add test coverage for P2445R1 (std::forward_like)

tests/std/tests/P2445R1_forward_like/test.cpp

@@ -0,0 +1,111 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <type_traits>
+#include <utility>
+
+using namespace std;
+
+struct U {}; // class type so const-qualification is not stripped from a prvalue
+using CU = const U;
+using T  = int;
+using CT = const T;
+
+U u{};
+const U& cu = u;
+
+static_assert(is_same_v<decltype(forward_like<T>(U{})), U&&>);
+static_assert(is_same_v<decltype(forward_like<T>(CU{})), CU&&>);
+static_assert(is_same_v<decltype(forward_like<T>(u)), U&&>);
+static_assert(is_same_v<decltype(forward_like<T>(cu)), CU&&>);
+static_assert(is_same_v<decltype(forward_like<T>(std::move(u))), U&&>);
+static_assert(is_same_v<decltype(forward_like<T>(std::move(cu))), CU&&>);
+
+static_assert(is_same_v<decltype(forward_like<CT>(U{})), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT>(CU{})), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT>(u)), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT>(cu)), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT>(std::move(u))), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT>(std::move(cu))), CU&&>);
+
+static_assert(is_same_v<decltype(forward_like<T&>(U{})), U&>);
+static_assert(is_same_v<decltype(forward_like<T&>(CU{})), CU&>);
+static_assert(is_same_v<decltype(forward_like<T&>(u)), U&>);
+static_assert(is_same_v<decltype(forward_like<T&>(cu)), CU&>);
+static_assert(is_same_v<decltype(forward_like<T&>(std::move(u))), U&>);
+static_assert(is_same_v<decltype(forward_like<T&>(std::move(cu))), CU&>);
+
+static_assert(is_same_v<decltype(forward_like<CT&>(U{})), CU&>);
+static_assert(is_same_v<decltype(forward_like<CT&>(CU{})), CU&>);
+static_assert(is_same_v<decltype(forward_like<CT&>(u)), CU&>);
+static_assert(is_same_v<decltype(forward_like<CT&>(cu)), CU&>);
+static_assert(is_same_v<decltype(forward_like<CT&>(std::move(u))), CU&>);
+static_assert(is_same_v<decltype(forward_like<CT&>(std::move(cu))), CU&>);
+
+static_assert(is_same_v<decltype(forward_like<T&&>(U{})), U&&>);
+static_assert(is_same_v<decltype(forward_like<T&&>(CU{})), CU&&>);
+static_assert(is_same_v<decltype(forward_like<T&&>(u)), U&&>);
+static_assert(is_same_v<decltype(forward_like<T&&>(cu)), CU&&>);
+static_assert(is_same_v<decltype(forward_like<T&&>(std::move(u))), U&&>);
+static_assert(is_same_v<decltype(forward_like<T&&>(std::move(cu))), CU&&>);
+
+static_assert(is_same_v<decltype(forward_like<CT&&>(U{})), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT&&>(CU{})), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT&&>(u)), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT&&>(cu)), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT&&>(std::move(u))), CU&&>);
+static_assert(is_same_v<decltype(forward_like<CT&&>(std::move(cu))), CU&&>);
+
+static_assert(noexcept(forward_like<T>(u)));
+
+static_assert(is_same_v<decltype(forward_like<U&>(u)), U&>);
+static_assert(is_same_v<decltype(forward_like<CU&>(cu)), CU&>);
+static_assert(is_same_v<decltype(forward_like<U&&>(std::move(u))), U&&>);
+static_assert(is_same_v<decltype(forward_like<CU&&>(std::move(cu))), CU&&>);
+
+struct NoCtorCopyMove {
+    NoCtorCopyMove()                      = delete;
+    NoCtorCopyMove(const NoCtorCopyMove&) = delete;
+    NoCtorCopyMove(NoCtorCopyMove&&)      = delete;
+};
+
+static_assert(is_same_v<decltype(forward_like<CT&&>(declval<NoCtorCopyMove>())), const NoCtorCopyMove&&>);
+static_assert(is_same_v<decltype(forward_like<CT&>(declval<NoCtorCopyMove>())), const NoCtorCopyMove&>);
+static_assert(is_same_v<decltype(forward_like<T&&>(declval<NoCtorCopyMove>())), NoCtorCopyMove&&>);
+static_assert(is_same_v<decltype(forward_like<T&>(declval<NoCtorCopyMove>())), NoCtorCopyMove&>);
+
+static_assert(noexcept(forward_like<T>(declval<NoCtorCopyMove>())));
+
+constexpr bool test() {
+    {
+        int val       = 1729;
+        auto&& result = forward_like<const double&>(val);
+        static_assert(is_same_v<decltype(result), const int&>);
+        assert(&result == &val);
+    }
+    {
+        int val       = 1729;
+        auto&& result = forward_like<double&>(val);
+        static_assert(is_same_v<decltype(result), int&>);
+        assert(&result == &val);
+    }
+    {
+        int val       = 1729;
+        auto&& result = forward_like<const double&&>(val);
+        static_assert(is_same_v<decltype(result), const int&&>);
+        assert(&result == &val);
+    }
+    {
+        int val       = 1729;
+        auto&& result = forward_like<double&&>(val);
+        static_assert(is_same_v<decltype(result), int&&>);
+        assert(&result == &val);
+    }
+    return true;
+}
+
+int main() {
+    assert(test());
+    static_assert(test());
+}