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 50template <class _Iter> 51class _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 62private: 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 72protected: 73 _Iter current; 74 75public: 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 95 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator() : __t_(), current() {} 96 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 > > 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 112 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator() : current() {} 113 114 _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 > > 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 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 >= 20 186 _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 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 205template <class _Iter1, class _Iter2> 206inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool 207operator==(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 217template <class _Iter1, class _Iter2> 218inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool 219operator<(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 229template <class _Iter1, class _Iter2> 230inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool 231operator!=(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 241template <class _Iter1, class _Iter2> 242inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool 243operator>(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 253template <class _Iter1, class _Iter2> 254inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool 255operator>=(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 265template <class _Iter1, class _Iter2> 266inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool 267operator<=(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 278template <class _Iter1, three_way_comparable_with<_Iter1> _Iter2> 279_LIBCPP_HIDE_FROM_ABI constexpr compare_three_way_result_t<_Iter1, _Iter2> 280operator<=>(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 286template <class _Iter1, class _Iter2> 287inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 auto 288operator-(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 293template <class _Iter1, class _Iter2> 294inline _LIBCPP_HIDE_FROM_ABI typename reverse_iterator<_Iter1>::difference_type 295operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) { 296 return __y.base() - __x.base(); 297} 298#endif 299 300template <class _Iter> 301inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator<_Iter> 302operator+(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 307template <class _Iter1, class _Iter2> 308 requires(!sized_sentinel_for<_Iter1, _Iter2>) 309inline 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 313template <class _Iter> 314inline _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 320template <class _Iter> 321using __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. 346template <class _Iter> 347class __unconstrained_reverse_iterator { 348 _Iter __iter_; 349 350public: 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; 365 _LIBCPP_HIDE_FROM_ABI constexpr explicit __unconstrained_reverse_iterator(_Iter __iter) : __iter_(__iter) {} 366 367 _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> 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 469template <template <class> class _RevIter1, template <class> class _RevIter2, class _Iter> 470struct __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 475 __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 } 479 480 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 486template <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>>> 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 495template <class _Iter, bool __b> 496struct __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 501template <class _Iter, bool __b> 502struct __unwrap_iter_impl<reverse_iterator<__unconstrained_reverse_iterator<_Iter>>, __b> 503 : __unwrap_reverse_iter_impl<reverse_iterator, __unconstrained_reverse_iterator, _Iter> {}; 504 505template <class _Iter, bool __b> 506struct __unwrap_iter_impl<__unconstrained_reverse_iterator<reverse_iterator<_Iter>>, __b> 507 : __unwrap_reverse_iter_impl<__unconstrained_reverse_iterator, reverse_iterator, _Iter> {}; 508 509template <class _Iter, bool __b> 510struct __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