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 <__memory/addressof.h> 29 #include <__ranges/access.h> 30 #include <__ranges/concepts.h> 31 #include <__ranges/subrange.h> 32 #include <__utility/move.h> 33 #include <type_traits> 34 35 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 36 # pragma GCC system_header 37 #endif 38 39 _LIBCPP_BEGIN_NAMESPACE_STD 40 41 _LIBCPP_SUPPRESS_DEPRECATED_PUSH 42 template <class _Iter> 43 class _LIBCPP_TEMPLATE_VIS reverse_iterator 44 #if _LIBCPP_STD_VER <= 14 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES) 45 : public iterator<typename iterator_traits<_Iter>::iterator_category, 46 typename iterator_traits<_Iter>::value_type, 47 typename iterator_traits<_Iter>::difference_type, 48 typename iterator_traits<_Iter>::pointer, 49 typename iterator_traits<_Iter>::reference> 50 #endif 51 { 52 _LIBCPP_SUPPRESS_DEPRECATED_POP 53 private: 54 #ifndef _LIBCPP_ABI_NO_ITERATOR_BASES 55 _Iter __t; // no longer used as of LWG #2360, not removed due to ABI break 56 #endif 57 58 #if _LIBCPP_STD_VER > 17 59 static_assert(__is_cpp17_bidirectional_iterator<_Iter>::value || bidirectional_iterator<_Iter>, 60 "reverse_iterator<It> requires It to be a bidirectional iterator."); 61 #endif // _LIBCPP_STD_VER > 17 62 63 protected: 64 _Iter current; 65 public: 66 using iterator_type = _Iter; 67 68 using iterator_category = _If<__is_cpp17_random_access_iterator<_Iter>::value, 69 random_access_iterator_tag, 70 typename iterator_traits<_Iter>::iterator_category>; 71 using pointer = typename iterator_traits<_Iter>::pointer; 72 #if _LIBCPP_STD_VER > 17 73 using iterator_concept = _If<__is_cpp17_random_access_iterator<_Iter>::value, 74 random_access_iterator_tag, 75 bidirectional_iterator_tag>; 76 using value_type = iter_value_t<_Iter>; 77 using difference_type = iter_difference_t<_Iter>; 78 using reference = iter_reference_t<_Iter>; 79 #else 80 using value_type = typename iterator_traits<_Iter>::value_type; 81 using difference_type = typename iterator_traits<_Iter>::difference_type; 82 using reference = typename iterator_traits<_Iter>::reference; 83 #endif 84 85 #ifndef _LIBCPP_ABI_NO_ITERATOR_BASES 86 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 87 reverse_iterator() : __t(), current() {} 88 89 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 90 explicit reverse_iterator(_Iter __x) : __t(__x), current(__x) {} 91 92 template <class _Up, class = __enable_if_t< 93 !is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value 94 > > 95 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 96 reverse_iterator(const reverse_iterator<_Up>& __u) 97 : __t(__u.base()), current(__u.base()) 98 { } 99 100 template <class _Up, class = __enable_if_t< 101 !is_same<_Up, _Iter>::value && 102 is_convertible<_Up const&, _Iter>::value && 103 is_assignable<_Iter&, _Up const&>::value 104 > > 105 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 106 reverse_iterator& operator=(const reverse_iterator<_Up>& __u) { 107 __t = current = __u.base(); 108 return *this; 109 } 110 #else 111 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 112 reverse_iterator() : current() {} 113 114 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 115 explicit reverse_iterator(_Iter __x) : current(__x) {} 116 117 template <class _Up, class = __enable_if_t< 118 !is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value 119 > > 120 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 121 reverse_iterator(const reverse_iterator<_Up>& __u) 122 : current(__u.base()) 123 { } 124 125 template <class _Up, class = __enable_if_t< 126 !is_same<_Up, _Iter>::value && 127 is_convertible<_Up const&, _Iter>::value && 128 is_assignable<_Iter&, _Up const&>::value 129 > > 130 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 131 reverse_iterator& operator=(const reverse_iterator<_Up>& __u) { 132 current = __u.base(); 133 return *this; 134 } 135 #endif 136 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 137 _Iter base() const {return current;} 138 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 139 reference operator*() const {_Iter __tmp = current; return *--__tmp;} 140 141 #if _LIBCPP_STD_VER > 17 142 _LIBCPP_INLINE_VISIBILITY 143 constexpr pointer operator->() const 144 requires is_pointer_v<_Iter> || requires(const _Iter __i) { __i.operator->(); } 145 { 146 if constexpr (is_pointer_v<_Iter>) { 147 return std::prev(current); 148 } else { 149 return std::prev(current).operator->(); 150 } 151 } 152 #else 153 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 154 pointer operator->() const { 155 return std::addressof(operator*()); 156 } 157 #endif // _LIBCPP_STD_VER > 17 158 159 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 160 reverse_iterator& operator++() {--current; return *this;} 161 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 162 reverse_iterator operator++(int) {reverse_iterator __tmp(*this); --current; return __tmp;} 163 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 164 reverse_iterator& operator--() {++current; return *this;} 165 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 166 reverse_iterator operator--(int) {reverse_iterator __tmp(*this); ++current; return __tmp;} 167 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 168 reverse_iterator operator+(difference_type __n) const {return reverse_iterator(current - __n);} 169 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 170 reverse_iterator& operator+=(difference_type __n) {current -= __n; return *this;} 171 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 172 reverse_iterator operator-(difference_type __n) const {return reverse_iterator(current + __n);} 173 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 174 reverse_iterator& operator-=(difference_type __n) {current += __n; return *this;} 175 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 176 reference operator[](difference_type __n) const {return *(*this + __n);} 177 178 #if _LIBCPP_STD_VER > 17 179 _LIBCPP_HIDE_FROM_ABI friend constexpr 180 iter_rvalue_reference_t<_Iter> iter_move(const reverse_iterator& __i) 181 noexcept(is_nothrow_copy_constructible_v<_Iter> && 182 noexcept(ranges::iter_move(--declval<_Iter&>()))) { 183 auto __tmp = __i.base(); 184 return ranges::iter_move(--__tmp); 185 } 186 187 template <indirectly_swappable<_Iter> _Iter2> 188 _LIBCPP_HIDE_FROM_ABI friend constexpr 189 void iter_swap(const reverse_iterator& __x, const reverse_iterator<_Iter2>& __y) 190 noexcept(is_nothrow_copy_constructible_v<_Iter> && 191 is_nothrow_copy_constructible_v<_Iter2> && 192 noexcept(ranges::iter_swap(--declval<_Iter&>(), --declval<_Iter2&>()))) { 193 auto __xtmp = __x.base(); 194 auto __ytmp = __y.base(); 195 ranges::iter_swap(--__xtmp, --__ytmp); 196 } 197 #endif // _LIBCPP_STD_VER > 17 198 }; 199 200 template <class _Iter> 201 struct __is_reverse_iterator : false_type {}; 202 203 template <class _Iter> 204 struct __is_reverse_iterator<reverse_iterator<_Iter> > : true_type {}; 205 206 template <class _Iter1, class _Iter2> 207 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 208 bool 209 operator==(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 210 #if _LIBCPP_STD_VER > 17 211 requires requires { 212 { __x.base() == __y.base() } -> convertible_to<bool>; 213 } 214 #endif // _LIBCPP_STD_VER > 17 215 { 216 return __x.base() == __y.base(); 217 } 218 219 template <class _Iter1, class _Iter2> 220 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 221 bool 222 operator<(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 223 #if _LIBCPP_STD_VER > 17 224 requires requires { 225 { __x.base() > __y.base() } -> convertible_to<bool>; 226 } 227 #endif // _LIBCPP_STD_VER > 17 228 { 229 return __x.base() > __y.base(); 230 } 231 232 template <class _Iter1, class _Iter2> 233 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 234 bool 235 operator!=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 236 #if _LIBCPP_STD_VER > 17 237 requires requires { 238 { __x.base() != __y.base() } -> convertible_to<bool>; 239 } 240 #endif // _LIBCPP_STD_VER > 17 241 { 242 return __x.base() != __y.base(); 243 } 244 245 template <class _Iter1, class _Iter2> 246 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 247 bool 248 operator>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 249 #if _LIBCPP_STD_VER > 17 250 requires requires { 251 { __x.base() < __y.base() } -> convertible_to<bool>; 252 } 253 #endif // _LIBCPP_STD_VER > 17 254 { 255 return __x.base() < __y.base(); 256 } 257 258 template <class _Iter1, class _Iter2> 259 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 260 bool 261 operator>=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 262 #if _LIBCPP_STD_VER > 17 263 requires requires { 264 { __x.base() <= __y.base() } -> convertible_to<bool>; 265 } 266 #endif // _LIBCPP_STD_VER > 17 267 { 268 return __x.base() <= __y.base(); 269 } 270 271 template <class _Iter1, class _Iter2> 272 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 273 bool 274 operator<=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 275 #if _LIBCPP_STD_VER > 17 276 requires requires { 277 { __x.base() >= __y.base() } -> convertible_to<bool>; 278 } 279 #endif // _LIBCPP_STD_VER > 17 280 { 281 return __x.base() >= __y.base(); 282 } 283 284 #if _LIBCPP_STD_VER > 17 285 template <class _Iter1, three_way_comparable_with<_Iter1> _Iter2> 286 _LIBCPP_HIDE_FROM_ABI constexpr 287 compare_three_way_result_t<_Iter1, _Iter2> 288 operator<=>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 289 { 290 return __y.base() <=> __x.base(); 291 } 292 #endif // _LIBCPP_STD_VER > 17 293 294 #ifndef _LIBCPP_CXX03_LANG 295 template <class _Iter1, class _Iter2> 296 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 297 auto 298 operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 299 -> decltype(__y.base() - __x.base()) 300 { 301 return __y.base() - __x.base(); 302 } 303 #else 304 template <class _Iter1, class _Iter2> 305 inline _LIBCPP_INLINE_VISIBILITY 306 typename reverse_iterator<_Iter1>::difference_type 307 operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) 308 { 309 return __y.base() - __x.base(); 310 } 311 #endif 312 313 template <class _Iter> 314 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 315 reverse_iterator<_Iter> 316 operator+(typename reverse_iterator<_Iter>::difference_type __n, const reverse_iterator<_Iter>& __x) 317 { 318 return reverse_iterator<_Iter>(__x.base() - __n); 319 } 320 321 #if _LIBCPP_STD_VER > 17 322 template <class _Iter1, class _Iter2> 323 requires (!sized_sentinel_for<_Iter1, _Iter2>) 324 inline constexpr bool disable_sized_sentinel_for<reverse_iterator<_Iter1>, reverse_iterator<_Iter2>> = true; 325 #endif // _LIBCPP_STD_VER > 17 326 327 #if _LIBCPP_STD_VER > 11 328 template <class _Iter> 329 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 330 reverse_iterator<_Iter> make_reverse_iterator(_Iter __i) 331 { 332 return reverse_iterator<_Iter>(__i); 333 } 334 #endif 335 336 #if _LIBCPP_STD_VER <= 17 337 template <class _Iter> 338 using __unconstrained_reverse_iterator = reverse_iterator<_Iter>; 339 #else 340 341 // __unconstrained_reverse_iterator allows us to use reverse iterators in the implementation of algorithms by working 342 // around a language issue in C++20. 343 // In C++20, when a reverse iterator wraps certain C++20-hostile iterators, calling comparison operators on it will 344 // result in a compilation error. However, calling comparison operators on the pristine hostile iterator is not 345 // an error. Thus, we cannot use reverse_iterators in the implementation of an algorithm that accepts a 346 // C++20-hostile iterator. This class is an internal workaround -- it is a copy of reverse_iterator with 347 // tweaks to make it support hostile iterators. 348 // 349 // A C++20-hostile iterator is one that defines a comparison operator where one of the arguments is an exact match 350 // and the other requires an implicit conversion, for example: 351 // friend bool operator==(const BaseIter&, const DerivedIter&); 352 // 353 // C++20 rules for rewriting equality operators create another overload of this function with parameters reversed: 354 // friend bool operator==(const DerivedIter&, const BaseIter&); 355 // 356 // This creates an ambiguity in overload resolution. 357 // 358 // Clang treats this ambiguity differently in different contexts. When operator== is actually called in the function 359 // body, the code is accepted with a warning. When a concept requires operator== to be a valid expression, however, 360 // it evaluates to false. Thus, the implementation of reverse_iterator::operator== can actually call operator== on its 361 // base iterators, but the constraints on reverse_iterator::operator== prevent it from being considered during overload 362 // resolution. This class simply removes the problematic constraints from comparison functions. 363 template <class _Iter> 364 class __unconstrained_reverse_iterator { 365 _Iter __iter_; 366 367 public: 368 static_assert(__is_cpp17_bidirectional_iterator<_Iter>::value); 369 370 using iterator_type = _Iter; 371 using iterator_category = 372 _If<__is_cpp17_random_access_iterator<_Iter>::value, random_access_iterator_tag, __iterator_category_type<_Iter>>; 373 using pointer = __iterator_pointer_type<_Iter>; 374 using value_type = iter_value_t<_Iter>; 375 using difference_type = iter_difference_t<_Iter>; 376 using reference = iter_reference_t<_Iter>; 377 378 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator() = default; 379 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator(const __unconstrained_reverse_iterator&) = default; 380 _LIBCPP_HIDE_FROM_ABI constexpr explicit __unconstrained_reverse_iterator(_Iter __iter) : __iter_(__iter) {} 381 382 _LIBCPP_HIDE_FROM_ABI constexpr _Iter base() const { return __iter_; } 383 _LIBCPP_HIDE_FROM_ABI constexpr reference operator*() const { 384 auto __tmp = __iter_; 385 return *--__tmp; 386 } 387 388 _LIBCPP_HIDE_FROM_ABI constexpr pointer operator->() const { 389 if constexpr (is_pointer_v<_Iter>) { 390 return std::prev(__iter_); 391 } else { 392 return std::prev(__iter_).operator->(); 393 } 394 } 395 396 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator++() { 397 --__iter_; 398 return *this; 399 } 400 401 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator++(int) { 402 auto __tmp = *this; 403 --__iter_; 404 return __tmp; 405 } 406 407 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator--() { 408 ++__iter_; 409 return *this; 410 } 411 412 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator--(int) { 413 auto __tmp = *this; 414 ++__iter_; 415 return __tmp; 416 } 417 418 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator+=(difference_type __n) { 419 __iter_ -= __n; 420 return *this; 421 } 422 423 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator& operator-=(difference_type __n) { 424 __iter_ += __n; 425 return *this; 426 } 427 428 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator+(difference_type __n) const { 429 return __unconstrained_reverse_iterator(__iter_ - __n); 430 } 431 432 _LIBCPP_HIDE_FROM_ABI constexpr __unconstrained_reverse_iterator operator-(difference_type __n) const { 433 return __unconstrained_reverse_iterator(__iter_ + __n); 434 } 435 436 _LIBCPP_HIDE_FROM_ABI constexpr difference_type operator-(const __unconstrained_reverse_iterator& __other) const { 437 return __other.__iter_ - __iter_; 438 } 439 440 _LIBCPP_HIDE_FROM_ABI constexpr auto operator[](difference_type __n) const { return *(*this + __n); } 441 442 // Deliberately unconstrained unlike the comparison functions in `reverse_iterator` -- see the class comment for the 443 // rationale. 444 _LIBCPP_HIDE_FROM_ABI friend constexpr bool 445 operator==(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) { 446 return __lhs.base() == __rhs.base(); 447 } 448 449 _LIBCPP_HIDE_FROM_ABI friend constexpr bool 450 operator!=(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) { 451 return __lhs.base() != __rhs.base(); 452 } 453 454 _LIBCPP_HIDE_FROM_ABI friend constexpr bool 455 operator<(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) { 456 return __lhs.base() > __rhs.base(); 457 } 458 459 _LIBCPP_HIDE_FROM_ABI friend constexpr bool 460 operator>(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) { 461 return __lhs.base() < __rhs.base(); 462 } 463 464 _LIBCPP_HIDE_FROM_ABI friend constexpr bool 465 operator<=(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) { 466 return __lhs.base() >= __rhs.base(); 467 } 468 469 _LIBCPP_HIDE_FROM_ABI friend constexpr bool 470 operator>=(const __unconstrained_reverse_iterator& __lhs, const __unconstrained_reverse_iterator& __rhs) { 471 return __lhs.base() <= __rhs.base(); 472 } 473 }; 474 475 template <class _Iter> 476 struct __is_reverse_iterator<__unconstrained_reverse_iterator<_Iter>> : true_type {}; 477 478 #endif // _LIBCPP_STD_VER <= 17 479 480 template <template <class> class _RevIter1, template <class> class _RevIter2, class _Iter> 481 struct __unwrap_reverse_iter_impl { 482 using _UnwrappedIter = decltype(__unwrap_iter_impl<_Iter>::__unwrap(std::declval<_Iter>())); 483 using _ReverseWrapper = _RevIter1<_RevIter2<_Iter> >; 484 485 static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ReverseWrapper 486 __rewrap(_ReverseWrapper __orig_iter, _UnwrappedIter __unwrapped_iter) { 487 return _ReverseWrapper( 488 _RevIter2<_Iter>(__unwrap_iter_impl<_Iter>::__rewrap(__orig_iter.base().base(), __unwrapped_iter))); 489 } 490 491 static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _UnwrappedIter __unwrap(_ReverseWrapper __i) _NOEXCEPT { 492 return __unwrap_iter_impl<_Iter>::__unwrap(__i.base().base()); 493 } 494 }; 495 496 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES) 497 template <ranges::bidirectional_range _Range> 498 _LIBCPP_HIDE_FROM_ABI constexpr ranges:: 499 subrange<reverse_iterator<ranges::iterator_t<_Range>>, reverse_iterator<ranges::iterator_t<_Range>>> 500 __reverse_range(_Range&& __range) { 501 auto __first = ranges::begin(__range); 502 return {std::make_reverse_iterator(ranges::next(__first, ranges::end(__range))), std::make_reverse_iterator(__first)}; 503 } 504 #endif 505 506 template <class _Iter, bool __b> 507 struct __unwrap_iter_impl<reverse_iterator<reverse_iterator<_Iter> >, __b> 508 : __unwrap_reverse_iter_impl<reverse_iterator, reverse_iterator, _Iter> {}; 509 510 #if _LIBCPP_STD_VER > 17 511 512 template <class _Iter, bool __b> 513 struct __unwrap_iter_impl<reverse_iterator<__unconstrained_reverse_iterator<_Iter>>, __b> 514 : __unwrap_reverse_iter_impl<reverse_iterator, __unconstrained_reverse_iterator, _Iter> {}; 515 516 template <class _Iter, bool __b> 517 struct __unwrap_iter_impl<__unconstrained_reverse_iterator<reverse_iterator<_Iter>>, __b> 518 : __unwrap_reverse_iter_impl<__unconstrained_reverse_iterator, reverse_iterator, _Iter> {}; 519 520 template <class _Iter, bool __b> 521 struct __unwrap_iter_impl<__unconstrained_reverse_iterator<__unconstrained_reverse_iterator<_Iter>>, __b> 522 : __unwrap_reverse_iter_impl<__unconstrained_reverse_iterator, __unconstrained_reverse_iterator, _Iter> {}; 523 524 #endif // _LIBCPP_STD_VER > 17 525 526 _LIBCPP_END_NAMESPACE_STD 527 528 #endif // _LIBCPP___ITERATOR_REVERSE_ITERATOR_H 529