libstdc++
ranges
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1 // <ranges> -*- C++ -*-
2 
3 // Copyright (C) 2019-2021 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/ranges
26  * This is a Standard C++ Library header.
27  * @ingroup concepts
28  */
29 
30 #ifndef _GLIBCXX_RANGES
31 #define _GLIBCXX_RANGES 1
32 
33 #if __cplusplus > 201703L
34 
35 #pragma GCC system_header
36 
37 #include <concepts>
38 
39 #if __cpp_lib_concepts
40 
41 #include <compare>
42 #include <initializer_list>
43 #include <iterator>
44 #include <optional>
45 #include <tuple>
46 #include <bits/ranges_util.h>
47 #include <bits/refwrap.h>
48 
49 /**
50  * @defgroup ranges Ranges
51  *
52  * Components for dealing with ranges of elements.
53  */
54 
55 namespace std _GLIBCXX_VISIBILITY(default)
56 {
57 _GLIBCXX_BEGIN_NAMESPACE_VERSION
58 namespace ranges
59 {
60  // [range.access] customization point objects
61  // [range.req] range and view concepts
62  // [range.dangling] dangling iterator handling
63  // Defined in <bits/ranges_base.h>
64 
65  // [view.interface] View interface
66  // [range.subrange] Sub-ranges
67  // Defined in <bits/ranges_util.h>
68 
69  // C++20 24.6 [range.factories] Range factories
70 
71  /// A view that contains no elements.
72  template<typename _Tp> requires is_object_v<_Tp>
73  class empty_view
74  : public view_interface<empty_view<_Tp>>
75  {
76  public:
77  static constexpr _Tp* begin() noexcept { return nullptr; }
78  static constexpr _Tp* end() noexcept { return nullptr; }
79  static constexpr _Tp* data() noexcept { return nullptr; }
80  static constexpr size_t size() noexcept { return 0; }
81  static constexpr bool empty() noexcept { return true; }
82  };
83 
84  template<typename _Tp>
85  inline constexpr bool enable_borrowed_range<empty_view<_Tp>> = true;
86 
87  namespace __detail
88  {
89  template<typename _Tp>
90  concept __boxable = copy_constructible<_Tp> && is_object_v<_Tp>;
91 
92  template<__boxable _Tp>
93  struct __box : std::optional<_Tp>
94  {
95  using std::optional<_Tp>::optional;
96 
97  constexpr
98  __box()
99  noexcept(is_nothrow_default_constructible_v<_Tp>)
100  requires default_initializable<_Tp>
101  : std::optional<_Tp>{std::in_place}
102  { }
103 
104  __box(const __box&) = default;
105  __box(__box&&) = default;
106 
107  using std::optional<_Tp>::operator=;
108 
109  // _GLIBCXX_RESOLVE_LIB_DEFECTS
110  // 3477. Simplify constraints for semiregular-box
111  __box&
112  operator=(const __box& __that)
113  noexcept(is_nothrow_copy_constructible_v<_Tp>)
114  requires (!copyable<_Tp>)
115  {
116  if (this != std::__addressof(__that))
117  {
118  if ((bool)__that)
119  this->emplace(*__that);
120  else
121  this->reset();
122  }
123  return *this;
124  }
125 
126  __box&
127  operator=(__box&& __that)
128  noexcept(is_nothrow_move_constructible_v<_Tp>)
129  requires (!movable<_Tp>)
130  {
131  if (this != std::__addressof(__that))
132  {
133  if ((bool)__that)
134  this->emplace(std::move(*__that));
135  else
136  this->reset();
137  }
138  return *this;
139  }
140  };
141 
142  // For types which are already copyable, this specialization of the
143  // copyable wrapper stores the object directly without going through
144  // std::optional. It provides just the subset of the primary template's
145  // API that we currently use.
146  template<__boxable _Tp>
147  requires copyable<_Tp>
148  struct __box<_Tp>
149  {
150  private:
151  [[no_unique_address]] _Tp _M_value = _Tp();
152 
153  public:
154  __box() requires default_initializable<_Tp> = default;
155 
156  constexpr explicit
157  __box(const _Tp& __t)
158  noexcept(is_nothrow_copy_constructible_v<_Tp>)
159  : _M_value(__t)
160  { }
161 
162  constexpr explicit
163  __box(_Tp&& __t)
164  noexcept(is_nothrow_move_constructible_v<_Tp>)
165  : _M_value(std::move(__t))
166  { }
167 
168  template<typename... _Args>
169  requires constructible_from<_Tp, _Args...>
170  constexpr explicit
171  __box(in_place_t, _Args&&... __args)
172  noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
173  : _M_value(std::forward<_Args>(__args)...)
174  { }
175 
176  constexpr bool
177  has_value() const noexcept
178  { return true; };
179 
180  constexpr _Tp&
181  operator*() noexcept
182  { return _M_value; }
183 
184  constexpr const _Tp&
185  operator*() const noexcept
186  { return _M_value; }
187 
188  constexpr _Tp*
189  operator->() noexcept
190  { return std::__addressof(_M_value); }
191 
192  constexpr const _Tp*
193  operator->() const noexcept
194  { return std::__addressof(_M_value); }
195  };
196  } // namespace __detail
197 
198  /// A view that contains exactly one element.
199  template<copy_constructible _Tp> requires is_object_v<_Tp>
200  class single_view : public view_interface<single_view<_Tp>>
201  {
202  public:
203  single_view() = default;
204 
205  constexpr explicit
206  single_view(const _Tp& __t)
207  : _M_value(__t)
208  { }
209 
210  constexpr explicit
211  single_view(_Tp&& __t)
212  : _M_value(std::move(__t))
213  { }
214 
215  // _GLIBCXX_RESOLVE_LIB_DEFECTS
216  // 3428. single_view's in place constructor should be explicit
217  template<typename... _Args>
218  requires constructible_from<_Tp, _Args...>
219  constexpr explicit
220  single_view(in_place_t, _Args&&... __args)
221  : _M_value{in_place, std::forward<_Args>(__args)...}
222  { }
223 
224  constexpr _Tp*
225  begin() noexcept
226  { return data(); }
227 
228  constexpr const _Tp*
229  begin() const noexcept
230  { return data(); }
231 
232  constexpr _Tp*
233  end() noexcept
234  { return data() + 1; }
235 
236  constexpr const _Tp*
237  end() const noexcept
238  { return data() + 1; }
239 
240  static constexpr size_t
241  size() noexcept
242  { return 1; }
243 
244  constexpr _Tp*
245  data() noexcept
246  { return _M_value.operator->(); }
247 
248  constexpr const _Tp*
249  data() const noexcept
250  { return _M_value.operator->(); }
251 
252  private:
253  [[no_unique_address]] __detail::__box<_Tp> _M_value;
254  };
255 
256  template<typename _Tp>
257  single_view(_Tp) -> single_view<_Tp>;
258 
259  namespace __detail
260  {
261  template<typename _Wp>
262  constexpr auto __to_signed_like(_Wp __w) noexcept
263  {
264  if constexpr (!integral<_Wp>)
265  return iter_difference_t<_Wp>();
266  else if constexpr (sizeof(iter_difference_t<_Wp>) > sizeof(_Wp))
267  return iter_difference_t<_Wp>(__w);
268  else if constexpr (sizeof(ptrdiff_t) > sizeof(_Wp))
269  return ptrdiff_t(__w);
270  else if constexpr (sizeof(long long) > sizeof(_Wp))
271  return (long long)(__w);
272 #ifdef __SIZEOF_INT128__
273  else if constexpr (__SIZEOF_INT128__ > sizeof(_Wp))
274  return __int128(__w);
275 #endif
276  else
277  return __max_diff_type(__w);
278  }
279 
280  template<typename _Wp>
281  using __iota_diff_t = decltype(__to_signed_like(std::declval<_Wp>()));
282 
283  template<typename _It>
284  concept __decrementable = incrementable<_It>
285  && requires(_It __i)
286  {
287  { --__i } -> same_as<_It&>;
288  { __i-- } -> same_as<_It>;
289  };
290 
291  template<typename _It>
292  concept __advanceable = __decrementable<_It> && totally_ordered<_It>
293  && requires( _It __i, const _It __j, const __iota_diff_t<_It> __n)
294  {
295  { __i += __n } -> same_as<_It&>;
296  { __i -= __n } -> same_as<_It&>;
297  _It(__j + __n);
298  _It(__n + __j);
299  _It(__j - __n);
300  { __j - __j } -> convertible_to<__iota_diff_t<_It>>;
301  };
302 
303  template<typename _Winc>
304  struct __iota_view_iter_cat
305  { };
306 
307  template<incrementable _Winc>
308  struct __iota_view_iter_cat<_Winc>
309  { using iterator_category = input_iterator_tag; };
310  } // namespace __detail
311 
312  template<weakly_incrementable _Winc,
313  semiregular _Bound = unreachable_sentinel_t>
314  requires std::__detail::__weakly_eq_cmp_with<_Winc, _Bound>
315  && copyable<_Winc>
316  class iota_view : public view_interface<iota_view<_Winc, _Bound>>
317  {
318  private:
319  struct _Sentinel;
320 
321  struct _Iterator : __detail::__iota_view_iter_cat<_Winc>
322  {
323  private:
324  static auto
325  _S_iter_concept()
326  {
327  using namespace __detail;
328  if constexpr (__advanceable<_Winc>)
329  return random_access_iterator_tag{};
330  else if constexpr (__decrementable<_Winc>)
331  return bidirectional_iterator_tag{};
332  else if constexpr (incrementable<_Winc>)
333  return forward_iterator_tag{};
334  else
335  return input_iterator_tag{};
336  }
337 
338  public:
339  using iterator_concept = decltype(_S_iter_concept());
340  // iterator_category defined in __iota_view_iter_cat
341  using value_type = _Winc;
342  using difference_type = __detail::__iota_diff_t<_Winc>;
343 
344  _Iterator() requires default_initializable<_Winc> = default;
345 
346  constexpr explicit
347  _Iterator(_Winc __value)
348  : _M_value(__value) { }
349 
350  constexpr _Winc
351  operator*() const noexcept(is_nothrow_copy_constructible_v<_Winc>)
352  { return _M_value; }
353 
354  constexpr _Iterator&
355  operator++()
356  {
357  ++_M_value;
358  return *this;
359  }
360 
361  constexpr void
362  operator++(int)
363  { ++*this; }
364 
365  constexpr _Iterator
366  operator++(int) requires incrementable<_Winc>
367  {
368  auto __tmp = *this;
369  ++*this;
370  return __tmp;
371  }
372 
373  constexpr _Iterator&
374  operator--() requires __detail::__decrementable<_Winc>
375  {
376  --_M_value;
377  return *this;
378  }
379 
380  constexpr _Iterator
381  operator--(int) requires __detail::__decrementable<_Winc>
382  {
383  auto __tmp = *this;
384  --*this;
385  return __tmp;
386  }
387 
388  constexpr _Iterator&
389  operator+=(difference_type __n) requires __detail::__advanceable<_Winc>
390  {
391  using __detail::__is_integer_like;
392  using __detail::__is_signed_integer_like;
393  if constexpr (__is_integer_like<_Winc>
394  && !__is_signed_integer_like<_Winc>)
395  {
396  if (__n >= difference_type(0))
397  _M_value += static_cast<_Winc>(__n);
398  else
399  _M_value -= static_cast<_Winc>(-__n);
400  }
401  else
402  _M_value += __n;
403  return *this;
404  }
405 
406  constexpr _Iterator&
407  operator-=(difference_type __n) requires __detail::__advanceable<_Winc>
408  {
409  using __detail::__is_integer_like;
410  using __detail::__is_signed_integer_like;
411  if constexpr (__is_integer_like<_Winc>
412  && !__is_signed_integer_like<_Winc>)
413  {
414  if (__n >= difference_type(0))
415  _M_value -= static_cast<_Winc>(__n);
416  else
417  _M_value += static_cast<_Winc>(-__n);
418  }
419  else
420  _M_value -= __n;
421  return *this;
422  }
423 
424  constexpr _Winc
425  operator[](difference_type __n) const
426  requires __detail::__advanceable<_Winc>
427  { return _Winc(_M_value + __n); }
428 
429  friend constexpr bool
430  operator==(const _Iterator& __x, const _Iterator& __y)
431  requires equality_comparable<_Winc>
432  { return __x._M_value == __y._M_value; }
433 
434  friend constexpr bool
435  operator<(const _Iterator& __x, const _Iterator& __y)
436  requires totally_ordered<_Winc>
437  { return __x._M_value < __y._M_value; }
438 
439  friend constexpr bool
440  operator>(const _Iterator& __x, const _Iterator& __y)
441  requires totally_ordered<_Winc>
442  { return __y < __x; }
443 
444  friend constexpr bool
445  operator<=(const _Iterator& __x, const _Iterator& __y)
446  requires totally_ordered<_Winc>
447  { return !(__y < __x); }
448 
449  friend constexpr bool
450  operator>=(const _Iterator& __x, const _Iterator& __y)
451  requires totally_ordered<_Winc>
452  { return !(__x < __y); }
453 
454 #ifdef __cpp_lib_three_way_comparison
455  friend constexpr auto
456  operator<=>(const _Iterator& __x, const _Iterator& __y)
457  requires totally_ordered<_Winc> && three_way_comparable<_Winc>
458  { return __x._M_value <=> __y._M_value; }
459 #endif
460 
461  friend constexpr _Iterator
462  operator+(_Iterator __i, difference_type __n)
463  requires __detail::__advanceable<_Winc>
464  {
465  __i += __n;
466  return __i;
467  }
468 
469  friend constexpr _Iterator
470  operator+(difference_type __n, _Iterator __i)
471  requires __detail::__advanceable<_Winc>
472  { return __i += __n; }
473 
474  friend constexpr _Iterator
475  operator-(_Iterator __i, difference_type __n)
476  requires __detail::__advanceable<_Winc>
477  {
478  __i -= __n;
479  return __i;
480  }
481 
482  friend constexpr difference_type
483  operator-(const _Iterator& __x, const _Iterator& __y)
484  requires __detail::__advanceable<_Winc>
485  {
486  using __detail::__is_integer_like;
487  using __detail::__is_signed_integer_like;
488  using _Dt = difference_type;
489  if constexpr (__is_integer_like<_Winc>)
490  {
491  if constexpr (__is_signed_integer_like<_Winc>)
492  return _Dt(_Dt(__x._M_value) - _Dt(__y._M_value));
493  else
494  return (__y._M_value > __x._M_value)
495  ? _Dt(-_Dt(__y._M_value - __x._M_value))
496  : _Dt(__x._M_value - __y._M_value);
497  }
498  else
499  return __x._M_value - __y._M_value;
500  }
501 
502  private:
503  _Winc _M_value = _Winc();
504 
505  friend iota_view;
506  friend _Sentinel;
507  };
508 
509  struct _Sentinel
510  {
511  private:
512  constexpr bool
513  _M_equal(const _Iterator& __x) const
514  { return __x._M_value == _M_bound; }
515 
516  constexpr auto
517  _M_distance_from(const _Iterator& __x) const
518  { return _M_bound - __x._M_value; }
519 
520  _Bound _M_bound = _Bound();
521 
522  public:
523  _Sentinel() = default;
524 
525  constexpr explicit
526  _Sentinel(_Bound __bound)
527  : _M_bound(__bound) { }
528 
529  friend constexpr bool
530  operator==(const _Iterator& __x, const _Sentinel& __y)
531  { return __y._M_equal(__x); }
532 
533  friend constexpr iter_difference_t<_Winc>
534  operator-(const _Iterator& __x, const _Sentinel& __y)
535  requires sized_sentinel_for<_Bound, _Winc>
536  { return -__y._M_distance_from(__x); }
537 
538  friend constexpr iter_difference_t<_Winc>
539  operator-(const _Sentinel& __x, const _Iterator& __y)
540  requires sized_sentinel_for<_Bound, _Winc>
541  { return __x._M_distance_from(__y); }
542 
543  friend iota_view;
544  };
545 
546  _Winc _M_value = _Winc();
547  [[no_unique_address]] _Bound _M_bound = _Bound();
548 
549  public:
550  iota_view() requires default_initializable<_Winc> = default;
551 
552  constexpr explicit
553  iota_view(_Winc __value)
554  : _M_value(__value)
555  { }
556 
557  constexpr
558  iota_view(type_identity_t<_Winc> __value,
559  type_identity_t<_Bound> __bound)
560  : _M_value(__value), _M_bound(__bound)
561  {
562  if constexpr (totally_ordered_with<_Winc, _Bound>)
563  __glibcxx_assert( bool(__value <= __bound) );
564  }
565 
566  constexpr
567  iota_view(_Iterator __first, _Iterator __last)
568  requires same_as<_Winc, _Bound>
569  : iota_view(__first._M_value, __last._M_value)
570  { }
571 
572  constexpr
573  iota_view(_Iterator __first, unreachable_sentinel_t __last)
574  requires same_as<_Bound, unreachable_sentinel_t>
575  : iota_view(__first._M_value, __last)
576  { }
577 
578  constexpr
579  iota_view(_Iterator __first, _Sentinel __last)
580  requires (!same_as<_Winc, _Bound>) && (!same_as<_Bound, unreachable_sentinel_t>)
581  : iota_view(__first._M_value, __last._M_bound)
582  { }
583 
584  constexpr _Iterator
585  begin() const { return _Iterator{_M_value}; }
586 
587  constexpr auto
588  end() const
589  {
590  if constexpr (same_as<_Bound, unreachable_sentinel_t>)
591  return unreachable_sentinel;
592  else
593  return _Sentinel{_M_bound};
594  }
595 
596  constexpr _Iterator
597  end() const requires same_as<_Winc, _Bound>
598  { return _Iterator{_M_bound}; }
599 
600  constexpr auto
601  size() const
602  requires (same_as<_Winc, _Bound> && __detail::__advanceable<_Winc>)
603  || (integral<_Winc> && integral<_Bound>)
604  || sized_sentinel_for<_Bound, _Winc>
605  {
606  using __detail::__is_integer_like;
607  using __detail::__to_unsigned_like;
608  if constexpr (integral<_Winc> && integral<_Bound>)
609  {
610  using _Up = make_unsigned_t<decltype(_M_bound - _M_value)>;
611  return _Up(_M_bound) - _Up(_M_value);
612  }
613  else if constexpr (__is_integer_like<_Winc>)
614  return __to_unsigned_like(_M_bound) - __to_unsigned_like(_M_value);
615  else
616  return __to_unsigned_like(_M_bound - _M_value);
617  }
618  };
619 
620  template<typename _Winc, typename _Bound>
621  requires (!__detail::__is_integer_like<_Winc>
622  || !__detail::__is_integer_like<_Bound>
623  || (__detail::__is_signed_integer_like<_Winc>
624  == __detail::__is_signed_integer_like<_Bound>))
625  iota_view(_Winc, _Bound) -> iota_view<_Winc, _Bound>;
626 
627  template<weakly_incrementable _Winc, semiregular _Bound>
628  inline constexpr bool
629  enable_borrowed_range<iota_view<_Winc, _Bound>> = true;
630 
631 namespace views
632 {
633  template<typename _Tp>
634  inline constexpr empty_view<_Tp> empty{};
635 
636  struct _Single
637  {
638  template<typename _Tp>
639  constexpr auto
640  operator()(_Tp&& __e) const
641  { return single_view<decay_t<_Tp>>(std::forward<_Tp>(__e)); }
642  };
643 
644  inline constexpr _Single single{};
645 
646  struct _Iota
647  {
648  template<typename _Tp>
649  constexpr auto
650  operator()(_Tp&& __e) const
651  { return iota_view(std::forward<_Tp>(__e)); }
652 
653  template<typename _Tp, typename _Up>
654  constexpr auto
655  operator()(_Tp&& __e, _Up&& __f) const
656  { return iota_view(std::forward<_Tp>(__e), std::forward<_Up>(__f)); }
657  };
658 
659  inline constexpr _Iota iota{};
660 } // namespace views
661 
662  namespace __detail
663  {
664  template<typename _Val, typename _CharT, typename _Traits>
665  concept __stream_extractable
666  = requires(basic_istream<_CharT, _Traits>& is, _Val& t) { is >> t; };
667  } // namespace __detail
668 
669  template<movable _Val, typename _CharT,
670  typename _Traits = char_traits<_CharT>>
671  requires default_initializable<_Val>
672  && __detail::__stream_extractable<_Val, _CharT, _Traits>
673  class basic_istream_view
674  : public view_interface<basic_istream_view<_Val, _CharT, _Traits>>
675  {
676  public:
677  basic_istream_view() = default;
678 
679  constexpr explicit
680  basic_istream_view(basic_istream<_CharT, _Traits>& __stream)
681  : _M_stream(std::__addressof(__stream))
682  { }
683 
684  constexpr auto
685  begin()
686  {
687  if (_M_stream != nullptr)
688  *_M_stream >> _M_object;
689  return _Iterator{this};
690  }
691 
692  constexpr default_sentinel_t
693  end() const noexcept
694  { return default_sentinel; }
695 
696  private:
697  basic_istream<_CharT, _Traits>* _M_stream = nullptr;
698  _Val _M_object = _Val();
699 
700  struct _Iterator
701  {
702  public:
703  using iterator_concept = input_iterator_tag;
704  using difference_type = ptrdiff_t;
705  using value_type = _Val;
706 
707  _Iterator() = default;
708 
709  constexpr explicit
710  _Iterator(basic_istream_view* __parent) noexcept
711  : _M_parent(__parent)
712  { }
713 
714  _Iterator(const _Iterator&) = delete;
715  _Iterator(_Iterator&&) = default;
716  _Iterator& operator=(const _Iterator&) = delete;
717  _Iterator& operator=(_Iterator&&) = default;
718 
719  _Iterator&
720  operator++()
721  {
722  __glibcxx_assert(_M_parent->_M_stream != nullptr);
723  *_M_parent->_M_stream >> _M_parent->_M_object;
724  return *this;
725  }
726 
727  void
728  operator++(int)
729  { ++*this; }
730 
731  _Val&
732  operator*() const
733  {
734  __glibcxx_assert(_M_parent->_M_stream != nullptr);
735  return _M_parent->_M_object;
736  }
737 
738  friend bool
739  operator==(const _Iterator& __x, default_sentinel_t)
740  { return __x._M_at_end(); }
741 
742  private:
743  basic_istream_view* _M_parent = nullptr;
744 
745  bool
746  _M_at_end() const
747  { return _M_parent == nullptr || !*_M_parent->_M_stream; }
748  };
749 
750  friend _Iterator;
751  };
752 
753  template<typename _Val, typename _CharT, typename _Traits>
754  basic_istream_view<_Val, _CharT, _Traits>
755  istream_view(basic_istream<_CharT, _Traits>& __s)
756  { return basic_istream_view<_Val, _CharT, _Traits>{__s}; }
757 
758  // C++20 24.7 [range.adaptors] Range adaptors
759 
760 namespace __detail
761 {
762  struct _Empty { };
763 
764  // Alias for a type that is conditionally present
765  // (and is an empty type otherwise).
766  // Data members using this alias should use [[no_unique_address]] so that
767  // they take no space when not needed.
768  template<bool _Present, typename _Tp>
769  using __maybe_present_t = conditional_t<_Present, _Tp, _Empty>;
770 
771  // Alias for a type that is conditionally const.
772  template<bool _Const, typename _Tp>
773  using __maybe_const_t = conditional_t<_Const, const _Tp, _Tp>;
774 
775 } // namespace __detail
776 
777 namespace views::__adaptor
778 {
779  // True if the range adaptor _Adaptor can be applied with _Args.
780  template<typename _Adaptor, typename... _Args>
781  concept __adaptor_invocable
782  = requires { std::declval<_Adaptor>()(declval<_Args>()...); };
783 
784  // True if the range adaptor non-closure _Adaptor can be partially applied
785  // with _Args.
786  template<typename _Adaptor, typename... _Args>
787  concept __adaptor_partial_app_viable = (_Adaptor::_S_arity > 1)
788  && (sizeof...(_Args) == _Adaptor::_S_arity - 1)
789  && (constructible_from<decay_t<_Args>, _Args> && ...);
790 
791  template<typename _Adaptor, typename... _Args>
792  struct _Partial;
793 
794  template<typename _Lhs, typename _Rhs>
795  struct _Pipe;
796 
797  // The base class of every range adaptor closure.
798  //
799  // The derived class should define the optional static data member
800  // _S_has_simple_call_op to true if the behavior of this adaptor is
801  // independent of the constness/value category of the adaptor object.
802  struct _RangeAdaptorClosure
803  {
804  // range | adaptor is equivalent to adaptor(range).
805  template<typename _Self, typename _Range>
806  requires derived_from<remove_cvref_t<_Self>, _RangeAdaptorClosure>
807  && __adaptor_invocable<_Self, _Range>
808  friend constexpr auto
809  operator|(_Range&& __r, _Self&& __self)
810  { return std::forward<_Self>(__self)(std::forward<_Range>(__r)); }
811 
812  // Compose the adaptors __lhs and __rhs into a pipeline, returning
813  // another range adaptor closure object.
814  template<typename _Lhs, typename _Rhs>
815  requires derived_from<_Lhs, _RangeAdaptorClosure>
816  && derived_from<_Rhs, _RangeAdaptorClosure>
817  friend constexpr auto
818  operator|(_Lhs __lhs, _Rhs __rhs)
819  { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; }
820  };
821 
822  // The base class of every range adaptor non-closure.
823  //
824  // The static data member _Derived::_S_arity must contain the total number of
825  // arguments that the adaptor takes, and the class _Derived must introduce
826  // _RangeAdaptor::operator() into the class scope via a using-declaration.
827  //
828  // The optional static data member _Derived::_S_has_simple_extra_args should
829  // be defined to true if the behavior of this adaptor is independent of the
830  // constness/value category of the extra arguments. This data member could
831  // also be defined as a variable template parameterized by the types of the
832  // extra arguments.
833  template<typename _Derived>
834  struct _RangeAdaptor
835  {
836  // Partially apply the arguments __args to the range adaptor _Derived,
837  // returning a range adaptor closure object.
838  template<typename... _Args>
839  requires __adaptor_partial_app_viable<_Derived, _Args...>
840  constexpr auto
841  operator()(_Args&&... __args) const
842  {
843  return _Partial<_Derived, decay_t<_Args>...>{std::forward<_Args>(__args)...};
844  }
845  };
846 
847  // True if the range adaptor closure _Adaptor has a simple operator(), i.e.
848  // one that's not overloaded according to constness or value category of the
849  // _Adaptor object.
850  template<typename _Adaptor>
851  concept __closure_has_simple_call_op = _Adaptor::_S_has_simple_call_op;
852 
853  // True if the behavior of the range adaptor non-closure _Adaptor is
854  // independent of the value category of its extra arguments _Args.
855  template<typename _Adaptor, typename... _Args>
856  concept __adaptor_has_simple_extra_args = _Adaptor::_S_has_simple_extra_args
857  || _Adaptor::template _S_has_simple_extra_args<_Args...>;
858 
859  // A range adaptor closure that represents partial application of
860  // the range adaptor _Adaptor with arguments _Args.
861  template<typename _Adaptor, typename... _Args>
862  struct _Partial : _RangeAdaptorClosure
863  {
864  tuple<_Args...> _M_args;
865 
866  constexpr
867  _Partial(_Args... __args)
868  : _M_args(std::move(__args)...)
869  { }
870 
871  // Invoke _Adaptor with arguments __r, _M_args... according to the
872  // value category of this _Partial object.
873  template<typename _Range>
874  requires __adaptor_invocable<_Adaptor, _Range, const _Args&...>
875  constexpr auto
876  operator()(_Range&& __r) const &
877  {
878  auto __forwarder = [&__r] (const auto&... __args) {
879  return _Adaptor{}(std::forward<_Range>(__r), __args...);
880  };
881  return std::apply(__forwarder, _M_args);
882  }
883 
884  template<typename _Range>
885  requires __adaptor_invocable<_Adaptor, _Range, _Args...>
886  constexpr auto
887  operator()(_Range&& __r) &&
888  {
889  auto __forwarder = [&__r] (auto&... __args) {
890  return _Adaptor{}(std::forward<_Range>(__r), std::move(__args)...);
891  };
892  return std::apply(__forwarder, _M_args);
893  }
894 
895  template<typename _Range>
896  constexpr auto
897  operator()(_Range&& __r) const && = delete;
898  };
899 
900  // A lightweight specialization of the above primary template for
901  // the common case where _Adaptor accepts a single extra argument.
902  template<typename _Adaptor, typename _Arg>
903  struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure
904  {
905  _Arg _M_arg;
906 
907  constexpr
908  _Partial(_Arg __arg)
909  : _M_arg(std::move(__arg))
910  { }
911 
912  template<typename _Range>
913  requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
914  constexpr auto
915  operator()(_Range&& __r) const &
916  { return _Adaptor{}(std::forward<_Range>(__r), _M_arg); }
917 
918  template<typename _Range>
919  requires __adaptor_invocable<_Adaptor, _Range, _Arg>
920  constexpr auto
921  operator()(_Range&& __r) &&
922  { return _Adaptor{}(std::forward<_Range>(__r), std::move(_M_arg)); }
923 
924  template<typename _Range>
925  constexpr auto
926  operator()(_Range&& __r) const && = delete;
927  };
928 
929  // Partial specialization of the primary template for the case where the extra
930  // arguments of the adaptor can always be safely and efficiently forwarded by
931  // const reference. This lets us get away with a single operator() overload,
932  // which makes overload resolution failure diagnostics more concise.
933  template<typename _Adaptor, typename... _Args>
934  requires __adaptor_has_simple_extra_args<_Adaptor, _Args...>
935  && (is_trivially_copyable_v<_Args> && ...)
936  struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure
937  {
938  tuple<_Args...> _M_args;
939 
940  constexpr
941  _Partial(_Args... __args)
942  : _M_args(std::move(__args)...)
943  { }
944 
945  // Invoke _Adaptor with arguments __r, const _M_args&... regardless
946  // of the value category of this _Partial object.
947  template<typename _Range>
948  requires __adaptor_invocable<_Adaptor, _Range, const _Args&...>
949  constexpr auto
950  operator()(_Range&& __r) const
951  {
952  auto __forwarder = [&__r] (const auto&... __args) {
953  return _Adaptor{}(std::forward<_Range>(__r), __args...);
954  };
955  return std::apply(__forwarder, _M_args);
956  }
957 
958  static constexpr bool _S_has_simple_call_op = true;
959  };
960 
961  // A lightweight specialization of the above template for the common case
962  // where _Adaptor accepts a single extra argument.
963  template<typename _Adaptor, typename _Arg>
964  requires __adaptor_has_simple_extra_args<_Adaptor, _Arg>
965  && is_trivially_copyable_v<_Arg>
966  struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure
967  {
968  _Arg _M_arg;
969 
970  constexpr
971  _Partial(_Arg __arg)
972  : _M_arg(std::move(__arg))
973  { }
974 
975  template<typename _Range>
976  requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
977  constexpr auto
978  operator()(_Range&& __r) const
979  { return _Adaptor{}(std::forward<_Range>(__r), _M_arg); }
980 
981  static constexpr bool _S_has_simple_call_op = true;
982  };
983 
984  template<typename _Lhs, typename _Rhs, typename _Range>
985  concept __pipe_invocable
986  = requires { std::declval<_Rhs>()(std::declval<_Lhs>()(std::declval<_Range>())); };
987 
988  // A range adaptor closure that represents composition of the range
989  // adaptor closures _Lhs and _Rhs.
990  template<typename _Lhs, typename _Rhs>
991  struct _Pipe : _RangeAdaptorClosure
992  {
993  [[no_unique_address]] _Lhs _M_lhs;
994  [[no_unique_address]] _Rhs _M_rhs;
995 
996  constexpr
997  _Pipe(_Lhs __lhs, _Rhs __rhs)
998  : _M_lhs(std::move(__lhs)), _M_rhs(std::move(__rhs))
999  { }
1000 
1001  // Invoke _M_rhs(_M_lhs(__r)) according to the value category of this
1002  // range adaptor closure object.
1003  template<typename _Range>
1004  requires __pipe_invocable<const _Lhs&, const _Rhs&, _Range>
1005  constexpr auto
1006  operator()(_Range&& __r) const &
1007  { return _M_rhs(_M_lhs(std::forward<_Range>(__r))); }
1008 
1009  template<typename _Range>
1010  requires __pipe_invocable<_Lhs, _Rhs, _Range>
1011  constexpr auto
1012  operator()(_Range&& __r) &&
1013  { return std::move(_M_rhs)(std::move(_M_lhs)(std::forward<_Range>(__r))); }
1014 
1015  template<typename _Range>
1016  constexpr auto
1017  operator()(_Range&& __r) const && = delete;
1018  };
1019 
1020  // A partial specialization of the above primary template for the case where
1021  // both adaptor operands have a simple operator(). This in turn lets us
1022  // implement composition using a single simple operator(), which makes
1023  // overload resolution failure diagnostics more concise.
1024  template<typename _Lhs, typename _Rhs>
1025  requires __closure_has_simple_call_op<_Lhs>
1026  && __closure_has_simple_call_op<_Rhs>
1027  struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure
1028  {
1029  [[no_unique_address]] _Lhs _M_lhs;
1030  [[no_unique_address]] _Rhs _M_rhs;
1031 
1032  constexpr
1033  _Pipe(_Lhs __lhs, _Rhs __rhs)
1034  : _M_lhs(std::move(__lhs)), _M_rhs(std::move(__rhs))
1035  { }
1036 
1037  template<typename _Range>
1038  requires __pipe_invocable<const _Lhs&, const _Rhs&, _Range>
1039  constexpr auto
1040  operator()(_Range&& __r) const
1041  { return _M_rhs(_M_lhs(std::forward<_Range>(__r))); }
1042 
1043  static constexpr bool _S_has_simple_call_op = true;
1044  };
1045 } // namespace views::__adaptor
1046 
1047  template<range _Range> requires is_object_v<_Range>
1048  class ref_view : public view_interface<ref_view<_Range>>
1049  {
1050  private:
1051  _Range* _M_r = nullptr;
1052 
1053  static void _S_fun(_Range&); // not defined
1054  static void _S_fun(_Range&&) = delete;
1055 
1056  public:
1057  constexpr
1058  ref_view() noexcept = default;
1059 
1060  template<__detail::__not_same_as<ref_view> _Tp>
1061  requires convertible_to<_Tp, _Range&>
1062  && requires { _S_fun(declval<_Tp>()); }
1063  constexpr
1064  ref_view(_Tp&& __t)
1065  : _M_r(std::__addressof(static_cast<_Range&>(std::forward<_Tp>(__t))))
1066  { }
1067 
1068  constexpr _Range&
1069  base() const
1070  { return *_M_r; }
1071 
1072  constexpr iterator_t<_Range>
1073  begin() const
1074  { return ranges::begin(*_M_r); }
1075 
1076  constexpr sentinel_t<_Range>
1077  end() const
1078  { return ranges::end(*_M_r); }
1079 
1080  constexpr bool
1081  empty() const requires requires { ranges::empty(*_M_r); }
1082  { return ranges::empty(*_M_r); }
1083 
1084  constexpr auto
1085  size() const requires sized_range<_Range>
1086  { return ranges::size(*_M_r); }
1087 
1088  constexpr auto
1089  data() const requires contiguous_range<_Range>
1090  { return ranges::data(*_M_r); }
1091  };
1092 
1093  template<typename _Range>
1094  ref_view(_Range&) -> ref_view<_Range>;
1095 
1096  template<typename _Tp>
1097  inline constexpr bool enable_borrowed_range<ref_view<_Tp>> = true;
1098 
1099  namespace views
1100  {
1101  namespace __detail
1102  {
1103  template<typename _Range>
1104  concept __can_ref_view = requires { ref_view{std::declval<_Range>()}; };
1105 
1106  template<typename _Range>
1107  concept __can_subrange = requires { subrange{std::declval<_Range>()}; };
1108  } // namespace __detail
1109 
1110  struct _All : __adaptor::_RangeAdaptorClosure
1111  {
1112  template<viewable_range _Range>
1113  requires view<decay_t<_Range>>
1114  || __detail::__can_ref_view<_Range>
1115  || __detail::__can_subrange<_Range>
1116  constexpr auto
1117  operator()(_Range&& __r) const
1118  {
1119  if constexpr (view<decay_t<_Range>>)
1120  return std::forward<_Range>(__r);
1121  else if constexpr (__detail::__can_ref_view<_Range>)
1122  return ref_view{std::forward<_Range>(__r)};
1123  else
1124  return subrange{std::forward<_Range>(__r)};
1125  }
1126 
1127  static constexpr bool _S_has_simple_call_op = true;
1128  };
1129 
1130  inline constexpr _All all;
1131 
1132  template<viewable_range _Range>
1133  using all_t = decltype(all(std::declval<_Range>()));
1134  } // namespace views
1135 
1136  namespace __detail
1137  {
1138  template<typename _Tp>
1139  struct __non_propagating_cache
1140  {
1141  // When _Tp is not an object type (e.g. is a reference type), we make
1142  // __non_propagating_cache<_Tp> empty rather than ill-formed so that
1143  // users can easily conditionally declare data members with this type
1144  // (such as join_view::_M_inner).
1145  };
1146 
1147  template<typename _Tp>
1148  requires is_object_v<_Tp>
1149  struct __non_propagating_cache<_Tp> : protected _Optional_base<_Tp>
1150  {
1151  __non_propagating_cache() = default;
1152 
1153  constexpr
1154  __non_propagating_cache(const __non_propagating_cache&) noexcept
1155  { }
1156 
1157  constexpr
1158  __non_propagating_cache(__non_propagating_cache&& __other) noexcept
1159  { __other._M_reset(); }
1160 
1161  constexpr __non_propagating_cache&
1162  operator=(const __non_propagating_cache& __other) noexcept
1163  {
1164  if (std::__addressof(__other) != this)
1165  this->_M_reset();
1166  return *this;
1167  }
1168 
1169  constexpr __non_propagating_cache&
1170  operator=(__non_propagating_cache&& __other) noexcept
1171  {
1172  this->_M_reset();
1173  __other._M_reset();
1174  return *this;
1175  }
1176 
1177  constexpr _Tp&
1178  operator*() noexcept
1179  { return this->_M_get(); }
1180 
1181  constexpr const _Tp&
1182  operator*() const noexcept
1183  { return this->_M_get(); }
1184 
1185  template<typename _Iter>
1186  _Tp&
1187  _M_emplace_deref(const _Iter& __i)
1188  {
1189  this->_M_reset();
1190  // Using _Optional_base::_M_construct to initialize from '*__i'
1191  // would incur an extra move due to the indirection, so we instead
1192  // use placement new directly.
1193  ::new ((void *) std::__addressof(this->_M_payload._M_payload)) _Tp(*__i);
1194  this->_M_payload._M_engaged = true;
1195  return this->_M_get();
1196  }
1197  };
1198 
1199  template<range _Range>
1200  struct _CachedPosition
1201  {
1202  constexpr bool
1203  _M_has_value() const
1204  { return false; }
1205 
1206  constexpr iterator_t<_Range>
1207  _M_get(const _Range&) const
1208  {
1209  __glibcxx_assert(false);
1210  __builtin_unreachable();
1211  }
1212 
1213  constexpr void
1214  _M_set(const _Range&, const iterator_t<_Range>&) const
1215  { }
1216  };
1217 
1218  template<forward_range _Range>
1219  struct _CachedPosition<_Range>
1220  : protected __non_propagating_cache<iterator_t<_Range>>
1221  {
1222  constexpr bool
1223  _M_has_value() const
1224  { return this->_M_is_engaged(); }
1225 
1226  constexpr iterator_t<_Range>
1227  _M_get(const _Range&) const
1228  {
1229  __glibcxx_assert(_M_has_value());
1230  return **this;
1231  }
1232 
1233  constexpr void
1234  _M_set(const _Range&, const iterator_t<_Range>& __it)
1235  {
1236  __glibcxx_assert(!_M_has_value());
1237  std::construct_at(std::__addressof(this->_M_payload._M_payload),
1238  in_place, __it);
1239  this->_M_payload._M_engaged = true;
1240  }
1241  };
1242 
1243  template<random_access_range _Range>
1244  requires (sizeof(range_difference_t<_Range>)
1245  <= sizeof(iterator_t<_Range>))
1246  struct _CachedPosition<_Range>
1247  {
1248  private:
1249  range_difference_t<_Range> _M_offset = -1;
1250 
1251  public:
1252  _CachedPosition() = default;
1253 
1254  constexpr
1255  _CachedPosition(const _CachedPosition&) = default;
1256 
1257  constexpr
1258  _CachedPosition(_CachedPosition&& __other) noexcept
1259  { *this = std::move(__other); }
1260 
1261  constexpr _CachedPosition&
1262  operator=(const _CachedPosition&) = default;
1263 
1264  constexpr _CachedPosition&
1265  operator=(_CachedPosition&& __other) noexcept
1266  {
1267  // Propagate the cached offset, but invalidate the source.
1268  _M_offset = __other._M_offset;
1269  __other._M_offset = -1;
1270  return *this;
1271  }
1272 
1273  constexpr bool
1274  _M_has_value() const
1275  { return _M_offset >= 0; }
1276 
1277  constexpr iterator_t<_Range>
1278  _M_get(_Range& __r) const
1279  {
1280  __glibcxx_assert(_M_has_value());
1281  return ranges::begin(__r) + _M_offset;
1282  }
1283 
1284  constexpr void
1285  _M_set(_Range& __r, const iterator_t<_Range>& __it)
1286  {
1287  __glibcxx_assert(!_M_has_value());
1288  _M_offset = __it - ranges::begin(__r);
1289  }
1290  };
1291  } // namespace __detail
1292 
1293  namespace __detail
1294  {
1295  template<typename _Base>
1296  struct __filter_view_iter_cat
1297  { };
1298 
1299  template<forward_range _Base>
1300  struct __filter_view_iter_cat<_Base>
1301  {
1302  private:
1303  static auto
1304  _S_iter_cat()
1305  {
1306  using _Cat = typename iterator_traits<iterator_t<_Base>>::iterator_category;
1307  if constexpr (derived_from<_Cat, bidirectional_iterator_tag>)
1308  return bidirectional_iterator_tag{};
1309  else if constexpr (derived_from<_Cat, forward_iterator_tag>)
1310  return forward_iterator_tag{};
1311  else
1312  return _Cat{};
1313  }
1314  public:
1315  using iterator_category = decltype(_S_iter_cat());
1316  };
1317  } // namespace __detail
1318 
1319  template<input_range _Vp,
1320  indirect_unary_predicate<iterator_t<_Vp>> _Pred>
1321  requires view<_Vp> && is_object_v<_Pred>
1322  class filter_view : public view_interface<filter_view<_Vp, _Pred>>
1323  {
1324  private:
1325  struct _Sentinel;
1326 
1327  struct _Iterator : __detail::__filter_view_iter_cat<_Vp>
1328  {
1329  private:
1330  static constexpr auto
1331  _S_iter_concept()
1332  {
1333  if constexpr (bidirectional_range<_Vp>)
1334  return bidirectional_iterator_tag{};
1335  else if constexpr (forward_range<_Vp>)
1336  return forward_iterator_tag{};
1337  else
1338  return input_iterator_tag{};
1339  }
1340 
1341  friend filter_view;
1342 
1343  using _Vp_iter = iterator_t<_Vp>;
1344 
1345  _Vp_iter _M_current = _Vp_iter();
1346  filter_view* _M_parent = nullptr;
1347 
1348  public:
1349  using iterator_concept = decltype(_S_iter_concept());
1350  // iterator_category defined in __filter_view_iter_cat
1351  using value_type = range_value_t<_Vp>;
1352  using difference_type = range_difference_t<_Vp>;
1353 
1354  _Iterator() requires default_initializable<_Vp_iter> = default;
1355 
1356  constexpr
1357  _Iterator(filter_view* __parent, _Vp_iter __current)
1358  : _M_current(std::move(__current)),
1359  _M_parent(__parent)
1360  { }
1361 
1362  constexpr const _Vp_iter&
1363  base() const & noexcept
1364  { return _M_current; }
1365 
1366  constexpr _Vp_iter
1367  base() &&
1368  { return std::move(_M_current); }
1369 
1370  constexpr range_reference_t<_Vp>
1371  operator*() const
1372  { return *_M_current; }
1373 
1374  constexpr _Vp_iter
1375  operator->() const
1376  requires __detail::__has_arrow<_Vp_iter>
1377  && copyable<_Vp_iter>
1378  { return _M_current; }
1379 
1380  constexpr _Iterator&
1381  operator++()
1382  {
1383  _M_current = ranges::find_if(std::move(++_M_current),
1384  ranges::end(_M_parent->_M_base),
1385  std::ref(*_M_parent->_M_pred));
1386  return *this;
1387  }
1388 
1389  constexpr void
1390  operator++(int)
1391  { ++*this; }
1392 
1393  constexpr _Iterator
1394  operator++(int) requires forward_range<_Vp>
1395  {
1396  auto __tmp = *this;
1397  ++*this;
1398  return __tmp;
1399  }
1400 
1401  constexpr _Iterator&
1402  operator--() requires bidirectional_range<_Vp>
1403  {
1404  do
1405  --_M_current;
1406  while (!std::__invoke(*_M_parent->_M_pred, *_M_current));
1407  return *this;
1408  }
1409 
1410  constexpr _Iterator
1411  operator--(int) requires bidirectional_range<_Vp>
1412  {
1413  auto __tmp = *this;
1414  --*this;
1415  return __tmp;
1416  }
1417 
1418  friend constexpr bool
1419  operator==(const _Iterator& __x, const _Iterator& __y)
1420  requires equality_comparable<_Vp_iter>
1421  { return __x._M_current == __y._M_current; }
1422 
1423  friend constexpr range_rvalue_reference_t<_Vp>
1424  iter_move(const _Iterator& __i)
1425  noexcept(noexcept(ranges::iter_move(__i._M_current)))
1426  { return ranges::iter_move(__i._M_current); }
1427 
1428  friend constexpr void
1429  iter_swap(const _Iterator& __x, const _Iterator& __y)
1430  noexcept(noexcept(ranges::iter_swap(__x._M_current, __y._M_current)))
1431  requires indirectly_swappable<_Vp_iter>
1432  { ranges::iter_swap(__x._M_current, __y._M_current); }
1433  };
1434 
1435  struct _Sentinel
1436  {
1437  private:
1438  sentinel_t<_Vp> _M_end = sentinel_t<_Vp>();
1439 
1440  constexpr bool
1441  __equal(const _Iterator& __i) const
1442  { return __i._M_current == _M_end; }
1443 
1444  public:
1445  _Sentinel() = default;
1446 
1447  constexpr explicit
1448  _Sentinel(filter_view* __parent)
1449  : _M_end(ranges::end(__parent->_M_base))
1450  { }
1451 
1452  constexpr sentinel_t<_Vp>
1453  base() const
1454  { return _M_end; }
1455 
1456  friend constexpr bool
1457  operator==(const _Iterator& __x, const _Sentinel& __y)
1458  { return __y.__equal(__x); }
1459  };
1460 
1461  [[no_unique_address]] __detail::__box<_Pred> _M_pred;
1462  [[no_unique_address]] __detail::_CachedPosition<_Vp> _M_cached_begin;
1463  _Vp _M_base = _Vp();
1464 
1465  public:
1466  filter_view() requires default_initializable<_Vp> = default;
1467 
1468  constexpr
1469  filter_view(_Vp __base, _Pred __pred)
1470  : _M_pred(std::move(__pred)), _M_base(std::move(__base))
1471  { }
1472 
1473  constexpr _Vp
1474  base() const& requires copy_constructible<_Vp>
1475  { return _M_base; }
1476 
1477  constexpr _Vp
1478  base() &&
1479  { return std::move(_M_base); }
1480 
1481  constexpr const _Pred&
1482  pred() const
1483  { return *_M_pred; }
1484 
1485  constexpr _Iterator
1486  begin()
1487  {
1488  if (_M_cached_begin._M_has_value())
1489  return {this, _M_cached_begin._M_get(_M_base)};
1490 
1491  __glibcxx_assert(_M_pred.has_value());
1492  auto __it = ranges::find_if(ranges::begin(_M_base),
1493  ranges::end(_M_base),
1494  std::ref(*_M_pred));
1495  _M_cached_begin._M_set(_M_base, __it);
1496  return {this, std::move(__it)};
1497  }
1498 
1499  constexpr auto
1500  end()
1501  {
1502  if constexpr (common_range<_Vp>)
1503  return _Iterator{this, ranges::end(_M_base)};
1504  else
1505  return _Sentinel{this};
1506  }
1507  };
1508 
1509  template<typename _Range, typename _Pred>
1510  filter_view(_Range&&, _Pred) -> filter_view<views::all_t<_Range>, _Pred>;
1511 
1512  namespace views
1513  {
1514  namespace __detail
1515  {
1516  template<typename _Range, typename _Pred>
1517  concept __can_filter_view
1518  = requires { filter_view(std::declval<_Range>(), std::declval<_Pred>()); };
1519  } // namespace __detail
1520 
1521  struct _Filter : __adaptor::_RangeAdaptor<_Filter>
1522  {
1523  template<viewable_range _Range, typename _Pred>
1524  requires __detail::__can_filter_view<_Range, _Pred>
1525  constexpr auto
1526  operator()(_Range&& __r, _Pred&& __p) const
1527  {
1528  return filter_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
1529  }
1530 
1531  using _RangeAdaptor<_Filter>::operator();
1532  static constexpr int _S_arity = 2;
1533  static constexpr bool _S_has_simple_extra_args = true;
1534  };
1535 
1536  inline constexpr _Filter filter;
1537  } // namespace views
1538 
1539  template<input_range _Vp, copy_constructible _Fp>
1540  requires view<_Vp> && is_object_v<_Fp>
1541  && regular_invocable<_Fp&, range_reference_t<_Vp>>
1542  && std::__detail::__can_reference<invoke_result_t<_Fp&,
1543  range_reference_t<_Vp>>>
1544  class transform_view : public view_interface<transform_view<_Vp, _Fp>>
1545  {
1546  private:
1547  template<bool _Const>
1548  using _Base = __detail::__maybe_const_t<_Const, _Vp>;
1549 
1550  template<bool _Const>
1551  struct __iter_cat
1552  { };
1553 
1554  template<bool _Const>
1555  requires forward_range<_Base<_Const>>
1556  struct __iter_cat<_Const>
1557  {
1558  private:
1559  static auto
1560  _S_iter_cat()
1561  {
1562  using _Base = transform_view::_Base<_Const>;
1563  using _Res = invoke_result_t<_Fp&, range_reference_t<_Base>>;
1564  if constexpr (is_lvalue_reference_v<_Res>)
1565  {
1566  using _Cat
1567  = typename iterator_traits<iterator_t<_Base>>::iterator_category;
1568  if constexpr (derived_from<_Cat, contiguous_iterator_tag>)
1569  return random_access_iterator_tag{};
1570  else
1571  return _Cat{};
1572  }
1573  else
1574  return input_iterator_tag{};
1575  }
1576  public:
1577  using iterator_category = decltype(_S_iter_cat());
1578  };
1579 
1580  template<bool _Const>
1581  struct _Sentinel;
1582 
1583  template<bool _Const>
1584  struct _Iterator : __iter_cat<_Const>
1585  {
1586  private:
1587  using _Parent = __detail::__maybe_const_t<_Const, transform_view>;
1588  using _Base = transform_view::_Base<_Const>;
1589 
1590  static auto
1591  _S_iter_concept()
1592  {
1593  if constexpr (random_access_range<_Base>)
1594  return random_access_iterator_tag{};
1595  else if constexpr (bidirectional_range<_Base>)
1596  return bidirectional_iterator_tag{};
1597  else if constexpr (forward_range<_Base>)
1598  return forward_iterator_tag{};
1599  else
1600  return input_iterator_tag{};
1601  }
1602 
1603  using _Base_iter = iterator_t<_Base>;
1604 
1605  _Base_iter _M_current = _Base_iter();
1606  _Parent* _M_parent = nullptr;
1607 
1608  public:
1609  using iterator_concept = decltype(_S_iter_concept());
1610  // iterator_category defined in __transform_view_iter_cat
1611  using value_type
1612  = remove_cvref_t<invoke_result_t<_Fp&, range_reference_t<_Base>>>;
1613  using difference_type = range_difference_t<_Base>;
1614 
1615  _Iterator() requires default_initializable<_Base_iter> = default;
1616 
1617  constexpr
1618  _Iterator(_Parent* __parent, _Base_iter __current)
1619  : _M_current(std::move(__current)),
1620  _M_parent(__parent)
1621  { }
1622 
1623  constexpr
1624  _Iterator(_Iterator<!_Const> __i)
1625  requires _Const
1626  && convertible_to<iterator_t<_Vp>, _Base_iter>
1627  : _M_current(std::move(__i._M_current)), _M_parent(__i._M_parent)
1628  { }
1629 
1630  constexpr const _Base_iter&
1631  base() const & noexcept
1632  { return _M_current; }
1633 
1634  constexpr _Base_iter
1635  base() &&
1636  { return std::move(_M_current); }
1637 
1638  constexpr decltype(auto)
1639  operator*() const
1640  noexcept(noexcept(std::__invoke(*_M_parent->_M_fun, *_M_current)))
1641  { return std::__invoke(*_M_parent->_M_fun, *_M_current); }
1642 
1643  constexpr _Iterator&
1644  operator++()
1645  {
1646  ++_M_current;
1647  return *this;
1648  }
1649 
1650  constexpr void
1651  operator++(int)
1652  { ++_M_current; }
1653 
1654  constexpr _Iterator
1655  operator++(int) requires forward_range<_Base>
1656  {
1657  auto __tmp = *this;
1658  ++*this;
1659  return __tmp;
1660  }
1661 
1662  constexpr _Iterator&
1663  operator--() requires bidirectional_range<_Base>
1664  {
1665  --_M_current;
1666  return *this;
1667  }
1668 
1669  constexpr _Iterator
1670  operator--(int) requires bidirectional_range<_Base>
1671  {
1672  auto __tmp = *this;
1673  --*this;
1674  return __tmp;
1675  }
1676 
1677  constexpr _Iterator&
1678  operator+=(difference_type __n) requires random_access_range<_Base>
1679  {
1680  _M_current += __n;
1681  return *this;
1682  }
1683 
1684  constexpr _Iterator&
1685  operator-=(difference_type __n) requires random_access_range<_Base>
1686  {
1687  _M_current -= __n;
1688  return *this;
1689  }
1690 
1691  constexpr decltype(auto)
1692  operator[](difference_type __n) const
1693  requires random_access_range<_Base>
1694  { return std::__invoke(*_M_parent->_M_fun, _M_current[__n]); }
1695 
1696  friend constexpr bool
1697  operator==(const _Iterator& __x, const _Iterator& __y)
1698  requires equality_comparable<_Base_iter>
1699  { return __x._M_current == __y._M_current; }
1700 
1701  friend constexpr bool
1702  operator<(const _Iterator& __x, const _Iterator& __y)
1703  requires random_access_range<_Base>
1704  { return __x._M_current < __y._M_current; }
1705 
1706  friend constexpr bool
1707  operator>(const _Iterator& __x, const _Iterator& __y)
1708  requires random_access_range<_Base>
1709  { return __y < __x; }
1710 
1711  friend constexpr bool
1712  operator<=(const _Iterator& __x, const _Iterator& __y)
1713  requires random_access_range<_Base>
1714  { return !(__y < __x); }
1715 
1716  friend constexpr bool
1717  operator>=(const _Iterator& __x, const _Iterator& __y)
1718  requires random_access_range<_Base>
1719  { return !(__x < __y); }
1720 
1721 #ifdef __cpp_lib_three_way_comparison
1722  friend constexpr auto
1723  operator<=>(const _Iterator& __x, const _Iterator& __y)
1724  requires random_access_range<_Base>
1725  && three_way_comparable<_Base_iter>
1726  { return __x._M_current <=> __y._M_current; }
1727 #endif
1728 
1729  friend constexpr _Iterator
1730  operator+(_Iterator __i, difference_type __n)
1731  requires random_access_range<_Base>
1732  { return {__i._M_parent, __i._M_current + __n}; }
1733 
1734  friend constexpr _Iterator
1735  operator+(difference_type __n, _Iterator __i)
1736  requires random_access_range<_Base>
1737  { return {__i._M_parent, __i._M_current + __n}; }
1738 
1739  friend constexpr _Iterator
1740  operator-(_Iterator __i, difference_type __n)
1741  requires random_access_range<_Base>
1742  { return {__i._M_parent, __i._M_current - __n}; }
1743 
1744  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1745  // 3483. transform_view::iterator's difference is overconstrained
1746  friend constexpr difference_type
1747  operator-(const _Iterator& __x, const _Iterator& __y)
1748  requires sized_sentinel_for<iterator_t<_Base>, iterator_t<_Base>>
1749  { return __x._M_current - __y._M_current; }
1750 
1751  friend constexpr decltype(auto)
1752  iter_move(const _Iterator& __i) noexcept(noexcept(*__i))
1753  {
1754  if constexpr (is_lvalue_reference_v<decltype(*__i)>)
1755  return std::move(*__i);
1756  else
1757  return *__i;
1758  }
1759 
1760  friend _Iterator<!_Const>;
1761  template<bool> friend struct _Sentinel;
1762  };
1763 
1764  template<bool _Const>
1765  struct _Sentinel
1766  {
1767  private:
1768  using _Parent = __detail::__maybe_const_t<_Const, transform_view>;
1769  using _Base = transform_view::_Base<_Const>;
1770 
1771  template<bool _Const2>
1772  constexpr auto
1773  __distance_from(const _Iterator<_Const2>& __i) const
1774  { return _M_end - __i._M_current; }
1775 
1776  template<bool _Const2>
1777  constexpr bool
1778  __equal(const _Iterator<_Const2>& __i) const
1779  { return __i._M_current == _M_end; }
1780 
1781  sentinel_t<_Base> _M_end = sentinel_t<_Base>();
1782 
1783  public:
1784  _Sentinel() = default;
1785 
1786  constexpr explicit
1787  _Sentinel(sentinel_t<_Base> __end)
1788  : _M_end(__end)
1789  { }
1790 
1791  constexpr
1792  _Sentinel(_Sentinel<!_Const> __i)
1793  requires _Const
1794  && convertible_to<sentinel_t<_Vp>, sentinel_t<_Base>>
1795  : _M_end(std::move(__i._M_end))
1796  { }
1797 
1798  constexpr sentinel_t<_Base>
1799  base() const
1800  { return _M_end; }
1801 
1802  template<bool _Const2>
1803  requires sentinel_for<sentinel_t<_Base>,
1804  iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
1805  friend constexpr bool
1806  operator==(const _Iterator<_Const2>& __x, const _Sentinel& __y)
1807  { return __y.__equal(__x); }
1808 
1809  template<bool _Const2,
1810  typename _Base2 = __detail::__maybe_const_t<_Const2, _Vp>>
1811  requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
1812  friend constexpr range_difference_t<_Base2>
1813  operator-(const _Iterator<_Const2>& __x, const _Sentinel& __y)
1814  { return -__y.__distance_from(__x); }
1815 
1816  template<bool _Const2,
1817  typename _Base2 = __detail::__maybe_const_t<_Const2, _Vp>>
1818  requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
1819  friend constexpr range_difference_t<_Base2>
1820  operator-(const _Sentinel& __y, const _Iterator<_Const2>& __x)
1821  { return __y.__distance_from(__x); }
1822 
1823  friend _Sentinel<!_Const>;
1824  };
1825 
1826  [[no_unique_address]] __detail::__box<_Fp> _M_fun;
1827  _Vp _M_base = _Vp();
1828 
1829  public:
1830  transform_view() requires default_initializable<_Vp> = default;
1831 
1832  constexpr
1833  transform_view(_Vp __base, _Fp __fun)
1834  : _M_fun(std::move(__fun)), _M_base(std::move(__base))
1835  { }
1836 
1837  constexpr _Vp
1838  base() const& requires copy_constructible<_Vp>
1839  { return _M_base ; }
1840 
1841  constexpr _Vp
1842  base() &&
1843  { return std::move(_M_base); }
1844 
1845  constexpr _Iterator<false>
1846  begin()
1847  { return _Iterator<false>{this, ranges::begin(_M_base)}; }
1848 
1849  constexpr _Iterator<true>
1850  begin() const
1851  requires range<const _Vp>
1852  && regular_invocable<const _Fp&, range_reference_t<const _Vp>>
1853  { return _Iterator<true>{this, ranges::begin(_M_base)}; }
1854 
1855  constexpr _Sentinel<false>
1856  end()
1857  { return _Sentinel<false>{ranges::end(_M_base)}; }
1858 
1859  constexpr _Iterator<false>
1860  end() requires common_range<_Vp>
1861  { return _Iterator<false>{this, ranges::end(_M_base)}; }
1862 
1863  constexpr _Sentinel<true>
1864  end() const
1865  requires range<const _Vp>
1866  && regular_invocable<const _Fp&, range_reference_t<const _Vp>>
1867  { return _Sentinel<true>{ranges::end(_M_base)}; }
1868 
1869  constexpr _Iterator<true>
1870  end() const
1871  requires common_range<const _Vp>
1872  && regular_invocable<const _Fp&, range_reference_t<const _Vp>>
1873  { return _Iterator<true>{this, ranges::end(_M_base)}; }
1874 
1875  constexpr auto
1876  size() requires sized_range<_Vp>
1877  { return ranges::size(_M_base); }
1878 
1879  constexpr auto
1880  size() const requires sized_range<const _Vp>
1881  { return ranges::size(_M_base); }
1882  };
1883 
1884  template<typename _Range, typename _Fp>
1885  transform_view(_Range&&, _Fp) -> transform_view<views::all_t<_Range>, _Fp>;
1886 
1887  namespace views
1888  {
1889  namespace __detail
1890  {
1891  template<typename _Range, typename _Fp>
1892  concept __can_transform_view
1893  = requires { transform_view(std::declval<_Range>(), std::declval<_Fp>()); };
1894  } // namespace __detail
1895 
1896  struct _Transform : __adaptor::_RangeAdaptor<_Transform>
1897  {
1898  template<viewable_range _Range, typename _Fp>
1899  requires __detail::__can_transform_view<_Range, _Fp>
1900  constexpr auto
1901  operator()(_Range&& __r, _Fp&& __f) const
1902  {
1903  return transform_view(std::forward<_Range>(__r), std::forward<_Fp>(__f));
1904  }
1905 
1906  using _RangeAdaptor<_Transform>::operator();
1907  static constexpr int _S_arity = 2;
1908  static constexpr bool _S_has_simple_extra_args = true;
1909  };
1910 
1911  inline constexpr _Transform transform;
1912  } // namespace views
1913 
1914  template<view _Vp>
1915  class take_view : public view_interface<take_view<_Vp>>
1916  {
1917  private:
1918  template<bool _Const>
1919  using _CI = counted_iterator<
1920  iterator_t<__detail::__maybe_const_t<_Const, _Vp>>>;
1921 
1922  template<bool _Const>
1923  struct _Sentinel
1924  {
1925  private:
1926  using _Base = __detail::__maybe_const_t<_Const, _Vp>;
1927  sentinel_t<_Base> _M_end = sentinel_t<_Base>();
1928 
1929  public:
1930  _Sentinel() = default;
1931 
1932  constexpr explicit
1933  _Sentinel(sentinel_t<_Base> __end)
1934  : _M_end(__end)
1935  { }
1936 
1937  constexpr
1938  _Sentinel(_Sentinel<!_Const> __s)
1939  requires _Const && convertible_to<sentinel_t<_Vp>, sentinel_t<_Base>>
1940  : _M_end(std::move(__s._M_end))
1941  { }
1942 
1943  constexpr sentinel_t<_Base>
1944  base() const
1945  { return _M_end; }
1946 
1947  friend constexpr bool
1948  operator==(const _CI<_Const>& __y, const _Sentinel& __x)
1949  { return __y.count() == 0 || __y.base() == __x._M_end; }
1950 
1951  template<bool _OtherConst = !_Const,
1952  typename _Base2 = __detail::__maybe_const_t<_OtherConst, _Vp>>
1953  requires sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
1954  friend constexpr bool
1955  operator==(const _CI<_OtherConst>& __y, const _Sentinel& __x)
1956  { return __y.count() == 0 || __y.base() == __x._M_end; }
1957 
1958  friend _Sentinel<!_Const>;
1959  };
1960 
1961  range_difference_t<_Vp> _M_count = 0;
1962  _Vp _M_base = _Vp();
1963 
1964  public:
1965  take_view() requires default_initializable<_Vp> = default;
1966 
1967  constexpr
1968  take_view(_Vp base, range_difference_t<_Vp> __count)
1969  : _M_count(std::move(__count)), _M_base(std::move(base))
1970  { }
1971 
1972  constexpr _Vp
1973  base() const& requires copy_constructible<_Vp>
1974  { return _M_base; }
1975 
1976  constexpr _Vp
1977  base() &&
1978  { return std::move(_M_base); }
1979 
1980  constexpr auto
1981  begin() requires (!__detail::__simple_view<_Vp>)
1982  {
1983  if constexpr (sized_range<_Vp>)
1984  {
1985  if constexpr (random_access_range<_Vp>)
1986  return ranges::begin(_M_base);
1987  else
1988  {
1989  auto __sz = size();
1990  return counted_iterator(ranges::begin(_M_base), __sz);
1991  }
1992  }
1993  else
1994  return counted_iterator(ranges::begin(_M_base), _M_count);
1995  }
1996 
1997  constexpr auto
1998  begin() const requires range<const _Vp>
1999  {
2000  if constexpr (sized_range<const _Vp>)
2001  {
2002  if constexpr (random_access_range<const _Vp>)
2003  return ranges::begin(_M_base);
2004  else
2005  {
2006  auto __sz = size();
2007  return counted_iterator(ranges::begin(_M_base), __sz);
2008  }
2009  }
2010  else
2011  return counted_iterator(ranges::begin(_M_base), _M_count);
2012  }
2013 
2014  constexpr auto
2015  end() requires (!__detail::__simple_view<_Vp>)
2016  {
2017  if constexpr (sized_range<_Vp>)
2018  {
2019  if constexpr (random_access_range<_Vp>)
2020  return ranges::begin(_M_base) + size();
2021  else
2022  return default_sentinel;
2023  }
2024  else
2025  return _Sentinel<false>{ranges::end(_M_base)};
2026  }
2027 
2028  constexpr auto
2029  end() const requires range<const _Vp>
2030  {
2031  if constexpr (sized_range<const _Vp>)
2032  {
2033  if constexpr (random_access_range<const _Vp>)
2034  return ranges::begin(_M_base) + size();
2035  else
2036  return default_sentinel;
2037  }
2038  else
2039  return _Sentinel<true>{ranges::end(_M_base)};
2040  }
2041 
2042  constexpr auto
2043  size() requires sized_range<_Vp>
2044  {
2045  auto __n = ranges::size(_M_base);
2046  return std::min(__n, static_cast<decltype(__n)>(_M_count));
2047  }
2048 
2049  constexpr auto
2050  size() const requires sized_range<const _Vp>
2051  {
2052  auto __n = ranges::size(_M_base);
2053  return std::min(__n, static_cast<decltype(__n)>(_M_count));
2054  }
2055  };
2056 
2057  // _GLIBCXX_RESOLVE_LIB_DEFECTS
2058  // 3447. Deduction guides for take_view and drop_view have different
2059  // constraints
2060  template<typename _Range>
2061  take_view(_Range&&, range_difference_t<_Range>)
2062  -> take_view<views::all_t<_Range>>;
2063 
2064  template<typename _Tp>
2065  inline constexpr bool enable_borrowed_range<take_view<_Tp>>
2066  = enable_borrowed_range<_Tp>;
2067 
2068  namespace views
2069  {
2070  namespace __detail
2071  {
2072  template<typename _Range, typename _Tp>
2073  concept __can_take_view
2074  = requires { take_view(std::declval<_Range>(), std::declval<_Tp>()); };
2075  } // namespace __detail
2076 
2077  struct _Take : __adaptor::_RangeAdaptor<_Take>
2078  {
2079  template<viewable_range _Range, typename _Tp>
2080  requires __detail::__can_take_view<_Range, _Tp>
2081  constexpr auto
2082  operator()(_Range&& __r, _Tp&& __n) const
2083  {
2084  return take_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
2085  }
2086 
2087  using _RangeAdaptor<_Take>::operator();
2088  static constexpr int _S_arity = 2;
2089  // The count argument of views::take is not always simple -- it can be
2090  // e.g. a move-only class that's implicitly convertible to the difference
2091  // type. But an integer-like count argument is surely simple.
2092  template<typename _Tp>
2093  static constexpr bool _S_has_simple_extra_args
2094  = ranges::__detail::__is_integer_like<_Tp>;
2095  };
2096 
2097  inline constexpr _Take take;
2098  } // namespace views
2099 
2100  template<view _Vp, typename _Pred>
2101  requires input_range<_Vp> && is_object_v<_Pred>
2102  && indirect_unary_predicate<const _Pred, iterator_t<_Vp>>
2103  class take_while_view : public view_interface<take_while_view<_Vp, _Pred>>
2104  {
2105  template<bool _Const>
2106  struct _Sentinel
2107  {
2108  private:
2109  using _Base = __detail::__maybe_const_t<_Const, _Vp>;
2110 
2111  sentinel_t<_Base> _M_end = sentinel_t<_Base>();
2112  const _Pred* _M_pred = nullptr;
2113 
2114  public:
2115  _Sentinel() = default;
2116 
2117  constexpr explicit
2118  _Sentinel(sentinel_t<_Base> __end, const _Pred* __pred)
2119  : _M_end(__end), _M_pred(__pred)
2120  { }
2121 
2122  constexpr
2123  _Sentinel(_Sentinel<!_Const> __s)
2124  requires _Const && convertible_to<sentinel_t<_Vp>, sentinel_t<_Base>>
2125  : _M_end(__s._M_end), _M_pred(__s._M_pred)
2126  { }
2127 
2128  constexpr sentinel_t<_Base>
2129  base() const { return _M_end; }
2130 
2131  friend constexpr bool
2132  operator==(const iterator_t<_Base>& __x, const _Sentinel& __y)
2133  { return __y._M_end == __x || !std::__invoke(*__y._M_pred, *__x); }
2134 
2135  template<bool _OtherConst = !_Const,
2136  typename _Base2 = __detail::__maybe_const_t<_OtherConst, _Vp>>
2137  requires sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
2138  friend constexpr bool
2139  operator==(const iterator_t<_Base2>& __x, const _Sentinel& __y)
2140  { return __y._M_end == __x || !std::__invoke(*__y._M_pred, *__x); }
2141 
2142  friend _Sentinel<!_Const>;
2143  };
2144 
2145  [[no_unique_address]] __detail::__box<_Pred> _M_pred;
2146  _Vp _M_base = _Vp();
2147 
2148  public:
2149  take_while_view() requires default_initializable<_Vp> = default;
2150 
2151  constexpr
2152  take_while_view(_Vp base, _Pred __pred)
2153  : _M_pred(std::move(__pred)), _M_base(std::move(base))
2154  { }
2155 
2156  constexpr _Vp
2157  base() const& requires copy_constructible<_Vp>
2158  { return _M_base; }
2159 
2160  constexpr _Vp
2161  base() &&
2162  { return std::move(_M_base); }
2163 
2164  constexpr const _Pred&
2165  pred() const
2166  { return *_M_pred; }
2167 
2168  constexpr auto
2169  begin() requires (!__detail::__simple_view<_Vp>)
2170  { return ranges::begin(_M_base); }
2171 
2172  constexpr auto
2173  begin() const requires range<const _Vp>
2174  && indirect_unary_predicate<const _Pred, iterator_t<const _Vp>>
2175  { return ranges::begin(_M_base); }
2176 
2177  constexpr auto
2178  end() requires (!__detail::__simple_view<_Vp>)
2179  { return _Sentinel<false>(ranges::end(_M_base),
2180  std::__addressof(*_M_pred)); }
2181 
2182  constexpr auto
2183  end() const requires range<const _Vp>
2184  && indirect_unary_predicate<const _Pred, iterator_t<const _Vp>>
2185  { return _Sentinel<true>(ranges::end(_M_base),
2186  std::__addressof(*_M_pred)); }
2187  };
2188 
2189  template<typename _Range, typename _Pred>
2190  take_while_view(_Range&&, _Pred)
2191  -> take_while_view<views::all_t<_Range>, _Pred>;
2192 
2193  namespace views
2194  {
2195  namespace __detail
2196  {
2197  template<typename _Range, typename _Pred>
2198  concept __can_take_while_view
2199  = requires { take_while_view(std::declval<_Range>(), std::declval<_Pred>()); };
2200  } // namespace __detail
2201 
2202  struct _TakeWhile : __adaptor::_RangeAdaptor<_TakeWhile>
2203  {
2204  template<viewable_range _Range, typename _Pred>
2205  requires __detail::__can_take_while_view<_Range, _Pred>
2206  constexpr auto
2207  operator()(_Range&& __r, _Pred&& __p) const
2208  {
2209  return take_while_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
2210  }
2211 
2212  using _RangeAdaptor<_TakeWhile>::operator();
2213  static constexpr int _S_arity = 2;
2214  static constexpr bool _S_has_simple_extra_args = true;
2215  };
2216 
2217  inline constexpr _TakeWhile take_while;
2218  } // namespace views
2219 
2220  template<view _Vp>
2221  class drop_view : public view_interface<drop_view<_Vp>>
2222  {
2223  private:
2224  range_difference_t<_Vp> _M_count = 0;
2225  _Vp _M_base = _Vp();
2226 
2227  // ranges::next(begin(base), count, end(base)) is O(1) if _Vp satisfies
2228  // both random_access_range and sized_range. Otherwise, cache its result.
2229  static constexpr bool _S_needs_cached_begin
2230  = !(random_access_range<const _Vp> && sized_range<const _Vp>);
2231  [[no_unique_address]]
2232  __detail::__maybe_present_t<_S_needs_cached_begin,
2233  __detail::_CachedPosition<_Vp>>
2234  _M_cached_begin;
2235 
2236  public:
2237  drop_view() requires default_initializable<_Vp> = default;
2238 
2239  constexpr
2240  drop_view(_Vp __base, range_difference_t<_Vp> __count)
2241  : _M_count(__count), _M_base(std::move(__base))
2242  { __glibcxx_assert(__count >= 0); }
2243 
2244  constexpr _Vp
2245  base() const& requires copy_constructible<_Vp>
2246  { return _M_base; }
2247 
2248  constexpr _Vp
2249  base() &&
2250  { return std::move(_M_base); }
2251 
2252  // This overload is disabled for simple views with constant-time begin().
2253  constexpr auto
2254  begin()
2255  requires (!(__detail::__simple_view<_Vp>
2256  && random_access_range<const _Vp>
2257  && sized_range<const _Vp>))
2258  {
2259  if constexpr (_S_needs_cached_begin)
2260  if (_M_cached_begin._M_has_value())
2261  return _M_cached_begin._M_get(_M_base);
2262 
2263  auto __it = ranges::next(ranges::begin(_M_base),
2264  _M_count, ranges::end(_M_base));
2265  if constexpr (_S_needs_cached_begin)
2266  _M_cached_begin._M_set(_M_base, __it);
2267  return __it;
2268  }
2269 
2270  // _GLIBCXX_RESOLVE_LIB_DEFECTS
2271  // 3482. drop_view's const begin should additionally require sized_range
2272  constexpr auto
2273  begin() const
2274  requires random_access_range<const _Vp> && sized_range<const _Vp>
2275  {
2276  return ranges::next(ranges::begin(_M_base), _M_count,
2277  ranges::end(_M_base));
2278  }
2279 
2280  constexpr auto
2281  end() requires (!__detail::__simple_view<_Vp>)
2282  { return ranges::end(_M_base); }
2283 
2284  constexpr auto
2285  end() const requires range<const _Vp>
2286  { return ranges::end(_M_base); }
2287 
2288  constexpr auto
2289  size() requires sized_range<_Vp>
2290  {
2291  const auto __s = ranges::size(_M_base);
2292  const auto __c = static_cast<decltype(__s)>(_M_count);
2293  return __s < __c ? 0 : __s - __c;
2294  }
2295 
2296  constexpr auto
2297  size() const requires sized_range<const _Vp>
2298  {
2299  const auto __s = ranges::size(_M_base);
2300  const auto __c = static_cast<decltype(__s)>(_M_count);
2301  return __s < __c ? 0 : __s - __c;
2302  }
2303  };
2304 
2305  template<typename _Range>
2306  drop_view(_Range&&, range_difference_t<_Range>)
2307  -> drop_view<views::all_t<_Range>>;
2308 
2309  template<typename _Tp>
2310  inline constexpr bool enable_borrowed_range<drop_view<_Tp>>
2311  = enable_borrowed_range<_Tp>;
2312 
2313  namespace views
2314  {
2315  namespace __detail
2316  {
2317  template<typename _Range, typename _Tp>
2318  concept __can_drop_view
2319  = requires { drop_view(std::declval<_Range>(), std::declval<_Tp>()); };
2320  } // namespace __detail
2321 
2322  struct _Drop : __adaptor::_RangeAdaptor<_Drop>
2323  {
2324  template<viewable_range _Range, typename _Tp>
2325  requires __detail::__can_drop_view<_Range, _Tp>
2326  constexpr auto
2327  operator()(_Range&& __r, _Tp&& __n) const
2328  {
2329  return drop_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
2330  }
2331 
2332  using _RangeAdaptor<_Drop>::operator();
2333  static constexpr int _S_arity = 2;
2334  template<typename _Tp>
2335  static constexpr bool _S_has_simple_extra_args
2336  = _Take::_S_has_simple_extra_args<_Tp>;
2337  };
2338 
2339  inline constexpr _Drop drop;
2340  } // namespace views
2341 
2342  template<view _Vp, typename _Pred>
2343  requires input_range<_Vp> && is_object_v<_Pred>
2344  && indirect_unary_predicate<const _Pred, iterator_t<_Vp>>
2345  class drop_while_view : public view_interface<drop_while_view<_Vp, _Pred>>
2346  {
2347  private:
2348  [[no_unique_address]] __detail::__box<_Pred> _M_pred;
2349  [[no_unique_address]] __detail::_CachedPosition<_Vp> _M_cached_begin;
2350  _Vp _M_base = _Vp();
2351 
2352  public:
2353  drop_while_view() requires default_initializable<_Vp> = default;
2354 
2355  constexpr
2356  drop_while_view(_Vp __base, _Pred __pred)
2357  : _M_pred(std::move(__pred)), _M_base(std::move(__base))
2358  { }
2359 
2360  constexpr _Vp
2361  base() const& requires copy_constructible<_Vp>
2362  { return _M_base; }
2363 
2364  constexpr _Vp
2365  base() &&
2366  { return std::move(_M_base); }
2367 
2368  constexpr const _Pred&
2369  pred() const
2370  { return *_M_pred; }
2371 
2372  constexpr auto
2373  begin()
2374  {
2375  if (_M_cached_begin._M_has_value())
2376  return _M_cached_begin._M_get(_M_base);
2377 
2378  __glibcxx_assert(_M_pred.has_value());
2379  auto __it = ranges::find_if_not(ranges::begin(_M_base),
2380  ranges::end(_M_base),
2381  std::cref(*_M_pred));
2382  _M_cached_begin._M_set(_M_base, __it);
2383  return __it;
2384  }
2385 
2386  constexpr auto
2387  end()
2388  { return ranges::end(_M_base); }
2389  };
2390 
2391  template<typename _Range, typename _Pred>
2392  drop_while_view(_Range&&, _Pred)
2393  -> drop_while_view<views::all_t<_Range>, _Pred>;
2394 
2395  template<typename _Tp, typename _Pred>
2396  inline constexpr bool enable_borrowed_range<drop_while_view<_Tp, _Pred>>
2397  = enable_borrowed_range<_Tp>;
2398 
2399  namespace views
2400  {
2401  namespace __detail
2402  {
2403  template<typename _Range, typename _Pred>
2404  concept __can_drop_while_view
2405  = requires { drop_while_view(std::declval<_Range>(), std::declval<_Pred>()); };
2406  } // namespace __detail
2407 
2408  struct _DropWhile : __adaptor::_RangeAdaptor<_DropWhile>
2409  {
2410  template<viewable_range _Range, typename _Pred>
2411  requires __detail::__can_drop_while_view<_Range, _Pred>
2412  constexpr auto
2413  operator()(_Range&& __r, _Pred&& __p) const
2414  {
2415  return drop_while_view(std::forward<_Range>(__r),
2416  std::forward<_Pred>(__p));
2417  }
2418 
2419  using _RangeAdaptor<_DropWhile>::operator();
2420  static constexpr int _S_arity = 2;
2421  static constexpr bool _S_has_simple_extra_args = true;
2422  };
2423 
2424  inline constexpr _DropWhile drop_while;
2425  } // namespace views
2426 
2427  template<input_range _Vp>
2428  requires view<_Vp> && input_range<range_reference_t<_Vp>>
2429  class join_view : public view_interface<join_view<_Vp>>
2430  {
2431  private:
2432  using _InnerRange = range_reference_t<_Vp>;
2433 
2434  template<bool _Const>
2435  using _Base = __detail::__maybe_const_t<_Const, _Vp>;
2436 
2437  template<bool _Const>
2438  using _Outer_iter = iterator_t<_Base<_Const>>;
2439 
2440  template<bool _Const>
2441  using _Inner_iter = iterator_t<range_reference_t<_Base<_Const>>>;
2442 
2443  template<bool _Const>
2444  static constexpr bool _S_ref_is_glvalue
2445  = is_reference_v<range_reference_t<_Base<_Const>>>;
2446 
2447  template<bool _Const>
2448  struct __iter_cat
2449  { };
2450 
2451  template<bool _Const>
2452  requires _S_ref_is_glvalue<_Const>
2453  && forward_range<_Base<_Const>>
2454  && forward_range<range_reference_t<_Base<_Const>>>
2455  struct __iter_cat<_Const>
2456  {
2457  private:
2458  static constexpr auto
2459  _S_iter_cat()
2460  {
2461  using _Outer_iter = join_view::_Outer_iter<_Const>;
2462  using _Inner_iter = join_view::_Inner_iter<_Const>;
2463  using _OuterCat = typename iterator_traits<_Outer_iter>::iterator_category;
2464  using _InnerCat = typename iterator_traits<_Inner_iter>::iterator_category;
2465  if constexpr (derived_from<_OuterCat, bidirectional_iterator_tag>
2466  && derived_from<_InnerCat, bidirectional_iterator_tag>
2467  && common_range<range_reference_t<_Base<_Const>>>)
2468  return bidirectional_iterator_tag{};
2469  else if constexpr (derived_from<_OuterCat, forward_iterator_tag>
2470  && derived_from<_InnerCat, forward_iterator_tag>)
2471  return forward_iterator_tag{};
2472  else
2473  return input_iterator_tag{};
2474  }
2475  public:
2476  using iterator_category = decltype(_S_iter_cat());
2477  };
2478 
2479  template<bool _Const>
2480  struct _Sentinel;
2481 
2482  template<bool _Const>
2483  struct _Iterator : __iter_cat<_Const>
2484  {
2485  private:
2486  using _Parent = __detail::__maybe_const_t<_Const, join_view>;
2487  using _Base = join_view::_Base<_Const>;
2488 
2489  static constexpr bool _S_ref_is_glvalue
2490  = join_view::_S_ref_is_glvalue<_Const>;
2491 
2492  constexpr void
2493  _M_satisfy()
2494  {
2495  auto __update_inner = [this] (const iterator_t<_Base>& __x) -> auto&& {
2496  if constexpr (_S_ref_is_glvalue)
2497  return *__x;
2498  else
2499  return _M_parent->_M_inner._M_emplace_deref(__x);
2500  };
2501 
2502  for (; _M_outer != ranges::end(_M_parent->_M_base); ++_M_outer)
2503  {
2504  auto&& __inner = __update_inner(_M_outer);
2505  _M_inner = ranges::begin(__inner);
2506  if (_M_inner != ranges::end(__inner))
2507  return;
2508  }
2509 
2510  if constexpr (_S_ref_is_glvalue)
2511  _M_inner = _Inner_iter();
2512  }
2513 
2514  static constexpr auto
2515  _S_iter_concept()
2516  {
2517  if constexpr (_S_ref_is_glvalue
2518  && bidirectional_range<_Base>
2519  && bidirectional_range<range_reference_t<_Base>>
2520  && common_range<range_reference_t<_Base>>)
2521  return bidirectional_iterator_tag{};
2522  else if constexpr (_S_ref_is_glvalue
2523  && forward_range<_Base>
2524  && forward_range<range_reference_t<_Base>>)
2525  return forward_iterator_tag{};
2526  else
2527  return input_iterator_tag{};
2528  }
2529 
2530  using _Outer_iter = join_view::_Outer_iter<_Const>;
2531  using _Inner_iter = join_view::_Inner_iter<_Const>;
2532 
2533  _Outer_iter _M_outer = _Outer_iter();
2534  _Inner_iter _M_inner = _Inner_iter();
2535  _Parent* _M_parent = nullptr;
2536 
2537  public:
2538  using iterator_concept = decltype(_S_iter_concept());
2539  // iterator_category defined in __join_view_iter_cat
2540  using value_type = range_value_t<range_reference_t<_Base>>;
2541  using difference_type
2542  = common_type_t<range_difference_t<_Base>,
2543  range_difference_t<range_reference_t<_Base>>>;
2544 
2545  _Iterator() requires (default_initializable<_Outer_iter>
2546  && default_initializable<_Inner_iter>)
2547  = default;
2548 
2549  constexpr
2550  _Iterator(_Parent* __parent, _Outer_iter __outer)
2551  : _M_outer(std::move(__outer)),
2552  _M_parent(__parent)
2553  { _M_satisfy(); }
2554 
2555  constexpr
2556  _Iterator(_Iterator<!_Const> __i)
2557  requires _Const
2558  && convertible_to<iterator_t<_Vp>, _Outer_iter>
2559  && convertible_to<iterator_t<_InnerRange>, _Inner_iter>
2560  : _M_outer(std::move(__i._M_outer)), _M_inner(std::move(__i._M_inner)),
2561  _M_parent(__i._M_parent)
2562  { }
2563 
2564  constexpr decltype(auto)
2565  operator*() const
2566  { return *_M_inner; }
2567 
2568  // _GLIBCXX_RESOLVE_LIB_DEFECTS
2569  // 3500. join_view::iterator::operator->() is bogus
2570  constexpr _Inner_iter
2571  operator->() const
2572  requires __detail::__has_arrow<_Inner_iter>
2573  && copyable<_Inner_iter>
2574  { return _M_inner; }
2575 
2576  constexpr _Iterator&
2577  operator++()
2578  {
2579  auto&& __inner_range = [this] () -> auto&& {
2580  if constexpr (_S_ref_is_glvalue)
2581  return *_M_outer;
2582  else
2583  return *_M_parent->_M_inner;
2584  }();
2585  if (++_M_inner == ranges::end(__inner_range))
2586  {
2587  ++_M_outer;
2588  _M_satisfy();
2589  }
2590  return *this;
2591  }
2592 
2593  constexpr void
2594  operator++(int)
2595  { ++*this; }
2596 
2597  constexpr _Iterator
2598  operator++(int)
2599  requires _S_ref_is_glvalue && forward_range<_Base>
2600  && forward_range<range_reference_t<_Base>>
2601  {
2602  auto __tmp = *this;
2603  ++*this;
2604  return __tmp;
2605  }
2606 
2607  constexpr _Iterator&
2608  operator--()
2609  requires _S_ref_is_glvalue && bidirectional_range<_Base>
2610  && bidirectional_range<range_reference_t<_Base>>
2611  && common_range<range_reference_t<_Base>>
2612  {
2613  if (_M_outer == ranges::end(_M_parent->_M_base))
2614  _M_inner = ranges::end(*--_M_outer);
2615  while (_M_inner == ranges::begin(*_M_outer))
2616  _M_inner = ranges::end(*--_M_outer);
2617  --_M_inner;
2618  return *this;
2619  }
2620 
2621  constexpr _Iterator
2622  operator--(int)
2623  requires _S_ref_is_glvalue && bidirectional_range<_Base>
2624  && bidirectional_range<range_reference_t<_Base>>
2625  && common_range<range_reference_t<_Base>>
2626  {
2627  auto __tmp = *this;
2628  --*this;
2629  return __tmp;
2630  }
2631 
2632  friend constexpr bool
2633  operator==(const _Iterator& __x, const _Iterator& __y)
2634  requires _S_ref_is_glvalue
2635  && equality_comparable<_Outer_iter>
2636  && equality_comparable<_Inner_iter>
2637  {
2638  return (__x._M_outer == __y._M_outer
2639  && __x._M_inner == __y._M_inner);
2640  }
2641 
2642  friend constexpr decltype(auto)
2643  iter_move(const _Iterator& __i)
2644  noexcept(noexcept(ranges::iter_move(__i._M_inner)))
2645  { return ranges::iter_move(__i._M_inner); }
2646 
2647  friend constexpr void
2648  iter_swap(const _Iterator& __x, const _Iterator& __y)
2649  noexcept(noexcept(ranges::iter_swap(__x._M_inner, __y._M_inner)))
2650  requires indirectly_swappable<_Inner_iter>
2651  { return ranges::iter_swap(__x._M_inner, __y._M_inner); }
2652 
2653  friend _Iterator<!_Const>;
2654  template<bool> friend struct _Sentinel;
2655  };
2656 
2657  template<bool _Const>
2658  struct _Sentinel
2659  {
2660  private:
2661  using _Parent = __detail::__maybe_const_t<_Const, join_view>;
2662  using _Base = join_view::_Base<_Const>;
2663 
2664  template<bool _Const2>
2665  constexpr bool
2666  __equal(const _Iterator<_Const2>& __i) const
2667  { return __i._M_outer == _M_end; }
2668 
2669  sentinel_t<_Base> _M_end = sentinel_t<_Base>();
2670 
2671  public:
2672  _Sentinel() = default;
2673 
2674  constexpr explicit
2675  _Sentinel(_Parent* __parent)
2676  : _M_end(ranges::end(__parent->_M_base))
2677  { }
2678 
2679  constexpr
2680  _Sentinel(_Sentinel<!_Const> __s)
2681  requires _Const && convertible_to<sentinel_t<_Vp>, sentinel_t<_Base>>
2682  : _M_end(std::move(__s._M_end))
2683  { }
2684 
2685  template<bool _Const2>
2686  requires sentinel_for<sentinel_t<_Base>,
2687  iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
2688  friend constexpr bool
2689  operator==(const _Iterator<_Const2>& __x, const _Sentinel& __y)
2690  { return __y.__equal(__x); }
2691 
2692  friend _Sentinel<!_Const>;
2693  };
2694 
2695  [[no_unique_address]]
2696  __detail::__non_propagating_cache<remove_cv_t<_InnerRange>> _M_inner;
2697  _Vp _M_base = _Vp();
2698 
2699  public:
2700  join_view() requires default_initializable<_Vp> = default;
2701 
2702  constexpr explicit
2703  join_view(_Vp __base)
2704  : _M_base(std::move(__base))
2705  { }
2706 
2707  constexpr _Vp
2708  base() const& requires copy_constructible<_Vp>
2709  { return _M_base; }
2710 
2711  constexpr _Vp
2712  base() &&
2713  { return std::move(_M_base); }
2714 
2715  constexpr auto
2716  begin()
2717  {
2718  constexpr bool __use_const
2719  = (__detail::__simple_view<_Vp>
2720  && is_reference_v<range_reference_t<_Vp>>);
2721  return _Iterator<__use_const>{this, ranges::begin(_M_base)};
2722  }
2723 
2724  constexpr auto
2725  begin() const
2726  requires input_range<const _Vp>
2727  && is_reference_v<range_reference_t<const _Vp>>
2728  {
2729  return _Iterator<true>{this, ranges::begin(_M_base)};
2730  }
2731 
2732  constexpr auto
2733  end()
2734  {
2735  if constexpr (forward_range<_Vp> && is_reference_v<_InnerRange>
2736  && forward_range<_InnerRange>
2737  && common_range<_Vp> && common_range<_InnerRange>)
2738  return _Iterator<__detail::__simple_view<_Vp>>{this,
2739  ranges::end(_M_base)};
2740  else
2741  return _Sentinel<__detail::__simple_view<_Vp>>{this};
2742  }
2743 
2744  constexpr auto
2745  end() const
2746  requires input_range<const _Vp>
2747  && is_reference_v<range_reference_t<const _Vp>>
2748  {
2749  if constexpr (forward_range<const _Vp>
2750  && is_reference_v<range_reference_t<const _Vp>>
2751  && forward_range<range_reference_t<const _Vp>>
2752  && common_range<const _Vp>
2753  && common_range<range_reference_t<const _Vp>>)
2754  return _Iterator<true>{this, ranges::end(_M_base)};
2755  else
2756  return _Sentinel<true>{this};
2757  }
2758  };
2759 
2760  template<typename _Range>
2761  explicit join_view(_Range&&) -> join_view<views::all_t<_Range>>;
2762 
2763  namespace views
2764  {
2765  namespace __detail
2766  {
2767  template<typename _Range>
2768  concept __can_join_view
2769  = requires { join_view<all_t<_Range>>{std::declval<_Range>()}; };
2770  } // namespace __detail
2771 
2772  struct _Join : __adaptor::_RangeAdaptorClosure
2773  {
2774  template<viewable_range _Range>
2775  requires __detail::__can_join_view<_Range>
2776  constexpr auto
2777  operator()(_Range&& __r) const
2778  {
2779  // _GLIBCXX_RESOLVE_LIB_DEFECTS
2780  // 3474. Nesting join_views is broken because of CTAD
2781  return join_view<all_t<_Range>>{std::forward<_Range>(__r)};
2782  }
2783 
2784  static constexpr bool _S_has_simple_call_op = true;
2785  };
2786 
2787  inline constexpr _Join join;
2788  } // namespace views
2789 
2790  namespace __detail
2791  {
2792  template<auto>
2793  struct __require_constant;
2794 
2795  template<typename _Range>
2796  concept __tiny_range = sized_range<_Range>
2797  && requires
2798  { typename __require_constant<remove_reference_t<_Range>::size()>; }
2799  && (remove_reference_t<_Range>::size() <= 1);
2800 
2801  template<typename _Base>
2802  struct __split_view_outer_iter_cat
2803  { };
2804 
2805  template<forward_range _Base>
2806  struct __split_view_outer_iter_cat<_Base>
2807  { using iterator_category = input_iterator_tag; };
2808 
2809  template<typename _Base>
2810  struct __split_view_inner_iter_cat
2811  { };
2812 
2813  template<forward_range _Base>
2814  struct __split_view_inner_iter_cat<_Base>
2815  {
2816  private:
2817  static constexpr auto
2818  _S_iter_cat()
2819  {
2820  using _Cat = typename iterator_traits<iterator_t<_Base>>::iterator_category;
2821  if constexpr (derived_from<_Cat, forward_iterator_tag>)
2822  return forward_iterator_tag{};
2823  else
2824  return _Cat{};
2825  }
2826  public:
2827  using iterator_category = decltype(_S_iter_cat());
2828  };
2829  }
2830 
2831  template<input_range _Vp, forward_range _Pattern>
2832  requires view<_Vp> && view<_Pattern>
2833  && indirectly_comparable<iterator_t<_Vp>, iterator_t<_Pattern>,
2834  ranges::equal_to>
2835  && (forward_range<_Vp> || __detail::__tiny_range<_Pattern>)
2836  class split_view : public view_interface<split_view<_Vp, _Pattern>>
2837  {
2838  private:
2839  template<bool _Const>
2840  using _Base = __detail::__maybe_const_t<_Const, _Vp>;
2841 
2842  template<bool _Const>
2843  struct _InnerIter;
2844 
2845  template<bool _Const>
2846  struct _OuterIter
2847  : __detail::__split_view_outer_iter_cat<_Base<_Const>>
2848  {
2849  private:
2850  using _Parent = __detail::__maybe_const_t<_Const, split_view>;
2851  using _Base = split_view::_Base<_Const>;
2852 
2853  constexpr bool
2854  __at_end() const
2855  { return __current() == ranges::end(_M_parent->_M_base); }
2856 
2857  // [range.split.outer] p1
2858  // Many of the following specifications refer to the notional member
2859  // current of outer-iterator. current is equivalent to current_ if
2860  // V models forward_range, and parent_->current_ otherwise.
2861  constexpr auto&
2862  __current() noexcept
2863  {
2864  if constexpr (forward_range<_Vp>)
2865  return _M_current;
2866  else
2867  return _M_parent->_M_current;
2868  }
2869 
2870  constexpr auto&
2871  __current() const noexcept
2872  {
2873  if constexpr (forward_range<_Vp>)
2874  return _M_current;
2875  else
2876  return _M_parent->_M_current;
2877  }
2878 
2879  _Parent* _M_parent = nullptr;
2880 
2881  // XXX: _M_current is present only if "V models forward_range"
2882  [[no_unique_address]]
2883  __detail::__maybe_present_t<forward_range<_Vp>,
2884  iterator_t<_Base>> _M_current;
2885 
2886  public:
2887  using iterator_concept = conditional_t<forward_range<_Base>,
2888  forward_iterator_tag,
2889  input_iterator_tag>;
2890  // iterator_category defined in __split_view_outer_iter_cat
2891  using difference_type = range_difference_t<_Base>;
2892 
2893  struct value_type : view_interface<value_type>
2894  {
2895  private:
2896  _OuterIter _M_i = _OuterIter();
2897 
2898  public:
2899  value_type() = default;
2900 
2901  constexpr explicit
2902  value_type(_OuterIter __i)
2903  : _M_i(std::move(__i))
2904  { }
2905 
2906  constexpr _InnerIter<_Const>
2907  begin() const
2908  { return _InnerIter<_Const>{_M_i}; }
2909 
2910  constexpr default_sentinel_t
2911  end() const noexcept
2912  { return default_sentinel; }
2913  };
2914 
2915  _OuterIter() = default;
2916 
2917  constexpr explicit
2918  _OuterIter(_Parent* __parent) requires (!forward_range<_Base>)
2919  : _M_parent(__parent)
2920  { }
2921 
2922  constexpr
2923  _OuterIter(_Parent* __parent, iterator_t<_Base> __current)
2924  requires forward_range<_Base>
2925  : _M_parent(__parent),
2926  _M_current(std::move(__current))
2927  { }
2928 
2929  constexpr
2930  _OuterIter(_OuterIter<!_Const> __i)
2931  requires _Const
2932  && convertible_to<iterator_t<_Vp>, iterator_t<_Base>>
2933  : _M_parent(__i._M_parent), _M_current(std::move(__i._M_current))
2934  { }
2935 
2936  constexpr value_type
2937  operator*() const
2938  { return value_type{*this}; }
2939 
2940  constexpr _OuterIter&
2941  operator++()
2942  {
2943  // _GLIBCXX_RESOLVE_LIB_DEFECTS
2944  // 3505. split_view::outer-iterator::operator++ misspecified
2945  const auto __end = ranges::end(_M_parent->_M_base);
2946  if (__current() == __end)
2947  return *this;
2948  const auto [__pbegin, __pend] = subrange{_M_parent->_M_pattern};
2949  if (__pbegin == __pend)
2950  ++__current();
2951  else if constexpr (__detail::__tiny_range<_Pattern>)
2952  {
2953  __current() = ranges::find(std::move(__current()), __end,
2954  *__pbegin);
2955  if (__current() != __end)
2956  ++__current();
2957  }
2958  else
2959  do
2960  {
2961  auto [__b, __p]
2962  = ranges::mismatch(__current(), __end, __pbegin, __pend);
2963  if (__p == __pend)
2964  {
2965  __current() = __b;
2966  break;
2967  }
2968  } while (++__current() != __end);
2969  return *this;
2970  }
2971 
2972  constexpr decltype(auto)
2973  operator++(int)
2974  {
2975  if constexpr (forward_range<_Base>)
2976  {
2977  auto __tmp = *this;
2978  ++*this;
2979  return __tmp;
2980  }
2981  else
2982  ++*this;
2983  }
2984 
2985  friend constexpr bool
2986  operator==(const _OuterIter& __x, const _OuterIter& __y)
2987  requires forward_range<_Base>
2988  { return __x._M_current == __y._M_current; }
2989 
2990  friend constexpr bool
2991  operator==(const _OuterIter& __x, default_sentinel_t)
2992  { return __x.__at_end(); };
2993 
2994  friend _OuterIter<!_Const>;
2995  friend _InnerIter<_Const>;
2996  };
2997 
2998  template<bool _Const>
2999  struct _InnerIter
3000  : __detail::__split_view_inner_iter_cat<_Base<_Const>>
3001  {
3002  private:
3003  using _Base = split_view::_Base<_Const>;
3004 
3005  constexpr bool
3006  __at_end() const
3007  {
3008  auto [__pcur, __pend] = subrange{_M_i._M_parent->_M_pattern};
3009  auto __end = ranges::end(_M_i._M_parent->_M_base);
3010  if constexpr (__detail::__tiny_range<_Pattern>)
3011  {
3012  const auto& __cur = _M_i_current();
3013  if (__cur == __end)
3014  return true;
3015  if (__pcur == __pend)
3016  return _M_incremented;
3017  return *__cur == *__pcur;
3018  }
3019  else
3020  {
3021  auto __cur = _M_i_current();
3022  if (__cur == __end)
3023  return true;
3024  if (__pcur == __pend)
3025  return _M_incremented;
3026  do
3027  {
3028  if (*__cur != *__pcur)
3029  return false;
3030  if (++__pcur == __pend)
3031  return true;
3032  } while (++__cur != __end);
3033  return false;
3034  }
3035  }
3036 
3037  constexpr auto&
3038  _M_i_current() noexcept
3039  { return _M_i.__current(); }
3040 
3041  constexpr auto&
3042  _M_i_current() const noexcept
3043  { return _M_i.__current(); }
3044 
3045  _OuterIter<_Const> _M_i = _OuterIter<_Const>();
3046  bool _M_incremented = false;
3047 
3048  public:
3049  using iterator_concept
3050  = typename _OuterIter<_Const>::iterator_concept;
3051  // iterator_category defined in __split_view_inner_iter_cat
3052  using value_type = range_value_t<_Base>;
3053  using difference_type = range_difference_t<_Base>;
3054 
3055  _InnerIter() = default;
3056 
3057  constexpr explicit
3058  _InnerIter(_OuterIter<_Const> __i)
3059  : _M_i(std::move(__i))
3060  { }
3061 
3062  constexpr const iterator_t<_Base>&
3063  base() const& noexcept
3064  { return _M_i_current(); }
3065 
3066  constexpr iterator_t<_Base>
3067  base() && requires forward_range<_Vp>
3068  { return std::move(_M_i_current()); }
3069 
3070  constexpr decltype(auto)
3071  operator*() const
3072  { return *_M_i_current(); }
3073 
3074  constexpr _InnerIter&
3075  operator++()
3076  {
3077  _M_incremented = true;
3078  if constexpr (!forward_range<_Base>)
3079  if constexpr (_Pattern::size() == 0)
3080  return *this;
3081  ++_M_i_current();
3082  return *this;
3083  }
3084 
3085  constexpr decltype(auto)
3086  operator++(int)
3087  {
3088  if constexpr (forward_range<_Base>)
3089  {
3090  auto __tmp = *this;
3091  ++*this;
3092  return __tmp;
3093  }
3094  else
3095  ++*this;
3096  }
3097 
3098  friend constexpr bool
3099  operator==(const _InnerIter& __x, const _InnerIter& __y)
3100  requires forward_range<_Base>
3101  { return __x._M_i == __y._M_i; }
3102 
3103  friend constexpr bool
3104  operator==(const _InnerIter& __x, default_sentinel_t)
3105  { return __x.__at_end(); }
3106 
3107  friend constexpr decltype(auto)
3108  iter_move(const _InnerIter& __i)
3109  noexcept(noexcept(ranges::iter_move(__i._M_i_current())))
3110  { return ranges::iter_move(__i._M_i_current()); }
3111 
3112  friend constexpr void
3113  iter_swap(const _InnerIter& __x, const _InnerIter& __y)
3114  noexcept(noexcept(ranges::iter_swap(__x._M_i_current(),
3115  __y._M_i_current())))
3116  requires indirectly_swappable<iterator_t<_Base>>
3117  { ranges::iter_swap(__x._M_i_current(), __y._M_i_current()); }
3118  };
3119 
3120  _Pattern _M_pattern = _Pattern();
3121  // XXX: _M_current is "present only if !forward_range<V>"
3122  [[no_unique_address]]
3123  __detail::__maybe_present_t<!forward_range<_Vp>,
3124  iterator_t<_Vp>> _M_current;
3125  _Vp _M_base = _Vp();
3126 
3127 
3128  public:
3129  split_view() requires (default_initializable<_Vp>
3130  && default_initializable<_Pattern>
3131  && (forward_range<_Vp>
3132  || default_initializable<iterator_t<_Vp>>))
3133  = default;
3134 
3135  constexpr
3136  split_view(_Vp __base, _Pattern __pattern)
3137  : _M_pattern(std::move(__pattern)), _M_base(std::move(__base))
3138  { }
3139 
3140  template<input_range _Range>
3141  requires constructible_from<_Vp, views::all_t<_Range>>
3142  && constructible_from<_Pattern, single_view<range_value_t<_Range>>>
3143  constexpr
3144  split_view(_Range&& __r, range_value_t<_Range> __e)
3145  : _M_pattern(views::single(std::move(__e))),
3146  _M_base(views::all(std::forward<_Range>(__r)))
3147  { }
3148 
3149  constexpr _Vp
3150  base() const& requires copy_constructible<_Vp>
3151  { return _M_base; }
3152 
3153  constexpr _Vp
3154  base() &&
3155  { return std::move(_M_base); }
3156 
3157  constexpr auto
3158  begin()
3159  {
3160  if constexpr (forward_range<_Vp>)
3161  {
3162  constexpr bool __simple
3163  = __detail::__simple_view<_Vp> && __detail::__simple_view<_Pattern>;
3164  return _OuterIter<__simple>{this, ranges::begin(_M_base)};
3165  }
3166  else
3167  {
3168  _M_current = ranges::begin(_M_base);
3169  return _OuterIter<false>{this};
3170  }
3171  }
3172 
3173  constexpr auto
3174  begin() const requires forward_range<_Vp> && forward_range<const _Vp>
3175  {
3176  return _OuterIter<true>{this, ranges::begin(_M_base)};
3177  }
3178 
3179  constexpr auto
3180  end() requires forward_range<_Vp> && common_range<_Vp>
3181  {
3182  constexpr bool __simple
3183  = __detail::__simple_view<_Vp> && __detail::__simple_view<_Pattern>;
3184  return _OuterIter<__simple>{this, ranges::end(_M_base)};
3185  }
3186 
3187  constexpr auto
3188  end() const
3189  {
3190  if constexpr (forward_range<_Vp>
3191  && forward_range<const _Vp>
3192  && common_range<const _Vp>)
3193  return _OuterIter<true>{this, ranges::end(_M_base)};
3194  else
3195  return default_sentinel;
3196  }
3197  };
3198 
3199  template<typename _Range, typename _Pattern>
3200  split_view(_Range&&, _Pattern&&)
3201  -> split_view<views::all_t<_Range>, views::all_t<_Pattern>>;
3202 
3203  template<input_range _Range>
3204  split_view(_Range&&, range_value_t<_Range>)
3205  -> split_view<views::all_t<_Range>, single_view<range_value_t<_Range>>>;
3206 
3207  namespace views
3208  {
3209  namespace __detail
3210  {
3211  template<typename _Range, typename _Pattern>
3212  concept __can_split_view
3213  = requires { split_view(std::declval<_Range>(), std::declval<_Pattern>()); };
3214  } // namespace __detail
3215 
3216  struct _Split : __adaptor::_RangeAdaptor<_Split>
3217  {
3218  template<viewable_range _Range, typename _Pattern>
3219  requires __detail::__can_split_view<_Range, _Pattern>
3220  constexpr auto
3221  operator()(_Range&& __r, _Pattern&& __f) const
3222  {
3223  return split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
3224  }
3225 
3226  using _RangeAdaptor<_Split>::operator();
3227  static constexpr int _S_arity = 2;
3228  // The pattern argument of views::split is not always simple -- it can be
3229  // a non-view range, the value category of which affects whether the call
3230  // is well-formed. But a scalar or a view pattern argument is surely
3231  // simple.
3232  template<typename _Pattern>
3233  static constexpr bool _S_has_simple_extra_args
3234  = is_scalar_v<_Pattern> || (view<_Pattern>
3235  && copy_constructible<_Pattern>);
3236  };
3237 
3238  inline constexpr _Split split;
3239  } // namespace views
3240 
3241  namespace views
3242  {
3243  struct _Counted
3244  {
3245  template<input_or_output_iterator _Iter>
3246  constexpr auto
3247  operator()(_Iter __i, iter_difference_t<_Iter> __n) const
3248  {
3249  if constexpr (random_access_iterator<_Iter>)
3250  return subrange(__i, __i + __n);
3251  else
3252  return subrange(counted_iterator(std::move(__i), __n),
3253  default_sentinel);
3254  }
3255  };
3256 
3257  inline constexpr _Counted counted{};
3258  } // namespace views
3259 
3260  template<view _Vp>
3261  requires (!common_range<_Vp>) && copyable<iterator_t<_Vp>>
3262  class common_view : public view_interface<common_view<_Vp>>
3263  {
3264  private:
3265  _Vp _M_base = _Vp();
3266 
3267  public:
3268  common_view() requires default_initializable<_Vp> = default;
3269 
3270  constexpr explicit
3271  common_view(_Vp __r)
3272  : _M_base(std::move(__r))
3273  { }
3274 
3275  /* XXX: LWG 3280 didn't remove this constructor, but I think it should?
3276  template<viewable_range _Range>
3277  requires (!common_range<_Range>)
3278  && constructible_from<_Vp, views::all_t<_Range>>
3279  constexpr explicit
3280  common_view(_Range&& __r)
3281  : _M_base(views::all(std::forward<_Range>(__r)))
3282  { }
3283  */
3284 
3285  constexpr _Vp
3286  base() const& requires copy_constructible<_Vp>
3287  { return _M_base; }
3288 
3289  constexpr _Vp
3290  base() &&
3291  { return std::move(_M_base); }
3292 
3293  constexpr auto
3294  begin()
3295  {
3296  if constexpr (random_access_range<_Vp> && sized_range<_Vp>)
3297  return ranges::begin(_M_base);
3298  else
3299  return common_iterator<iterator_t<_Vp>, sentinel_t<_Vp>>
3300  (ranges::begin(_M_base));
3301  }
3302 
3303  constexpr auto
3304  begin() const requires range<const _Vp>
3305  {
3306  if constexpr (random_access_range<const _Vp> && sized_range<const _Vp>)
3307  return ranges::begin(_M_base);
3308  else
3309  return common_iterator<iterator_t<const _Vp>, sentinel_t<const _Vp>>
3310  (ranges::begin(_M_base));
3311  }
3312 
3313  constexpr auto
3314  end()
3315  {
3316  if constexpr (random_access_range<_Vp> && sized_range<_Vp>)
3317  return ranges::begin(_M_base) + ranges::size(_M_base);
3318  else
3319  return common_iterator<iterator_t<_Vp>, sentinel_t<_Vp>>
3320  (ranges::end(_M_base));
3321  }
3322 
3323  constexpr auto
3324  end() const requires range<const _Vp>
3325  {
3326  if constexpr (random_access_range<const _Vp> && sized_range<const _Vp>)
3327  return ranges::begin(_M_base) + ranges::size(_M_base);
3328  else
3329  return common_iterator<iterator_t<const _Vp>, sentinel_t<const _Vp>>
3330  (ranges::end(_M_base));
3331  }
3332 
3333  constexpr auto
3334  size() requires sized_range<_Vp>
3335  { return ranges::size(_M_base); }
3336 
3337  constexpr auto
3338  size() const requires sized_range<const _Vp>
3339  { return ranges::size(_M_base); }
3340  };
3341 
3342  template<typename _Range>
3343  common_view(_Range&&) -> common_view<views::all_t<_Range>>;
3344 
3345  template<typename _Tp>
3346  inline constexpr bool enable_borrowed_range<common_view<_Tp>>
3347  = enable_borrowed_range<_Tp>;
3348 
3349  namespace views
3350  {
3351  namespace __detail
3352  {
3353  template<typename _Range>
3354  concept __already_common = common_range<_Range>
3355  && requires { views::all(std::declval<_Range>()); };
3356 
3357  template<typename _Range>
3358  concept __can_common_view
3359  = requires { common_view{std::declval<_Range>()}; };
3360  } // namespace __detail
3361 
3362  struct _Common : __adaptor::_RangeAdaptorClosure
3363  {
3364  template<viewable_range _Range>
3365  requires __detail::__already_common<_Range>
3366  || __detail::__can_common_view<_Range>
3367  constexpr auto
3368  operator()(_Range&& __r) const
3369  {
3370  if constexpr (__detail::__already_common<_Range>)
3371  return views::all(std::forward<_Range>(__r));
3372  else
3373  return common_view{std::forward<_Range>(__r)};
3374  }
3375 
3376  static constexpr bool _S_has_simple_call_op = true;
3377  };
3378 
3379  inline constexpr _Common common;
3380  } // namespace views
3381 
3382  template<view _Vp>
3383  requires bidirectional_range<_Vp>
3384  class reverse_view : public view_interface<reverse_view<_Vp>>
3385  {
3386  private:
3387  static constexpr bool _S_needs_cached_begin
3388  = !common_range<_Vp> && !random_access_range<_Vp>;
3389 
3390  [[no_unique_address]]
3391  __detail::__maybe_present_t<_S_needs_cached_begin,
3392  __detail::_CachedPosition<_Vp>>
3393  _M_cached_begin;
3394  _Vp _M_base = _Vp();
3395 
3396  public:
3397  reverse_view() requires default_initializable<_Vp> = default;
3398 
3399  constexpr explicit
3400  reverse_view(_Vp __r)
3401  : _M_base(std::move(__r))
3402  { }
3403 
3404  constexpr _Vp
3405  base() const& requires copy_constructible<_Vp>
3406  { return _M_base; }
3407 
3408  constexpr _Vp
3409  base() &&
3410  { return std::move(_M_base); }
3411 
3412  constexpr reverse_iterator<iterator_t<_Vp>>
3413  begin()
3414  {
3415  if constexpr (_S_needs_cached_begin)
3416  if (_M_cached_begin._M_has_value())
3417  return std::make_reverse_iterator(_M_cached_begin._M_get(_M_base));
3418 
3419  auto __it = ranges::next(ranges::begin(_M_base), ranges::end(_M_base));
3420  if constexpr (_S_needs_cached_begin)
3421  _M_cached_begin._M_set(_M_base, __it);
3422  return std::make_reverse_iterator(std::move(__it));
3423  }
3424 
3425  constexpr auto
3426  begin() requires common_range<_Vp>
3427  { return std::make_reverse_iterator(ranges::end(_M_base)); }
3428 
3429  constexpr auto
3430  begin() const requires common_range<const _Vp>
3431  { return std::make_reverse_iterator(ranges::end(_M_base)); }
3432 
3433  constexpr reverse_iterator<iterator_t<_Vp>>
3434  end()
3435  { return std::make_reverse_iterator(ranges::begin(_M_base)); }
3436 
3437  constexpr auto
3438  end() const requires common_range<const _Vp>
3439  { return std::make_reverse_iterator(ranges::begin(_M_base)); }
3440 
3441  constexpr auto
3442  size() requires sized_range<_Vp>
3443  { return ranges::size(_M_base); }
3444 
3445  constexpr auto
3446  size() const requires sized_range<const _Vp>
3447  { return ranges::size(_M_base); }
3448  };
3449 
3450  template<typename _Range>
3451  reverse_view(_Range&&) -> reverse_view<views::all_t<_Range>>;
3452 
3453  template<typename _Tp>
3454  inline constexpr bool enable_borrowed_range<reverse_view<_Tp>>
3455  = enable_borrowed_range<_Tp>;
3456 
3457  namespace views
3458  {
3459  namespace __detail
3460  {
3461  template<typename>
3462  inline constexpr bool __is_reversible_subrange = false;
3463 
3464  template<typename _Iter, subrange_kind _Kind>
3465  inline constexpr bool
3466  __is_reversible_subrange<subrange<reverse_iterator<_Iter>,
3467  reverse_iterator<_Iter>,
3468  _Kind>> = true;
3469 
3470  template<typename>
3471  inline constexpr bool __is_reverse_view = false;
3472 
3473  template<typename _Vp>
3474  inline constexpr bool __is_reverse_view<reverse_view<_Vp>> = true;
3475 
3476  template<typename _Range>
3477  concept __can_reverse_view
3478  = requires { reverse_view{std::declval<_Range>()}; };
3479  } // namespace __detail
3480 
3481  struct _Reverse : __adaptor::_RangeAdaptorClosure
3482  {
3483  template<viewable_range _Range>
3484  requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
3485  || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
3486  || __detail::__can_reverse_view<_Range>
3487  constexpr auto
3488  operator()(_Range&& __r) const
3489  {
3490  using _Tp = remove_cvref_t<_Range>;
3491  if constexpr (__detail::__is_reverse_view<_Tp>)
3492  return std::forward<_Range>(__r).base();
3493  else if constexpr (__detail::__is_reversible_subrange<_Tp>)
3494  {
3495  using _Iter = decltype(ranges::begin(__r).base());
3496  if constexpr (sized_range<_Tp>)
3497  return subrange<_Iter, _Iter, subrange_kind::sized>
3498  {__r.end().base(), __r.begin().base(), __r.size()};
3499  else
3500  return subrange<_Iter, _Iter, subrange_kind::unsized>
3501  {__r.end().base(), __r.begin().base()};
3502  }
3503  else
3504  return reverse_view{std::forward<_Range>(__r)};
3505  }
3506 
3507  static constexpr bool _S_has_simple_call_op = true;
3508  };
3509 
3510  inline constexpr _Reverse reverse;
3511  } // namespace views
3512 
3513  namespace __detail
3514  {
3515  template<typename _Tp, size_t _Nm>
3516  concept __has_tuple_element = requires(_Tp __t)
3517  {
3518  typename tuple_size<_Tp>::type;
3519  requires _Nm < tuple_size_v<_Tp>;
3520  typename tuple_element_t<_Nm, _Tp>;
3521  { std::get<_Nm>(__t) }
3522  -> convertible_to<const tuple_element_t<_Nm, _Tp>&>;
3523  };
3524 
3525  template<typename _Tp, size_t _Nm>
3526  concept __returnable_element
3527  = is_reference_v<_Tp> || move_constructible<tuple_element_t<_Nm, _Tp>>;
3528  }
3529 
3530  template<input_range _Vp, size_t _Nm>
3531  requires view<_Vp>
3532  && __detail::__has_tuple_element<range_value_t<_Vp>, _Nm>
3533  && __detail::__has_tuple_element<remove_reference_t<range_reference_t<_Vp>>,
3534  _Nm>
3535  && __detail::__returnable_element<range_reference_t<_Vp>, _Nm>
3536  class elements_view : public view_interface<elements_view<_Vp, _Nm>>
3537  {
3538  public:
3539  elements_view() requires default_initializable<_Vp> = default;
3540 
3541  constexpr explicit
3542  elements_view(_Vp base)
3543  : _M_base(std::move(base))
3544  { }
3545 
3546  constexpr _Vp
3547  base() const& requires copy_constructible<_Vp>
3548  { return _M_base; }
3549 
3550  constexpr _Vp
3551  base() &&
3552  { return std::move(_M_base); }
3553 
3554  constexpr auto
3555  begin() requires (!__detail::__simple_view<_Vp>)
3556  { return _Iterator<false>(ranges::begin(_M_base)); }
3557 
3558  constexpr auto
3559  begin() const requires range<const _Vp>
3560  { return _Iterator<true>(ranges::begin(_M_base)); }
3561 
3562  constexpr auto
3563  end() requires (!__detail::__simple_view<_Vp> && !common_range<_Vp>)
3564  { return _Sentinel<false>{ranges::end(_M_base)}; }
3565 
3566  constexpr auto
3567  end() requires (!__detail::__simple_view<_Vp> && common_range<_Vp>)
3568  { return _Iterator<false>{ranges::end(_M_base)}; }
3569 
3570  constexpr auto
3571  end() const requires range<const _Vp>
3572  { return _Sentinel<true>{ranges::end(_M_base)}; }
3573 
3574  constexpr auto
3575  end() const requires common_range<const _Vp>
3576  { return _Iterator<true>{ranges::end(_M_base)}; }
3577 
3578  constexpr auto
3579  size() requires sized_range<_Vp>
3580  { return ranges::size(_M_base); }
3581 
3582  constexpr auto
3583  size() const requires sized_range<const _Vp>
3584  { return ranges::size(_M_base); }
3585 
3586  private:
3587  template<bool _Const>
3588  using _Base = __detail::__maybe_const_t<_Const, _Vp>;
3589 
3590  template<bool _Const>
3591  struct __iter_cat
3592  { };
3593 
3594  template<bool _Const>
3595  requires forward_range<_Base<_Const>>
3596  struct __iter_cat<_Const>
3597  {
3598  private:
3599  static auto _S_iter_cat()
3600  {
3601  using _Base = elements_view::_Base<_Const>;
3602  using _Cat = typename iterator_traits<iterator_t<_Base>>::iterator_category;
3603  using _Res = decltype((std::get<_Nm>(*std::declval<iterator_t<_Base>>())));
3604  if constexpr (!is_lvalue_reference_v<_Res>)
3605  return input_iterator_tag{};
3606  else if constexpr (derived_from<_Cat, random_access_iterator_tag>)
3607  return random_access_iterator_tag{};
3608  else
3609  return _Cat{};
3610  }
3611  public:
3612  using iterator_category = decltype(_S_iter_cat());
3613  };
3614 
3615  template<bool _Const>
3616  struct _Sentinel;
3617 
3618  template<bool _Const>
3619  struct _Iterator : __iter_cat<_Const>
3620  {
3621  private:
3622  using _Base = elements_view::_Base<_Const>;
3623 
3624  iterator_t<_Base> _M_current = iterator_t<_Base>();
3625 
3626  static constexpr decltype(auto)
3627  _S_get_element(const iterator_t<_Base>& __i)
3628  {
3629  if constexpr (is_reference_v<range_reference_t<_Base>>)
3630  return std::get<_Nm>(*__i);
3631  else
3632  {
3633  using _Et = remove_cv_t<tuple_element_t<_Nm, range_reference_t<_Base>>>;
3634  return static_cast<_Et>(std::get<_Nm>(*__i));
3635  }
3636  }
3637 
3638  static auto
3639  _S_iter_concept()
3640  {
3641  if constexpr (random_access_range<_Base>)
3642  return random_access_iterator_tag{};
3643  else if constexpr (bidirectional_range<_Base>)
3644  return bidirectional_iterator_tag{};
3645  else if constexpr (forward_range<_Base>)
3646  return forward_iterator_tag{};
3647  else
3648  return input_iterator_tag{};
3649  }
3650 
3651  friend _Iterator<!_Const>;
3652 
3653  public:
3654  using iterator_concept = decltype(_S_iter_concept());
3655  // iterator_category defined in elements_view::__iter_cat
3656  using value_type
3657  = remove_cvref_t<tuple_element_t<_Nm, range_value_t<_Base>>>;
3658  using difference_type = range_difference_t<_Base>;
3659 
3660  _Iterator() requires default_initializable<iterator_t<_Base>> = default;
3661 
3662  constexpr explicit
3663  _Iterator(iterator_t<_Base> current)
3664  : _M_current(std::move(current))
3665  { }
3666 
3667  constexpr
3668  _Iterator(_Iterator<!_Const> i)
3669  requires _Const && convertible_to<iterator_t<_Vp>, iterator_t<_Base>>
3670  : _M_current(std::move(i._M_current))
3671  { }
3672 
3673  constexpr const iterator_t<_Base>&
3674  base() const& noexcept
3675  { return _M_current; }
3676 
3677  constexpr iterator_t<_Base>
3678  base() &&
3679  { return std::move(_M_current); }
3680 
3681  constexpr decltype(auto)
3682  operator*() const
3683  { return _S_get_element(_M_current); }
3684 
3685  constexpr _Iterator&
3686  operator++()
3687  {
3688  ++_M_current;
3689  return *this;
3690  }
3691 
3692  constexpr void
3693  operator++(int)
3694  { ++_M_current; }
3695 
3696  constexpr _Iterator
3697  operator++(int) requires forward_range<_Base>
3698  {
3699  auto __tmp = *this;
3700  ++_M_current;
3701  return __tmp;
3702  }
3703 
3704  constexpr _Iterator&
3705  operator--() requires bidirectional_range<_Base>
3706  {
3707  --_M_current;
3708  return *this;
3709  }
3710 
3711  constexpr _Iterator
3712  operator--(int) requires bidirectional_range<_Base>
3713  {
3714  auto __tmp = *this;
3715  --_M_current;
3716  return __tmp;
3717  }
3718 
3719  constexpr _Iterator&
3720  operator+=(difference_type __n)
3721  requires random_access_range<_Base>
3722  {
3723  _M_current += __n;
3724  return *this;
3725  }
3726 
3727  constexpr _Iterator&
3728  operator-=(difference_type __n)
3729  requires random_access_range<_Base>
3730  {
3731  _M_current -= __n;
3732  return *this;
3733  }
3734 
3735  constexpr decltype(auto)
3736  operator[](difference_type __n) const
3737  requires random_access_range<_Base>
3738  { return _S_get_element(_M_current + __n); }
3739 
3740  friend constexpr bool
3741  operator==(const _Iterator& __x, const _Iterator& __y)
3742  requires equality_comparable<iterator_t<_Base>>
3743  { return __x._M_current == __y._M_current; }
3744 
3745  friend constexpr bool
3746  operator<(const _Iterator& __x, const _Iterator& __y)
3747  requires random_access_range<_Base>
3748  { return __x._M_current < __y._M_current; }
3749 
3750  friend constexpr bool
3751  operator>(const _Iterator& __x, const _Iterator& __y)
3752  requires random_access_range<_Base>
3753  { return __y._M_current < __x._M_current; }
3754 
3755  friend constexpr bool
3756  operator<=(const _Iterator& __x, const _Iterator& __y)
3757  requires random_access_range<_Base>
3758  { return !(__y._M_current > __x._M_current); }
3759 
3760  friend constexpr bool
3761  operator>=(const _Iterator& __x, const _Iterator& __y)
3762  requires random_access_range<_Base>
3763  { return !(__x._M_current > __y._M_current); }
3764 
3765 #ifdef __cpp_lib_three_way_comparison
3766  friend constexpr auto
3767  operator<=>(const _Iterator& __x, const _Iterator& __y)
3768  requires random_access_range<_Base>
3769  && three_way_comparable<iterator_t<_Base>>
3770  { return __x._M_current <=> __y._M_current; }
3771 #endif
3772 
3773  friend constexpr _Iterator
3774  operator+(const _Iterator& __x, difference_type __y)
3775  requires random_access_range<_Base>
3776  { return _Iterator{__x} += __y; }
3777 
3778  friend constexpr _Iterator
3779  operator+(difference_type __x, const _Iterator& __y)
3780  requires random_access_range<_Base>
3781  { return __y + __x; }
3782 
3783  friend constexpr _Iterator
3784  operator-(const _Iterator& __x, difference_type __y)
3785  requires random_access_range<_Base>
3786  { return _Iterator{__x} -= __y; }
3787 
3788  // _GLIBCXX_RESOLVE_LIB_DEFECTS
3789  // 3483. transform_view::iterator's difference is overconstrained
3790  friend constexpr difference_type
3791  operator-(const _Iterator& __x, const _Iterator& __y)
3792  requires sized_sentinel_for<iterator_t<_Base>, iterator_t<_Base>>
3793  { return __x._M_current - __y._M_current; }
3794 
3795  template <bool> friend struct _Sentinel;
3796  };
3797 
3798  template<bool _Const>
3799  struct _Sentinel
3800  {
3801  private:
3802  template<bool _Const2>
3803  constexpr bool
3804  _M_equal(const _Iterator<_Const2>& __x) const
3805  { return __x._M_current == _M_end; }
3806 
3807  template<bool _Const2>
3808  constexpr auto
3809  _M_distance_from(const _Iterator<_Const2>& __i) const
3810  { return _M_end - __i._M_current; }
3811 
3812  using _Base = elements_view::_Base<_Const>;
3813  sentinel_t<_Base> _M_end = sentinel_t<_Base>();
3814 
3815  public:
3816  _Sentinel() = default;
3817 
3818  constexpr explicit
3819  _Sentinel(sentinel_t<_Base> __end)
3820  : _M_end(std::move(__end))
3821  { }
3822 
3823  constexpr
3824  _Sentinel(_Sentinel<!_Const> __other)
3825  requires _Const
3826  && convertible_to<sentinel_t<_Vp>, sentinel_t<_Base>>
3827  : _M_end(std::move(__other._M_end))
3828  { }
3829 
3830  constexpr sentinel_t<_Base>
3831  base() const
3832  { return _M_end; }
3833 
3834  template<bool _Const2>
3835  requires sentinel_for<sentinel_t<_Base>,
3836  iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
3837  friend constexpr bool
3838  operator==(const _Iterator<_Const2>& __x, const _Sentinel& __y)
3839  { return __y._M_equal(__x); }
3840 
3841  template<bool _Const2,
3842  typename _Base2 = __detail::__maybe_const_t<_Const2, _Vp>>
3843  requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
3844  friend constexpr range_difference_t<_Base2>
3845  operator-(const _Iterator<_Const2>& __x, const _Sentinel& __y)
3846  { return -__y._M_distance_from(__x); }
3847 
3848  template<bool _Const2,
3849  typename _Base2 = __detail::__maybe_const_t<_Const2, _Vp>>
3850  requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
3851  friend constexpr range_difference_t<_Base2>
3852  operator-(const _Sentinel& __x, const _Iterator<_Const2>& __y)
3853  { return __x._M_distance_from(__y); }
3854 
3855  friend _Sentinel<!_Const>;
3856  };
3857 
3858  _Vp _M_base = _Vp();
3859  };
3860 
3861  template<typename _Tp, size_t _Nm>
3862  inline constexpr bool enable_borrowed_range<elements_view<_Tp, _Nm>>
3863  = enable_borrowed_range<_Tp>;
3864 
3865  template<typename _Range>
3866  using keys_view = elements_view<views::all_t<_Range>, 0>;
3867 
3868  template<typename _Range>
3869  using values_view = elements_view<views::all_t<_Range>, 1>;
3870 
3871  namespace views
3872  {
3873  namespace __detail
3874  {
3875  template<size_t _Nm, typename _Range>
3876  concept __can_elements_view
3877  = requires { elements_view<all_t<_Range>, _Nm>{std::declval<_Range>()}; };
3878  } // namespace __detail
3879 
3880  template<size_t _Nm>
3881  struct _Elements : __adaptor::_RangeAdaptorClosure
3882  {
3883  template<viewable_range _Range>
3884  requires __detail::__can_elements_view<_Nm, _Range>
3885  constexpr auto
3886  operator()(_Range&& __r) const
3887  {
3888  return elements_view<all_t<_Range>, _Nm>{std::forward<_Range>(__r)};
3889  }
3890 
3891  static constexpr bool _S_has_simple_call_op = true;
3892  };
3893 
3894  template<size_t _Nm>
3895  inline constexpr _Elements<_Nm> elements;
3896  inline constexpr auto keys = elements<0>;
3897  inline constexpr auto values = elements<1>;
3898  } // namespace views
3899 
3900 } // namespace ranges
3901 
3902  namespace views = ranges::views;
3903 
3904 _GLIBCXX_END_NAMESPACE_VERSION
3905 } // namespace
3906 #endif // library concepts
3907 #endif // C++2a
3908 #endif /* _GLIBCXX_RANGES */