1 // Copyright (C) 2018-2019 Free Software Foundation, Inc.
3 // This file is part of the GNU ISO C++ Library. This library is free
4 // software; you can redistribute it and/or modify it under the
5 // terms of the GNU General Public License as published by the
6 // Free Software Foundation; either version 3, or (at your option)
9 // This library is distributed in the hope that it will be useful,
10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 // GNU General Public License for more details.
14 // You should have received a copy of the GNU General Public License along
15 // with this library; see the file COPYING3. If not see
16 // <http://www.gnu.org/licenses/>.
18 // { dg-options "-std=gnu++2a" }
19 // { dg-do compile { target c++2a } }
21 #include <type_traits>
23 template<typename T
, typename U
> struct expect_same
;
24 template<typename T
> struct expect_same
<T
, T
> : std::true_type
{ };
26 template<typename T
, typename U
= T
>
27 constexpr bool check()
29 using std::unwrap_reference
;
30 using T2
= typename unwrap_reference
<T
>::type
;
31 static_assert(expect_same
<T2
, typename unwrap_reference
<T2
>::type
>::value
);
32 return expect_same
<T2
, U
>::value
;
38 static_assert( check
<int>() );
39 static_assert( check
<const int>() );
40 static_assert( check
<const int&>() );
41 static_assert( check
<const int*>() );
42 static_assert( check
<const int*&>() );
44 // reference_wrapper types should get unwrapped:
45 static_assert( check
<std::reference_wrapper
<int>, int&>() );
46 static_assert( check
<std::reference_wrapper
<const int>, const int&>() );
47 static_assert( check
<std::reference_wrapper
<long>, long&>() );
49 // But not cv-qualified reference_wrapper types:
50 static_assert( check
<const std::reference_wrapper
<int>>() );
51 static_assert( check
<volatile std::reference_wrapper
<int>>() );
52 static_assert( check
<const volatile std::reference_wrapper
<int>>() );
54 // Or references to reference_wrapper types:
55 static_assert( check
<std::reference_wrapper
<int>&>() );
56 static_assert( check
<std::reference_wrapper
<int>&&>() );
57 static_assert( check
<const std::reference_wrapper
<int>&>() );