1// Pair implementation -*- C++ -*-
2
3// Copyright (C) 2001-2026 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<size_t _Int, class _Tp1, class _Tp2>
105 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
106 get(pair<_Tp1, _Tp2>& __in) noexcept;
107
108 template<size_t _Int, class _Tp1, class _Tp2>
109 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
110 get(pair<_Tp1, _Tp2>&& __in) noexcept;
111
112 template<size_t _Int, class _Tp1, class _Tp2>
113 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
114 get(const pair<_Tp1, _Tp2>& __in) noexcept;
115
116 template<size_t _Int, class _Tp1, class _Tp2>
117 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
118 get(const pair<_Tp1, _Tp2>&& __in) noexcept;
119
120 template<size_t __i, typename... _Elements>
121 constexpr __tuple_element_t<__i, tuple<_Elements...>>&
122 get(tuple<_Elements...>& __t) noexcept;
123
124 template<size_t __i, typename... _Elements>
125 constexpr const __tuple_element_t<__i, tuple<_Elements...>>&
126 get(const tuple<_Elements...>& __t) noexcept;
127
128 template<size_t __i, typename... _Elements>
129 constexpr __tuple_element_t<__i, tuple<_Elements...>>&&
130 get(tuple<_Elements...>&& __t) noexcept;
131
132 template<size_t __i, typename... _Elements>
133 constexpr const __tuple_element_t<__i, tuple<_Elements...>>&&
134 get(const tuple<_Elements...>&& __t) noexcept;
135
136 template<size_t _Int, typename _Tp, size_t _Nm>
137 constexpr _Tp&
138 get(array<_Tp, _Nm>&) noexcept;
139
140 template<size_t _Int, typename _Tp, size_t _Nm>
141 constexpr _Tp&&
142 get(array<_Tp, _Nm>&&) noexcept;
143
144 template<size_t _Int, typename _Tp, size_t _Nm>
145 constexpr const _Tp&
146 get(const array<_Tp, _Nm>&) noexcept;
147
148 template<size_t _Int, typename _Tp, size_t _Nm>
149 constexpr const _Tp&&
150 get(const array<_Tp, _Nm>&&) noexcept;
151
152#if __glibcxx_tuple_like >= 202311 // >= C++26
153 template<typename _Tp>
154 class complex;
155
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 /// @endcond
237#endif // C++11
238
239 /// @cond undocumented
240
241#if __glibcxx_tuple_like // >= C++23
242 template<typename _Tp>
243 inline constexpr bool __is_tuple_v = false;
244
245 template<typename... _Ts>
246 inline constexpr bool __is_tuple_v<tuple<_Ts...>> = true;
247
248 // TODO: Reuse __is_tuple_like from <type_traits>?
249 template<typename _Tp>
250 inline constexpr bool __is_tuple_like_v = false;
251
252 template<typename... _Elements>
253 inline constexpr bool __is_tuple_like_v<tuple<_Elements...>> = true;
254
255 template<typename _T1, typename _T2>
256 inline constexpr bool __is_tuple_like_v<pair<_T1, _T2>> = true;
257
258 template<typename _Tp, size_t _Nm>
259 inline constexpr bool __is_tuple_like_v<array<_Tp, _Nm>> = true;
260
261 // __is_tuple_like_v<subrange> is defined in <bits/ranges_util.h>.
262
263 template<typename _Tp>
264 concept __tuple_like = __is_tuple_like_v<remove_cvref_t<_Tp>>;
265
266 template<typename _Tp>
267 concept __pair_like = __tuple_like<_Tp> && tuple_size_v<remove_cvref_t<_Tp>> == 2;
268
269 template<typename _Tp, typename _Tuple>
270 concept __eligible_tuple_like
271 = __detail::__different_from<_Tp, _Tuple> && __tuple_like<_Tp>
272 && (tuple_size_v<remove_cvref_t<_Tp>> == tuple_size_v<_Tuple>)
273 && !ranges::__detail::__is_subrange<remove_cvref_t<_Tp>>;
274
275 template<typename _Tp, typename _Pair>
276 concept __eligible_pair_like
277 = __detail::__different_from<_Tp, _Pair> && __pair_like<_Tp>
278 && !ranges::__detail::__is_subrange<remove_cvref_t<_Tp>>;
279#endif // C++23
280
281 template<typename _U1, typename _U2> class __pair_base
282 {
283#if __cplusplus >= 201103L && ! __cpp_lib_concepts
284 template<typename _T1, typename _T2> friend struct pair;
285 __pair_base() = default;
286 ~__pair_base() = default;
287 __pair_base(const __pair_base&) = default;
288 __pair_base& operator=(const __pair_base&) = delete;
289#endif // C++11
290 };
291
292 /// @endcond
293
294 /**
295 * @brief Struct holding two objects (or references) of arbitrary type.
296 *
297 * @tparam _T1 Type of the `first` member.
298 * @tparam _T2 Type of the `second` member.
299 *
300 * <https://gcc.gnu.org/onlinedocs/libstdc++/manual/utilities.html>
301 *
302 * @headerfile utility
303 */
304 template<typename _T1, typename _T2>
305 struct pair
306 : public __pair_base<_T1, _T2>
307 {
308 typedef _T1 first_type; ///< The type of the `first` member
309 typedef _T2 second_type; ///< The type of the `second` member
310
311 _T1 first; ///< The first member
312 _T2 second; ///< The second member
313
314#if __cplusplus >= 201103L
315 constexpr pair(const pair&) = default; ///< Copy constructor
316 constexpr pair(pair&&) = default; ///< Move constructor
317
318 template<typename... _Args1, typename... _Args2>
319 _GLIBCXX20_CONSTEXPR
320 pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
321
322 /// Swap the first members and then the second members.
323 _GLIBCXX20_CONSTEXPR void
324 swap(pair& __p)
325 noexcept(__and_<__is_nothrow_swappable<_T1>,
326 __is_nothrow_swappable<_T2>>::value)
327 {
328 using std::swap;
329 swap(first, __p.first);
330 swap(second, __p.second);
331 }
332
333#if __glibcxx_ranges_zip // >= C++23
334 // As an extension, we constrain the const swap member function in order
335 // to continue accepting explicit instantiation of pairs whose elements
336 // are not all const swappable. Without this constraint, such an
337 // explicit instantiation would also instantiate the ill-formed body of
338 // this function and yield a hard error. This constraint shouldn't
339 // affect the behavior of valid programs.
340 constexpr void
341 swap(const pair& __p) const
342 noexcept(__and_v<__is_nothrow_swappable<const _T1>,
343 __is_nothrow_swappable<const _T2>>)
344 requires is_swappable_v<const _T1> && is_swappable_v<const _T2>
345 {
346 using std::swap;
347 swap(first, __p.first);
348 swap(second, __p.second);
349 }
350#endif // C++23
351
352 private:
353 template<typename... _Args1, size_t... _Indexes1,
354 typename... _Args2, size_t... _Indexes2>
355 _GLIBCXX20_CONSTEXPR
356 pair(tuple<_Args1...>&, tuple<_Args2...>&,
357 _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
358 public:
359
360#if __cpp_lib_concepts
361 // C++20 implementation using concepts, explicit(bool), fully constexpr.
362
363 /// Default constructor
364 constexpr
365 explicit(__not_<__and_<__is_implicitly_default_constructible<_T1>,
366 __is_implicitly_default_constructible<_T2>>>())
367 pair()
368 noexcept(is_nothrow_default_constructible_v<_T1>
369 && is_nothrow_default_constructible_v<_T2>)
370 requires is_default_constructible_v<_T1>
371 && is_default_constructible_v<_T2>
372 : first(), second()
373 { }
374
375 private:
376
377 /// @cond undocumented
378 template<typename _U1, typename _U2>
379 static constexpr bool
380 _S_constructible()
381 {
382 if constexpr (is_constructible_v<_T1, _U1>)
383 return is_constructible_v<_T2, _U2>;
384 return false;
385 }
386
387 template<typename _U1, typename _U2>
388 static constexpr bool
389 _S_nothrow_constructible()
390 {
391 if constexpr (is_nothrow_constructible_v<_T1, _U1>)
392 return is_nothrow_constructible_v<_T2, _U2>;
393 return false;
394 }
395
396 template<typename _U1, typename _U2>
397 static constexpr bool
398 _S_convertible()
399 {
400 if constexpr (is_convertible_v<_U1, _T1>)
401 return is_convertible_v<_U2, _T2>;
402 return false;
403 }
404
405 // True if construction from _U1 and _U2 would create a dangling ref.
406 template<typename _U1, typename _U2>
407 static constexpr bool
408 _S_dangles()
409 {
410#if __has_builtin(__reference_constructs_from_temporary)
411 if constexpr (__reference_constructs_from_temporary(_T1, _U1&&))
412 return true;
413 else
414 return __reference_constructs_from_temporary(_T2, _U2&&);
415#else
416 return false;
417#endif
418 }
419
420#if __glibcxx_tuple_like // >= C++23
421 template<typename _UPair>
422 static constexpr bool
423 _S_constructible_from_pair_like()
424 {
425 return _S_constructible<decltype(std::get<0>(std::declval<_UPair>())),
426 decltype(std::get<1>(std::declval<_UPair>()))>();
427 }
428
429 template<typename _UPair>
430 static constexpr bool
431 _S_convertible_from_pair_like()
432 {
433 return _S_convertible<decltype(std::get<0>(std::declval<_UPair>())),
434 decltype(std::get<1>(std::declval<_UPair>()))>();
435 }
436
437 template<typename _UPair>
438 static constexpr bool
439 _S_dangles_from_pair_like()
440 {
441 return _S_dangles<decltype(std::get<0>(std::declval<_UPair>())),
442 decltype(std::get<1>(std::declval<_UPair>()))>();
443 }
444#endif // C++23
445 /// @endcond
446
447 public:
448
449 /// Constructor accepting lvalues of `first_type` and `second_type`
450 constexpr explicit(!_S_convertible<const _T1&, const _T2&>())
451 pair(const type_identity_t<_T1>& __x, const _T2& __y)
452 noexcept(_S_nothrow_constructible<const _T1&, const _T2&>())
453 requires (_S_constructible<const _T1&, const _T2&>())
454 : first(__x), second(__y)
455 { }
456
457 /// Constructor accepting two values of arbitrary types
458#if __cplusplus > 202002L
459 template<typename _U1 = _T1, typename _U2 = _T2>
460#else
461 template<typename _U1, typename _U2>
462#endif
463 requires (_S_constructible<_U1, _U2>()) && (!_S_dangles<_U1, _U2>())
464 constexpr explicit(!_S_convertible<_U1, _U2>())
465 pair(_U1&& __x, _U2&& __y)
466 noexcept(_S_nothrow_constructible<_U1, _U2>())
467 : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
468 { }
469
470#if __cplusplus > 202002L
471 template<typename _U1 = _T1, typename _U2 = _T2>
472#else
473 template<typename _U1, typename _U2>
474#endif
475 requires (_S_constructible<_U1, _U2>()) && (_S_dangles<_U1, _U2>())
476 constexpr explicit(!_S_convertible<_U1, _U2>())
477 pair(_U1&&, _U2&&) = delete;
478
479 /// Converting constructor from a const `pair<U1, U2>` lvalue
480 template<typename _U1, typename _U2>
481 requires (_S_constructible<const _U1&, const _U2&>())
482 && (!_S_dangles<_U1, _U2>())
483 constexpr explicit(!_S_convertible<const _U1&, const _U2&>())
484 pair(const pair<_U1, _U2>& __p)
485 noexcept(_S_nothrow_constructible<const _U1&, const _U2&>())
486 : first(__p.first), second(__p.second)
487 { }
488
489 template<typename _U1, typename _U2>
490 requires (_S_constructible<const _U1&, const _U2&>())
491 && (_S_dangles<const _U1&, const _U2&>())
492 constexpr explicit(!_S_convertible<const _U1&, const _U2&>())
493 pair(const pair<_U1, _U2>&) = delete;
494
495 /// Converting constructor from a non-const `pair<U1, U2>` rvalue
496 template<typename _U1, typename _U2>
497 requires (_S_constructible<_U1, _U2>()) && (!_S_dangles<_U1, _U2>())
498 constexpr explicit(!_S_convertible<_U1, _U2>())
499 pair(pair<_U1, _U2>&& __p)
500 noexcept(_S_nothrow_constructible<_U1, _U2>())
501 : first(std::forward<_U1>(__p.first)),
502 second(std::forward<_U2>(__p.second))
503 { }
504
505 template<typename _U1, typename _U2>
506 requires (_S_constructible<_U1, _U2>()) && (_S_dangles<_U1, _U2>())
507 constexpr explicit(!_S_convertible<_U1, _U2>())
508 pair(pair<_U1, _U2>&&) = delete;
509
510#if __glibcxx_ranges_zip // >= C++23
511 /// Converting constructor from a non-const `pair<U1, U2>` lvalue
512 template<typename _U1, typename _U2>
513 requires (_S_constructible<_U1&, _U2&>()) && (!_S_dangles<_U1&, _U2&>())
514 constexpr explicit(!_S_convertible<_U1&, _U2&>())
515 pair(pair<_U1, _U2>& __p)
516 noexcept(_S_nothrow_constructible<_U1&, _U2&>())
517 : first(__p.first), second(__p.second)
518 { }
519
520 template<typename _U1, typename _U2>
521 requires (_S_constructible<_U1&, _U2&>()) && (_S_dangles<_U1&, _U2&>())
522 constexpr explicit(!_S_convertible<_U1&, _U2&>())
523 pair(pair<_U1, _U2>&) = delete;
524
525 /// Converting constructor from a const `pair<U1, U2>` rvalue
526 template<typename _U1, typename _U2>
527 requires (_S_constructible<const _U1, const _U2>())
528 && (!_S_dangles<const _U1, const _U2>())
529 constexpr explicit(!_S_convertible<const _U1, const _U2>())
530 pair(const pair<_U1, _U2>&& __p)
531 noexcept(_S_nothrow_constructible<const _U1, const _U2>())
532 : first(std::forward<const _U1>(__p.first)),
533 second(std::forward<const _U2>(__p.second))
534 { }
535
536 template<typename _U1, typename _U2>
537 requires (_S_constructible<const _U1, const _U2>())
538 && (_S_dangles<const _U1, const _U2>())
539 constexpr explicit(!_S_convertible<const _U1, const _U2>())
540 pair(const pair<_U1, _U2>&&) = delete;
541#endif // C++23
542
543#if __glibcxx_tuple_like // >= C++23
544 template<__eligible_pair_like<pair> _UPair>
545 requires (_S_constructible_from_pair_like<_UPair>())
546 && (!_S_dangles_from_pair_like<_UPair>())
547 constexpr explicit(!_S_convertible_from_pair_like<_UPair>())
548 pair(_UPair&& __p)
549 : first(std::get<0>(std::forward<_UPair>(__p))),
550 second(std::get<1>(std::forward<_UPair>(__p)))
551 { }
552
553 template<__eligible_pair_like<pair> _UPair>
554 requires (_S_constructible_from_pair_like<_UPair>())
555 && (_S_dangles_from_pair_like<_UPair>())
556 constexpr explicit(!_S_convertible_from_pair_like<_UPair>())
557 pair(_UPair&&) = delete;
558#endif // C++23
559
560 private:
561 /// @cond undocumented
562 template<typename _U1, typename _U2>
563 static constexpr bool
564 _S_assignable()
565 {
566 if constexpr (is_assignable_v<_T1&, _U1>)
567 return is_assignable_v<_T2&, _U2>;
568 return false;
569 }
570
571 template<typename _U1, typename _U2>
572 static constexpr bool
573 _S_const_assignable()
574 {
575 if constexpr (is_assignable_v<const _T1&, _U1>)
576 return is_assignable_v<const _T2&, _U2>;
577 return false;
578 }
579
580 template<typename _U1, typename _U2>
581 static constexpr bool
582 _S_nothrow_assignable()
583 {
584 if constexpr (is_nothrow_assignable_v<_T1&, _U1>)
585 return is_nothrow_assignable_v<_T2&, _U2>;
586 return false;
587 }
588
589#if __glibcxx_tuple_like // >= C++23
590 template<typename _UPair>
591 static constexpr bool
592 _S_assignable_from_tuple_like()
593 {
594 return _S_assignable<decltype(std::get<0>(std::declval<_UPair>())),
595 decltype(std::get<1>(std::declval<_UPair>()))>();
596 }
597
598 template<typename _UPair>
599 static constexpr bool
600 _S_const_assignable_from_tuple_like()
601 {
602 return _S_const_assignable<decltype(std::get<0>(std::declval<_UPair>())),
603 decltype(std::get<1>(std::declval<_UPair>()))>();
604 }
605#endif // C++23
606 /// @endcond
607
608 public:
609
610 pair& operator=(const pair&) = delete;
611
612 /// Copy assignment operator
613 constexpr pair&
614 operator=(const pair& __p)
615 noexcept(_S_nothrow_assignable<const _T1&, const _T2&>())
616 requires (_S_assignable<const _T1&, const _T2&>())
617 {
618 first = __p.first;
619 second = __p.second;
620 return *this;
621 }
622
623 /// Move assignment operator
624 constexpr pair&
625 operator=(pair&& __p)
626 noexcept(_S_nothrow_assignable<_T1, _T2>())
627 requires (_S_assignable<_T1, _T2>())
628 {
629 first = std::forward<first_type>(__p.first);
630 second = std::forward<second_type>(__p.second);
631 return *this;
632 }
633
634 /// Converting assignment from a const `pair<U1, U2>` lvalue
635 template<typename _U1, typename _U2>
636 constexpr pair&
637 operator=(const pair<_U1, _U2>& __p)
638 noexcept(_S_nothrow_assignable<const _U1&, const _U2&>())
639 requires (_S_assignable<const _U1&, const _U2&>())
640 {
641 first = __p.first;
642 second = __p.second;
643 return *this;
644 }
645
646 /// Converting assignment from a non-const `pair<U1, U2>` rvalue
647 template<typename _U1, typename _U2>
648 constexpr pair&
649 operator=(pair<_U1, _U2>&& __p)
650 noexcept(_S_nothrow_assignable<_U1, _U2>())
651 requires (_S_assignable<_U1, _U2>())
652 {
653 first = std::forward<_U1>(__p.first);
654 second = std::forward<_U2>(__p.second);
655 return *this;
656 }
657
658#if __glibcxx_ranges_zip // >= C++23
659 /// Copy assignment operator (const)
660 constexpr const pair&
661 operator=(const pair& __p) const
662 requires (_S_const_assignable<const first_type&, const second_type&>())
663 {
664 first = __p.first;
665 second = __p.second;
666 return *this;
667 }
668
669 /// Move assignment operator (const)
670 constexpr const pair&
671 operator=(pair&& __p) const
672 requires (_S_const_assignable<first_type, second_type>())
673 {
674 first = std::forward<first_type>(__p.first);
675 second = std::forward<second_type>(__p.second);
676 return *this;
677 }
678
679 /// Converting assignment from a const `pair<U1, U2>` lvalue
680 template<typename _U1, typename _U2>
681 constexpr const pair&
682 operator=(const pair<_U1, _U2>& __p) const
683 requires (_S_const_assignable<const _U1&, const _U2&>())
684 {
685 first = __p.first;
686 second = __p.second;
687 return *this;
688 }
689
690 /// Converting assignment from a non-const `pair<U1, U2>` rvalue
691 template<typename _U1, typename _U2>
692 constexpr const pair&
693 operator=(pair<_U1, _U2>&& __p) const
694 requires (_S_const_assignable<_U1, _U2>())
695 {
696 first = std::forward<_U1>(__p.first);
697 second = std::forward<_U2>(__p.second);
698 return *this;
699 }
700#endif // C++23
701
702#if __glibcxx_tuple_like // >= C++23
703 template<__eligible_pair_like<pair> _UPair>
704 requires (_S_assignable_from_tuple_like<_UPair>())
705 constexpr pair&
706 operator=(_UPair&& __p)
707 {
708 first = std::get<0>(std::forward<_UPair>(__p));
709 second = std::get<1>(std::forward<_UPair>(__p));
710 return *this;
711 }
712
713 template<__eligible_pair_like<pair> _UPair>
714 requires (_S_const_assignable_from_tuple_like<_UPair>())
715 constexpr const pair&
716 operator=(_UPair&& __p) const
717 {
718 first = std::get<0>(std::forward<_UPair>(__p));
719 second = std::get<1>(std::forward<_UPair>(__p));
720 return *this;
721 }
722#endif // C++23
723
724#else // !__cpp_lib_concepts
725 // C++11/14/17 implementation using enable_if, partially constexpr.
726
727 /// @cond undocumented
728 // Error if construction from _U1 and _U2 would create a dangling ref.
729#if __has_builtin(__reference_constructs_from_temporary) \
730 && defined _GLIBCXX_DEBUG
731# define __glibcxx_no_dangling_refs(_U1, _U2) \
732 static_assert(!__reference_constructs_from_temporary(_T1, _U1) \
733 && !__reference_constructs_from_temporary(_T2, _U2), \
734 "std::pair constructor creates a dangling reference")
735#else
736# define __glibcxx_no_dangling_refs(_U1, _U2)
737#endif
738 /// @endcond
739
740 /** The default constructor creates @c first and @c second using their
741 * respective default constructors. */
742 template <typename _U1 = _T1,
743 typename _U2 = _T2,
744 typename enable_if<__and_<
745 __is_implicitly_default_constructible<_U1>,
746 __is_implicitly_default_constructible<_U2>>
747 ::value, bool>::type = true>
748 constexpr pair()
749 : first(), second() { }
750
751 template <typename _U1 = _T1,
752 typename _U2 = _T2,
753 typename enable_if<__and_<
754 is_default_constructible<_U1>,
755 is_default_constructible<_U2>,
756 __not_<
757 __and_<__is_implicitly_default_constructible<_U1>,
758 __is_implicitly_default_constructible<_U2>>>>
759 ::value, bool>::type = false>
760 explicit constexpr pair()
761 : first(), second() { }
762
763 // Shortcut for constraining the templates that don't take pairs.
764 /// @cond undocumented
765 using _PCCP = _PCC<true, _T1, _T2>;
766 /// @endcond
767
768 /// Construct from two const lvalues, allowing implicit conversions.
769 template<typename _U1 = _T1, typename _U2=_T2, typename
770 enable_if<_PCCP::template
771 _ConstructiblePair<_U1, _U2>()
772 && _PCCP::template
773 _ImplicitlyConvertiblePair<_U1, _U2>(),
774 bool>::type=true>
775 constexpr pair(const _T1& __a, const _T2& __b)
776 : first(__a), second(__b) { }
777
778 /// Construct from two const lvalues, disallowing implicit conversions.
779 template<typename _U1 = _T1, typename _U2=_T2, typename
780 enable_if<_PCCP::template
781 _ConstructiblePair<_U1, _U2>()
782 && !_PCCP::template
783 _ImplicitlyConvertiblePair<_U1, _U2>(),
784 bool>::type=false>
785 explicit constexpr pair(const _T1& __a, const _T2& __b)
786 : first(__a), second(__b) { }
787
788 // Shortcut for constraining the templates that take pairs.
789 /// @cond undocumented
790 template <typename _U1, typename _U2>
791 using _PCCFP = _PCC<!is_same<_T1, _U1>::value
792 || !is_same<_T2, _U2>::value,
793 _T1, _T2>;
794 /// @endcond
795
796 template<typename _U1, typename _U2, typename
797 enable_if<_PCCFP<_U1, _U2>::template
798 _ConstructiblePair<_U1, _U2>()
799 && _PCCFP<_U1, _U2>::template
800 _ImplicitlyConvertiblePair<_U1, _U2>(),
801 bool>::type=true>
802 constexpr pair(const pair<_U1, _U2>& __p)
803 : first(__p.first), second(__p.second)
804 { __glibcxx_no_dangling_refs(const _U1&, const _U2&); }
805
806 template<typename _U1, typename _U2, typename
807 enable_if<_PCCFP<_U1, _U2>::template
808 _ConstructiblePair<_U1, _U2>()
809 && !_PCCFP<_U1, _U2>::template
810 _ImplicitlyConvertiblePair<_U1, _U2>(),
811 bool>::type=false>
812 explicit constexpr pair(const pair<_U1, _U2>& __p)
813 : first(__p.first), second(__p.second)
814 { __glibcxx_no_dangling_refs(const _U1&, const _U2&); }
815
816#if _GLIBCXX_USE_DEPRECATED
817#if defined(__DEPRECATED)
818# define _GLIBCXX_DEPRECATED_PAIR_CTOR \
819 __attribute__ ((__deprecated__ ("use 'nullptr' instead of '0' to " \
820 "initialize std::pair of move-only " \
821 "type and pointer")))
822#else
823# define _GLIBCXX_DEPRECATED_PAIR_CTOR
824#endif
825
826 private:
827 /// @cond undocumented
828
829 // A type which can be constructed from literal zero, but not nullptr
830 struct __zero_as_null_pointer_constant
831 {
832 __zero_as_null_pointer_constant(int __zero_as_null_pointer_constant::*)
833 { }
834 template<typename _Tp,
835 typename = __enable_if_t<is_null_pointer<_Tp>::value>>
836 __zero_as_null_pointer_constant(_Tp) = delete;
837 };
838 /// @endcond
839 public:
840
841 // Deprecated extensions to DR 811.
842 // These allow construction from an rvalue and a literal zero,
843 // in cases where the standard says the zero should be deduced as int
844 template<typename _U1,
845 __enable_if_t<__and_<__not_<is_reference<_U1>>,
846 is_pointer<_T2>,
847 is_constructible<_T1, _U1>,
848 __not_<is_constructible<_T1, const _U1&>>,
849 is_convertible<_U1, _T1>>::value,
850 bool> = true>
851 _GLIBCXX_DEPRECATED_PAIR_CTOR
852 constexpr
853 pair(_U1&& __x, __zero_as_null_pointer_constant, ...)
854 : first(std::forward<_U1>(__x)), second(nullptr)
855 { __glibcxx_no_dangling_refs(_U1&&, std::nullptr_t); }
856
857 template<typename _U1,
858 __enable_if_t<__and_<__not_<is_reference<_U1>>,
859 is_pointer<_T2>,
860 is_constructible<_T1, _U1>,
861 __not_<is_constructible<_T1, const _U1&>>,
862 __not_<is_convertible<_U1, _T1>>>::value,
863 bool> = false>
864 _GLIBCXX_DEPRECATED_PAIR_CTOR
865 explicit constexpr
866 pair(_U1&& __x, __zero_as_null_pointer_constant, ...)
867 : first(std::forward<_U1>(__x)), second(nullptr)
868 { __glibcxx_no_dangling_refs(_U1&&, std::nullptr_t); }
869
870 template<typename _U2,
871 __enable_if_t<__and_<is_pointer<_T1>,
872 __not_<is_reference<_U2>>,
873 is_constructible<_T2, _U2>,
874 __not_<is_constructible<_T2, const _U2&>>,
875 is_convertible<_U2, _T2>>::value,
876 bool> = true>
877 _GLIBCXX_DEPRECATED_PAIR_CTOR
878 constexpr
879 pair(__zero_as_null_pointer_constant, _U2&& __y, ...)
880 : first(nullptr), second(std::forward<_U2>(__y))
881 { __glibcxx_no_dangling_refs(std::nullptr_t, _U2&&); }
882
883 template<typename _U2,
884 __enable_if_t<__and_<is_pointer<_T1>,
885 __not_<is_reference<_U2>>,
886 is_constructible<_T2, _U2>,
887 __not_<is_constructible<_T2, const _U2&>>,
888 __not_<is_convertible<_U2, _T2>>>::value,
889 bool> = false>
890 _GLIBCXX_DEPRECATED_PAIR_CTOR
891 explicit constexpr
892 pair(__zero_as_null_pointer_constant, _U2&& __y, ...)
893 : first(nullptr), second(std::forward<_U2>(__y))
894 { __glibcxx_no_dangling_refs(std::nullptr_t, _U2&&); }
895#undef _GLIBCXX_DEPRECATED_PAIR_CTOR
896#endif
897
898 template<typename _U1, typename _U2, typename
899 enable_if<_PCCP::template
900 _MoveConstructiblePair<_U1, _U2>()
901 && _PCCP::template
902 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
903 bool>::type=true>
904 constexpr pair(_U1&& __x, _U2&& __y)
905 : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
906 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
907
908 template<typename _U1, typename _U2, typename
909 enable_if<_PCCP::template
910 _MoveConstructiblePair<_U1, _U2>()
911 && !_PCCP::template
912 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
913 bool>::type=false>
914 explicit constexpr pair(_U1&& __x, _U2&& __y)
915 : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
916 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
917
918
919 template<typename _U1, typename _U2, typename
920 enable_if<_PCCFP<_U1, _U2>::template
921 _MoveConstructiblePair<_U1, _U2>()
922 && _PCCFP<_U1, _U2>::template
923 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
924 bool>::type=true>
925 constexpr pair(pair<_U1, _U2>&& __p)
926 : first(std::forward<_U1>(__p.first)),
927 second(std::forward<_U2>(__p.second))
928 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
929
930 template<typename _U1, typename _U2, typename
931 enable_if<_PCCFP<_U1, _U2>::template
932 _MoveConstructiblePair<_U1, _U2>()
933 && !_PCCFP<_U1, _U2>::template
934 _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
935 bool>::type=false>
936 explicit constexpr pair(pair<_U1, _U2>&& __p)
937 : first(std::forward<_U1>(__p.first)),
938 second(std::forward<_U2>(__p.second))
939 { __glibcxx_no_dangling_refs(_U1&&, _U2&&); }
940
941#undef __glibcxx_no_dangling_refs
942
943 pair&
944 operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
945 is_copy_assignable<_T2>>::value,
946 const pair&, const __nonesuch&> __p)
947 {
948 first = __p.first;
949 second = __p.second;
950 return *this;
951 }
952
953 pair&
954 operator=(__conditional_t<__and_<is_move_assignable<_T1>,
955 is_move_assignable<_T2>>::value,
956 pair&&, __nonesuch&&> __p)
957 noexcept(__and_<is_nothrow_move_assignable<_T1>,
958 is_nothrow_move_assignable<_T2>>::value)
959 {
960 first = std::forward<first_type>(__p.first);
961 second = std::forward<second_type>(__p.second);
962 return *this;
963 }
964
965 template<typename _U1, typename _U2>
966 typename enable_if<__and_<is_assignable<_T1&, const _U1&>,
967 is_assignable<_T2&, const _U2&>>::value,
968 pair&>::type
969 operator=(const pair<_U1, _U2>& __p)
970 {
971 first = __p.first;
972 second = __p.second;
973 return *this;
974 }
975
976 template<typename _U1, typename _U2>
977 typename enable_if<__and_<is_assignable<_T1&, _U1&&>,
978 is_assignable<_T2&, _U2&&>>::value,
979 pair&>::type
980 operator=(pair<_U1, _U2>&& __p)
981 {
982 first = std::forward<_U1>(__p.first);
983 second = std::forward<_U2>(__p.second);
984 return *this;
985 }
986#endif // lib concepts
987#else
988 // C++03 implementation
989
990 // _GLIBCXX_RESOLVE_LIB_DEFECTS
991 // 265. std::pair::pair() effects overly restrictive
992 /** The default constructor creates @c first and @c second using their
993 * respective default constructors. */
994 pair() : first(), second() { }
995
996 /// Two objects may be passed to a `pair` constructor to be copied.
997 pair(const _T1& __a, const _T2& __b)
998 : first(__a), second(__b) { }
999
1000 /// Templated constructor to convert from other pairs.
1001 template<typename _U1, typename _U2>
1002 pair(const pair<_U1, _U2>& __p)
1003 : first(__p.first), second(__p.second)
1004 {
1005#if __has_builtin(__reference_constructs_from_temporary)
1006#pragma GCC diagnostic push
1007#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
1008 typedef int _DanglingCheck1[
1009 __reference_constructs_from_temporary(_T1, const _U1&) ? -1 : 1
1010 ];
1011 typedef int _DanglingCheck2[
1012 __reference_constructs_from_temporary(_T2, const _U2&) ? -1 : 1
1013 ];
1014#pragma GCC diagnostic pop
1015#endif
1016 }
1017#endif // C++11
1018 };
1019
1020 /// @relates pair @{
1021
1022#if __cpp_deduction_guides >= 201606
1023 template<typename _T1, typename _T2> pair(_T1, _T2) -> pair<_T1, _T2>;
1024#endif
1025
1026#if __cpp_lib_three_way_comparison
1027 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1028 // 3865. Sorting a range of pairs
1029
1030 /// Two pairs are equal iff their members are equal.
1031 template<typename _T1, typename _T2, typename _U1, typename _U2>
1032 [[nodiscard]]
1033 constexpr bool
1034 operator==(const pair<_T1, _T2>& __x, const pair<_U1, _U2>& __y)
1035 requires requires {
1036 { __x.first == __y.first } -> __detail::__boolean_testable;
1037 { __x.second == __y.second } -> __detail::__boolean_testable;
1038 }
1039 { return __x.first == __y.first && __x.second == __y.second; }
1040
1041 /** Defines a lexicographical order for pairs.
1042 *
1043 * For two pairs of comparable types, `P` is ordered before `Q` if
1044 * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
1045 * are equivalent (neither is less than the other) and `P.second` is
1046 * less than `Q.second`.
1047 */
1048 template<typename _T1, typename _T2, typename _U1, typename _U2>
1049 [[nodiscard]]
1050 constexpr common_comparison_category_t<__detail::__synth3way_t<_T1, _U1>,
1051 __detail::__synth3way_t<_T2, _U2>>
1052 operator<=>(const pair<_T1, _T2>& __x, const pair<_U1, _U2>& __y)
1053 {
1054 if (auto __c = __detail::__synth3way(__x.first, __y.first); __c != 0)
1055 return __c;
1056 return __detail::__synth3way(__x.second, __y.second);
1057 }
1058#else
1059 /// Two pairs of the same type are equal iff their members are equal.
1060 template<typename _T1, typename _T2>
1061 _GLIBCXX_NODISCARD
1062 inline _GLIBCXX_CONSTEXPR bool
1063 operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1064 { return __x.first == __y.first && __x.second == __y.second; }
1065
1066 /** Defines a lexicographical order for pairs.
1067 *
1068 * For two pairs of the same type, `P` is ordered before `Q` if
1069 * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
1070 * are equivalent (neither is less than the other) and `P.second` is less
1071 * than `Q.second`.
1072 */
1073 template<typename _T1, typename _T2>
1074 _GLIBCXX_NODISCARD
1075 inline _GLIBCXX_CONSTEXPR bool
1076 operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1077 { return __x.first < __y.first
1078 || (!(__y.first < __x.first) && __x.second < __y.second); }
1079
1080 /// Uses @c operator== to find the result.
1081 template<typename _T1, typename _T2>
1082 _GLIBCXX_NODISCARD
1083 inline _GLIBCXX_CONSTEXPR bool
1084 operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1085 { return !(__x == __y); }
1086
1087 /// Uses @c operator< to find the result.
1088 template<typename _T1, typename _T2>
1089 _GLIBCXX_NODISCARD
1090 inline _GLIBCXX_CONSTEXPR bool
1091 operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1092 { return __y < __x; }
1093
1094 /// Uses @c operator< to find the result.
1095 template<typename _T1, typename _T2>
1096 _GLIBCXX_NODISCARD
1097 inline _GLIBCXX_CONSTEXPR bool
1098 operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1099 { return !(__y < __x); }
1100
1101 /// Uses @c operator< to find the result.
1102 template<typename _T1, typename _T2>
1103 _GLIBCXX_NODISCARD
1104 inline _GLIBCXX_CONSTEXPR bool
1105 operator>=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1106 { return !(__x < __y); }
1107#endif // !(three_way_comparison && concepts)
1108
1109#if __cplusplus >= 201103L
1110 /** Swap overload for pairs. Calls std::pair::swap().
1111 *
1112 * @note This std::swap overload is not declared in C++03 mode,
1113 * which has performance implications, e.g. see https://gcc.gnu.org/PR38466
1114 */
1115 template<typename _T1, typename _T2>
1116 _GLIBCXX20_CONSTEXPR inline
1117#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1118 // Constrained free swap overload, see p0185r1
1119 typename enable_if<__and_<__is_swappable<_T1>,
1120 __is_swappable<_T2>>::value>::type
1121#else
1122 void
1123#endif
1124 swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
1125 noexcept(noexcept(__x.swap(__y)))
1126 { __x.swap(__y); }
1127
1128#if __glibcxx_ranges_zip // >= C++23
1129 template<typename _T1, typename _T2>
1130 requires is_swappable_v<const _T1> && is_swappable_v<const _T2>
1131 constexpr void
1132 swap(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
1133 noexcept(noexcept(__x.swap(__y)))
1134 { __x.swap(__y); }
1135#endif // C++23
1136
1137#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1138 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1139 // 2766. Swapping non-swappable types
1140 template<typename _T1, typename _T2>
1141 typename enable_if<!__and_<__is_swappable<_T1>,
1142 __is_swappable<_T2>>::value>::type
1143 swap(pair<_T1, _T2>&, pair<_T1, _T2>&) = delete;
1144#endif
1145#endif // __cplusplus >= 201103L
1146
1147 /// @} relates pair
1148
1149 /**
1150 * @brief A convenience wrapper for creating a pair from two objects.
1151 * @param __x The first object.
1152 * @param __y The second object.
1153 * @return A newly-constructed pair<> object of the appropriate type.
1154 *
1155 * The C++98 standard says the objects are passed by reference-to-const,
1156 * but C++03 says they are passed by value (this was LWG issue #181).
1157 *
1158 * Since C++11 they have been passed by forwarding reference and then
1159 * forwarded to the new members of the pair. To create a pair with a
1160 * member of reference type, pass a `reference_wrapper` to this function.
1161 */
1162 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1163 // 181. make_pair() unintended behavior
1164#if __cplusplus >= 201103L
1165 // NB: DR 706.
1166 template<typename _T1, typename _T2>
1167 constexpr pair<typename __decay_and_strip<_T1>::__type,
1168 typename __decay_and_strip<_T2>::__type>
1169 make_pair(_T1&& __x, _T2&& __y)
1170 {
1171 typedef typename __decay_and_strip<_T1>::__type __ds_type1;
1172 typedef typename __decay_and_strip<_T2>::__type __ds_type2;
1173 typedef pair<__ds_type1, __ds_type2> __pair_type;
1174 return __pair_type(std::forward<_T1>(__x), std::forward<_T2>(__y));
1175 }
1176#else
1177 template<typename _T1, typename _T2>
1178 inline pair<_T1, _T2>
1179 make_pair(_T1 __x, _T2 __y)
1180 { return pair<_T1, _T2>(__x, __y); }
1181#endif
1182
1183 /// @}
1184
1185#if __cplusplus >= 201103L
1186 // Various functions which give std::pair a tuple-like interface.
1187
1188 /// @cond undocumented
1189 template<typename _T1, typename _T2>
1190 struct __is_tuple_like_impl<pair<_T1, _T2>> : true_type
1191 { };
1192 /// @endcond
1193
1194 /// Partial specialization for std::pair
1195 template<class _Tp1, class _Tp2>
1196 struct tuple_size<pair<_Tp1, _Tp2>>
1197 : public integral_constant<size_t, 2> { };
1198
1199 /// Partial specialization for std::pair
1200 template<class _Tp1, class _Tp2>
1201 struct tuple_element<0, pair<_Tp1, _Tp2>>
1202 { typedef _Tp1 type; };
1203
1204 /// Partial specialization for std::pair
1205 template<class _Tp1, class _Tp2>
1206 struct tuple_element<1, pair<_Tp1, _Tp2>>
1207 { typedef _Tp2 type; };
1208
1209#if __cplusplus >= 201703L
1210 template<typename _Tp1, typename _Tp2>
1211 inline constexpr size_t tuple_size_v<pair<_Tp1, _Tp2>> = 2;
1212
1213 template<typename _Tp1, typename _Tp2>
1214 inline constexpr size_t tuple_size_v<const pair<_Tp1, _Tp2>> = 2;
1215#endif
1216
1217#if __cplusplus >= 201103L
1218#pragma GCC diagnostic push
1219#pragma GCC diagnostic ignored "-Wc++14-extensions" // variable templates
1220#pragma GCC diagnostic ignored "-Wc++17-extensions" // inline variables
1221 template<typename _Tp>
1222 inline constexpr bool __is_pair = false;
1223
1224 template<typename _Tp, typename _Up>
1225 inline constexpr bool __is_pair<pair<_Tp, _Up>> = true;
1226#pragma GCC diagnostic pop
1227#endif
1228
1229 /// @cond undocumented
1230 template<size_t _Int>
1231 struct __pair_get;
1232
1233 template<>
1234 struct __pair_get<0>
1235 {
1236 template<typename _Tp1, typename _Tp2>
1237 static constexpr _Tp1&
1238 __get(pair<_Tp1, _Tp2>& __pair) noexcept
1239 { return __pair.first; }
1240
1241 template<typename _Tp1, typename _Tp2>
1242 static constexpr _Tp1&&
1243 __move_get(pair<_Tp1, _Tp2>&& __pair) noexcept
1244 { return std::forward<_Tp1>(__pair.first); }
1245
1246 template<typename _Tp1, typename _Tp2>
1247 static constexpr const _Tp1&
1248 __const_get(const pair<_Tp1, _Tp2>& __pair) noexcept
1249 { return __pair.first; }
1250
1251 template<typename _Tp1, typename _Tp2>
1252 static constexpr const _Tp1&&
1253 __const_move_get(const pair<_Tp1, _Tp2>&& __pair) noexcept
1254 { return std::forward<const _Tp1>(__pair.first); }
1255 };
1256
1257 template<>
1258 struct __pair_get<1>
1259 {
1260 template<typename _Tp1, typename _Tp2>
1261 static constexpr _Tp2&
1262 __get(pair<_Tp1, _Tp2>& __pair) noexcept
1263 { return __pair.second; }
1264
1265 template<typename _Tp1, typename _Tp2>
1266 static constexpr _Tp2&&
1267 __move_get(pair<_Tp1, _Tp2>&& __pair) noexcept
1268 { return std::forward<_Tp2>(__pair.second); }
1269
1270 template<typename _Tp1, typename _Tp2>
1271 static constexpr const _Tp2&
1272 __const_get(const pair<_Tp1, _Tp2>& __pair) noexcept
1273 { return __pair.second; }
1274
1275 template<typename _Tp1, typename _Tp2>
1276 static constexpr const _Tp2&&
1277 __const_move_get(const pair<_Tp1, _Tp2>&& __pair) noexcept
1278 { return std::forward<const _Tp2>(__pair.second); }
1279 };
1280 /// @endcond
1281
1282 /** @{
1283 * std::get overloads for accessing members of std::pair
1284 */
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>::__get(__in); }
1290
1291 template<size_t _Int, class _Tp1, class _Tp2>
1292 constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
1293 get(pair<_Tp1, _Tp2>&& __in) noexcept
1294 { return __pair_get<_Int>::__move_get(std::move(__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_get(__in); }
1300
1301 template<size_t _Int, class _Tp1, class _Tp2>
1302 constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
1303 get(const pair<_Tp1, _Tp2>&& __in) noexcept
1304 { return __pair_get<_Int>::__const_move_get(std::move(__in)); }
1305
1306
1307#ifdef __glibcxx_tuples_by_type // C++ >= 14
1308 template <typename _Tp, typename _Up>
1309 constexpr _Tp&
1310 get(pair<_Tp, _Up>& __p) noexcept
1311 { return __p.first; }
1312
1313 template <typename _Tp, typename _Up>
1314 constexpr const _Tp&
1315 get(const pair<_Tp, _Up>& __p) noexcept
1316 { return __p.first; }
1317
1318 template <typename _Tp, typename _Up>
1319 constexpr _Tp&&
1320 get(pair<_Tp, _Up>&& __p) noexcept
1321 { return std::forward<_Tp>(__p.first); }
1322
1323 template <typename _Tp, typename _Up>
1324 constexpr const _Tp&&
1325 get(const pair<_Tp, _Up>&& __p) noexcept
1326 { return std::forward<const _Tp>(__p.first); }
1327
1328 template <typename _Tp, typename _Up>
1329 constexpr _Tp&
1330 get(pair<_Up, _Tp>& __p) noexcept
1331 { return __p.second; }
1332
1333 template <typename _Tp, typename _Up>
1334 constexpr const _Tp&
1335 get(const pair<_Up, _Tp>& __p) noexcept
1336 { return __p.second; }
1337
1338 template <typename _Tp, typename _Up>
1339 constexpr _Tp&&
1340 get(pair<_Up, _Tp>&& __p) noexcept
1341 { return std::forward<_Tp>(__p.second); }
1342
1343 template <typename _Tp, typename _Up>
1344 constexpr const _Tp&&
1345 get(const pair<_Up, _Tp>&& __p) noexcept
1346 { return std::forward<const _Tp>(__p.second); }
1347#endif // __glibcxx_tuples_by_type
1348
1349
1350#if __glibcxx_ranges_zip // >= C++23
1351 template<typename _T1, typename _T2, typename _U1, typename _U2,
1352 template<typename> class _TQual, template<typename> class _UQual>
1353 requires requires { typename pair<common_reference_t<_TQual<_T1>, _UQual<_U1>>,
1354 common_reference_t<_TQual<_T2>, _UQual<_U2>>>; }
1355 struct basic_common_reference<pair<_T1, _T2>, pair<_U1, _U2>, _TQual, _UQual>
1356 {
1357 using type = pair<common_reference_t<_TQual<_T1>, _UQual<_U1>>,
1358 common_reference_t<_TQual<_T2>, _UQual<_U2>>>;
1359 };
1360
1361 template<typename _T1, typename _T2, typename _U1, typename _U2>
1362 requires requires { typename pair<common_type_t<_T1, _U1>, common_type_t<_T2, _U2>>; }
1363 struct common_type<pair<_T1, _T2>, pair<_U1, _U2>>
1364 { using type = pair<common_type_t<_T1, _U1>, common_type_t<_T2, _U2>>; };
1365#endif // C++23
1366
1367 /// @}
1368#endif // C++11
1369
1370_GLIBCXX_END_NAMESPACE_VERSION
1371} // namespace std
1372
1373#endif /* _STL_PAIR_H */
1374