */
+    [[nodiscard]] inline meta_associative_container::size_type meta_associative_container::size() const ENTT_NOEXCEPT {
+        return size_fn(storage);
+    }
+
+
+    /*! @copydoc meta_sequence_container::clear */
+    inline bool meta_associative_container::clear() {
+        return clear_fn(storage);
+    }
+
+
+    /*! @copydoc meta_sequence_container::begin */
+    [[nodiscard]] inline meta_associative_container::iterator meta_associative_container::begin() {
+        return begin_fn(storage);
+    }
+
+
+    /*! @copydoc meta_sequence_container::end */
+    [[nodiscard]] inline meta_associative_container::iterator meta_associative_container::end() {
+        return end_fn(storage);
+    }
+
+
+    /**
+     * @brief Inserts an element (a key/value pair) into a container.
+     * @param key The key of the element to insert.
+     * @param value The value of the element to insert.
+     * @return A bool denoting whether the insertion took place.
+     */
+    inline bool meta_associative_container::insert(meta_any key, meta_any value = {}) {
+        return insert_fn(storage, key, value);
+    }
+
+
+    /**
+     * @brief Removes the specified element from a container.
+     * @param key The key of the element to remove.
+     * @return A bool denoting whether the removal took place.
+     */
+    inline bool meta_associative_container::erase(meta_any key) {
+        return erase_fn(storage, key);
+    }
+
+
+    /**
+     * @brief Returns an iterator to the element with a given key, if any.
+     * @param key The key of the element to search.
+     * @return An iterator to the element with the given key, if any.
+     */
+    [[nodiscard]] inline meta_associative_container::iterator meta_associative_container::find(meta_any key) {
+        return find_fn(storage, key);
+    }
+
+
+    /**
+     * @brief Returns false if a proxy is invalid, true otherwise.
+     * @return False if the proxy is invalid, true otherwise.
+     */
+    [[nodiscard]] inline meta_associative_container::operator bool() const ENTT_NOEXCEPT {
+        return static_cast<bool>(storage);
+    }
+
+
+}
+
+
+#endif
+
+// #include "node.hpp"
+
+// #include "policy.hpp"
+#ifndef ENTT_META_POLICY_HPP
+#define ENTT_META_POLICY_HPP
+
+
+namespace entt {
+
+
+    /*! @brief Empty class type used to request the _as ref_ policy. */
+    struct as_ref_t {};
+
+
+    /*! @brief Empty class type used to request the _as cref_ policy. */
+    struct as_cref_t {};
+
+
+    /*! @brief Empty class type used to request the _as-is_ policy. */
+    struct as_is_t {};
+
+
+    /*! @brief Empty class type used to request the _as void_ policy. */
+    struct as_void_t {};
+
+
+}
+
+
+#endif
+
+// #include "utility.hpp"
+#ifndef ENTT_META_UTILITY_HPP
+#define ENTT_META_UTILITY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "meta.hpp"
+
+// #include "node.hpp"
+
+// #include "policy.hpp"
+
+
+
+namespace entt {
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename, typename>
+    struct meta_function_descriptor;
+
+
+    /**
+     * @brief Meta function descriptor.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Ret Function return type.
+     * @tparam Class Actual owner of the member function.
+     * @tparam Args Function arguments.
+     */
+    template<typename Type, typename Ret, typename Class, typename... Args>
+    struct meta_function_descriptor<Type, Ret(Class::*)(Args...) const> {
+        /*! @brief Meta function return type. */
+        using return_type = Ret;
+        /*! @brief Meta function arguments. */
+        using args_type = std::conditional_t<std::is_same_v<Type, Class>, type_list<Args...>, type_list<const Class&, Args...>>;
+
+        /*! @brief True if the meta function is const, false otherwise. */
+        static constexpr auto is_const = true;
+        /*! @brief True if the meta function is static, false otherwise. */
+        static constexpr auto is_static = !std::is_same_v<Type, Class>;
+    };
+
+
+    /**
+     * @brief Meta function descriptor.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Ret Function return type.
+     * @tparam Class Actual owner of the member function.
+     * @tparam Args Function arguments.
+     */
+    template<typename Type, typename Ret, typename Class, typename... Args>
+    struct meta_function_descriptor<Type, Ret(Class::*)(Args...)> {
+        /*! @brief Meta function return type. */
+        using return_type = Ret;
+        /*! @brief Meta function arguments. */
+        using args_type = std::conditional_t<std::is_same_v<Type, Class>, type_list<Args...>, type_list<Class&, Args...>>;
+
+        /*! @brief True if the meta function is const, false otherwise. */
+        static constexpr auto is_const = false;
+        /*! @brief True if the meta function is static, false otherwise. */
+        static constexpr auto is_static = !std::is_same_v<Type, Class>;
+    };
+
+
+    /**
+     * @brief Meta function descriptor.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Ret Function return type.
+     * @tparam Args Function arguments.
+     */
+    template<typename Type, typename Ret, typename... Args>
+    struct meta_function_descriptor<Type, Ret(*)(Args...)> {
+        /*! @brief Meta function return type. */
+        using return_type = Ret;
+        /*! @brief Meta function arguments. */
+        using args_type = type_list<Args...>;
+
+        /*! @brief True if the meta function is const, false otherwise. */
+        static constexpr auto is_const = false;
+        /*! @brief True if the meta function is static, false otherwise. */
+        static constexpr auto is_static = true;
+    };
+
+
+    /**
+     * @brief Meta function helper.
+     *
+     * Converts a function type to be associated with a reflected type into its meta
+     * function descriptor.
+     *
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Candidate The actual function to associate with the reflected type.
+     */
+    template<typename Type, typename Candidate>
+    class meta_function_helper {
+        template<typename Ret, typename... Args, typename Class>
+        static constexpr meta_function_descriptor<Type, Ret(Class::*)(Args...) const> get_rid_of_noexcept(Ret(Class::*)(Args...) const);
+
+        template<typename Ret, typename... Args, typename Class>
+        static constexpr meta_function_descriptor<Type, Ret(Class::*)(Args...)> get_rid_of_noexcept(Ret(Class::*)(Args...));
+
+        template<typename Ret, typename... Args>
+        static constexpr meta_function_descriptor<Type, Ret(*)(Args...)> get_rid_of_noexcept(Ret(*)(Args...));
+
+    public:
+        /*! @brief The meta function descriptor of the given function. */
+        using type = decltype(get_rid_of_noexcept(std::declval<Candidate>()));
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Candidate The actual function to associate with the reflected type.
+     */
+    template<typename Type, typename Candidate>
+    using meta_function_helper_t = typename meta_function_helper<Type, Candidate>::type;
+
+
+    /**
+     * @brief Returns the meta type of the i-th element of a list of arguments.
+     * @tparam Args Actual types of arguments.
+     * @return The meta type of the i-th element of the list of arguments.
+     */
+    template<typename... Args>
+    [[nodiscard]] static meta_type meta_arg(type_list<Args...>, const std::size_t index) ENTT_NOEXCEPT {
+        return internal::meta_arg_node(type_list<Args...>{}, index);
+    }
+
+
+    /**
+     * @brief Constructs an instance given a list of erased parameters, if possible.
+     * @tparam Type Actual type of the instance to construct.
+     * @tparam Args Types of arguments expected.
+     * @tparam Index Indexes to use to extract erased arguments from their list.
+     * @param args Parameters to use to construct the instance.
+     * @return A meta any containing the new instance, if any.
+     */
+    template<typename Type, typename... Args, std::size_t... Index>
+    [[nodiscard]] meta_any meta_construct(meta_any* const args, std::index_sequence<Index...>) {
+        if (((args + Index)->allow_cast<Args>() && ...)) {
+            return Type{ (args + Index)->cast<Args>()... };
+        }
+
+        return {};
+    }
+
+
+    /**
+     * @brief Sets the value of a given variable.
+     * @tparam Type Reflected type to which the variable is associated.
+     * @tparam Data The actual variable to set.
+     * @param instance An opaque instance of the underlying type, if required.
+     * @param value Parameter to use to set the variable.
+     * @return True in case of success, false otherwise.
+     */
+    template<typename Type, auto Data>
+    [[nodiscard]] bool meta_setter([[maybe_unused]] meta_handle instance, [[maybe_unused]] meta_any value) {
+        if constexpr (!std::is_same_v<decltype(Data), Type> && !std::is_same_v<decltype(Data), std::nullptr_t>) {
+            if constexpr (std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
+                using data_type = type_list_element_t<1u, typename meta_function_helper_t<Type, decltype(Data)>::args_type>;
+
+                if (auto* const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
+                    Data(*clazz, value.cast<data_type>());
+                    return true;
+                }
+            }
+            else if constexpr (std::is_member_function_pointer_v<decltype(Data)>) {
+                using data_type = type_list_element_t<0u, typename meta_function_helper_t<Type, decltype(Data)>::args_type>;
+
+                if (auto* const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
+                    (clazz->*Data)(value.cast<data_type>());
+                    return true;
+                }
+            }
+            else if constexpr (std::is_member_object_pointer_v<decltype(Data)>) {
+                using data_type = std::remove_reference_t<decltype(std::declval<Type>().*Data)>;
+
+                if constexpr (!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
+                    if (auto* const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
+                        clazz->*Data = value.cast<data_type>();
+                        return true;
+                    }
+                }
+            }
+            else {
+                using data_type = std::remove_reference_t<decltype(*Data)>;
+
+                if constexpr (!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
+                    if (value.allow_cast<data_type>()) {
+                        *Data = value.cast<data_type>();
+                        return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+
+
+    /**
+     * @brief Wraps a value depending on the given policy.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @tparam Type Type of value to wrap.
+     * @param value Value to wrap.
+     * @return A meta any containing the returned value.
+     */
+    template<typename Policy = as_is_t, typename Type>
+    meta_any meta_dispatch(Type&& value) {
+        if constexpr (std::is_same_v<Policy, as_void_t>) {
+            return meta_any{ std::in_place_type<void>, std::forward<Type>(value) };
+        }
+        else if constexpr (std::is_same_v<Policy, as_ref_t>) {
+            return meta_any{ std::in_place_type<Type>, std::forward<Type>(value) };
+        }
+        else if constexpr (std::is_same_v<Policy, as_cref_t>) {
+            static_assert(std::is_lvalue_reference_v<Type>, "Invalid type");
+            return meta_any{ std::in_place_type<const std::remove_reference_t<Type>&>, std::as_const(value) };
+        }
+        else {
+            static_assert(std::is_same_v<Policy, as_is_t>, "Policy not supported");
+            return meta_any{ std::forward<Type>(value) };
+        }
+    }
+
+
+    /**
+     * @brief Gets the value of a given variable.
+     * @tparam Type Reflected type to which the variable is associated.
+     * @tparam Data The actual variable to get.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @param instance An opaque instance of the underlying type, if required.
+     * @return A meta any containing the value of the underlying variable.
+     */
+    template<typename Type, auto Data, typename Policy = as_is_t>
+    [[nodiscard]] meta_any meta_getter([[maybe_unused]] meta_handle instance) {
+        if constexpr (std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
+            auto* const clazz = instance->try_cast<std::conditional_t<std::is_invocable_v<decltype(Data), const Type&>, const Type, Type>>();
+            return clazz ? meta_dispatch<Policy>(Data(*clazz)) : meta_any{};
+        }
+        else if constexpr (std::is_member_function_pointer_v<decltype(Data)>) {
+            auto* const clazz = instance->try_cast<std::conditional_t<std::is_invocable_v<decltype(Data), const Type&>, const Type, Type>>();
+            return clazz ? meta_dispatch<Policy>((clazz->*Data)()) : meta_any{};
+        }
+        else if constexpr (std::is_member_object_pointer_v<decltype(Data)>) {
+            if constexpr (!std::is_array_v<std::remove_cv_t<std::remove_reference_t<decltype(std::declval<Type>().*Data)>>>) {
+                if (auto* clazz = instance->try_cast<Type>(); clazz) {
+                    return meta_dispatch<Policy>(clazz->*Data);
+                }
+                else if (auto* fallback = instance->try_cast<const Type>(); fallback) {
+                    return meta_dispatch<Policy>(fallback->*Data);
+                }
+            }
+
+            return meta_any{};
+        }
+        else if constexpr (std::is_pointer_v<decltype(Data)>) {
+            if constexpr (std::is_array_v<std::remove_pointer_t<decltype(Data)>>) {
+                return meta_any{};
+            }
+            else {
+                return meta_dispatch<Policy>(*Data);
+            }
+        }
+        else {
+            return meta_dispatch<Policy>(Data);
+        }
+    }
+
+
+    /**
+     * @brief Invokes a function given a list of erased parameters, if possible.
+     * @tparam Type Reflected type to which the function is associated.
+     * @tparam Candidate The actual function to invoke.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @tparam Index Indexes to use to extract erased arguments from their list.
+     * @param instance An opaque instance of the underlying type, if required.
+     * @param args Parameters to use to invoke the function.
+     * @return A meta any containing the returned value, if any.
+     */
+    template<typename Type, auto Candidate, typename Policy = as_is_t, std::size_t... Index>
+    [[nodiscard]] std::enable_if_t<!std::is_invocable_v<decltype(Candidate)>, meta_any> meta_invoke([[maybe_unused]] meta_handle instance, meta_any* args, std::index_sequence<Index...>) {
+        using descriptor = meta_function_helper_t<Type, decltype(Candidate)>;
+
+        const auto invoke = [](auto&& maybe_clazz, auto &&... other) {
+            if constexpr (std::is_member_function_pointer_v<decltype(Candidate)>) {
+                if constexpr (std::is_void_v<typename descriptor::return_type>) {
+                    (std::forward<decltype(maybe_clazz)>(maybe_clazz).*Candidate)(std::forward<decltype(other)>(other)...);
+                    return meta_any{ std::in_place_type<void> };
+                }
+                else {
+                    return meta_dispatch<Policy>((std::forward<decltype(maybe_clazz)>(maybe_clazz).*Candidate)(std::forward<decltype(other)>(other)...));
+                }
+            }
+            else {
+                if constexpr (std::is_void_v<typename descriptor::return_type>) {
+                    Candidate(std::forward<decltype(maybe_clazz)>(maybe_clazz), std::forward<decltype(other)>(other)...);
+                    return meta_any{ std::in_place_type<void> };
+                }
+                else {
+                    return meta_dispatch<Policy>(Candidate(std::forward<decltype(maybe_clazz)>(maybe_clazz), std::forward<decltype(other)>(other)...));
+                }
+            }
+        };
+
+        if constexpr (std::is_invocable_v<decltype(Candidate), const Type&, type_list_element_t<Index, typename descriptor::args_type>...>) {
+            if (const auto* const clazz = instance->try_cast<const Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
+                return invoke(*clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
+            }
+        }
+        else if constexpr (std::is_invocable_v<decltype(Candidate), Type&, type_list_element_t<Index, typename descriptor::args_type>...>) {
+            if (auto* const clazz = instance->try_cast<Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
+                return invoke(*clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
+            }
+        }
+        else {
+            if (((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
+                return invoke((args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
+            }
+        }
+
+        return meta_any{};
+    }
+
+
+    /**
+     * @brief Invokes a function given a list of erased parameters, if possible.
+     * @tparam Type Reflected type to which the function is associated.
+     * @tparam Candidate The actual function to invoke.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @tparam Index Indexes to use to extract erased arguments from their list.
+     * @return A meta any containing the returned value, if any.
+     */
+    template<typename Type, auto Candidate, typename Policy = as_is_t, std::size_t... Index>
+    [[nodiscard]] std::enable_if_t<std::is_invocable_v<decltype(Candidate)>, meta_any> meta_invoke(meta_handle, meta_any*, std::index_sequence<Index...>) {
+        if constexpr (std::is_void_v<decltype(Candidate())>) {
+            Candidate();
+            return meta_any{ std::in_place_type<void> };
+        }
+        else {
+            return meta_dispatch<Policy>(Candidate());
+        }
+    }
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Node>
+        [[nodiscard]] bool find_if(const Node* candidate, const Node* node) ENTT_NOEXCEPT {
+            return node && (node == candidate || find_if(candidate, node->next));
+        }
+
+
+        template<typename Id, typename Node>
+        [[nodiscard]] bool find_if_not(const Id id, Node* node, const Node* owner) ENTT_NOEXCEPT {
+            if constexpr (std::is_pointer_v<Id>) {
+                return node && ((*node->id == *id && node != owner) || find_if_not(id, node->next, owner));
+            }
+            else {
+                return node && ((node->id == id && node != owner) || find_if_not(id, node->next, owner));
+            }
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Meta factory to be used for reflection purposes.
+      *
+      * The meta factory is an utility class used to reflect types, data members and
+      * functions of all sorts. This class ensures that the underlying web of types
+      * is built correctly and performs some checks in debug mode to ensure that
+      * there are no subtle errors at runtime.
+      */
+    template<typename...>
+    struct meta_factory;
+
+
+    /**
+     * @brief Extended meta factory to be used for reflection purposes.
+     * @tparam Type Reflected type for which the factory was created.
+     * @tparam Spec Property specialization pack used to disambiguate overloads.
+     */
+    template<typename Type, typename... Spec>
+    struct meta_factory<Type, Spec...> : public meta_factory<Type> {
+    private:
+        template<std::size_t Step = 0, std::size_t... Index, typename... Property, typename... Other>
+        void unpack(std::index_sequence<Index...>, std::tuple<Property...> property, Other &&... other) {
+            unroll<Step>(choice<3>, std::move(std::get<Index>(property))..., std::forward<Other>(other)...);
+        }
+
+        template<std::size_t Step = 0, typename... Property, typename... Other>
+        void unroll(choice_t<3>, std::tuple<Property...> property, Other &&... other) {
+            unpack<Step>(std::index_sequence_for<Property...>{}, std::move(property), std::forward<Other>(other)...);
+        }
+
+        template<std::size_t Step = 0, typename... Property, typename... Other>
+        void unroll(choice_t<2>, std::pair<Property...> property, Other &&... other) {
+            assign<Step>(std::move(property.first), std::move(property.second));
+            unroll<Step + 1>(choice<3>, std::forward<Other>(other)...);
+        }
+
+        template<std::size_t Step = 0, typename Property, typename... Other>
+        std::enable_if_t<!std::is_invocable_v<Property>>
+            unroll(choice_t<1>, Property&& property, Other &&... other) {
+            assign<Step>(std::forward<Property>(property));
+            unroll<Step + 1>(choice<3>, std::forward<Other>(other)...);
+        }
+
+        template<std::size_t Step = 0, typename Func, typename... Other>
+        void unroll(choice_t<0>, Func&& invocable, Other &&... other) {
+            unroll<Step>(choice<3>, std::forward<Func>(invocable)(), std::forward<Other>(other)...);
+        }
+
+        template<std::size_t>
+        void unroll(choice_t<0>) {}
+
+        template<std::size_t = 0, typename Key>
+        void assign(Key&& key, meta_any value = {}) {
+            static meta_any property[2u]{};
+
+            static internal::meta_prop_node node{
+                nullptr,
+                property[0u],
+                property[1u]
+            };
+
+            entt::meta_any instance{ std::forward<Key>(key) };
+            ENTT_ASSERT(!internal::find_if_not(&instance, *curr, &node), "Duplicate key");
+            property[0u] = std::move(instance);
+            property[1u] = std::move(value);
+
+            if (!internal::find_if(&node, *curr)) {
+                node.next = *curr;
+                *curr = &node;
+            }
+        }
+
+    public:
+        /**
+         * @brief Constructs an extended factory from a given node.
+         * @param target The underlying node to which to assign the properties.
+         */
+        meta_factory(internal::meta_prop_node** target) ENTT_NOEXCEPT
+            : curr{ target }
+        {}
+
+        /**
+         * @brief Assigns a property to the last meta object created.
+         *
+         * Both the key and the value (if any) must be at least copy constructible.
+         *
+         * @tparam PropertyOrKey Type of the property or property key.
+         * @tparam Value Optional type of the property value.
+         * @param property_or_key Property or property key.
+         * @param value Optional property value.
+         * @return A meta factory for the parent type.
+         */
+        template<typename PropertyOrKey, typename... Value>
+        auto prop(PropertyOrKey&& property_or_key, Value &&... value)&& {
+            if constexpr (sizeof...(Value) == 0) {
+                unroll(choice<3>, std::forward<PropertyOrKey>(property_or_key));
+            }
+            else {
+                assign(std::forward<PropertyOrKey>(property_or_key), std::forward<Value>(value)...);
+            }
+
+            return meta_factory<Type, Spec..., PropertyOrKey, Value...>{curr};
+        }
+
+        /**
+         * @brief Assigns properties to the last meta object created.
+         *
+         * Both the keys and the values (if any) must be at least copy
+         * constructible.
+         *
+         * @tparam Property Types of the properties.
+         * @param property Properties to assign to the last meta object created.
+         * @return A meta factory for the parent type.
+         */
+        template <typename... Property>
+        auto props(Property... property)&& {
+            unroll(choice<3>, std::forward<Property>(property)...);
+            return meta_factory<Type, Spec..., Property...>{curr};
+        }
+
+    private:
+        internal::meta_prop_node** curr;
+    };
+
+
+    /**
+     * @brief Basic meta factory to be used for reflection purposes.
+     * @tparam Type Reflected type for which the factory was created.
+     */
+    template<typename Type>
+    struct meta_factory<Type> {
+        /**
+         * @brief Makes a meta type _searchable_.
+         * @param id Optional unique identifier.
+         * @return An extended meta factory for the given type.
+         */
+        auto type(const id_type id = type_hash<Type>::value()) {
+            auto* const node = internal::meta_info<Type>::resolve();
+
+            ENTT_ASSERT(!internal::find_if_not(id, *internal::meta_context::global(), node), "Duplicate identifier");
+            node->id = id;
+
+            if (!internal::find_if(node, *internal::meta_context::global())) {
+                node->next = *internal::meta_context::global();
+                *internal::meta_context::global() = node;
+            }
+
+            return meta_factory<Type, Type>{&node->prop};
+        }
+
+        /**
+         * @brief Assigns a meta base to a meta type.
+         *
+         * A reflected base class must be a real base class of the reflected type.
+         *
+         * @tparam Base Type of the base class to assign to the meta type.
+         * @return A meta factory for the parent type.
+         */
+        template<typename Base>
+        auto base() ENTT_NOEXCEPT {
+            static_assert(std::is_base_of_v<Base, Type>, "Invalid base type");
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_base_node node{
+                type,
+                nullptr,
+                &internal::meta_info<Base>::resolve,
+                [](const void* instance) ENTT_NOEXCEPT -> const void* {
+                    return static_cast<const Base*>(static_cast<const Type*>(instance));
+                }
+            };
+
+            if (!internal::find_if(&node, type->base)) {
+                node.next = type->base;
+                type->base = &node;
+            }
+
+            return meta_factory<Type>{};
+        }
+
+        /**
+         * @brief Assigns a meta conversion function to a meta type.
+         *
+         * Conversion functions can be either free functions or member
+         * functions.<br/>
+         * In case of free functions, they must accept a const reference to an
+         * instance of the parent type as an argument. In case of member functions,
+         * they should have no arguments at all.
+         *
+         * @tparam Candidate The actual function to use for the conversion.
+         * @return A meta factory for the parent type.
+         */
+        template<auto Candidate>
+        std::enable_if_t<std::is_member_function_pointer_v<decltype(Candidate)>, meta_factory<Type>> conv() ENTT_NOEXCEPT {
+            using conv_type = std::invoke_result_t<decltype(Candidate), Type&>;
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_conv_node node{
+                type,
+                nullptr,
+                &internal::meta_info<conv_type>::resolve,
+                [](const void* instance) -> meta_any {
+                    return (static_cast<const Type*>(instance)->*Candidate)();
+                }
+            };
+
+            if (!internal::find_if(&node, type->conv)) {
+                node.next = type->conv;
+                type->conv = &node;
+            }
+
+            return meta_factory<Type>{};
+        }
+
+        /*! @copydoc conv */
+        template<auto Candidate>
+        std::enable_if_t<!std::is_member_function_pointer_v<decltype(Candidate)>, meta_factory<Type>> conv() ENTT_NOEXCEPT {
+            using conv_type = std::invoke_result_t<decltype(Candidate), Type&>;
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_conv_node node{
+                type,
+                nullptr,
+                &internal::meta_info<conv_type>::resolve,
+                [](const void* instance) -> meta_any {
+                    return Candidate(*static_cast<const Type*>(instance));
+                }
+            };
+
+            if (!internal::find_if(&node, type->conv)) {
+                node.next = type->conv;
+                type->conv = &node;
+            }
+
+            return meta_factory<Type>{};
+        }
+
+        /**
+         * @brief Assigns a meta conversion function to a meta type.
+         *
+         * The given type must be such that an instance of the reflected type can be
+         * converted to it.
+         *
+         * @tparam To Type of the conversion function to assign to the meta type.
+         * @return A meta factory for the parent type.
+         */
+        template<typename To>
+        auto conv() ENTT_NOEXCEPT {
+            static_assert(std::is_convertible_v<Type, To>, "Could not convert to the required type");
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_conv_node node{
+                type,
+                nullptr,
+                &internal::meta_info<To>::resolve,
+                [](const void* instance) -> meta_any {
+                    return static_cast<To>(*static_cast<const Type*>(instance));
+                }
+            };
+
+            if (!internal::find_if(&node, type->conv)) {
+                node.next = type->conv;
+                type->conv = &node;
+            }
+
+            return meta_factory<Type>{};
+        }
+
+        /**
+         * @brief Assigns a meta constructor to a meta type.
+         *
+         * Both member functions and free function can be assigned to meta types in
+         * the role of constructors. All that is required is that they return an
+         * instance of the underlying type.<br/>
+         * From a client's point of view, nothing changes if a constructor of a meta
+         * type is a built-in one or not.
+         *
+         * @tparam Candidate The actual function to use as a constructor.
+         * @tparam Policy Optional policy (no policy set by default).
+         * @return An extended meta factory for the parent type.
+         */
+        template<auto Candidate, typename Policy = as_is_t>
+        auto ctor() ENTT_NOEXCEPT {
+            using descriptor = meta_function_helper_t<Type, decltype(Candidate)>;
+            static_assert(std::is_same_v<std::decay_t<typename descriptor::return_type>, Type>, "The function doesn't return an object of the required type");
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_ctor_node node{
+                type,
+                nullptr,
+                nullptr,
+                descriptor::args_type::size,
+                [](const typename internal::meta_ctor_node::size_type index) ENTT_NOEXCEPT {
+                    return meta_arg(typename descriptor::args_type{}, index);
+                },
+                [](meta_any* const args) {
+                    return meta_invoke<Type, Candidate, Policy>({}, args, std::make_index_sequence<descriptor::args_type::size>{});
+                }
+            };
+
+            if (!internal::find_if(&node, type->ctor)) {
+                node.next = type->ctor;
+                type->ctor = &node;
+            }
+
+            return meta_factory<Type, std::integral_constant<decltype(Candidate), Candidate>>{&node.prop};
+        }
+
+        /**
+         * @brief Assigns a meta constructor to a meta type.
+         *
+         * A meta constructor is uniquely identified by the types of its arguments
+         * and is such that there exists an actual constructor of the underlying
+         * type that can be invoked with parameters whose types are those given.
+         *
+         * @tparam Args Types of arguments to use to construct an instance.
+         * @return An extended meta factory for the parent type.
+         */
+        template<typename... Args>
+        auto ctor() ENTT_NOEXCEPT {
+            using descriptor = meta_function_helper_t<Type, Type(*)(Args...)>;
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_ctor_node node{
+                type,
+                nullptr,
+                nullptr,
+                descriptor::args_type::size,
+                [](const typename internal::meta_ctor_node::size_type index) ENTT_NOEXCEPT {
+                    return meta_arg(typename descriptor::args_type{}, index);
+                },
+                [](meta_any* const args) {
+                    return meta_construct<Type, Args...>(args, std::make_index_sequence<descriptor::args_type::size>{});
+                }
+            };
+
+            if (!internal::find_if(&node, type->ctor)) {
+                node.next = type->ctor;
+                type->ctor = &node;
+            }
+
+            return meta_factory<Type, Type(Args...)>{&node.prop};
+        }
+
+        /**
+         * @brief Assigns a meta destructor to a meta type.
+         *
+         * Free functions can be assigned to meta types in the role of destructors.
+         * The signature of the function should identical to the following:
+         *
+         * @code{.cpp}
+         * void(Type &);
+         * @endcode
+         *
+         * The purpose is to give users the ability to free up resources that
+         * require special treatment before an object is actually destroyed.
+         *
+         * @tparam Func The actual function to use as a destructor.
+         * @return A meta factory for the parent type.
+         */
+        template<auto Func>
+        auto dtor() ENTT_NOEXCEPT {
+            static_assert(std::is_invocable_v<decltype(Func), Type&>, "The function doesn't accept an object of the type provided");
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            type->dtor = [](void* instance) {
+                Func(*static_cast<Type*>(instance));
+            };
+
+            return meta_factory<Type>{};
+        }
+
+        /**
+         * @brief Assigns a meta data to a meta type.
+         *
+         * Both data members and static and global variables, as well as constants
+         * of any kind, can be assigned to a meta type.<br/>
+         * From a client's point of view, all the variables associated with the
+         * reflected object will appear as if they were part of the type itself.
+         *
+         * @tparam Data The actual variable to attach to the meta type.
+         * @tparam Policy Optional policy (no policy set by default).
+         * @param id Unique identifier.
+         * @return An extended meta factory for the parent type.
+         */
+        template<auto Data, typename Policy = as_is_t>
+        auto data(const id_type id) ENTT_NOEXCEPT {
+            if constexpr (std::is_member_object_pointer_v<decltype(Data)>) {
+                return data<Data, Data, Policy>(id);
+            }
+            else {
+                using data_type = std::remove_pointer_t<decltype(Data)>;
+                auto* const type = internal::meta_info<Type>::resolve();
+
+                static internal::meta_data_node node{
+                    {},
+                    type,
+                    nullptr,
+                    nullptr,
+                    std::is_same_v<Type, data_type> || std::is_const_v<data_type>,
+                    true,
+                    &internal::meta_info<data_type>::resolve,
+                    &meta_setter<Type, Data>,
+                    &meta_getter<Type, Data, Policy>
+                };
+
+                ENTT_ASSERT(!internal::find_if_not(id, type->data, &node), "Duplicate identifier");
+                node.id = id;
+
+                if (!internal::find_if(&node, type->data)) {
+                    node.next = type->data;
+                    type->data = &node;
+                }
+
+                return meta_factory<Type, std::integral_constant<decltype(Data), Data>>{&node.prop};
+            }
+        }
+
+        /**
+         * @brief Assigns a meta data to a meta type by means of its setter and
+         * getter.
+         *
+         * Setters and getters can be either free functions, member functions or a
+         * mix of them.<br/>
+         * In case of free functions, setters and getters must accept a reference to
+         * an instance of the parent type as their first argument. A setter has then
+         * an extra argument of a type convertible to that of the parameter to
+         * set.<br/>
+         * In case of member functions, getters have no arguments at all, while
+         * setters has an argument of a type convertible to that of the parameter to
+         * set.
+         *
+         * @tparam Setter The actual function to use as a setter.
+         * @tparam Getter The actual function to use as a getter.
+         * @tparam Policy Optional policy (no policy set by default).
+         * @param id Unique identifier.
+         * @return An extended meta factory for the parent type.
+         */
+        template<auto Setter, auto Getter, typename Policy = as_is_t>
+        auto data(const id_type id) ENTT_NOEXCEPT {
+            using underlying_type = std::remove_reference_t<std::invoke_result_t<decltype(Getter), Type&>>;
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_data_node node{
+                {},
+                type,
+                nullptr,
+                nullptr,
+                std::is_same_v<decltype(Setter), std::nullptr_t> || (std::is_member_object_pointer_v<decltype(Setter)> && std::is_const_v<underlying_type>),
+                false,
+                &internal::meta_info<underlying_type>::resolve,
+                &meta_setter<Type, Setter>,
+                &meta_getter<Type, Getter, Policy>
+            };
+
+            ENTT_ASSERT(!internal::find_if_not(id, type->data, &node), "Duplicate identifier");
+            node.id = id;
+
+            if (!internal::find_if(&node, type->data)) {
+                node.next = type->data;
+                type->data = &node;
+            }
+
+            return meta_factory<Type, std::integral_constant<decltype(Setter), Setter>, std::integral_constant<decltype(Getter), Getter>>{&node.prop};
+        }
+
+        /**
+         * @brief Assigns a meta funcion to a meta type.
+         *
+         * Both member functions and free functions can be assigned to a meta
+         * type.<br/>
+         * From a client's point of view, all the functions associated with the
+         * reflected object will appear as if they were part of the type itself.
+         *
+         * @tparam Candidate The actual function to attach to the meta type.
+         * @tparam Policy Optional policy (no policy set by default).
+         * @param id Unique identifier.
+         * @return An extended meta factory for the parent type.
+         */
+        template<auto Candidate, typename Policy = as_is_t>
+        auto func(const id_type id) ENTT_NOEXCEPT {
+            using descriptor = meta_function_helper_t<Type, decltype(Candidate)>;
+            auto* const type = internal::meta_info<Type>::resolve();
+
+            static internal::meta_func_node node{
+                {},
+                type,
+                nullptr,
+                nullptr,
+                descriptor::args_type::size,
+                descriptor::is_const,
+                descriptor::is_static,
+                &internal::meta_info<std::conditional_t<std::is_same_v<Policy, as_void_t>, void, typename descriptor::return_type>>::resolve,
+                [](const typename internal::meta_func_node::size_type index) ENTT_NOEXCEPT {
+                    return meta_arg(typename descriptor::args_type{}, index);
+                },
+                [](meta_handle instance, meta_any* args) {
+                    return meta_invoke<Type, Candidate, Policy>(std::move(instance), args, std::make_index_sequence<descriptor::args_type::size>{});
+                }
+            };
+
+            for (auto* it = &type->func; *it; it = &(*it)->next) {
+                if (*it == &node) {
+                    *it = node.next;
+                    break;
+                }
+            }
+
+            internal::meta_func_node** it = &type->func;
+            for (; *it && (*it)->id != id; it = &(*it)->next);
+            for (; *it && (*it)->id == id && (*it)->arity < node.arity; it = &(*it)->next);
+
+            node.id = id;
+            node.next = *it;
+            *it = &node;
+
+            return meta_factory<Type, std::integral_constant<decltype(Candidate), Candidate>>{&node.prop};
+        }
+    };
+
+
+    /**
+     * @brief Utility function to use for reflection.
+     *
+     * This is the point from which everything starts.<br/>
+     * By invoking this function with a type that is not yet reflected, a meta type
+     * is created to which it will be possible to attach meta objects through a
+     * dedicated factory.
+     *
+     * @tparam Type Type to reflect.
+     * @return A meta factory for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] auto meta() ENTT_NOEXCEPT {
+        auto* const node = internal::meta_info<Type>::resolve();
+        // extended meta factory to allow assigning properties to opaque meta types
+        return meta_factory<Type, Type>{&node->prop};
+    }
+
+
+}
+
+
+#endif
+
+// #include "meta/meta.hpp"
+#ifndef ENTT_META_META_HPP
+#define ENTT_META_META_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/any.hpp"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/utility.hpp"
+
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "adl_pointer.hpp"
+
+// #include "ctx.hpp"
+
+// #include "node.hpp"
+
+// #include "range.hpp"
+
+// #include "type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    class meta_any;
+    class meta_type;
+
+
+    /*! @brief Proxy object for sequence containers. */
+    class meta_sequence_container {
+        template<typename>
+        struct meta_sequence_container_proxy;
+
+        class meta_iterator;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Meta iterator type. */
+        using iterator = meta_iterator;
+
+        /*! @brief Default constructor. */
+        meta_sequence_container() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Construct a proxy object for sequence containers.
+         * @tparam Type Type of container to wrap.
+         * @param instance The container to wrap.
+         */
+        template<typename Type>
+        meta_sequence_container(std::in_place_type_t<Type>, any instance) ENTT_NOEXCEPT
+            : value_type_fn{ &meta_sequence_container_proxy<Type>::value_type },
+            size_fn{ &meta_sequence_container_proxy<Type>::size },
+            resize_fn{ &meta_sequence_container_proxy<Type>::resize },
+            clear_fn{ &meta_sequence_container_proxy<Type>::clear },
+            begin_fn{ &meta_sequence_container_proxy<Type>::begin },
+            end_fn{ &meta_sequence_container_proxy<Type>::end },
+            insert_fn{ &meta_sequence_container_proxy<Type>::insert },
+            erase_fn{ &meta_sequence_container_proxy<Type>::erase },
+            get_fn{ &meta_sequence_container_proxy<Type>::get },
+            storage{ std::move(instance) }
+        {}
+
+        [[nodiscard]] inline meta_type value_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline size_type size() const ENTT_NOEXCEPT;
+        inline bool resize(size_type);
+        inline bool clear();
+        [[nodiscard]] inline iterator begin();
+        [[nodiscard]] inline iterator end();
+        inline std::pair<iterator, bool> insert(iterator, meta_any);
+        inline std::pair<iterator, bool> erase(iterator);
+        [[nodiscard]] inline meta_any operator[](size_type);
+        [[nodiscard]] inline explicit operator bool() const ENTT_NOEXCEPT;
+
+    private:
+        meta_type(*value_type_fn)() ENTT_NOEXCEPT = nullptr;
+        size_type(*size_fn)(const any&) ENTT_NOEXCEPT = nullptr;
+        bool(*resize_fn)(any&, size_type) = nullptr;
+        bool(*clear_fn)(any&) = nullptr;
+        iterator(*begin_fn)(any&) = nullptr;
+        iterator(*end_fn)(any&) = nullptr;
+        std::pair<iterator, bool>(*insert_fn)(any&, iterator, meta_any&) = nullptr;
+        std::pair<iterator, bool>(*erase_fn)(any&, iterator) = nullptr;
+        meta_any(*get_fn)(any&, size_type) = nullptr;
+        any storage{};
+    };
+
+
+    /*! @brief Proxy object for associative containers. */
+    class meta_associative_container {
+        template<typename>
+        struct meta_associative_container_proxy;
+
+        class meta_iterator;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Meta iterator type. */
+        using iterator = meta_iterator;
+
+        /*! @brief Default constructor. */
+        meta_associative_container() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Construct a proxy object for associative containers.
+         * @tparam Type Type of container to wrap.
+         * @param instance The container to wrap.
+         */
+        template<typename Type>
+        meta_associative_container(std::in_place_type_t<Type>, any instance) ENTT_NOEXCEPT
+            : key_only_container{ is_key_only_meta_associative_container_v<Type> },
+            key_type_fn{ &meta_associative_container_proxy<Type>::key_type },
+            mapped_type_fn{ &meta_associative_container_proxy<Type>::mapped_type },
+            value_type_fn{ &meta_associative_container_proxy<Type>::value_type },
+            size_fn{ &meta_associative_container_proxy<Type>::size },
+            clear_fn{ &meta_associative_container_proxy<Type>::clear },
+            begin_fn{ &meta_associative_container_proxy<Type>::begin },
+            end_fn{ &meta_associative_container_proxy<Type>::end },
+            insert_fn{ &meta_associative_container_proxy<Type>::insert },
+            erase_fn{ &meta_associative_container_proxy<Type>::erase },
+            find_fn{ &meta_associative_container_proxy<Type>::find },
+            storage{ std::move(instance) }
+        {}
+
+        [[nodiscard]] inline bool key_only() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline meta_type key_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline meta_type mapped_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline meta_type value_type() const ENTT_NOEXCEPT;
+        [[nodiscard]] inline size_type size() const ENTT_NOEXCEPT;
+        inline bool clear();
+        [[nodiscard]] inline iterator begin();
+        [[nodiscard]] inline iterator end();
+        inline bool insert(meta_any, meta_any);
+        inline bool erase(meta_any);
+        [[nodiscard]] inline iterator find(meta_any);
+        [[nodiscard]] inline explicit operator bool() const ENTT_NOEXCEPT;
+
+    private:
+        bool key_only_container{};
+        meta_type(*key_type_fn)() ENTT_NOEXCEPT = nullptr;
+        meta_type(*mapped_type_fn)() ENTT_NOEXCEPT = nullptr;
+        meta_type(*value_type_fn)() ENTT_NOEXCEPT = nullptr;
+        size_type(*size_fn)(const any&) ENTT_NOEXCEPT = nullptr;
+        bool(*clear_fn)(any&) = nullptr;
+        iterator(*begin_fn)(any&) = nullptr;
+        iterator(*end_fn)(any&) = nullptr;
+        bool(*insert_fn)(any&, meta_any&, meta_any&) = nullptr;
+        bool(*erase_fn)(any&, meta_any&) = nullptr;
+        iterator(*find_fn)(any&, meta_any&) = nullptr;
+        any storage{};
+    };
+
+
+    /*! @brief Opaque wrapper for values of any type. */
+    class meta_any {
+        enum class operation { DTOR, DEREF, SEQ, ASSOC };
+
+        using vtable_type = void(const operation, const any&, void*);
+
+        template<typename Type>
+        static void basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                switch (op) {
+                case operation::DTOR:
+                    if (auto* curr = static_cast<internal::meta_type_node*>(to); curr->dtor && from.owner()) {
+                        curr->dtor(const_cast<any&>(from).data());
+                    }
+                    break;
+                case operation::DEREF:
+                    if constexpr (is_meta_pointer_like_v<Type>) {
+                        using element_type = std::remove_const_t<typename std::pointer_traits<Type>::element_type>;
+
+                        if constexpr (std::is_function_v<element_type>) {
+                            *static_cast<meta_any*>(to) = any_cast<Type>(from);
+                        }
+                        else if constexpr (!std::is_same_v<std::remove_const_t<typename std::pointer_traits<Type>::element_type>, void>) {
+                            using in_place_type = decltype(adl_meta_pointer_like<Type>::dereference(any_cast<const Type&>(from)));
+                            static_cast<meta_any*>(to)->emplace<in_place_type>(adl_meta_pointer_like<Type>::dereference(any_cast<const Type&>(from)));
+                        }
+                    }
+                case operation::SEQ:
+                    if constexpr (is_complete_v<meta_sequence_container_traits<Type>>) {
+                        *static_cast<meta_sequence_container*>(to) = { std::in_place_type<Type>, std::move(const_cast<any&>(from)) };
+                    }
+                    break;
+                case operation::ASSOC:
+                    if constexpr (is_complete_v<meta_associative_container_traits<Type>>) {
+                        *static_cast<meta_associative_container*>(to) = { std::in_place_type<Type>, std::move(const_cast<any&>(from)) };
+                    }
+                    break;
+                }
+            }
+        }
+
+        meta_any(const meta_any& other, any ref) ENTT_NOEXCEPT
+            : storage{ std::move(ref) },
+            node{ storage ? other.node : nullptr },
+            vtable{ storage ? other.vtable : &basic_vtable<void> }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        meta_any() ENTT_NOEXCEPT
+            : storage{},
+            node{},
+            vtable{ &basic_vtable<void> }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit meta_any(std::in_place_type_t<Type>, Args &&... args)
+            : storage{ std::in_place_type<Type>, std::forward<Args>(args)... },
+            node{ internal::meta_info<Type>::resolve() },
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> }
+        {}
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        meta_any(std::reference_wrapper<Type> value)
+            : meta_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>>>
+        meta_any(Type&& value)
+            : storage{ std::forward<Type>(value) },
+            node{ internal::meta_info<std::decay_t<Type>>::resolve() },
+            vtable{ &basic_vtable<std::decay_t<Type>> }
+        {}
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        meta_any(const meta_any& other) = default;
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        meta_any(meta_any&& other) ENTT_NOEXCEPT
+            : storage{ std::move(other.storage) },
+            node{ std::exchange(other.node, nullptr) },
+            vtable{ std::exchange(other.vtable, &basic_vtable<void>) }
+        {}
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~meta_any() {
+            vtable(operation::DTOR, storage, node);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This meta any object.
+         */
+        meta_any& operator=(const meta_any& other) {
+            std::exchange(vtable, other.vtable)(operation::DTOR, storage, node);
+            storage = other.storage;
+            node = other.node;
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This meta any object.
+         */
+        meta_any& operator=(meta_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, std::exchange(other.vtable, &basic_vtable<void>))(operation::DTOR, storage, node);
+            storage = std::move(other.storage);
+            node = std::exchange(other.node, nullptr);
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This meta any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_meta<T &>, emplace<Type &> or forward_as_meta instead")]]
+        meta_any& operator=(std::reference_wrapper<Type> value) {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This meta any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>, meta_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the underlying object.
+         * @return The type of the underlying object, if any.
+         */
+        [[nodiscard]] inline meta_type type() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /**
+         * @brief Invokes the underlying function, if possible.
+         *
+         * @sa meta_func::invoke
+         *
+         * @tparam Args Types of arguments to use to invoke the function.
+         * @param id Unique identifier.
+         * @param args Parameters to use to invoke the function.
+         * @return A wrapper containing the returned value, if any.
+         */
+        template<typename... Args>
+        meta_any invoke(const id_type id, Args &&... args) const;
+
+        /*! @copydoc invoke */
+        template<typename... Args>
+        meta_any invoke(const id_type id, Args &&... args);
+
+        /**
+         * @brief Sets the value of a given variable.
+         *
+         * The type of the value must be such that a cast or conversion to the type
+         * of the variable is possible. Otherwise, invoking the setter does nothing.
+         *
+         * @tparam Type Type of value to assign.
+         * @param id Unique identifier.
+         * @param value Parameter to use to set the underlying variable.
+         * @return True in case of success, false otherwise.
+         */
+        template<typename Type>
+        bool set(const id_type id, Type&& value);
+
+        /**
+         * @brief Gets the value of a given variable.
+         * @param id Unique identifier.
+         * @return A wrapper containing the value of the underlying variable.
+         */
+        [[nodiscard]] meta_any get(const id_type id) const;
+
+        /*! @copydoc get */
+        [[nodiscard]] meta_any get(const id_type id);
+
+        /**
+         * @brief Tries to cast an instance to a given type.
+         * @tparam Type Type to which to cast the instance.
+         * @return A (possibly null) pointer to the contained instance.
+         */
+        template<typename Type>
+        [[nodiscard]] const Type* try_cast() const {
+            if (node) {
+                if (const auto info = type_id<Type>(); node->info == info) {
+                    return any_cast<Type>(&storage);
+                }
+                else if (const auto* base = internal::meta_visit<&internal::meta_type_node::base>([info](const auto* curr) { return curr->type()->info == info; }, node); base) {
+                    return static_cast<const Type*>(base->cast(storage.data()));
+                }
+            }
+
+            return nullptr;
+        }
+
+        /*! @copydoc try_cast */
+        template<typename Type>
+        [[nodiscard]] Type* try_cast() {
+            if (node) {
+                if (const auto info = type_id<Type>(); node->info == info) {
+                    return any_cast<Type>(&storage);
+                }
+                else if (const auto* base = internal::meta_visit<&internal::meta_type_node::base>([info](const auto* curr) { return curr->type()->info == info; }, node); base) {
+                    return static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(base->cast(static_cast<constness_as_t<any, Type> &>(storage).data())));
+                }
+            }
+
+            return nullptr;
+        }
+
+        /**
+         * @brief Tries to cast an instance to a given type.
+         *
+         * The type of the instance must be such that the cast is possible.
+         *
+         * @warning
+         * Attempting to perform an invalid cast results in undefined behavior.
+         *
+         * @tparam Type Type to which to cast the instance.
+         * @return A reference to the contained instance.
+         */
+        template<typename Type>
+        [[nodiscard]] Type cast() const {
+            auto* const instance = try_cast<std::remove_reference_t<Type>>();
+            ENTT_ASSERT(instance, "Invalid instance");
+            return static_cast<Type>(*instance);
+        }
+
+        /*! @copydoc cast */
+        template<typename Type>
+        [[nodiscard]] Type cast() {
+            // forces const on non-reference types to make them work also with wrappers for const references
+            auto* const instance = try_cast<std::remove_reference_t<const Type>>();
+            ENTT_ASSERT(instance, "Invalid instance");
+            return static_cast<Type>(*instance);
+        }
+
+        /**
+         * @brief Converts an object in such a way that a given cast becomes viable.
+         * @tparam Type Type to which the cast is requested.
+         * @return A valid meta any object if there exists a viable conversion, an
+         * invalid one otherwise.
+         */
+        template<typename Type>
+        [[nodiscard]] meta_any allow_cast() const {
+            if (try_cast<std::remove_reference_t<Type>>() != nullptr) {
+                return as_ref();
+            }
+            else if (node) {
+                if (const auto* const conv = internal::meta_visit<&internal::meta_type_node::conv>([info = type_id<Type>()](const auto* curr) { return curr->type()->info == info; }, node); conv) {
+                    return conv->conv(storage.data());
+                }
+            }
+
+            return {};
+        }
+
+        /**
+         * @brief Converts an object in such a way that a given cast becomes viable.
+         * @tparam Type Type to which the cast is requested.
+         * @return True if there exists a viable conversion, false otherwise.
+         */
+        template<typename Type>
+        bool allow_cast() {
+            // forces const on non-reference types to make them work also with wrappers for const references
+            if (try_cast<std::remove_reference_t<const Type>>() != nullptr) {
+                return true;
+            }
+            else if (node) {
+                if (const auto* const conv = internal::meta_visit<&internal::meta_type_node::conv>([info = type_id<Type>()](const auto* curr) { return curr->type()->info == info; }, node); conv) {
+                    *this = conv->conv(std::as_const(storage).data());
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, storage, node);
+            storage.emplace<Type>(std::forward<Args>(args)...);
+            node = internal::meta_info<Type>::resolve();
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, storage, node);
+            storage.reset();
+            node = nullptr;
+        }
+
+        /**
+         * @brief Returns a sequence container proxy.
+         * @return A sequence container proxy for the underlying object.
+         */
+        [[nodiscard]] meta_sequence_container as_sequence_container() ENTT_NOEXCEPT {
+            meta_sequence_container proxy;
+            vtable(operation::SEQ, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /*! @copydoc as_sequence_container */
+        [[nodiscard]] meta_sequence_container as_sequence_container() const ENTT_NOEXCEPT {
+            meta_sequence_container proxy;
+            vtable(operation::SEQ, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /**
+         * @brief Returns an associative container proxy.
+         * @return An associative container proxy for the underlying object.
+         */
+        [[nodiscard]] meta_associative_container as_associative_container() ENTT_NOEXCEPT {
+            meta_associative_container proxy;
+            vtable(operation::ASSOC, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /*! @copydoc as_associative_container */
+        [[nodiscard]] meta_associative_container as_associative_container() const ENTT_NOEXCEPT {
+            meta_associative_container proxy;
+            vtable(operation::ASSOC, storage.as_ref(), &proxy);
+            return proxy;
+        }
+
+        /**
+         * @brief Indirection operator for dereferencing opaque objects.
+         * @return A wrapper that shares a reference to an unmanaged object if the
+         * wrapped element is dereferenceable, an invalid meta any otherwise.
+         */
+        [[nodiscard]] meta_any operator*() const ENTT_NOEXCEPT {
+            meta_any ret{};
+            vtable(operation::DEREF, storage, &ret);
+            return ret;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is invalid, true otherwise.
+         * @return False if the wrapper is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_any& other) const {
+            return (!node && !other.node) || (node && other.node && node->info == other.node->info && storage == other.storage);
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] meta_any as_ref() ENTT_NOEXCEPT {
+            return meta_any{ *this, storage.as_ref() };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] meta_any as_ref() const ENTT_NOEXCEPT {
+            return meta_any{ *this, storage.as_ref() };
+        }
+
+    private:
+        any storage;
+        internal::meta_type_node* node;
+        vtable_type* vtable;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const meta_any& lhs, const meta_any& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, typename... Args>
+    meta_any make_meta(Args &&... args) {
+        return meta_any{ std::in_place_type<Type>, std::forward<Args>(args)... };
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<typename Type>
+    meta_any forward_as_meta(Type&& value) {
+        return meta_any{ std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value) };
+    }
+
+
+    /**
+     * @brief Opaque pointers to instances of any type.
+     *
+     * A handle doesn't perform copies and isn't responsible for the contained
+     * object. It doesn't prolong the lifetime of the pointed instance.<br/>
+     * Handles are used to generate references to actual objects when needed.
+     */
+    struct meta_handle {
+        /*! @brief Default constructor. */
+        meta_handle() = default;
+
+
+        /*! @brief Default copy constructor, deleted on purpose. */
+        meta_handle(const meta_handle&) = delete;
+
+        /*! @brief Default move constructor. */
+        meta_handle(meta_handle&&) = default;
+
+        /**
+         * @brief Default copy assignment operator, deleted on purpose.
+         * @return This meta handle.
+         */
+        meta_handle& operator=(const meta_handle&) = delete;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This meta handle.
+         */
+        meta_handle& operator=(meta_handle&&) = default;
+
+        /**
+         * @brief Creates a handle that points to an unmanaged object.
+         * @tparam Type Type of object to use to initialize the handle.
+         * @param value An instance of an object to use to initialize the handle.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_handle>>>
+        meta_handle(Type& value) ENTT_NOEXCEPT
+            : meta_handle{}
+        {
+            if constexpr (std::is_same_v<std::decay_t<Type>, meta_any>) {
+                any = value.as_ref();
+            }
+            else {
+                any.emplace<Type&>(value);
+            }
+        }
+
+        /**
+         * @brief Returns false if a handle is invalid, true otherwise.
+         * @return False if the handle is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(any);
+        }
+
+        /**
+         * @brief Access operator for accessing the contained opaque object.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] meta_any* operator->() {
+            return &any;
+        }
+
+        /*! @copydoc operator-> */
+        [[nodiscard]] const meta_any* operator->() const {
+            return &any;
+        }
+
+    private:
+        meta_any any;
+    };
+
+
+    /*! @brief Opaque wrapper for properties of any type. */
+    struct meta_prop {
+        /*! @brief Node type. */
+        using node_type = internal::meta_prop_node;
+
+        /**
+         * @brief Constructs an instance from a given node.
+         * @param curr The underlying node with which to construct the instance.
+         */
+        meta_prop(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /**
+         * @brief Returns the stored key as a const reference.
+         * @return A wrapper containing the key stored with the property.
+         */
+        [[nodiscard]] meta_any key() const {
+            return node->id.as_ref();
+        }
+
+        /**
+         * @brief Returns the stored value by copy.
+         * @return A wrapper containing the value stored with the property.
+         */
+        [[nodiscard]] meta_any value() const {
+            return node->value;
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for constructors. */
+    struct meta_ctor {
+        /*! @brief Node type. */
+        using node_type = internal::meta_ctor_node;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename node_type::size_type;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_ctor(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /**
+         * @brief Returns the type to which an object belongs.
+         * @return The type to which the object belongs.
+         */
+        [[nodiscard]] inline meta_type parent() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns the number of arguments accepted by a constructor.
+         * @return The number of arguments accepted by the constructor.
+         */
+        [[nodiscard]] size_type arity() const ENTT_NOEXCEPT {
+            return node->arity;
+        }
+
+        /**
+         * @brief Returns the type of the i-th argument of a constructor.
+         * @param index Index of the argument of which to return the type.
+         * @return The type of the i-th argument of a constructor.
+         */
+        [[nodiscard]] meta_type arg(size_type index) const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Creates an instance of the underlying type, if possible.
+         *
+         * Parameters must be such that a cast or conversion to the required types
+         * is possible. Otherwise, an empty and thus invalid wrapper is returned.
+         *
+         * @param args Parameters to use to construct the instance.
+         * @param sz Number of parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        [[nodiscard]] meta_any invoke(meta_any* const args, const size_type sz) const {
+            return sz == arity() ? node->invoke(args) : meta_any{};
+        }
+
+        /**
+         * @copybrief invoke
+         *
+         * @sa invoke
+         *
+         * @tparam Args Types of arguments to use to construct the instance.
+         * @param args Parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        [[nodiscard]] meta_any invoke([[maybe_unused]] Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return invoke(arguments, sizeof...(Args));
+        }
+
+        /**
+         * @brief Returns a range to use to visit all properties.
+         * @return An iterable range to use to visit all properties.
+         */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for data members. */
+    struct meta_data {
+        /*! @brief Node type. */
+        using node_type = internal::meta_data_node;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_data(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /*! @copydoc meta_type::id */
+        [[nodiscard]] id_type id() const ENTT_NOEXCEPT {
+            return node->id;
+        }
+
+        /*! @copydoc meta_ctor::parent */
+        [[nodiscard]] inline meta_type parent() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Indicates whether a data member is constant or not.
+         * @return True if the data member is constant, false otherwise.
+         */
+        [[nodiscard]] bool is_const() const ENTT_NOEXCEPT {
+            return node->is_const;
+        }
+
+        /**
+         * @brief Indicates whether a data member is static or not.
+         * @return True if the data member is static, false otherwise.
+         */
+        [[nodiscard]] bool is_static() const ENTT_NOEXCEPT {
+            return node->is_static;
+        }
+
+        /*! @copydoc meta_any::type */
+        [[nodiscard]] inline meta_type type() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Sets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the setter results in an undefined
+         * behavior.<br/>
+         * The type of the value must be such that a cast or conversion to the type
+         * of the variable is possible. Otherwise, invoking the setter does nothing.
+         *
+         * @tparam Type Type of value to assign.
+         * @param instance An opaque instance of the underlying type.
+         * @param value Parameter to use to set the underlying variable.
+         * @return True in case of success, false otherwise.
+         */
+        template<typename Type>
+        bool set(meta_handle instance, Type&& value) const {
+            return node->set && node->set(std::move(instance), std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Gets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the getter results in an undefined behavior.
+         *
+         * @param instance An opaque instance of the underlying type.
+         * @return A wrapper containing the value of the underlying variable.
+         */
+        [[nodiscard]] meta_any get(meta_handle instance) const {
+            return node->get(std::move(instance));
+        }
+
+        /*! @copydoc meta_ctor::prop */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for member functions. */
+    struct meta_func {
+        /*! @brief Node type. */
+        using node_type = internal::meta_func_node;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename node_type::size_type;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_func(const node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /*! @copydoc meta_type::id */
+        [[nodiscard]] id_type id() const ENTT_NOEXCEPT {
+            return node->id;
+        }
+
+        /*! @copydoc meta_ctor::parent */
+        [[nodiscard]] inline meta_type parent() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns the number of arguments accepted by a member function.
+         * @return The number of arguments accepted by the member function.
+         */
+        [[nodiscard]] size_type arity() const ENTT_NOEXCEPT {
+            return node->arity;
+        }
+
+        /**
+         * @brief Indicates whether a member function is constant or not.
+         * @return True if the member function is constant, false otherwise.
+         */
+        [[nodiscard]] bool is_const() const ENTT_NOEXCEPT {
+            return node->is_const;
+        }
+
+        /**
+         * @brief Indicates whether a member function is static or not.
+         * @return True if the member function is static, false otherwise.
+         */
+        [[nodiscard]] bool is_static() const ENTT_NOEXCEPT {
+            return node->is_static;
+        }
+
+        /**
+         * @brief Returns the return type of a member function.
+         * @return The return type of the member function.
+         */
+        [[nodiscard]] inline meta_type ret() const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Returns the type of the i-th argument of a member function.
+         * @param index Index of the argument of which to return the type.
+         * @return The type of the i-th argument of a member function.
+         */
+        [[nodiscard]] inline meta_type arg(size_type index) const ENTT_NOEXCEPT;
+
+        /**
+         * @brief Invokes the underlying function, if possible.
+         *
+         * To invoke a member function, the parameters must be such that a cast or
+         * conversion to the required types is possible. Otherwise, an empty and
+         * thus invalid wrapper is returned.<br/>
+         * It must be possible to cast the instance to the parent type of the member
+         * function. Otherwise, invoking the underlying function results in an
+         * undefined behavior.
+         *
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @param sz Number of parameters to use to invoke the function.
+         * @return A wrapper containing the returned value, if any.
+         */
+        meta_any invoke(meta_handle instance, meta_any* const args, const size_type sz) const {
+            return sz == arity() ? node->invoke(std::move(instance), args) : meta_any{};
+        }
+
+        /**
+         * @copybrief invoke
+         *
+         * @sa invoke
+         *
+         * @tparam Args Types of arguments to use to invoke the function.
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        meta_any invoke(meta_handle instance, Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return invoke(std::move(instance), arguments, sizeof...(Args));
+        }
+
+        /*! @copydoc meta_ctor::prop */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+    private:
+        const node_type* node;
+    };
+
+
+    /*! @brief Opaque wrapper for types. */
+    class meta_type {
+        static bool can_cast_or_convert(const internal::meta_type_node* type, const type_info info) ENTT_NOEXCEPT {
+            if (type->info == info) {
+                return true;
+            }
+
+            for (const auto* curr = type->conv; curr; curr = curr->next) {
+                if (curr->type()->info == info) {
+                    return true;
+                }
+            }
+
+            for (const auto* curr = type->base; curr; curr = curr->next) {
+                if (auto* target = curr->type(); can_cast_or_convert(target, info)) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        template<typename... Args, auto... Index>
+        [[nodiscard]] static const internal::meta_ctor_node* ctor(const internal::meta_ctor_node* curr, std::index_sequence<Index...>) {
+            for (; curr; curr = curr->next) {
+                if (curr->arity == sizeof...(Args) && (can_cast_or_convert(internal::meta_info<Args>::resolve(), curr->arg(Index).info()) && ...)) {
+                    return curr;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<auto... Member, typename Node>
+        void unregister_all(Node** curr) {
+            while (*curr) {
+                (unregister_all(&((*curr)->*Member)), ...);
+                *curr = std::exchange((*curr)->next, nullptr);
+            }
+        }
+
+    public:
+        /*! @brief Node type. */
+        using node_type = internal::meta_type_node;
+        /*! @brief Node type. */
+        using base_node_type = internal::meta_base_node;
+        /*! @brief Unsigned integer type. */
+        using size_type = typename node_type::size_type;
+
+        /*! @copydoc meta_prop::meta_prop */
+        meta_type(node_type* curr = nullptr) ENTT_NOEXCEPT
+            : node{ curr }
+        {}
+
+        /**
+         * @brief Constructs an instance from a given base node.
+         * @param curr The base node with which to construct the instance.
+         */
+        meta_type(base_node_type* curr) ENTT_NOEXCEPT
+            : node{ curr ? curr->type() : nullptr }
+        {}
+
+        /**
+         * @brief Returns the type info object of the underlying type.
+         * @return The type info object of the underlying type.
+         */
+        [[nodiscard]] type_info info() const ENTT_NOEXCEPT {
+            return node->info;
+        }
+
+        /**
+         * @brief Returns the identifier assigned to a type.
+         * @return The identifier assigned to the type.
+         */
+        [[nodiscard]] id_type id() const ENTT_NOEXCEPT {
+            return node->id;
+        }
+
+        /**
+         * @brief Returns the size of the underlying type if known.
+         * @return The size of the underlying type if known, 0 otherwise.
+         */
+        [[nodiscard]] size_type size_of() const ENTT_NOEXCEPT {
+            return node->size_of;
+        }
+
+        /**
+         * @brief Checks whether a type refers to void or not.
+         * @return True if the underlying type is void, false otherwise.
+         */
+        [[nodiscard]] bool is_void() const ENTT_NOEXCEPT {
+            return node->is_void;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an integral type or not.
+         * @return True if the underlying type is an integral type, false otherwise.
+         */
+        [[nodiscard]] bool is_integral() const ENTT_NOEXCEPT {
+            return node->is_integral;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a floating-point type or not.
+         * @return True if the underlying type is a floating-point type, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_floating_point() const ENTT_NOEXCEPT {
+            return node->is_floating_point;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an array type or not.
+         * @return True if the underlying type is an array type, false otherwise.
+         */
+        [[nodiscard]] bool is_array() const ENTT_NOEXCEPT {
+            return node->is_array;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an enum or not.
+         * @return True if the underlying type is an enum, false otherwise.
+         */
+        [[nodiscard]] bool is_enum() const ENTT_NOEXCEPT {
+            return node->is_enum;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an union or not.
+         * @return True if the underlying type is an union, false otherwise.
+         */
+        [[nodiscard]] bool is_union() const ENTT_NOEXCEPT {
+            return node->is_union;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a class or not.
+         * @return True if the underlying type is a class, false otherwise.
+         */
+        [[nodiscard]] bool is_class() const ENTT_NOEXCEPT {
+            return node->is_class;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a pointer or not.
+         * @return True if the underlying type is a pointer, false otherwise.
+         */
+        [[nodiscard]] bool is_pointer() const ENTT_NOEXCEPT {
+            return node->is_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a function pointer or not.
+         * @return True if the underlying type is a function pointer, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_function_pointer() const ENTT_NOEXCEPT {
+            return node->is_function_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a pointer to data member or not.
+         * @return True if the underlying type is a pointer to data member, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_member_object_pointer() const ENTT_NOEXCEPT {
+            return node->is_member_object_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a pointer to member function or
+         * not.
+         * @return True if the underlying type is a pointer to member function,
+         * false otherwise.
+         */
+        [[nodiscard]] bool is_member_function_pointer() const ENTT_NOEXCEPT {
+            return node->is_member_function_pointer;
+        }
+
+        /**
+         * @brief Checks whether a type is a pointer-like type or not.
+         * @return True if the underlying type is a pointer-like one, false
+         * otherwise.
+         */
+        [[nodiscard]] bool is_pointer_like() const ENTT_NOEXCEPT {
+            return node->is_pointer_like;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a sequence container or not.
+         * @return True if the type is a sequence container, false otherwise.
+         */
+        [[nodiscard]] bool is_sequence_container() const ENTT_NOEXCEPT {
+            return node->is_sequence_container;
+        }
+
+        /**
+         * @brief Checks whether a type refers to an associative container or not.
+         * @return True if the type is an associative container, false otherwise.
+         */
+        [[nodiscard]] bool is_associative_container() const ENTT_NOEXCEPT {
+            return node->is_associative_container;
+        }
+
+        /**
+         * @brief Checks whether a type refers to a recognized class template
+         * specialization or not.
+         * @return True if the type is a recognized class template specialization,
+         * false otherwise.
+         */
+        [[nodiscard]] bool is_template_specialization() const ENTT_NOEXCEPT {
+            return node->template_info.is_template_specialization;
+        }
+
+        /**
+         * @brief Returns the number of template arguments, if any.
+         * @return The number of template arguments, if any.
+         */
+        [[nodiscard]] size_type template_arity() const ENTT_NOEXCEPT {
+            return node->template_info.arity;
+        }
+
+        /**
+         * @brief Returns a tag for the class template of the underlying type.
+         *
+         * @sa meta_class_template_tag
+         *
+         * @return The tag for the class template of the underlying type.
+         */
+        [[nodiscard]] inline meta_type template_type() const ENTT_NOEXCEPT {
+            return is_template_specialization() ? node->template_info.type() : meta_type{};
+        }
+
+        /**
+         * @brief Returns the type of the i-th template argument of a type.
+         * @param index Index of the template argument of which to return the type.
+         * @return The type of the i-th template argument of a type.
+         */
+        [[nodiscard]] inline meta_type template_arg(size_type index) const ENTT_NOEXCEPT {
+            return index < template_arity() ? node->template_info.arg(index) : meta_type{};
+        }
+
+        /**
+         * @brief Provides the number of dimensions of an array type.
+         * @return The number of dimensions in case of array types, 0 otherwise.
+         */
+        [[nodiscard]] size_type rank() const ENTT_NOEXCEPT {
+            return node->rank;
+        }
+
+        /**
+         * @brief The number of elements along the given dimension of an array type.
+         * @param dim The dimension of which to return the number of elements.
+         * @return The number of elements along the given dimension in case of array
+         * types, 0 otherwise.
+         */
+        [[nodiscard]] size_type extent(size_type dim = {}) const ENTT_NOEXCEPT {
+            return node->extent(dim);
+        }
+
+        /**
+         * @brief Provides the type for which the pointer is defined.
+         * @return The type for which the pointer is defined or this type if it
+         * doesn't refer to a pointer type.
+         */
+        [[nodiscard]] meta_type remove_pointer() const ENTT_NOEXCEPT {
+            return node->remove_pointer();
+        }
+
+        /**
+         * @brief Provides the type for which the array is defined.
+         * @return The type for which the array is defined or this type if it
+         * doesn't refer to an array type.
+         */
+        [[nodiscard]] meta_type remove_extent() const ENTT_NOEXCEPT {
+            return node->remove_extent();
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level base meta types.
+         * @return An iterable range to use to visit top-level base meta types.
+         */
+        [[nodiscard]] meta_range<meta_type, internal::meta_base_node> base() const ENTT_NOEXCEPT {
+            return node->base;
+        }
+
+        /**
+         * @brief Returns the base meta type associated with a given identifier.
+         * @param id Unique identifier.
+         * @return The base meta type associated with the given identifier, if any.
+         */
+        [[nodiscard]] meta_type base(const id_type id) const {
+            return internal::meta_visit<&node_type::base>([id](const auto* curr) { return curr->type()->id == id; }, node);
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level constructors.
+         * @return An iterable range to use to visit top-level constructors.
+         */
+        [[nodiscard]] meta_range<meta_ctor> ctor() const ENTT_NOEXCEPT {
+            return node->ctor;
+        }
+
+        /**
+         * @brief Returns a constructor for a given list of types of arguments.
+         * @tparam Args Constructor arguments.
+         * @return The requested constructor, if any.
+         */
+        template<typename... Args>
+        [[nodiscard]] meta_ctor ctor() const {
+            return ctor<Args...>(node->ctor, std::make_index_sequence<sizeof...(Args)>{});
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level data.
+         * @return An iterable range to use to visit top-level data.
+         */
+        [[nodiscard]] meta_range<meta_data> data() const ENTT_NOEXCEPT {
+            return node->data;
+        }
+
+        /**
+         * @brief Returns the data associated with a given identifier.
+         *
+         * The data of the base classes will also be visited, if any.
+         *
+         * @param id Unique identifier.
+         * @return The data associated with the given identifier, if any.
+         */
+        [[nodiscard]] meta_data data(const id_type id) const {
+            return internal::meta_visit<&node_type::data>([id](const auto* curr) { return curr->id == id; }, node);
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level functions.
+         * @return An iterable range to use to visit top-level functions.
+         */
+        [[nodiscard]] meta_range<meta_func> func() const ENTT_NOEXCEPT {
+            return node->func;
+        }
+
+        /**
+         * @brief Returns the function associated with a given identifier.
+         *
+         * The functions of the base classes will also be visited, if any.<br/>
+         * In the case of overloaded functions, the first one with the required
+         * identifier will be returned.
+         *
+         * @param id Unique identifier.
+         * @return The function associated with the given identifier, if any.
+         */
+        [[nodiscard]] meta_func func(const id_type id) const {
+            return internal::meta_visit<&node_type::func>([id](const auto* curr) { return curr->id == id; }, node);
+        }
+
+        /**
+         * @brief Creates an instance of the underlying type, if possible.
+         *
+         * Parameters must be such that a cast or conversion to the required types
+         * is possible. Otherwise, an empty and thus invalid wrapper is returned.
+         *
+         * @param args Parameters to use to construct the instance.
+         * @param sz Number of parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        [[nodiscard]] meta_any construct(meta_any* const args, const size_type sz) const {
+            meta_any ret{};
+            internal::meta_visit<&node_type::ctor>([args, sz, &ret](const auto* curr) { return (curr->arity == sz) && (ret = curr->invoke(args)); }, node);
+            return ret;
+        }
+
+        /**
+         * @copybrief construct
+         *
+         * @sa construct
+         *
+         * @tparam Args Types of arguments to use to construct the instance.
+         * @param args Parameters to use to construct the instance.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        [[nodiscard]] meta_any construct(Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return construct(arguments, sizeof...(Args));
+        }
+
+        /**
+         * @brief Invokes a function given an identifier, if possible.
+         *
+         * It must be possible to cast the instance to the parent type of the member
+         * function. Otherwise, invoking the underlying function results in an
+         * undefined behavior.
+         *
+         * @sa meta_func::invoke
+         *
+         * @param id Unique identifier.
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @param sz Number of parameters to use to invoke the function.
+         * @return A wrapper containing the returned value, if any.
+         */
+        meta_any invoke(const id_type id, meta_handle instance, meta_any* const args, const size_type sz) const {
+            const internal::meta_func_node* candidate{};
+            size_type extent{ sz + 1u };
+            bool ambiguous{};
+
+            for (auto* it = internal::meta_visit<&node_type::func>([id, sz](const auto* curr) { return curr->id == id && curr->arity == sz; }, node); it && it->id == id && it->arity == sz; it = it->next) {
+                size_type direct{};
+                size_type ext{};
+
+                for (size_type next{}; next < sz && next == (direct + ext); ++next) {
+                    const auto type = args[next].type();
+                    const auto req = it->arg(next).info();
+                    type.info() == req ? ++direct : (ext += can_cast_or_convert(type.node, req));
+                }
+
+                if ((direct + ext) == sz) {
+                    if (ext < extent) {
+                        candidate = it;
+                        extent = ext;
+                        ambiguous = false;
+                    }
+                    else if (ext == extent) {
+                        ambiguous = true;
+                    }
+                }
+            }
+
+            return (candidate && !ambiguous) ? candidate->invoke(std::move(instance), args) : meta_any{};
+        }
+
+        /**
+         * @copybrief invoke
+         *
+         * @sa invoke
+         *
+         * @param id Unique identifier.
+         * @tparam Args Types of arguments to use to invoke the function.
+         * @param instance An opaque instance of the underlying type.
+         * @param args Parameters to use to invoke the function.
+         * @return A wrapper containing the new instance, if any.
+         */
+        template<typename... Args>
+        meta_any invoke(const id_type id, meta_handle instance, Args &&... args) const {
+            meta_any arguments[sizeof...(Args) + 1u]{ std::forward<Args>(args)... };
+            return invoke(id, std::move(instance), arguments, sizeof...(Args));
+        }
+
+        /**
+         * @brief Sets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the setter results in an undefined
+         * behavior.<br/>
+         * The type of the value must be such that a cast or conversion to the type
+         * of the variable is possible. Otherwise, invoking the setter does nothing.
+         *
+         * @tparam Type Type of value to assign.
+         * @param id Unique identifier.
+         * @param instance An opaque instance of the underlying type.
+         * @param value Parameter to use to set the underlying variable.
+         * @return True in case of success, false otherwise.
+         */
+        template<typename Type>
+        bool set(const id_type id, meta_handle instance, Type&& value) const {
+            const auto candidate = data(id);
+            return candidate && candidate.set(std::move(instance), std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Gets the value of a given variable.
+         *
+         * It must be possible to cast the instance to the parent type of the data
+         * member. Otherwise, invoking the getter results in an undefined behavior.
+         *
+         * @param id Unique identifier.
+         * @param instance An opaque instance of the underlying type.
+         * @return A wrapper containing the value of the underlying variable.
+         */
+        [[nodiscard]] meta_any get(const id_type id, meta_handle instance) const {
+            const auto candidate = data(id);
+            return candidate ? candidate.get(std::move(instance)) : meta_any{};
+        }
+
+        /**
+         * @brief Returns a range to use to visit top-level properties.
+         * @return An iterable range to use to visit top-level properties.
+         */
+        [[nodiscard]] meta_range<meta_prop> prop() const ENTT_NOEXCEPT {
+            return node->prop;
+        }
+
+        /**
+         * @brief Returns the property associated with a given key.
+         *
+         * Properties of the base classes will also be visited, if any.
+         *
+         * @param key The key to use to search for a property.
+         * @return The property associated with the given key, if any.
+         */
+        [[nodiscard]] meta_prop prop(meta_any key) const {
+            return internal::meta_visit<&node_type::prop>([&key](const auto* curr) { return curr->id == key; }, node);
+        }
+
+        /**
+         * @brief Returns true if an object is valid, false otherwise.
+         * @return True if the object is valid, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(node == nullptr);
+        }
+
+        /**
+         * @brief Checks if two objects refer to the same type.
+         * @param other The object with which to compare.
+         * @return True if the objects refer to the same type, false otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_type& other) const ENTT_NOEXCEPT {
+            return (!node && !other.node) || (node && other.node && node->info == other.node->info);
+        }
+
+        /**
+         * @brief Resets a type and all its parts.
+         *
+         * This function resets a type and all its data members, member functions
+         * and properties, as well as its constructors, destructors and conversion
+         * functions if any.<br/>
+         * Base classes aren't reset but the link between the two types is removed.
+         *
+         * The type is also removed from the list of searchable types.
+         */
+        void reset() ENTT_NOEXCEPT {
+            for (auto** it = internal::meta_context::global(); *it; it = &(*it)->next) {
+                if (*it == node) {
+                    *it = (*it)->next;
+                    break;
+                }
+            }
+
+            unregister_all(&node->prop);
+            unregister_all(&node->base);
+            unregister_all(&node->conv);
+            unregister_all<&internal::meta_ctor_node::prop>(&node->ctor);
+            unregister_all<&internal::meta_data_node::prop>(&node->data);
+            unregister_all<&internal::meta_func_node::prop>(&node->func);
+
+            node->id = {};
+            node->ctor = node->def_ctor;
+            node->dtor = nullptr;
+        }
+
+    private:
+        node_type* node;
+    };
+
+
+    /**
+     * @brief Checks if two objects refer to the same type.
+     * @param lhs An object, either valid or not.
+     * @param rhs An object, either valid or not.
+     * @return False if the objects refer to the same node, true otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const meta_type& lhs, const meta_type& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    [[nodiscard]] inline meta_type meta_any::type() const ENTT_NOEXCEPT {
+        return node;
+    }
+
+
+    template<typename... Args>
+    meta_any meta_any::invoke(const id_type id, Args &&... args) const {
+        return type().invoke(id, *this, std::forward<Args>(args)...);
+    }
+
+
+    template<typename... Args>
+    meta_any meta_any::invoke(const id_type id, Args &&... args) {
+        return type().invoke(id, *this, std::forward<Args>(args)...);
+    }
+
+
+    template<typename Type>
+    bool meta_any::set(const id_type id, Type&& value) {
+        return type().set(id, *this, std::forward<Type>(value));
+    }
+
+
+    [[nodiscard]] inline meta_any meta_any::get(const id_type id) const {
+        return type().get(id, *this);
+    }
+
+
+    [[nodiscard]] inline meta_any meta_any::get(const id_type id) {
+        return type().get(id, *this);
+    }
+
+
+    [[nodiscard]] inline meta_type meta_ctor::parent() const ENTT_NOEXCEPT {
+        return node->parent;
+    }
+
+
+    [[nodiscard]] inline meta_type meta_ctor::arg(size_type index) const ENTT_NOEXCEPT {
+        return index < arity() ? node->arg(index) : meta_type{};
+    }
+
+
+    [[nodiscard]] inline meta_type meta_data::parent() const ENTT_NOEXCEPT {
+        return node->parent;
+    }
+
+
+    [[nodiscard]] inline meta_type meta_data::type() const ENTT_NOEXCEPT {
+        return node->type();
+    }
+
+
+    [[nodiscard]] inline meta_type meta_func::parent() const ENTT_NOEXCEPT {
+        return node->parent;
+    }
+
+
+    [[nodiscard]] inline meta_type meta_func::ret() const ENTT_NOEXCEPT {
+        return node->ret();
+    }
+
+
+    [[nodiscard]] inline meta_type meta_func::arg(size_type index) const ENTT_NOEXCEPT {
+        return index < arity() ? node->arg(index) : meta_type{};
+    }
+
+
+    /*! @brief Opaque iterator for sequence containers. */
+    class meta_sequence_container::meta_iterator {
+        /*! @brief A sequence container can access the underlying iterator. */
+        friend class meta_sequence_container;
+
+        enum class operation { INCR, DEREF };
+
+        using vtable_type = void(const operation, const any&, void*);
+
+        template<typename It>
+        static void basic_vtable(const operation op, const any& from, void* to) {
+            switch (op) {
+            case operation::INCR:
+                ++any_cast<It&>(const_cast<any&>(from));
+                break;
+            case operation::DEREF:
+                static_cast<meta_any*>(to)->emplace<typename std::iterator_traits<It>::reference>(*any_cast<const It&>(from));
+                break;
+            }
+        }
+
+    public:
+        /*! @brief Signed integer type. */
+        using difference_type = std::ptrdiff_t;
+        /*! @brief Type of elements returned by the iterator. */
+        using value_type = meta_any;
+        /*! @brief Pointer type, `void` on purpose. */
+        using pointer = void;
+        /*! @brief Reference type, it is **not** an actual reference. */
+        using reference = value_type;
+        /*! @brief Iterator category. */
+        using iterator_category = std::input_iterator_tag;
+
+        /*! @brief Default constructor. */
+        meta_iterator() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Constructs a meta iterator from a given iterator.
+         * @tparam It Type of actual iterator with which to build the meta iterator.
+         * @param iter The actual iterator with which to build the meta iterator.
+         */
+        template<typename It>
+        meta_iterator(It iter)
+            : vtable{ &basic_vtable<It> },
+            handle{ std::move(iter) }
+        {}
+
+        /*! @brief Pre-increment operator. @return This iterator. */
+        meta_iterator& operator++() ENTT_NOEXCEPT {
+            return vtable(operation::INCR, handle, nullptr), * this;
+        }
+
+        /*! @brief Post-increment operator. @return This iterator. */
+        meta_iterator operator++(int) ENTT_NOEXCEPT {
+            meta_iterator orig = *this;
+            return ++(*this), orig;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return True if the iterators refer to the same element, false otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return handle == other.handle;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return False if the iterators refer to the same element, true otherwise.
+         */
+        [[nodiscard]] bool operator!=(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return !(*this == other);
+        }
+
+        /**
+         * @brief Indirection operator.
+         * @return The element to which the iterator points.
+         */
+        [[nodiscard]] reference operator*() const {
+            meta_any other;
+            vtable(operation::DEREF, handle, &other);
+            return other;
+        }
+
+        /**
+         * @brief Returns false if an iterator is invalid, true otherwise.
+         * @return False if the iterator is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(handle);
+        }
+
+    private:
+        vtable_type* vtable{};
+        any handle{};
+    };
+
+
+    template<typename Type>
+    struct meta_sequence_container::meta_sequence_container_proxy {
+        using traits_type = meta_sequence_container_traits<Type>;
+
+        [[nodiscard]] static meta_type value_type() ENTT_NOEXCEPT {
+            return internal::meta_info<typename Type::value_type>::resolve();
+        }
+
+        [[nodiscard]] static size_type size(const any& container) ENTT_NOEXCEPT {
+            return traits_type::size(any_cast<const Type&>(container));
+        }
+
+        [[nodiscard]] static bool resize(any& container, size_type sz) {
+            auto* const cont = any_cast<Type>(&container);
+            return cont && traits_type::resize(*cont, sz);
+        }
+
+        [[nodiscard]] static bool clear(any& container) {
+            auto* const cont = any_cast<Type>(&container);
+            return cont && traits_type::clear(*cont);
+        }
+
+        [[nodiscard]] static iterator begin(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ traits_type::begin(*cont) };
+            }
+
+            return iterator{ traits_type::cbegin(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static iterator end(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ traits_type::end(*cont) };
+            }
+
+            return iterator{ traits_type::cend(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static std::pair<iterator, bool> insert(any& container, iterator it, meta_any& value) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                // this abomination is necessary because only on macos value_type and const_reference are different types for std::vector<bool>
+                if (value.allow_cast<typename Type::const_reference>() || value.allow_cast<typename Type::value_type>()) {
+                    const auto* element = value.try_cast<std::remove_reference_t<typename Type::const_reference>>();
+                    auto ret = traits_type::insert(*cont, any_cast<const typename Type::iterator&>(it.handle), element ? *element : value.cast<typename Type::value_type>());
+                    return { iterator{std::move(ret.first)}, ret.second };
+                }
+            }
+
+            return {};
+        }
+
+        [[nodiscard]] static std::pair<iterator, bool> erase(any& container, iterator it) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                auto ret = traits_type::erase(*cont, any_cast<const typename Type::iterator&>(it.handle));
+                return { iterator{std::move(ret.first)}, ret.second };
+            }
+
+            return {};
+        }
+
+        [[nodiscard]] static meta_any get(any& container, size_type pos) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return meta_any{ std::in_place_type<typename Type::reference>, traits_type::get(*cont, pos) };
+            }
+
+            return meta_any{ std::in_place_type<typename Type::const_reference>, traits_type::cget(any_cast<const Type&>(container), pos) };
+        }
+    };
+
+
+    /**
+     * @brief Returns the meta value type of a container.
+     * @return The meta value type of the container.
+     */
+    [[nodiscard]] inline meta_type meta_sequence_container::value_type() const ENTT_NOEXCEPT {
+        return value_type_fn();
+    }
+
+
+    /**
+     * @brief Returns the size of a container.
+     * @return The size of the container.
+     */
+    [[nodiscard]] inline meta_sequence_container::size_type meta_sequence_container::size() const ENTT_NOEXCEPT {
+        return size_fn(storage);
+    }
+
+
+    /**
+     * @brief Resizes a container to contain a given number of elements.
+     * @param sz The new size of the container.
+     * @return True in case of success, false otherwise.
+     */
+    inline bool meta_sequence_container::resize(size_type sz) {
+        return resize_fn(storage, sz);
+    }
+
+
+    /**
+     * @brief Clears the content of a container.
+     * @return True in case of success, false otherwise.
+     */
+    inline bool meta_sequence_container::clear() {
+        return clear_fn(storage);
+    }
+
+
+    /**
+     * @brief Returns an iterator to the first element of a container.
+     * @return An iterator to the first element of the container.
+     */
+    [[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::begin() {
+        return begin_fn(storage);
+    }
+
+
+    /**
+     * @brief Returns an iterator that is past the last element of a container.
+     * @return An iterator that is past the last element of the container.
+     */
+    [[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::end() {
+        return end_fn(storage);
+    }
+
+
+    /**
+     * @brief Inserts an element at a specified location of a container.
+     * @param it Iterator before which the element will be inserted.
+     * @param value Element value to insert.
+     * @return A pair consisting of an iterator to the inserted element (in case of
+     * success) and a bool denoting whether the insertion took place.
+     */
+    inline std::pair<meta_sequence_container::iterator, bool> meta_sequence_container::insert(iterator it, meta_any value) {
+        return insert_fn(storage, it, value);
+    }
+
+
+    /**
+     * @brief Removes a given element from a container.
+     * @param it Iterator to the element to remove.
+     * @return A pair consisting of an iterator following the last removed element
+     * (in case of success) and a bool denoting whether the insertion took place.
+     */
+    inline std::pair<meta_sequence_container::iterator, bool> meta_sequence_container::erase(iterator it) {
+        return erase_fn(storage, it);
+    }
+
+
+    /**
+     * @brief Returns a reference to the element at a given location of a container
+     * (no bounds checking is performed).
+     * @param pos The position of the element to return.
+     * @return A reference to the requested element properly wrapped.
+     */
+    [[nodiscard]] inline meta_any meta_sequence_container::operator[](size_type pos) {
+        return get_fn(storage, pos);
+    }
+
+
+    /**
+     * @brief Returns false if a proxy is invalid, true otherwise.
+     * @return False if the proxy is invalid, true otherwise.
+     */
+    [[nodiscard]] inline meta_sequence_container::operator bool() const ENTT_NOEXCEPT {
+        return static_cast<bool>(storage);
+    }
+
+
+    /*! @brief Opaque iterator for associative containers. */
+    class meta_associative_container::meta_iterator {
+        enum operation { INCR, DEREF };
+
+        using vtable_type = void(const operation, const any&, void*);
+
+        template<bool KeyOnly, typename It>
+        static void basic_vtable(const operation op, const any& from, void* to) {
+            switch (op) {
+            case operation::INCR:
+                ++any_cast<It&>(const_cast<any&>(from));
+                break;
+            case operation::DEREF:
+                const auto& it = any_cast<const It&>(from);
+                if constexpr (KeyOnly) {
+                    static_cast<std::pair<meta_any, meta_any>*>(to)->first.emplace<decltype(*it)>(*it);
+                }
+                else {
+                    static_cast<std::pair<meta_any, meta_any>*>(to)->first.emplace<decltype((it->first))>(it->first);
+                    static_cast<std::pair<meta_any, meta_any>*>(to)->second.emplace<decltype((it->second))>(it->second);
+                }
+                break;
+            }
+        }
+
+    public:
+        /*! @brief Signed integer type. */
+        using difference_type = std::ptrdiff_t;
+        /*! @brief Type of elements returned by the iterator. */
+        using value_type = std::pair<meta_any, meta_any>;
+        /*! @brief Pointer type, `void` on purpose. */
+        using pointer = void;
+        /*! @brief Reference type, it is **not** an actual reference. */
+        using reference = value_type;
+        /*! @brief Iterator category. */
+        using iterator_category = std::input_iterator_tag;
+
+        /*! @brief Default constructor. */
+        meta_iterator() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Constructs an meta iterator from a given iterator.
+         * @tparam KeyOnly True if the container is also key-only, false otherwise.
+         * @tparam It Type of actual iterator with which to build the meta iterator.
+         * @param iter The actual iterator with which to build the meta iterator.
+         */
+        template<bool KeyOnly, typename It>
+        meta_iterator(std::integral_constant<bool, KeyOnly>, It iter)
+            : vtable{ &basic_vtable<KeyOnly, It> },
+            handle{ std::move(iter) }
+        {}
+
+        /*! @brief Pre-increment operator. @return This iterator. */
+        meta_iterator& operator++() ENTT_NOEXCEPT {
+            return vtable(operation::INCR, handle, nullptr), * this;
+        }
+
+        /*! @brief Post-increment operator. @return This iterator. */
+        meta_iterator operator++(int) ENTT_NOEXCEPT {
+            meta_iterator orig = *this;
+            return ++(*this), orig;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return True if the iterators refer to the same element, false otherwise.
+         */
+        [[nodiscard]] bool operator==(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return handle == other.handle;
+        }
+
+        /**
+         * @brief Checks if two iterators refer to the same element.
+         * @param other The iterator with which to compare.
+         * @return False if the iterators refer to the same element, true otherwise.
+         */
+        [[nodiscard]] bool operator!=(const meta_iterator& other) const ENTT_NOEXCEPT {
+            return !(*this == other);
+        }
+
+        /**
+         * @brief Indirection operator.
+         * @return The element to which the iterator points.
+         */
+        [[nodiscard]] reference operator*() const {
+            reference other;
+            vtable(operation::DEREF, handle, &other);
+            return other;
+        }
+
+        /**
+         * @brief Returns false if an iterator is invalid, true otherwise.
+         * @return False if the iterator is invalid, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(handle);
+        }
+
+    private:
+        vtable_type* vtable{};
+        any handle{};
+    };
+
+
+    template<typename Type>
+    struct meta_associative_container::meta_associative_container_proxy {
+        using traits_type = meta_associative_container_traits<Type>;
+
+        [[nodiscard]] static meta_type key_type() ENTT_NOEXCEPT {
+            return internal::meta_info<typename Type::key_type>::resolve();
+        }
+
+        [[nodiscard]] static meta_type mapped_type() ENTT_NOEXCEPT {
+            if constexpr (is_key_only_meta_associative_container_v<Type>) {
+                return meta_type{};
+            }
+            else {
+                return internal::meta_info<typename Type::mapped_type>::resolve();
+            }
+        }
+
+        [[nodiscard]] static meta_type value_type() ENTT_NOEXCEPT {
+            return internal::meta_info<typename Type::value_type>::resolve();
+        }
+
+        [[nodiscard]] static size_type size(const any& container) ENTT_NOEXCEPT {
+            return traits_type::size(any_cast<const Type&>(container));
+        }
+
+        [[nodiscard]] static bool clear(any& container) {
+            auto* const cont = any_cast<Type>(&container);
+            return cont && traits_type::clear(*cont);
+        }
+
+        [[nodiscard]] static iterator begin(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::begin(*cont) };
+            }
+
+            return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::cbegin(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static iterator end(any& container) {
+            if (auto* const cont = any_cast<Type>(&container); cont) {
+                return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::end(*cont) };
+            }
+
+            return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::cend(any_cast<const Type&>(container)) };
+        }
+
+        [[nodiscard]] static bool insert(any& container, meta_any& key, meta_any& value) {
+            if (auto* const cont = any_cast<Type>(&container); cont && key.allow_cast<const typename Type::key_type&>()) {
+                if constexpr (is_key_only_meta_associative_container_v<Type>) {
+                    return traits_type::insert(*cont, key.cast<const typename Type::key_type&>());
+                }
+                else {
+                    return value.allow_cast<const typename Type::mapped_type&>()
+                        && traits_type::insert(*cont, key.cast<const typename Type::key_type&>(), value.cast<const typename Type::mapped_type&>());
+                }
+            }
+
+            return false;
+        }
+
+        [[nodiscard]] static bool erase(any& container, meta_any& key) {
+            if (auto* const cont = any_cast<Type>(&container); cont && key.allow_cast<const typename Type::key_type&>()) {
+                return traits_type::erase(*cont, key.cast<const typename Type::key_type&>());
+            }
+
+            return false;
+        }
+
+        [[nodiscard]] static iterator find(any& container, meta_any& key) {
+            if (key.allow_cast<const typename Type::key_type&>()) {
+                if (auto* const cont = any_cast<Type>(&container); cont) {
+                    return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::find(*cont, key.cast<const typename Type::key_type&>()) };
+                }
+
+                return iterator{ is_key_only_meta_associative_container<Type>{}, traits_type::cfind(any_cast<const Type&>(container), key.cast<const typename Type::key_type&>()) };
+            }
+
+            return {};
+        }
+    };
+
+
+    /**
+     * @brief Returns true if a container is also key-only, false otherwise.
+     * @return True if the associative container is also key-only, false otherwise.
+     */
+    [[nodiscard]] inline bool meta_associative_container::key_only() const ENTT_NOEXCEPT {
+        return key_only_container;
+    }
+
+
+    /**
+     * @brief Returns the meta key type of a container.
+     * @return The meta key type of the a container.
+     */
+    [[nodiscard]] inline meta_type meta_associative_container::key_type() const ENTT_NOEXCEPT {
+        return key_type_fn();
+    }
+
+
+    /**
+     * @brief Returns the meta mapped type of a container.
+     * @return The meta mapped type of the a container.
+     */
+    [[nodiscard]] inline meta_type meta_associative_container::mapped_type() const ENTT_NOEXCEPT {
+        return mapped_type_fn();
+    }
+
+
+    /*! @copydoc meta_sequence_container::value_type */
+    [[nodiscard]] inline meta_type meta_associative_container::value_type() const ENTT_NOEXCEPT {
+        return value_type_fn();
+    }
+
+
+    /*! @copydoc meta_sequence_container::size */
+    [[nodiscard]] inline meta_associative_container::size_type meta_associative_container::size() const ENTT_NOEXCEPT {
+        return size_fn(storage);
+    }
+
+
+    /*! @copydoc meta_sequence_container::clear */
+    inline bool meta_associative_container::clear() {
+        return clear_fn(storage);
+    }
+
+
+    /*! @copydoc meta_sequence_container::begin */
+    [[nodiscard]] inline meta_associative_container::iterator meta_associative_container::begin() {
+        return begin_fn(storage);
+    }
+
+
+    /*! @copydoc meta_sequence_container::end */
+    [[nodiscard]] inline meta_associative_container::iterator meta_associative_container::end() {
+        return end_fn(storage);
+    }
+
+
+    /**
+     * @brief Inserts an element (a key/value pair) into a container.
+     * @param key The key of the element to insert.
+     * @param value The value of the element to insert.
+     * @return A bool denoting whether the insertion took place.
+     */
+    inline bool meta_associative_container::insert(meta_any key, meta_any value = {}) {
+        return insert_fn(storage, key, value);
+    }
+
+
+    /**
+     * @brief Removes the specified element from a container.
+     * @param key The key of the element to remove.
+     * @return A bool denoting whether the removal took place.
+     */
+    inline bool meta_associative_container::erase(meta_any key) {
+        return erase_fn(storage, key);
+    }
+
+
+    /**
+     * @brief Returns an iterator to the element with a given key, if any.
+     * @param key The key of the element to search.
+     * @return An iterator to the element with the given key, if any.
+     */
+    [[nodiscard]] inline meta_associative_container::iterator meta_associative_container::find(meta_any key) {
+        return find_fn(storage, key);
+    }
+
+
+    /**
+     * @brief Returns false if a proxy is invalid, true otherwise.
+     * @return False if the proxy is invalid, true otherwise.
+     */
+    [[nodiscard]] inline meta_associative_container::operator bool() const ENTT_NOEXCEPT {
+        return static_cast<bool>(storage);
+    }
+
+
+}
+
+
+#endif
+
+// #include "meta/node.hpp"
+#ifndef ENTT_META_NODE_HPP
+#define ENTT_META_NODE_HPP
+
+
+#include <cstddef>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_info.hpp"
+
+// #include "../core/type_traits.hpp"
+
+// #include "type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    class meta_any;
+    class meta_type;
+    struct meta_handle;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct meta_type_node;
+
+
+        struct meta_prop_node {
+            meta_prop_node* next;
+            const meta_any& id;
+            meta_any& value;
+        };
+
+
+        struct meta_base_node {
+            meta_type_node* const parent;
+            meta_base_node* next;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            const void* (* const cast)(const void*) ENTT_NOEXCEPT;
+        };
+
+
+        struct meta_conv_node {
+            meta_type_node* const parent;
+            meta_conv_node* next;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            meta_any(* const conv)(const void*);
+        };
+
+
+        struct meta_ctor_node {
+            using size_type = std::size_t;
+            meta_type_node* const parent;
+            meta_ctor_node* next;
+            meta_prop_node* prop;
+            const size_type arity;
+            meta_type(* const arg)(const size_type) ENTT_NOEXCEPT;
+            meta_any(* const invoke)(meta_any* const);
+        };
+
+
+        struct meta_data_node {
+            id_type id;
+            meta_type_node* const parent;
+            meta_data_node* next;
+            meta_prop_node* prop;
+            const bool is_const;
+            const bool is_static;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            bool(* const set)(meta_handle, meta_any);
+            meta_any(* const get)(meta_handle);
+        };
+
+
+        struct meta_func_node {
+            using size_type = std::size_t;
+            id_type id;
+            meta_type_node* const parent;
+            meta_func_node* next;
+            meta_prop_node* prop;
+            const size_type arity;
+            const bool is_const;
+            const bool is_static;
+            meta_type_node* (* const ret)() ENTT_NOEXCEPT;
+            meta_type(* const arg)(const size_type) ENTT_NOEXCEPT;
+            meta_any(* const invoke)(meta_handle, meta_any*);
+        };
+
+
+        struct meta_template_info {
+            using size_type = std::size_t;
+            const bool is_template_specialization;
+            const size_type arity;
+            meta_type_node* (* const type)() ENTT_NOEXCEPT;
+            meta_type_node* (* const arg)(const size_type) ENTT_NOEXCEPT;
+        };
+
+
+        struct meta_type_node {
+            using size_type = std::size_t;
+            const type_info info;
+            id_type id;
+            meta_type_node* next;
+            meta_prop_node* prop;
+            const size_type size_of;
+            const bool is_void;
+            const bool is_integral;
+            const bool is_floating_point;
+            const bool is_array;
+            const bool is_enum;
+            const bool is_union;
+            const bool is_class;
+            const bool is_pointer;
+            const bool is_function_pointer;
+            const bool is_member_object_pointer;
+            const bool is_member_function_pointer;
+            const bool is_pointer_like;
+            const bool is_sequence_container;
+            const bool is_associative_container;
+            const meta_template_info template_info;
+            const size_type rank;
+            size_type(* const extent)(const size_type) ENTT_NOEXCEPT;
+            meta_type_node* (* const remove_pointer)() ENTT_NOEXCEPT;
+            meta_type_node* (* const remove_extent)() ENTT_NOEXCEPT;
+            meta_ctor_node* const def_ctor;
+            meta_ctor_node* ctor{ nullptr };
+            meta_base_node* base{ nullptr };
+            meta_conv_node* conv{ nullptr };
+            meta_data_node* data{ nullptr };
+            meta_func_node* func{ nullptr };
+            void(*dtor)(void*) { nullptr };
+        };
+
+
+        template<auto Member, typename Op, typename Node>
+        auto meta_visit(const Op& op, const Node* node)
+            -> std::decay_t<decltype(node->*Member)> {
+            for (auto* curr = node->*Member; curr; curr = curr->next) {
+                if (op(curr)) {
+                    return curr;
+                }
+            }
+
+            if constexpr (std::is_same_v<Node, meta_type_node>) {
+                for (auto* curr = node->base; curr; curr = curr->next) {
+                    if (auto* ret = meta_visit<Member>(op, curr->type()); ret) {
+                        return ret;
+                    }
+                }
+            }
+
+            return nullptr;
+        }
+
+
+        template<typename... Args>
+        meta_type_node* meta_arg_node(type_list<Args...>, const std::size_t index) ENTT_NOEXCEPT;
+
+
+        template<typename Type>
+        class ENTT_API meta_node {
+            static_assert(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>, "Invalid type");
+
+            template<std::size_t... Index>
+            [[nodiscard]] static auto extent(const meta_type_node::size_type dim, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+                meta_type_node::size_type ext{};
+                ((ext = (dim == Index ? std::extent_v<Type, Index> : ext)), ...);
+                return ext;
+            }
+
+            [[nodiscard]] static meta_ctor_node* meta_default_constructor([[maybe_unused]] meta_type_node* type) ENTT_NOEXCEPT {
+                if constexpr (std::is_default_constructible_v<Type>) {
+                    static meta_ctor_node node{
+                        type,
+                        nullptr,
+                        nullptr,
+                        0u,
+                        nullptr,
+                        [](meta_any* const) { return meta_any{std::in_place_type<Type>}; }
+                    };
+
+                    return &node;
+                }
+                else {
+                    return nullptr;
+                }
+            }
+
+            [[nodiscard]] static meta_template_info meta_template_descriptor() ENTT_NOEXCEPT {
+                if constexpr (is_complete_v<meta_template_traits<Type>>) {
+                    return {
+                        true,
+                        meta_template_traits<Type>::args_type::size,
+                        &meta_node<typename meta_template_traits<Type>::class_type>::resolve,
+                        [](const std::size_t index) ENTT_NOEXCEPT {
+                            return meta_arg_node(typename meta_template_traits<Type>::args_type{}, index);
+                        }
+                    };
+                }
+                else {
+                    return { false, 0u, nullptr, nullptr };
+                }
+            }
+
+        public:
+            [[nodiscard]] static meta_type_node* resolve() ENTT_NOEXCEPT {
+                static meta_type_node node{
+                    type_id<Type>(),
+                    {},
+                    nullptr,
+                    nullptr,
+                    size_of_v<Type>,
+                    std::is_void_v<Type>,
+                    std::is_integral_v<Type>,
+                    std::is_floating_point_v<Type>,
+                    std::is_array_v<Type>,
+                    std::is_enum_v<Type>,
+                    std::is_union_v<Type>,
+                    std::is_class_v<Type>,
+                    std::is_pointer_v<Type>,
+                    std::is_pointer_v<Type> && std::is_function_v<std::remove_pointer_t<Type>>,
+                    std::is_member_object_pointer_v<Type>,
+                    std::is_member_function_pointer_v<Type>,
+                    is_meta_pointer_like_v<Type>,
+                    is_complete_v<meta_sequence_container_traits<Type>>,
+                    is_complete_v<meta_associative_container_traits<Type>>,
+                    meta_template_descriptor(),
+                    std::rank_v<Type>,
+                    [](meta_type_node::size_type dim) ENTT_NOEXCEPT { return extent(dim, std::make_index_sequence<std::rank_v<Type>>{}); },
+                    & meta_node<std::remove_cv_t<std::remove_reference_t<std::remove_pointer_t<Type>>>>::resolve,
+                    & meta_node<std::remove_cv_t<std::remove_reference_t<std::remove_extent_t<Type>>>>::resolve,
+                    meta_default_constructor(&node),
+                    meta_default_constructor(&node)
+                };
+
+                return &node;
+            }
+        };
+
+
+        template<typename Type>
+        struct meta_info : meta_node<std::remove_cv_t<std::remove_reference_t<Type>>> {};
+
+
+        template<typename... Args>
+        meta_type_node* meta_arg_node(type_list<Args...>, const std::size_t index) ENTT_NOEXCEPT {
+            meta_type_node* args[sizeof...(Args) + 1u]{ nullptr, internal::meta_info<Args>::resolve()... };
+            return args[index + 1u];
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+}
+
+
+#endif
+
+// #include "meta/pointer.hpp"
+#ifndef ENTT_META_POINTER_HPP
+#define ENTT_META_POINTER_HPP
+
+
+#include <memory>
+#include <type_traits>
+// #include "type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Makes plain pointers pointer-like types for the meta system.
+     * @tparam Type Element type.
+     */
+    template<typename Type>
+    struct is_meta_pointer_like<Type*>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Partial specialization used to reject pointers to arrays.
+     * @tparam Type Type of elements of the array.
+     * @tparam N Number of elements of the array.
+     */
+    template<typename Type, std::size_t N>
+    struct is_meta_pointer_like<Type(*)[N]>
+        : std::false_type
+    {};
+
+
+    /**
+     * @brief Makes `std::shared_ptr`s of any type pointer-like types for the meta
+     * system.
+     * @tparam Type Element type.
+     */
+    template<typename Type>
+    struct is_meta_pointer_like<std::shared_ptr<Type>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Makes `std::unique_ptr`s of any type pointer-like types for the meta
+     * system.
+     * @tparam Type Element type.
+     * @tparam Args Other arguments.
+     */
+    template<typename Type, typename... Args>
+    struct is_meta_pointer_like<std::unique_ptr<Type, Args...>>
+        : std::true_type
+    {};
+
+
+}
+
+
+#endif
+
+// #include "meta/policy.hpp"
+#ifndef ENTT_META_POLICY_HPP
+#define ENTT_META_POLICY_HPP
+
+
+namespace entt {
+
+
+    /*! @brief Empty class type used to request the _as ref_ policy. */
+    struct as_ref_t {};
+
+
+    /*! @brief Empty class type used to request the _as cref_ policy. */
+    struct as_cref_t {};
+
+
+    /*! @brief Empty class type used to request the _as-is_ policy. */
+    struct as_is_t {};
+
+
+    /*! @brief Empty class type used to request the _as void_ policy. */
+    struct as_void_t {};
+
+
+}
+
+
+#endif
+
+// #include "meta/range.hpp"
+#ifndef ENTT_META_RANGE_HPP
+#define ENTT_META_RANGE_HPP
+
+
+#include <cstddef>
+#include <iterator>
+
+
+namespace entt {
+
+
+    /**
+     * @brief Iterable range to use to iterate all types of meta objects.
+     * @tparam Type Type of meta objects returned.
+     * @tparam Node Type of meta nodes iterated.
+     */
+    template<typename Type, typename Node = typename Type::node_type>
+    class meta_range {
+        struct range_iterator {
+            using difference_type = std::ptrdiff_t;
+            using value_type = Type;
+            using pointer = void;
+            using reference = value_type;
+            using iterator_category = std::input_iterator_tag;
+            using node_type = Node;
+
+            range_iterator() ENTT_NOEXCEPT = default;
+
+            range_iterator(node_type* head) ENTT_NOEXCEPT
+                : it{ head }
+            {}
+
+            range_iterator& operator++() ENTT_NOEXCEPT {
+                return (it = it->next), * this;
+            }
+
+            range_iterator operator++(int) ENTT_NOEXCEPT {
+                range_iterator orig = *this;
+                return ++(*this), orig;
+            }
+
+            [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
+                return it;
+            }
+
+            [[nodiscard]] bool operator==(const range_iterator& other) const ENTT_NOEXCEPT {
+                return other.it == it;
+            }
+
+            [[nodiscard]] bool operator!=(const range_iterator& other) const ENTT_NOEXCEPT {
+                return !(*this == other);
+            }
+
+        private:
+            node_type* it{};
+        };
+
+    public:
+        /*! @brief Node type. */
+        using node_type = Node;
+        /*! @brief Input iterator type. */
+        using iterator = range_iterator;
+
+        /*! @brief Default constructor. */
+        meta_range() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Constructs a meta range from a given node.
+         * @param head The underlying node with which to construct the range.
+         */
+        meta_range(node_type* head)
+            : node{ head }
+        {}
+
+        /**
+         * @brief Returns an iterator to the beginning.
+         * @return An iterator to the first meta object of the range.
+         */
+        [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
+            return iterator{ node };
+        }
+
+        /**
+         * @brief Returns an iterator to the end.
+         * @return An iterator to the element following the last meta object of the
+         * range.
+         */
+        [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
+            return iterator{};
+        }
+
+    private:
+        node_type* node{ nullptr };
+    };
+
+
+}
+
+
+#endif
+
+// #include "meta/resolve.hpp"
+#ifndef ENTT_META_RESOLVE_HPP
+#define ENTT_META_RESOLVE_HPP
+
+
+#include <algorithm>
+// #include "../core/type_info.hpp"
+
+// #include "ctx.hpp"
+
+// #include "meta.hpp"
+
+// #include "node.hpp"
+
+// #include "range.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Returns the meta type associated with a given type.
+     * @tparam Type Type to use to search for a meta type.
+     * @return The meta type associated with the given type, if any.
+     */
+    template<typename Type>
+    [[nodiscard]] meta_type resolve() ENTT_NOEXCEPT {
+        return internal::meta_info<Type>::resolve();
+    }
+
+
+    /**
+     * @brief Returns a range to use to visit all meta types.
+     * @return An iterable range to use to visit all meta types.
+     */
+    [[nodiscard]] inline meta_range<meta_type> resolve() {
+        return *internal::meta_context::global();
+    }
+
+
+    /**
+     * @brief Returns the meta type associated with a given identifier, if any.
+     * @param id Unique identifier.
+     * @return The meta type associated with the given identifier, if any.
+     */
+    [[nodiscard]] inline meta_type resolve(const id_type id) ENTT_NOEXCEPT {
+        for (auto* curr = *internal::meta_context::global(); curr; curr = curr->next) {
+            if (curr->id == id) {
+                return curr;
+            }
+        }
+
+        return {};
+    }
+
+
+    /**
+     * @brief Returns the meta type associated with a given type info object, if
+     * any.
+     * @param info The type info object of the requested type.
+     * @return The meta type associated with the given type info object, if any.
+     */
+    [[nodiscard]] inline meta_type resolve(const type_info info) ENTT_NOEXCEPT {
+        for (auto* curr = *internal::meta_context::global(); curr; curr = curr->next) {
+            if (curr->info == info) {
+                return curr;
+            }
+        }
+
+        return {};
+    }
+
+
+}
+
+
+#endif
+
+// #include "meta/template.hpp"
+#ifndef ENTT_META_TEMPLATE_HPP
+#define ENTT_META_TEMPLATE_HPP
+
+
+// #include "../core/type_traits.hpp"
+
+
+
+namespace entt {
+
+
+    /*! @brief Utility class to disambiguate class templates. */
+    template<template<typename...> typename>
+    struct meta_class_template_tag {};
+
+
+    /**
+     * @brief General purpose traits class for generating meta template information.
+     * @tparam Clazz Type of class template.
+     * @tparam Args Types of template arguments.
+     */
+    template<template<typename...> typename Clazz, typename... Args>
+    struct meta_template_traits<Clazz<Args...>> {
+        /*! @brief Wrapped class template. */
+        using class_type = meta_class_template_tag<Clazz>;
+        /*! @brief List of template arguments. */
+        using args_type = type_list<Args...>;
+    };
+
+
+}
+
+
+#endif
+
+// #include "meta/type_traits.hpp"
+#ifndef ENTT_META_TYPE_TRAITS_HPP
+#define ENTT_META_TYPE_TRAITS_HPP
+
+
+#include <type_traits>
+
+
+namespace entt {
+
+
+    /**
+     * @brief Traits class template to be specialized to enable support for meta
+     * template information.
+     */
+    template<typename>
+    struct meta_template_traits;
+
+
+    /**
+     * @brief Traits class template to be specialized to enable support for meta
+     * sequence containers.
+     */
+    template<typename>
+    struct meta_sequence_container_traits;
+
+
+    /**
+     * @brief Traits class template to be specialized to enable support for meta
+     * associative containers.
+     */
+    template<typename>
+    struct meta_associative_container_traits;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a meta associative
+     * container claims to wrap a key-only type, false otherwise.
+     * @tparam Type Potentially key-only meta associative container type.
+     */
+    template<typename, typename = void>
+    struct is_key_only_meta_associative_container : std::true_type {};
+
+
+    /*! @copydoc is_key_only_meta_associative_container */
+    template<typename Type>
+    struct is_key_only_meta_associative_container<Type, std::void_t<typename meta_associative_container_traits<Type>::type::mapped_type>>
+        : std::false_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type Potentially key-only meta associative container type.
+     */
+    template<typename Type>
+    inline constexpr auto is_key_only_meta_associative_container_v = is_key_only_meta_associative_container<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is a
+     * pointer-like type from the point of view of the meta system, false otherwise.
+     * @tparam Type Potentially pointer-like type.
+     */
+    template<typename>
+    struct is_meta_pointer_like : std::false_type {};
+
+
+    /**
+     * @brief Partial specialization to ensure that const pointer-like types are
+     * also accepted.
+     * @tparam Type Potentially pointer-like type.
+     */
+    template<typename Type>
+    struct is_meta_pointer_like<const Type> : is_meta_pointer_like<Type> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type Potentially pointer-like type.
+     */
+    template<typename Type>
+    inline constexpr auto is_meta_pointer_like_v = is_meta_pointer_like<Type>::value;
+
+
+}
+
+
+#endif
+
+// #include "meta/utility.hpp"
+#ifndef ENTT_META_UTILITY_HPP
+#define ENTT_META_UTILITY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "../core/type_traits.hpp"
+
+// #include "meta.hpp"
+
+// #include "node.hpp"
+
+// #include "policy.hpp"
+
+
+
+namespace entt {
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename, typename>
+    struct meta_function_descriptor;
+
+
+    /**
+     * @brief Meta function descriptor.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Ret Function return type.
+     * @tparam Class Actual owner of the member function.
+     * @tparam Args Function arguments.
+     */
+    template<typename Type, typename Ret, typename Class, typename... Args>
+    struct meta_function_descriptor<Type, Ret(Class::*)(Args...) const> {
+        /*! @brief Meta function return type. */
+        using return_type = Ret;
+        /*! @brief Meta function arguments. */
+        using args_type = std::conditional_t<std::is_same_v<Type, Class>, type_list<Args...>, type_list<const Class&, Args...>>;
+
+        /*! @brief True if the meta function is const, false otherwise. */
+        static constexpr auto is_const = true;
+        /*! @brief True if the meta function is static, false otherwise. */
+        static constexpr auto is_static = !std::is_same_v<Type, Class>;
+    };
+
+
+    /**
+     * @brief Meta function descriptor.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Ret Function return type.
+     * @tparam Class Actual owner of the member function.
+     * @tparam Args Function arguments.
+     */
+    template<typename Type, typename Ret, typename Class, typename... Args>
+    struct meta_function_descriptor<Type, Ret(Class::*)(Args...)> {
+        /*! @brief Meta function return type. */
+        using return_type = Ret;
+        /*! @brief Meta function arguments. */
+        using args_type = std::conditional_t<std::is_same_v<Type, Class>, type_list<Args...>, type_list<Class&, Args...>>;
+
+        /*! @brief True if the meta function is const, false otherwise. */
+        static constexpr auto is_const = false;
+        /*! @brief True if the meta function is static, false otherwise. */
+        static constexpr auto is_static = !std::is_same_v<Type, Class>;
+    };
+
+
+    /**
+     * @brief Meta function descriptor.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Ret Function return type.
+     * @tparam Args Function arguments.
+     */
+    template<typename Type, typename Ret, typename... Args>
+    struct meta_function_descriptor<Type, Ret(*)(Args...)> {
+        /*! @brief Meta function return type. */
+        using return_type = Ret;
+        /*! @brief Meta function arguments. */
+        using args_type = type_list<Args...>;
+
+        /*! @brief True if the meta function is const, false otherwise. */
+        static constexpr auto is_const = false;
+        /*! @brief True if the meta function is static, false otherwise. */
+        static constexpr auto is_static = true;
+    };
+
+
+    /**
+     * @brief Meta function helper.
+     *
+     * Converts a function type to be associated with a reflected type into its meta
+     * function descriptor.
+     *
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Candidate The actual function to associate with the reflected type.
+     */
+    template<typename Type, typename Candidate>
+    class meta_function_helper {
+        template<typename Ret, typename... Args, typename Class>
+        static constexpr meta_function_descriptor<Type, Ret(Class::*)(Args...) const> get_rid_of_noexcept(Ret(Class::*)(Args...) const);
+
+        template<typename Ret, typename... Args, typename Class>
+        static constexpr meta_function_descriptor<Type, Ret(Class::*)(Args...)> get_rid_of_noexcept(Ret(Class::*)(Args...));
+
+        template<typename Ret, typename... Args>
+        static constexpr meta_function_descriptor<Type, Ret(*)(Args...)> get_rid_of_noexcept(Ret(*)(Args...));
+
+    public:
+        /*! @brief The meta function descriptor of the given function. */
+        using type = decltype(get_rid_of_noexcept(std::declval<Candidate>()));
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type Reflected type to which the meta function is associated.
+     * @tparam Candidate The actual function to associate with the reflected type.
+     */
+    template<typename Type, typename Candidate>
+    using meta_function_helper_t = typename meta_function_helper<Type, Candidate>::type;
+
+
+    /**
+     * @brief Returns the meta type of the i-th element of a list of arguments.
+     * @tparam Args Actual types of arguments.
+     * @return The meta type of the i-th element of the list of arguments.
+     */
+    template<typename... Args>
+    [[nodiscard]] static meta_type meta_arg(type_list<Args...>, const std::size_t index) ENTT_NOEXCEPT {
+        return internal::meta_arg_node(type_list<Args...>{}, index);
+    }
+
+
+    /**
+     * @brief Constructs an instance given a list of erased parameters, if possible.
+     * @tparam Type Actual type of the instance to construct.
+     * @tparam Args Types of arguments expected.
+     * @tparam Index Indexes to use to extract erased arguments from their list.
+     * @param args Parameters to use to construct the instance.
+     * @return A meta any containing the new instance, if any.
+     */
+    template<typename Type, typename... Args, std::size_t... Index>
+    [[nodiscard]] meta_any meta_construct(meta_any* const args, std::index_sequence<Index...>) {
+        if (((args + Index)->allow_cast<Args>() && ...)) {
+            return Type{ (args + Index)->cast<Args>()... };
+        }
+
+        return {};
+    }
+
+
+    /**
+     * @brief Sets the value of a given variable.
+     * @tparam Type Reflected type to which the variable is associated.
+     * @tparam Data The actual variable to set.
+     * @param instance An opaque instance of the underlying type, if required.
+     * @param value Parameter to use to set the variable.
+     * @return True in case of success, false otherwise.
+     */
+    template<typename Type, auto Data>
+    [[nodiscard]] bool meta_setter([[maybe_unused]] meta_handle instance, [[maybe_unused]] meta_any value) {
+        if constexpr (!std::is_same_v<decltype(Data), Type> && !std::is_same_v<decltype(Data), std::nullptr_t>) {
+            if constexpr (std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
+                using data_type = type_list_element_t<1u, typename meta_function_helper_t<Type, decltype(Data)>::args_type>;
+
+                if (auto* const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
+                    Data(*clazz, value.cast<data_type>());
+                    return true;
+                }
+            }
+            else if constexpr (std::is_member_function_pointer_v<decltype(Data)>) {
+                using data_type = type_list_element_t<0u, typename meta_function_helper_t<Type, decltype(Data)>::args_type>;
+
+                if (auto* const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
+                    (clazz->*Data)(value.cast<data_type>());
+                    return true;
+                }
+            }
+            else if constexpr (std::is_member_object_pointer_v<decltype(Data)>) {
+                using data_type = std::remove_reference_t<decltype(std::declval<Type>().*Data)>;
+
+                if constexpr (!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
+                    if (auto* const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
+                        clazz->*Data = value.cast<data_type>();
+                        return true;
+                    }
+                }
+            }
+            else {
+                using data_type = std::remove_reference_t<decltype(*Data)>;
+
+                if constexpr (!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
+                    if (value.allow_cast<data_type>()) {
+                        *Data = value.cast<data_type>();
+                        return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+
+
+    /**
+     * @brief Wraps a value depending on the given policy.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @tparam Type Type of value to wrap.
+     * @param value Value to wrap.
+     * @return A meta any containing the returned value.
+     */
+    template<typename Policy = as_is_t, typename Type>
+    meta_any meta_dispatch(Type&& value) {
+        if constexpr (std::is_same_v<Policy, as_void_t>) {
+            return meta_any{ std::in_place_type<void>, std::forward<Type>(value) };
+        }
+        else if constexpr (std::is_same_v<Policy, as_ref_t>) {
+            return meta_any{ std::in_place_type<Type>, std::forward<Type>(value) };
+        }
+        else if constexpr (std::is_same_v<Policy, as_cref_t>) {
+            static_assert(std::is_lvalue_reference_v<Type>, "Invalid type");
+            return meta_any{ std::in_place_type<const std::remove_reference_t<Type>&>, std::as_const(value) };
+        }
+        else {
+            static_assert(std::is_same_v<Policy, as_is_t>, "Policy not supported");
+            return meta_any{ std::forward<Type>(value) };
+        }
+    }
+
+
+    /**
+     * @brief Gets the value of a given variable.
+     * @tparam Type Reflected type to which the variable is associated.
+     * @tparam Data The actual variable to get.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @param instance An opaque instance of the underlying type, if required.
+     * @return A meta any containing the value of the underlying variable.
+     */
+    template<typename Type, auto Data, typename Policy = as_is_t>
+    [[nodiscard]] meta_any meta_getter([[maybe_unused]] meta_handle instance) {
+        if constexpr (std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
+            auto* const clazz = instance->try_cast<std::conditional_t<std::is_invocable_v<decltype(Data), const Type&>, const Type, Type>>();
+            return clazz ? meta_dispatch<Policy>(Data(*clazz)) : meta_any{};
+        }
+        else if constexpr (std::is_member_function_pointer_v<decltype(Data)>) {
+            auto* const clazz = instance->try_cast<std::conditional_t<std::is_invocable_v<decltype(Data), const Type&>, const Type, Type>>();
+            return clazz ? meta_dispatch<Policy>((clazz->*Data)()) : meta_any{};
+        }
+        else if constexpr (std::is_member_object_pointer_v<decltype(Data)>) {
+            if constexpr (!std::is_array_v<std::remove_cv_t<std::remove_reference_t<decltype(std::declval<Type>().*Data)>>>) {
+                if (auto* clazz = instance->try_cast<Type>(); clazz) {
+                    return meta_dispatch<Policy>(clazz->*Data);
+                }
+                else if (auto* fallback = instance->try_cast<const Type>(); fallback) {
+                    return meta_dispatch<Policy>(fallback->*Data);
+                }
+            }
+
+            return meta_any{};
+        }
+        else if constexpr (std::is_pointer_v<decltype(Data)>) {
+            if constexpr (std::is_array_v<std::remove_pointer_t<decltype(Data)>>) {
+                return meta_any{};
+            }
+            else {
+                return meta_dispatch<Policy>(*Data);
+            }
+        }
+        else {
+            return meta_dispatch<Policy>(Data);
+        }
+    }
+
+
+    /**
+     * @brief Invokes a function given a list of erased parameters, if possible.
+     * @tparam Type Reflected type to which the function is associated.
+     * @tparam Candidate The actual function to invoke.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @tparam Index Indexes to use to extract erased arguments from their list.
+     * @param instance An opaque instance of the underlying type, if required.
+     * @param args Parameters to use to invoke the function.
+     * @return A meta any containing the returned value, if any.
+     */
+    template<typename Type, auto Candidate, typename Policy = as_is_t, std::size_t... Index>
+    [[nodiscard]] std::enable_if_t<!std::is_invocable_v<decltype(Candidate)>, meta_any> meta_invoke([[maybe_unused]] meta_handle instance, meta_any* args, std::index_sequence<Index...>) {
+        using descriptor = meta_function_helper_t<Type, decltype(Candidate)>;
+
+        const auto invoke = [](auto&& maybe_clazz, auto &&... other) {
+            if constexpr (std::is_member_function_pointer_v<decltype(Candidate)>) {
+                if constexpr (std::is_void_v<typename descriptor::return_type>) {
+                    (std::forward<decltype(maybe_clazz)>(maybe_clazz).*Candidate)(std::forward<decltype(other)>(other)...);
+                    return meta_any{ std::in_place_type<void> };
+                }
+                else {
+                    return meta_dispatch<Policy>((std::forward<decltype(maybe_clazz)>(maybe_clazz).*Candidate)(std::forward<decltype(other)>(other)...));
+                }
+            }
+            else {
+                if constexpr (std::is_void_v<typename descriptor::return_type>) {
+                    Candidate(std::forward<decltype(maybe_clazz)>(maybe_clazz), std::forward<decltype(other)>(other)...);
+                    return meta_any{ std::in_place_type<void> };
+                }
+                else {
+                    return meta_dispatch<Policy>(Candidate(std::forward<decltype(maybe_clazz)>(maybe_clazz), std::forward<decltype(other)>(other)...));
+                }
+            }
+        };
+
+        if constexpr (std::is_invocable_v<decltype(Candidate), const Type&, type_list_element_t<Index, typename descriptor::args_type>...>) {
+            if (const auto* const clazz = instance->try_cast<const Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
+                return invoke(*clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
+            }
+        }
+        else if constexpr (std::is_invocable_v<decltype(Candidate), Type&, type_list_element_t<Index, typename descriptor::args_type>...>) {
+            if (auto* const clazz = instance->try_cast<Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
+                return invoke(*clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
+            }
+        }
+        else {
+            if (((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
+                return invoke((args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
+            }
+        }
+
+        return meta_any{};
+    }
+
+
+    /**
+     * @brief Invokes a function given a list of erased parameters, if possible.
+     * @tparam Type Reflected type to which the function is associated.
+     * @tparam Candidate The actual function to invoke.
+     * @tparam Policy Optional policy (no policy set by default).
+     * @tparam Index Indexes to use to extract erased arguments from their list.
+     * @return A meta any containing the returned value, if any.
+     */
+    template<typename Type, auto Candidate, typename Policy = as_is_t, std::size_t... Index>
+    [[nodiscard]] std::enable_if_t<std::is_invocable_v<decltype(Candidate)>, meta_any> meta_invoke(meta_handle, meta_any*, std::index_sequence<Index...>) {
+        if constexpr (std::is_void_v<decltype(Candidate())>) {
+            Candidate();
+            return meta_any{ std::in_place_type<void> };
+        }
+        else {
+            return meta_dispatch<Policy>(Candidate());
+        }
+    }
+
+
+}
+
+
+#endif
+
+// #include "platform/android-ndk-r17.hpp"
+#ifndef ENTT_PLATFORM_ANDROID_NDK_R17_HPP
+#define ENTT_PLATFORM_ANDROID_NDK_R17_HPP
+
+
+/**
+ * @cond TURN_OFF_DOXYGEN
+ * Internal details not to be documented.
+ */
+
+
+#ifdef __ANDROID__
+#include <android/ndk-version.h>
+#if __NDK_MAJOR__ == 17
+
+
+#include <functional>
+#include <type_traits>
+#include <utility>
+
+
+namespace std {
+
+
+    namespace internal {
+
+
+        template<typename Func, typename... Args>
+        constexpr auto is_invocable(int) -> decltype(std::invoke(std::declval<Func>(), std::declval<Args>()...), std::true_type{});
+
+
+        template<typename, typename...>
+        constexpr std::false_type is_invocable(...);
+
+
+        template<typename Ret, typename Func, typename... Args>
+        constexpr auto is_invocable_r(int)
+            ->std::enable_if_t<decltype(std::is_convertible_v<decltype(std::invoke(std::declval<Func>(), std::declval<Args>()...)), Ret>, std::true_type > ;
+
+
+        template<typename, typename, typename...>
+        constexpr std::false_type is_invocable_r(...);
+
+
+    }
+
+
+    template<typename Func, typename... Args>
+    struct is_invocable : decltype(internal::is_invocable<Func, Args...>(0)) {};
+
+
+    template<typename Func, typename... Argsv>
+    inline constexpr bool is_invocable_v = std::is_invocable<Func, Args...>::value;
+
+
+    template<typename Ret, typename Func, typename... Args>
+    struct is_invocable_r : decltype(internal::is_invocable_r<Ret, Func, Args...>(0)) {};
+
+
+    template<typename Ret, typename Func, typename... Args>
+    inline constexpr bool is_invocable_r_v = std::is_invocable_r<Ret, Func, Args...>::value;
+
+
+    template<typename Func, typename...Args>
+    struct invoke_result {
+        using type = decltype(std::invoke(std::declval<Func>(), std::declval<Args>()...));
+    };
+
+
+    template<typename Func, typename... Args>
+    using invoke_result_t = typename std::invoke_result<Func, Args...>::type;
+
+
+}
+
+
+#endif
+#endif
+
+
+/**
+ * Internal details not to be documented.
+ * @endcond
+ */
+
+
+#endif
+
+ // #include "poly/poly.hpp"
+#ifndef ENTT_POLY_POLY_HPP
+#define ENTT_POLY_POLY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "../core/any.hpp"
+#ifndef ENTT_CORE_ANY_HPP
+#define ENTT_CORE_ANY_HPP
+
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "../core/utility.hpp"
+#ifndef ENTT_CORE_UTILITY_HPP
+#define ENTT_CORE_UTILITY_HPP
+
+
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Identity function object (waiting for C++20). */
+    struct identity {
+        /**
+         * @brief Returns its argument unchanged.
+         * @tparam Type Type of the argument.
+         * @param value The actual argument.
+         * @return The submitted value as-is.
+         */
+        template<class Type>
+        [[nodiscard]] constexpr Type&& operator()(Type&& value) const ENTT_NOEXCEPT {
+            return std::forward<Type>(value);
+        }
+    };
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded members of a class.
+     * @tparam Type Type of the desired overload.
+     * @tparam Class Type of class to which the member belongs.
+     * @param member A valid pointer to a member.
+     * @return Pointer to the member.
+     */
+    template<typename Type, typename Class>
+    [[nodiscard]] constexpr auto overload(Type Class::* member) ENTT_NOEXCEPT { return member; }
+
+
+    /**
+     * @brief Constant utility to disambiguate overloaded functions.
+     * @tparam Func Function type of the desired overload.
+     * @param func A valid pointer to a function.
+     * @return Pointer to the function.
+     */
+    template<typename Func>
+    [[nodiscard]] constexpr auto overload(Func* func) ENTT_NOEXCEPT { return func; }
+
+
+    /**
+     * @brief Helper type for visitors.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    struct overloaded : Func... {
+        using Func::operator()...;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Func Types of function objects.
+     */
+    template<class... Func>
+    overloaded(Func...)
+        ->overloaded<Func...>;
+
+
+    /**
+     * @brief Basic implementation of a y-combinator.
+     * @tparam Func Type of a potentially recursive function.
+     */
+    template<class Func>
+    struct y_combinator {
+        /**
+         * @brief Constructs a y-combinator from a given function.
+         * @param recursive A potentially recursive function.
+         */
+        y_combinator(Func recursive) :
+            func{ std::move(recursive) }
+        {}
+
+        /**
+         * @brief Invokes a y-combinator and therefore its underlying function.
+         * @tparam Args Types of arguments to use to invoke the underlying function.
+         * @param args Parameters to use to invoke the underlying function.
+         * @return Return value of the underlying function, if any.
+         */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) const {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc operator()() */
+        template <class... Args>
+        decltype(auto) operator()(Args &&... args) {
+            return func(*this, std::forward<Args>(args)...);
+        }
+
+    private:
+        Func func;
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+// #include "type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief A SBO friendly, type-safe container for single values of any type.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<std::size_t Len, std::size_t Align>
+    class basic_any {
+        enum class operation : std::uint8_t { COPY, MOVE, DTOR, COMP, ADDR, CADDR, TYPE };
+        enum class policy : std::uint8_t { OWNER, REF, CREF };
+
+        using storage_type = std::aligned_storage_t<Len + !Len, Align>;
+        using vtable_type = const void* (const operation, const basic_any&, void*);
+
+        template<typename Type>
+        static constexpr bool in_situ = Len && alignof(Type) <= alignof(storage_type) && sizeof(Type) <= sizeof(storage_type) && std::is_nothrow_move_constructible_v<Type>;
+
+        template<typename Type>
+        [[nodiscard]] static constexpr policy type_to_policy() {
+            if constexpr (std::is_lvalue_reference_v<Type>) {
+                if constexpr (std::is_const_v<std::remove_reference_t<Type>>) {
+                    return policy::CREF;
+                }
+                else {
+                    return policy::REF;
+                }
+            }
+            else {
+                return policy::OWNER;
+            }
+        }
+
+        template<typename Type>
+        [[nodiscard]] static bool compare(const void* lhs, const void* rhs) {
+            if constexpr (!std::is_function_v<Type> && is_equality_comparable_v<Type>) {
+                return *static_cast<const Type*>(lhs) == *static_cast<const Type*>(rhs);
+            }
+            else {
+                return lhs == rhs;
+            }
+        }
+
+        template<typename Type>
+        static const void* basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const basic_any& from, [[maybe_unused]] void* to) {
+            static_assert(std::is_same_v<std::remove_reference_t<std::remove_const_t<Type>>, Type>, "Invalid type");
+
+            if constexpr (!std::is_void_v<Type>) {
+                const Type* instance = (in_situ<Type> && from.mode == policy::OWNER)
+                    ? ENTT_LAUNDER(reinterpret_cast<const Type*>(&from.storage))
+                    : static_cast<const Type*>(from.instance);
+
+                switch (op) {
+                case operation::COPY:
+                    if constexpr (std::is_copy_constructible_v<Type>) {
+                        static_cast<basic_any*>(to)->emplace<Type>(*instance);
+                    }
+                    break;
+                case operation::MOVE:
+                    if constexpr (in_situ<Type>) {
+                        if (from.mode == policy::OWNER) {
+                            return new (&static_cast<basic_any*>(to)->storage) Type{ std::move(*const_cast<Type*>(instance)) };
+                        }
+                    }
+
+                    return (static_cast<basic_any*>(to)->instance = std::exchange(const_cast<basic_any&>(from).instance, nullptr));
+                case operation::DTOR:
+                    if (from.mode == policy::OWNER) {
+                        if constexpr (in_situ<Type>) {
+                            instance->~Type();
+                        }
+                        else if constexpr (std::is_array_v<Type>) {
+                            delete[] instance;
+                        }
+                        else {
+                            delete instance;
+                        }
+                    }
+                    break;
+                case operation::COMP:
+                    return compare<Type>(instance, (*static_cast<const basic_any**>(to))->data()) ? to : nullptr;
+                case operation::ADDR:
+                    if (from.mode == policy::CREF) {
+                        return nullptr;
+                    }
+                    [[fallthrough]];
+                case operation::CADDR:
+                    return instance;
+                case operation::TYPE:
+                    *static_cast<type_info*>(to) = type_id<Type>();
+                    break;
+                }
+            }
+
+            return nullptr;
+        }
+
+        template<typename Type, typename... Args>
+        void initialize([[maybe_unused]] Args &&... args) {
+            if constexpr (!std::is_void_v<Type>) {
+                if constexpr (std::is_lvalue_reference_v<Type>) {
+                    static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
+                    instance = (std::addressof(args), ...);
+                }
+                else if constexpr (in_situ<Type>) {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        new (&storage) Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        new (&storage) Type(std::forward<Args>(args)...);
+                    }
+                }
+                else {
+                    if constexpr (sizeof...(Args) != 0u && std::is_aggregate_v<Type>) {
+                        instance = new Type{ std::forward<Args>(args)... };
+                    }
+                    else {
+                        instance = new Type(std::forward<Args>(args)...);
+                    }
+                }
+            }
+        }
+
+        basic_any(const basic_any& other, const policy pol) ENTT_NOEXCEPT
+            : instance{ other.data() },
+            vtable{ other.vtable },
+            mode{ pol }
+        {}
+
+    public:
+        /*! @brief Size of the internal storage. */
+        static constexpr auto length = Len;
+        /*! @brief Alignment requirement. */
+        static constexpr auto alignment = Align;
+
+        /*! @brief Default constructor. */
+        basic_any() ENTT_NOEXCEPT
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {}
+
+        /**
+         * @brief Constructs a wrapper by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_any(std::in_place_type_t<Type>, Args &&... args)
+            : instance{},
+            vtable{ &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>> },
+            mode{ type_to_policy<Type>() }
+        {
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Constructs a wrapper that holds an unmanaged object.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type>
+        basic_any(std::reference_wrapper<Type> value) ENTT_NOEXCEPT
+            : basic_any{}
+        {
+            // invokes deprecated assignment operator (and avoids issues with vs2017)
+            *this = value;
+        }
+
+        /**
+         * @brief Constructs a wrapper from a given value.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
+        basic_any(Type&& value)
+            : instance{},
+            vtable{ &basic_vtable<std::decay_t<Type>> },
+            mode{ policy::OWNER }
+        {
+            initialize<std::decay_t<Type>>(std::forward<Type>(value));
+        }
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_any(const basic_any& other)
+            : instance{},
+            vtable{ &basic_vtable<void> },
+            mode{ policy::OWNER }
+        {
+            other.vtable(operation::COPY, other, this);
+        }
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_any(basic_any&& other) ENTT_NOEXCEPT
+            : instance{},
+            vtable{ other.vtable },
+            mode{ other.mode }
+        {
+            vtable(operation::MOVE, other, this);
+        }
+
+        /*! @brief Frees the internal storage, whatever it means. */
+        ~basic_any() {
+            vtable(operation::DTOR, *this, nullptr);
+        }
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This any object.
+         */
+        basic_any& operator=(const basic_any& other) {
+            reset();
+            other.vtable(operation::COPY, other, this);
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This any object.
+         */
+        basic_any& operator=(basic_any&& other) ENTT_NOEXCEPT {
+            std::exchange(vtable, other.vtable)(operation::DTOR, *this, nullptr);
+            other.vtable(operation::MOVE, other, this);
+            mode = other.mode;
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        [[deprecated("Use std::in_place_type<T &>, entt::make_any<T &>, emplace<Type &> or forward_as_any instead")]]
+        basic_any& operator=(std::reference_wrapper<Type> value) ENTT_NOEXCEPT {
+            emplace<Type&>(value.get());
+            return *this;
+        }
+
+        /**
+         * @brief Value assignment operator.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @param value An instance of an object to use to initialize the wrapper.
+         * @return This any object.
+         */
+        template<typename Type>
+        std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any&>
+            operator=(Type&& value) {
+            emplace<std::decay_t<Type>>(std::forward<Type>(value));
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            type_info info{};
+            vtable(operation::TYPE, *this, &info);
+            return info;
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return vtable(operation::CADDR, *this, nullptr);
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return const_cast<void*>(vtable(operation::ADDR, *this, nullptr));
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the wrapper.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            std::exchange(vtable, &basic_vtable<std::remove_const_t<std::remove_reference_t<Type>>>)(operation::DTOR, *this, nullptr);
+            mode = type_to_policy<Type>();
+            initialize<Type>(std::forward<Args>(args)...);
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            std::exchange(vtable, &basic_vtable<void>)(operation::DTOR, *this, nullptr);
+            mode = policy::OWNER;
+        }
+
+        /**
+         * @brief Returns false if a wrapper is empty, true otherwise.
+         * @return False if the wrapper is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable(operation::CADDR, *this, nullptr) == nullptr);
+        }
+
+        /**
+         * @brief Checks if two wrappers differ in their content.
+         * @param other Wrapper with which to compare.
+         * @return False if the two objects differ in their content, true otherwise.
+         */
+        bool operator==(const basic_any& other) const ENTT_NOEXCEPT {
+            const basic_any* trampoline = &other;
+            return type() == other.type() && (vtable(operation::COMP, *this, &trampoline) || !other.data());
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A wrapper that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_any as_ref() ENTT_NOEXCEPT {
+            return basic_any{ *this, (mode == policy::CREF ? policy::CREF : policy::REF) };
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_any as_ref() const ENTT_NOEXCEPT {
+            return basic_any{ *this, policy::CREF };
+        }
+
+        /**
+         * @brief Returns true if a wrapper owns its object, false otherwise.
+         * @return True if the wrapper owns its object, false otherwise.
+         */
+        [[nodiscard]] bool owner() const ENTT_NOEXCEPT {
+            return (mode == policy::OWNER);
+        }
+
+    private:
+        union { const void* instance; storage_type storage; };
+        vtable_type* vtable;
+        policy mode;
+    };
+
+
+    /**
+     * @brief Checks if two wrappers differ in their content.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param lhs A wrapper, either empty or not.
+     * @param rhs A wrapper, either empty or not.
+     * @return True if the two wrappers differ in their content, false otherwise.
+     */
+    template<std::size_t Len, std::size_t Align>
+    [[nodiscard]] inline bool operator!=(const basic_any<Len, Align>& lhs, const basic_any<Len, Align>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Performs type-safe access to the contained object.
+     * @tparam Type Type to which conversion is required.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     * @param data Target any object.
+     * @return The element converted to the requested type.
+     */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(const basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        const auto* const instance = any_cast<std::remove_reference_t<Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(*instance);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type any_cast(basic_any<Len, Align>&& data) ENTT_NOEXCEPT {
+        // forces const on non-reference types to make them work also with wrappers for const references
+        auto* const instance = any_cast<std::remove_reference_t<const Type>>(&data);
+        ENTT_ASSERT(instance, "Invalid instance");
+        return static_cast<Type>(std::move(*instance));
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    const Type* any_cast(const basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        return (data->type() == type_id<Type>() ? static_cast<const Type*>(data->data()) : nullptr);
+    }
+
+
+    /*! @copydoc any_cast */
+    template<typename Type, std::size_t Len, std::size_t Align>
+    Type* any_cast(basic_any<Len, Align>* data) ENTT_NOEXCEPT {
+        // last attempt to make wrappers for const references return their values
+        return (data->type() == type_id<Type>() ? static_cast<Type*>(static_cast<constness_as_t<basic_any<Len, Align>, Type> *>(data)->data()) : nullptr);
+    }
+
+
+    /**
+     * @brief Constructs a wrapper from a given type, passing it all arguments.
+     * @tparam Type Type of object to use to initialize the wrapper.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Args Types of arguments to use to construct the new instance.
+     * @param args Parameters to use to construct the instance.
+     * @return A properly initialized wrapper for an object of the given type.
+     */
+    template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
+    basic_any<Len, Align> make_any(Args &&... args) {
+        return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
+    }
+
+
+    /**
+     * @brief Forwards its argument and avoids copies for lvalue references.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     * @tparam Type Type of argument to use to construct the new instance.
+     * @param value Parameter to use to construct the instance.
+     * @return A properly initialized and not necessarily owning wrapper.
+     */
+    template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
+    basic_any<Len, Align> forward_as_any(Type&& value) {
+        return basic_any<Len, Align>{std::in_place_type<std::conditional_t<std::is_rvalue_reference_v<Type>, std::decay_t<Type>, Type>>, std::forward<Type>(value)};
+    }
+
+
+}
+
+
+#endif
+
+// #include "../core/type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+
+// #include "hashed_string.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "../core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_POLY_FWD_HPP
+#define ENTT_POLY_FWD_HPP
+
+
+#include <type_traits>
+
+
+namespace entt {
+
+
+    template<typename, std::size_t Len, std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_poly;
+
+
+    /**
+     * @brief Alias declaration for the most common use case.
+     * @tparam Concept Concept descriptor.
+     */
+    template<typename Concept>
+    using poly = basic_poly<Concept, sizeof(double[2])>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /*! @brief Inspector class used to infer the type of the virtual table. */
+    struct poly_inspector {
+        /**
+         * @brief Generic conversion operator (definition only).
+         * @tparam Type Type to which conversion is requested.
+         */
+        template <class Type>
+        operator Type && () const;
+
+        /**
+         * @brief Dummy invocation function (definition only).
+         * @tparam Member Index of the function to invoke.
+         * @tparam Args Types of arguments to pass to the function.
+         * @param args The arguments to pass to the function.
+         * @return A poly inspector convertible to any type.
+         */
+        template<auto Member, typename... Args>
+        poly_inspector invoke(Args &&... args) const;
+
+        /*! @copydoc invoke */
+        template<auto Member, typename... Args>
+        poly_inspector invoke(Args &&... args);
+    };
+
+
+    /**
+     * @brief Static virtual table factory.
+     * @tparam Concept Concept descriptor.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Alignment requirement.
+     */
+    template<typename Concept, std::size_t Len, std::size_t Align>
+    class poly_vtable {
+        using inspector = typename Concept::template type<poly_inspector>;
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(*)(inspector&, Args...))->Ret(*)(basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(*)(const inspector&, Args...))->Ret(*)(const basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(*)(Args...))->Ret(*)(const basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(inspector::*)(Args...))->Ret(*)(basic_any<Len, Align>&, Args...);
+
+        template<typename Ret, typename... Args>
+        static auto vtable_entry(Ret(inspector::*)(Args...) const)->Ret(*)(const basic_any<Len, Align>&, Args...);
+
+        template<auto... Candidate>
+        static auto make_vtable(value_list<Candidate...>)
+            -> decltype(std::make_tuple(vtable_entry(Candidate)...));
+
+        template<typename... Func>
+        [[nodiscard]] static constexpr auto make_vtable(type_list<Func...>) {
+            if constexpr (sizeof...(Func) == 0) {
+                return decltype(make_vtable(typename Concept::template impl<inspector>{})){};
+            }
+            else if constexpr ((std::is_function_v<Func> && ...)) {
+                return decltype(std::make_tuple(vtable_entry(std::declval<Func inspector::*>())...)){};
+            }
+        }
+
+        template<typename Type, auto Candidate, typename Ret, typename Any, typename... Args>
+        static void fill_vtable_entry(Ret(*&entry)(Any&, Args...)) {
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
+                entry = +[](Any&, Args... args) -> Ret {
+                    return std::invoke(Candidate, std::forward<Args>(args)...);
+                };
+            }
+            else {
+                entry = +[](Any& instance, Args... args) -> Ret {
+                    return static_cast<Ret>(std::invoke(Candidate, any_cast<constness_as_t<Type, Any>&>(instance), std::forward<Args>(args)...));
+                };
+            }
+        }
+
+        template<typename Type, auto... Index>
+        [[nodiscard]] static auto fill_vtable(std::index_sequence<Index...>) {
+            type impl{};
+            (fill_vtable_entry<Type, value_list_element_v<Index, typename Concept::template impl<Type>>>(std::get<Index>(impl)), ...);
+            return impl;
+        }
+
+    public:
+        /*! @brief Virtual table type. */
+        using type = decltype(make_vtable(Concept{}));
+
+        /**
+         * @brief Returns a static virtual table for a specific concept and type.
+         * @tparam Type The type for which to generate the virtual table.
+         * @return A static virtual table for the given concept and type.
+         */
+        template<typename Type>
+        [[nodiscard]] static const auto* instance() {
+            static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Type differs from its decayed form");
+            static const auto vtable = fill_vtable<Type>(std::make_index_sequence<Concept::template impl<Type>::size>{});
+            return &vtable;
+        }
+    };
+
+
+    /**
+     * @brief Poly base class used to inject functionalities into concepts.
+     * @tparam Poly The outermost poly class.
+     */
+    template<typename Poly>
+    struct poly_base {
+        /**
+         * @brief Invokes a function from the static virtual table.
+         * @tparam Member Index of the function to invoke.
+         * @tparam Args Types of arguments to pass to the function.
+         * @param self A reference to the poly object that made the call.
+         * @param args The arguments to pass to the function.
+         * @return The return value of the invoked function, if any.
+         */
+        template<auto Member, typename... Args>
+        [[nodiscard]] decltype(auto) invoke(const poly_base& self, Args &&... args) const {
+            const auto& poly = static_cast<const Poly&>(self);
+            return std::get<Member>(*poly.vtable)(poly.storage, std::forward<Args>(args)...);
+        }
+
+        /*! @copydoc invoke */
+        template<auto Member, typename... Args>
+        [[nodiscard]] decltype(auto) invoke(poly_base& self, Args &&... args) {
+            auto& poly = static_cast<Poly&>(self);
+            return std::get<Member>(*poly.vtable)(poly.storage, std::forward<Args>(args)...);
+        }
+    };
+
+
+    /**
+     * @brief Shortcut for calling `poly_base<Type>::invoke`.
+     * @tparam Member Index of the function to invoke.
+     * @tparam Poly A fully defined poly object.
+     * @tparam Args Types of arguments to pass to the function.
+     * @param self A reference to the poly object that made the call.
+     * @param args The arguments to pass to the function.
+     * @return The return value of the invoked function, if any.
+     */
+    template<auto Member, typename Poly, typename... Args>
+    decltype(auto) poly_call(Poly&& self, Args &&... args) {
+        return std::forward<Poly>(self).template invoke<Member>(self, std::forward<Args>(args)...);
+    }
+
+
+    /**
+     * @brief Static polymorphism made simple and within everyone's reach.
+     *
+     * Static polymorphism is a very powerful tool in C++, albeit sometimes
+     * cumbersome to obtain.<br/>
+     * This class aims to make it simple and easy to use.
+     *
+     * @note
+     * Both deduced and defined static virtual tables are supported.<br/>
+     * Moreover, the `poly` class template also works with unmanaged objects.
+     *
+     * @tparam Concept Concept descriptor.
+     * @tparam Len Size of the storage reserved for the small buffer optimization.
+     * @tparam Align Optional alignment requirement.
+     */
+    template<typename Concept, std::size_t Len, std::size_t Align>
+    class basic_poly : private Concept::template type<poly_base<basic_poly<Concept, Len, Align>>> {
+        /*! @brief A poly base is allowed to snoop into a poly object. */
+        friend struct poly_base<basic_poly>;
+
+        using vtable_type = typename poly_vtable<Concept, Len, Align>::type;
+
+    public:
+        /*! @brief Concept type. */
+        using concept_type = typename Concept::template type<poly_base<basic_poly>>;
+
+        /*! @brief Default constructor. */
+        basic_poly() ENTT_NOEXCEPT
+            : storage{},
+            vtable{}
+        {}
+
+        /**
+         * @brief Constructs a poly by directly initializing the new object.
+         * @tparam Type Type of object to use to initialize the poly.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        explicit basic_poly(std::in_place_type_t<Type>, Args &&... args)
+            : storage{ std::in_place_type<Type>, std::forward<Args>(args)... },
+            vtable{ poly_vtable<Concept, Len, Align>::template instance<std::remove_const_t<std::remove_reference_t<Type>>>() }
+        {}
+
+        /**
+         * @brief Constructs a poly from a given value.
+         * @tparam Type Type of object to use to initialize the poly.
+         * @param value An instance of an object to use to initialize the poly.
+         */
+        template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, basic_poly>>>
+        basic_poly(Type&& value) ENTT_NOEXCEPT
+            : basic_poly{ std::in_place_type<std::remove_cv_t<std::remove_reference_t<Type>>>, std::forward<Type>(value) }
+        {}
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        basic_poly(const basic_poly& other) = default;
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        basic_poly(basic_poly&& other) ENTT_NOEXCEPT
+            : basic_poly{}
+        {
+            swap(*this, other);
+        }
+
+        /**
+         * @brief Assignment operator.
+         * @param other The instance to assign from.
+         * @return This poly object.
+         */
+        basic_poly& operator=(basic_poly other) {
+            swap(other, *this);
+            return *this;
+        }
+
+        /**
+         * @brief Returns the type of the contained object.
+         * @return The type of the contained object, if any.
+         */
+        [[nodiscard]] type_info type() const ENTT_NOEXCEPT {
+            return storage.type();
+        }
+
+        /**
+         * @brief Returns an opaque pointer to the contained instance.
+         * @return An opaque pointer the contained instance, if any.
+         */
+        [[nodiscard]] const void* data() const ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] void* data() ENTT_NOEXCEPT {
+            return storage.data();
+        }
+
+        /**
+         * @brief Replaces the contained object by creating a new instance directly.
+         * @tparam Type Type of object to use to initialize the poly.
+         * @tparam Args Types of arguments to use to construct the new instance.
+         * @param args Parameters to use to construct the instance.
+         */
+        template<typename Type, typename... Args>
+        void emplace(Args &&... args) {
+            *this = basic_poly{ std::in_place_type<Type>, std::forward<Args>(args)... };
+        }
+
+        /*! @brief Destroys contained object */
+        void reset() {
+            *this = basic_poly{};
+        }
+
+        /**
+         * @brief Returns false if a poly is empty, true otherwise.
+         * @return False if the poly is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return !(vtable == nullptr);
+        }
+
+        /**
+         * @brief Returns a pointer to the underlying concept.
+         * @return A pointer to the underlying concept.
+         */
+        [[nodiscard]] concept_type* operator->() ENTT_NOEXCEPT {
+            return this;
+        }
+
+        /*! @copydoc operator-> */
+        [[nodiscard]] const concept_type* operator->() const ENTT_NOEXCEPT {
+            return this;
+        }
+
+        /**
+         * @brief Swaps two poly objects.
+         * @param lhs A valid poly object.
+         * @param rhs A valid poly object.
+         */
+        friend void swap(basic_poly& lhs, basic_poly& rhs) {
+            using std::swap;
+            swap(lhs.storage, rhs.storage);
+            swap(lhs.vtable, rhs.vtable);
+        }
+
+        /**
+         * @brief Aliasing constructor.
+         * @return A poly that shares a reference to an unmanaged object.
+         */
+        [[nodiscard]] basic_poly as_ref() ENTT_NOEXCEPT {
+            basic_poly ref = std::as_const(*this).as_ref();
+            ref.storage = storage.as_ref();
+            return ref;
+        }
+
+        /*! @copydoc as_ref */
+        [[nodiscard]] basic_poly as_ref() const ENTT_NOEXCEPT {
+            basic_poly ref{};
+            ref.storage = storage.as_ref();
+            ref.vtable = vtable;
+            return ref;
+        }
+
+    private:
+        basic_any<Len, Align> storage;
+        const vtable_type* vtable;
+    };
+
+
+}
+
+
+#endif
+
+// #include "process/process.hpp"
+#ifndef ENTT_PROCESS_PROCESS_HPP
+#define ENTT_PROCESS_PROCESS_HPP
+
+
+#include <utility>
+#include <type_traits>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Base class for processes.
+     *
+     * This class stays true to the CRTP idiom. Derived classes must specify what's
+     * the intended type for elapsed times.<br/>
+     * A process should expose publicly the following member functions whether
+     * required:
+     *
+     * * @code{.cpp}
+     *   void update(Delta, void *);
+     *   @endcode
+     *
+     *   It's invoked once per tick until a process is explicitly aborted or it
+     *   terminates either with or without errors. Even though it's not mandatory to
+     *   declare this member function, as a rule of thumb each process should at
+     *   least define it to work properly. The `void *` parameter is an opaque
+     *   pointer to user data (if any) forwarded directly to the process during an
+     *   update.
+     *
+     * * @code{.cpp}
+     *   void init();
+     *   @endcode
+     *
+     *   It's invoked when the process joins the running queue of a scheduler. This
+     *   happens as soon as it's attached to the scheduler if the process is a top
+     *   level one, otherwise when it replaces its parent if the process is a
+     *   continuation.
+     *
+     * * @code{.cpp}
+     *   void succeeded();
+     *   @endcode
+     *
+     *   It's invoked in case of success, immediately after an update and during the
+     *   same tick.
+     *
+     * * @code{.cpp}
+     *   void failed();
+     *   @endcode
+     *
+     *   It's invoked in case of errors, immediately after an update and during the
+     *   same tick.
+     *
+     * * @code{.cpp}
+     *   void aborted();
+     *   @endcode
+     *
+     *   It's invoked only if a process is explicitly aborted. There is no guarantee
+     *   that it executes in the same tick, this depends solely on whether the
+     *   process is aborted immediately or not.
+     *
+     * Derived classes can change the internal state of a process by invoking the
+     * `succeed` and `fail` protected member functions and even pause or unpause the
+     * process itself.
+     *
+     * @sa scheduler
+     *
+     * @tparam Derived Actual type of process that extends the class template.
+     * @tparam Delta Type to use to provide elapsed time.
+     */
+    template<typename Derived, typename Delta>
+    class process {
+        enum class state : unsigned int {
+            UNINITIALIZED = 0,
+            RUNNING,
+            PAUSED,
+            SUCCEEDED,
+            FAILED,
+            ABORTED,
+            FINISHED,
+            REJECTED
+        };
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::UNINITIALIZED>)
+            -> decltype(std::declval<Target>().init(), void()) {
+            static_cast<Target*>(this)->init();
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::RUNNING>, Delta delta, void* data)
+            -> decltype(std::declval<Target>().update(delta, data), void()) {
+            static_cast<Target*>(this)->update(delta, data);
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::SUCCEEDED>)
+            -> decltype(std::declval<Target>().succeeded(), void()) {
+            static_cast<Target*>(this)->succeeded();
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::FAILED>)
+            -> decltype(std::declval<Target>().failed(), void()) {
+            static_cast<Target*>(this)->failed();
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::ABORTED>)
+            -> decltype(std::declval<Target>().aborted(), void()) {
+            static_cast<Target*>(this)->aborted();
+        }
+
+        void next(...) const ENTT_NOEXCEPT {}
+
+    protected:
+        /**
+         * @brief Terminates a process with success if it's still alive.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * alive.
+         */
+        void succeed() ENTT_NOEXCEPT {
+            if (alive()) {
+                current = state::SUCCEEDED;
+            }
+        }
+
+        /**
+         * @brief Terminates a process with errors if it's still alive.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * alive.
+         */
+        void fail() ENTT_NOEXCEPT {
+            if (alive()) {
+                current = state::FAILED;
+            }
+        }
+
+        /**
+         * @brief Stops a process if it's in a running state.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * running.
+         */
+        void pause() ENTT_NOEXCEPT {
+            if (current == state::RUNNING) {
+                current = state::PAUSED;
+            }
+        }
+
+        /**
+         * @brief Restarts a process if it's paused.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * paused.
+         */
+        void unpause() ENTT_NOEXCEPT {
+            if (current == state::PAUSED) {
+                current = state::RUNNING;
+            }
+        }
+
+    public:
+        /*! @brief Type used to provide elapsed time. */
+        using delta_type = Delta;
+
+        /*! @brief Default destructor. */
+        virtual ~process() {
+            static_assert(std::is_base_of_v<process, Derived>, "Incorrect use of the class template");
+        }
+
+        /**
+         * @brief Aborts a process if it's still alive.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * alive.
+         *
+         * @param immediately Requests an immediate operation.
+         */
+        void abort(const bool immediately = false) {
+            if (alive()) {
+                current = state::ABORTED;
+
+                if (immediately) {
+                    tick({});
+                }
+            }
+        }
+
+        /**
+         * @brief Returns true if a process is either running or paused.
+         * @return True if the process is still alive, false otherwise.
+         */
+        [[nodiscard]] bool alive() const ENTT_NOEXCEPT {
+            return current == state::RUNNING || current == state::PAUSED;
+        }
+
+        /**
+         * @brief Returns true if a process is already terminated.
+         * @return True if the process is terminated, false otherwise.
+         */
+        [[nodiscard]] bool finished() const ENTT_NOEXCEPT {
+            return current == state::FINISHED;
+        }
+
+        /**
+         * @brief Returns true if a process is currently paused.
+         * @return True if the process is paused, false otherwise.
+         */
+        [[nodiscard]] bool paused() const ENTT_NOEXCEPT {
+            return current == state::PAUSED;
+        }
+
+        /**
+         * @brief Returns true if a process terminated with errors.
+         * @return True if the process terminated with errors, false otherwise.
+         */
+        [[nodiscard]] bool rejected() const ENTT_NOEXCEPT {
+            return current == state::REJECTED;
+        }
+
+        /**
+         * @brief Updates a process and its internal state if required.
+         * @param delta Elapsed time.
+         * @param data Optional data.
+         */
+        void tick(const Delta delta, void* data = nullptr) {
+            switch (current) {
+            case state::UNINITIALIZED:
+                next(std::integral_constant<state, state::UNINITIALIZED>{});
+                current = state::RUNNING;
+                break;
+            case state::RUNNING:
+                next(std::integral_constant<state, state::RUNNING>{}, delta, data);
+                break;
+            default:
+                // suppress warnings
+                break;
+            }
+
+            // if it's dead, it must be notified and removed immediately
+            switch (current) {
+            case state::SUCCEEDED:
+                next(std::integral_constant<state, state::SUCCEEDED>{});
+                current = state::FINISHED;
+                break;
+            case state::FAILED:
+                next(std::integral_constant<state, state::FAILED>{});
+                current = state::REJECTED;
+                break;
+            case state::ABORTED:
+                next(std::integral_constant<state, state::ABORTED>{});
+                current = state::REJECTED;
+                break;
+            default:
+                // suppress warnings
+                break;
+            }
+        }
+
+    private:
+        state current{ state::UNINITIALIZED };
+    };
+
+
+    /**
+     * @brief Adaptor for lambdas and functors to turn them into processes.
+     *
+     * Lambdas and functors can't be used directly with a scheduler for they are not
+     * properly defined processes with managed life cycles.<br/>
+     * This class helps in filling the gap and turning lambdas and functors into
+     * full featured processes usable by a scheduler.
+     *
+     * The signature of the function call operator should be equivalent to the
+     * following:
+     *
+     * @code{.cpp}
+     * void(Delta delta, void *data, auto succeed, auto fail);
+     * @endcode
+     *
+     * Where:
+     *
+     * * `delta` is the elapsed time.
+     * * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
+     * * `succeed` is a function to call when a process terminates with success.
+     * * `fail` is a function to call when a process terminates with errors.
+     *
+     * The signature of the function call operator of both `succeed` and `fail`
+     * is equivalent to the following:
+     *
+     * @code{.cpp}
+     * void();
+     * @endcode
+     *
+     * Usually users shouldn't worry about creating adaptors. A scheduler will
+     * create them internally each and avery time a lambda or a functor is used as
+     * a process.
+     *
+     * @sa process
+     * @sa scheduler
+     *
+     * @tparam Func Actual type of process.
+     * @tparam Delta Type to use to provide elapsed time.
+     */
+    template<typename Func, typename Delta>
+    struct process_adaptor : process<process_adaptor<Func, Delta>, Delta>, private Func {
+        /**
+         * @brief Constructs a process adaptor from a lambda or a functor.
+         * @tparam Args Types of arguments to use to initialize the actual process.
+         * @param args Parameters to use to initialize the actual process.
+         */
+        template<typename... Args>
+        process_adaptor(Args &&... args)
+            : Func{ std::forward<Args>(args)... }
+        {}
+
+        /**
+         * @brief Updates a process and its internal state if required.
+         * @param delta Elapsed time.
+         * @param data Optional data.
+         */
+        void update(const Delta delta, void* data) {
+            Func::operator()(delta, data, [this]() { this->succeed(); }, [this]() { this->fail(); });
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "process/scheduler.hpp"
+#ifndef ENTT_PROCESS_SCHEDULER_HPP
+#define ENTT_PROCESS_SCHEDULER_HPP
+
+
+#include <vector>
+#include <memory>
+#include <utility>
+#include <algorithm>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "process.hpp"
+#ifndef ENTT_PROCESS_PROCESS_HPP
+#define ENTT_PROCESS_PROCESS_HPP
+
+
+#include <utility>
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Base class for processes.
+     *
+     * This class stays true to the CRTP idiom. Derived classes must specify what's
+     * the intended type for elapsed times.<br/>
+     * A process should expose publicly the following member functions whether
+     * required:
+     *
+     * * @code{.cpp}
+     *   void update(Delta, void *);
+     *   @endcode
+     *
+     *   It's invoked once per tick until a process is explicitly aborted or it
+     *   terminates either with or without errors. Even though it's not mandatory to
+     *   declare this member function, as a rule of thumb each process should at
+     *   least define it to work properly. The `void *` parameter is an opaque
+     *   pointer to user data (if any) forwarded directly to the process during an
+     *   update.
+     *
+     * * @code{.cpp}
+     *   void init();
+     *   @endcode
+     *
+     *   It's invoked when the process joins the running queue of a scheduler. This
+     *   happens as soon as it's attached to the scheduler if the process is a top
+     *   level one, otherwise when it replaces its parent if the process is a
+     *   continuation.
+     *
+     * * @code{.cpp}
+     *   void succeeded();
+     *   @endcode
+     *
+     *   It's invoked in case of success, immediately after an update and during the
+     *   same tick.
+     *
+     * * @code{.cpp}
+     *   void failed();
+     *   @endcode
+     *
+     *   It's invoked in case of errors, immediately after an update and during the
+     *   same tick.
+     *
+     * * @code{.cpp}
+     *   void aborted();
+     *   @endcode
+     *
+     *   It's invoked only if a process is explicitly aborted. There is no guarantee
+     *   that it executes in the same tick, this depends solely on whether the
+     *   process is aborted immediately or not.
+     *
+     * Derived classes can change the internal state of a process by invoking the
+     * `succeed` and `fail` protected member functions and even pause or unpause the
+     * process itself.
+     *
+     * @sa scheduler
+     *
+     * @tparam Derived Actual type of process that extends the class template.
+     * @tparam Delta Type to use to provide elapsed time.
+     */
+    template<typename Derived, typename Delta>
+    class process {
+        enum class state : unsigned int {
+            UNINITIALIZED = 0,
+            RUNNING,
+            PAUSED,
+            SUCCEEDED,
+            FAILED,
+            ABORTED,
+            FINISHED,
+            REJECTED
+        };
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::UNINITIALIZED>)
+            -> decltype(std::declval<Target>().init(), void()) {
+            static_cast<Target*>(this)->init();
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::RUNNING>, Delta delta, void* data)
+            -> decltype(std::declval<Target>().update(delta, data), void()) {
+            static_cast<Target*>(this)->update(delta, data);
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::SUCCEEDED>)
+            -> decltype(std::declval<Target>().succeeded(), void()) {
+            static_cast<Target*>(this)->succeeded();
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::FAILED>)
+            -> decltype(std::declval<Target>().failed(), void()) {
+            static_cast<Target*>(this)->failed();
+        }
+
+        template<typename Target = Derived>
+        auto next(std::integral_constant<state, state::ABORTED>)
+            -> decltype(std::declval<Target>().aborted(), void()) {
+            static_cast<Target*>(this)->aborted();
+        }
+
+        void next(...) const ENTT_NOEXCEPT {}
+
+    protected:
+        /**
+         * @brief Terminates a process with success if it's still alive.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * alive.
+         */
+        void succeed() ENTT_NOEXCEPT {
+            if (alive()) {
+                current = state::SUCCEEDED;
+            }
+        }
+
+        /**
+         * @brief Terminates a process with errors if it's still alive.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * alive.
+         */
+        void fail() ENTT_NOEXCEPT {
+            if (alive()) {
+                current = state::FAILED;
+            }
+        }
+
+        /**
+         * @brief Stops a process if it's in a running state.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * running.
+         */
+        void pause() ENTT_NOEXCEPT {
+            if (current == state::RUNNING) {
+                current = state::PAUSED;
+            }
+        }
+
+        /**
+         * @brief Restarts a process if it's paused.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * paused.
+         */
+        void unpause() ENTT_NOEXCEPT {
+            if (current == state::PAUSED) {
+                current = state::RUNNING;
+            }
+        }
+
+    public:
+        /*! @brief Type used to provide elapsed time. */
+        using delta_type = Delta;
+
+        /*! @brief Default destructor. */
+        virtual ~process() {
+            static_assert(std::is_base_of_v<process, Derived>, "Incorrect use of the class template");
+        }
+
+        /**
+         * @brief Aborts a process if it's still alive.
+         *
+         * The function is idempotent and it does nothing if the process isn't
+         * alive.
+         *
+         * @param immediately Requests an immediate operation.
+         */
+        void abort(const bool immediately = false) {
+            if (alive()) {
+                current = state::ABORTED;
+
+                if (immediately) {
+                    tick({});
+                }
+            }
+        }
+
+        /**
+         * @brief Returns true if a process is either running or paused.
+         * @return True if the process is still alive, false otherwise.
+         */
+        [[nodiscard]] bool alive() const ENTT_NOEXCEPT {
+            return current == state::RUNNING || current == state::PAUSED;
+        }
+
+        /**
+         * @brief Returns true if a process is already terminated.
+         * @return True if the process is terminated, false otherwise.
+         */
+        [[nodiscard]] bool finished() const ENTT_NOEXCEPT {
+            return current == state::FINISHED;
+        }
+
+        /**
+         * @brief Returns true if a process is currently paused.
+         * @return True if the process is paused, false otherwise.
+         */
+        [[nodiscard]] bool paused() const ENTT_NOEXCEPT {
+            return current == state::PAUSED;
+        }
+
+        /**
+         * @brief Returns true if a process terminated with errors.
+         * @return True if the process terminated with errors, false otherwise.
+         */
+        [[nodiscard]] bool rejected() const ENTT_NOEXCEPT {
+            return current == state::REJECTED;
+        }
+
+        /**
+         * @brief Updates a process and its internal state if required.
+         * @param delta Elapsed time.
+         * @param data Optional data.
+         */
+        void tick(const Delta delta, void* data = nullptr) {
+            switch (current) {
+            case state::UNINITIALIZED:
+                next(std::integral_constant<state, state::UNINITIALIZED>{});
+                current = state::RUNNING;
+                break;
+            case state::RUNNING:
+                next(std::integral_constant<state, state::RUNNING>{}, delta, data);
+                break;
+            default:
+                // suppress warnings
+                break;
+            }
+
+            // if it's dead, it must be notified and removed immediately
+            switch (current) {
+            case state::SUCCEEDED:
+                next(std::integral_constant<state, state::SUCCEEDED>{});
+                current = state::FINISHED;
+                break;
+            case state::FAILED:
+                next(std::integral_constant<state, state::FAILED>{});
+                current = state::REJECTED;
+                break;
+            case state::ABORTED:
+                next(std::integral_constant<state, state::ABORTED>{});
+                current = state::REJECTED;
+                break;
+            default:
+                // suppress warnings
+                break;
+            }
+        }
+
+    private:
+        state current{ state::UNINITIALIZED };
+    };
+
+
+    /**
+     * @brief Adaptor for lambdas and functors to turn them into processes.
+     *
+     * Lambdas and functors can't be used directly with a scheduler for they are not
+     * properly defined processes with managed life cycles.<br/>
+     * This class helps in filling the gap and turning lambdas and functors into
+     * full featured processes usable by a scheduler.
+     *
+     * The signature of the function call operator should be equivalent to the
+     * following:
+     *
+     * @code{.cpp}
+     * void(Delta delta, void *data, auto succeed, auto fail);
+     * @endcode
+     *
+     * Where:
+     *
+     * * `delta` is the elapsed time.
+     * * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
+     * * `succeed` is a function to call when a process terminates with success.
+     * * `fail` is a function to call when a process terminates with errors.
+     *
+     * The signature of the function call operator of both `succeed` and `fail`
+     * is equivalent to the following:
+     *
+     * @code{.cpp}
+     * void();
+     * @endcode
+     *
+     * Usually users shouldn't worry about creating adaptors. A scheduler will
+     * create them internally each and avery time a lambda or a functor is used as
+     * a process.
+     *
+     * @sa process
+     * @sa scheduler
+     *
+     * @tparam Func Actual type of process.
+     * @tparam Delta Type to use to provide elapsed time.
+     */
+    template<typename Func, typename Delta>
+    struct process_adaptor : process<process_adaptor<Func, Delta>, Delta>, private Func {
+        /**
+         * @brief Constructs a process adaptor from a lambda or a functor.
+         * @tparam Args Types of arguments to use to initialize the actual process.
+         * @param args Parameters to use to initialize the actual process.
+         */
+        template<typename... Args>
+        process_adaptor(Args &&... args)
+            : Func{ std::forward<Args>(args)... }
+        {}
+
+        /**
+         * @brief Updates a process and its internal state if required.
+         * @param delta Elapsed time.
+         * @param data Optional data.
+         */
+        void update(const Delta delta, void* data) {
+            Func::operator()(delta, data, [this]() { this->succeed(); }, [this]() { this->fail(); });
+        }
+    };
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Cooperative scheduler for processes.
+     *
+     * A cooperative scheduler runs processes and helps managing their life cycles.
+     *
+     * Each process is invoked once per tick. If a process terminates, it's
+     * removed automatically from the scheduler and it's never invoked again.<br/>
+     * A process can also have a child. In this case, the process is replaced with
+     * its child when it terminates if it returns with success. In case of errors,
+     * both the process and its child are discarded.
+     *
+     * Example of use (pseudocode):
+     *
+     * @code{.cpp}
+     * scheduler.attach([](auto delta, void *, auto succeed, auto fail) {
+     *     // code
+     * }).then<my_process>(arguments...);
+     * @endcode
+     *
+     * In order to invoke all scheduled processes, call the `update` member function
+     * passing it the elapsed time to forward to the tasks.
+     *
+     * @sa process
+     *
+     * @tparam Delta Type to use to provide elapsed time.
+     */
+    template<typename Delta>
+    class scheduler {
+        struct process_handler {
+            using instance_type = std::unique_ptr<void, void(*)(void*)>;
+            using update_fn_type = bool(process_handler&, Delta, void*);
+            using abort_fn_type = void(process_handler&, bool);
+            using next_type = std::unique_ptr<process_handler>;
+
+            instance_type instance;
+            update_fn_type* update;
+            abort_fn_type* abort;
+            next_type next;
+        };
+
+        struct continuation {
+            continuation(process_handler* ref)
+                : handler{ ref }
+            {}
+
+            template<typename Proc, typename... Args>
+            continuation then(Args &&... args) {
+                static_assert(std::is_base_of_v<process<Proc, Delta>, Proc>, "Invalid process type");
+                auto proc = typename process_handler::instance_type{ new Proc{std::forward<Args>(args)...}, &scheduler::deleter<Proc> };
+                handler->next.reset(new process_handler{ std::move(proc), &scheduler::update<Proc>, &scheduler::abort<Proc>, nullptr });
+                handler = handler->next.get();
+                return *this;
+            }
+
+            template<typename Func>
+            continuation then(Func&& func) {
+                return then<process_adaptor<std::decay_t<Func>, Delta>>(std::forward<Func>(func));
+            }
+
+        private:
+            process_handler* handler;
+        };
+
+        template<typename Proc>
+        [[nodiscard]] static bool update(process_handler& handler, const Delta delta, void* data) {
+            auto* process = static_cast<Proc*>(handler.instance.get());
+            process->tick(delta, data);
+
+            if (process->rejected()) {
+                return true;
+            }
+            else if (process->finished()) {
+                if (handler.next) {
+                    handler = std::move(*handler.next);
+                    // forces the process to exit the uninitialized state
+                    return handler.update(handler, {}, nullptr);
+                }
+
+                return true;
+            }
+
+            return false;
+        }
+
+        template<typename Proc>
+        static void abort(process_handler& handler, const bool immediately) {
+            static_cast<Proc*>(handler.instance.get())->abort(immediately);
+        }
+
+        template<typename Proc>
+        static void deleter(void* proc) {
+            delete static_cast<Proc*>(proc);
+        }
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+
+        /*! @brief Default constructor. */
+        scheduler() = default;
+
+        /*! @brief Default move constructor. */
+        scheduler(scheduler&&) = default;
+
+        /*! @brief Default move assignment operator. @return This scheduler. */
+        scheduler& operator=(scheduler&&) = default;
+
+        /**
+         * @brief Number of processes currently scheduled.
+         * @return Number of processes currently scheduled.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return handlers.size();
+        }
+
+        /**
+         * @brief Returns true if at least a process is currently scheduled.
+         * @return True if there are scheduled processes, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return handlers.empty();
+        }
+
+        /**
+         * @brief Discards all scheduled processes.
+         *
+         * Processes aren't aborted. They are discarded along with their children
+         * and never executed again.
+         */
+        void clear() {
+            handlers.clear();
+        }
+
+        /**
+         * @brief Schedules a process for the next tick.
+         *
+         * Returned value is an opaque object that can be used to attach a child to
+         * the given process. The child is automatically scheduled when the process
+         * terminates and only if the process returns with success.
+         *
+         * Example of use (pseudocode):
+         *
+         * @code{.cpp}
+         * // schedules a task in the form of a process class
+         * scheduler.attach<my_process>(arguments...)
+         * // appends a child in the form of a lambda function
+         * .then([](auto delta, void *, auto succeed, auto fail) {
+         *     // code
+         * })
+         * // appends a child in the form of another process class
+         * .then<my_other_process>();
+         * @endcode
+         *
+         * @tparam Proc Type of process to schedule.
+         * @tparam Args Types of arguments to use to initialize the process.
+         * @param args Parameters to use to initialize the process.
+         * @return An opaque object to use to concatenate processes.
+         */
+        template<typename Proc, typename... Args>
+        auto attach(Args &&... args) {
+            static_assert(std::is_base_of_v<process<Proc, Delta>, Proc>, "Invalid process type");
+            auto proc = typename process_handler::instance_type{ new Proc{std::forward<Args>(args)...}, &scheduler::deleter<Proc> };
+            process_handler handler{ std::move(proc), &scheduler::update<Proc>, &scheduler::abort<Proc>, nullptr };
+            // forces the process to exit the uninitialized state
+            handler.update(handler, {}, nullptr);
+            return continuation{ &handlers.emplace_back(std::move(handler)) };
+        }
+
+        /**
+         * @brief Schedules a process for the next tick.
+         *
+         * A process can be either a lambda or a functor. The scheduler wraps both
+         * of them in a process adaptor internally.<br/>
+         * The signature of the function call operator should be equivalent to the
+         * following:
+         *
+         * @code{.cpp}
+         * void(Delta delta, void *data, auto succeed, auto fail);
+         * @endcode
+         *
+         * Where:
+         *
+         * * `delta` is the elapsed time.
+         * * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
+         * * `succeed` is a function to call when a process terminates with success.
+         * * `fail` is a function to call when a process terminates with errors.
+         *
+         * The signature of the function call operator of both `succeed` and `fail`
+         * is equivalent to the following:
+         *
+         * @code{.cpp}
+         * void();
+         * @endcode
+         *
+         * Returned value is an opaque object that can be used to attach a child to
+         * the given process. The child is automatically scheduled when the process
+         * terminates and only if the process returns with success.
+         *
+         * Example of use (pseudocode):
+         *
+         * @code{.cpp}
+         * // schedules a task in the form of a lambda function
+         * scheduler.attach([](auto delta, void *, auto succeed, auto fail) {
+         *     // code
+         * })
+         * // appends a child in the form of another lambda function
+         * .then([](auto delta, void *, auto succeed, auto fail) {
+         *     // code
+         * })
+         * // appends a child in the form of a process class
+         * .then<my_process>(arguments...);
+         * @endcode
+         *
+         * @sa process_adaptor
+         *
+         * @tparam Func Type of process to schedule.
+         * @param func Either a lambda or a functor to use as a process.
+         * @return An opaque object to use to concatenate processes.
+         */
+        template<typename Func>
+        auto attach(Func&& func) {
+            using Proc = process_adaptor<std::decay_t<Func>, Delta>;
+            return attach<Proc>(std::forward<Func>(func));
+        }
+
+        /**
+         * @brief Updates all scheduled processes.
+         *
+         * All scheduled processes are executed in no specific order.<br/>
+         * If a process terminates with success, it's replaced with its child, if
+         * any. Otherwise, if a process terminates with an error, it's removed along
+         * with its child.
+         *
+         * @param delta Elapsed time.
+         * @param data Optional data.
+         */
+        void update(const Delta delta, void* data = nullptr) {
+            auto sz = handlers.size();
+
+            for (auto pos = handlers.size(); pos; --pos) {
+                auto& handler = handlers[pos - 1];
+
+                if (const auto dead = handler.update(handler, delta, data); dead) {
+                    std::swap(handler, handlers[--sz]);
+                }
+            }
+
+            handlers.erase(handlers.begin() + sz, handlers.end());
+        }
+
+        /**
+         * @brief Aborts all scheduled processes.
+         *
+         * Unless an immediate operation is requested, the abort is scheduled for
+         * the next tick. Processes won't be executed anymore in any case.<br/>
+         * Once a process is fully aborted and thus finished, it's discarded along
+         * with its child, if any.
+         *
+         * @param immediately Requests an immediate operation.
+         */
+        void abort(const bool immediately = false) {
+            decltype(handlers) exec;
+            exec.swap(handlers);
+
+            for (auto&& handler : exec) {
+                handler.abort(handler, immediately);
+            }
+
+            std::move(handlers.begin(), handlers.end(), std::back_inserter(exec));
+            handlers.swap(exec);
+        }
+
+    private:
+        std::vector<process_handler> handlers{};
+    };
+
+
+}
+
+
+#endif
+
+// #include "resource/cache.hpp"
+#ifndef ENTT_RESOURCE_CACHE_HPP
+#define ENTT_RESOURCE_CACHE_HPP
+
+
+#include <type_traits>
+#include <unordered_map>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "../core/fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+// #include "handle.hpp"
+#ifndef ENTT_RESOURCE_HANDLE_HPP
+#define ENTT_RESOURCE_HANDLE_HPP
+
+
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+#ifndef ENTT_RESOURCE_FWD_HPP
+#define ENTT_RESOURCE_FWD_HPP
+
+
+namespace entt {
+
+
+    template<typename>
+    struct resource_cache;
+
+
+    template<typename>
+    class resource_handle;
+
+
+    template<typename, typename>
+    class resource_loader;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Shared resource handle.
+     *
+     * A shared resource handle is a small class that wraps a resource and keeps it
+     * alive even if it's deleted from the cache. It can be either copied or
+     * moved. A handle shares a reference to the same resource with all the other
+     * handles constructed for the same identifier.<br/>
+     * As a rule of thumb, resources should never be copied nor moved. Handles are
+     * the way to go to keep references to them.
+     *
+     * @tparam Resource Type of resource managed by a handle.
+     */
+    template<typename Resource>
+    class resource_handle {
+        /*! @brief Resource handles are friends with each other. */
+        template<typename>
+        friend class resource_handle;
+
+    public:
+        /*! @brief Default constructor. */
+        resource_handle() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Creates a handle from a shared pointer, namely a resource.
+         * @param res A pointer to a properly initialized resource.
+         */
+        resource_handle(std::shared_ptr<Resource> res) ENTT_NOEXCEPT
+            : resource{ std::move(res) }
+        {}
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        resource_handle(const resource_handle<Resource>& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        resource_handle(resource_handle<Resource>&& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Copy constructs a handle which shares ownership of the resource.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to copy from.
+         */
+        template<typename Other, typename = std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>>>
+        resource_handle(const resource_handle<Other>& other) ENTT_NOEXCEPT
+            : resource{ other.resource }
+        {}
+
+        /**
+         * @brief Move constructs a handle which takes ownership of the resource.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to move from.
+         */
+        template<typename Other, typename = std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>>>
+        resource_handle(resource_handle<Other>&& other) ENTT_NOEXCEPT
+            : resource{ std::move(other.resource) }
+        {}
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This resource handle.
+         */
+        resource_handle& operator=(const resource_handle<Resource>& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This resource handle.
+         */
+        resource_handle& operator=(resource_handle<Resource>&& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Copy assignment operator from foreign handle.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to copy from.
+         * @return This resource handle.
+         */
+        template<typename Other>
+        std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>, resource_handle&>
+            operator=(const resource_handle<Other>& other) ENTT_NOEXCEPT {
+            resource = other.resource;
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator from foreign handle.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to move from.
+         * @return This resource handle.
+         */
+        template<typename Other>
+        std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>, resource_handle&>
+            operator=(resource_handle<Other>&& other) ENTT_NOEXCEPT {
+            resource = std::move(other.resource);
+            return *this;
+        }
+
+        /**
+         * @brief Gets a reference to the managed resource.
+         *
+         * @warning
+         * The behavior is undefined if the handle doesn't contain a resource.
+         *
+         * @return A reference to the managed resource.
+         */
+        [[nodiscard]] const Resource& get() const ENTT_NOEXCEPT {
+            ENTT_ASSERT(static_cast<bool>(resource), "Invalid resource");
+            return *resource;
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] Resource& get() ENTT_NOEXCEPT {
+            return const_cast<Resource&>(std::as_const(*this).get());
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] operator const Resource& () const ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] operator Resource& () ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] const Resource& operator *() const ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] Resource& operator *() ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /**
+         * @brief Gets a pointer to the managed resource.
+         *
+         * @warning
+         * The behavior is undefined if the handle doesn't contain a resource.
+         *
+         * @return A pointer to the managed resource or `nullptr` if the handle
+         * contains no resource at all.
+         */
+        [[nodiscard]] const Resource* operator->() const ENTT_NOEXCEPT {
+            return resource.get();
+        }
+
+        /*! @copydoc operator-> */
+        [[nodiscard]] Resource* operator->() ENTT_NOEXCEPT {
+            return const_cast<Resource*>(std::as_const(*this).operator->());
+        }
+
+        /**
+         * @brief Returns true if a handle contains a resource, false otherwise.
+         * @return True if the handle contains a resource, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(resource);
+        }
+
+    private:
+        std::shared_ptr<Resource> resource;
+    };
+
+
+}
+
+
+#endif
+
+// #include "loader.hpp"
+#ifndef ENTT_RESOURCE_LOADER_HPP
+#define ENTT_RESOURCE_LOADER_HPP
+
+
+// #include "fwd.hpp"
+
+// #include "handle.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Base class for resource loaders.
+     *
+     * Resource loaders must inherit from this class and stay true to the CRTP
+     * idiom. Moreover, a resource loader must expose a public, const member
+     * function named `load` that accepts a variable number of arguments and returns
+     * a handle to the resource just created.<br/>
+     * As an example:
+     *
+     * @code{.cpp}
+     * struct my_resource {};
+     *
+     * struct my_loader: entt::resource_loader<my_loader, my_resource> {
+     *     resource_handle<my_resource> load(int value) const {
+     *         // use the integer value somehow
+     *         return std::make_shared<my_resource>();
+     *     }
+     * };
+     * @endcode
+     *
+     * In general, resource loaders should not have a state or retain data of any
+     * type. They should let the cache manage their resources instead.
+     *
+     * @note
+     * Base class and CRTP idiom aren't strictly required with the current
+     * implementation. One could argue that a cache can easily work with loaders of
+     * any type. However, future changes won't be breaking ones by forcing the use
+     * of a base class today and that's why the model is already in its place.
+     *
+     * @tparam Loader Type of the derived class.
+     * @tparam Resource Type of resource for which to use the loader.
+     */
+    template<typename Loader, typename Resource>
+    class resource_loader {
+        /*! @brief Resource loaders are friends of their caches. */
+        template<typename Other>
+        friend struct resource_cache;
+
+        /**
+         * @brief Loads the resource and returns it.
+         * @tparam Args Types of arguments for the loader.
+         * @param args Arguments for the loader.
+         * @return The resource just loaded or an empty pointer in case of errors.
+         */
+        template<typename... Args>
+        [[nodiscard]] resource_handle<Resource> get(Args &&... args) const {
+            return static_cast<const Loader*>(this)->load(std::forward<Args>(args)...);
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Simple cache for resources of a given type.
+     *
+     * Minimal implementation of a cache for resources of a given type. It doesn't
+     * offer much functionalities but it's suitable for small or medium sized
+     * applications and can be freely inherited to add targeted functionalities for
+     * large sized applications.
+     *
+     * @tparam Resource Type of resources managed by a cache.
+     */
+    template<typename Resource>
+    struct resource_cache {
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Type of resources managed by a cache. */
+        using resource_type = Resource;
+
+        /*! @brief Default constructor. */
+        resource_cache() = default;
+
+        /*! @brief Default move constructor. */
+        resource_cache(resource_cache&&) = default;
+
+        /*! @brief Default move assignment operator. @return This cache. */
+        resource_cache& operator=(resource_cache&&) = default;
+
+        /**
+         * @brief Number of resources managed by a cache.
+         * @return Number of resources currently stored.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return resources.size();
+        }
+
+        /**
+         * @brief Returns true if a cache contains no resources, false otherwise.
+         * @return True if the cache contains no resources, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return resources.empty();
+        }
+
+        /**
+         * @brief Clears a cache and discards all its resources.
+         *
+         * Handles are not invalidated and the memory used by a resource isn't
+         * freed as long as at least a handle keeps the resource itself alive.
+         */
+        void clear() ENTT_NOEXCEPT {
+            resources.clear();
+        }
+
+        /**
+         * @brief Loads the resource that corresponds to a given identifier.
+         *
+         * In case an identifier isn't already present in the cache, it loads its
+         * resource and stores it aside for future uses. Arguments are forwarded
+         * directly to the loader in order to construct properly the requested
+         * resource.
+         *
+         * @note
+         * If the identifier is already present in the cache, this function does
+         * nothing and the arguments are simply discarded.
+         *
+         * @warning
+         * If the resource cannot be loaded correctly, the returned handle will be
+         * invalid and any use of it will result in undefined behavior.
+         *
+         * @tparam Loader Type of loader to use to load the resource if required.
+         * @tparam Args Types of arguments to use to load the resource if required.
+         * @param id Unique resource identifier.
+         * @param args Arguments to use to load the resource if required.
+         * @return A handle for the given resource.
+         */
+        template<typename Loader, typename... Args>
+        resource_handle<Resource> load(const id_type id, Args &&... args) {
+            if (auto it = resources.find(id); it == resources.cend()) {
+                if (auto handle = temp<Loader>(std::forward<Args>(args)...); handle) {
+                    return (resources[id] = std::move(handle));
+                }
+            }
+            else {
+                return it->second;
+            }
+
+            return {};
+        }
+
+        /**
+         * @brief Reloads a resource or loads it for the first time if not present.
+         *
+         * Equivalent to the following snippet (pseudocode):
+         *
+         * @code{.cpp}
+         * cache.discard(id);
+         * cache.load(id, args...);
+         * @endcode
+         *
+         * Arguments are forwarded directly to the loader in order to construct
+         * properly the requested resource.
+         *
+         * @warning
+         * If the resource cannot be loaded correctly, the returned handle will be
+         * invalid and any use of it will result in undefined behavior.
+         *
+         * @tparam Loader Type of loader to use to load the resource.
+         * @tparam Args Types of arguments to use to load the resource.
+         * @param id Unique resource identifier.
+         * @param args Arguments to use to load the resource.
+         * @return A handle for the given resource.
+         */
+        template<typename Loader, typename... Args>
+        resource_handle<Resource> reload(const id_type id, Args &&... args) {
+            return (discard(id), load<Loader>(id, std::forward<Args>(args)...));
+        }
+
+        /**
+         * @brief Creates a temporary handle for a resource.
+         *
+         * Arguments are forwarded directly to the loader in order to construct
+         * properly the requested resource. The handle isn't stored aside and the
+         * cache isn't in charge of the lifetime of the resource itself.
+         *
+         * @tparam Loader Type of loader to use to load the resource.
+         * @tparam Args Types of arguments to use to load the resource.
+         * @param args Arguments to use to load the resource.
+         * @return A handle for the given resource.
+         */
+        template<typename Loader, typename... Args>
+        [[nodiscard]] resource_handle<Resource> temp(Args &&... args) const {
+            return Loader{}.get(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Creates a handle for a given resource identifier.
+         *
+         * A resource handle can be in a either valid or invalid state. In other
+         * terms, a resource handle is properly initialized with a resource if the
+         * cache contains the resource itself. Otherwise the returned handle is
+         * uninitialized and accessing it results in undefined behavior.
+         *
+         * @sa resource_handle
+         *
+         * @param id Unique resource identifier.
+         * @return A handle for the given resource.
+         */
+        [[nodiscard]] resource_handle<Resource> handle(const id_type id) const {
+            if (auto it = resources.find(id); it != resources.cend()) {
+                return it->second;
+            }
+
+            return {};
+        }
+
+        /**
+         * @brief Checks if a cache contains a given identifier.
+         * @param id Unique resource identifier.
+         * @return True if the cache contains the resource, false otherwise.
+         */
+        [[nodiscard]] bool contains(const id_type id) const {
+            return (resources.find(id) != resources.cend());
+        }
+
+        /**
+         * @brief Discards the resource that corresponds to a given identifier.
+         *
+         * Handles are not invalidated and the memory used by the resource isn't
+         * freed as long as at least a handle keeps the resource itself alive.
+         *
+         * @param id Unique resource identifier.
+         */
+        void discard(const id_type id) {
+            if (auto it = resources.find(id); it != resources.end()) {
+                resources.erase(it);
+            }
+        }
+
+        /**
+         * @brief Iterates all resources.
+         *
+         * The function object is invoked for each element. It is provided with
+         * either the resource identifier, the resource handle or both of them.<br/>
+         * The signature of the function must be equivalent to one of the following
+         * forms:
+         *
+         * @code{.cpp}
+         * void(const entt::id_type);
+         * void(entt::resource_handle<Resource>);
+         * void(const entt::id_type, entt::resource_handle<Resource>);
+         * @endcode
+         *
+         * @tparam Func Type of the function object to invoke.
+         * @param func A valid function object.
+         */
+        template <typename Func>
+        void each(Func func) const {
+            auto begin = resources.begin();
+            auto end = resources.end();
+
+            while (begin != end) {
+                auto curr = begin++;
+
+                if constexpr (std::is_invocable_v<Func, id_type>) {
+                    func(curr->first);
+                }
+                else if constexpr (std::is_invocable_v<Func, resource_handle<Resource>>) {
+                    func(curr->second);
+                }
+                else {
+                    func(curr->first, curr->second);
+                }
+            }
+        }
+
+    private:
+        std::unordered_map<id_type, resource_handle<Resource>> resources;
+    };
+
+
+}
+
+
+#endif
+
+// #include "resource/handle.hpp"
+#ifndef ENTT_RESOURCE_HANDLE_HPP
+#define ENTT_RESOURCE_HANDLE_HPP
+
+
+#include <memory>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Shared resource handle.
+     *
+     * A shared resource handle is a small class that wraps a resource and keeps it
+     * alive even if it's deleted from the cache. It can be either copied or
+     * moved. A handle shares a reference to the same resource with all the other
+     * handles constructed for the same identifier.<br/>
+     * As a rule of thumb, resources should never be copied nor moved. Handles are
+     * the way to go to keep references to them.
+     *
+     * @tparam Resource Type of resource managed by a handle.
+     */
+    template<typename Resource>
+    class resource_handle {
+        /*! @brief Resource handles are friends with each other. */
+        template<typename>
+        friend class resource_handle;
+
+    public:
+        /*! @brief Default constructor. */
+        resource_handle() ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Creates a handle from a shared pointer, namely a resource.
+         * @param res A pointer to a properly initialized resource.
+         */
+        resource_handle(std::shared_ptr<Resource> res) ENTT_NOEXCEPT
+            : resource{ std::move(res) }
+        {}
+
+        /**
+         * @brief Copy constructor.
+         * @param other The instance to copy from.
+         */
+        resource_handle(const resource_handle<Resource>& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Move constructor.
+         * @param other The instance to move from.
+         */
+        resource_handle(resource_handle<Resource>&& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Copy constructs a handle which shares ownership of the resource.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to copy from.
+         */
+        template<typename Other, typename = std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>>>
+        resource_handle(const resource_handle<Other>& other) ENTT_NOEXCEPT
+            : resource{ other.resource }
+        {}
+
+        /**
+         * @brief Move constructs a handle which takes ownership of the resource.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to move from.
+         */
+        template<typename Other, typename = std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>>>
+        resource_handle(resource_handle<Other>&& other) ENTT_NOEXCEPT
+            : resource{ std::move(other.resource) }
+        {}
+
+        /**
+         * @brief Copy assignment operator.
+         * @param other The instance to copy from.
+         * @return This resource handle.
+         */
+        resource_handle& operator=(const resource_handle<Resource>& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Move assignment operator.
+         * @param other The instance to move from.
+         * @return This resource handle.
+         */
+        resource_handle& operator=(resource_handle<Resource>&& other) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Copy assignment operator from foreign handle.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to copy from.
+         * @return This resource handle.
+         */
+        template<typename Other>
+        std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>, resource_handle&>
+            operator=(const resource_handle<Other>& other) ENTT_NOEXCEPT {
+            resource = other.resource;
+            return *this;
+        }
+
+        /**
+         * @brief Move assignment operator from foreign handle.
+         * @tparam Other Type of resource managed by the received handle.
+         * @param other The handle to move from.
+         * @return This resource handle.
+         */
+        template<typename Other>
+        std::enable_if_t<!std::is_same_v<Other, Resource>&& std::is_base_of_v<Resource, Other>, resource_handle&>
+            operator=(resource_handle<Other>&& other) ENTT_NOEXCEPT {
+            resource = std::move(other.resource);
+            return *this;
+        }
+
+        /**
+         * @brief Gets a reference to the managed resource.
+         *
+         * @warning
+         * The behavior is undefined if the handle doesn't contain a resource.
+         *
+         * @return A reference to the managed resource.
+         */
+        [[nodiscard]] const Resource& get() const ENTT_NOEXCEPT {
+            ENTT_ASSERT(static_cast<bool>(resource), "Invalid resource");
+            return *resource;
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] Resource& get() ENTT_NOEXCEPT {
+            return const_cast<Resource&>(std::as_const(*this).get());
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] operator const Resource& () const ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] operator Resource& () ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] const Resource& operator *() const ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /*! @copydoc get */
+        [[nodiscard]] Resource& operator *() ENTT_NOEXCEPT {
+            return get();
+        }
+
+        /**
+         * @brief Gets a pointer to the managed resource.
+         *
+         * @warning
+         * The behavior is undefined if the handle doesn't contain a resource.
+         *
+         * @return A pointer to the managed resource or `nullptr` if the handle
+         * contains no resource at all.
+         */
+        [[nodiscard]] const Resource* operator->() const ENTT_NOEXCEPT {
+            return resource.get();
+        }
+
+        /*! @copydoc operator-> */
+        [[nodiscard]] Resource* operator->() ENTT_NOEXCEPT {
+            return const_cast<Resource*>(std::as_const(*this).operator->());
+        }
+
+        /**
+         * @brief Returns true if a handle contains a resource, false otherwise.
+         * @return True if the handle contains a resource, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(resource);
+        }
+
+    private:
+        std::shared_ptr<Resource> resource;
+    };
+
+
+}
+
+
+#endif
+
+// #include "resource/loader.hpp"
+#ifndef ENTT_RESOURCE_LOADER_HPP
+#define ENTT_RESOURCE_LOADER_HPP
+
+
+// #include "fwd.hpp"
+
+// #include "handle.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Base class for resource loaders.
+     *
+     * Resource loaders must inherit from this class and stay true to the CRTP
+     * idiom. Moreover, a resource loader must expose a public, const member
+     * function named `load` that accepts a variable number of arguments and returns
+     * a handle to the resource just created.<br/>
+     * As an example:
+     *
+     * @code{.cpp}
+     * struct my_resource {};
+     *
+     * struct my_loader: entt::resource_loader<my_loader, my_resource> {
+     *     resource_handle<my_resource> load(int value) const {
+     *         // use the integer value somehow
+     *         return std::make_shared<my_resource>();
+     *     }
+     * };
+     * @endcode
+     *
+     * In general, resource loaders should not have a state or retain data of any
+     * type. They should let the cache manage their resources instead.
+     *
+     * @note
+     * Base class and CRTP idiom aren't strictly required with the current
+     * implementation. One could argue that a cache can easily work with loaders of
+     * any type. However, future changes won't be breaking ones by forcing the use
+     * of a base class today and that's why the model is already in its place.
+     *
+     * @tparam Loader Type of the derived class.
+     * @tparam Resource Type of resource for which to use the loader.
+     */
+    template<typename Loader, typename Resource>
+    class resource_loader {
+        /*! @brief Resource loaders are friends of their caches. */
+        template<typename Other>
+        friend struct resource_cache;
+
+        /**
+         * @brief Loads the resource and returns it.
+         * @tparam Args Types of arguments for the loader.
+         * @param args Arguments for the loader.
+         * @return The resource just loaded or an empty pointer in case of errors.
+         */
+        template<typename... Args>
+        [[nodiscard]] resource_handle<Resource> get(Args &&... args) const {
+            return static_cast<const Loader*>(this)->load(std::forward<Args>(args)...);
+        }
+    };
+
+
+}
+
+
+#endif
+
+// #include "signal/delegate.hpp"
+#ifndef ENTT_SIGNAL_DELEGATE_HPP
+#define ENTT_SIGNAL_DELEGATE_HPP
+
+
+#include <tuple>
+#include <cstddef>
+#include <utility>
+#include <functional>
+#include <type_traits>
+// #include "../core/type_traits.hpp"
+#ifndef ENTT_CORE_TYPE_TRAITS_HPP
+#define ENTT_CORE_TYPE_TRAITS_HPP
+
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Utility class to disambiguate overloaded functions.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    struct choice_t
+        // Unfortunately, doxygen cannot parse such a construct.
+        /*! @cond TURN_OFF_DOXYGEN */
+        : choice_t<N - 1>
+        /*! @endcond */
+    {};
+
+
+    /*! @copybrief choice_t */
+    template<>
+    struct choice_t<0> {};
+
+
+    /**
+     * @brief Variable template for the choice trick.
+     * @tparam N Number of choices available.
+     */
+    template<std::size_t N>
+    inline constexpr choice_t<N> choice{};
+
+
+    /**
+     * @brief Identity type trait.
+     *
+     * Useful to establish non-deduced contexts in template argument deduction
+     * (waiting for C++20) or to provide types through function arguments.
+     *
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    struct type_identity {
+        /*! @brief Identity type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type.
+     */
+    template<typename Type>
+    using type_identity_t = typename type_identity<Type>::type;
+
+
+    /**
+     * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
+     * @tparam Type The type of which to return the size.
+     * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
+     */
+    template<typename Type, typename = void>
+    struct size_of : std::integral_constant<std::size_t, 0u> {};
+
+
+    /*! @copydoc size_of */
+    template<typename Type>
+    struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
+        : std::integral_constant<std::size_t, sizeof(Type)>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type of which to return the size.
+     */
+    template<class Type>
+    inline constexpr std::size_t size_of_v = size_of<Type>::value;
+
+
+    /**
+     * @brief Using declaration to be used to _repeat_ the same type a number of
+     * times equal to the size of a given parameter pack.
+     * @tparam Type A type to repeat.
+     */
+    template<typename Type, typename>
+    using unpack_as_t = Type;
+
+
+    /**
+     * @brief Helper variable template to be used to _repeat_ the same value a
+     * number of times equal to the size of a given parameter pack.
+     * @tparam Value A value to repeat.
+     */
+    template<auto Value, typename>
+    inline constexpr auto unpack_as_v = Value;
+
+
+    /**
+     * @brief Wraps a static constant.
+     * @tparam Value A static constant.
+     */
+    template<auto Value>
+    using integral_constant = std::integral_constant<decltype(Value), Value>;
+
+
+    /**
+     * @brief Alias template to facilitate the creation of named values.
+     * @tparam Value A constant value at least convertible to `id_type`.
+     */
+    template<id_type Value>
+    using tag = integral_constant<Value>;
+
+
+    /**
+     * @brief A class to use to push around lists of types, nothing more.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list {
+        /*! @brief Type list type. */
+        using type = type_list;
+        /*! @brief Compile-time number of elements in the type list. */
+        static constexpr auto size = sizeof...(Type);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct type_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Index Index of the type to return.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<std::size_t Index, typename Type, typename... Other>
+    struct type_list_element<Index, type_list<Type, Other...>>
+        : type_list_element<Index - 1u, type_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Type First type provided by the type list.
+     * @tparam Other Other types provided by the type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_element<0u, type_list<Type, Other...>> {
+        /*! @brief Searched type. */
+        using type = Type;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the type to return.
+     * @tparam List Type list to search into.
+     */
+    template<std::size_t Index, typename List>
+    using type_list_element_t = typename type_list_element<Index, List>::type;
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @return A type list composed by the types of both the type lists.
+     */
+    template<typename... Type, typename... Other>
+    constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_cat;
+
+
+    /*! @brief Concatenates multiple type lists. */
+    template<>
+    struct type_list_cat<> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     * @tparam List Other type lists, if any.
+     */
+    template<typename... Type, typename... Other, typename... List>
+    struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple type lists.
+     * @tparam Type Types provided by the type list.
+     */
+    template<typename... Type>
+    struct type_list_cat<type_list<Type...>> {
+        /*! @brief A type list composed by the types of all the type lists. */
+        using type = type_list<Type...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists to concatenate.
+     */
+    template<typename... List>
+    using type_list_cat_t = typename type_list_cat<List...>::type;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename>
+    struct type_list_unique;
+
+
+    /**
+     * @brief Removes duplicates types from a type list.
+     * @tparam Type One of the types provided by the given type list.
+     * @tparam Other The other types provided by the given type list.
+     */
+    template<typename Type, typename... Other>
+    struct type_list_unique<type_list<Type, Other...>> {
+        /*! @brief A type list without duplicate types. */
+        using type = std::conditional_t<
+            std::disjunction_v<std::is_same<Type, Other>...>,
+            typename type_list_unique<type_list<Other...>>::type,
+            type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>
+        >;
+    };
+
+
+    /*! @brief Removes duplicates types from a type list. */
+    template<>
+    struct type_list_unique<type_list<>> {
+        /*! @brief A type list without duplicate types. */
+        using type = type_list<>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Type A type list.
+     */
+    template<typename Type>
+    using type_list_unique_t = typename type_list_unique<Type>::type;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a type list contains a
+     * given type, false otherwise.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<typename List, typename Type>
+    struct type_list_contains;
+
+
+    /**
+     * @copybrief type_list_contains
+     * @tparam Type Types provided by the type list.
+     * @tparam Other Type to look for.
+     */
+    template<typename... Type, typename Other>
+    struct type_list_contains<type_list<Type...>, Other> : std::disjunction<std::is_same<Type, Other>...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam List Type list.
+     * @tparam Type Type to look for.
+     */
+    template<class List, typename Type>
+    inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct type_list_diff;
+
+
+    /**
+     * @brief Computes the difference between two type lists.
+     * @tparam Type Types provided by the first type list.
+     * @tparam Other Types provided by the second type list.
+     */
+    template<typename... Type, typename... Other>
+    struct type_list_diff<type_list<Type...>, type_list<Other...>> {
+        /*! @brief A type list that is the difference between the two type lists. */
+        using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Type lists between which to compute the difference.
+     */
+    template<typename... List>
+    using type_list_diff_t = typename type_list_diff<List...>::type;
+
+
+    /**
+     * @brief A class to use to push around lists of constant values, nothing more.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list {
+        /*! @brief Value list type. */
+        using type = value_list;
+        /*! @brief Compile-time number of elements in the value list. */
+        static constexpr auto size = sizeof...(Value);
+    };
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<std::size_t, typename>
+    struct value_list_element;
+
+
+    /**
+     * @brief Provides compile-time indexed access to the values of a value list.
+     * @tparam Index Index of the value to return.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<std::size_t Index, auto Value, auto... Other>
+    struct value_list_element<Index, value_list<Value, Other...>>
+        : value_list_element<Index - 1u, value_list<Other...>>
+    {};
+
+
+    /**
+     * @brief Provides compile-time indexed access to the types of a type list.
+     * @tparam Value First value provided by the value list.
+     * @tparam Other Other values provided by the value list.
+     */
+    template<auto Value, auto... Other>
+    struct value_list_element<0u, value_list<Value, Other...>> {
+        /*! @brief Searched value. */
+        static constexpr auto value = Value;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Index Index of the value to return.
+     * @tparam List Value list to search into.
+     */
+    template<std::size_t Index, typename List>
+    inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @return A value list composed by the values of both the value lists.
+     */
+    template<auto... Value, auto... Other>
+    constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) { return {}; }
+
+
+    /*! @brief Primary template isn't defined on purpose. */
+    template<typename...>
+    struct value_list_cat;
+
+
+    /*! @brief Concatenates multiple value lists. */
+    template<>
+    struct value_list_cat<> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<>;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the first value list.
+     * @tparam Other Values provided by the second value list.
+     * @tparam List Other value lists, if any.
+     */
+    template<auto... Value, auto... Other, typename... List>
+    struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
+    };
+
+
+    /**
+     * @brief Concatenates multiple value lists.
+     * @tparam Value Values provided by the value list.
+     */
+    template<auto... Value>
+    struct value_list_cat<value_list<Value...>> {
+        /*! @brief A value list composed by the values of all the value lists. */
+        using type = value_list<Value...>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam List Value lists to concatenate.
+     */
+    template<typename... List>
+    using value_list_cat_t = typename value_list_cat<List...>::type;
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        [[nodiscard]] constexpr bool is_equality_comparable(...) { return false; }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<0>)
+            -> decltype(std::declval<Type>() == std::declval<Type>()) {
+            return true;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<1>)
+            -> decltype(std::declval<typename Type::value_type>(), std::declval<Type>() == std::declval<Type>()) {
+            if constexpr (std::is_same_v<typename Type::value_type, Type>) {
+                return is_equality_comparable<Type>(choice<0>);
+            }
+            else {
+                return is_equality_comparable<typename Type::value_type>(choice<2>);
+            }
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto is_equality_comparable(choice_t<2>)
+            -> decltype(std::declval<typename Type::mapped_type>(), std::declval<Type>() == std::declval<Type>()) {
+            return is_equality_comparable<typename Type::key_type>(choice<2>) && is_equality_comparable<typename Type::mapped_type>(choice<2>);
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Provides the member constant `value` to true if a given type is
+      * equality comparable, false otherwise.
+      * @tparam Type The type to test.
+      */
+    template<typename Type, typename = void>
+    struct is_equality_comparable : std::bool_constant<internal::is_equality_comparable<Type>(choice<2>)> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<class Type>
+    inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;
+
+
+    /*! @brief Same as std::is_invocable, but with tuples. */
+    template<typename, typename>
+    struct is_applicable : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @copybrief is_applicable
+     * @tparam Func A valid function type.
+     * @tparam Tuple Tuple-like type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, template<typename...> class Tuple, typename... Args>
+    struct is_applicable<Func, const Tuple<Args...>> : std::is_invocable<Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Func, typename Args>
+    inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;
+
+
+    /*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
+    template<typename, typename, typename>
+    struct is_applicable_r : std::false_type {};
+
+
+    /**
+     * @copybrief is_applicable_r
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename... Args>
+    struct is_applicable_r<Ret, Func, std::tuple<Args...>> : std::is_invocable_r<Ret, Func, Args...> {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Ret The type to which the return type of the function should be
+     * convertible.
+     * @tparam Func A valid function type.
+     * @tparam Args The list of arguments to use to probe the function type.
+     */
+    template<typename Ret, typename Func, typename Args>
+    inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is
+     * complete, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_complete : std::false_type {};
+
+
+    /*! @copydoc is_complete */
+    template<typename Type>
+    struct is_complete<Type, std::void_t<decltype(sizeof(Type))>> : std::true_type {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_complete_v = is_complete<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is an
+     * iterator, false otherwise.
+     * @tparam Type The type to test.
+     */
+    template<typename Type, typename = void>
+    struct is_iterator : std::false_type {};
+
+
+    /*! @copydoc is_iterator */
+    template<typename Type>
+    struct is_iterator<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>
+        : std::true_type
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     */
+    template<typename Type>
+    inline constexpr bool is_iterator_v = is_iterator<Type>::value;
+
+
+    /**
+     * @brief Provides the member constant `value` to true if a given type is of the
+     * required iterator type, false otherwise.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It, typename = void>
+    struct is_iterator_type : std::false_type {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<is_iterator_v<Type>&& std::is_same_v<Type, It>>>
+        : std::true_type
+    {};
+
+
+    /*! @copydoc is_iterator_type */
+    template<typename Type, typename It>
+    struct is_iterator_type<Type, It, std::enable_if_t<!std::is_same_v<Type, It>, std::void_t<typename It::iterator_type>>>
+        : is_iterator_type<Type, typename It::iterator_type>
+    {};
+
+
+    /**
+     * @brief Helper variable template.
+     * @tparam Type The type to test.
+     * @tparam It Required iterator type.
+     */
+    template<typename Type, typename It>
+    inline constexpr bool is_iterator_type_v = is_iterator_type<Type, It>::value;
+
+
+    /**
+     * @brief Transcribes the constness of a type to another type.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    struct constness_as {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::remove_const_t<To>;
+    };
+
+
+    /*! @copydoc constness_as */
+    template<typename To, typename From>
+    struct constness_as<To, const From> {
+        /*! @brief The type resulting from the transcription of the constness. */
+        using type = std::add_const_t<To>;
+    };
+
+
+    /**
+     * @brief Alias template to facilitate the transcription of the constness.
+     * @tparam To The type to which to transcribe the constness.
+     * @tparam From The type from which to transcribe the constness.
+     */
+    template<typename To, typename From>
+    using constness_as_t = typename constness_as<To, From>::type;
+
+
+    /**
+     * @brief Extracts the class of a non-static member object or function.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    class member_class {
+        static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...));
+
+        template<typename Class, typename Ret, typename... Args>
+        static Class* clazz(Ret(Class::*)(Args...) const);
+
+        template<typename Class, typename Type>
+        static Class* clazz(Type Class::*);
+
+    public:
+        /*! @brief The class of the given non-static member object or function. */
+        using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
+    };
+
+
+    /**
+     * @brief Helper type.
+     * @tparam Member A pointer to a non-static member object or function.
+     */
+    template<typename Member>
+    using member_class_t = typename member_class<Member>::type;
+
+
+}
+
+
+#endif
+
+// #include "../config/config.h"
+#ifndef ENTT_CONFIG_CONFIG_H
+#define ENTT_CONFIG_CONFIG_H
+
+
+#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
+#   define ENTT_NOEXCEPT noexcept
+#   define ENTT_THROW throw
+#   define ENTT_TRY try
+#   define ENTT_CATCH catch(...)
+#else
+#   define ENTT_NOEXCEPT
+#   define ENTT_THROW
+#   define ENTT_TRY if(true)
+#   define ENTT_CATCH if(false)
+#endif
+
+
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L
+#   include <new>
+#   define ENTT_LAUNDER(expr) std::launder(expr)
+#else
+#   define ENTT_LAUNDER(expr) expr
+#endif
+
+
+#ifndef ENTT_USE_ATOMIC
+#   define ENTT_MAYBE_ATOMIC(Type) Type
+#else
+#   include <atomic>
+#   define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
+#endif
+
+
+#ifndef ENTT_ID_TYPE
+#   include <cstdint>
+#   define ENTT_ID_TYPE std::uint32_t
+#endif
+
+
+#ifdef ENTT_SPARSE_PAGE
+static_assert(ENTT_SPARSE_PAGE && ((ENTT_SPARSE_PAGE& (ENTT_SPARSE_PAGE - 1)) == 0), "ENTT_SPARSE_PAGE must be a power of two");
+#else
+#   define ENTT_SPARSE_PAGE 4096
+#endif
+
+
+#ifdef ENTT_PACKED_PAGE
+static_assert(ENTT_PACKED_PAGE && ((ENTT_PACKED_PAGE& (ENTT_PACKED_PAGE - 1)) == 0), "ENTT_PACKED_PAGE must be a power of two");
+#else
+#   define ENTT_PACKED_PAGE 1024
+#endif
+
+
+#ifdef ENTT_DISABLE_ASSERT
+#   undef ENTT_ASSERT
+#   define ENTT_ASSERT(...) (void(0))
+#elif !defined ENTT_ASSERT
+#   include <cassert>
+#   define ENTT_ASSERT(condition, ...) assert(condition)
+#endif
+
+
+#ifdef ENTT_NO_ETO
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::false_type
+#else
+#   include <type_traits>
+#   define ENTT_IGNORE_IF_EMPTY std::true_type
+#endif
+
+
+#ifndef ENTT_STANDARD_CPP
+#    if defined __clang__ || defined __GNUC__
+#       define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '='
+#       define ENTT_PRETTY_FUNCTION_SUFFIX ']'
+#    elif defined _MSC_VER
+#       define ENTT_PRETTY_FUNCTION __FUNCSIG__
+#       define ENTT_PRETTY_FUNCTION_PREFIX '<'
+#       define ENTT_PRETTY_FUNCTION_SUFFIX '>'
+#   endif
+#endif
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Ret, typename... Args>
+        auto function_pointer(Ret(*)(Args...))->Ret(*)(Args...);
+
+
+        template<typename Ret, typename Type, typename... Args, typename Other>
+        auto function_pointer(Ret(*)(Type, Args...), Other&&)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...), Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...) const, Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Type, typename... Other>
+        auto function_pointer(Type Class::*, Other &&...)->Type(*)();
+
+
+        template<typename... Type>
+        using function_pointer_t = decltype(internal::function_pointer(std::declval<Type>()...));
+
+
+        template<typename... Class, typename Ret, typename... Args>
+        [[nodiscard]] constexpr auto index_sequence_for(Ret(*)(Args...)) {
+            return std::index_sequence_for<Class..., Args...>{};
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Used to wrap a function or a member of a specified type. */
+    template<auto>
+    struct connect_arg_t {};
+
+
+    /*! @brief Constant of type connect_arg_t used to disambiguate calls. */
+    template<auto Func>
+    inline constexpr connect_arg_t<Func> connect_arg{};
+
+
+    /**
+     * @brief Basic delegate implementation.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     */
+    template<typename>
+    class delegate;
+
+
+    /**
+     * @brief Utility class to use to send around functions and members.
+     *
+     * Unmanaged delegate for function pointers and members. Users of this class are
+     * in charge of disconnecting instances before deleting them.
+     *
+     * A delegate can be used as a general purpose invoker without memory overhead
+     * for free functions possibly with payloads and bound or unbound members.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class delegate<Ret(Args...)> {
+        template<auto Candidate, std::size_t... Index>
+        [[nodiscard]] auto wrap(std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void*, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type&, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type*, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+    public:
+        /*! @brief Function type of the contained target. */
+        using function_type = Ret(const void*, Args...);
+        /*! @brief Function type of the delegate. */
+        using type = Ret(Args...);
+        /*! @brief Return type of the delegate. */
+        using result_type = Ret;
+
+        /*! @brief Default constructor. */
+        delegate() ENTT_NOEXCEPT
+            : fn{ nullptr }, data{ nullptr }
+        {}
+
+        /**
+         * @brief Constructs a delegate and connects a free function or an unbound
+         * member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        delegate(connect_arg_t<Candidate>) ENTT_NOEXCEPT {
+            connect<Candidate>();
+        }
+
+        /**
+         * @brief Constructs a delegate and connects a free function with payload or
+         * a bound member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        delegate(connect_arg_t<Candidate>, Type&& value_or_instance) ENTT_NOEXCEPT {
+            connect<Candidate>(std::forward<Type>(value_or_instance));
+        }
+
+        /**
+         * @brief Constructs a delegate and connects an user defined function with
+         * optional payload.
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        delegate(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            connect(function, payload);
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a delegate.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        void connect() ENTT_NOEXCEPT {
+            data = nullptr;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
+                fn = [](const void*, Args... args) -> Ret {
+                    return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
+                };
+            }
+            else if constexpr (std::is_member_pointer_v<decltype(Candidate)>) {
+                fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+            else {
+                fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the delegate.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the delegate itself.
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid reference that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type& value_or_instance) ENTT_NOEXCEPT {
+            data = &value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type&, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * @sa connect(Type &)
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type* value_or_instance) ENTT_NOEXCEPT {
+            data = value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type*, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects an user defined function with optional payload to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of an instance overcomes
+         * the one of the delegate.<br/>
+         * The payload is returned as the first argument to the target function in
+         * all cases.
+         *
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        void connect(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            fn = function;
+            data = payload;
+        }
+
+        /**
+         * @brief Resets a delegate.
+         *
+         * After a reset, a delegate cannot be invoked anymore.
+         */
+        void reset() ENTT_NOEXCEPT {
+            fn = nullptr;
+            data = nullptr;
+        }
+
+        /**
+         * @brief Returns the instance or the payload linked to a delegate, if any.
+         * @return An opaque pointer to the underlying data.
+         */
+        [[nodiscard]] const void* instance() const ENTT_NOEXCEPT {
+            return data;
+        }
+
+        /**
+         * @brief Triggers a delegate.
+         *
+         * The delegate invokes the underlying function and returns the result.
+         *
+         * @warning
+         * Attempting to trigger an invalid delegate results in undefined
+         * behavior.
+         *
+         * @param args Arguments to use to invoke the underlying function.
+         * @return The value returned by the underlying function.
+         */
+        Ret operator()(Args... args) const {
+            ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
+            return fn(data, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Checks whether a delegate actually stores a listener.
+         * @return False if the delegate is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            // no need to test also data
+            return !(fn == nullptr);
+        }
+
+        /**
+         * @brief Compares the contents of two delegates.
+         * @param other Delegate with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const delegate<Ret(Args...)>& other) const ENTT_NOEXCEPT {
+            return fn == other.fn && data == other.data;
+        }
+
+    private:
+        function_type* fn;
+        const void* data;
+    };
+
+
+    /**
+     * @brief Compares the contents of two delegates.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     * @param lhs A valid delegate object.
+     * @param rhs A valid delegate object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    template<typename Ret, typename... Args>
+    [[nodiscard]] bool operator!=(const delegate<Ret(Args...)>& lhs, const delegate<Ret(Args...)>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     */
+    template<auto Candidate>
+    delegate(connect_arg_t<Candidate>)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     * @tparam Type Type of class or type of payload.
+     */
+    template<auto Candidate, typename Type>
+    delegate(connect_arg_t<Candidate>, Type&&)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    delegate(Ret(*)(const void*, Args...), const void* = nullptr)
+        ->delegate<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
+// #include "signal/dispatcher.hpp"
+#ifndef ENTT_SIGNAL_DISPATCHER_HPP
+#define ENTT_SIGNAL_DISPATCHER_HPP
+
+
+#include <cstddef>
+#include <memory>
+#include <type_traits>
+#include <utility>
+#include <vector>
+// #include "../config/config.h"
+
+// #include "../core/fwd.hpp"
+#ifndef ENTT_CORE_FWD_HPP
+#define ENTT_CORE_FWD_HPP
+
+
+#include <type_traits>
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(typename std::aligned_storage_t<Len + !Len>)>
+    class basic_any;
+
+
+    /*! @brief Alias declaration for type identifiers. */
+    using id_type = ENTT_ID_TYPE;
+
+
+    /*! @brief Alias declaration for the most common use case. */
+    using any = basic_any<>;
+
+
+}
+
+
+#endif
+
+// #include "../core/type_info.hpp"
+#ifndef ENTT_CORE_TYPE_INFO_HPP
+#define ENTT_CORE_TYPE_INFO_HPP
+
+
+#include <string_view>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "../core/attribute.h"
+#ifndef ENTT_CORE_ATTRIBUTE_H
+#define ENTT_CORE_ATTRIBUTE_H
+
+
+#ifndef ENTT_EXPORT
+#   if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
+#       define ENTT_EXPORT __declspec(dllexport)
+#       define ENTT_IMPORT __declspec(dllimport)
+#       define ENTT_HIDDEN
+#   elif defined __GNUC__ && __GNUC__ >= 4
+#       define ENTT_EXPORT __attribute__((visibility("default")))
+#       define ENTT_IMPORT __attribute__((visibility("default")))
+#       define ENTT_HIDDEN __attribute__((visibility("hidden")))
+#   else /* Unsupported compiler */
+#       define ENTT_EXPORT
+#       define ENTT_IMPORT
+#       define ENTT_HIDDEN
+#   endif
+#endif
+
+
+#ifndef ENTT_API
+#   if defined ENTT_API_EXPORT
+#       define ENTT_API ENTT_EXPORT
+#   elif defined ENTT_API_IMPORT
+#       define ENTT_API ENTT_IMPORT
+#   else /* No API */
+#       define ENTT_API
+#   endif
+#endif
+
+
+#endif
+
+// #include "hashed_string.hpp"
+#ifndef ENTT_CORE_HASHED_STRING_HPP
+#define ENTT_CORE_HASHED_STRING_HPP
+
+
+#include <cstddef>
+#include <cstdint>
+// #include "../config/config.h"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename>
+        struct fnv1a_traits;
+
+
+        template<>
+        struct fnv1a_traits<std::uint32_t> {
+            using type = std::uint32_t;
+            static constexpr std::uint32_t offset = 2166136261;
+            static constexpr std::uint32_t prime = 16777619;
+        };
+
+
+        template<>
+        struct fnv1a_traits<std::uint64_t> {
+            using type = std::uint64_t;
+            static constexpr std::uint64_t offset = 14695981039346656037ull;
+            static constexpr std::uint64_t prime = 1099511628211ull;
+        };
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Zero overhead unique identifier.
+      *
+      * A hashed string is a compile-time tool that allows users to use
+      * human-readable identifers in the codebase while using their numeric
+      * counterparts at runtime.<br/>
+      * Because of that, a hashed string can also be used in constant expressions if
+      * required.
+      *
+      * @tparam Char Character type.
+      */
+    template<typename Char>
+    class basic_hashed_string {
+        using traits_type = internal::fnv1a_traits<id_type>;
+
+        struct const_wrapper {
+            // non-explicit constructor on purpose
+            constexpr const_wrapper(const Char* curr) ENTT_NOEXCEPT: str{ curr } {}
+            const Char* str;
+        };
+
+        // Fowler–Noll–Vo hash function v. 1a - the good
+        [[nodiscard]] static constexpr id_type helper(const Char* curr) ENTT_NOEXCEPT {
+            auto value = traits_type::offset;
+
+            while (*curr != 0) {
+                value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
+            }
+
+            return value;
+        }
+
+    public:
+        /*! @brief Character type. */
+        using value_type = Char;
+        /*! @brief Unsigned integer type. */
+        using hash_type = id_type;
+
+        /**
+         * @brief Returns directly the numeric representation of a string view.
+         * @param str Human-readable identifer.
+         * @param size Length of the string to hash.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static constexpr hash_type value(const value_type* str, std::size_t size) ENTT_NOEXCEPT {
+            id_type partial{ traits_type::offset };
+            while (size--) { partial = (partial ^ (str++)[0]) * traits_type::prime; }
+            return partial;
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * const auto value = basic_hashed_string<char>::to_value("my.png");
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param str Human-readable identifer.
+         * @return The numeric representation of the string.
+         */
+        template<std::size_t N>
+        [[nodiscard]] static constexpr hash_type value(const value_type(&str)[N]) ENTT_NOEXCEPT {
+            return helper(str);
+        }
+
+        /**
+         * @brief Returns directly the numeric representation of a string.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         * @return The numeric representation of the string.
+         */
+        [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
+            return helper(wrapper.str);
+        }
+
+        /*! @brief Constructs an empty hashed string. */
+        constexpr basic_hashed_string() ENTT_NOEXCEPT
+            : str{ nullptr }, hash{}
+        {}
+
+        /**
+         * @brief Constructs a hashed string from an array of const characters.
+         *
+         * Forcing template resolution avoids implicit conversions. An
+         * human-readable identifier can be anything but a plain, old bunch of
+         * characters.<br/>
+         * Example of use:
+         * @code{.cpp}
+         * basic_hashed_string<char> hs{"my.png"};
+         * @endcode
+         *
+         * @tparam N Number of characters of the identifier.
+         * @param curr Human-readable identifer.
+         */
+        template<std::size_t N>
+        constexpr basic_hashed_string(const value_type(&curr)[N]) ENTT_NOEXCEPT
+            : str{ curr }, hash{ helper(curr) }
+        {}
+
+        /**
+         * @brief Explicit constructor on purpose to avoid constructing a hashed
+         * string directly from a `const value_type *`.
+         * @param wrapper Helps achieving the purpose by relying on overloading.
+         */
+        explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
+            : str{ wrapper.str }, hash{ helper(wrapper.str) }
+        {}
+
+        /**
+         * @brief Returns the human-readable representation of a hashed string.
+         * @return The string used to initialize the instance.
+         */
+        [[nodiscard]] constexpr const value_type* data() const ENTT_NOEXCEPT {
+            return str;
+        }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
+            return hash;
+        }
+
+        /*! @copydoc data */
+        [[nodiscard]] constexpr operator const value_type* () const ENTT_NOEXCEPT { return data(); }
+
+        /**
+         * @brief Returns the numeric representation of a hashed string.
+         * @return The numeric representation of the instance.
+         */
+        [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
+
+        /**
+         * @brief Compares two hashed strings.
+         * @param other Hashed string with which to compare.
+         * @return True if the two hashed strings are identical, false otherwise.
+         */
+        [[nodiscard]] constexpr bool operator==(const basic_hashed_string& other) const ENTT_NOEXCEPT {
+            return hash == other.hash;
+        }
+
+    private:
+        const value_type* str;
+        hash_type hash;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the character type of the hashed string directly from a
+     * human-readable identifer provided to the constructor.
+     *
+     * @tparam Char Character type.
+     * @tparam N Number of characters of the identifier.
+     * @param str Human-readable identifer.
+     */
+    template<typename Char, std::size_t N>
+    basic_hashed_string(const Char(&str)[N])
+        ->basic_hashed_string<Char>;
+
+
+    /**
+     * @brief Compares two hashed strings.
+     * @tparam Char Character type.
+     * @param lhs A valid hashed string.
+     * @param rhs A valid hashed string.
+     * @return True if the two hashed strings are identical, false otherwise.
+     */
+    template<typename Char>
+    [[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char>& lhs, const basic_hashed_string<Char>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_string = basic_hashed_string<char>;
+
+
+    /*! @brief Aliases for common character types. */
+    using hashed_wstring = basic_hashed_string<wchar_t>;
+
+
+    inline namespace literals {
+
+
+        /**
+         * @brief User defined literal for hashed strings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed string.
+         */
+        [[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_string{ str };
+        }
+
+
+        /**
+         * @brief User defined literal for hashed wstrings.
+         * @param str The literal without its suffix.
+         * @return A properly initialized hashed wstring.
+         */
+        [[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t* str, std::size_t) ENTT_NOEXCEPT {
+            return entt::hashed_wstring{ str };
+        }
+
+
+    }
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        struct ENTT_API type_seq final {
+            [[nodiscard]] static id_type next() ENTT_NOEXCEPT {
+                static ENTT_MAYBE_ATOMIC(id_type) value {};
+                return value++;
+            }
+        };
+
+
+        template<typename Type>
+        [[nodiscard]] constexpr auto stripped_type_name() ENTT_NOEXCEPT {
+#if defined ENTT_PRETTY_FUNCTION
+            std::string_view pretty_function{ ENTT_PRETTY_FUNCTION };
+            auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
+            auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
+            return value;
+#else
+            return std::string_view{ "" };
+#endif
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr std::string_view type_name(int) ENTT_NOEXCEPT {
+            constexpr auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static std::string_view type_name(char) ENTT_NOEXCEPT {
+            static const auto value = stripped_type_name<Type>();
+            return value;
+        }
+
+
+        template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
+        [[nodiscard]] static constexpr id_type type_hash(int) ENTT_NOEXCEPT {
+            constexpr auto stripped = stripped_type_name<Type>();
+            constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
+            return value;
+        }
+
+
+        template<typename Type>
+        [[nodiscard]] static id_type type_hash(char) ENTT_NOEXCEPT {
+            static const auto value = [](const auto stripped) {
+                return hashed_string::value(stripped.data(), stripped.size());
+            }(stripped_type_name<Type>());
+            return value;
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /**
+      * @brief Type sequential identifier.
+      * @tparam Type Type for which to generate a sequential identifier.
+      */
+    template<typename Type, typename = void>
+    struct ENTT_API type_seq final {
+        /**
+         * @brief Returns the sequential identifier of a given type.
+         * @return The sequential identifier of a given type.
+         */
+        [[nodiscard]] static id_type value() ENTT_NOEXCEPT {
+            static const id_type value = internal::type_seq::next();
+            return value;
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /**
+     * @brief Type hash.
+     * @tparam Type Type for which to generate a hash value.
+     */
+    template<typename Type, typename = void>
+    struct type_hash final {
+        /**
+         * @brief Returns the numeric representation of a given type.
+         * @return The numeric representation of the given type.
+         */
+#if defined ENTT_PRETTY_FUNCTION
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return internal::type_hash<Type>(0);
+#else
+        [[nodiscard]] static constexpr id_type value() ENTT_NOEXCEPT {
+            return type_seq<Type>::value();
+#endif
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator id_type() const ENTT_NOEXCEPT { return value(); }
+        };
+
+
+    /**
+     * @brief Type name.
+     * @tparam Type Type for which to generate a name.
+     */
+    template<typename Type, typename = void>
+    struct type_name final {
+        /**
+         * @brief Returns the name of a given type.
+         * @return The name of the given type.
+         */
+        [[nodiscard]] static constexpr std::string_view value() ENTT_NOEXCEPT {
+            return internal::type_name<Type>(0);
+        }
+
+        /*! @copydoc value */
+        [[nodiscard]] constexpr operator std::string_view() const ENTT_NOEXCEPT { return value(); }
+    };
+
+
+    /*! @brief Implementation specific information about a type. */
+    class type_info final {
+        template<typename>
+        friend type_info type_id() ENTT_NOEXCEPT;
+
+        type_info(id_type seq_v, id_type hash_v, std::string_view name_v) ENTT_NOEXCEPT
+            : seq_value{ seq_v },
+            hash_value{ hash_v },
+            name_value{ name_v }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        type_info() ENTT_NOEXCEPT
+            : type_info({}, {}, {})
+        {}
+
+        /*! @brief Default copy constructor. */
+        type_info(const type_info&) ENTT_NOEXCEPT = default;
+        /*! @brief Default move constructor. */
+        type_info(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default copy assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(const type_info&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Default move assignment operator.
+         * @return This type info object.
+         */
+        type_info& operator=(type_info&&) ENTT_NOEXCEPT = default;
+
+        /**
+         * @brief Checks if a type info object is properly initialized.
+         * @return True if the object is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return name_value.data() != nullptr;
+        }
+
+        /**
+         * @brief Type sequential identifier.
+         * @return Type sequential identifier.
+         */
+        [[nodiscard]] id_type seq() const ENTT_NOEXCEPT {
+            return seq_value;
+        }
+
+        /**
+         * @brief Type hash.
+         * @return Type hash.
+         */
+        [[nodiscard]] id_type hash() const ENTT_NOEXCEPT {
+            return hash_value;
+        }
+
+        /**
+         * @brief Type name.
+         * @return Type name.
+         */
+        [[nodiscard]] std::string_view name() const ENTT_NOEXCEPT {
+            return name_value;
+        }
+
+        /**
+         * @brief Compares the contents of two type info objects.
+         * @param other Object with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const type_info& other) const ENTT_NOEXCEPT {
+            return hash_value == other.hash_value;
+        }
+
+    private:
+        id_type seq_value;
+        id_type hash_value;
+        std::string_view name_value;
+    };
+
+
+    /**
+     * @brief Compares the contents of two type info objects.
+     * @param lhs A type info object.
+     * @param rhs A type info object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    [[nodiscard]] inline bool operator!=(const type_info& lhs, const type_info& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Returns the type info object for a given type.
+     * @tparam Type Type for which to generate a type info object.
+     * @return The type info object for the given type.
+     */
+    template<typename Type>
+    [[nodiscard]] type_info type_id() ENTT_NOEXCEPT {
+        return type_info{
+            type_seq<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value(),
+            type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()
+        };
+    }
+
+
+    }
+
+
+#endif
+
+// #include "sigh.hpp"
+#ifndef ENTT_SIGNAL_SIGH_HPP
+#define ENTT_SIGNAL_SIGH_HPP
+
+
+#include <vector>
+#include <utility>
+#include <iterator>
+#include <algorithm>
+#include <functional>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "delegate.hpp"
+#ifndef ENTT_SIGNAL_DELEGATE_HPP
+#define ENTT_SIGNAL_DELEGATE_HPP
+
+
+#include <tuple>
+#include <cstddef>
+#include <utility>
+#include <functional>
+#include <type_traits>
+// #include "../core/type_traits.hpp"
+
+// #include "../config/config.h"
+
+
+
+namespace entt {
+
+
+    /**
+     * @cond TURN_OFF_DOXYGEN
+     * Internal details not to be documented.
+     */
+
+
+    namespace internal {
+
+
+        template<typename Ret, typename... Args>
+        auto function_pointer(Ret(*)(Args...))->Ret(*)(Args...);
+
+
+        template<typename Ret, typename Type, typename... Args, typename Other>
+        auto function_pointer(Ret(*)(Type, Args...), Other&&)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...), Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Ret, typename... Args, typename... Other>
+        auto function_pointer(Ret(Class::*)(Args...) const, Other &&...)->Ret(*)(Args...);
+
+
+        template<typename Class, typename Type, typename... Other>
+        auto function_pointer(Type Class::*, Other &&...)->Type(*)();
+
+
+        template<typename... Type>
+        using function_pointer_t = decltype(internal::function_pointer(std::declval<Type>()...));
+
+
+        template<typename... Class, typename Ret, typename... Args>
+        [[nodiscard]] constexpr auto index_sequence_for(Ret(*)(Args...)) {
+            return std::index_sequence_for<Class..., Args...>{};
+        }
+
+
+    }
+
+
+    /**
+     * Internal details not to be documented.
+     * @endcond
+     */
+
+
+     /*! @brief Used to wrap a function or a member of a specified type. */
+    template<auto>
+    struct connect_arg_t {};
+
+
+    /*! @brief Constant of type connect_arg_t used to disambiguate calls. */
+    template<auto Func>
+    inline constexpr connect_arg_t<Func> connect_arg{};
+
+
+    /**
+     * @brief Basic delegate implementation.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     */
+    template<typename>
+    class delegate;
+
+
+    /**
+     * @brief Utility class to use to send around functions and members.
+     *
+     * Unmanaged delegate for function pointers and members. Users of this class are
+     * in charge of disconnecting instances before deleting them.
+     *
+     * A delegate can be used as a general purpose invoker without memory overhead
+     * for free functions possibly with payloads and bound or unbound members.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class delegate<Ret(Args...)> {
+        template<auto Candidate, std::size_t... Index>
+        [[nodiscard]] auto wrap(std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void*, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type&, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+        template<auto Candidate, typename Type, std::size_t... Index>
+        [[nodiscard]] auto wrap(Type*, std::index_sequence<Index...>) ENTT_NOEXCEPT {
+            return [](const void* payload, Args... args) -> Ret {
+                [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
+                Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
+            };
+        }
+
+    public:
+        /*! @brief Function type of the contained target. */
+        using function_type = Ret(const void*, Args...);
+        /*! @brief Function type of the delegate. */
+        using type = Ret(Args...);
+        /*! @brief Return type of the delegate. */
+        using result_type = Ret;
+
+        /*! @brief Default constructor. */
+        delegate() ENTT_NOEXCEPT
+            : fn{ nullptr }, data{ nullptr }
+        {}
+
+        /**
+         * @brief Constructs a delegate and connects a free function or an unbound
+         * member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        delegate(connect_arg_t<Candidate>) ENTT_NOEXCEPT {
+            connect<Candidate>();
+        }
+
+        /**
+         * @brief Constructs a delegate and connects a free function with payload or
+         * a bound member.
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        delegate(connect_arg_t<Candidate>, Type&& value_or_instance) ENTT_NOEXCEPT {
+            connect<Candidate>(std::forward<Type>(value_or_instance));
+        }
+
+        /**
+         * @brief Constructs a delegate and connects an user defined function with
+         * optional payload.
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        delegate(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            connect(function, payload);
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a delegate.
+         * @tparam Candidate Function or member to connect to the delegate.
+         */
+        template<auto Candidate>
+        void connect() ENTT_NOEXCEPT {
+            data = nullptr;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
+                fn = [](const void*, Args... args) -> Ret {
+                    return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
+                };
+            }
+            else if constexpr (std::is_member_pointer_v<decltype(Candidate)>) {
+                fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+            else {
+                fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the delegate.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the delegate itself.
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid reference that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type& value_or_instance) ENTT_NOEXCEPT {
+            data = &value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type&, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * delegate.
+         *
+         * @sa connect(Type &)
+         *
+         * @tparam Candidate Function or member to connect to the delegate.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void connect(Type* value_or_instance) ENTT_NOEXCEPT {
+            data = value_or_instance;
+
+            if constexpr (std::is_invocable_r_v<Ret, decltype(Candidate), Type*, Args...>) {
+                fn = [](const void* payload, Args... args) -> Ret {
+                    Type* curr = static_cast<Type*>(const_cast<constness_as_t<void, Type> *>(payload));
+                    return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
+                };
+            }
+            else {
+                fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
+            }
+        }
+
+        /**
+         * @brief Connects an user defined function with optional payload to a
+         * delegate.
+         *
+         * The delegate isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of an instance overcomes
+         * the one of the delegate.<br/>
+         * The payload is returned as the first argument to the target function in
+         * all cases.
+         *
+         * @param function Function to connect to the delegate.
+         * @param payload User defined arbitrary data.
+         */
+        void connect(function_type* function, const void* payload = nullptr) ENTT_NOEXCEPT {
+            fn = function;
+            data = payload;
+        }
+
+        /**
+         * @brief Resets a delegate.
+         *
+         * After a reset, a delegate cannot be invoked anymore.
+         */
+        void reset() ENTT_NOEXCEPT {
+            fn = nullptr;
+            data = nullptr;
+        }
+
+        /**
+         * @brief Returns the instance or the payload linked to a delegate, if any.
+         * @return An opaque pointer to the underlying data.
+         */
+        [[nodiscard]] const void* instance() const ENTT_NOEXCEPT {
+            return data;
+        }
+
+        /**
+         * @brief Triggers a delegate.
+         *
+         * The delegate invokes the underlying function and returns the result.
+         *
+         * @warning
+         * Attempting to trigger an invalid delegate results in undefined
+         * behavior.
+         *
+         * @param args Arguments to use to invoke the underlying function.
+         * @return The value returned by the underlying function.
+         */
+        Ret operator()(Args... args) const {
+            ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
+            return fn(data, std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Checks whether a delegate actually stores a listener.
+         * @return False if the delegate is empty, true otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            // no need to test also data
+            return !(fn == nullptr);
+        }
+
+        /**
+         * @brief Compares the contents of two delegates.
+         * @param other Delegate with which to compare.
+         * @return False if the two contents differ, true otherwise.
+         */
+        [[nodiscard]] bool operator==(const delegate<Ret(Args...)>& other) const ENTT_NOEXCEPT {
+            return fn == other.fn && data == other.data;
+        }
+
+    private:
+        function_type* fn;
+        const void* data;
+    };
+
+
+    /**
+     * @brief Compares the contents of two delegates.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     * @param lhs A valid delegate object.
+     * @param rhs A valid delegate object.
+     * @return True if the two contents differ, false otherwise.
+     */
+    template<typename Ret, typename... Args>
+    [[nodiscard]] bool operator!=(const delegate<Ret(Args...)>& lhs, const delegate<Ret(Args...)>& rhs) ENTT_NOEXCEPT {
+        return !(lhs == rhs);
+    }
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     */
+    template<auto Candidate>
+    delegate(connect_arg_t<Candidate>)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Candidate Function or member to connect to the delegate.
+     * @tparam Type Type of class or type of payload.
+     */
+    template<auto Candidate, typename Type>
+    delegate(connect_arg_t<Candidate>, Type&&)
+        ->delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;
+
+
+    /**
+     * @brief Deduction guide.
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    delegate(Ret(*)(const void*, Args...), const void* = nullptr)
+        ->delegate<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
+// #include "fwd.hpp"
+#ifndef ENTT_SIGNAL_FWD_HPP
+#define ENTT_SIGNAL_FWD_HPP
+
+
+namespace entt {
+
+
+    template<typename>
+    class delegate;
+
+
+    class dispatcher;
+
+
+    template<typename>
+    class emitter;
+
+
+    class connection;
+
+
+    struct scoped_connection;
+
+
+    template<typename>
+    class sink;
+
+
+    template<typename>
+    class sigh;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Sink class.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     *
+     * @tparam Function A valid function type.
+     */
+    template<typename Function>
+    class sink;
+
+
+    /**
+     * @brief Unmanaged signal handler.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     *
+     * @tparam Function A valid function type.
+     */
+    template<typename Function>
+    class sigh;
+
+
+    /**
+     * @brief Unmanaged signal handler.
+     *
+     * It works directly with references to classes and pointers to member functions
+     * as well as pointers to free functions. Users of this class are in charge of
+     * disconnecting instances before deleting them.
+     *
+     * This class serves mainly two purposes:
+     *
+     * * Creating signals to use later to notify a bunch of listeners.
+     * * Collecting results from a set of functions like in a voting system.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class sigh<Ret(Args...)> {
+        /*! @brief A sink is allowed to modify a signal. */
+        friend class sink<Ret(Args...)>;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Sink type. */
+        using sink_type = sink<Ret(Args...)>;
+
+        /**
+         * @brief Instance type when it comes to connecting member functions.
+         * @tparam Class Type of class to which the member function belongs.
+         */
+        template<typename Class>
+        using instance_type = Class*;
+
+        /**
+         * @brief Number of listeners connected to the signal.
+         * @return Number of listeners currently connected.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return calls.size();
+        }
+
+        /**
+         * @brief Returns false if at least a listener is connected to the signal.
+         * @return True if the signal has no listeners connected, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return calls.empty();
+        }
+
+        /**
+         * @brief Triggers a signal.
+         *
+         * All the listeners are notified. Order isn't guaranteed.
+         *
+         * @param args Arguments to use to invoke listeners.
+         */
+        void publish(Args... args) const {
+            for (auto&& call : std::as_const(calls)) {
+                call(args...);
+            }
+        }
+
+        /**
+         * @brief Collects return values from the listeners.
+         *
+         * The collector must expose a call operator with the following properties:
+         *
+         * * The return type is either `void` or such that it's convertible to
+         *   `bool`. In the second case, a true value will stop the iteration.
+         * * The list of parameters is empty if `Ret` is `void`, otherwise it
+         *   contains a single element such that `Ret` is convertible to it.
+         *
+         * @tparam Func Type of collector to use, if any.
+         * @param func A valid function object.
+         * @param args Arguments to use to invoke listeners.
+         */
+        template<typename Func>
+        void collect(Func func, Args... args) const {
+            for (auto&& call : calls) {
+                if constexpr (std::is_void_v<Ret>) {
+                    if constexpr (std::is_invocable_r_v<bool, Func>) {
+                        call(args...);
+                        if (func()) { break; }
+                    }
+                    else {
+                        call(args...);
+                        func();
+                    }
+                }
+                else {
+                    if constexpr (std::is_invocable_r_v<bool, Func, Ret>) {
+                        if (func(call(args...))) { break; }
+                    }
+                    else {
+                        func(call(args...));
+                    }
+                }
+            }
+        }
+
+    private:
+        std::vector<delegate<Ret(Args...)>> calls;
+    };
+
+
+    /**
+     * @brief Connection class.
+     *
+     * Opaque object the aim of which is to allow users to release an already
+     * estabilished connection without having to keep a reference to the signal or
+     * the sink that generated it.
+     */
+    class connection {
+        /*! @brief A sink is allowed to create connection objects. */
+        template<typename>
+        friend class sink;
+
+        connection(delegate<void(void*)> fn, void* ref)
+            : disconnect{ fn }, signal{ ref }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        connection() = default;
+
+        /**
+         * @brief Checks whether a connection is properly initialized.
+         * @return True if the connection is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(disconnect);
+        }
+
+        /*! @brief Breaks the connection. */
+        void release() {
+            if (disconnect) {
+                disconnect(signal);
+                disconnect.reset();
+            }
+        }
+
+    private:
+        delegate<void(void*)> disconnect;
+        void* signal{};
+    };
+
+
+    /**
+     * @brief Scoped connection class.
+     *
+     * Opaque object the aim of which is to allow users to release an already
+     * estabilished connection without having to keep a reference to the signal or
+     * the sink that generated it.<br/>
+     * A scoped connection automatically breaks the link between the two objects
+     * when it goes out of scope.
+     */
+    struct scoped_connection {
+        /*! @brief Default constructor. */
+        scoped_connection() = default;
+
+        /**
+         * @brief Constructs a scoped connection from a basic connection.
+         * @param other A valid connection object.
+         */
+        scoped_connection(const connection& other)
+            : conn{ other }
+        {}
+
+        /*! @brief Default copy constructor, deleted on purpose. */
+        scoped_connection(const scoped_connection&) = delete;
+
+        /*! @brief Automatically breaks the link on destruction. */
+        ~scoped_connection() {
+            conn.release();
+        }
+
+        /**
+         * @brief Default copy assignment operator, deleted on purpose.
+         * @return This scoped connection.
+         */
+        scoped_connection& operator=(const scoped_connection&) = delete;
+
+        /**
+         * @brief Acquires a connection.
+         * @param other The connection object to acquire.
+         * @return This scoped connection.
+         */
+        scoped_connection& operator=(connection other) {
+            conn = std::move(other);
+            return *this;
+        }
+
+        /**
+         * @brief Checks whether a scoped connection is properly initialized.
+         * @return True if the connection is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(conn);
+        }
+
+        /*! @brief Breaks the connection. */
+        void release() {
+            conn.release();
+        }
+
+    private:
+        connection conn;
+    };
+
+
+    /**
+     * @brief Sink class.
+     *
+     * A sink is used to connect listeners to signals and to disconnect them.<br/>
+     * The function type for a listener is the one of the signal to which it
+     * belongs.
+     *
+     * The clear separation between a signal and a sink permits to store the former
+     * as private data member without exposing the publish functionality to the
+     * users of the class.
+     *
+     * @warning
+     * Lifetime of a sink must not overcome that of the signal to which it refers.
+     * In any other case, attempting to use a sink results in undefined behavior.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class sink<Ret(Args...)> {
+        using signal_type = sigh<Ret(Args...)>;
+        using difference_type = typename std::iterator_traits<typename decltype(signal_type::calls)::iterator>::difference_type;
+
+        template<auto Candidate, typename Type>
+        static void release(Type value_or_instance, void* signal) {
+            sink{ *static_cast<signal_type*>(signal) }.disconnect<Candidate>(value_or_instance);
+        }
+
+        template<auto Candidate>
+        static void release(void* signal) {
+            sink{ *static_cast<signal_type*>(signal) }.disconnect<Candidate>();
+        }
+
+    public:
+        /**
+         * @brief Constructs a sink that is allowed to modify a given signal.
+         * @param ref A valid reference to a signal object.
+         */
+        sink(sigh<Ret(Args...)>& ref) ENTT_NOEXCEPT
+            : offset{},
+            signal{ &ref }
+        {}
+
+        /**
+         * @brief Returns false if at least a listener is connected to the sink.
+         * @return True if the sink has no listeners connected, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return signal->calls.empty();
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given free function or an
+         * unbound member.
+         * @tparam Function A valid free function pointer.
+         * @return A properly initialized sink object.
+         */
+        template<auto Function>
+        [[nodiscard]] sink before() {
+            delegate<Ret(Args...)> call{};
+            call.template connect<Function>();
+
+            const auto& calls = signal->calls;
+            const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));
+
+            sink other{ *this };
+            other.offset = std::distance(it, calls.cend());
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before a free function with payload
+         * or a bound member.
+         * @tparam Candidate Member or free function to look for.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<auto Candidate, typename Type>
+        [[nodiscard]] sink before(Type&& value_or_instance) {
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+
+            const auto& calls = signal->calls;
+            const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));
+
+            sink other{ *this };
+            other.offset = std::distance(it, calls.cend());
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given instance or specific
+         * payload.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<typename Type>
+        [[nodiscard]] sink before(Type& value_or_instance) {
+            return before(&value_or_instance);
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given instance or specific
+         * payload.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<typename Type>
+        [[nodiscard]] sink before(Type* value_or_instance) {
+            sink other{ *this };
+
+            if (value_or_instance) {
+                const auto& calls = signal->calls;
+                const auto it = std::find_if(calls.cbegin(), calls.cend(), [value_or_instance](const auto& delegate) {
+                    return delegate.instance() == value_or_instance;
+                    });
+
+                other.offset = std::distance(it, calls.cend());
+            }
+
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before anything else.
+         * @return A properly initialized sink object.
+         */
+        [[nodiscard]] sink before() {
+            sink other{ *this };
+            other.offset = signal->calls.size();
+            return other;
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a signal.
+         *
+         * The signal handler performs checks to avoid multiple connections for the
+         * same function.
+         *
+         * @tparam Candidate Function or member to connect to the signal.
+         * @return A properly initialized connection object.
+         */
+        template<auto Candidate>
+        connection connect() {
+            disconnect<Candidate>();
+
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>();
+            signal->calls.insert(signal->calls.end() - offset, std::move(call));
+
+            delegate<void(void*)> conn{};
+            conn.template connect<&release<Candidate>>();
+            return { std::move(conn), signal };
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * signal.
+         *
+         * The signal isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the signal. On the other side, the signal handler performs
+         * checks to avoid multiple connections for the same function.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the signal itself.
+         *
+         * @tparam Candidate Function or member to connect to the signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized connection object.
+         */
+        template<auto Candidate, typename Type>
+        connection connect(Type&& value_or_instance) {
+            disconnect<Candidate>(value_or_instance);
+
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+            signal->calls.insert(signal->calls.end() - offset, std::move(call));
+
+            delegate<void(void*)> conn{};
+            conn.template connect<&release<Candidate, Type>>(value_or_instance);
+            return { std::move(conn), signal };
+        }
+
+        /**
+         * @brief Disconnects a free function or an unbound member from a signal.
+         * @tparam Candidate Function or member to disconnect from the signal.
+         */
+        template<auto Candidate>
+        void disconnect() {
+            auto& calls = signal->calls;
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>();
+            calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
+        }
+
+        /**
+         * @brief Disconnects a free function with payload or a bound member from a
+         * signal.
+         * @tparam Candidate Function or member to disconnect from the signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void disconnect(Type&& value_or_instance) {
+            auto& calls = signal->calls;
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+            calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
+        }
+
+        /**
+         * @brief Disconnects free functions with payload or bound members from a
+         * signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type& value_or_instance) {
+            disconnect(&value_or_instance);
+        }
+
+        /**
+         * @brief Disconnects free functions with payload or bound members from a
+         * signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type* value_or_instance) {
+            if (value_or_instance) {
+                auto& calls = signal->calls;
+                calls.erase(std::remove_if(calls.begin(), calls.end(), [value_or_instance](const auto& delegate) {
+                    return delegate.instance() == value_or_instance;
+                    }), calls.end());
+            }
+        }
+
+        /*! @brief Disconnects all the listeners from a signal. */
+        void disconnect() {
+            signal->calls.clear();
+        }
+
+    private:
+        difference_type offset;
+        signal_type* signal;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the function type of a sink directly from the signal it
+     * refers to.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    sink(sigh<Ret(Args...)>&)
+        ->sink<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Basic dispatcher implementation.
+     *
+     * A dispatcher can be used either to trigger an immediate event or to enqueue
+     * events to be published all together once per tick.<br/>
+     * Listeners are provided in the form of member functions. For each event of
+     * type `Event`, listeners are such that they can be invoked with an argument of
+     * type `Event &`, no matter what the return type is.
+     *
+     * The dispatcher creates instances of the `sigh` class internally. Refer to the
+     * documentation of the latter for more details.
+     */
+    class dispatcher {
+        struct basic_pool {
+            virtual ~basic_pool() = default;
+            virtual void publish() = 0;
+            virtual void disconnect(void*) = 0;
+            virtual void clear() ENTT_NOEXCEPT = 0;
+        };
+
+        template<typename Event>
+        struct pool_handler final : basic_pool {
+            static_assert(std::is_same_v<Event, std::decay_t<Event>>, "Invalid event type");
+
+            using signal_type = sigh<void(Event&)>;
+            using sink_type = typename signal_type::sink_type;
+
+            void publish() override {
+                const auto length = events.size();
+
+                for (std::size_t pos{}; pos < length; ++pos) {
+                    signal.publish(events[pos]);
+                }
+
+                events.erase(events.cbegin(), events.cbegin() + length);
+            }
+
+            void disconnect(void* instance) override {
+                sink().disconnect(instance);
+            }
+
+            void clear() ENTT_NOEXCEPT override {
+                events.clear();
+            }
+
+            [[nodiscard]] sink_type sink() ENTT_NOEXCEPT {
+                return entt::sink{ signal };
+            }
+
+            template<typename... Args>
+            void trigger(Args &&... args) {
+                Event instance{ std::forward<Args>(args)... };
+                signal.publish(instance);
+            }
+
+            template<typename... Args>
+            void enqueue(Args &&... args) {
+                if constexpr (std::is_aggregate_v<Event>) {
+                    events.push_back(Event{ std::forward<Args>(args)... });
+                }
+                else {
+                    events.emplace_back(std::forward<Args>(args)...);
+                }
+            }
+
+        private:
+            signal_type signal{};
+            std::vector<Event> events;
+        };
+
+        template<typename Event>
+        [[nodiscard]] pool_handler<Event>& assure() {
+            const auto index = type_seq<Event>::value();
+
+            if (!(index < pools.size())) {
+                pools.resize(std::size_t(index) + 1u);
+            }
+
+            if (!pools[index]) {
+                pools[index].reset(new pool_handler<Event>{});
+            }
+
+            return static_cast<pool_handler<Event> &>(*pools[index]);
+        }
+
+    public:
+        /*! @brief Default constructor. */
+        dispatcher() = default;
+
+        /*! @brief Default move constructor. */
+        dispatcher(dispatcher&&) = default;
+
+        /*! @brief Default move assignment operator. @return This dispatcher. */
+        dispatcher& operator=(dispatcher&&) = default;
+
+        /**
+         * @brief Returns a sink object for the given event.
+         *
+         * A sink is an opaque object used to connect listeners to events.
+         *
+         * The function type for a listener is _compatible_ with:
+         * @code{.cpp}
+         * void(Event &);
+         * @endcode
+         *
+         * The order of invocation of the listeners isn't guaranteed.
+         *
+         * @sa sink
+         *
+         * @tparam Event Type of event of which to get the sink.
+         * @return A temporary sink object.
+         */
+        template<typename Event>
+        [[nodiscard]] auto sink() {
+            return assure<Event>().sink();
+        }
+
+        /**
+         * @brief Triggers an immediate event of the given type.
+         *
+         * All the listeners registered for the given type are immediately notified.
+         * The event is discarded after the execution.
+         *
+         * @tparam Event Type of event to trigger.
+         * @tparam Args Types of arguments to use to construct the event.
+         * @param args Arguments to use to construct the event.
+         */
+        template<typename Event, typename... Args>
+        void trigger(Args &&... args) {
+            assure<Event>().trigger(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Triggers an immediate event of the given type.
+         *
+         * All the listeners registered for the given type are immediately notified.
+         * The event is discarded after the execution.
+         *
+         * @tparam Event Type of event to trigger.
+         * @param event An instance of the given type of event.
+         */
+        template<typename Event>
+        void trigger(Event&& event) {
+            assure<std::decay_t<Event>>().trigger(std::forward<Event>(event));
+        }
+
+        /**
+         * @brief Enqueues an event of the given type.
+         *
+         * An event of the given type is queued. No listener is invoked. Use the
+         * `update` member function to notify listeners when ready.
+         *
+         * @tparam Event Type of event to enqueue.
+         * @tparam Args Types of arguments to use to construct the event.
+         * @param args Arguments to use to construct the event.
+         */
+        template<typename Event, typename... Args>
+        void enqueue(Args &&... args) {
+            assure<Event>().enqueue(std::forward<Args>(args)...);
+        }
+
+        /**
+         * @brief Enqueues an event of the given type.
+         *
+         * An event of the given type is queued. No listener is invoked. Use the
+         * `update` member function to notify listeners when ready.
+         *
+         * @tparam Event Type of event to enqueue.
+         * @param event An instance of the given type of event.
+         */
+        template<typename Event>
+        void enqueue(Event&& event) {
+            assure<std::decay_t<Event>>().enqueue(std::forward<Event>(event));
+        }
+
+        /**
+         * @brief Utility function to disconnect everything related to a given value
+         * or instance from a dispatcher.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type& value_or_instance) {
+            disconnect(&value_or_instance);
+        }
+
+        /**
+         * @brief Utility function to disconnect everything related to a given value
+         * or instance from a dispatcher.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type* value_or_instance) {
+            for (auto&& cpool : pools) {
+                if (cpool) {
+                    cpool->disconnect(value_or_instance);
+                }
+            }
+        }
+
+        /**
+         * @brief Discards all the events queued so far.
+         *
+         * If no types are provided, the dispatcher will clear all the existing
+         * pools.
+         *
+         * @tparam Event Type of events to discard.
+         */
+        template<typename... Event>
+        void clear() {
+            if constexpr (sizeof...(Event) == 0) {
+                for (auto&& cpool : pools) {
+                    if (cpool) {
+                        cpool->clear();
+                    }
+                }
+            }
+            else {
+                (assure<Event>().clear(), ...);
+            }
+        }
+
+        /**
+         * @brief Delivers all the pending events of the given type.
+         *
+         * This method is blocking and it doesn't return until all the events are
+         * delivered to the registered listeners. It's responsibility of the users
+         * to reduce at a minimum the time spent in the bodies of the listeners.
+         *
+         * @tparam Event Type of events to send.
+         */
+        template<typename Event>
+        void update() {
+            assure<Event>().publish();
+        }
+
+        /**
+         * @brief Delivers all the pending events.
+         *
+         * This method is blocking and it doesn't return until all the events are
+         * delivered to the registered listeners. It's responsibility of the users
+         * to reduce at a minimum the time spent in the bodies of the listeners.
+         */
+        void update() const {
+            for (auto pos = pools.size(); pos; --pos) {
+                if (auto&& cpool = pools[pos - 1]; cpool) {
+                    cpool->publish();
+                }
+            }
+        }
+
+    private:
+        std::vector<std::unique_ptr<basic_pool>> pools;
+    };
+
+
+}
+
+
+#endif
+
+// #include "signal/emitter.hpp"
+#ifndef ENTT_SIGNAL_EMITTER_HPP
+#define ENTT_SIGNAL_EMITTER_HPP
+
+
+#include <algorithm>
+#include <functional>
+#include <iterator>
+#include <list>
+#include <memory>
+#include <type_traits>
+#include <utility>
+#include <vector>
+// #include "../config/config.h"
+
+// #include "../core/fwd.hpp"
+
+// #include "../core/type_info.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief General purpose event emitter.
+     *
+     * The emitter class template follows the CRTP idiom. To create a custom emitter
+     * type, derived classes must inherit directly from the base class as:
+     *
+     * @code{.cpp}
+     * struct my_emitter: emitter<my_emitter> {
+     *     // ...
+     * }
+     * @endcode
+     *
+     * Pools for the type of events are created internally on the fly. It's not
+     * required to specify in advance the full list of accepted types.<br/>
+     * Moreover, whenever an event is published, an emitter provides the listeners
+     * with a reference to itself along with a reference to the event. Therefore
+     * listeners have an handy way to work with it without incurring in the need of
+     * capturing a reference to the emitter.
+     *
+     * @tparam Derived Actual type of emitter that extends the class template.
+     */
+    template<typename Derived>
+    class emitter {
+        struct basic_pool {
+            virtual ~basic_pool() = default;
+            virtual bool empty() const ENTT_NOEXCEPT = 0;
+            virtual void clear() ENTT_NOEXCEPT = 0;
+        };
+
+        template<typename Event>
+        struct pool_handler final : basic_pool {
+            static_assert(std::is_same_v<Event, std::decay_t<Event>>, "Invalid event type");
+
+            using listener_type = std::function<void(Event&, Derived&)>;
+            using element_type = std::pair<bool, listener_type>;
+            using container_type = std::list<element_type>;
+            using connection_type = typename container_type::iterator;
+
+            [[nodiscard]] bool empty() const ENTT_NOEXCEPT override {
+                auto pred = [](auto&& element) { return element.first; };
+
+                return std::all_of(once_list.cbegin(), once_list.cend(), pred) &&
+                    std::all_of(on_list.cbegin(), on_list.cend(), pred);
+            }
+
+            void clear() ENTT_NOEXCEPT override {
+                if (publishing) {
+                    for (auto&& element : once_list) {
+                        element.first = true;
+                    }
+
+                    for (auto&& element : on_list) {
+                        element.first = true;
+                    }
+                }
+                else {
+                    once_list.clear();
+                    on_list.clear();
+                }
+            }
+
+            connection_type once(listener_type listener) {
+                return once_list.emplace(once_list.cend(), false, std::move(listener));
+            }
+
+            connection_type on(listener_type listener) {
+                return on_list.emplace(on_list.cend(), false, std::move(listener));
+            }
+
+            void erase(connection_type conn) {
+                conn->first = true;
+
+                if (!publishing) {
+                    auto pred = [](auto&& element) { return element.first; };
+                    once_list.remove_if(pred);
+                    on_list.remove_if(pred);
+                }
+            }
+
+            void publish(Event& event, Derived& ref) {
+                container_type swap_list;
+                once_list.swap(swap_list);
+
+                publishing = true;
+
+                for (auto&& element : on_list) {
+                    element.first ? void() : element.second(event, ref);
+                }
+
+                for (auto&& element : swap_list) {
+                    element.first ? void() : element.second(event, ref);
+                }
+
+                publishing = false;
+
+                on_list.remove_if([](auto&& element) { return element.first; });
+            }
+
+        private:
+            bool publishing{ false };
+            container_type once_list{};
+            container_type on_list{};
+        };
+
+        template<typename Event>
+        [[nodiscard]] pool_handler<Event>* assure() {
+            const auto index = type_seq<Event>::value();
+
+            if (!(index < pools.size())) {
+                pools.resize(std::size_t(index) + 1u);
+            }
+
+            if (!pools[index]) {
+                pools[index].reset(new pool_handler<Event>{});
+            }
+
+            return static_cast<pool_handler<Event> *>(pools[index].get());
+        }
+
+        template<typename Event>
+        [[nodiscard]] const pool_handler<Event>* assure() const {
+            const auto index = type_seq<Event>::value();
+            return (!(index < pools.size()) || !pools[index]) ? nullptr : static_cast<const pool_handler<Event> *>(pools[index].get());
+        }
+
+    public:
+        /** @brief Type of listeners accepted for the given event. */
+        template<typename Event>
+        using listener = typename pool_handler<Event>::listener_type;
+
+        /**
+         * @brief Generic connection type for events.
+         *
+         * Type of the connection object returned by the event emitter whenever a
+         * listener for the given type is registered.<br/>
+         * It can be used to break connections still in use.
+         *
+         * @tparam Event Type of event for which the connection is created.
+         */
+        template<typename Event>
+        struct connection : private pool_handler<Event>::connection_type {
+            /** @brief Event emitters are friend classes of connections. */
+            friend class emitter;
+
+            /*! @brief Default constructor. */
+            connection() = default;
+
+            /**
+             * @brief Creates a connection that wraps its underlying instance.
+             * @param conn A connection object to wrap.
+             */
+            connection(typename pool_handler<Event>::connection_type conn)
+                : pool_handler<Event>::connection_type{ std::move(conn) }
+            {}
+        };
+
+        /*! @brief Default constructor. */
+        emitter() = default;
+
+        /*! @brief Default destructor. */
+        virtual ~emitter() {
+            static_assert(std::is_base_of_v<emitter<Derived>, Derived>, "Incorrect use of the class template");
+        }
+
+        /*! @brief Default move constructor. */
+        emitter(emitter&&) = default;
+
+        /*! @brief Default move assignment operator. @return This emitter. */
+        emitter& operator=(emitter&&) = default;
+
+        /**
+         * @brief Emits the given event.
+         *
+         * All the listeners registered for the specific event type are invoked with
+         * the given event. The event type must either have a proper constructor for
+         * the arguments provided or be an aggregate type.
+         *
+         * @tparam Event Type of event to publish.
+         * @tparam Args Types of arguments to use to construct the event.
+         * @param args Parameters to use to initialize the event.
+         */
+        template<typename Event, typename... Args>
+        void publish(Args &&... args) {
+            Event instance{ std::forward<Args>(args)... };
+            assure<Event>()->publish(instance, *static_cast<Derived*>(this));
+        }
+
+        /**
+         * @brief Registers a long-lived listener with the event emitter.
+         *
+         * This method can be used to register a listener designed to be invoked
+         * more than once for the given event type.<br/>
+         * The connection returned by the method can be freely discarded. It's meant
+         * to be used later to disconnect the listener if required.
+         *
+         * The listener is as a callable object that can be moved and the type of
+         * which is _compatible_ with `void(Event &, Derived &)`.
+         *
+         * @note
+         * Whenever an event is emitted, the emitter provides the listener with a
+         * reference to the derived class. Listeners don't have to capture those
+         * instances for later uses.
+         *
+         * @tparam Event Type of event to which to connect the listener.
+         * @param instance The listener to register.
+         * @return Connection object that can be used to disconnect the listener.
+         */
+        template<typename Event>
+        connection<Event> on(listener<Event> instance) {
+            return assure<Event>()->on(std::move(instance));
+        }
+
+        /**
+         * @brief Registers a short-lived listener with the event emitter.
+         *
+         * This method can be used to register a listener designed to be invoked
+         * only once for the given event type.<br/>
+         * The connection returned by the method can be freely discarded. It's meant
+         * to be used later to disconnect the listener if required.
+         *
+         * The listener is as a callable object that can be moved and the type of
+         * which is _compatible_ with `void(Event &, Derived &)`.
+         *
+         * @note
+         * Whenever an event is emitted, the emitter provides the listener with a
+         * reference to the derived class. Listeners don't have to capture those
+         * instances for later uses.
+         *
+         * @tparam Event Type of event to which to connect the listener.
+         * @param instance The listener to register.
+         * @return Connection object that can be used to disconnect the listener.
+         */
+        template<typename Event>
+        connection<Event> once(listener<Event> instance) {
+            return assure<Event>()->once(std::move(instance));
+        }
+
+        /**
+         * @brief Disconnects a listener from the event emitter.
+         *
+         * Do not use twice the same connection to disconnect a listener, it results
+         * in undefined behavior. Once used, discard the connection object.
+         *
+         * @tparam Event Type of event of the connection.
+         * @param conn A valid connection.
+         */
+        template<typename Event>
+        void erase(connection<Event> conn) {
+            assure<Event>()->erase(std::move(conn));
+        }
+
+        /**
+         * @brief Disconnects all the listeners for the given event type.
+         *
+         * All the connections previously returned for the given event are
+         * invalidated. Using them results in undefined behavior.
+         *
+         * @tparam Event Type of event to reset.
+         */
+        template<typename Event>
+        void clear() {
+            assure<Event>()->clear();
+        }
+
+        /**
+         * @brief Disconnects all the listeners.
+         *
+         * All the connections previously returned are invalidated. Using them
+         * results in undefined behavior.
+         */
+        void clear() ENTT_NOEXCEPT {
+            for (auto&& cpool : pools) {
+                if (cpool) {
+                    cpool->clear();
+                }
+            }
+        }
+
+        /**
+         * @brief Checks if there are listeners registered for the specific event.
+         * @tparam Event Type of event to test.
+         * @return True if there are no listeners registered, false otherwise.
+         */
+        template<typename Event>
+        [[nodiscard]] bool empty() const {
+            const auto* cpool = assure<Event>();
+            return !cpool || cpool->empty();
+        }
+
+        /**
+         * @brief Checks if there are listeners registered with the event emitter.
+         * @return True if there are no listeners registered, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return std::all_of(pools.cbegin(), pools.cend(), [](auto&& cpool) {
+                return !cpool || cpool->empty();
+                });
+        }
+
+    private:
+        std::vector<std::unique_ptr<basic_pool>> pools{};
+    };
+
+
+}
+
+
+#endif
+
+// #include "signal/sigh.hpp"
+#ifndef ENTT_SIGNAL_SIGH_HPP
+#define ENTT_SIGNAL_SIGH_HPP
+
+
+#include <vector>
+#include <utility>
+#include <iterator>
+#include <algorithm>
+#include <functional>
+#include <type_traits>
+// #include "../config/config.h"
+
+// #include "delegate.hpp"
+
+// #include "fwd.hpp"
+
+
+
+namespace entt {
+
+
+    /**
+     * @brief Sink class.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     *
+     * @tparam Function A valid function type.
+     */
+    template<typename Function>
+    class sink;
+
+
+    /**
+     * @brief Unmanaged signal handler.
+     *
+     * Primary template isn't defined on purpose. All the specializations give a
+     * compile-time error unless the template parameter is a function type.
+     *
+     * @tparam Function A valid function type.
+     */
+    template<typename Function>
+    class sigh;
+
+
+    /**
+     * @brief Unmanaged signal handler.
+     *
+     * It works directly with references to classes and pointers to member functions
+     * as well as pointers to free functions. Users of this class are in charge of
+     * disconnecting instances before deleting them.
+     *
+     * This class serves mainly two purposes:
+     *
+     * * Creating signals to use later to notify a bunch of listeners.
+     * * Collecting results from a set of functions like in a voting system.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class sigh<Ret(Args...)> {
+        /*! @brief A sink is allowed to modify a signal. */
+        friend class sink<Ret(Args...)>;
+
+    public:
+        /*! @brief Unsigned integer type. */
+        using size_type = std::size_t;
+        /*! @brief Sink type. */
+        using sink_type = sink<Ret(Args...)>;
+
+        /**
+         * @brief Instance type when it comes to connecting member functions.
+         * @tparam Class Type of class to which the member function belongs.
+         */
+        template<typename Class>
+        using instance_type = Class*;
+
+        /**
+         * @brief Number of listeners connected to the signal.
+         * @return Number of listeners currently connected.
+         */
+        [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
+            return calls.size();
+        }
+
+        /**
+         * @brief Returns false if at least a listener is connected to the signal.
+         * @return True if the signal has no listeners connected, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return calls.empty();
+        }
+
+        /**
+         * @brief Triggers a signal.
+         *
+         * All the listeners are notified. Order isn't guaranteed.
+         *
+         * @param args Arguments to use to invoke listeners.
+         */
+        void publish(Args... args) const {
+            for (auto&& call : std::as_const(calls)) {
+                call(args...);
+            }
+        }
+
+        /**
+         * @brief Collects return values from the listeners.
+         *
+         * The collector must expose a call operator with the following properties:
+         *
+         * * The return type is either `void` or such that it's convertible to
+         *   `bool`. In the second case, a true value will stop the iteration.
+         * * The list of parameters is empty if `Ret` is `void`, otherwise it
+         *   contains a single element such that `Ret` is convertible to it.
+         *
+         * @tparam Func Type of collector to use, if any.
+         * @param func A valid function object.
+         * @param args Arguments to use to invoke listeners.
+         */
+        template<typename Func>
+        void collect(Func func, Args... args) const {
+            for (auto&& call : calls) {
+                if constexpr (std::is_void_v<Ret>) {
+                    if constexpr (std::is_invocable_r_v<bool, Func>) {
+                        call(args...);
+                        if (func()) { break; }
+                    }
+                    else {
+                        call(args...);
+                        func();
+                    }
+                }
+                else {
+                    if constexpr (std::is_invocable_r_v<bool, Func, Ret>) {
+                        if (func(call(args...))) { break; }
+                    }
+                    else {
+                        func(call(args...));
+                    }
+                }
+            }
+        }
+
+    private:
+        std::vector<delegate<Ret(Args...)>> calls;
+    };
+
+
+    /**
+     * @brief Connection class.
+     *
+     * Opaque object the aim of which is to allow users to release an already
+     * estabilished connection without having to keep a reference to the signal or
+     * the sink that generated it.
+     */
+    class connection {
+        /*! @brief A sink is allowed to create connection objects. */
+        template<typename>
+        friend class sink;
+
+        connection(delegate<void(void*)> fn, void* ref)
+            : disconnect{ fn }, signal{ ref }
+        {}
+
+    public:
+        /*! @brief Default constructor. */
+        connection() = default;
+
+        /**
+         * @brief Checks whether a connection is properly initialized.
+         * @return True if the connection is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(disconnect);
+        }
+
+        /*! @brief Breaks the connection. */
+        void release() {
+            if (disconnect) {
+                disconnect(signal);
+                disconnect.reset();
+            }
+        }
+
+    private:
+        delegate<void(void*)> disconnect;
+        void* signal{};
+    };
+
+
+    /**
+     * @brief Scoped connection class.
+     *
+     * Opaque object the aim of which is to allow users to release an already
+     * estabilished connection without having to keep a reference to the signal or
+     * the sink that generated it.<br/>
+     * A scoped connection automatically breaks the link between the two objects
+     * when it goes out of scope.
+     */
+    struct scoped_connection {
+        /*! @brief Default constructor. */
+        scoped_connection() = default;
+
+        /**
+         * @brief Constructs a scoped connection from a basic connection.
+         * @param other A valid connection object.
+         */
+        scoped_connection(const connection& other)
+            : conn{ other }
+        {}
+
+        /*! @brief Default copy constructor, deleted on purpose. */
+        scoped_connection(const scoped_connection&) = delete;
+
+        /*! @brief Automatically breaks the link on destruction. */
+        ~scoped_connection() {
+            conn.release();
+        }
+
+        /**
+         * @brief Default copy assignment operator, deleted on purpose.
+         * @return This scoped connection.
+         */
+        scoped_connection& operator=(const scoped_connection&) = delete;
+
+        /**
+         * @brief Acquires a connection.
+         * @param other The connection object to acquire.
+         * @return This scoped connection.
+         */
+        scoped_connection& operator=(connection other) {
+            conn = std::move(other);
+            return *this;
+        }
+
+        /**
+         * @brief Checks whether a scoped connection is properly initialized.
+         * @return True if the connection is properly initialized, false otherwise.
+         */
+        [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
+            return static_cast<bool>(conn);
+        }
+
+        /*! @brief Breaks the connection. */
+        void release() {
+            conn.release();
+        }
+
+    private:
+        connection conn;
+    };
+
+
+    /**
+     * @brief Sink class.
+     *
+     * A sink is used to connect listeners to signals and to disconnect them.<br/>
+     * The function type for a listener is the one of the signal to which it
+     * belongs.
+     *
+     * The clear separation between a signal and a sink permits to store the former
+     * as private data member without exposing the publish functionality to the
+     * users of the class.
+     *
+     * @warning
+     * Lifetime of a sink must not overcome that of the signal to which it refers.
+     * In any other case, attempting to use a sink results in undefined behavior.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    class sink<Ret(Args...)> {
+        using signal_type = sigh<Ret(Args...)>;
+        using difference_type = typename std::iterator_traits<typename decltype(signal_type::calls)::iterator>::difference_type;
+
+        template<auto Candidate, typename Type>
+        static void release(Type value_or_instance, void* signal) {
+            sink{ *static_cast<signal_type*>(signal) }.disconnect<Candidate>(value_or_instance);
+        }
+
+        template<auto Candidate>
+        static void release(void* signal) {
+            sink{ *static_cast<signal_type*>(signal) }.disconnect<Candidate>();
+        }
+
+    public:
+        /**
+         * @brief Constructs a sink that is allowed to modify a given signal.
+         * @param ref A valid reference to a signal object.
+         */
+        sink(sigh<Ret(Args...)>& ref) ENTT_NOEXCEPT
+            : offset{},
+            signal{ &ref }
+        {}
+
+        /**
+         * @brief Returns false if at least a listener is connected to the sink.
+         * @return True if the sink has no listeners connected, false otherwise.
+         */
+        [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
+            return signal->calls.empty();
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given free function or an
+         * unbound member.
+         * @tparam Function A valid free function pointer.
+         * @return A properly initialized sink object.
+         */
+        template<auto Function>
+        [[nodiscard]] sink before() {
+            delegate<Ret(Args...)> call{};
+            call.template connect<Function>();
+
+            const auto& calls = signal->calls;
+            const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));
+
+            sink other{ *this };
+            other.offset = std::distance(it, calls.cend());
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before a free function with payload
+         * or a bound member.
+         * @tparam Candidate Member or free function to look for.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<auto Candidate, typename Type>
+        [[nodiscard]] sink before(Type&& value_or_instance) {
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+
+            const auto& calls = signal->calls;
+            const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));
+
+            sink other{ *this };
+            other.offset = std::distance(it, calls.cend());
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given instance or specific
+         * payload.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<typename Type>
+        [[nodiscard]] sink before(Type& value_or_instance) {
+            return before(&value_or_instance);
+        }
+
+        /**
+         * @brief Returns a sink that connects before a given instance or specific
+         * payload.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid pointer that fits the purpose.
+         * @return A properly initialized sink object.
+         */
+        template<typename Type>
+        [[nodiscard]] sink before(Type* value_or_instance) {
+            sink other{ *this };
+
+            if (value_or_instance) {
+                const auto& calls = signal->calls;
+                const auto it = std::find_if(calls.cbegin(), calls.cend(), [value_or_instance](const auto& delegate) {
+                    return delegate.instance() == value_or_instance;
+                    });
+
+                other.offset = std::distance(it, calls.cend());
+            }
+
+            return other;
+        }
+
+        /**
+         * @brief Returns a sink that connects before anything else.
+         * @return A properly initialized sink object.
+         */
+        [[nodiscard]] sink before() {
+            sink other{ *this };
+            other.offset = signal->calls.size();
+            return other;
+        }
+
+        /**
+         * @brief Connects a free function or an unbound member to a signal.
+         *
+         * The signal handler performs checks to avoid multiple connections for the
+         * same function.
+         *
+         * @tparam Candidate Function or member to connect to the signal.
+         * @return A properly initialized connection object.
+         */
+        template<auto Candidate>
+        connection connect() {
+            disconnect<Candidate>();
+
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>();
+            signal->calls.insert(signal->calls.end() - offset, std::move(call));
+
+            delegate<void(void*)> conn{};
+            conn.template connect<&release<Candidate>>();
+            return { std::move(conn), signal };
+        }
+
+        /**
+         * @brief Connects a free function with payload or a bound member to a
+         * signal.
+         *
+         * The signal isn't responsible for the connected object or the payload.
+         * Users must always guarantee that the lifetime of the instance overcomes
+         * the one of the signal. On the other side, the signal handler performs
+         * checks to avoid multiple connections for the same function.<br/>
+         * When used to connect a free function with payload, its signature must be
+         * such that the instance is the first argument before the ones used to
+         * define the signal itself.
+         *
+         * @tparam Candidate Function or member to connect to the signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         * @return A properly initialized connection object.
+         */
+        template<auto Candidate, typename Type>
+        connection connect(Type&& value_or_instance) {
+            disconnect<Candidate>(value_or_instance);
+
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+            signal->calls.insert(signal->calls.end() - offset, std::move(call));
+
+            delegate<void(void*)> conn{};
+            conn.template connect<&release<Candidate, Type>>(value_or_instance);
+            return { std::move(conn), signal };
+        }
+
+        /**
+         * @brief Disconnects a free function or an unbound member from a signal.
+         * @tparam Candidate Function or member to disconnect from the signal.
+         */
+        template<auto Candidate>
+        void disconnect() {
+            auto& calls = signal->calls;
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>();
+            calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
+        }
+
+        /**
+         * @brief Disconnects a free function with payload or a bound member from a
+         * signal.
+         * @tparam Candidate Function or member to disconnect from the signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<auto Candidate, typename Type>
+        void disconnect(Type&& value_or_instance) {
+            auto& calls = signal->calls;
+            delegate<Ret(Args...)> call{};
+            call.template connect<Candidate>(value_or_instance);
+            calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
+        }
+
+        /**
+         * @brief Disconnects free functions with payload or bound members from a
+         * signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type& value_or_instance) {
+            disconnect(&value_or_instance);
+        }
+
+        /**
+         * @brief Disconnects free functions with payload or bound members from a
+         * signal.
+         * @tparam Type Type of class or type of payload.
+         * @param value_or_instance A valid object that fits the purpose.
+         */
+        template<typename Type>
+        void disconnect(Type* value_or_instance) {
+            if (value_or_instance) {
+                auto& calls = signal->calls;
+                calls.erase(std::remove_if(calls.begin(), calls.end(), [value_or_instance](const auto& delegate) {
+                    return delegate.instance() == value_or_instance;
+                    }), calls.end());
+            }
+        }
+
+        /*! @brief Disconnects all the listeners from a signal. */
+        void disconnect() {
+            signal->calls.clear();
+        }
+
+    private:
+        difference_type offset;
+        signal_type* signal;
+    };
+
+
+    /**
+     * @brief Deduction guide.
+     *
+     * It allows to deduce the function type of a sink directly from the signal it
+     * refers to.
+     *
+     * @tparam Ret Return type of a function type.
+     * @tparam Args Types of arguments of a function type.
+     */
+    template<typename Ret, typename... Args>
+    sink(sigh<Ret(Args...)>&)
+        ->sink<Ret(Args...)>;
+
+
+}
+
+
+#endif
+
diff --git a/Dependencies/stb_image/build.lua b/Dependencies/stb_image/build.lua
index b7d7b87..b93665c 100644
--- a/Dependencies/stb_image/build.lua
+++ b/Dependencies/stb_image/build.lua
@@ -15,8 +15,8 @@ project "stb_image"
 	-- Project Files ---
 	files
 	{
-		"**.c",
-		"**.h",
+		"stb_image.c",
+		"stb_image.h",
 
 		"build.lua"
 	}
diff --git a/Engine/build.lua b/Engine/build.lua
index 909f385..bc6173f 100644
--- a/Engine/build.lua
+++ b/Engine/build.lua
@@ -49,6 +49,7 @@ project "Engine"
 		(dependenciesdir .. "imgui/"),
 		(dependenciesdir .. "stb_image/"),
 		(dependenciesdir .. "glm/"),
+		(dependenciesdir .. "entt/"),
 	}
 
 	links
@@ -56,7 +57,8 @@ project "Engine"
 		"GLFW"  ,
 		"GLAD"  ,
 		"ImGui" ,
-		"stb_image" ,
+		"stb_image",
+		"entt",
 	}
 	
 	--- Filters ---
diff --git a/Engine/src/Engine/Base.h b/Engine/src/Engine/Base.h
index de25713..a671a63 100644
--- a/Engine/src/Engine/Base.h
+++ b/Engine/src/Engine/Base.h
@@ -35,7 +35,6 @@
 #define BIT(x) 1 << x
 
 // assertions
-// #todo: log to file in distribution builds
 #if defined(LIGHT_DIST)
 	#define LT_ENGINE_ASSERT(x, ...) { if(!(x)) { LT_FILE_CRITICAL(__VA_ARGS__); throw ::Light::FailedEngineAssertion(__FILE__, __LINE__); } }
 	#define LT_CLIENT_ASSERT(x, ...) { if(!(x)) { LT_FILE_CRITICAL(__VA_ARGS__); throw ::Light::FailedClientAssertion(__FILE__, __LINE__); } }
diff --git a/Engine/src/Engine/Debug/Logger.h b/Engine/src/Engine/Debug/Logger.h
index 4a643cc..f06d132 100644
--- a/Engine/src/Engine/Debug/Logger.h
+++ b/Engine/src/Engine/Debug/Logger.h
@@ -8,7 +8,6 @@
 
 #define LT_LOG_FILE_LOCATION "Logs/Logger.txt";
 
-// #todo: log function signature 
 // File
 #define LT_FILE_INFO(...)       ::Light::Logger::GetFileLogger()->log(spdlog::level::info    , __VA_ARGS__)
 #define LT_FILE_WARN(...)       ::Light::Logger::GetFileLogger()->log(spdlog::level::warn    , __VA_ARGS__)
diff --git a/Engine/src/Engine/Utility/ResourceManager.cpp b/Engine/src/Engine/Utility/ResourceManager.cpp
index c6e5098..6200033 100644
--- a/Engine/src/Engine/Utility/ResourceManager.cpp
+++ b/Engine/src/Engine/Utility/ResourceManager.cpp
@@ -29,12 +29,12 @@ namespace Light {
 	{
 		// delim
 		std::string delim = GraphicsContext::GetGraphicsAPI() == GraphicsAPI::OpenGL ? "GLSL" :
-		                    GraphicsContext::GetGraphicsAPI() == GraphicsAPI::DirectX ? "HLSL" : NULL;
+		                    GraphicsContext::GetGraphicsAPI() == GraphicsAPI::DirectX ? "HLSL" : "";
 
 		// check
-		LT_ENGINE_ASSERT(!vertexSource.empty(), "ResourceManager::CreateShader: 'vertexSource' is empty");
-		LT_ENGINE_ASSERT(!vertexSource.empty(), "ResourceManager::CreateShader: 'pixelSource' is empty");
-		LT_ENGINE_ASSERT(!delim.empty(), "ResourceManager::LoadShader: invalid/unsupported 'GraphicsAPI': {}", GraphicsContext::GetGraphicsAPI());
+		LT_ENGINE_ASSERT(!vertexSource.empty(), "ResourceManager::CreateShaderImpl: 'vertexSource' is empty");
+		LT_ENGINE_ASSERT(!vertexSource.empty(), "ResourceManager::CreateShaderImpl: 'pixelSource' is empty");
+		LT_ENGINE_ASSERT(!delim.empty(), "ResourceManager::CreateShaderImpl: invalid/unsupported 'GraphicsAPI': {}", GraphicsContext::GetGraphicsAPI());
 
 		// save to string
 		std::string vsSource = vertexSource;
@@ -51,8 +51,8 @@ namespace Light {
 	void ResourceManager::LoadShaderImpl(const std::string& name, const std::string& vertexPath, const std::string& pixelPath)
 	{
 		// check
-		LT_ENGINE_ASSERT(!vertexPath.empty(), "ResourceManager::LoadShader: 'vertexPath' is empty");
-		LT_ENGINE_ASSERT(!pixelPath.empty(), "ResourceManager::LoadShader: 'pixelPath' is empty");
+		LT_ENGINE_ASSERT(!vertexPath.empty(), "ResourceManager::LoadShaderImpl: 'vertexPath' is empty");
+		LT_ENGINE_ASSERT(!pixelPath.empty(), "ResourceManager::LoadShaderImpl: 'pixelPath' is empty");
 
 		std::string vPath = vertexPath + (GraphicsContext::GetGraphicsAPI() == GraphicsAPI::OpenGL ? ".glsl" : ".hlsl");
 		std::string pPath = pixelPath  + (GraphicsContext::GetGraphicsAPI() == GraphicsAPI::OpenGL ? ".glsl" : ".hlsl");
@@ -80,11 +80,11 @@ namespace Light {
 		unsigned char* pixels = stbi_load(path.c_str(), &width, &height, &components, desiredComponents);
 		
 		// check
-		LT_ENGINE_ASSERT(pixels, "ResourceManager::LoadTexture: failed to load texture <{}>, 'path': {}", name, path);
+		LT_ENGINE_ASSERT(pixels, "ResourceManager::LoadTextureImpl: failed to load texture <{}>, 'path': {}", name, path);
 		if (components != desiredComponents)
 		{
-			LT_ENGINE_WARN("ResourceManager::LoadTexture: image file compoenents != 'desiredComponents' ({} - {})", components, desiredComponents);
-			LT_ENGINE_WARN("ResourceManager::LoadTexture: <{}> 'path': {}", name, path);
+			LT_ENGINE_WARN("ResourceManager::LoadTextureImpl: image file compoenents != 'desiredComponents' ({} - {})", components, desiredComponents);
+			LT_ENGINE_WARN("ResourceManager::LoadTextureImpl: <{}> 'path': {}", name, path);
 		}
 
 		// create texture
diff --git a/Engine/src/Platform/GraphicsAPI/DirectX/dxGraphicsContext.cpp b/Engine/src/Platform/GraphicsAPI/DirectX/dxGraphicsContext.cpp
index 51b1fdb..c51c59e 100644
--- a/Engine/src/Platform/GraphicsAPI/DirectX/dxGraphicsContext.cpp
+++ b/Engine/src/Platform/GraphicsAPI/DirectX/dxGraphicsContext.cpp
@@ -38,8 +38,8 @@ namespace Light {
 		DXGI_SWAP_CHAIN_DESC sd = { 0 };
 
 		// buffer desc
-		sd.BufferDesc.Width = 800u;
-		sd.BufferDesc.Height = 600u;
+		sd.BufferDesc.Width = 1u;
+		sd.BufferDesc.Height = 1u;
 		sd.BufferDesc.RefreshRate.Numerator = NULL; // :#todo
 		sd.BufferDesc.RefreshRate.Denominator = NULL; // :#todo
 		sd.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
diff --git a/Engine/src/Platform/GraphicsAPI/OpenGL/glShader.cpp b/Engine/src/Platform/GraphicsAPI/OpenGL/glShader.cpp
index a350ad4..5f463f6 100644
--- a/Engine/src/Platform/GraphicsAPI/OpenGL/glShader.cpp
+++ b/Engine/src/Platform/GraphicsAPI/OpenGL/glShader.cpp
@@ -76,8 +76,6 @@ namespace Light {
 		// delete shaders (free memory)
 		glDeleteShader(vertexShader);
 		glDeleteShader(fragmentShader);
-
-		// #todo: validate program
 	}
 
 	glShader::~glShader()
diff --git a/Mirror/build.lua b/Mirror/build.lua
index 54dc0f7..48de4d0 100644
--- a/Mirror/build.lua
+++ b/Mirror/build.lua
@@ -43,6 +43,7 @@ project "Mirror"
 		"GLAD",
 		"ImGui",
 		"stb_image" ,
+		"entt",
 	}
 
 	--- Filters ---
diff --git a/Sandbox/build.lua b/Sandbox/build.lua
index c3f326b..fedbbea 100644
--- a/Sandbox/build.lua
+++ b/Sandbox/build.lua
@@ -43,6 +43,7 @@ project "Sandbox"
 		"GLAD",
 		"ImGui",
 		"stb_image" ,
+		"entt",
 	}
 
 	--- Filters ---