type_traits: std::tuple traits specialization for entt::type_list and entt::value_list (#1011)

src/entt/core/type_traits.hpp

@@ -3,6 +3,7 @@
 
 #include <cstddef>
 #include <iterator>
+#include <tuple>
 #include <type_traits>
 #include <utility>
 #include "../config/config.h"
@@ -387,8 +388,19 @@ template<auto Value, auto... Other>
 struct value_list_element<0u, value_list<Value, Other...>> {
     /*! @brief Searched value. */
     static constexpr auto value = Value;
+
+    /*! @brief Searched type. */
+    using type = decltype(Value);
 };
 
+/**
+ * @brief Helper type.
+ * @tparam Index Index of the type to return.
+ * @tparam List Value list to search into.
+ */
+template<std::size_t Index, typename List>
+using value_list_element_t = typename value_list_element<Index, List>::type;
+
 /**
  * @brief Helper type.
  * @tparam Index Index of the value to return.
@@ -894,4 +906,16 @@ using nth_argument_t = typename nth_argument<Index, Candidate>::type;
 
 } // namespace entt
 
+template <typename... Type>
+struct std::tuple_size<entt::type_list<Type...>>: std::integral_constant<std::size_t, entt::type_list<Type...>::size> {};
+
+template <std::size_t Index, typename... Type>
+struct std::tuple_element<Index, entt::type_list<Type...>>: entt::type_list_element<Index, entt::type_list<Type...>> {};
+
+template <auto... Value>
+struct std::tuple_size<entt::value_list<Value...>>: std::integral_constant<std::size_t, entt::value_list<Value...>::size> {};
+
+template <std::size_t Index, auto... Value>
+struct std::tuple_element<Index, entt::value_list<Value...>>: entt::value_list_element<Index, entt::value_list<Value...>> {};
+
 #endif

test/entt/core/type_traits.cpp

@@ -238,3 +238,27 @@ TEST(Tag, Functionalities) {
     static_assert(entt::tag<"foobar"_hs>::value == entt::hashed_string::value("foobar"));
     static_assert(std::is_same_v<typename entt::tag<"foobar"_hs>::value_type, entt::id_type>);
 }
+
+TEST(TypeList, TupleSize) {
+    ASSERT_EQ(std::tuple_size_v<entt::type_list<>>, 0u);
+    ASSERT_EQ(std::tuple_size_v<entt::type_list<int>>, 1u);
+    ASSERT_EQ((std::tuple_size_v<entt::type_list<int, float>>), 2u);
+}
+
+TEST(TypeList, TupleElement) {
+    ASSERT_TRUE((std::is_same_v<int, std::tuple_element_t<0, entt::type_list<int>>>));
+    ASSERT_TRUE((std::is_same_v<int, std::tuple_element_t<0, entt::type_list<int, float>>>));
+    ASSERT_TRUE((std::is_same_v<float, std::tuple_element_t<1, entt::type_list<int, float>>>));
+}
+
+TEST(ValueList, TupleSize) {
+    ASSERT_EQ(std::tuple_size_v<entt::value_list<>>, 0u);
+    ASSERT_EQ(std::tuple_size_v<entt::value_list<42>>, 1u);
+    ASSERT_EQ((std::tuple_size_v<entt::value_list<42, 'a'>>), 2u);
+}
+
+TEST(ValueList, TupleElement) {
+    ASSERT_TRUE((std::is_same_v<int, std::tuple_element_t<0, entt::value_list<42>>>));
+    ASSERT_TRUE((std::is_same_v<int, std::tuple_element_t<0, entt::value_list<42, 'a'>>>));
+    ASSERT_TRUE((std::is_same_v<char, std::tuple_element_t<1, entt::value_list<42, 'a'>>>));
+}