added type_list_size and type_list_size_v

src/entt/core/type_traits.hpp

@@ -10,15 +10,32 @@
 namespace entt {
 
 
+/*! @brief A class to use to push around lists of types, nothing more. */
+template<typename...>
+struct type_list {};
+
+
+/*! @brief Primary template isn't defined on purpose. */
+template<typename>
+struct type_list_size;
+
+
 /**
- * @brief A class to use to push around lists of types, nothing more.
- * @tparam Type Types provided by the given type list.
+ * @brief Compile-time number of elements in a type list.
+ * @tparam Type Types provided by the type list.
  */
 template<typename... Type>
-struct type_list {
-    /*! @brief Unsigned integer type. */
-    static constexpr auto size = sizeof...(Type);
-};
+struct type_list_size<type_list<Type...>>
+        : std::integral_constant<std::size_t, sizeof...(Type)>
+{};
+
+
+/**
+ * @brief Helper variable template.
+ * @tparam List Type list.
+ */
+template<class List>
+constexpr auto type_list_size_v = type_list_size<List>::value;
 
 
 /*! @brief Primary template isn't defined on purpose. */
@@ -145,9 +162,6 @@ struct is_named_type<Type, std::void_t<named_type_traits_t<std::decay_t<Type>>>>
 
 /**
  * @brief Helper variable template.
- *
- * True if a given type has a name, false otherwise.
- *
  * @tparam Type Potentially named type.
  */
 template<class Type>

test/entt/core/type_traits.cpp

@@ -5,8 +5,8 @@ TEST(TypeList, Functionalities) {
     using type = entt::type_list<int, char>;
     using other = entt::type_list<double>;
 
-    ASSERT_EQ((type::size), (decltype(type::size){2}));
-    ASSERT_EQ((other::size), (decltype(other::size){1}));
+    ASSERT_EQ(entt::type_list_size_v<type>, 2u);
+    ASSERT_EQ(entt::type_list_size_v<other>, 1u);
     ASSERT_TRUE((std::is_same_v<entt::type_list_cat_t<type, other, type, other>, entt::type_list<int, char, double, int, char, double>>));
     ASSERT_TRUE((std::is_same_v<entt::type_list_cat_t<type, other>, entt::type_list<int, char, double>>));
     ASSERT_TRUE((std::is_same_v<entt::type_list_cat_t<type, type>, entt::type_list<int, char, int, char>>));