libstdc++
iterator_concepts.h
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1 // Concepts and traits for use with iterators -*- C++ -*-
2 
3 // Copyright (C) 2019-2024 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
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9 // any later version.
10 
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15 
16 // Under Section 7 of GPL version 3, you are granted additional
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18 // 3.1, as published by the Free Software Foundation.
19 
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24 
25 /** @file bits/iterator_concepts.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{iterator}
28  */
29 
30 #ifndef _ITERATOR_CONCEPTS_H
31 #define _ITERATOR_CONCEPTS_H 1
32 
33 #pragma GCC system_header
34 
35 #if __cplusplus >= 202002L
36 #include <concepts>
37 #include <bits/ptr_traits.h> // to_address
38 #include <bits/ranges_cmp.h> // identity, ranges::less
39 
40 namespace std _GLIBCXX_VISIBILITY(default)
41 {
42 _GLIBCXX_BEGIN_NAMESPACE_VERSION
43 
44  /** A sentinel type that can be used to check for the end of a range.
45  *
46  * For some iterator types the past-the-end sentinel value is independent
47  * of the underlying sequence, and a default sentinel can be used with them.
48  * For example, a `std::counted_iterator` keeps a count of how many elements
49  * remain, and so checking for the past-the-end value only requires checking
50  * if that count has reached zero. A past-the-end `std::istream_iterator` is
51  * equal to the default-constructed value, which can be easily checked.
52  *
53  * Comparing iterators of these types to `std::default_sentinel` is a
54  * convenient way to check if the end has been reached.
55  *
56  * @since C++20
57  */
58  struct default_sentinel_t { };
59 
60  /// A default sentinel value.
62 
63 #if __cpp_lib_concepts
64  struct input_iterator_tag;
65  struct output_iterator_tag;
66  struct forward_iterator_tag;
67  struct bidirectional_iterator_tag;
68  struct random_access_iterator_tag;
69  struct contiguous_iterator_tag;
70 
71  template<typename _Iterator>
72  struct iterator_traits;
73 
74  template<typename _Tp> requires is_object_v<_Tp>
75  struct iterator_traits<_Tp*>;
76 
77  template<typename _Iterator, typename>
78  struct __iterator_traits;
79 
80  namespace __detail
81  {
82  template<typename _Tp>
83  using __with_ref = _Tp&;
84 
85  template<typename _Tp>
86  concept __can_reference = requires { typename __with_ref<_Tp>; };
87 
88  template<typename _Tp>
89  concept __dereferenceable = requires(_Tp& __t)
90  {
91  { *__t } -> __can_reference;
92  };
93  } // namespace __detail
94 
95  template<__detail::__dereferenceable _Tp>
96  using iter_reference_t = decltype(*std::declval<_Tp&>());
97 
98  namespace ranges
99  {
100  /// @cond undocumented
101  namespace __imove
102  {
103  void iter_move() = delete;
104 
105  template<typename _Tp>
106  concept __adl_imove
107  = (std::__detail::__class_or_enum<remove_reference_t<_Tp>>)
108  && requires(_Tp&& __t) { iter_move(static_cast<_Tp&&>(__t)); };
109 
110  struct _IterMove
111  {
112  private:
113  template<typename _Tp>
114  struct __result
115  { using type = iter_reference_t<_Tp>; };
116 
117  template<typename _Tp>
118  requires __adl_imove<_Tp>
119  struct __result<_Tp>
120  { using type = decltype(iter_move(std::declval<_Tp>())); };
121 
122  template<typename _Tp>
123  requires (!__adl_imove<_Tp>)
124  && is_lvalue_reference_v<iter_reference_t<_Tp>>
125  struct __result<_Tp>
126  { using type = remove_reference_t<iter_reference_t<_Tp>>&&; };
127 
128  template<typename _Tp>
129  static constexpr bool
130  _S_noexcept()
131  {
132  if constexpr (__adl_imove<_Tp>)
133  return noexcept(iter_move(std::declval<_Tp>()));
134  else
135  return noexcept(*std::declval<_Tp>());
136  }
137 
138  public:
139  // The result type of iter_move(std::declval<_Tp>())
140  template<std::__detail::__dereferenceable _Tp>
141  using __type = typename __result<_Tp>::type;
142 
143  template<std::__detail::__dereferenceable _Tp>
144  [[nodiscard]]
145  constexpr __type<_Tp>
146  operator()(_Tp&& __e) const
147  noexcept(_S_noexcept<_Tp>())
148  {
149  if constexpr (__adl_imove<_Tp>)
150  return iter_move(static_cast<_Tp&&>(__e));
151  else if constexpr (is_lvalue_reference_v<iter_reference_t<_Tp>>)
152  return static_cast<__type<_Tp>>(*__e);
153  else
154  return *__e;
155  }
156  };
157  } // namespace __imove
158  /// @endcond
159 
160  inline namespace _Cpo {
161  inline constexpr __imove::_IterMove iter_move{};
162  }
163  } // namespace ranges
164 
165  template<__detail::__dereferenceable _Tp>
166  requires __detail::__can_reference<ranges::__imove::_IterMove::__type<_Tp&>>
167  using iter_rvalue_reference_t = ranges::__imove::_IterMove::__type<_Tp&>;
168 
169  template<typename> struct incrementable_traits { };
170 
171  template<typename _Tp> requires is_object_v<_Tp>
172  struct incrementable_traits<_Tp*>
173  { using difference_type = ptrdiff_t; };
174 
175  template<typename _Iter>
176  struct incrementable_traits<const _Iter>
177  : incrementable_traits<_Iter> { };
178 
179  template<typename _Tp> requires requires { typename _Tp::difference_type; }
180  struct incrementable_traits<_Tp>
181  { using difference_type = typename _Tp::difference_type; };
182 
183  template<typename _Tp>
184  requires (!requires { typename _Tp::difference_type; }
185  && requires(const _Tp& __a, const _Tp& __b)
186  { { __a - __b } -> integral; })
187  struct incrementable_traits<_Tp>
188  {
189  using difference_type
190  = make_signed_t<decltype(std::declval<_Tp>() - std::declval<_Tp>())>;
191  };
192 
193 #if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
194  // __int128 is incrementable even if !integral<__int128>
195  template<>
196  struct incrementable_traits<__int128>
197  { using difference_type = __int128; };
198 
199  template<>
200  struct incrementable_traits<unsigned __int128>
201  { using difference_type = __int128; };
202 #endif
203 
204  namespace __detail
205  {
206  // An iterator such that iterator_traits<_Iter> names a specialization
207  // generated from the primary template.
208  template<typename _Iter>
209  concept __primary_traits_iter
210  = __is_base_of(__iterator_traits<_Iter, void>, iterator_traits<_Iter>);
211 
212  template<typename _Iter, typename _Tp>
213  struct __iter_traits_impl
214  { using type = iterator_traits<_Iter>; };
215 
216  template<typename _Iter, typename _Tp>
217  requires __primary_traits_iter<_Iter>
218  struct __iter_traits_impl<_Iter, _Tp>
219  { using type = _Tp; };
220 
221  // ITER_TRAITS
222  template<typename _Iter, typename _Tp = _Iter>
223  using __iter_traits = typename __iter_traits_impl<_Iter, _Tp>::type;
224 
225  template<typename _Tp>
226  using __iter_diff_t = typename
227  __iter_traits<_Tp, incrementable_traits<_Tp>>::difference_type;
228  } // namespace __detail
229 
230  template<typename _Tp>
231  using iter_difference_t = __detail::__iter_diff_t<remove_cvref_t<_Tp>>;
232 
233  namespace __detail
234  {
235  template<typename> struct __cond_value_type { };
236 
237  template<typename _Tp> requires is_object_v<_Tp>
238  struct __cond_value_type<_Tp>
239  { using value_type = remove_cv_t<_Tp>; };
240 
241  template<typename _Tp>
242  concept __has_member_value_type
243  = requires { typename _Tp::value_type; };
244 
245  template<typename _Tp>
246  concept __has_member_element_type
247  = requires { typename _Tp::element_type; };
248 
249  } // namespace __detail
250 
251  template<typename> struct indirectly_readable_traits { };
252 
253  template<typename _Tp>
254  struct indirectly_readable_traits<_Tp*>
255  : __detail::__cond_value_type<_Tp>
256  { };
257 
258  template<typename _Iter> requires is_array_v<_Iter>
259  struct indirectly_readable_traits<_Iter>
260  { using value_type = remove_cv_t<remove_extent_t<_Iter>>; };
261 
262  template<typename _Iter>
263  struct indirectly_readable_traits<const _Iter>
264  : indirectly_readable_traits<_Iter>
265  { };
266 
267  template<__detail::__has_member_value_type _Tp>
268  struct indirectly_readable_traits<_Tp>
269  : __detail::__cond_value_type<typename _Tp::value_type>
270  { };
271 
272  template<__detail::__has_member_element_type _Tp>
273  struct indirectly_readable_traits<_Tp>
274  : __detail::__cond_value_type<typename _Tp::element_type>
275  { };
276 
277  // _GLIBCXX_RESOLVE_LIB_DEFECTS
278  // 3446. indirectly_readable_traits ambiguity for types with both [...]
279  template<__detail::__has_member_value_type _Tp>
280  requires __detail::__has_member_element_type<_Tp>
281  && same_as<remove_cv_t<typename _Tp::element_type>,
282  remove_cv_t<typename _Tp::value_type>>
283  struct indirectly_readable_traits<_Tp>
284  : __detail::__cond_value_type<typename _Tp::value_type>
285  { };
286 
287  // _GLIBCXX_RESOLVE_LIB_DEFECTS
288  // 3541. indirectly_readable_traits should be SFINAE-friendly for all types
289  template<__detail::__has_member_value_type _Tp>
290  requires __detail::__has_member_element_type<_Tp>
291  struct indirectly_readable_traits<_Tp>
292  { };
293 
294  namespace __detail
295  {
296  template<typename _Tp>
297  using __iter_value_t = typename
298  __iter_traits<_Tp, indirectly_readable_traits<_Tp>>::value_type;
299  } // namespace __detail
300 
301  template<typename _Tp>
302  using iter_value_t = __detail::__iter_value_t<remove_cvref_t<_Tp>>;
303 
304  namespace __detail
305  {
306  // _GLIBCXX_RESOLVE_LIB_DEFECTS
307  // 3420. cpp17-iterator should check [type] looks like an iterator first
308  template<typename _Iter>
309  concept __cpp17_iterator = requires(_Iter __it)
310  {
311  { *__it } -> __can_reference;
312  { ++__it } -> same_as<_Iter&>;
313  { *__it++ } -> __can_reference;
314  } && copyable<_Iter>;
315 
316  template<typename _Iter>
317  concept __cpp17_input_iterator = __cpp17_iterator<_Iter>
318  && equality_comparable<_Iter>
319  && requires(_Iter __it)
320  {
321  typename incrementable_traits<_Iter>::difference_type;
322  typename indirectly_readable_traits<_Iter>::value_type;
323  typename common_reference_t<iter_reference_t<_Iter>&&,
324  typename indirectly_readable_traits<_Iter>::value_type&>;
325  typename common_reference_t<decltype(*__it++)&&,
326  typename indirectly_readable_traits<_Iter>::value_type&>;
327  requires signed_integral<
328  typename incrementable_traits<_Iter>::difference_type>;
329  };
330 
331  template<typename _Iter>
332  concept __cpp17_fwd_iterator = __cpp17_input_iterator<_Iter>
333  && constructible_from<_Iter>
334  && is_lvalue_reference_v<iter_reference_t<_Iter>>
335  && same_as<remove_cvref_t<iter_reference_t<_Iter>>,
336  typename indirectly_readable_traits<_Iter>::value_type>
337  && requires(_Iter __it)
338  {
339  { __it++ } -> convertible_to<const _Iter&>;
340  { *__it++ } -> same_as<iter_reference_t<_Iter>>;
341  };
342 
343  template<typename _Iter>
344  concept __cpp17_bidi_iterator = __cpp17_fwd_iterator<_Iter>
345  && requires(_Iter __it)
346  {
347  { --__it } -> same_as<_Iter&>;
348  { __it-- } -> convertible_to<const _Iter&>;
349  { *__it-- } -> same_as<iter_reference_t<_Iter>>;
350  };
351 
352  template<typename _Iter>
353  concept __cpp17_randacc_iterator = __cpp17_bidi_iterator<_Iter>
354  && totally_ordered<_Iter>
355  && requires(_Iter __it,
356  typename incrementable_traits<_Iter>::difference_type __n)
357  {
358  { __it += __n } -> same_as<_Iter&>;
359  { __it -= __n } -> same_as<_Iter&>;
360  { __it + __n } -> same_as<_Iter>;
361  { __n + __it } -> same_as<_Iter>;
362  { __it - __n } -> same_as<_Iter>;
363  { __it - __it } -> same_as<decltype(__n)>;
364  { __it[__n] } -> convertible_to<iter_reference_t<_Iter>>;
365  };
366 
367  template<typename _Iter>
368  concept __iter_with_nested_types = requires {
369  typename _Iter::iterator_category;
370  typename _Iter::value_type;
371  typename _Iter::difference_type;
372  typename _Iter::reference;
373  };
374 
375  template<typename _Iter>
376  concept __iter_without_nested_types = !__iter_with_nested_types<_Iter>;
377 
378  template<typename _Iter>
379  concept __iter_without_category
380  = !requires { typename _Iter::iterator_category; };
381 
382  } // namespace __detail
383 
384  template<typename _Iterator>
385  requires __detail::__iter_with_nested_types<_Iterator>
386  struct __iterator_traits<_Iterator, void>
387  {
388  private:
389  template<typename _Iter>
390  struct __ptr
391  { using type = void; };
392 
393  template<typename _Iter> requires requires { typename _Iter::pointer; }
394  struct __ptr<_Iter>
395  { using type = typename _Iter::pointer; };
396 
397  public:
398  using iterator_category = typename _Iterator::iterator_category;
399  using value_type = typename _Iterator::value_type;
400  using difference_type = typename _Iterator::difference_type;
401  using pointer = typename __ptr<_Iterator>::type;
402  using reference = typename _Iterator::reference;
403  };
404 
405  template<typename _Iterator>
406  requires __detail::__iter_without_nested_types<_Iterator>
407  && __detail::__cpp17_input_iterator<_Iterator>
408  struct __iterator_traits<_Iterator, void>
409  {
410  private:
411  template<typename _Iter>
412  struct __cat
413  { using type = input_iterator_tag; };
414 
415  template<typename _Iter>
416  requires requires { typename _Iter::iterator_category; }
417  struct __cat<_Iter>
418  { using type = typename _Iter::iterator_category; };
419 
420  template<typename _Iter>
421  requires __detail::__iter_without_category<_Iter>
422  && __detail::__cpp17_randacc_iterator<_Iter>
423  struct __cat<_Iter>
424  { using type = random_access_iterator_tag; };
425 
426  template<typename _Iter>
427  requires __detail::__iter_without_category<_Iter>
428  && __detail::__cpp17_bidi_iterator<_Iter>
429  struct __cat<_Iter>
430  { using type = bidirectional_iterator_tag; };
431 
432  template<typename _Iter>
433  requires __detail::__iter_without_category<_Iter>
434  && __detail::__cpp17_fwd_iterator<_Iter>
435  struct __cat<_Iter>
436  { using type = forward_iterator_tag; };
437 
438  template<typename _Iter>
439  struct __ptr
440  { using type = void; };
441 
442  template<typename _Iter> requires requires { typename _Iter::pointer; }
443  struct __ptr<_Iter>
444  { using type = typename _Iter::pointer; };
445 
446  template<typename _Iter>
447  requires (!requires { typename _Iter::pointer; }
448  && requires(_Iter& __it) { __it.operator->(); })
449  struct __ptr<_Iter>
450  { using type = decltype(std::declval<_Iter&>().operator->()); };
451 
452  template<typename _Iter>
453  struct __ref
454  { using type = iter_reference_t<_Iter>; };
455 
456  template<typename _Iter> requires requires { typename _Iter::reference; }
457  struct __ref<_Iter>
458  { using type = typename _Iter::reference; };
459 
460  public:
461  using iterator_category = typename __cat<_Iterator>::type;
462  using value_type
463  = typename indirectly_readable_traits<_Iterator>::value_type;
464  using difference_type
465  = typename incrementable_traits<_Iterator>::difference_type;
466  using pointer = typename __ptr<_Iterator>::type;
467  using reference = typename __ref<_Iterator>::type;
468  };
469 
470  template<typename _Iterator>
471  requires __detail::__iter_without_nested_types<_Iterator>
472  && __detail::__cpp17_iterator<_Iterator>
473  struct __iterator_traits<_Iterator, void>
474  {
475  private:
476  template<typename _Iter>
477  struct __diff
478  { using type = void; };
479 
480  template<typename _Iter>
481  requires requires
482  { typename incrementable_traits<_Iter>::difference_type; }
483  struct __diff<_Iter>
484  {
485  using type = typename incrementable_traits<_Iter>::difference_type;
486  };
487 
488  public:
489  using iterator_category = output_iterator_tag;
490  using value_type = void;
491  using difference_type = typename __diff<_Iterator>::type;
492  using pointer = void;
493  using reference = void;
494  };
495 
496  namespace __detail
497  {
498  template<typename _Iter>
499  struct __iter_concept_impl;
500 
501  // ITER_CONCEPT(I) is ITER_TRAITS(I)::iterator_concept if that is valid.
502  template<typename _Iter>
503  requires requires { typename __iter_traits<_Iter>::iterator_concept; }
504  struct __iter_concept_impl<_Iter>
505  { using type = typename __iter_traits<_Iter>::iterator_concept; };
506 
507  // Otherwise, ITER_TRAITS(I)::iterator_category if that is valid.
508  template<typename _Iter>
509  requires (!requires { typename __iter_traits<_Iter>::iterator_concept; }
510  && requires { typename __iter_traits<_Iter>::iterator_category; })
511  struct __iter_concept_impl<_Iter>
512  { using type = typename __iter_traits<_Iter>::iterator_category; };
513 
514  // Otherwise, random_access_tag if iterator_traits<I> is not specialized.
515  template<typename _Iter>
516  requires (!requires { typename __iter_traits<_Iter>::iterator_concept; }
517  && !requires { typename __iter_traits<_Iter>::iterator_category; }
518  && __primary_traits_iter<_Iter>)
519  struct __iter_concept_impl<_Iter>
520  { using type = random_access_iterator_tag; };
521 
522  // Otherwise, there is no ITER_CONCEPT(I) type.
523  template<typename _Iter>
524  struct __iter_concept_impl
525  { };
526 
527  // ITER_CONCEPT
528  template<typename _Iter>
529  using __iter_concept = typename __iter_concept_impl<_Iter>::type;
530 
531  template<typename _In>
532  concept __indirectly_readable_impl = requires
533  {
534  typename iter_value_t<_In>;
535  typename iter_reference_t<_In>;
536  typename iter_rvalue_reference_t<_In>;
537  requires same_as<iter_reference_t<const _In>,
538  iter_reference_t<_In>>;
539  requires same_as<iter_rvalue_reference_t<const _In>,
540  iter_rvalue_reference_t<_In>>;
541  }
542  && common_reference_with<iter_reference_t<_In>&&, iter_value_t<_In>&>
543  && common_reference_with<iter_reference_t<_In>&&,
544  iter_rvalue_reference_t<_In>&&>
545  && common_reference_with<iter_rvalue_reference_t<_In>&&,
546  const iter_value_t<_In>&>;
547 
548  } // namespace __detail
549 
550  /// Requirements for types that are readable by applying operator*.
551  template<typename _In>
552  concept indirectly_readable
553  = __detail::__indirectly_readable_impl<remove_cvref_t<_In>>;
554 
555  template<indirectly_readable _Tp>
556  using iter_common_reference_t
557  = common_reference_t<iter_reference_t<_Tp>, iter_value_t<_Tp>&>;
558 
559  /// Requirements for writing a value into an iterator's referenced object.
560  template<typename _Out, typename _Tp>
561  concept indirectly_writable = requires(_Out&& __o, _Tp&& __t)
562  {
563  *__o = std::forward<_Tp>(__t);
564  *std::forward<_Out>(__o) = std::forward<_Tp>(__t);
565  const_cast<const iter_reference_t<_Out>&&>(*__o)
566  = std::forward<_Tp>(__t);
567  const_cast<const iter_reference_t<_Out>&&>(*std::forward<_Out>(__o))
568  = std::forward<_Tp>(__t);
569  };
570 
571  namespace ranges::__detail
572  {
573  class __max_diff_type;
574  class __max_size_type;
575 
576  __extension__
577  template<typename _Tp>
578  concept __is_signed_int128
579 #if __SIZEOF_INT128__
580  = same_as<_Tp, __int128>;
581 #else
582  = false;
583 #endif
584 
585  __extension__
586  template<typename _Tp>
587  concept __is_unsigned_int128
588 #if __SIZEOF_INT128__
589  = same_as<_Tp, unsigned __int128>;
590 #else
591  = false;
592 #endif
593 
594  template<typename _Tp>
595  concept __cv_bool = same_as<const volatile _Tp, const volatile bool>;
596 
597  template<typename _Tp>
598  concept __integral_nonbool = integral<_Tp> && !__cv_bool<_Tp>;
599 
600  template<typename _Tp>
601  concept __is_int128 = __is_signed_int128<_Tp> || __is_unsigned_int128<_Tp>;
602 
603  template<typename _Tp>
604  concept __is_integer_like = __integral_nonbool<_Tp>
605  || __is_int128<_Tp>
606  || same_as<_Tp, __max_diff_type> || same_as<_Tp, __max_size_type>;
607 
608  template<typename _Tp>
609  concept __is_signed_integer_like = signed_integral<_Tp>
610  || __is_signed_int128<_Tp>
611  || same_as<_Tp, __max_diff_type>;
612 
613  } // namespace ranges::__detail
614 
615  namespace __detail { using ranges::__detail::__is_signed_integer_like; }
616 
617  /// Requirements on types that can be incremented with ++.
618  template<typename _Iter>
619  concept weakly_incrementable = movable<_Iter>
620  && requires(_Iter __i)
621  {
622  typename iter_difference_t<_Iter>;
623  requires __detail::__is_signed_integer_like<iter_difference_t<_Iter>>;
624  { ++__i } -> same_as<_Iter&>;
625  __i++;
626  };
627 
628  template<typename _Iter>
629  concept incrementable = regular<_Iter> && weakly_incrementable<_Iter>
630  && requires(_Iter __i) { { __i++ } -> same_as<_Iter>; };
631 
632  template<typename _Iter>
633  concept input_or_output_iterator
634  = requires(_Iter __i) { { *__i } -> __detail::__can_reference; }
635  && weakly_incrementable<_Iter>;
636 
637  template<typename _Sent, typename _Iter>
638  concept sentinel_for = semiregular<_Sent>
639  && input_or_output_iterator<_Iter>
640  && __detail::__weakly_eq_cmp_with<_Sent, _Iter>;
641 
642  template<typename _Sent, typename _Iter>
643  inline constexpr bool disable_sized_sentinel_for = false;
644 
645  template<typename _Sent, typename _Iter>
646  concept sized_sentinel_for = sentinel_for<_Sent, _Iter>
647  && !disable_sized_sentinel_for<remove_cv_t<_Sent>, remove_cv_t<_Iter>>
648  && requires(const _Iter& __i, const _Sent& __s)
649  {
650  { __s - __i } -> same_as<iter_difference_t<_Iter>>;
651  { __i - __s } -> same_as<iter_difference_t<_Iter>>;
652  };
653 
654  template<typename _Iter>
655  concept input_iterator = input_or_output_iterator<_Iter>
656  && indirectly_readable<_Iter>
657  && requires { typename __detail::__iter_concept<_Iter>; }
658  && derived_from<__detail::__iter_concept<_Iter>, input_iterator_tag>;
659 
660  template<typename _Iter, typename _Tp>
661  concept output_iterator = input_or_output_iterator<_Iter>
662  && indirectly_writable<_Iter, _Tp>
663  && requires(_Iter __i, _Tp&& __t) { *__i++ = std::forward<_Tp>(__t); };
664 
665  template<typename _Iter>
666  concept forward_iterator = input_iterator<_Iter>
667  && derived_from<__detail::__iter_concept<_Iter>, forward_iterator_tag>
668  && incrementable<_Iter> && sentinel_for<_Iter, _Iter>;
669 
670  template<typename _Iter>
671  concept bidirectional_iterator = forward_iterator<_Iter>
672  && derived_from<__detail::__iter_concept<_Iter>,
673  bidirectional_iterator_tag>
674  && requires(_Iter __i)
675  {
676  { --__i } -> same_as<_Iter&>;
677  { __i-- } -> same_as<_Iter>;
678  };
679 
680  template<typename _Iter>
681  concept random_access_iterator = bidirectional_iterator<_Iter>
682  && derived_from<__detail::__iter_concept<_Iter>,
683  random_access_iterator_tag>
684  && totally_ordered<_Iter> && sized_sentinel_for<_Iter, _Iter>
685  && requires(_Iter __i, const _Iter __j,
686  const iter_difference_t<_Iter> __n)
687  {
688  { __i += __n } -> same_as<_Iter&>;
689  { __j + __n } -> same_as<_Iter>;
690  { __n + __j } -> same_as<_Iter>;
691  { __i -= __n } -> same_as<_Iter&>;
692  { __j - __n } -> same_as<_Iter>;
693  { __j[__n] } -> same_as<iter_reference_t<_Iter>>;
694  };
695 
696  template<typename _Iter>
697  concept contiguous_iterator = random_access_iterator<_Iter>
698  && derived_from<__detail::__iter_concept<_Iter>, contiguous_iterator_tag>
699  && is_lvalue_reference_v<iter_reference_t<_Iter>>
700  && same_as<iter_value_t<_Iter>, remove_cvref_t<iter_reference_t<_Iter>>>
701  && requires(const _Iter& __i)
702  {
703  { std::to_address(__i) }
704  -> same_as<add_pointer_t<iter_reference_t<_Iter>>>;
705  };
706 
707  // [indirectcallable], indirect callable requirements
708 
709  // [indirectcallable.indirectinvocable], indirect callables
710 
711  template<typename _Fn, typename _Iter>
712  concept indirectly_unary_invocable = indirectly_readable<_Iter>
713  && copy_constructible<_Fn> && invocable<_Fn&, iter_value_t<_Iter>&>
714  && invocable<_Fn&, iter_reference_t<_Iter>>
715  && invocable<_Fn&, iter_common_reference_t<_Iter>>
716  && common_reference_with<invoke_result_t<_Fn&, iter_value_t<_Iter>&>,
717  invoke_result_t<_Fn&, iter_reference_t<_Iter>>>;
718 
719  template<typename _Fn, typename _Iter>
720  concept indirectly_regular_unary_invocable = indirectly_readable<_Iter>
721  && copy_constructible<_Fn>
722  && regular_invocable<_Fn&, iter_value_t<_Iter>&>
723  && regular_invocable<_Fn&, iter_reference_t<_Iter>>
724  && regular_invocable<_Fn&, iter_common_reference_t<_Iter>>
725  && common_reference_with<invoke_result_t<_Fn&, iter_value_t<_Iter>&>,
726  invoke_result_t<_Fn&, iter_reference_t<_Iter>>>;
727 
728  template<typename _Fn, typename _Iter>
729  concept indirect_unary_predicate = indirectly_readable<_Iter>
730  && copy_constructible<_Fn> && predicate<_Fn&, iter_value_t<_Iter>&>
731  && predicate<_Fn&, iter_reference_t<_Iter>>
732  && predicate<_Fn&, iter_common_reference_t<_Iter>>;
733 
734  template<typename _Fn, typename _I1, typename _I2>
735  concept indirect_binary_predicate
736  = indirectly_readable<_I1> && indirectly_readable<_I2>
737  && copy_constructible<_Fn>
738  && predicate<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
739  && predicate<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
740  && predicate<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
741  && predicate<_Fn&, iter_reference_t<_I1>, iter_reference_t<_I2>>
742  && predicate<_Fn&, iter_common_reference_t<_I1>,
743  iter_common_reference_t<_I2>>;
744 
745  template<typename _Fn, typename _I1, typename _I2 = _I1>
746  concept indirect_equivalence_relation
747  = indirectly_readable<_I1> && indirectly_readable<_I2>
748  && copy_constructible<_Fn>
749  && equivalence_relation<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
750  && equivalence_relation<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
751  && equivalence_relation<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
752  && equivalence_relation<_Fn&, iter_reference_t<_I1>,
753  iter_reference_t<_I2>>
754  && equivalence_relation<_Fn&, iter_common_reference_t<_I1>,
755  iter_common_reference_t<_I2>>;
756 
757  template<typename _Fn, typename _I1, typename _I2 = _I1>
758  concept indirect_strict_weak_order
759  = indirectly_readable<_I1> && indirectly_readable<_I2>
760  && copy_constructible<_Fn>
761  && strict_weak_order<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
762  && strict_weak_order<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
763  && strict_weak_order<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
764  && strict_weak_order<_Fn&, iter_reference_t<_I1>, iter_reference_t<_I2>>
765  && strict_weak_order<_Fn&, iter_common_reference_t<_I1>,
766  iter_common_reference_t<_I2>>;
767 
768  template<typename _Fn, typename... _Is>
769  requires (indirectly_readable<_Is> && ...)
770  && invocable<_Fn, iter_reference_t<_Is>...>
771  using indirect_result_t = invoke_result_t<_Fn, iter_reference_t<_Is>...>;
772 
773  namespace __detail
774  {
775  template<typename _Iter, typename _Proj>
776  struct __projected
777  {
778  struct __type
779  {
780  using value_type = remove_cvref_t<indirect_result_t<_Proj&, _Iter>>;
781  indirect_result_t<_Proj&, _Iter> operator*() const; // not defined
782  };
783  };
784 
785  template<weakly_incrementable _Iter, typename _Proj>
786  struct __projected<_Iter, _Proj>
787  {
788  struct __type
789  {
790  using value_type = remove_cvref_t<indirect_result_t<_Proj&, _Iter>>;
791  using difference_type = iter_difference_t<_Iter>;
792  indirect_result_t<_Proj&, _Iter> operator*() const; // not defined
793  };
794  };
795  } // namespace __detail
796 
797  /// [projected], projected
798  template<indirectly_readable _Iter,
799  indirectly_regular_unary_invocable<_Iter> _Proj>
800  using projected = typename __detail::__projected<_Iter, _Proj>::__type;
801 
802  // [alg.req], common algorithm requirements
803 
804  /// [alg.req.ind.move], concept `indirectly_movable`
805 
806  template<typename _In, typename _Out>
807  concept indirectly_movable = indirectly_readable<_In>
808  && indirectly_writable<_Out, iter_rvalue_reference_t<_In>>;
809 
810  template<typename _In, typename _Out>
811  concept indirectly_movable_storable = indirectly_movable<_In, _Out>
812  && indirectly_writable<_Out, iter_value_t<_In>>
813  && movable<iter_value_t<_In>>
814  && constructible_from<iter_value_t<_In>, iter_rvalue_reference_t<_In>>
815  && assignable_from<iter_value_t<_In>&, iter_rvalue_reference_t<_In>>;
816 
817  /// [alg.req.ind.copy], concept `indirectly_copyable`
818  template<typename _In, typename _Out>
819  concept indirectly_copyable = indirectly_readable<_In>
820  && indirectly_writable<_Out, iter_reference_t<_In>>;
821 
822  template<typename _In, typename _Out>
823  concept indirectly_copyable_storable = indirectly_copyable<_In, _Out>
824  && indirectly_writable<_Out, iter_value_t<_In>&>
825  && indirectly_writable<_Out, const iter_value_t<_In>&>
826  && indirectly_writable<_Out, iter_value_t<_In>&&>
827  && indirectly_writable<_Out, const iter_value_t<_In>&&>
828  && copyable<iter_value_t<_In>>
829  && constructible_from<iter_value_t<_In>, iter_reference_t<_In>>
830  && assignable_from<iter_value_t<_In>&, iter_reference_t<_In>>;
831 
832 namespace ranges
833 {
834  /// @cond undocumented
835  namespace __iswap
836  {
837  template<typename _It1, typename _It2>
838  void iter_swap(_It1, _It2) = delete;
839 
840  template<typename _Tp, typename _Up>
841  concept __adl_iswap
842  = (std::__detail::__class_or_enum<remove_reference_t<_Tp>>
843  || std::__detail::__class_or_enum<remove_reference_t<_Up>>)
844  && requires(_Tp&& __t, _Up&& __u) {
845  iter_swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
846  };
847 
848  template<typename _Xp, typename _Yp>
849  constexpr iter_value_t<_Xp>
850  __iter_exchange_move(_Xp&& __x, _Yp&& __y)
851  noexcept(noexcept(iter_value_t<_Xp>(iter_move(__x)))
852  && noexcept(*__x = iter_move(__y)))
853  {
854  iter_value_t<_Xp> __old_value(iter_move(__x));
855  *__x = iter_move(__y);
856  return __old_value;
857  }
858 
859  struct _IterSwap
860  {
861  private:
862  template<typename _Tp, typename _Up>
863  static constexpr bool
864  _S_noexcept()
865  {
866  if constexpr (__adl_iswap<_Tp, _Up>)
867  return noexcept(iter_swap(std::declval<_Tp>(),
868  std::declval<_Up>()));
869  else if constexpr (indirectly_readable<_Tp>
870  && indirectly_readable<_Up>
871  && swappable_with<iter_reference_t<_Tp>, iter_reference_t<_Up>>)
872  return noexcept(ranges::swap(*std::declval<_Tp>(),
873  *std::declval<_Up>()));
874  else
875  return noexcept(*std::declval<_Tp>()
876  = __iswap::__iter_exchange_move(std::declval<_Up>(),
877  std::declval<_Tp>()));
878  }
879 
880  public:
881  template<typename _Tp, typename _Up>
882  requires __adl_iswap<_Tp, _Up>
883  || (indirectly_readable<remove_reference_t<_Tp>>
884  && indirectly_readable<remove_reference_t<_Up>>
885  && swappable_with<iter_reference_t<_Tp>, iter_reference_t<_Up>>)
886  || (indirectly_movable_storable<_Tp, _Up>
887  && indirectly_movable_storable<_Up, _Tp>)
888  constexpr void
889  operator()(_Tp&& __e1, _Up&& __e2) const
890  noexcept(_S_noexcept<_Tp, _Up>())
891  {
892  if constexpr (__adl_iswap<_Tp, _Up>)
893  iter_swap(static_cast<_Tp&&>(__e1), static_cast<_Up&&>(__e2));
894  else if constexpr (indirectly_readable<_Tp>
895  && indirectly_readable<_Up>
896  && swappable_with<iter_reference_t<_Tp>, iter_reference_t<_Up>>)
897  ranges::swap(*__e1, *__e2);
898  else
899  *__e1 = __iswap::__iter_exchange_move(__e2, __e1);
900  }
901  };
902  } // namespace __iswap
903  /// @endcond
904 
905  inline namespace _Cpo {
906  inline constexpr __iswap::_IterSwap iter_swap{};
907  }
908 
909 } // namespace ranges
910 
911  /// [alg.req.ind.swap], concept `indirectly_swappable`
912  template<typename _I1, typename _I2 = _I1>
913  concept indirectly_swappable
914  = indirectly_readable<_I1> && indirectly_readable<_I2>
915  && requires(const _I1 __i1, const _I2 __i2)
916  {
917  ranges::iter_swap(__i1, __i1);
918  ranges::iter_swap(__i2, __i2);
919  ranges::iter_swap(__i1, __i2);
920  ranges::iter_swap(__i2, __i1);
921  };
922 
923  /// [alg.req.ind.cmp], concept `indirectly_comparable`
924  template<typename _I1, typename _I2, typename _Rel, typename _P1 = identity,
925  typename _P2 = identity>
926  concept indirectly_comparable
927  = indirect_binary_predicate<_Rel, projected<_I1, _P1>,
928  projected<_I2, _P2>>;
929 
930  /// [alg.req.permutable], concept `permutable`
931  template<typename _Iter>
932  concept permutable = forward_iterator<_Iter>
933  && indirectly_movable_storable<_Iter, _Iter>
934  && indirectly_swappable<_Iter, _Iter>;
935 
936  /// [alg.req.mergeable], concept `mergeable`
937  template<typename _I1, typename _I2, typename _Out,
938  typename _Rel = ranges::less, typename _P1 = identity,
939  typename _P2 = identity>
940  concept mergeable = input_iterator<_I1> && input_iterator<_I2>
941  && weakly_incrementable<_Out> && indirectly_copyable<_I1, _Out>
942  && indirectly_copyable<_I2, _Out>
943  && indirect_strict_weak_order<_Rel, projected<_I1, _P1>,
944  projected<_I2, _P2>>;
945 
946  /// [alg.req.sortable], concept `sortable`
947  template<typename _Iter, typename _Rel = ranges::less,
948  typename _Proj = identity>
949  concept sortable = permutable<_Iter>
950  && indirect_strict_weak_order<_Rel, projected<_Iter, _Proj>>;
951 
952  struct unreachable_sentinel_t
953  {
954  template<weakly_incrementable _It>
955  friend constexpr bool
956  operator==(unreachable_sentinel_t, const _It&) noexcept
957  { return false; }
958  };
959 
960  inline constexpr unreachable_sentinel_t unreachable_sentinel{};
961 
962  // This is the namespace for [range.access] CPOs.
963  namespace ranges::__access
964  {
965  using std::__detail::__class_or_enum;
966 
967  struct _Decay_copy final
968  {
969  template<typename _Tp>
970  constexpr decay_t<_Tp>
971  operator()(_Tp&& __t) const
972  noexcept(is_nothrow_convertible_v<_Tp, decay_t<_Tp>>)
973  { return std::forward<_Tp>(__t); }
974  } inline constexpr __decay_copy{};
975 
976  template<typename _Tp>
977  concept __member_begin = requires(_Tp& __t)
978  {
979  { __decay_copy(__t.begin()) } -> input_or_output_iterator;
980  };
981 
982  // Poison pill so that unqualified lookup doesn't find std::begin.
983  void begin() = delete;
984 
985  template<typename _Tp>
986  concept __adl_begin = __class_or_enum<remove_reference_t<_Tp>>
987  && requires(_Tp& __t)
988  {
989  { __decay_copy(begin(__t)) } -> input_or_output_iterator;
990  };
991 
992  // Simplified version of std::ranges::begin that only supports lvalues,
993  // for use by __range_iter_t below.
994  template<typename _Tp>
995  requires is_array_v<_Tp> || __member_begin<_Tp&> || __adl_begin<_Tp&>
996  auto
997  __begin(_Tp& __t)
998  {
999  if constexpr (is_array_v<_Tp>)
1000  return __t + 0;
1001  else if constexpr (__member_begin<_Tp&>)
1002  return __t.begin();
1003  else
1004  return begin(__t);
1005  }
1006  } // namespace ranges::__access
1007 
1008  namespace __detail
1009  {
1010  // Implementation of std::ranges::iterator_t, without using ranges::begin.
1011  template<typename _Tp>
1012  using __range_iter_t
1013  = decltype(ranges::__access::__begin(std::declval<_Tp&>()));
1014 
1015  } // namespace __detail
1016 
1017 #endif // C++20 library concepts
1018 _GLIBCXX_END_NAMESPACE_VERSION
1019 } // namespace std
1020 #endif // C++20
1021 #endif // _ITERATOR_CONCEPTS_H
ISO C++ entities toplevel namespace is std.
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:241
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition: type_traits:2470
Definition: simd.h:306
typename common_reference< _Tp... >::type common_reference_t
Definition: type_traits:3914
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition: type_traits:1718
constexpr complex< _Tp > operator*(const complex< _Tp > &__x, const complex< _Tp > &__y)
Return new complex value x times y.
Definition: complex:400
_Tp * begin(valarray< _Tp > &__va) noexcept
Return an iterator pointing to the first element of the valarray.
Definition: valarray:1227
constexpr default_sentinel_t default_sentinel
A default sentinel value.