... and in passing use requires-clauses instead of void_t based SFINAE.
This is a non-functional change that'll simplify implementing the
P2655R3 change to common_reference.
PR c++/120446
libstdc++-v3/ChangeLog:
* include/std/type_traits (__common_reference_impl): Rewrite
partial specializations to use requires-clause instead of
an additional void_t template parameter. Consolidate the
partial specializations corresponding to bullet 1.
---
libstdc++-v3/include/std/type_traits | 38 +++++++++-------------------
1 file changed, 12 insertions(+), 26 deletions(-)
diff --git a/libstdc++-v3/include/std/type_traits
b/libstdc++-v3/include/std/type_traits
index 77ebb7e2c2f9..8b5110464e50 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -4208,7 +4208,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
{ using type = _Tp0; };
/// @cond undocumented
- template<typename _Tp1, typename _Tp2, int _Bullet = 1, typename = void>
+ template<typename _Tp1, typename _Tp2, int _Bullet = 1>
struct __common_reference_impl
: __common_reference_impl<_Tp1, _Tp2, _Bullet + 1>
{ };
@@ -4221,46 +4221,32 @@ template<typename _Ret, typename _Fn, typename... _Args>
// If T1 and T2 are reference types and COMMON-REF(T1, T2) is well-formed,
...
template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1&, _Tp2&, 1,
- void_t<__common_ref<_Tp1&, _Tp2&>>>
- { using type = __common_ref<_Tp1&, _Tp2&>; };
-
- template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1&&, _Tp2&&, 1,
- void_t<__common_ref<_Tp1&&, _Tp2&&>>>
- { using type = __common_ref<_Tp1&&, _Tp2&&>; };
-
- template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1&, _Tp2&&, 1,
- void_t<__common_ref<_Tp1&, _Tp2&&>>>
- { using type = __common_ref<_Tp1&, _Tp2&&>; };
-
- template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1&&, _Tp2&, 1,
- void_t<__common_ref<_Tp1&&, _Tp2&>>>
- { using type = __common_ref<_Tp1&&, _Tp2&>; };
+ requires is_reference_v<_Tp1> && is_reference_v<_Tp2>
+ && requires { typename __common_ref<_Tp1, _Tp2>; }
+ struct __common_reference_impl<_Tp1, _Tp2, 1>
+ { using type = __common_ref<_Tp1, _Tp2>; };
// Otherwise, if basic_common_reference<...>::type is well-formed, ...
template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1, _Tp2, 2,
- void_t<__basic_common_ref<_Tp1, _Tp2>>>
+ requires requires { typename __basic_common_ref<_Tp1, _Tp2>; }
+ struct __common_reference_impl<_Tp1, _Tp2, 2>
{ using type = __basic_common_ref<_Tp1, _Tp2>; };
// Otherwise, if COND-RES(T1, T2) is well-formed, ...
template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1, _Tp2, 3,
- void_t<__cond_res<_Tp1, _Tp2>>>
+ requires requires { typename __cond_res<_Tp1, _Tp2>; }
+ struct __common_reference_impl<_Tp1, _Tp2, 3>
{ using type = __cond_res<_Tp1, _Tp2>; };
// Otherwise, if common_type_t<T1, T2> is well-formed, ...
template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1, _Tp2, 4,
- void_t<common_type_t<_Tp1, _Tp2>>>
+ requires requires { typename common_type_t<_Tp1, _Tp2>; }
+ struct __common_reference_impl<_Tp1, _Tp2, 4>
{ using type = common_type_t<_Tp1, _Tp2>; };
// Otherwise, there shall be no member type.
template<typename _Tp1, typename _Tp2>
- struct __common_reference_impl<_Tp1, _Tp2, 5, void>
+ struct __common_reference_impl<_Tp1, _Tp2, 5>
{ };
// Otherwise, if sizeof...(T) is greater than two, ...
--
2.51.0.491.g4b71b29477
