entity.hpp

#ifndef ENTT_ENTITY_ENTITY_HPP
#define ENTT_ENTITY_ENTITY_HPP
 
#include <cstddef>
#include <cstdint>
#include <type_traits>
#include "../config/config.h"
#include "fwd.hpp"
 
namespace entt {
 
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;
 
    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;
 
    static constexpr entity_type entity_mask = 0xFFFFFFFF;
    static constexpr entity_type version_mask = 0xFFFFFFFF;
    static constexpr std::size_t entity_shift = 32u;
};
 
} // namespace internal
 
template<typename Type>
class entt_traits: internal::entt_traits<Type> {
    using base_type = internal::entt_traits<Type>;
 
public:
    using value_type = Type;
    using entity_type = typename base_type::entity_type;
    using version_type = typename base_type::version_type;
    static constexpr entity_type reserved = base_type::entity_mask | (base_type::version_mask << base_type::entity_shift);
    static constexpr auto page_size = ENTT_SPARSE_PAGE;
 
    [[nodiscard]] static constexpr entity_type to_integral(const value_type value) ENTT_NOEXCEPT {
        return static_cast<entity_type>(value);
    }
 
    [[nodiscard]] static constexpr entity_type to_entity(const value_type value) ENTT_NOEXCEPT {
        return (to_integral(value) & base_type::entity_mask);
    }
 
    [[nodiscard]] static constexpr version_type to_version(const value_type value) ENTT_NOEXCEPT {
        return (to_integral(value) >> base_type::entity_shift);
    }
 
    [[nodiscard]] static constexpr value_type construct(const entity_type entity, const version_type version) ENTT_NOEXCEPT {
        return value_type{(entity & base_type::entity_mask) | (static_cast<entity_type>(version) << base_type::entity_shift)};
    }
 
    [[nodiscard]] static constexpr value_type combine(const entity_type lhs, const entity_type rhs) ENTT_NOEXCEPT {
        constexpr auto mask = (base_type::version_mask << base_type::entity_shift);
        return value_type{(lhs & base_type::entity_mask) | (rhs & mask)};
    }
};
 
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::entity_type to_integral(const Entity value) ENTT_NOEXCEPT {
    return entt_traits<Entity>::to_integral(value);
}
 
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::entity_type to_entity(const Entity value) ENTT_NOEXCEPT {
    return entt_traits<Entity>::to_entity(value);
}
 
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::version_type to_version(const Entity value) ENTT_NOEXCEPT {
    return entt_traits<Entity>::to_version(value);
}
 
struct null_t {
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::combine(entity_traits::reserved, entity_traits::reserved);
    }
 
    [[nodiscard]] constexpr bool operator==([[maybe_unused]] const null_t other) const ENTT_NOEXCEPT {
        return true;
    }
 
    [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const null_t other) const ENTT_NOEXCEPT {
        return false;
    }
 
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::to_entity(entity) == entity_traits::to_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);
}
 
struct tombstone_t {
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const ENTT_NOEXCEPT {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::combine(entity_traits::reserved, entity_traits::reserved);
    }
 
    [[nodiscard]] constexpr bool operator==([[maybe_unused]] const tombstone_t other) const ENTT_NOEXCEPT {
        return true;
    }
 
    [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const tombstone_t other) const ENTT_NOEXCEPT {
        return false;
    }
 
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::to_version(entity) == entity_traits::to_version(*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 tombstone_t other) ENTT_NOEXCEPT {
    return other.operator==(entity);
}
 
template<typename Entity>
[[nodiscard]] constexpr bool operator!=(const Entity entity, const tombstone_t other) ENTT_NOEXCEPT {
    return !(other == entity);
}
 
inline constexpr null_t null{};
 
inline constexpr tombstone_t tombstone{};
 
} // namespace entt
 
#endif