Implement P0318R1 unwrap_ref_decay and unwrap_reference * include/std/type_traits (unwrap_reference, unwrap_reference_t) (unwrap_ref_decay, unwrap_ref_decay_t): New traits and aliases. * testsuite/20_util/unwrap_reference/1.cc: New test. * testsuite/20_util/unwrap_reference/2.cc: New test.
Tested x86_64-linux, committed to trunk.
commit 5c164b36d9859e73cdac91ce551887a6c72620c7 Author: Jonathan Wakely <jwak...@redhat.com> Date: Sun Nov 11 01:25:44 2018 +0000 Implement P0318R1 unwrap_ref_decay and unwrap_reference Implement P0318R1 unwrap_ref_decay and unwrap_reference * include/std/type_traits (unwrap_reference, unwrap_reference_t) (unwrap_ref_decay, unwrap_ref_decay_t): New traits and aliases. * testsuite/20_util/unwrap_reference/1.cc: New test. * testsuite/20_util/unwrap_reference/2.cc: New test. diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index 86b58ccf225..60094f9897b 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -3015,6 +3015,20 @@ template <typename _From, typename _To> template<typename _Tp> using type_identity_t = typename type_identity<_Tp>::type; + /// Unwrap a reference_wrapper + template<typename _Tp> + struct unwrap_reference { using type = _Tp; }; + + template<typename _Tp> + struct unwrap_reference<reference_wrapper<_Tp>> { using type = _Tp&; }; + + /// Decay type and if it's a reference_wrapper, unwrap it + template<typename _Tp> + struct unwrap_ref_decay : unwrap_reference<decay_t<_Tp>> { }; + + template<typename _Tp> + using unwrap_ref_decay_t = typename unwrap_ref_decay<_Tp>::type; + #endif // C++2a _GLIBCXX_END_NAMESPACE_VERSION diff --git a/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc b/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc new file mode 100644 index 00000000000..d259db91418 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc @@ -0,0 +1,58 @@ +// Copyright (C) 2018 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// <http://www.gnu.org/licenses/>. + +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include <type_traits> + +template<typename T, typename U> struct expect_same; +template<typename T> struct expect_same<T, T> : std::true_type { }; + +template<typename T, typename U = T> + constexpr bool check() + { + using std::unwrap_reference; + using T2 = typename unwrap_reference<T>::type; + static_assert(expect_same<T2, typename unwrap_reference<T2>::type>::value); + return expect_same<T2, U>::value; + } + +void +test01() +{ + static_assert( check<int>() ); + static_assert( check<const int>() ); + static_assert( check<const int&>() ); + static_assert( check<const int*>() ); + static_assert( check<const int*&>() ); + + // reference_wrapper types should get unwrapped: + static_assert( check<std::reference_wrapper<int>, int&>() ); + static_assert( check<std::reference_wrapper<const int>, const int&>() ); + static_assert( check<std::reference_wrapper<long>, long&>() ); + + // But not cv-qualified reference_wrapper types: + static_assert( check<const std::reference_wrapper<int>>() ); + static_assert( check<volatile std::reference_wrapper<int>>() ); + static_assert( check<const volatile std::reference_wrapper<int>>() ); + + // Or references to reference_wrapper types: + static_assert( check<std::reference_wrapper<int>&>() ); + static_assert( check<std::reference_wrapper<int>&&>() ); + static_assert( check<const std::reference_wrapper<int>&>() ); +} diff --git a/libstdc++-v3/testsuite/20_util/unwrap_reference/2.cc b/libstdc++-v3/testsuite/20_util/unwrap_reference/2.cc new file mode 100644 index 00000000000..47bfa71975e --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/unwrap_reference/2.cc @@ -0,0 +1,51 @@ +// Copyright (C) 2018 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// <http://www.gnu.org/licenses/>. + +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include <type_traits> + +template<typename T, typename U> struct expect_same; +template<typename T> struct expect_same<T, T> : std::true_type { }; + +template<typename T, typename U = std::decay_t<T>> + constexpr bool check() + { + using T2 = typename std::unwrap_ref_decay<T>::type; + static_assert(expect_same<T2, std::unwrap_ref_decay_t<T>>::value); + return expect_same<T2, U>::value; + } + +void +test01() +{ + static_assert( check<int>() ); + static_assert( check<const int>() ); + static_assert( check<const int&>() ); + static_assert( check<const int*>() ); + static_assert( check<const int*&>() ); + + // reference_wrapper types (including cv and references) get unwrapped: + static_assert( check<std::reference_wrapper<int>, int&>() ); + static_assert( check<std::reference_wrapper<int>&, int&>() ); + static_assert( check<const std::reference_wrapper<int>, int&>() ); + static_assert( check<const std::reference_wrapper<int>&, int&>() ); + static_assert( check<std::reference_wrapper<const int>, const int&>() ); + static_assert( check<std::reference_wrapper<const int>&, const int&>() ); + static_assert( check<std::reference_wrapper<long>, long&>() ); +}