component: yet another piece to fully support non-movable types (see #905)

src/entt/entity/component.hpp

@@ -14,8 +14,8 @@ namespace entt {
 
 namespace internal {
 
-template<typename, typename = void>
-struct in_place_delete: std::false_type {};
+template<typename Type, typename = void>
+struct in_place_delete: std::bool_constant<!(std::is_move_constructible_v<Type> && std::is_move_assignable_v<Type>)> {};
 
 template<typename Type>
 struct in_place_delete<Type, std::enable_if_t<Type::in_place_delete>>

test/entt/entity/component.cpp

@@ -1,6 +1,19 @@
 #include <gtest/gtest.h>
 #include <entt/entity/component.hpp>
 
+struct empty {};
+
+struct non_empty {
+    int value;
+};
+
+struct non_movable {
+    non_movable() = default;
+    non_movable(const non_movable &) = delete;
+    non_movable &operator=(const non_movable &) = delete;
+    int value;
+};
+
 struct self_contained {
     static constexpr auto in_place_delete = true;
     static constexpr auto page_size = 4u;
@@ -15,36 +28,39 @@ struct entt::component_traits<traits_based> {
     static constexpr auto page_size = 8u;
 };
 
-struct default_params_empty {};
-struct default_params_non_empty {
-    int value;
-};
-
 TEST(Component, VoidType) {
     using traits = entt::component_traits<void>;
 
-    static_assert(!traits::in_place_delete);
+    static_assert(traits::in_place_delete);
     static_assert(entt::ignore_as_empty_v<typename traits::type>);
     // we don't really care about this thanks to ignore_as_empty_v
     static_assert(traits::page_size != 0u);
 }
 
-TEST(Component, DefaultParamsEmpty) {
-    using traits = entt::component_traits<default_params_empty>;
+TEST(Component, Empty) {
+    using traits = entt::component_traits<empty>;
 
     static_assert(!traits::in_place_delete);
     static_assert(entt::ignore_as_empty_v<typename traits::type>);
     static_assert(traits::page_size == 0u);
 }
 
-TEST(Component, DefaultParamsNonEmpty) {
-    using traits = entt::component_traits<default_params_non_empty>;
+TEST(Component, NonEmpty) {
+    using traits = entt::component_traits<non_empty>;
 
     static_assert(!traits::in_place_delete);
     static_assert(!entt::ignore_as_empty_v<typename traits::type>);
     static_assert(traits::page_size == ENTT_PACKED_PAGE);
 }
 
+TEST(Component, NonMovable) {
+    using traits = entt::component_traits<non_movable>;
+
+    static_assert(traits::in_place_delete);
+    static_assert(!entt::ignore_as_empty_v<typename traits::type>);
+    static_assert(traits::page_size == ENTT_PACKED_PAGE);
+}
+
 TEST(Component, SelfContained) {
     using traits = entt::component_traits<self_contained>;