1 // -*- C++ -*-
2 //===----------------------------------------------------------------------===//
3 //
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef _LIBCPP___ITERATOR_REVERSE_ITERATOR_H
11 #define _LIBCPP___ITERATOR_REVERSE_ITERATOR_H
12 
13 #include <__algorithm/unwrap_iter.h>
14 #include <__compare/compare_three_way_result.h>
15 #include <__compare/three_way_comparable.h>
16 #include <__concepts/convertible_to.h>
17 #include <__config>
18 #include <__iterator/advance.h>
19 #include <__iterator/concepts.h>
20 #include <__iterator/incrementable_traits.h>
21 #include <__iterator/iter_move.h>
22 #include <__iterator/iter_swap.h>
23 #include <__iterator/iterator.h>
24 #include <__iterator/iterator_traits.h>
25 #include <__iterator/next.h>
26 #include <__iterator/prev.h>
27 #include <__iterator/readable_traits.h>
28 #include <__iterator/segmented_iterator.h>
29 #include <__memory/addressof.h>
30 #include <__ranges/access.h>
31 #include <__ranges/concepts.h>
32 #include <__ranges/subrange.h>
33 #include <__type_traits/conditional.h>
34 #include <__type_traits/enable_if.h>
35 #include <__type_traits/is_assignable.h>
36 #include <__type_traits/is_convertible.h>
37 #include <__type_traits/is_nothrow_copy_constructible.h>
38 #include <__type_traits/is_pointer.h>
39 #include <__type_traits/is_same.h>
40 #include <__utility/declval.h>
41 #include <__utility/move.h>
42 
43 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
44 #  pragma GCC system_header
45 #endif
46 
47 _LIBCPP_BEGIN_NAMESPACE_STD
48 
49 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
50 template <class _Iter>
51 class _LIBCPP_TEMPLATE_VIS reverse_iterator
52 #if _LIBCPP_STD_VER <= 14 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
53     : public iterator<typename iterator_traits<_Iter>::iterator_category,
54                       typename iterator_traits<_Iter>::value_type,
55                       typename iterator_traits<_Iter>::difference_type,
56                       typename iterator_traits<_Iter>::pointer,
57                       typename iterator_traits<_Iter>::reference>
58 #endif
59 {
60   _LIBCPP_SUPPRESS_DEPRECATED_POP
61 
62 private:
63 #ifndef _LIBCPP_ABI_NO_ITERATOR_BASES
64   _Iter __t_; // no longer used as of LWG #2360, not removed due to ABI break
65 #endif
66 
67 #if _LIBCPP_STD_VER >= 20
68   static_assert(__has_bidirectional_iterator_category<_Iter>::value || bidirectional_iterator<_Iter>,
69                 "reverse_iterator<It> requires It to be a bidirectional iterator.");
70 #endif // _LIBCPP_STD_VER >= 20
71 
72 protected:
73   _Iter current;
74 
75 public:
76   using iterator_type = _Iter;
77 
78   using iterator_category =
79       _If<__has_random_access_iterator_category<_Iter>::value,
80           random_access_iterator_tag,
81           typename iterator_traits<_Iter>::iterator_category>;
82   using pointer = typename iterator_traits<_Iter>::pointer;
83 #if _LIBCPP_STD_VER >= 20
84   using iterator_concept = _If<random_access_iterator<_Iter>, random_access_iterator_tag, bidirectional_iterator_tag>;
85   using value_type       = iter_value_t<_Iter>;
86   using difference_type  = iter_difference_t<_Iter>;
87   using reference        = iter_reference_t<_Iter>;
88 #else
89   using value_type      = typename iterator_traits<_Iter>::value_type;
90   using difference_type = typename iterator_traits<_Iter>::difference_type;
91   using reference       = typename iterator_traits<_Iter>::reference;
92 #endif
93 
94 #ifndef _LIBCPP_ABI_NO_ITERATOR_BASES
reverse_iterator()95   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator() : __t_(), current() {}
96 
reverse_iterator(_Iter __x)97   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 explicit reverse_iterator(_Iter __x) : __t_(__x), current(__x) {}
98 
99   template <class _Up,
100             class = __enable_if_t< !is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value > >
reverse_iterator(const reverse_iterator<_Up> & __u)101   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator(const reverse_iterator<_Up>& __u)
102       : __t_(__u.base()), current(__u.base()) {}
103 
104   template <class _Up,
105             class = __enable_if_t< !is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value &&
106                                    is_assignable<_Iter&, _Up const&>::value > >
107   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator=(const reverse_iterator<_Up>& __u) {
108     __t_ = current = __u.base();
109     return *this;
110   }
111 #else
reverse_iterator()112   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator() : current() {}
113 
reverse_iterator(_Iter __x)114   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 explicit reverse_iterator(_Iter __x) : current(__x) {}
115 
116   template <class _Up,
117             class = __enable_if_t< !is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value > >
reverse_iterator(const reverse_iterator<_Up> & __u)118   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator(const reverse_iterator<_Up>& __u)
119       : current(__u.base()) {}
120 
121   template <class _Up,
122             class = __enable_if_t< !is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value &&
123                                    is_assignable<_Iter&, _Up const&>::value > >
124   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator=(const reverse_iterator<_Up>& __u) {
125     current = __u.base();
126     return *this;
127   }
128 #endif
base()129   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _Iter base() const { return current; }
130   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reference operator*() const {
131     _Iter __tmp = current;
132     return *--__tmp;
133   }
134 
135 #if _LIBCPP_STD_VER >= 20
136   _LIBCPP_HIDE_FROM_ABI constexpr pointer operator->() const
137     requires is_pointer_v<_Iter> || requires(const _Iter __i) { __i.operator->(); }
138   {
139     if constexpr (is_pointer_v<_Iter>) {
140       return std::prev(current);
141     } else {
142       return std::prev(current).operator->();
143     }
144   }
145 #else
146   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pointer operator->() const { return std::addressof(operator*()); }
147 #endif // _LIBCPP_STD_VER >= 20
148 
149   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator++() {
150     --current;
151     return *this;
152   }
153   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator operator++(int) {
154     reverse_iterator __tmp(*this);
155     --current;
156     return __tmp;
157   }
158   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator--() {
159     ++current;
160     return *this;
161   }
162   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator operator--(int) {
163     reverse_iterator __tmp(*this);
164     ++current;
165     return __tmp;
166   }
167   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator operator+(difference_type __n) const {
168     return reverse_iterator(current - __n);
169   }
170   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator+=(difference_type __n) {
171     current -= __n;
172     return *this;
173   }
174   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator operator-(difference_type __n) const {
175     return reverse_iterator(current + __n);
176   }
177   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator-=(difference_type __n) {
178     current += __n;
179     return *this;
180   }
181   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reference operator[](difference_type __n) const {
182     return *(*this + __n);
183   }
184 
185 #if _LIBCPP_STD_VER >= 20
iter_move(const reverse_iterator & __i)186   _LIBCPP_HIDE_FROM_ABI friend constexpr iter_rvalue_reference_t<_Iter> iter_move(const reverse_iterator& __i) noexcept(
187       is_nothrow_copy_constructible_v<_Iter>&& noexcept(ranges::iter_move(--std::declval<_Iter&>()))) {
188     auto __tmp = __i.base();
189     return ranges::iter_move(--__tmp);
190   }
191 
192   template <indirectly_swappable<_Iter> _Iter2>
193   _LIBCPP_HIDE_FROM_ABI friend constexpr void
iter_swap(const reverse_iterator & __x,const reverse_iterator<_Iter2> & __y)194   iter_swap(const reverse_iterator& __x, const reverse_iterator<_Iter2>& __y) noexcept(
195       is_nothrow_copy_constructible_v<_Iter> &&
196       is_nothrow_copy_constructible_v<_Iter2>&& noexcept(
197           ranges::iter_swap(--std::declval<_Iter&>(), --std::declval<_Iter2&>()))) {
198     auto __xtmp = __x.base();
199     auto __ytmp = __y.base();
200     ranges::iter_swap(--__xtmp, --__ytmp);
201   }
202 #endif // _LIBCPP_STD_VER >= 20
203 };
204 
205 template <class _Iter1, class _Iter2>
206 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
207 operator==(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
208 #if _LIBCPP_STD_VER >= 20
209   requires requires {
210     { __x.base() == __y.base() } -> convertible_to<bool>;
211   }
212 #endif // _LIBCPP_STD_VER >= 20
213 {
214   return __x.base() == __y.base();
215 }
216 
217 template <class _Iter1, class _Iter2>
218 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
219 operator<(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
220 #if _LIBCPP_STD_VER >= 20
221   requires requires {
222     { __x.base() > __y.base() } -> convertible_to<bool>;
223   }
224 #endif // _LIBCPP_STD_VER >= 20
225 {
226   return __x.base() > __y.base();
227 }
228 
229 template <class _Iter1, class _Iter2>
230 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
231 operator!=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
232 #if _LIBCPP_STD_VER >= 20
233   requires requires {
234     { __x.base() != __y.base() } -> convertible_to<bool>;
235   }
236 #endif // _LIBCPP_STD_VER >= 20
237 {
238   return __x.base() != __y.base();
239 }
240 
241 template <class _Iter1, class _Iter2>
242 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
243 operator>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
244 #if _LIBCPP_STD_VER >= 20
245   requires requires {
246     { __x.base() < __y.base() } -> convertible_to<bool>;
247   }
248 #endif // _LIBCPP_STD_VER >= 20
249 {
250   return __x.base() < __y.base();
251 }
252 
253 template <class _Iter1, class _Iter2>
254 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
255 operator>=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
256 #if _LIBCPP_STD_VER >= 20
257   requires requires {
258     { __x.base() <= __y.base() } -> convertible_to<bool>;
259   }
260 #endif // _LIBCPP_STD_VER >= 20
261 {
262   return __x.base() <= __y.base();
263 }
264 
265 template <class _Iter1, class _Iter2>
266 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
267 operator<=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
268 #if _LIBCPP_STD_VER >= 20
269   requires requires {
270     { __x.base() >= __y.base() } -> convertible_to<bool>;
271   }
272 #endif // _LIBCPP_STD_VER >= 20
273 {
274   return __x.base() >= __y.base();
275 }
276 
277 #if _LIBCPP_STD_VER >= 20
278 template <class _Iter1, three_way_comparable_with<_Iter1> _Iter2>
279 _LIBCPP_HIDE_FROM_ABI constexpr compare_three_way_result_t<_Iter1, _Iter2>
280 operator<=>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) {
281   return __y.base() <=> __x.base();
282 }
283 #endif // _LIBCPP_STD_VER >= 20
284 
285 #ifndef _LIBCPP_CXX03_LANG
286 template <class _Iter1, class _Iter2>
287 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 auto
288 operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
289     -> decltype(__y.base() - __x.base()) {
290   return __y.base() - __x.base();
291 }
292 #else
293 template <class _Iter1, class _Iter2>
294 inline _LIBCPP_HIDE_FROM_ABI typename reverse_iterator<_Iter1>::difference_type
295 operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) {
296   return __y.base() - __x.base();
297 }
298 #endif
299 
300 template <class _Iter>
301 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator<_Iter>
302 operator+(typename reverse_iterator<_Iter>::difference_type __n, const reverse_iterator<_Iter>& __x) {
303   return reverse_iterator<_Iter>(__x.base() - __n);
304 }
305 
306 #if _LIBCPP_STD_VER >= 20
307 template <class _Iter1, class _Iter2>
308   requires(!sized_sentinel_for<_Iter1, _Iter2>)
309 inline constexpr bool disable_sized_sentinel_for<reverse_iterator<_Iter1>, reverse_iterator<_Iter2>> = true;
310 #endif // _LIBCPP_STD_VER >= 20
311 
312 #if _LIBCPP_STD_VER >= 14
313 template <class _Iter>
make_reverse_iterator(_Iter __i)314 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator<_Iter> make_reverse_iterator(_Iter __i) {
315   return reverse_iterator<_Iter>(__i);
316 }
317 #endif
318 
319 #if _LIBCPP_STD_VER <= 17
320 template <class _Iter>
321 using __unconstrained_reverse_iterator = reverse_iterator<_Iter>;
322 #else
323 
324 // __unconstrained_reverse_iterator allows us to use reverse iterators in the implementation of algorithms by working
325 // around a language issue in C++20.
326 // In C++20, when a reverse iterator wraps certain C++20-hostile iterators, calling comparison operators on it will
327 // result in a compilation error. However, calling comparison operators on the pristine hostile iterator is not
328 // an error. Thus, we cannot use reverse_iterators in the implementation of an algorithm that accepts a
329 // C++20-hostile iterator. This class is an internal workaround -- it is a copy of reverse_iterator with
330 // tweaks to make it support hostile iterators.
331 //
332 // A C++20-hostile iterator is one that defines a comparison operator where one of the arguments is an exact match
333 // and the other requires an implicit conversion, for example:
334 //   friend bool operator==(const BaseIter&, const DerivedIter&);
335 //
336 // C++20 rules for rewriting equality operators create another overload of this function with parameters reversed:
337 //   friend bool operator==(const DerivedIter&, const BaseIter&);
338 //
339 // This creates an ambiguity in overload resolution.
340 //
341 // Clang treats this ambiguity differently in different contexts. When operator== is actually called in the function
342 // body, the code is accepted with a warning. When a concept requires operator== to be a valid expression, however,
343 // it evaluates to false. Thus, the implementation of reverse_iterator::operator== can actually call operator== on its
344 // base iterators, but the constraints on reverse_iterator::operator== prevent it from being considered during overload
345 // resolution. This class simply removes the problematic constraints from comparison functions.
346 template <class _Iter>
347 class __unconstrained_reverse_iterator {
348   _Iter __iter_;
349 
350 public:
351   static_assert(__has_bidirectional_iterator_category<_Iter>::value || bidirectional_iterator<_Iter>);
352 
353   using iterator_type = _Iter;
354   using iterator_category =
355       _If<__has_random_access_iterator_category<_Iter>::value,
356           random_access_iterator_tag,
357           __iterator_category_type<_Iter>>;
358   using pointer         = __iterator_pointer_type<_Iter>;
359   using value_type      = iter_value_t<_Iter>;
360   using difference_type = iter_difference_t<_Iter>;
361   using reference       = iter_reference_t<_Iter>;
362 
363   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator()                                        = default;
364   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator(const __unconstrained_reverse_iterator&) = default;
__unconstrained_reverse_iterator(_Iter __iter)365   _LIBCPP_HIDE_FROM_ABI constexpr explicit __unconstrained_reverse_iterator(_Iter __iter) : __iter_(__iter) {}
366 
base()367   _LIBCPP_HIDE_FROM_ABI constexpr _Iter base() const { return __iter_; }
368   _LIBCPP_HIDE_FROM_ABI constexpr reference operator*() const {
369     auto __tmp = __iter_;
370     return *--__tmp;
371   }
372 
373   _LIBCPP_HIDE_FROM_ABI constexpr pointer operator->() const {
374     if constexpr (is_pointer_v<_Iter>) {
375       return std::prev(__iter_);
376     } else {
377       return std::prev(__iter_).operator->();
378     }
379   }
380 
381   _LIBCPP_HIDE_FROM_ABI friend constexpr iter_rvalue_reference_t<_Iter>
iter_move(const __unconstrained_reverse_iterator & __i)382   iter_move(const __unconstrained_reverse_iterator& __i) noexcept(
383       is_nothrow_copy_constructible_v<_Iter>&& noexcept(ranges::iter_move(--std::declval<_Iter&>()))) {
384     auto __tmp = __i.base();
385     return ranges::iter_move(--__tmp);
386   }
387 
388   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator++() {
389     --__iter_;
390     return *this;
391   }
392 
393   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator++(int) {
394     auto __tmp = *this;
395     --__iter_;
396     return __tmp;
397   }
398 
399   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator--() {
400     ++__iter_;
401     return *this;
402   }
403 
404   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator--(int) {
405     auto __tmp = *this;
406     ++__iter_;
407     return __tmp;
408   }
409 
410   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator+=(difference_type __n) {
411     __iter_ -= __n;
412     return *this;
413   }
414 
415   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator-=(difference_type __n) {
416     __iter_ += __n;
417     return *this;
418   }
419 
420   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator+(difference_type __n) const {
421     return __unconstrained_reverse_iterator(__iter_ - __n);
422   }
423 
424   _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator-(difference_type __n) const {
425     return __unconstrained_reverse_iterator(__iter_ + __n);
426   }
427 
428   _LIBCPP_HIDE_FROM_ABI constexpr difference_type operator-(const __unconstrained_reverse_iterator& __other) const {
429     return __other.__iter_ - __iter_;
430   }
431 
432   _LIBCPP_HIDE_FROM_ABI constexpr auto operator[](difference_type __n) const { return *(*this + __n); }
433 
434   // Deliberately unconstrained unlike the comparison functions in `reverse_iterator` -- see the class comment for the
435   // rationale.
436   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
437   operator==(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) {
438     return __lhs.base() == __rhs.base();
439   }
440 
441   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
442   operator!=(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) {
443     return __lhs.base() != __rhs.base();
444   }
445 
446   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
447   operator<(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) {
448     return __lhs.base() > __rhs.base();
449   }
450 
451   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
452   operator>(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) {
453     return __lhs.base() < __rhs.base();
454   }
455 
456   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
457   operator<=(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) {
458     return __lhs.base() >= __rhs.base();
459   }
460 
461   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
462   operator>=(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) {
463     return __lhs.base() <= __rhs.base();
464   }
465 };
466 
467 #endif // _LIBCPP_STD_VER <= 17
468 
469 template <template <class> class _RevIter1, template <class> class _RevIter2, class _Iter>
470 struct __unwrap_reverse_iter_impl {
471   using _UnwrappedIter  = decltype(__unwrap_iter_impl<_Iter>::__unwrap(std::declval<_Iter>()));
472   using _ReverseWrapper = _RevIter1<_RevIter2<_Iter> >;
473 
474   static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ReverseWrapper
__rewrap__unwrap_reverse_iter_impl475   __rewrap(_ReverseWrapper __orig_iter, _UnwrappedIter __unwrapped_iter) {
476     return _ReverseWrapper(
477         _RevIter2<_Iter>(__unwrap_iter_impl<_Iter>::__rewrap(__orig_iter.base().base(), __unwrapped_iter)));
478   }
479 
__unwrap__unwrap_reverse_iter_impl480   static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _UnwrappedIter __unwrap(_ReverseWrapper __i) _NOEXCEPT {
481     return __unwrap_iter_impl<_Iter>::__unwrap(__i.base().base());
482   }
483 };
484 
485 #if _LIBCPP_STD_VER >= 20
486 template <ranges::bidirectional_range _Range>
487 _LIBCPP_HIDE_FROM_ABI constexpr ranges::subrange<reverse_iterator<ranges::iterator_t<_Range>>,
488                                                  reverse_iterator<ranges::iterator_t<_Range>>>
__reverse_range(_Range && __range)489 __reverse_range(_Range&& __range) {
490   auto __first = ranges::begin(__range);
491   return {std::make_reverse_iterator(ranges::next(__first, ranges::end(__range))), std::make_reverse_iterator(__first)};
492 }
493 #endif
494 
495 template <class _Iter, bool __b>
496 struct __unwrap_iter_impl<reverse_iterator<reverse_iterator<_Iter> >, __b>
497     : __unwrap_reverse_iter_impl<reverse_iterator, reverse_iterator, _Iter> {};
498 
499 #if _LIBCPP_STD_VER >= 20
500 
501 template <class _Iter, bool __b>
502 struct __unwrap_iter_impl<reverse_iterator<__unconstrained_reverse_iterator<_Iter>>, __b>
503     : __unwrap_reverse_iter_impl<reverse_iterator, __unconstrained_reverse_iterator, _Iter> {};
504 
505 template <class _Iter, bool __b>
506 struct __unwrap_iter_impl<__unconstrained_reverse_iterator<reverse_iterator<_Iter>>, __b>
507     : __unwrap_reverse_iter_impl<__unconstrained_reverse_iterator, reverse_iterator, _Iter> {};
508 
509 template <class _Iter, bool __b>
510 struct __unwrap_iter_impl<__unconstrained_reverse_iterator<__unconstrained_reverse_iterator<_Iter>>, __b>
511     : __unwrap_reverse_iter_impl<__unconstrained_reverse_iterator, __unconstrained_reverse_iterator, _Iter> {};
512 
513 #endif // _LIBCPP_STD_VER >= 20
514 
515 _LIBCPP_END_NAMESPACE_STD
516 
517 #endif // _LIBCPP___ITERATOR_REVERSE_ITERATOR_H
518