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818ab71a | 1 | // Copyright (C) 2015-2016 Free Software Foundation, Inc. |
6af6bef4 JW |
2 | // |
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) | |
7 | // any later version. | |
8 | ||
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. | |
13 | ||
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/>. | |
17 | ||
52066eae | 18 | // { dg-do compile { target c++14 } } |
6af6bef4 JW |
19 | |
20 | #include <experimental/type_traits> | |
21 | ||
22 | using std::declval; | |
23 | using std::ptrdiff_t; | |
24 | using std::experimental::is_detected; | |
25 | using std::experimental::is_detected_exact; | |
26 | using std::experimental::detected_or_t; | |
27 | using std::experimental::is_same_v; | |
28 | ||
29 | // Examples taken from N4502 | |
30 | ||
31 | // archetypal helper alias for a copy assignment operation: | |
32 | template <class T> | |
33 | using copy_assign_t = decltype(declval<T&>() = declval<T const &>()); | |
34 | ||
35 | // plausible implementation for the is_assignable type trait: | |
36 | template <class T> | |
37 | using is_copy_assignable = is_detected<copy_assign_t, T>; | |
38 | ||
39 | // plausible implementation for an augmented is_assignable type trait | |
40 | // that also checks the return type: | |
41 | template <class T> | |
42 | using is_canonical_copy_assignable = is_detected_exact<T&, copy_assign_t, T>; | |
43 | ||
44 | struct A { }; | |
45 | struct B { B& operator=(const B&); }; | |
46 | struct C { void operator=(const C&); }; | |
47 | struct D { D& operator=(D&); }; | |
48 | struct E { E& operator=(E&&); }; | |
49 | ||
50 | static_assert( is_copy_assignable<A>::value, "A is copy assignable" ); | |
51 | static_assert( is_copy_assignable<B>::value, "B is copy assignable" ); | |
52 | static_assert( is_copy_assignable<C>::value, "C is copy assignable" ); | |
53 | static_assert( !is_copy_assignable<D>::value, "D is not copy assignable" ); | |
54 | static_assert( !is_copy_assignable<E>::value, "E is not copy assignable" ); | |
55 | ||
56 | static_assert( is_canonical_copy_assignable<A>::value, | |
57 | "A has canonical copy assignment" ); | |
58 | static_assert( is_canonical_copy_assignable<B>::value, | |
59 | "B has canonical copy assignment" ); | |
60 | static_assert( !is_canonical_copy_assignable<C>::value, | |
61 | "C does not have canonical copy assignment" ); | |
62 | static_assert( !is_canonical_copy_assignable<D>::value, | |
63 | "D does not have canonical copy assignment" ); | |
64 | static_assert( !is_canonical_copy_assignable<E>::value, | |
65 | "E does not have canonical copy assignment" ); | |
66 | ||
67 | // archetypal helper alias for a particular type member: | |
68 | template <class T> | |
69 | using diff_t = typename T::difference_type; | |
70 | // alias the type member, if it exists, otherwise alias ptrdiff_t: | |
71 | template <class Ptr> | |
72 | using difference_type = detected_or_t<ptrdiff_t, diff_t, Ptr>; | |
73 | ||
74 | struct has { using difference_type = char; }; | |
75 | struct has_not { }; | |
76 | struct inherits : has { }; | |
77 | struct hides : private has { }; | |
78 | struct reveals : private has { using has::difference_type; }; | |
79 | ||
80 | static_assert( is_same_v<difference_type<has>, char>, "has" ); | |
81 | static_assert( is_same_v<difference_type<has_not>, ptrdiff_t>, "has not" ); | |
82 | static_assert( is_same_v<difference_type<inherits>, char>, "inherits" ); | |
83 | static_assert( is_same_v<difference_type<hides>, ptrdiff_t>, "hides" ); | |
84 | static_assert( is_same_v<difference_type<reveals>, char>, "reveals" ); |