// #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