libstdc++
concepts
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1 // <concepts> -*- C++ -*-
2 
3 // Copyright (C) 2019-2025 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,
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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
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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 
50 namespace 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 constexpr 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.equalitycomparable], concept equality_comparable
300 
301  namespace __detail
302  {
303  template<typename _Tp, typename _Up>
304  concept __weakly_eq_cmp_with
305  = requires(__detail::__cref<_Tp> __t, __detail::__cref<_Up> __u) {
306  { __t == __u } -> __boolean_testable;
307  { __t != __u } -> __boolean_testable;
308  { __u == __t } -> __boolean_testable;
309  { __u != __t } -> __boolean_testable;
310  };
311  } // namespace __detail
312 
313  template<typename _Tp>
314  concept equality_comparable = __detail::__weakly_eq_cmp_with<_Tp, _Tp>;
315 
316  template<typename _Tp, typename _Up>
317  concept equality_comparable_with
318  = equality_comparable<_Tp> && equality_comparable<_Up>
319  && common_reference_with<__detail::__cref<_Tp>, __detail::__cref<_Up>>
320  && equality_comparable<common_reference_t<__detail::__cref<_Tp>,
321  __detail::__cref<_Up>>>
322  && __detail::__weakly_eq_cmp_with<_Tp, _Up>;
323 
324  namespace __detail
325  {
326  template<typename _Tp, typename _Up>
327  concept __partially_ordered_with
328  = requires(const remove_reference_t<_Tp>& __t,
329  const remove_reference_t<_Up>& __u) {
330  { __t < __u } -> __boolean_testable;
331  { __t > __u } -> __boolean_testable;
332  { __t <= __u } -> __boolean_testable;
333  { __t >= __u } -> __boolean_testable;
334  { __u < __t } -> __boolean_testable;
335  { __u > __t } -> __boolean_testable;
336  { __u <= __t } -> __boolean_testable;
337  { __u >= __t } -> __boolean_testable;
338  };
339  } // namespace __detail
340 
341  // [concept.totallyordered], concept totally_ordered
342  template<typename _Tp>
343  concept totally_ordered
344  = equality_comparable<_Tp>
345  && __detail::__partially_ordered_with<_Tp, _Tp>;
346 
347  template<typename _Tp, typename _Up>
348  concept totally_ordered_with
349  = totally_ordered<_Tp> && totally_ordered<_Up>
350  && equality_comparable_with<_Tp, _Up>
351  && totally_ordered<common_reference_t<__detail::__cref<_Tp>,
352  __detail::__cref<_Up>>>
353  && __detail::__partially_ordered_with<_Tp, _Up>;
354 
355  template<typename _Tp>
356  concept regular = semiregular<_Tp> && equality_comparable<_Tp>;
357 
358  // [concepts.callable], callable concepts
359 
360  /// [concept.invocable], concept invocable
361  template<typename _Fn, typename... _Args>
362  concept invocable = is_invocable_v<_Fn, _Args...>;
363 
364  /// [concept.regularinvocable], concept regular_invocable
365  template<typename _Fn, typename... _Args>
366  concept regular_invocable = invocable<_Fn, _Args...>;
367 
368  /// [concept.predicate], concept predicate
369  template<typename _Fn, typename... _Args>
370  concept predicate = regular_invocable<_Fn, _Args...>
371  && __detail::__boolean_testable<invoke_result_t<_Fn, _Args...>>;
372 
373  /// [concept.relation], concept relation
374  template<typename _Rel, typename _Tp, typename _Up>
375  concept relation
376  = predicate<_Rel, _Tp, _Tp> && predicate<_Rel, _Up, _Up>
377  && predicate<_Rel, _Tp, _Up> && predicate<_Rel, _Up, _Tp>;
378 
379  /// [concept.equiv], concept equivalence_relation
380  template<typename _Rel, typename _Tp, typename _Up>
381  concept equivalence_relation = relation<_Rel, _Tp, _Up>;
382 
383  /// [concept.strictweakorder], concept strict_weak_order
384  template<typename _Rel, typename _Tp, typename _Up>
385  concept strict_weak_order = relation<_Rel, _Tp, _Up>;
386 
387 _GLIBCXX_END_NAMESPACE_VERSION
388 } // namespace
389 #endif // __cpp_lib_concepts
390 
391 #endif /* _GLIBCXX_CONCEPTS */