meta: added meta context object

src/entt/meta/meta.hpp

@@ -318,7 +318,7 @@ class meta_any {
 
     template<typename Type>
     static Type * release(Type *instance) {
-        auto * const node = internal::meta_info<Type>::resolve();
+        const auto * const node = internal::meta_info<Type>::resolve();
         [[maybe_unused]] const bool destroyed = (!node->dtor || node->dtor->invoke(*instance));
         ENTT_ASSERT(destroyed);
         return instance;
@@ -1748,6 +1748,43 @@ private:
 };
 
 
+/*! @brief Opaque container for a meta context. */
+class meta_ctx {
+    auto ctx() const ENTT_NOEXCEPT {
+        return &internal::meta_info<>::local;
+    }
+
+public:
+    /*! @brief Default constructor. */
+    meta_ctx() ENTT_NOEXCEPT = default;
+
+    /*! @brief Default copy constructor, deleted on purpose. */
+    meta_ctx(const meta_ctx &) = delete;
+    /*! @brief Default move constructor, deleted on purpose. */
+    meta_ctx(meta_ctx &&) = delete;
+
+    /**
+     * @brief Copy assignment operator.
+     * @param other The instance to copy from.
+     * @return This meta object.
+     */
+    meta_ctx & operator=(const meta_ctx &other) {
+        internal::meta_info<>::ctx = other.ctx();
+        return *this;
+    }
+
+    /**
+     * @brief Move assignment operator.
+     * @param other The instance to move from.
+     * @return This meta object.
+     */
+    meta_ctx & operator=(meta_ctx &&other) {
+        internal::meta_info<>::ctx = other.ctx();
+        return *this;
+    }
+};
+
+
 /*! @copydoc operator!=(const meta_prop &, const meta_prop &) */
 inline bool operator!=(const meta_type &lhs, const meta_type &rhs) ENTT_NOEXCEPT {
     return !(lhs == rhs);