AssetHandles.h

#pragma once
 
#include <cstddef>
#include <cstdint>
#include <functional>
 
namespace Engine::Assets
{
    template <typename Tag>
    struct AssetHandle
    {
        uint32_t index = 0;

        uint32_t generation = 0;

        [[nodiscard]] bool isValid() const noexcept { return generation != 0; }

        explicit operator bool() const noexcept { return isValid(); }

        friend bool operator==(AssetHandle lhs, AssetHandle rhs) noexcept
        {
            return lhs.index == rhs.index && lhs.generation == rhs.generation;
        }

        friend bool operator!=(AssetHandle lhs, AssetHandle rhs) noexcept
        {
            return !(lhs == rhs);
        }
    };

    struct NullAssetHandle
    {
        template <typename Tag>
        [[nodiscard]] constexpr operator AssetHandle<Tag>() const noexcept
        {
            return {};
        }
    };

    inline constexpr NullAssetHandle Null{};

    template <typename Tag>
    struct AssetHandleHash
    {
        std::size_t operator()(AssetHandle<Tag> handle) const noexcept
        {
            return (static_cast<std::size_t>(handle.index) << 32u) ^ handle.generation;
        }
    };
 
    struct GltfHandleTag;
    struct GltfRenderableHandleTag;
    struct GeometryMeshHandleTag;
    struct MaterialHandleTag;
    struct Texture2DHandleTag;
    struct CubemapTextureHandleTag;
    struct RenderTargetTextureHandleTag;
    struct FontAtlasTextureHandleTag;
    struct AudioClipHandleTag;
    struct SkeletalMeshHandleTag;
    struct AnimationClipHandleTag;
    struct SkinHandleTag;
    struct SkeletonHandleTag;
    struct FontHandleTag;

    using GltfHandle = AssetHandle<GltfHandleTag>;

    using GltfRenderableHandle = AssetHandle<GltfRenderableHandleTag>;

    using GeometryMeshHandle = AssetHandle<GeometryMeshHandleTag>;

    using MaterialHandle = AssetHandle<MaterialHandleTag>;

    using Texture2DHandle = AssetHandle<Texture2DHandleTag>;

    using CubemapTextureHandle = AssetHandle<CubemapTextureHandleTag>;

    using RenderTargetTextureHandle = AssetHandle<RenderTargetTextureHandleTag>;

    using FontAtlasTextureHandle = AssetHandle<FontAtlasTextureHandleTag>;

    using AudioClipHandle = AssetHandle<AudioClipHandleTag>;

    using SkeletalMeshHandle = AssetHandle<SkeletalMeshHandleTag>;

    using AnimationClipHandle = AssetHandle<AnimationClipHandleTag>;

    using SkinHandle = AssetHandle<SkinHandleTag>;

    using SkeletonHandle = AssetHandle<SkeletonHandleTag>;

    using FontHandle = AssetHandle<FontHandleTag>;
}  // namespace Engine::Assets
 
namespace std
{
    template <typename Tag>
    struct hash<Engine::Assets::AssetHandle<Tag>> : Engine::Assets::AssetHandleHash<Tag>
    {
    };
}  // namespace std