The P0318R1 paper added to the C++2a draft recently was not the latest version of the paper, and should have included these changes. These changes will be made to the working draft via a Defect Report, so I'm applying them to libstdc++ now.
* include/std/type_traits (unwrap_reference_t): Define for C++2a. (unwrap_ref_decay): Remove inheritance from unwrap_reference. * testsuite/20_util/unwrap_reference/1.cc: Adjust test to use alias. Tested powerpc64le-linux, committed to trunk.
commit 9e09c9a4b99b3be725144aeaebe902783a9e70a3 Author: Jonathan Wakely <jwak...@redhat.com> Date: Tue Apr 23 10:58:22 2019 +0100 Corrections for C++2a std::unwrap_reference traits The P0318R1 paper added to the C++2a draft recently was not the latest version of the paper, and should have included these changes. These changes will be made to the working draft via a Defect Report, so I'm applying them to libstdc++ now. * include/std/type_traits (unwrap_reference_t): Define for C++2a. (unwrap_ref_decay): Remove inheritance from unwrap_reference. * testsuite/20_util/unwrap_reference/1.cc: Adjust test to use alias. diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index c3cb67a457d..e0ac5c88dfc 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -3067,9 +3067,12 @@ template <typename _From, typename _To> template<typename _Tp> struct unwrap_reference<reference_wrapper<_Tp>> { using type = _Tp&; }; + template<typename _Tp> + using unwrap_reference_t = typename unwrap_reference<_Tp>::type; + /// Decay type and if it's a reference_wrapper, unwrap it template<typename _Tp> - struct unwrap_ref_decay : unwrap_reference<decay_t<_Tp>> { }; + struct unwrap_ref_decay { using type = unwrap_reference_t<decay_t<_Tp>>; }; template<typename _Tp> using unwrap_ref_decay_t = typename unwrap_ref_decay<_Tp>::type; diff --git a/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc b/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc index 38feca4bb5b..243526725a0 100644 --- a/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc +++ b/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc @@ -28,7 +28,7 @@ template<typename T, typename U = T> { using std::unwrap_reference; using T2 = typename unwrap_reference<T>::type; - static_assert(expect_same<T2, typename unwrap_reference<T2>::type>::value); + static_assert(expect_same<T2, std::unwrap_reference_t<T2>>::value); return expect_same<T2, U>::value; }