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 {
 
 
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<>
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;
};
 
 
template<typename Entity>
[[nodiscard]] constexpr auto to_integral(const Entity entity) ENTT_NOEXCEPT {
    return static_cast<typename entt_traits<Entity>::entity_type>(entity);
}
 
 
struct null_t {
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
        return Entity{entt_traits<Entity>::entity_mask};
    }
 
    [[nodiscard]] constexpr bool operator==(const null_t &) const ENTT_NOEXCEPT {
        return true;
    }
 
    [[nodiscard]] constexpr bool operator!=(const null_t &) const ENTT_NOEXCEPT {
        return false;
    }
 
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity &entity) const ENTT_NOEXCEPT {
        return (to_integral(entity) & entt_traits<Entity>::entity_mask) == to_integral(static_cast<Entity>(*this));
    }
 
    template<typename Entity>
    [[nodiscard]] constexpr bool operator!=(const Entity &entity) const ENTT_NOEXCEPT {
        return !(entity == *this);
    }
};
 
 
template<typename Entity>
[[nodiscard]] constexpr bool operator==(const Entity &entity, const null_t &other) ENTT_NOEXCEPT {
    return other.operator==(entity);
}
 
 
template<typename Entity>
[[nodiscard]] constexpr bool operator!=(const Entity &entity, const null_t &other) ENTT_NOEXCEPT {
    return !(other == entity);
}
 
 
inline constexpr null_t null{};
 
 
}
 
 
#endif