1// Pair implementation -*- C++ -*-
2
3// Copyright (C) 2001-2025 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/*
26 *
27 * Copyright (c) 1994
28 * Hewlett-Packard Company
29 *
30 * Permission to use, copy, modify, distribute and sell this software
31 * and its documentation for any purpose is hereby granted without fee,
32 * provided that the above copyright notice appear in all copies and
33 * that both that copyright notice and this permission notice appear
34 * in supporting documentation. Hewlett-Packard Company makes no
35 * representations about the suitability of this software for any
36 * purpose. It is provided "as is" without express or implied warranty.
37 *
38 *
39 * Copyright (c) 1996,1997
40 * Silicon Graphics Computer Systems, Inc.
41 *
42 * Permission to use, copy, modify, distribute and sell this software
43 * and its documentation for any purpose is hereby granted without fee,
44 * provided that the above copyright notice appear in all copies and
45 * that both that copyright notice and this permission notice appear
46 * in supporting documentation. Silicon Graphics makes no
47 * representations about the suitability of this software for any
48 * purpose. It is provided "as is" without express or implied warranty.
49 */
50
51/** @file bits/stl_pair.h
52 * This is an internal header file, included by other library headers.
53 * Do not attempt to use it directly. @headername{utility}
54 */
55
56#ifndef _STL_PAIR_H
57#define _STL_PAIR_H 1
58
59#if __cplusplus >= 201103L
60# include <type_traits> // for std::__decay_and_strip
61# include <bits/move.h> // for std::move / std::forward, and std::swap
62# include <bits/utility.h> // for std::tuple_element, std::tuple_size
63#endif
64#if __cplusplus >= 202002L
65# include <compare>
66#endif
67
68namespace std _GLIBCXX_VISIBILITY(default)
69{
70_GLIBCXX_BEGIN_NAMESPACE_VERSION
71
72 /**
73 * @addtogroup utilities
74 * @{
75 */
76
77#if __cplusplus >= 201103L
78 /// Tag type for piecewise construction of std::pair objects.
79 struct piecewise_construct_t { explicit piecewise_construct_t() = default; };
80
81 /// Tag for piecewise construction of std::pair objects.
82 _GLIBCXX17_INLINE constexpr piecewise_construct_t piecewise_construct =
83 piecewise_construct_t();
84
85 /// @cond undocumented
86
87 // Forward declarations.
88 template<typename _T1, typename _T2>
89 struct pair;
90
91 template<typename...>
92 class tuple;
93
94 // Declarations of std::array and its std::get overloads, so that
95 // std::tuple_cat can use them if <tuple> is included before <array>.
96 // We also declare the other std::get overloads here so that they're
97 // visible to the P2165R4 tuple-like constructors of pair and tuple.
98 template<typename _Tp, size_t _Nm>
99 struct array;
100
101 template<size_t...>
102 struct _Index_tuple;
103
104 template<typename _Tp>
105 class complex;
106
107 template<size_t _Int, class _Tp1, class _Tp2>
108 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
109 get(pair<_Tp1, _Tp2>& __in) noexcept;
110
111 template<size_t _Int, class _Tp1, class _Tp2>
112 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
113 get(pair<_Tp1, _Tp2>&& __in) noexcept;
114
115 template<size_t _Int, class _Tp1, class _Tp2>
116 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
117 get(const pair<_Tp1, _Tp2>& __in) noexcept;
118
119 template<size_t _Int, class _Tp1, class _Tp2>
120 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
121 get(const pair<_Tp1, _Tp2>&& __in) noexcept;
122
123 template<size_t __i, typename... _Elements>
124 constexpr __tuple_element_t<__i, tuple<_Elements...>>&
125 get(tuple<_Elements...>& __t) noexcept;
126
127 template<size_t __i, typename... _Elements>
128 constexpr const __tuple_element_t<__i, tuple<_Elements...>>&
129 get(const tuple<_Elements...>& __t) noexcept;
130
131 template<size_t __i, typename... _Elements>
132 constexpr __tuple_element_t<__i, tuple<_Elements...>>&&
133 get(tuple<_Elements...>&& __t) noexcept;
134
135 template<size_t __i, typename... _Elements>
136 constexpr const __tuple_element_t<__i, tuple<_Elements...>>&&
137 get(const tuple<_Elements...>&& __t) noexcept;
138
139 template<size_t _Int, typename _Tp, size_t _Nm>
140 constexpr _Tp&
141 get(array<_Tp, _Nm>&) noexcept;
142
143 template<size_t _Int, typename _Tp, size_t _Nm>
144 constexpr _Tp&&
145 get(array<_Tp, _Nm>&&) noexcept;
146
147 template<size_t _Int, typename _Tp, size_t _Nm>
148 constexpr const _Tp&
149 get(const array<_Tp, _Nm>&) noexcept;
150
151 template<size_t _Int, typename _Tp, size_t _Nm>
152 constexpr const _Tp&&
153 get(const array<_Tp, _Nm>&&) noexcept;
154
155#if __glibcxx_tuple_like >= 202311 // >= C++26
156 template<size_t _Int, typename _Tp>
157 constexpr _Tp&
158 get(complex<_Tp>&) noexcept;
159 template<size_t _Int, typename _Tp>
160 constexpr _Tp&&
161 get(complex<_Tp>&&) noexcept;
162 template<size_t _Int, typename _Tp>
163 constexpr const _Tp&
164 get(const complex<_Tp>&) noexcept;
165 template<size_t _Int, typename _Tp>
166 constexpr const _Tp&&
167 get(const complex<_Tp>&&) noexcept;
168#endif
169
170#if ! __cpp_lib_concepts
171 // Concept utility functions, reused in conditionally-explicit
172 // constructors.
173 // See PR 70437, don't look at is_constructible or
174 // is_convertible if the types are the same to
175 // avoid querying those properties for incomplete types.
176 template <bool, typename _T1, typename _T2>
177 struct _PCC
178 {
179 template <typename _U1, typename _U2>
180 static constexpr bool _ConstructiblePair()
181 {
182 return __and_<is_constructible<_T1, const _U1&>,
183 is_constructible<_T2, const _U2&>>::value;
184 }
185
186 template <typename _U1, typename _U2>
187 static constexpr bool _ImplicitlyConvertiblePair()
188 {
189 return __and_<is_convertible<const _U1&, _T1>,
190 is_convertible<const _U2&, _T2>>::value;
191 }
192
193 template <typename _U1, typename _U2>
194 static constexpr bool _MoveConstructiblePair()
195 {
196 return __and_<is_constructible<_T1, _U1&&>,
197 is_constructible<_T2, _U2&&>>::value;
198 }
199
200 template <typename _U1, typename _U2>
201 static constexpr bool _ImplicitlyMoveConvertiblePair()
202 {
203 return __and_<is_convertible<_U1&&, _T1>,
204 is_convertible<_U2&&, _T2>>::value;
205 }
206 };
207
208 template <typename _T1, typename _T2>
209 struct _PCC<false, _T1, _T2>
210 {
211 template <typename _U1, typename _U2>
212 static constexpr bool _ConstructiblePair()
213 {
214 return false;
215 }
216
217 template <typename _U1, typename _U2>
218 static constexpr bool _ImplicitlyConvertiblePair()
219 {
220 return false;
221 }
222
223 template <typename _U1, typename _U2>
224 static constexpr bool _MoveConstructiblePair()
225 {
226 return false;
227 }
228
229 template <typename _U1, typename _U2>
230 static constexpr bool _ImplicitlyMoveConvertiblePair()
231 {
232 return false;
233 }
234 };
235#endif // lib concepts
236#endif // C++11
237
238#if __glibcxx_tuple_like // >= C++23
239 template<typename _Tp>
240 inline constexpr bool __is_tuple_v = false;
241
242 template<typename... _Ts>
243 inline constexpr bool __is_tuple_v<tuple<_Ts...>> = true;
244
245 // TODO: Reuse __is_tuple_like from <type_traits>?
246 template<typename _Tp>
247 inline constexpr bool __is_tuple_like_v = false;
248
249 template<typename... _Elements>
250 inline constexpr bool __is_tuple_like_v<tuple<_Elements...>> = true;
251
252 template<typename _T1, typename _T2>
253 inline constexpr bool __is_tuple_like_v<pair<_T1, _T2>> = true;
254
255 template<typename _Tp, size_t _Nm>
256 inline constexpr bool __is_tuple_like_v<array<_Tp, _Nm>> = true;
257
258 // __is_tuple_like_v<subrange> is defined in <bits/ranges_util.h>.
259
260 template<typename _Tp>
261 concept __tuple_like = __is_tuple_like_v<remove_cvref_t<_Tp>>;
262
263 template<typename _Tp>
264 concept __pair_like = __tuple_like<_Tp> && tuple_size_v<remove_cvref_t<_Tp>> == 2;
265
266 template<typename _Tp, typename _Tuple>
267 concept __eligible_tuple_like
268 = __detail::__different_from<_Tp, _Tuple> && __tuple_like<_Tp>
269 && (tuple_size_v<remove_cvref_t<_Tp>> == tuple_size_v<_Tuple>)
270 && !ranges::__detail::__is_subrange<remove_cvref_t<_Tp>>;
271
272 template<typename _Tp, typename _Pair>
273 concept __eligible_pair_like
274 = __detail::__different_from<_Tp, _Pair> && __pair_like<_Tp>
275 && !ranges::__detail::__is_subrange<remove_cvref_t<_Tp>>;
276#endif // C++23
277
278 template<typename _U1, typename _U2> class __pair_base
279 {
280#if __cplusplus >= 201103L && ! __cpp_lib_concepts
281 template<typename _T1, typename _T2> friend struct pair;
282 __pair_base() = default;
283 ~__pair_base() = default;
284 __pair_base(const __pair_base&) = default;
285 __pair_base& operator=(const __pair_base&) = delete;
286#endif // C++11
287 };
288
289 /// @endcond
290
291 /**
292 * @brief Struct holding two objects of arbitrary type.
293 *
294 * @tparam _T1 Type of first object.
295 * @tparam _T2 Type of second object.
296 *
297 * <https://gcc.gnu.org/onlinedocs/libstdc++/manual/utilities.html>
298 *
299 * @headerfile utility
300 */
301 template<typename _T1, typename _T2>
302 struct pair
303 : public __pair_base<_T1, _T2>
304 {
305 typedef _T1 first_type; ///< The type of the `first` member
306 typedef _T2 second_type; ///< The type of the `second` member
307
308 _T1 first; ///< The first member
309 _T2 second; ///< The second member
310
311#if __cplusplus >= 201103L
312 constexpr pair(const pair&) = default; ///< Copy constructor
313 constexpr pair(pair&&) = default; ///< Move constructor
314
315 template<typename... _Args1, typename... _Args2>
316 _GLIBCXX20_CONSTEXPR
317 pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
318
319 /// Swap the first members and then the second members.
320 _GLIBCXX20_CONSTEXPR void
321 swap(pair& __p)
322 noexcept(__and_<__is_nothrow_swappable<_T1>,
323 __is_nothrow_swappable<_T2>>::value)
324 {
325 using std::swap;
326 swap(first, __p.first);
327 swap(second, __p.second);
328 }
329
330#if __glibcxx_ranges_zip // >= C++23
331 // As an extension, we constrain the const swap member function in order
332 // to continue accepting explicit instantiation of pairs whose elements
333 // are not all const swappable. Without this constraint, such an
334 // explicit instantiation would also instantiate the ill-formed body of
335 // this function and yield a hard error. This constraint shouldn't
336 // affect the behavior of valid programs.
337 constexpr void
338 swap(const pair& __p) const
339 noexcept(__and_v<__is_nothrow_swappable<const _T1>,
340 __is_nothrow_swappable<const _T2>>)
341 requires is_swappable_v<const _T1> && is_swappable_v<const _T2>
342 {
343 using std::swap;
344 swap(first, __p.first);
345 swap(second, __p.second);
346 }
347#endif // C++23
348
349 private:
350 template<typename... _Args1, size_t... _Indexes1,
351 typename... _Args2, size_t... _Indexes2>
352 _GLIBCXX20_CONSTEXPR
353 pair(tuple<_Args1...>&, tuple<_Args2...>&,
354 _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
355 public:
356
357#if __cpp_lib_concepts
358 // C++20 implementation using concepts, explicit(bool), fully constexpr.
359
360 /// Default constructor
361 constexpr
362 explicit(__not_<__and_<__is_implicitly_default_constructible<_T1>,
363 __is_implicitly_default_constructible<_T2>>>())
364 pair()
365 noexcept(is_nothrow_default_constructible_v<_T1>
366 && is_nothrow_default_constructible_v<_T2>)
367 requires is_default_constructible_v<_T1>
368 && is_default_constructible_v<_T2>
369 : first(), second()
370 { }
371
372 private:
373
374 /// @cond undocumented
375 template<typename _U1, typename _U2>
376 static constexpr bool
377 _S_constructible()
378 {
379 if constexpr (is_constructible_v<_T1, _U1>)
380 return is_constructible_v<_T2, _U2>;
381 return false;
382 }
383
384 template<typename _U1, typename _U2>
385 static constexpr bool
386 _S_nothrow_constructible()
387 {
388 if constexpr (is_nothrow_constructible_v<_T1, _U1>)
389 return is_nothrow_constructible_v<_T2, _U2>;
390 return false;
391 }
392
393 template<typename _U1, typename _U2>
394 static constexpr bool
395 _S_convertible()
396 {
397 if constexpr (is_convertible_v<_U1, _T1>)
398 return is_convertible_v<_U2, _T2>;
399 return false;
400 }
401
402 // True if construction from _U1 and _U2 would create a dangling ref.
403 template<typename _U1, typename _U2>
404 static constexpr bool
405 _S_dangles()
406 {
407#if __has_builtin(__reference_constructs_from_temporary)
408 if constexpr (__reference_constructs_from_temporary(_T1, _U1&&))
409 return true;
410 else
411 return __reference_constructs_from_temporary(_T2, _U2&&);
412#else
413 return false;
414#endif
415 }
416
417#if __glibcxx_tuple_like // >= C++23
418 template<typename _UPair>
419 static constexpr bool
420 _S_constructible_from_pair_like()
421 {
422 return _S_constructible<decltype(std::get<0>(std::declval<_UPair>())),
423 decltype(std::get<1>(std::declval<_UPair>()))>();
424 }
425
426 template<typename _UPair>
427 static constexpr bool
428 _S_convertible_from_pair_like()
429 {
430 return _S_convertible<decltype(std::get<0>(std::declval<_UPair>())),
431 decltype(std::get<1>(std::declval<_UPair>()))>();
432 }
433
434 template<typename _UPair>
435 static constexpr bool
436 _S_dangles_from_pair_like()
437 {
438 return _S_dangles<decltype(std::get<0>(std::declval<_UPair>())),
439 decltype(std::get<1>(std::declval<_UPair>()))>();
440 }
441#endif // C++23
442 /// @endcond
443
444 public:
445
446 /// Constructor accepting lvalues of `first_type` and `second_type`
447 constexpr explicit(!_S_convertible<const _T1&, const _T2&>())
448 pair(const type_identity_t<_T1>& __x, const _T2& __y)
449 noexcept(_S_nothrow_constructible<const _T1&, const _T2&>())
450 requires (_S_constructible<const _T1&, const _T2&>())
451 : first(__x), second(__y)
452 { }
453
454 /// Constructor accepting two values of arbitrary types
455#if __cplusplus > 202002L
456 template<typename _U1 = _T1, typename _U2 = _T2>
457#else
458 template<typename _U1, typename _U2>
459#endif
460 requires (_S_constructible<_U1, _U2>()) && (!_S_dangles<_U1, _U2>())
461 constexpr explicit(!_S_convertible<_U1, _U2>())
462 pair(_U1&& __x, _U2&& __y)
463 noexcept(_S_nothrow_constructible<_U1, _U2>())
464 : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
465 { }
466
467#if __cplusplus > 202002L
468 template<typename _U1 = _T1, typename _U2 = _T2>
469#else
470 template<typename _U1, typename _U2>
471#endif
472 requires (_S_constructible<_U1, _U2>()) && (_S_dangles<_U1, _U2>())
473 constexpr explicit(!_S_convertible<_U1, _U2>())
474 pair(_U1&&, _U2&&) = delete;
475
476 /// Converting constructor from a const `pair<U1, U2>` lvalue
477 template<typename _U1, typename _U2>
478 requires (_S_constructible<const _U1&, const _U2&>())
479 && (!_S_dangles<_U1, _U2>())
480 constexpr explicit(!_S_convertible<const _U1&, const _U2&>())
481 pair(const pair<_U1, _U2>& __p)
482 noexcept(_S_nothrow_constructible<const _U1&, const _U2&>())
483 : first(__p.first), second(__p.second)
484 { }
485
486 template<typename _U1, typename _U2>
487 requires (_S_constructible<const _U1&, const _U2&>())
488 && (_S_dangles<const _U1&, const _U2&>())
489 constexpr explicit(!_S_convertible<const _U1&, const _U2&>())
490 pair(const pair<_U1, _U2>&) = delete;
491
492 /// Converting constructor from a non-const `pair<U1, U2>` rvalue
493 template<typename _U1, typename _U2>
494 requires (_S_constructible<_U1, _U2>()) && (!_S_dangles<_U1, _U2>())
495 constexpr explicit(!_S_convertible<_U1, _U2>())
496 pair(pair<_U1, _U2>&& __p)
497 noexcept(_S_nothrow_constructible<_U1, _U2>())
498 : first(std::forward<_U1>(__p.first)),
499 second(std::forward<_U2>(__p.second))
500 { }
501
502 template<typename _U1, typename _U2>
503 requires (_S_constructible<_U1, _U2>()) && (_S_dangles<_U1, _U2>())
504 constexpr explicit(!_S_convertible<_U1, _U2>())
505 pair(pair<_U1, _U2>&&) = delete;
506
507#if __glibcxx_ranges_zip // >= C++23
508 /// Converting constructor from a non-const `pair<U1, U2>` lvalue
509 template<typename _U1, typename _U2>
510 requires (_S_constructible<_U1&, _U2&>()) && (!_S_dangles<_U1&, _U2&>())
511 constexpr explicit(!_S_convertible<_U1&, _U2&>())
512 pair(pair<_U1, _U2>& __p)
513 noexcept(_S_nothrow_constructible<_U1&, _U2&>())
514 : first(__p.first), second(__p.second)
515 { }
516
517 template<typename _U1, typename _U2>
518 requires (_S_constructible<_U1&, _U2&>()) && (_S_dangles<_U1&, _U2&>())
519 constexpr explicit(!_S_convertible<_U1&, _U2&>())
520 pair(pair<_U1, _U2>&) = delete;
521
522 /// Converting constructor from a const `pair<U1, U2>` rvalue
523 template<typename _U1, typename _U2>
524 requires (_S_constructible<const _U1, const _U2>())
525 && (!_S_dangles<const _U1, const _U2>())
526 constexpr explicit(!_S_convertible<const _U1, const _U2>())
527 pair(const pair<_U1, _U2>&& __p)
528 noexcept(_S_nothrow_constructible<const _U1, const _U2>())
529 : first(std::forward<const _U1>(__p.first)),
530 second(std::forward<const _U2>(__p.second))
531 { }
532
533 template<typename _U1, typename _U2>
534 requires (_S_constructible<const _U1, const _U2>())
535 && (_S_dangles<const _U1, const _U2>())
536 constexpr explicit(!_S_convertible<const _U1, const _U2>())
537 pair(const pair<_U1, _U2>&&) = delete;
538#endif // C++23
539
540#if __glibcxx_tuple_like // >= C++23
541 template<__eligible_pair_like<pair> _UPair>
542 requires (_S_constructible_from_pair_like<_UPair>())
543 && (!_S_dangles_from_pair_like<_UPair>())
544 constexpr explicit(!_S_convertible_from_pair_like<_UPair>())
545 pair(_UPair&& __p)
546 : first(std::get<0>(std::forward<_UPair>(__p))),
547 second(std::get<1>(std::forward<_UPair>(__p)))
548 { }
549
550 template<__eligible_pair_like<pair> _UPair>
551 requires (_S_constructible_from_pair_like<_UPair>())
552 && (_S_dangles_from_pair_like<_UPair>())
553 constexpr explicit(!_S_convertible_from_pair_like<_UPair>())
554 pair(_UPair&&) = delete;
555#endif // C++23
556
557 private:
558 /// @cond undocumented
559 template<typename _U1, typename _U2>
560 static constexpr bool
561 _S_assignable()
562 {
563 if constexpr (is_assignable_v<_T1&, _U1>)
564 return is_assignable_v<_T2&, _U2>;
565 return false;
566 }
567
568 template<typename _U1, typename _U2>
569 static constexpr bool
570 _S_const_assignable()
571 {
572 if constexpr (is_assignable_v<const _T1&, _U1>)
573 return is_assignable_v<const _T2&, _U2>;
574 return false;
575 }
576
577 template<typename _U1, typename _U2>
578 static constexpr bool
579 _S_nothrow_assignable()
580 {
581 if constexpr (is_nothrow_assignable_v<_T1&, _U1>)
582 return is_nothrow_assignable_v<_T2&, _U2>;
583 return false;
584 }
585
586#if __glibcxx_tuple_like // >= C++23
587 template<typename _UPair>
588 static constexpr bool
589 _S_assignable_from_tuple_like()
590 {
591 return _S_assignable<decltype(std::get<0>(std::declval<_UPair>())),
592 decltype(std::get<1>(std::declval<_UPair>()))>();
593 }
594
595 template<typename _UPair>
596 static constexpr bool
597 _S_const_assignable_from_tuple_like()
598 {
599 return _S_const_assignable<decltype(std::get<0>(std::declval<_UPair>())),
600 decltype(std::get<1>(std::declval<_UPair>()))>();
601 }
602#endif // C++23
603 /// @endcond
604
605 public:
606
607 pair& operator=(const pair&) = delete;
608
609 /// Copy assignment operator
610 constexpr pair&
611 operator=(const pair& __p)
612 noexcept(_S_nothrow_assignable<const _T1&, const _T2&>())
613 requires (_S_assignable<const _T1&, const _T2&>())
614 {
615 first = __p.first;
616 second = __p.second;
617 return *this;
618 }
619
620 /// Move assignment operator
621 constexpr pair&
622 operator=(pair&& __p)
623 noexcept(_S_nothrow_assignable<_T1, _T2>())
624 requires (_S_assignable<_T1, _T2>())
625 {
626 first = std::forward<first_type>(__p.first);
627 second = std::forward<second_type>(__p.second);
628 return *this;
629 }
630
631 /// Converting assignment from a const `pair<U1, U2>` lvalue
632 template<typename _U1, typename _U2>
633 constexpr pair&
634 operator=(const pair<_U1, _U2>& __p)
635 noexcept(_S_nothrow_assignable<const _U1&, const _U2&>())
636 requires (_S_assignable<const _U1&, const _U2&>())
637 {
638 first = __p.first;
639 second = __p.second;
640 return *this;
641 }
642
643 /// Converting assignment from a non-const `pair<U1, U2>` rvalue
644 template<typename _U1, typename _U2>
645 constexpr pair&
646 operator=(pair<_U1, _U2>&& __p)
647 noexcept(_S_nothrow_assignable<_U1, _U2>())
648 requires (_S_assignable<_U1, _U2>())
649 {
650 first = std::forward<_U1>(__p.first);
651 second = std::forward<_U2>(__p.second);
652 return *this;
653 }
654
655#if __glibcxx_ranges_zip // >= C++23
656 /// Copy assignment operator (const)
657 constexpr const pair&
658 operator=(const pair& __p) const
659 requires (_S_const_assignable<const first_type&, const second_type&>())
660 {
661 first = __p.first;
662 second = __p.second;
663 return *this;
664 }
665
666 /// Move assignment operator (const)
667 constexpr const pair&
668 operator=(pair&& __p) const
669 requires (_S_const_assignable<first_type, second_type>())
670 {
671 first = std::forward<first_type>(__p.first);
672 second = std::forward<second_type>(__p.second);
673 return *this;
674 }
675
676 /// Converting assignment from a const `pair<U1, U2>` lvalue
677 template<typename _U1, typename _U2>
678 constexpr const pair&
679 operator=(const pair<_U1, _U2>& __p) const
680 requires (_S_const_assignable<const _U1&, const _U2&>())
681 {
682 first = __p.first;
683 second = __p.second;
684 return *this;
685 }
686
687 /// Converting assignment from a non-const `pair<U1, U2>` rvalue
688 template<typename _U1, typename _U2>
689 constexpr const pair&
690 operator=(pair<_U1, _U2>&& __p) const
691 requires (_S_const_assignable<_U1, _U2>())
692 {
693 first = std::forward<_U1>(__p.first);
694 second = std::forward<_U2>(__p.second);
695 return *this;
696 }
697#endif // C++23
698
699#if __glibcxx_tuple_like // >= C++23
700 template<__eligible_pair_like<pair> _UPair>
701 requires (_S_assignable_from_tuple_like<_UPair>())
702 constexpr pair&
703 operator=(_UPair&& __p)
704 {
705 first = std::get<0>(std::forward<_UPair>(__p));
706 second = std::get<1>(std::forward<_UPair>(__p));
707 return *this;
708 }
709
710 template<__eligible_pair_like<pair> _UPair>
711 requires (_S_const_assignable_from_tuple_like<_UPair>())
712 constexpr const pair&
713 operator=(_UPair&& __p) const
714 {
715 first = std::get<0>(std::forward<_UPair>(__p));
716 second = std::get<1>(std::forward<_UPair>(__p));
717 return *this;
718 }
719#endif // C++23
720
721#else // !__cpp_lib_concepts
722 // C++11/14/17 implementation using enable_if, partially constexpr.
723
724 /// @cond undocumented
725 // Error if construction from _U1 and _U2 would create a dangling ref.
726#if __has_builtin(__reference_constructs_from_temporary) \
727 && defined _GLIBCXX_DEBUG
728# define __glibcxx_no_dangling_refs(_U1, _U2) \
729 static_assert(!__reference_constructs_from_temporary(_T1, _U1) \
730 && !__reference_constructs_from_temporary(_T2, _U2), \
731 "std::pair constructor creates a dangling reference")
732#else
733# define __glibcxx_no_dangling_refs(_U1, _U2)
734#endif
735 /// @endcond
736
737 /** The default constructor creates @c first and @c second using their
738 * respective default constructors. */
739 template <typename _U1 = _T1,
740 typename _U2 = _T2,
741 typename enable_if<__and_<
742 __is_implicitly_default_constructible<_U1>,
743 __is_implicitly_default_constructible<_U2>>
744 ::value, bool>::type = true>
745 constexpr pair()
746 : first(), second() { }
747
748 template <typename _U1 = _T1,
749 typename _U2 = _T2,
750 typename enable_if<__and_<
751 is_default_constructible<_U1>,
752 is_default_constructible<_U2>,
753 __not_<
754 __and_<__is_implicitly_default_constructible<_U1>,
755 __is_implicitly_default_constructible<_U2>>>>
756 ::value, bool>::type = false>
757 explicit constexpr pair()
758 : first(), second() { }
759
760 // Shortcut for constraining the templates that don't take pairs.
761 /// @cond undocumented
762 using _PCCP = _PCC<true, _T1, _T2>;
763 /// @endcond
764
765 /// Construct from two const lvalues, allowing implicit conversions.
766 template<typename _U1 = _T1, typename _U2=_T2, typename
767 enable_if<_PCCP::template
768 _ConstructiblePair<_U1, _U2>()
769 && _PCCP::template
770 _ImplicitlyConvertiblePair<_U1, _U2>(),
771 bool>::type=true>
772 constexpr pair(const _T1& __a, const _T2& __b)
773 : first(__a), second(__b) { }
774
775 /// Construct from two const lvalues, disallowing implicit conversions.
776 template<typename _U1 = _T1, typename _U2=_T2, typename
777 enable_if<_PCCP::template
778 _ConstructiblePair<_U1, _U2>()
779 && !_PCCP::template
780 _ImplicitlyConvertiblePair<_U1, _U2>(),
781 bool>::type=false>
782 explicit constexpr pair(const _T1& __a, const _T2& __b)
783 : first(__a), second(__b) { }
784
785 // Shortcut for constraining the templates that take pairs.
786 /// @cond undocumented
787 template <typename _U1, typename _U2>
788 using _PCCFP = _PCC<!is_same<_T1, _U1>::value
789 || !is_same<_T2, _U2>::value,
790 _T1, _T2>;
791 /// @endcond
792
793 template<typename _U1, typename _U2, typename
794 enable_if<_PCCFP<_U1, _U2>::template
795 _ConstructiblePair<_U1, _U2>()
796 && _PCCFP<_U1, _U2>::template
797 _ImplicitlyConvertiblePair<_U1, _U2>(),
798 bool>::type=true>
799 constexpr pair(const pair<_U1, _U2>& __p)
800 : first(__p.first), second(__p.second)
801 { __glibcxx_no_dangling_refs(const _U1&, const _U2&); }
802
803 template<typename _U1, typename _U2, typename
804 enable_if<_PCCFP<_U1, _U2>::template
805 _ConstructiblePair<_U1, _U2>()
806 && !_PCCFP<_U1, _U2>::template
807 _ImplicitlyConvertiblePair<_U1, _U2>(),
808 bool>::type=false>
809 explicit constexpr pair(const pair<_U1, _U2>& __p)
810 : first(__p.first), second(__p.second)
811 { __glibcxx_no_dangling_refs(const _U1&, const _U2&); }
812
813#if _GLIBCXX_USE_DEPRECATED
814#if defined(__DEPRECATED)
815# define _GLIBCXX_DEPRECATED_PAIR_CTOR \
816 __attribute__ ((__deprecated__ ("use 'nullptr' instead of '0' to " \
817 "initialize std::pair of move-only " \
818 "type and pointer")))
819#else
820# define _GLIBCXX_DEPRECATED_PAIR_CTOR
821#endif
822
823 private:
824 /// @cond undocumented
825
826 // A type which can be constructed from literal zero, but not nullptr
827 struct __zero_as_null_pointer_constant
828 {
829 __zero_as_null_pointer_constant(int __zero_as_null_pointer_constant::*)
830 { }
831 template<typename _Tp,
832 typename = __enable_if_t<is_null_pointer<_Tp>::value>>
833 __zero_as_null_pointer_constant(_Tp) = delete;
834 };
835 /// @endcond
836 public:
837
838 // Deprecated extensions to DR 811.
839 // These allow construction from an rvalue and a literal zero,
840 // in cases where the standard says the zero should be deduced as int
841 template<typename _U1,
842 __enable_if_t<__and_<__not_<is_reference<_U1>>,
843 is_pointer<_T2>,
844 is_constructible<_T1, _U1>,
845 __not_<is_constructible<_T1, const _U1&>>,
846 is_convertible<_U1, _T1>>::value,
847 bool> = true>
848 _GLIBCXX_DEPRECATED_PAIR_CTOR
849 constexpr
850 pair(_U1&& __x, __zero_as_null_pointer_constant, ...)
851 : first(std::forward<_U1>(__x)), second(nullptr)
852 { __glibcxx_no_dangling_refs(_U1&&, std::nullptr_t); }
853
854 template<typename _U1,
855 __enable_if_t<__and_<__not_<is_reference<_U1>>,
856 is_pointer<_T2>,
857 is_constructible<_T1, _U1>,
858 __not_<is_constructible<_T1, const _U1&>>,
859 __not_<is_convertible<_U1, _T1>>>::value,
860 bool> = false>
861 _GLIBCXX_DEPRECATED_PAIR_CTOR
862 explicit constexpr
863 pair(_U1&& __x, __zero_as_null_pointer_constant, ...)
864 : first(std::forward<_U1>(__x)), second(nullptr)
865 { __glibcxx_no_dangling_refs(_U1&&, std::nullptr_t); }
866
867 template<typename _U2,
868 __enable_if_t<__and_<is_pointer<_T1>,
869 __not_<is_reference<_U2>>,
870 is_constructible<_T2, _U2>,
871 __not_<is_constructible<_T2, const _U2&>>,
872 is_convertible<_U2, _T2>>::value,
873 bool> = true>
874 _GLIBCXX_DEPRECATED_PAIR_CTOR
875 constexpr
876 pair(__zero_as_null_pointer_constant, _U2&& __y, ...)
877 : first(nullptr), second(std::forward<_U2>(__y))
878 { __glibcxx_no_dangling_refs(std::nullptr_t, _U2&&); }
879
880 template<typename _U2,
881 __enable_if_t<__and_<is_pointer<_T1>,
882 __not_<is_reference<_U2>>,
883 is_constructible<_T2, _U2>,
884 __not_<is_constructible<_T2, const _U2&>>,
885 __not_<is_convertible<_U2, _T2>>>::value,
886 bool> = false>
887 _GLIBCXX_DEPRECATED_PAIR_CTOR
888 explicit constexpr
889 pair(__zero_as_null_pointer_constant, _U2&& __y, ...)
890 : first(nullptr), second(std::forward<_U2>(__y))
891 { __glibcxx_no_dangling_refs(std::nullptr_t, _U2&&); }
892#undef _GLIBCXX_DEPRECATED_PAIR_CTOR
893#endif
894
895 template<typename _U1, typename _U2, typename
896 enable_if<_PCCP::template
897 _MoveConstructiblePair<_U1, _U2>()
898 && _PCCP::template
899 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
900 bool>::type=true>
901 constexpr pair(_U1&& __x, _U2&& __y)
902 : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
903 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
904
905 template<typename _U1, typename _U2, typename
906 enable_if<_PCCP::template
907 _MoveConstructiblePair<_U1, _U2>()
908 && !_PCCP::template
909 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
910 bool>::type=false>
911 explicit constexpr pair(_U1&& __x, _U2&& __y)
912 : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
913 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
914
915
916 template<typename _U1, typename _U2, typename
917 enable_if<_PCCFP<_U1, _U2>::template
918 _MoveConstructiblePair<_U1, _U2>()
919 && _PCCFP<_U1, _U2>::template
920 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
921 bool>::type=true>
922 constexpr pair(pair<_U1, _U2>&& __p)
923 : first(std::forward<_U1>(__p.first)),
924 second(std::forward<_U2>(__p.second))
925 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
926
927 template<typename _U1, typename _U2, typename
928 enable_if<_PCCFP<_U1, _U2>::template
929 _MoveConstructiblePair<_U1, _U2>()
930 && !_PCCFP<_U1, _U2>::template
931 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
932 bool>::type=false>
933 explicit constexpr pair(pair<_U1, _U2>&& __p)
934 : first(std::forward<_U1>(__p.first)),
935 second(std::forward<_U2>(__p.second))
936 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
937
938#undef __glibcxx_no_dangling_refs
939
940 pair&
941 operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
942 is_copy_assignable<_T2>>::value,
943 const pair&, const __nonesuch&> __p)
944 {
945 first = __p.first;
946 second = __p.second;
947 return *this;
948 }
949
950 pair&
951 operator=(__conditional_t<__and_<is_move_assignable<_T1>,
952 is_move_assignable<_T2>>::value,
953 pair&&, __nonesuch&&> __p)
954 noexcept(__and_<is_nothrow_move_assignable<_T1>,
955 is_nothrow_move_assignable<_T2>>::value)
956 {
957 first = std::forward<first_type>(__p.first);
958 second = std::forward<second_type>(__p.second);
959 return *this;
960 }
961
962 template<typename _U1, typename _U2>
963 typename enable_if<__and_<is_assignable<_T1&, const _U1&>,
964 is_assignable<_T2&, const _U2&>>::value,
965 pair&>::type
966 operator=(const pair<_U1, _U2>& __p)
967 {
968 first = __p.first;
969 second = __p.second;
970 return *this;
971 }
972
973 template<typename _U1, typename _U2>
974 typename enable_if<__and_<is_assignable<_T1&, _U1&&>,
975 is_assignable<_T2&, _U2&&>>::value,
976 pair&>::type
977 operator=(pair<_U1, _U2>&& __p)
978 {
979 first = std::forward<_U1>(__p.first);
980 second = std::forward<_U2>(__p.second);
981 return *this;
982 }
983#endif // lib concepts
984#else
985 // C++03 implementation
986
987 // _GLIBCXX_RESOLVE_LIB_DEFECTS
988 // 265. std::pair::pair() effects overly restrictive
989 /** The default constructor creates @c first and @c second using their
990 * respective default constructors. */
991 pair() : first(), second() { }
992
993 /// Two objects may be passed to a `pair` constructor to be copied.
994 pair(const _T1& __a, const _T2& __b)
995 : first(__a), second(__b) { }
996
997 /// Templated constructor to convert from other pairs.
998 template<typename _U1, typename _U2>
999 pair(const pair<_U1, _U2>& __p)
1000 : first(__p.first), second(__p.second)
1001 {
1002#if __has_builtin(__reference_constructs_from_temporary)
1003#pragma GCC diagnostic push
1004#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
1005 typedef int _DanglingCheck1[
1006 __reference_constructs_from_temporary(_T1, const _U1&) ? -1 : 1
1007 ];
1008 typedef int _DanglingCheck2[
1009 __reference_constructs_from_temporary(_T2, const _U2&) ? -1 : 1
1010 ];
1011#pragma GCC diagnostic pop
1012#endif
1013 }
1014#endif // C++11
1015 };
1016
1017 /// @relates pair @{
1018
1019#if __cpp_deduction_guides >= 201606
1020 template<typename _T1, typename _T2> pair(_T1, _T2) -> pair<_T1, _T2>;
1021#endif
1022
1023#if __cpp_lib_three_way_comparison
1024 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1025 // 3865. Sorting a range of pairs
1026
1027 /// Two pairs are equal iff their members are equal.
1028 template<typename _T1, typename _T2, typename _U1, typename _U2>
1029 [[nodiscard]]
1030 constexpr bool
1031 operator==(const pair<_T1, _T2>& __x, const pair<_U1, _U2>& __y)
1032 requires requires {
1033 { __x.first == __y.first } -> __detail::__boolean_testable;
1034 { __x.second == __y.second } -> __detail::__boolean_testable;
1035 }
1036 { return __x.first == __y.first && __x.second == __y.second; }
1037
1038 /** Defines a lexicographical order for pairs.
1039 *
1040 * For two pairs of comparable types, `P` is ordered before `Q` if
1041 * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
1042 * are equivalent (neither is less than the other) and `P.second` is
1043 * less than `Q.second`.
1044 */
1045 template<typename _T1, typename _T2, typename _U1, typename _U2>
1046 [[nodiscard]]
1047 constexpr common_comparison_category_t<__detail::__synth3way_t<_T1, _U1>,
1048 __detail::__synth3way_t<_T2, _U2>>
1049 operator<=>(const pair<_T1, _T2>& __x, const pair<_U1, _U2>& __y)
1050 {
1051 if (auto __c = __detail::__synth3way(__x.first, __y.first); __c != 0)
1052 return __c;
1053 return __detail::__synth3way(__x.second, __y.second);
1054 }
1055#else
1056 /// Two pairs of the same type are equal iff their members are equal.
1057 template<typename _T1, typename _T2>
1058 _GLIBCXX_NODISCARD
1059 inline _GLIBCXX_CONSTEXPR bool
1060 operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1061 { return __x.first == __y.first && __x.second == __y.second; }
1062
1063 /** Defines a lexicographical order for pairs.
1064 *
1065 * For two pairs of the same type, `P` is ordered before `Q` if
1066 * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
1067 * are equivalent (neither is less than the other) and `P.second` is less
1068 * than `Q.second`.
1069 */
1070 template<typename _T1, typename _T2>
1071 _GLIBCXX_NODISCARD
1072 inline _GLIBCXX_CONSTEXPR bool
1073 operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1074 { return __x.first < __y.first
1075 || (!(__y.first < __x.first) && __x.second < __y.second); }
1076
1077 /// Uses @c operator== to find the result.
1078 template<typename _T1, typename _T2>
1079 _GLIBCXX_NODISCARD
1080 inline _GLIBCXX_CONSTEXPR bool
1081 operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1082 { return !(__x == __y); }
1083
1084 /// Uses @c operator< to find the result.
1085 template<typename _T1, typename _T2>
1086 _GLIBCXX_NODISCARD
1087 inline _GLIBCXX_CONSTEXPR bool
1088 operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1089 { return __y < __x; }
1090
1091 /// Uses @c operator< to find the result.
1092 template<typename _T1, typename _T2>
1093 _GLIBCXX_NODISCARD
1094 inline _GLIBCXX_CONSTEXPR bool
1095 operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1096 { return !(__y < __x); }
1097
1098 /// Uses @c operator< to find the result.
1099 template<typename _T1, typename _T2>
1100 _GLIBCXX_NODISCARD
1101 inline _GLIBCXX_CONSTEXPR bool
1102 operator>=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1103 { return !(__x < __y); }
1104#endif // !(three_way_comparison && concepts)
1105
1106#if __cplusplus >= 201103L
1107 /** Swap overload for pairs. Calls std::pair::swap().
1108 *
1109 * @note This std::swap overload is not declared in C++03 mode,
1110 * which has performance implications, e.g. see https://gcc.gnu.org/PR38466
1111 */
1112 template<typename _T1, typename _T2>
1113 _GLIBCXX20_CONSTEXPR inline
1114#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1115 // Constrained free swap overload, see p0185r1
1116 typename enable_if<__and_<__is_swappable<_T1>,
1117 __is_swappable<_T2>>::value>::type
1118#else
1119 void
1120#endif
1121 swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
1122 noexcept(noexcept(__x.swap(__y)))
1123 { __x.swap(__y); }
1124
1125#if __glibcxx_ranges_zip // >= C++23
1126 template<typename _T1, typename _T2>
1127 requires is_swappable_v<const _T1> && is_swappable_v<const _T2>
1128 constexpr void
1129 swap(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1130 noexcept(noexcept(__x.swap(__y)))
1131 { __x.swap(__y); }
1132#endif // C++23
1133
1134#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1135 template<typename _T1, typename _T2>
1136 typename enable_if<!__and_<__is_swappable<_T1>,
1137 __is_swappable<_T2>>::value>::type
1138 swap(pair<_T1, _T2>&, pair<_T1, _T2>&) = delete;
1139#endif
1140#endif // __cplusplus >= 201103L
1141
1142 /// @} relates pair
1143
1144 /**
1145 * @brief A convenience wrapper for creating a pair from two objects.
1146 * @param __x The first object.
1147 * @param __y The second object.
1148 * @return A newly-constructed pair<> object of the appropriate type.
1149 *
1150 * The C++98 standard says the objects are passed by reference-to-const,
1151 * but C++03 says they are passed by value (this was LWG issue #181).
1152 *
1153 * Since C++11 they have been passed by forwarding reference and then
1154 * forwarded to the new members of the pair. To create a pair with a
1155 * member of reference type, pass a `reference_wrapper` to this function.
1156 */
1157 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1158 // 181. make_pair() unintended behavior
1159#if __cplusplus >= 201103L
1160 // NB: DR 706.
1161 template<typename _T1, typename _T2>
1162 constexpr pair<typename __decay_and_strip<_T1>::__type,
1163 typename __decay_and_strip<_T2>::__type>
1164 make_pair(_T1&& __x, _T2&& __y)
1165 {
1166 typedef typename __decay_and_strip<_T1>::__type __ds_type1;
1167 typedef typename __decay_and_strip<_T2>::__type __ds_type2;
1168 typedef pair<__ds_type1, __ds_type2> __pair_type;
1169 return __pair_type(std::forward<_T1>(__x), std::forward<_T2>(__y));
1170 }
1171#else
1172 template<typename _T1, typename _T2>
1173 inline pair<_T1, _T2>
1174 make_pair(_T1 __x, _T2 __y)
1175 { return pair<_T1, _T2>(__x, __y); }
1176#endif
1177
1178 /// @}
1179
1180#if __cplusplus >= 201103L
1181 // Various functions which give std::pair a tuple-like interface.
1182
1183 /// @cond undocumented
1184 template<typename _T1, typename _T2>
1185 struct __is_tuple_like_impl<pair<_T1, _T2>> : true_type
1186 { };
1187 /// @endcond
1188
1189 /// Partial specialization for std::pair
1190 template<class _Tp1, class _Tp2>
1191 struct tuple_size<pair<_Tp1, _Tp2>>
1192 : public integral_constant<size_t, 2> { };
1193
1194 /// Partial specialization for std::pair
1195 template<class _Tp1, class _Tp2>
1196 struct tuple_element<0, pair<_Tp1, _Tp2>>
1197 { typedef _Tp1 type; };
1198
1199 /// Partial specialization for std::pair
1200 template<class _Tp1, class _Tp2>
1201 struct tuple_element<1, pair<_Tp1, _Tp2>>
1202 { typedef _Tp2 type; };
1203
1204#if __cplusplus >= 201703L
1205 template<typename _Tp1, typename _Tp2>
1206 inline constexpr size_t tuple_size_v<pair<_Tp1, _Tp2>> = 2;
1207
1208 template<typename _Tp1, typename _Tp2>
1209 inline constexpr size_t tuple_size_v<const pair<_Tp1, _Tp2>> = 2;
1210#endif
1211
1212#if __cplusplus >= 201103L
1213#pragma GCC diagnostic push
1214#pragma GCC diagnostic ignored "-Wc++14-extensions" // variable templates
1215#pragma GCC diagnostic ignored "-Wc++17-extensions" // inline variables
1216 template<typename _Tp>
1217 inline constexpr bool __is_pair = false;
1218
1219 template<typename _Tp, typename _Up>
1220 inline constexpr bool __is_pair<pair<_Tp, _Up>> = true;
1221#pragma GCC diagnostic pop
1222#endif
1223
1224 /// @cond undocumented
1225 template<size_t _Int>
1226 struct __pair_get;
1227
1228 template<>
1229 struct __pair_get<0>
1230 {
1231 template<typename _Tp1, typename _Tp2>
1232 static constexpr _Tp1&
1233 __get(pair<_Tp1, _Tp2>& __pair) noexcept
1234 { return __pair.first; }
1235
1236 template<typename _Tp1, typename _Tp2>
1237 static constexpr _Tp1&&
1238 __move_get(pair<_Tp1, _Tp2>&& __pair) noexcept
1239 { return std::forward<_Tp1>(__pair.first); }
1240
1241 template<typename _Tp1, typename _Tp2>
1242 static constexpr const _Tp1&
1243 __const_get(const pair<_Tp1, _Tp2>& __pair) noexcept
1244 { return __pair.first; }
1245
1246 template<typename _Tp1, typename _Tp2>
1247 static constexpr const _Tp1&&
1248 __const_move_get(const pair<_Tp1, _Tp2>&& __pair) noexcept
1249 { return std::forward<const _Tp1>(__pair.first); }
1250 };
1251
1252 template<>
1253 struct __pair_get<1>
1254 {
1255 template<typename _Tp1, typename _Tp2>
1256 static constexpr _Tp2&
1257 __get(pair<_Tp1, _Tp2>& __pair) noexcept
1258 { return __pair.second; }
1259
1260 template<typename _Tp1, typename _Tp2>
1261 static constexpr _Tp2&&
1262 __move_get(pair<_Tp1, _Tp2>&& __pair) noexcept
1263 { return std::forward<_Tp2>(__pair.second); }
1264
1265 template<typename _Tp1, typename _Tp2>
1266 static constexpr const _Tp2&
1267 __const_get(const pair<_Tp1, _Tp2>& __pair) noexcept
1268 { return __pair.second; }
1269
1270 template<typename _Tp1, typename _Tp2>
1271 static constexpr const _Tp2&&
1272 __const_move_get(const pair<_Tp1, _Tp2>&& __pair) noexcept
1273 { return std::forward<const _Tp2>(__pair.second); }
1274 };
1275 /// @endcond
1276
1277 /** @{
1278 * std::get overloads for accessing members of std::pair
1279 */
1280
1281 template<size_t _Int, class _Tp1, class _Tp2>
1282 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
1283 get(pair<_Tp1, _Tp2>& __in) noexcept
1284 { return __pair_get<_Int>::__get(__in); }
1285
1286 template<size_t _Int, class _Tp1, class _Tp2>
1287 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
1288 get(pair<_Tp1, _Tp2>&& __in) noexcept
1289 { return __pair_get<_Int>::__move_get(std::move(__in)); }
1290
1291 template<size_t _Int, class _Tp1, class _Tp2>
1292 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
1293 get(const pair<_Tp1, _Tp2>& __in) noexcept
1294 { return __pair_get<_Int>::__const_get(__in); }
1295
1296 template<size_t _Int, class _Tp1, class _Tp2>
1297 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
1298 get(const pair<_Tp1, _Tp2>&& __in) noexcept
1299 { return __pair_get<_Int>::__const_move_get(std::move(__in)); }
1300
1301
1302#ifdef __glibcxx_tuples_by_type // C++ >= 14
1303 template <typename _Tp, typename _Up>
1304 constexpr _Tp&
1305 get(pair<_Tp, _Up>& __p) noexcept
1306 { return __p.first; }
1307
1308 template <typename _Tp, typename _Up>
1309 constexpr const _Tp&
1310 get(const pair<_Tp, _Up>& __p) noexcept
1311 { return __p.first; }
1312
1313 template <typename _Tp, typename _Up>
1314 constexpr _Tp&&
1315 get(pair<_Tp, _Up>&& __p) noexcept
1316 { return std::forward<_Tp>(__p.first); }
1317
1318 template <typename _Tp, typename _Up>
1319 constexpr const _Tp&&
1320 get(const pair<_Tp, _Up>&& __p) noexcept
1321 { return std::forward<const _Tp>(__p.first); }
1322
1323 template <typename _Tp, typename _Up>
1324 constexpr _Tp&
1325 get(pair<_Up, _Tp>& __p) noexcept
1326 { return __p.second; }
1327
1328 template <typename _Tp, typename _Up>
1329 constexpr const _Tp&
1330 get(const pair<_Up, _Tp>& __p) noexcept
1331 { return __p.second; }
1332
1333 template <typename _Tp, typename _Up>
1334 constexpr _Tp&&
1335 get(pair<_Up, _Tp>&& __p) noexcept
1336 { return std::forward<_Tp>(__p.second); }
1337
1338 template <typename _Tp, typename _Up>
1339 constexpr const _Tp&&
1340 get(const pair<_Up, _Tp>&& __p) noexcept
1341 { return std::forward<const _Tp>(__p.second); }
1342#endif // __glibcxx_tuples_by_type
1343
1344
1345#if __glibcxx_ranges_zip // >= C++23
1346 template<typename _T1, typename _T2, typename _U1, typename _U2,
1347 template<typename> class _TQual, template<typename> class _UQual>
1348 requires requires { typename pair<common_reference_t<_TQual<_T1>, _UQual<_U1>>,
1349 common_reference_t<_TQual<_T2>, _UQual<_U2>>>; }
1350 struct basic_common_reference<pair<_T1, _T2>, pair<_U1, _U2>, _TQual, _UQual>
1351 {
1352 using type = pair<common_reference_t<_TQual<_T1>, _UQual<_U1>>,
1353 common_reference_t<_TQual<_T2>, _UQual<_U2>>>;
1354 };
1355
1356 template<typename _T1, typename _T2, typename _U1, typename _U2>
1357 requires requires { typename pair<common_type_t<_T1, _U1>, common_type_t<_T2, _U2>>; }
1358 struct common_type<pair<_T1, _T2>, pair<_U1, _U2>>
1359 { using type = pair<common_type_t<_T1, _U1>, common_type_t<_T2, _U2>>; };
1360#endif // C++23
1361
1362 /// @}
1363#endif // C++11
1364
1365_GLIBCXX_END_NAMESPACE_VERSION
1366} // namespace std
1367
1368#endif /* _STL_PAIR_H */
1369