@@ -89,6 +89,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return static_cast<_Tp&&>(__t);
}
+#if __glibcxx_forward_like // C++ >= 23
+ template<typename _Tp, typename _Up>
+ [[nodiscard]]
+ constexpr decltype(auto)
+ forward_like(_Up&& __x) noexcept
+ {
+ constexpr bool __as_rval = is_rvalue_reference_v<_Tp&&>;
+
+ if constexpr (is_const_v<remove_reference_t<_Tp>>)
+ {
+ using _Up2 = remove_reference_t<_Up>;
+ if constexpr (__as_rval)
+ return static_cast<const _Up2&&>(__x);
+ else
+ return static_cast<const _Up2&>(__x);
+ }
+ else
+ {
+ if constexpr (__as_rval)
+ return static_cast<remove_reference_t<_Up>&&>(__x);
+ else
+ return static_cast<_Up&>(__x);
+ }
+ }
+#endif
+
/**
* @brief Convert a value to an rvalue.
* @param __t A thing of arbitrary type.
@@ -1542,6 +1542,14 @@ ftms = {
};
};
+ftms = {
+ name = forward_like;
+ values = {
+ v = 202207;
+ cxxmin = 23;
+ };
+};
+
ftms = {
name = ios_noreplace;
values = {
@@ -68,9 +68,10 @@
#include <bits/stl_relops.h>
#include <bits/stl_pair.h>
-#define __glibcxx_want_exchange_function
-#define __glibcxx_want_constexpr_algorithms
#define __glibcxx_want_as_const
+#define __glibcxx_want_constexpr_algorithms
+#define __glibcxx_want_exchange_function
+#define __glibcxx_want_forward_like
#define __glibcxx_want_integer_comparison_functions
#define __glibcxx_want_to_underlying
#define __glibcxx_want_unreachable
new file mode 100644
@@ -0,0 +1,59 @@
+// { dg-do compile { target c++23 } }
+// { dg-add-options no_pch }
+
+#include <utility>
+
+#ifndef __cpp_lib_forward_like
+# error "Feature-test macro for forward_like missing in <utility>"
+#elif __cpp_lib_forward_like != 202207L
+# error "Feature-test macro for forward_like has wrong value in <utility>"
+#endif
+
+template<typename T, typename U>
+using forward_like_t = decltype(std::forward_like<T>(std::declval<U>()));
+
+#if 0
+using std::is_same_v;
+#else
+#include <concepts>
+template<class T, class U> concept is_same_v = std::same_as<T, U>;
+#endif
+
+static_assert( is_same_v<forward_like_t<int, long>, long&&> );
+static_assert( is_same_v<forward_like_t<int&, long>, long&> );
+static_assert( is_same_v<forward_like_t<int&&, long>, long&&> );
+
+static_assert( is_same_v<forward_like_t<const int, long>, const long&&> );
+static_assert( is_same_v<forward_like_t<const int&, long>, const long&> );
+static_assert( is_same_v<forward_like_t<const int&&, long>, const long&&> );
+
+static_assert( is_same_v<forward_like_t<int, const long>, const long&&> );
+static_assert( is_same_v<forward_like_t<int&, const long>, const long&> );
+static_assert( is_same_v<forward_like_t<int&&, const long>, const long&&> );
+
+static_assert( is_same_v<forward_like_t<const int, long&>, const long&&> );
+static_assert( is_same_v<forward_like_t<const int&, long&>, const long&> );
+static_assert( is_same_v<forward_like_t<const int&&, long&>, const long&&> );
+
+static_assert( is_same_v<forward_like_t<int, const long&>, const long&&> );
+static_assert( is_same_v<forward_like_t<int&, const long&>, const long&> );
+static_assert( is_same_v<forward_like_t<int&&, const long&>, const long&&> );
+
+static_assert( is_same_v<forward_like_t<const int, long&&>, const long&&> );
+static_assert( is_same_v<forward_like_t<const int&, long&&>, const long&> );
+static_assert( is_same_v<forward_like_t<const int&&, long&&>, const long&&> );
+
+static_assert( is_same_v<forward_like_t<int, const long&&>, const long&&> );
+static_assert( is_same_v<forward_like_t<int&, const long&&>, const long&> );
+static_assert( is_same_v<forward_like_t<int&&, const long&&>, const long&&> );
+
+static_assert( is_same_v<forward_like_t<volatile int, long>, long&&> );
+static_assert( is_same_v<forward_like_t<volatile int&, long>, long&> );
+static_assert( is_same_v<forward_like_t<volatile int&&, long>, long&&> );
+
+static_assert( is_same_v<forward_like_t<const int, volatile long>,
+ const volatile long&&> );
+static_assert( is_same_v<forward_like_t<const int&, volatile long>,
+ const volatile long&> );
+static_assert( is_same_v<forward_like_t<const int&&, volatile long>,
+ const volatile long&&> );
new file mode 100644
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++23 } }
+
+#include <utility>
+
+auto x1 = std::forward_like<void>(1); // { dg-error "here" }
+// { dg-error "forming reference to void" "" { target *-*-* } 0 }
+auto x2 = std::forward_like<void()const>(1); // { dg-error "here" }
+// { dg-error "forming reference to qualified function" "" { target *-*-* } 0 }
+
+// { dg-prune-output "inconsistent deduction for auto return type" } // PR111484
new file mode 100644
@@ -0,0 +1,10 @@
+// { dg-do preprocess { target c++23 } }
+// { dg-add-options no_pch }
+
+#include <version>
+
+#ifndef __cpp_lib_forward_like
+# error "Feature-test macro for forward_like missing in <version>"
+#elif __cpp_lib_forward_like != 202207L
+# error "Feature-test macro for forward_like has wrong value in <version>"
+#endif