build: add entt library

include/entt/meta/pointer.hpp

@@ -0,0 +1,42 @@
+// IWYU pragma: always_keep
+
+#ifndef ENTT_META_POINTER_HPP
+#define ENTT_META_POINTER_HPP
+
+#include "../stl/memory.hpp"
+#include "../stl/type_traits.hpp"
+#include "type_traits.hpp"
+
+namespace entt {
+
+/**
+ * @brief Makes `stl::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<stl::shared_ptr<Type>>
+    : stl::true_type {};
+
+/**
+ * @brief Makes `stl::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<stl::unique_ptr<Type, Args...>>
+    : stl::true_type {};
+
+/**
+ * @brief Specialization for self-proclaimed meta pointer like types.
+ * @tparam Type Element type.
+ */
+template<typename Type>
+requires requires { typename Type::is_meta_pointer_like; }
+struct is_meta_pointer_like<Type>
+    : stl::true_type {};
+
+} // namespace entt
+
+#endif