build: add entt library

include/entt/meta/context.hpp

@@ -0,0 +1,47 @@
+#ifndef ENTT_META_CTX_HPP
+#define ENTT_META_CTX_HPP
+
+#include "../container/dense_map.hpp"
+#include "../core/fwd.hpp"
+#include "../stl/functional.hpp"
+#include "../stl/memory.hpp"
+#include "fwd.hpp"
+
+namespace entt {
+
+/*! @cond ENTT_INTERNAL */
+namespace internal {
+
+struct meta_type_node;
+
+struct meta_context {
+    using bucket_type = dense_map<id_type, stl::unique_ptr<meta_type_node>, stl::identity>;
+
+    bucket_type bucket;
+
+    [[nodiscard]] inline static meta_context &from(meta_ctx &);
+    [[nodiscard]] inline static const meta_context &from(const meta_ctx &);
+};
+
+} // namespace internal
+/*! @endcond */
+
+/*! @brief Opaque meta context type. */
+struct meta_ctx: private internal::meta_context {
+    // attorney idiom like model to access the base class
+    friend struct internal::meta_context;
+};
+
+/*! @cond ENTT_INTERNAL */
+[[nodiscard]] inline internal::meta_context &internal::meta_context::from(meta_ctx &ctx) {
+    return ctx;
+}
+
+[[nodiscard]] inline const internal::meta_context &internal::meta_context::from(const meta_ctx &ctx) {
+    return ctx;
+}
+/*! @endcond */
+
+} // namespace entt
+
+#endif