Merge pull request #212 from autobotoptimusprime/main 第十题

第十题 mq败.cpp

src/群友提交/第10题/mq败.cpp

@@ -0,0 +1,66 @@
+#include <iostream>
+#include <type_traits>
+#include <vector>
+
+namespace detail {
+    template<typename...>
+    constexpr bool always_false = false;
+
+    template<typename T>
+    using remove_cvref_t = std::remove_cv_t<std::remove_reference_t<T>>;
+
+    template<std::size_t N>
+    using size_constant = std::integral_constant<std::size_t, N>;
+
+    struct enable_as_any_type_helper {
+        template<typename T>
+        operator T () noexcept;
+    };
+
+    template<std::size_t I>
+    using enable_as_any_type = enable_as_any_type_helper;
+
+    template<typename Aggregate, typename IndexSequence, typename = void>
+    struct test_constructible_helper : std::false_type {};
+
+    template<typename Aggregate, std::size_t... Idx>
+    struct test_constructible_helper<Aggregate, std::index_sequence<Idx...>, std::void_t<decltype(Aggregate{{std::declval<enable_as_any_type<Idx>>()}...})>> : std::true_type {};
+
+    template<typename Aggregate, std::size_t N>
+    struct test_constructible : test_constructible_helper<Aggregate, std::make_index_sequence<N>> {};
+
+    template<std::size_t N, typename Aggregate> 
+    struct size_helper : std::conditional_t<test_constructible<Aggregate, N+1>::value, size_helper<N+1, Aggregate>, size_constant<N>> {};
+
+    template<typename T, typename = void>
+    struct size {
+        static_assert(always_false<T>, "type `T` must be an aggregate-type!");
+    };
+
+    template<typename Aggregate>
+    struct size<Aggregate, std::enable_if_t<std::is_aggregate_v<Aggregate>>> : size_helper<0, Aggregate> {};
+}
+
+template<typename Aggregate>
+constexpr std::size_t size = detail::size<Aggregate>::value;
+
+struct Pos {
+    int x;
+    int y;
+    int z;
+};
+
+struct Agg {
+    int i;
+    Pos pos;
+    int arr[4];
+    std::string str;
+    std::vector<int> vec;
+    float f;
+};
+
+auto main() ->int {
+    std::cout << size<Agg> << std::endl;
+    // 遍历成员那个就不写了, 😊
+    return 0;
+}