We implement this paper as a DR against C++20 (as do MSVC and libc++).
PR libstdc++/120446
libstdc++-v3/ChangeLog:
* include/bits/version.def (common_reference): New.
* include/bits/version.h: Regenerate.
* include/std/type_traits (__glibcxx_want_common_reference):
Define.
(__common_reference_impl<T1, T2, 1>): Add pointer convertibility
constraints as per P2655R3.
* testsuite/20_util/common_reference/p2655r3.cc: New test.
---
libstdc++-v3/include/bits/version.def | 8 ++++++++
libstdc++-v3/include/bits/version.h | 10 ++++++++++
libstdc++-v3/include/std/type_traits | 7 +++++++
.../testsuite/20_util/common_reference/p2655r3.cc | 15 +++++++++++++++
4 files changed, 40 insertions(+)
create mode 100644 libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc
diff --git a/libstdc++-v3/include/bits/version.def
b/libstdc++-v3/include/bits/version.def
index 83f1817bf8e4..e2b064e09b1e 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1793,6 +1793,14 @@ ftms = {
};
};
+ftms = {
+ name = common_reference;
+ values = {
+ v = 202302;
+ cxxmin = 20; // We treat P2655R3 as a DR against C++20.
+ };
+};
+
ftms = {
name = formatters;
values = {
diff --git a/libstdc++-v3/include/bits/version.h
b/libstdc++-v3/include/bits/version.h
index 0d6692d244a6..4581519d3a7d 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2001,6 +2001,16 @@
#endif /* !defined(__cpp_lib_flat_set) */
#undef __glibcxx_want_flat_set
+#if !defined(__cpp_lib_common_reference)
+# if (__cplusplus >= 202002L)
+# define __glibcxx_common_reference 202302L
+# if defined(__glibcxx_want_all) || defined(__glibcxx_want_common_reference)
+# define __cpp_lib_common_reference 202302L
+# endif
+# endif
+#endif /* !defined(__cpp_lib_common_reference) &&
defined(__glibcxx_want_common_reference) */
+#undef __glibcxx_want_common_reference
+
#if !defined(__cpp_lib_formatters)
# if (__cplusplus >= 202100L) && _GLIBCXX_HOSTED
# define __glibcxx_formatters 202302L
diff --git a/libstdc++-v3/include/std/type_traits
b/libstdc++-v3/include/std/type_traits
index 8b5110464e50..47cbf21b4c1d 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -41,6 +41,7 @@
#define __glibcxx_want_bool_constant
#define __glibcxx_want_bounded_array_traits
+#define __glibcxx_want_common_reference
#define __glibcxx_want_constant_wrapper
#define __glibcxx_want_has_unique_object_representations
#define __glibcxx_want_integral_constant_callable
@@ -4223,6 +4224,12 @@ template<typename _Ret, typename _Fn, typename... _Args>
template<typename _Tp1, typename _Tp2>
requires is_reference_v<_Tp1> && is_reference_v<_Tp2>
&& requires { typename __common_ref<_Tp1, _Tp2>; }
+#if __cpp_lib_common_reference // C++ >= 20
+ && is_convertible_v<add_pointer_t<_Tp1>,
+ add_pointer_t<__common_ref<_Tp1, _Tp2>>>
+ && is_convertible_v<add_pointer_t<_Tp2>,
+ add_pointer_t<__common_ref<_Tp1, _Tp2>>>
+#endif
struct __common_reference_impl<_Tp1, _Tp2, 1>
{ using type = __common_ref<_Tp1, _Tp2>; };
diff --git a/libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc
b/libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc
new file mode 100644
index 000000000000..4188dd2fb29f
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc
@@ -0,0 +1,15 @@
+// P2655R3 - common_reference_t of reference_wrapper Should Be a Reference Type
+// Implemented as a DR against C++20
+// { dg-do compile { target c++20 } }
+
+#include <type_traits>
+
+#if __cpp_lib_common_reference != 202302L
+# error "Feature-test macro __cpp_lib_common_reference has wrong value in
<type_traits>"
+#endif
+
+struct A { };
+struct B { operator A&() const; };
+
+static_assert( std::is_same_v<std::common_reference_t<A&, const B&>, A&> );
+static_assert( std::is_same_v<std::common_reference_t<const B&, A&>, A&> );
--
2.51.0.491.g4b71b29477
