libstdc++: concepts Source File

libstdc++

concepts
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1// <concepts> -*- C++ -*-
2
3// Copyright (C) 2019-2026 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file include/concepts
26 * This is a Standard C++ Library header.
27 * @ingroup concepts
28 */
29
30#ifndef _GLIBCXX_CONCEPTS
31#define _GLIBCXX_CONCEPTS 1
32
33#ifdef _GLIBCXX_SYSHDR
34#pragma GCC system_header
35#endif
36
37#define __glibcxx_want_concepts
38#include <bits/version.h>
39
40#ifdef __cpp_lib_concepts // C++ >= 20 && concepts
41/**
42 * @defgroup concepts Concepts
43 * @ingroup utilities
44 *
45 * Concepts for checking type requirements.
46 */
47
48#include <type_traits>
49
50namespace std _GLIBCXX_VISIBILITY(default)
51{
52_GLIBCXX_BEGIN_NAMESPACE_VERSION
53
54 // [concepts.lang], language-related concepts
55
56 namespace __detail
57 {
58 template<typename _Tp, typename _Up>
59 concept __same_as = std::is_same_v<_Tp, _Up>;
60 } // namespace __detail
61
62 /// [concept.same], concept same_as
63 template<typename _Tp, typename _Up>
64 concept same_as
65 = __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
66
67 namespace __detail
68 {
69 template<typename _Tp, typename _Up>
70 concept __different_from
71 = !same_as<remove_cvref_t<_Tp>, remove_cvref_t<_Up>>;
72 } // namespace __detail
73
74 /// [concept.derived], concept derived_from
75 template<typename _Derived, typename _Base>
76 concept derived_from = __is_base_of(_Base, _Derived)
77 && is_convertible_v<const volatile _Derived*, const volatile _Base*>;
78
79 /// [concept.convertible], concept convertible_to
80 template<typename _From, typename _To>
81 concept convertible_to = is_convertible_v<_From, _To>
82 && requires { static_cast<_To>(std::declval<_From>()); };
83
84 /// [concept.commonref], concept common_reference_with
85 template<typename _Tp, typename _Up>
86 concept common_reference_with
87 = same_as<common_reference_t<_Tp, _Up>, common_reference_t<_Up, _Tp>>
88 && convertible_to<_Tp, common_reference_t<_Tp, _Up>>
89 && convertible_to<_Up, common_reference_t<_Tp, _Up>>;
90
91 /// [concept.common], concept common_with
92 template<typename _Tp, typename _Up>
93 concept common_with
94 = same_as<common_type_t<_Tp, _Up>, common_type_t<_Up, _Tp>>
95 && requires {
96 static_cast<common_type_t<_Tp, _Up>>(std::declval<_Tp>());
97 static_cast<common_type_t<_Tp, _Up>>(std::declval<_Up>());
98 }
99 && common_reference_with<add_lvalue_reference_t<const _Tp>,
100 add_lvalue_reference_t<const _Up>>
101 && common_reference_with<add_lvalue_reference_t<common_type_t<_Tp, _Up>>,
102 common_reference_t<
103 add_lvalue_reference_t<const _Tp>,
104 add_lvalue_reference_t<const _Up>>>;
105
106 // [concepts.arithmetic], arithmetic concepts
107
108 template<typename _Tp>
109 concept integral = is_integral_v<_Tp>;
110
111 template<typename _Tp>
112 concept signed_integral = integral<_Tp> && is_signed_v<_Tp>;
113
114 template<typename _Tp>
115 concept unsigned_integral = integral<_Tp> && !signed_integral<_Tp>;
116
117 template<typename _Tp>
118 concept floating_point = is_floating_point_v<_Tp>;
119
120 namespace __detail
121 {
122 template<typename _Tp>
123 using __cref = const remove_reference_t<_Tp>&;
124
125 template<typename _Tp>
126 concept __class_or_enum
127 = is_class_v<_Tp> || is_union_v<_Tp> || is_enum_v<_Tp>;
128
129 template<typename _Tp>
130 constexpr bool __destructible_impl = false;
131 template<typename _Tp>
132 requires requires(_Tp& __t) { { __t.~_Tp() } noexcept; }
133 constexpr bool __destructible_impl<_Tp> = true;
134
135 template<typename _Tp>
136 constexpr bool __destructible = __destructible_impl<_Tp>;
137 template<typename _Tp>
138 constexpr bool __destructible<_Tp&> = true;
139 template<typename _Tp>
140 constexpr bool __destructible<_Tp&&> = true;
141 template<typename _Tp, size_t _Nm>
142 constexpr bool __destructible<_Tp[_Nm]> = __destructible<_Tp>;
143
144 } // namespace __detail
145
146 /// [concept.assignable], concept assignable_from
147 template<typename _Lhs, typename _Rhs>
148 concept assignable_from
149 = is_lvalue_reference_v<_Lhs>
150 && common_reference_with<__detail::__cref<_Lhs>, __detail::__cref<_Rhs>>
151 && requires(_Lhs __lhs, _Rhs&& __rhs) {
152 { __lhs = static_cast<_Rhs&&>(__rhs) } -> same_as<_Lhs>;
153 };
154
155 /// [concept.destructible], concept destructible
156 template<typename _Tp>
157 concept destructible = __detail::__destructible<_Tp>;
158
159 /// [concept.constructible], concept constructible_from
160 template<typename _Tp, typename... _Args>
161 concept constructible_from
162 = destructible<_Tp> && is_constructible_v<_Tp, _Args...>;
163
164 /// [concept.defaultinitializable], concept default_initializable
165 template<typename _Tp>
166 concept default_initializable = constructible_from<_Tp>
167 && requires
168 {
169 _Tp{};
170 (void) ::new _Tp;
171 };
172
173 /// [concept.moveconstructible], concept move_constructible
174 template<typename _Tp>
175 concept move_constructible
176 = constructible_from<_Tp, _Tp> && convertible_to<_Tp, _Tp>;
177
178 /// [concept.copyconstructible], concept copy_constructible
179 template<typename _Tp>
180 concept copy_constructible
181 = move_constructible<_Tp>
182 && constructible_from<_Tp, _Tp&> && convertible_to<_Tp&, _Tp>
183 && constructible_from<_Tp, const _Tp&> && convertible_to<const _Tp&, _Tp>
184 && constructible_from<_Tp, const _Tp> && convertible_to<const _Tp, _Tp>;
185
186 // [concept.swappable], concept swappable
187
188 namespace ranges
189 {
190 /// @cond undocumented
191 namespace __swap
192 {
193 template<typename _Tp> void swap(_Tp&, _Tp&) = delete;
194
195 template<typename _Tp, typename _Up>
196 concept __adl_swap
197 = (std::__detail::__class_or_enum<remove_reference_t<_Tp>>
198 || std::__detail::__class_or_enum<remove_reference_t<_Up>>)
199 && requires(_Tp&& __t, _Up&& __u) {
200 swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
201 };
202
203 struct _Swap
204 {
205 private:
206 template<typename _Tp, typename _Up>
207 static consteval bool
208 _S_noexcept()
209 {
210 if constexpr (__adl_swap<_Tp, _Up>)
211 return noexcept(swap(std::declval<_Tp>(), std::declval<_Up>()));
212 else
213 return is_nothrow_move_constructible_v<remove_reference_t<_Tp>>
214 && is_nothrow_move_assignable_v<remove_reference_t<_Tp>>;
215 }
216
217 public:
218 template<typename _Tp, typename _Up>
219 requires __adl_swap<_Tp, _Up>
220 || (same_as<_Tp, _Up> && is_lvalue_reference_v<_Tp>
221 && move_constructible<remove_reference_t<_Tp>>
222 && assignable_from<_Tp, remove_reference_t<_Tp>>)
223 constexpr void
224 operator()(_Tp&& __t, _Up&& __u) const
225 noexcept(_S_noexcept<_Tp, _Up>())
226 {
227 if constexpr (__adl_swap<_Tp, _Up>)
228 swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
229 else
230 {
231 auto __tmp = static_cast<remove_reference_t<_Tp>&&>(__t);
232 __t = static_cast<remove_reference_t<_Tp>&&>(__u);
233 __u = static_cast<remove_reference_t<_Tp>&&>(__tmp);
234 }
235 }
236
237 template<typename _Tp, typename _Up, size_t _Num>
238 requires requires(const _Swap& __swap, _Tp& __e1, _Up& __e2) {
239 __swap(__e1, __e2);
240 }
241 constexpr void
242 operator()(_Tp (&__e1)[_Num], _Up (&__e2)[_Num]) const
243 noexcept(noexcept(std::declval<const _Swap&>()(*__e1, *__e2)))
244 {
245 for (size_t __n = 0; __n < _Num; ++__n)
246 (*this)(__e1[__n], __e2[__n]);
247 }
248 };
249 } // namespace __swap
250 /// @endcond
251
252 inline namespace _Cpo {
253 inline constexpr __swap::_Swap swap{};
254 }
255 } // namespace ranges
256
257 template<typename _Tp>
258 concept swappable
259 = requires(_Tp& __a, _Tp& __b) { ranges::swap(__a, __b); };
260
261 template<typename _Tp, typename _Up>
262 concept swappable_with = common_reference_with<_Tp, _Up>
263 && requires(_Tp&& __t, _Up&& __u) {
264 ranges::swap(static_cast<_Tp&&>(__t), static_cast<_Tp&&>(__t));
265 ranges::swap(static_cast<_Up&&>(__u), static_cast<_Up&&>(__u));
266 ranges::swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
267 ranges::swap(static_cast<_Up&&>(__u), static_cast<_Tp&&>(__t));
268 };
269
270 // [concepts.object], Object concepts
271
272 template<typename _Tp>
273 concept movable = is_object_v<_Tp> && move_constructible<_Tp>
274 && assignable_from<_Tp&, _Tp> && swappable<_Tp>;
275
276 template<typename _Tp>
277 concept copyable = copy_constructible<_Tp> && movable<_Tp>
278 && assignable_from<_Tp&, _Tp&> && assignable_from<_Tp&, const _Tp&>
279 && assignable_from<_Tp&, const _Tp>;
280
281 template<typename _Tp>
282 concept semiregular = copyable<_Tp> && default_initializable<_Tp>;
283
284 // [concepts.compare], comparison concepts
285
286 // [concept.booleantestable], Boolean testability
287 namespace __detail
288 {
289 template<typename _Tp>
290 concept __boolean_testable_impl = convertible_to<_Tp, bool>;
291
292 template<typename _Tp>
293 concept __boolean_testable
294 = __boolean_testable_impl<_Tp>
295 && requires(_Tp&& __t)
296 { { !static_cast<_Tp&&>(__t) } -> __boolean_testable_impl; };
297 } // namespace __detail
298
299 // [concept.comparisoncommontype], helpers for comparison common types
300 namespace __detail
301 {
302 template<typename _Tp, typename _Up,
303 typename _Cref = common_reference_t<const _Tp&, const _Up&>>
304 concept __comparison_common_type_with_impl
305 = same_as<common_reference_t<const _Tp&, const _Up&>,
306 common_reference_t<const _Up&, const _Tp&>>
307 && requires {
308 requires convertible_to<const _Tp&, const _Cref&>
309 || convertible_to<_Tp, const _Cref&>;
310 requires convertible_to<const _Up&, const _Cref&>
311 || convertible_to<_Up, const _Cref&>;
312 };
313
314 template<typename _Tp, typename _Up>
315 concept __comparison_common_type_with
316 = __comparison_common_type_with_impl<remove_cvref_t<_Tp>,
317 remove_cvref_t<_Up>>;
318 } // namespace __detail
319
320 // [concept.equalitycomparable], concept equality_comparable
321
322 namespace __detail
323 {
324 template<typename _Tp, typename _Up>
325 concept __weakly_eq_cmp_with
326 = requires(__detail::__cref<_Tp> __t, __detail::__cref<_Up> __u) {
327 { __t == __u } -> __boolean_testable;
328 { __t != __u } -> __boolean_testable;
329 { __u == __t } -> __boolean_testable;
330 { __u != __t } -> __boolean_testable;
331 };
332 } // namespace __detail
333
334 template<typename _Tp>
335 concept equality_comparable = __detail::__weakly_eq_cmp_with<_Tp, _Tp>;
336
337 template<typename _Tp, typename _Up>
338 concept equality_comparable_with
339 = equality_comparable<_Tp> && equality_comparable<_Up>
340 && __detail::__comparison_common_type_with<_Tp, _Up>
341 && equality_comparable<common_reference_t<__detail::__cref<_Tp>,
342 __detail::__cref<_Up>>>
343 && __detail::__weakly_eq_cmp_with<_Tp, _Up>;
344
345 namespace __detail
346 {
347 template<typename _Tp, typename _Up>
348 concept __partially_ordered_with
349 = requires(const remove_reference_t<_Tp>& __t,
350 const remove_reference_t<_Up>& __u) {
351 { __t < __u } -> __boolean_testable;
352 { __t > __u } -> __boolean_testable;
353 { __t <= __u } -> __boolean_testable;
354 { __t >= __u } -> __boolean_testable;
355 { __u < __t } -> __boolean_testable;
356 { __u > __t } -> __boolean_testable;
357 { __u <= __t } -> __boolean_testable;
358 { __u >= __t } -> __boolean_testable;
359 };
360 } // namespace __detail
361
362 // [concept.totallyordered], concept totally_ordered
363 template<typename _Tp>
364 concept totally_ordered
365 = equality_comparable<_Tp>
366 && __detail::__partially_ordered_with<_Tp, _Tp>;
367
368 template<typename _Tp, typename _Up>
369 concept totally_ordered_with
370 = totally_ordered<_Tp> && totally_ordered<_Up>
371 && equality_comparable_with<_Tp, _Up>
372 && totally_ordered<common_reference_t<__detail::__cref<_Tp>,
373 __detail::__cref<_Up>>>
374 && __detail::__partially_ordered_with<_Tp, _Up>;
375
376 template<typename _Tp>
377 concept regular = semiregular<_Tp> && equality_comparable<_Tp>;
378
379 // [concepts.callable], callable concepts
380
381 /// [concept.invocable], concept invocable
382 template<typename _Fn, typename... _Args>
383 concept invocable = is_invocable_v<_Fn, _Args...>;
384
385 /// [concept.regularinvocable], concept regular_invocable
386 template<typename _Fn, typename... _Args>
387 concept regular_invocable = invocable<_Fn, _Args...>;
388
389 /// [concept.predicate], concept predicate
390 template<typename _Fn, typename... _Args>
391 concept predicate = regular_invocable<_Fn, _Args...>
392 && __detail::__boolean_testable<invoke_result_t<_Fn, _Args...>>;
393
394 /// [concept.relation], concept relation
395 template<typename _Rel, typename _Tp, typename _Up>
396 concept relation
397 = predicate<_Rel, _Tp, _Tp> && predicate<_Rel, _Up, _Up>
398 && predicate<_Rel, _Tp, _Up> && predicate<_Rel, _Up, _Tp>;
399
400 /// [concept.equiv], concept equivalence_relation
401 template<typename _Rel, typename _Tp, typename _Up>
402 concept equivalence_relation = relation<_Rel, _Tp, _Up>;
403
404 /// [concept.strictweakorder], concept strict_weak_order
405 template<typename _Rel, typename _Tp, typename _Up>
406 concept strict_weak_order = relation<_Rel, _Tp, _Up>;
407
408 namespace __detail
409 {
410 // operator<=> are automatically reversed, so we need to consider
411 // both directions if types are different.
412 template<typename _Tp, typename _Up>
413 concept __not_overloaded_spaceship
414 = ! requires(_Tp&& __t, _Up&& __u)
415 { operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
416 && ! requires(_Tp&& __t, _Up&& __u)
417 { static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); }
418 && (is_same_v<_Tp, _Up>
419 || (! requires(_Tp&& __t, _Up&& __u)
420 { operator<=>(static_cast<_Up&&>(__u), static_cast<_Tp&&>(__t)); }
421 && ! requires(_Tp&& __t, _Up&& __u)
422 { static_cast<_Up&&>(__u).operator<=>(static_cast<_Tp&&>(__t)); }));
423 }
424
425 // [expos.only.entity]
426 template<typename _Tp>
427 concept __constexpr_wrapper_like
428 = convertible_to<_Tp, decltype(_Tp::value)>
429 && equality_comparable_with<_Tp, decltype(_Tp::value)>
430 && bool_constant<_Tp() == _Tp::value>::value
431 && bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>::value;
432
433_GLIBCXX_END_NAMESPACE_VERSION
434} // namespace
435#endif // __cpp_lib_concepts
436
437#endif /* _GLIBCXX_CONCEPTS */
type_traits
version.h
std::common_reference_t
typename common_reference< _Tp... >::type common_reference_t
Definition type_traits:4299
std::add_lvalue_reference_t
typename add_lvalue_reference< _Tp >::type add_lvalue_reference_t
Alias template for add_lvalue_reference.
Definition type_traits:1917
std::remove_reference_t
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition type_traits:1913
std::common_type_t
typename common_type< _Tp... >::type common_type_t
Alias template for common_type.
Definition type_traits:2975
std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2741
std
ISO C++ entities toplevel namespace is std.
std::__detail
Implementation details not part of the namespace std interface.
std::same_as
[concept.same], concept same_as
Definition concepts:65
std::derived_from
[concept.derived], concept derived_from
Definition concepts:76
std::convertible_to
[concept.convertible], concept convertible_to
Definition concepts:81
std::common_reference_with
[concept.commonref], concept common_reference_with
Definition concepts:87
std::common_with
[concept.common], concept common_with
Definition concepts:94
std::assignable_from
[concept.assignable], concept assignable_from
Definition concepts:149
std::destructible
[concept.destructible], concept destructible
Definition concepts:157
std::constructible_from
[concept.constructible], concept constructible_from
Definition concepts:162
std::default_initializable
[concept.defaultinitializable], concept default_initializable
Definition concepts:166
std::move_constructible
[concept.moveconstructible], concept move_constructible
Definition concepts:176
std::copy_constructible
[concept.copyconstructible], concept copy_constructible
Definition concepts:181
std::invocable
[concept.invocable], concept invocable
Definition concepts:383
std::regular_invocable
[concept.regularinvocable], concept regular_invocable
Definition concepts:387
std::predicate
[concept.predicate], concept predicate
Definition concepts:391
std::relation
[concept.relation], concept relation
Definition concepts:397
std::equivalence_relation
[concept.equiv], concept equivalence_relation
Definition concepts:402
std::strict_weak_order
[concept.strictweakorder], concept strict_weak_order
Definition concepts:406