libstdc++
stl_pair.h
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1 // Pair implementation -*- C++ -*-
2 
3 // Copyright (C) 2001-2022 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
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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
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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 # define __cpp_lib_constexpr_utility 201811L
67 #endif
68 
69 namespace std _GLIBCXX_VISIBILITY(default)
70 {
71 _GLIBCXX_BEGIN_NAMESPACE_VERSION
72 
73  /**
74  * @addtogroup utilities
75  * @{
76  */
77 
78 #if __cplusplus >= 201103L
79  /// Tag type for piecewise construction of std::pair objects.
80  struct piecewise_construct_t { explicit piecewise_construct_t() = default; };
81 
82  /// Tag for piecewise construction of std::pair objects.
83  _GLIBCXX17_INLINE constexpr piecewise_construct_t piecewise_construct =
84  piecewise_construct_t();
85 
86  /// @cond undocumented
87 
88  // Forward declarations.
89  template<typename...>
90  class tuple;
91 
92  template<size_t...>
93  struct _Index_tuple;
94 
95 #if ! __cpp_lib_concepts
96  // Concept utility functions, reused in conditionally-explicit
97  // constructors.
98  // See PR 70437, don't look at is_constructible or
99  // is_convertible if the types are the same to
100  // avoid querying those properties for incomplete types.
101  template <bool, typename _T1, typename _T2>
102  struct _PCC
103  {
104  template <typename _U1, typename _U2>
105  static constexpr bool _ConstructiblePair()
106  {
107  return __and_<is_constructible<_T1, const _U1&>,
108  is_constructible<_T2, const _U2&>>::value;
109  }
110 
111  template <typename _U1, typename _U2>
112  static constexpr bool _ImplicitlyConvertiblePair()
113  {
114  return __and_<is_convertible<const _U1&, _T1>,
115  is_convertible<const _U2&, _T2>>::value;
116  }
117 
118  template <typename _U1, typename _U2>
119  static constexpr bool _MoveConstructiblePair()
120  {
121  return __and_<is_constructible<_T1, _U1&&>,
122  is_constructible<_T2, _U2&&>>::value;
123  }
124 
125  template <typename _U1, typename _U2>
126  static constexpr bool _ImplicitlyMoveConvertiblePair()
127  {
128  return __and_<is_convertible<_U1&&, _T1>,
129  is_convertible<_U2&&, _T2>>::value;
130  }
131  };
132 
133  template <typename _T1, typename _T2>
134  struct _PCC<false, _T1, _T2>
135  {
136  template <typename _U1, typename _U2>
137  static constexpr bool _ConstructiblePair()
138  {
139  return false;
140  }
141 
142  template <typename _U1, typename _U2>
143  static constexpr bool _ImplicitlyConvertiblePair()
144  {
145  return false;
146  }
147 
148  template <typename _U1, typename _U2>
149  static constexpr bool _MoveConstructiblePair()
150  {
151  return false;
152  }
153 
154  template <typename _U1, typename _U2>
155  static constexpr bool _ImplicitlyMoveConvertiblePair()
156  {
157  return false;
158  }
159  };
160 #endif // lib concepts
161 #endif // C++11
162 
163  template<typename _U1, typename _U2> class __pair_base
164  {
165 #if __cplusplus >= 201103L && ! __cpp_lib_concepts
166  template<typename _T1, typename _T2> friend struct pair;
167  __pair_base() = default;
168  ~__pair_base() = default;
169  __pair_base(const __pair_base&) = default;
170  __pair_base& operator=(const __pair_base&) = delete;
171 #endif // C++11
172  };
173 
174  /// @endcond
175 
176  /**
177  * @brief Struct holding two objects of arbitrary type.
178  *
179  * @tparam _T1 Type of first object.
180  * @tparam _T2 Type of second object.
181  *
182  * <https://gcc.gnu.org/onlinedocs/libstdc++/manual/utilities.html>
183  */
184  template<typename _T1, typename _T2>
185  struct pair
186  : public __pair_base<_T1, _T2>
187  {
188  typedef _T1 first_type; ///< The type of the `first` member
189  typedef _T2 second_type; ///< The type of the `second` member
190 
191  _T1 first; ///< The first member
192  _T2 second; ///< The second member
193 
194 #if __cplusplus >= 201103L
195  constexpr pair(const pair&) = default; ///< Copy constructor
196  constexpr pair(pair&&) = default; ///< Move constructor
197 
198  template<typename... _Args1, typename... _Args2>
199  _GLIBCXX20_CONSTEXPR
200  pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
201 
202  /// Swap the first members and then the second members.
203  _GLIBCXX20_CONSTEXPR void
204  swap(pair& __p)
205  noexcept(__and_<__is_nothrow_swappable<_T1>,
206  __is_nothrow_swappable<_T2>>::value)
207  {
208  using std::swap;
209  swap(first, __p.first);
210  swap(second, __p.second);
211  }
212 
213  private:
214  template<typename... _Args1, size_t... _Indexes1,
215  typename... _Args2, size_t... _Indexes2>
216  _GLIBCXX20_CONSTEXPR
217  pair(tuple<_Args1...>&, tuple<_Args2...>&,
218  _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
219  public:
220 
221 #if __cpp_lib_concepts
222  // C++20 implementation using concepts, explicit(bool), fully constexpr.
223 
224  /// Default constructor
225  constexpr
226  explicit(__not_<__and_<__is_implicitly_default_constructible<_T1>,
227  __is_implicitly_default_constructible<_T2>>>())
228  pair()
229  requires is_default_constructible_v<_T1>
230  && is_default_constructible_v<_T2>
231  : first(), second()
232  { }
233 
234  private:
235 
236  /// @cond undocumented
237  template<typename _U1, typename _U2>
238  static constexpr bool
239  _S_constructible()
240  {
241  if constexpr (is_constructible_v<_T1, _U1>)
242  return is_constructible_v<_T2, _U2>;
243  return false;
244  }
245 
246  template<typename _U1, typename _U2>
247  static constexpr bool
248  _S_nothrow_constructible()
249  {
250  if constexpr (is_nothrow_constructible_v<_T1, _U1>)
251  return is_nothrow_constructible_v<_T2, _U2>;
252  return false;
253  }
254 
255  template<typename _U1, typename _U2>
256  static constexpr bool
257  _S_convertible()
258  {
259  if constexpr (is_convertible_v<_U1, _T1>)
260  return is_convertible_v<_U2, _T2>;
261  return false;
262  }
263  /// @endcond
264 
265  public:
266 
267  /// Constructor accepting lvalues of `first_type` and `second_type`
268  constexpr explicit(!_S_convertible<const _T1&, const _T2&>())
269  pair(const _T1& __x, const _T2& __y)
270  noexcept(_S_nothrow_constructible<const _T1&, const _T2&>())
271  requires (_S_constructible<const _T1&, const _T2&>())
272  : first(__x), second(__y)
273  { }
274 
275  /// Constructor accepting two values of arbitrary types
276  template<typename _U1, typename _U2>
277  requires (_S_constructible<_U1, _U2>())
278  constexpr explicit(!_S_convertible<_U1, _U2>())
279  pair(_U1&& __x, _U2&& __y)
280  noexcept(_S_nothrow_constructible<_U1, _U2>())
281  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y))
282  { }
283 
284  /// Converting constructor from a `pair<U1, U2>` lvalue
285  template<typename _U1, typename _U2>
286  requires (_S_constructible<const _U1&, const _U2&>())
287  constexpr explicit(!_S_convertible<const _U1&, const _U2&>())
288  pair(const pair<_U1, _U2>& __p)
289  noexcept(_S_nothrow_constructible<const _U1&, const _U2&>())
290  : first(__p.first), second(__p.second)
291  { }
292 
293  /// Converting constructor from a `pair<U1, U2>` rvalue
294  template<typename _U1, typename _U2>
295  requires (_S_constructible<_U1, _U2>())
296  constexpr explicit(!_S_convertible<_U1, _U2>())
297  pair(pair<_U1, _U2>&& __p)
298  noexcept(_S_nothrow_constructible<_U1, _U2>())
299  : first(std::forward<_U1>(__p.first)),
300  second(std::forward<_U2>(__p.second))
301  { }
302 
303  private:
304  /// @cond undocumented
305  template<typename _U1, typename _U2>
306  static constexpr bool
307  _S_assignable()
308  {
309  if constexpr (is_assignable_v<_T1&, _U1>)
310  return is_assignable_v<_T2&, _U2>;
311  return false;
312  }
313 
314  template<typename _U1, typename _U2>
315  static constexpr bool
316  _S_nothrow_assignable()
317  {
318  if constexpr (is_nothrow_assignable_v<_T1&, _U1>)
319  return is_nothrow_assignable_v<_T2&, _U2>;
320  return false;
321  }
322  /// @endcond
323 
324  public:
325 
326  pair& operator=(const pair&) = delete;
327 
328  /// Copy assignment operator
329  constexpr pair&
330  operator=(const pair& __p)
331  noexcept(_S_nothrow_assignable<const _T1&, const _T2&>())
332  requires (_S_assignable<const _T1&, const _T2&>())
333  {
334  first = __p.first;
335  second = __p.second;
336  return *this;
337  }
338 
339  /// Move assignment operator
340  constexpr pair&
341  operator=(pair&& __p)
342  noexcept(_S_nothrow_assignable<_T1, _T2>())
343  requires (_S_assignable<_T1, _T2>())
344  {
345  first = std::forward<first_type>(__p.first);
346  second = std::forward<second_type>(__p.second);
347  return *this;
348  }
349 
350  /// Converting assignment from a `pair<U1, U2>` lvalue
351  template<typename _U1, typename _U2>
352  constexpr pair&
353  operator=(const pair<_U1, _U2>& __p)
354  noexcept(_S_nothrow_assignable<const _U1&, const _U2&>())
355  requires (_S_assignable<const _U1&, const _U2&>())
356  {
357  first = __p.first;
358  second = __p.second;
359  return *this;
360  }
361 
362  /// Converting assignment from a `pair<U1, U2>` rvalue
363  template<typename _U1, typename _U2>
364  constexpr pair&
365  operator=(pair<_U1, _U2>&& __p)
366  noexcept(_S_nothrow_assignable<_U1, _U2>())
367  requires (_S_assignable<_U1, _U2>())
368  {
369  first = std::forward<_U1>(__p.first);
370  second = std::forward<_U2>(__p.second);
371  return *this;
372  }
373 #else
374  // C++11/14/17 implementation using enable_if, partially constexpr.
375 
376  /** The default constructor creates @c first and @c second using their
377  * respective default constructors. */
378  template <typename _U1 = _T1,
379  typename _U2 = _T2,
380  typename enable_if<__and_<
381  __is_implicitly_default_constructible<_U1>,
382  __is_implicitly_default_constructible<_U2>>
383  ::value, bool>::type = true>
384  constexpr pair()
385  : first(), second() { }
386 
387  template <typename _U1 = _T1,
388  typename _U2 = _T2,
389  typename enable_if<__and_<
390  is_default_constructible<_U1>,
391  is_default_constructible<_U2>,
392  __not_<
393  __and_<__is_implicitly_default_constructible<_U1>,
394  __is_implicitly_default_constructible<_U2>>>>
395  ::value, bool>::type = false>
396  explicit constexpr pair()
397  : first(), second() { }
398 
399  // Shortcut for constraining the templates that don't take pairs.
400  /// @cond undocumented
401  using _PCCP = _PCC<true, _T1, _T2>;
402  /// @endcond
403 
404  /// Construct from two const lvalues, allowing implicit conversions.
405  template<typename _U1 = _T1, typename _U2=_T2, typename
406  enable_if<_PCCP::template
407  _ConstructiblePair<_U1, _U2>()
408  && _PCCP::template
409  _ImplicitlyConvertiblePair<_U1, _U2>(),
410  bool>::type=true>
411  constexpr pair(const _T1& __a, const _T2& __b)
412  : first(__a), second(__b) { }
413 
414  /// Construct from two const lvalues, disallowing implicit conversions.
415  template<typename _U1 = _T1, typename _U2=_T2, typename
416  enable_if<_PCCP::template
417  _ConstructiblePair<_U1, _U2>()
418  && !_PCCP::template
419  _ImplicitlyConvertiblePair<_U1, _U2>(),
420  bool>::type=false>
421  explicit constexpr pair(const _T1& __a, const _T2& __b)
422  : first(__a), second(__b) { }
423 
424  // Shortcut for constraining the templates that take pairs.
425  /// @cond undocumented
426  template <typename _U1, typename _U2>
427  using _PCCFP = _PCC<!is_same<_T1, _U1>::value
428  || !is_same<_T2, _U2>::value,
429  _T1, _T2>;
430  /// @endcond
431 
432  template<typename _U1, typename _U2, typename
433  enable_if<_PCCFP<_U1, _U2>::template
434  _ConstructiblePair<_U1, _U2>()
435  && _PCCFP<_U1, _U2>::template
436  _ImplicitlyConvertiblePair<_U1, _U2>(),
437  bool>::type=true>
438  constexpr pair(const pair<_U1, _U2>& __p)
439  : first(__p.first), second(__p.second) { }
440 
441  template<typename _U1, typename _U2, typename
442  enable_if<_PCCFP<_U1, _U2>::template
443  _ConstructiblePair<_U1, _U2>()
444  && !_PCCFP<_U1, _U2>::template
445  _ImplicitlyConvertiblePair<_U1, _U2>(),
446  bool>::type=false>
447  explicit constexpr pair(const pair<_U1, _U2>& __p)
448  : first(__p.first), second(__p.second) { }
449 
450 #if _GLIBCXX_USE_DEPRECATED
451 #if defined(__DEPRECATED)
452 # define _GLIBCXX_DEPRECATED_PAIR_CTOR \
453  __attribute__ ((__deprecated__ ("use 'nullptr' instead of '0' to " \
454  "initialize std::pair of move-only " \
455  "type and pointer")))
456 #else
457 # define _GLIBCXX_DEPRECATED_PAIR_CTOR
458 #endif
459 
460  private:
461  /// @cond undocumented
462 
463  // A type which can be constructed from literal zero, but not nullptr
464  struct __zero_as_null_pointer_constant
465  {
466  __zero_as_null_pointer_constant(int __zero_as_null_pointer_constant::*)
467  { }
468  template<typename _Tp,
469  typename = __enable_if_t<is_null_pointer<_Tp>::value>>
470  __zero_as_null_pointer_constant(_Tp) = delete;
471  };
472  /// @endcond
473  public:
474 
475  // Deprecated extensions to DR 811.
476  // These allow construction from an rvalue and a literal zero,
477  // in cases where the standard says the zero should be deduced as int
478  template<typename _U1,
479  __enable_if_t<__and_<__not_<is_reference<_U1>>,
480  is_pointer<_T2>,
481  is_constructible<_T1, _U1>,
482  __not_<is_constructible<_T1, const _U1&>>,
483  is_convertible<_U1, _T1>>::value,
484  bool> = true>
485  _GLIBCXX_DEPRECATED_PAIR_CTOR
486  constexpr
487  pair(_U1&& __x, __zero_as_null_pointer_constant, ...)
488  : first(std::forward<_U1>(__x)), second(nullptr) { }
489 
490  template<typename _U1,
491  __enable_if_t<__and_<__not_<is_reference<_U1>>,
492  is_pointer<_T2>,
493  is_constructible<_T1, _U1>,
494  __not_<is_constructible<_T1, const _U1&>>,
495  __not_<is_convertible<_U1, _T1>>>::value,
496  bool> = false>
497  _GLIBCXX_DEPRECATED_PAIR_CTOR
498  explicit constexpr
499  pair(_U1&& __x, __zero_as_null_pointer_constant, ...)
500  : first(std::forward<_U1>(__x)), second(nullptr) { }
501 
502  template<typename _U2,
503  __enable_if_t<__and_<is_pointer<_T1>,
504  __not_<is_reference<_U2>>,
505  is_constructible<_T2, _U2>,
506  __not_<is_constructible<_T2, const _U2&>>,
507  is_convertible<_U2, _T2>>::value,
508  bool> = true>
509  _GLIBCXX_DEPRECATED_PAIR_CTOR
510  constexpr
511  pair(__zero_as_null_pointer_constant, _U2&& __y, ...)
512  : first(nullptr), second(std::forward<_U2>(__y)) { }
513 
514  template<typename _U2,
515  __enable_if_t<__and_<is_pointer<_T1>,
516  __not_<is_reference<_U2>>,
517  is_constructible<_T2, _U2>,
518  __not_<is_constructible<_T2, const _U2&>>,
519  __not_<is_convertible<_U2, _T2>>>::value,
520  bool> = false>
521  _GLIBCXX_DEPRECATED_PAIR_CTOR
522  explicit constexpr
523  pair(__zero_as_null_pointer_constant, _U2&& __y, ...)
524  : first(nullptr), second(std::forward<_U2>(__y)) { }
525 #undef _GLIBCXX_DEPRECATED_PAIR_CTOR
526 #endif
527 
528  template<typename _U1, typename _U2, typename
529  enable_if<_PCCP::template
530  _MoveConstructiblePair<_U1, _U2>()
531  && _PCCP::template
532  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
533  bool>::type=true>
534  constexpr pair(_U1&& __x, _U2&& __y)
535  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
536 
537  template<typename _U1, typename _U2, typename
538  enable_if<_PCCP::template
539  _MoveConstructiblePair<_U1, _U2>()
540  && !_PCCP::template
541  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
542  bool>::type=false>
543  explicit constexpr pair(_U1&& __x, _U2&& __y)
544  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
545 
546 
547  template<typename _U1, typename _U2, typename
548  enable_if<_PCCFP<_U1, _U2>::template
549  _MoveConstructiblePair<_U1, _U2>()
550  && _PCCFP<_U1, _U2>::template
551  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
552  bool>::type=true>
553  constexpr pair(pair<_U1, _U2>&& __p)
554  : first(std::forward<_U1>(__p.first)),
555  second(std::forward<_U2>(__p.second)) { }
556 
557  template<typename _U1, typename _U2, typename
558  enable_if<_PCCFP<_U1, _U2>::template
559  _MoveConstructiblePair<_U1, _U2>()
560  && !_PCCFP<_U1, _U2>::template
561  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
562  bool>::type=false>
563  explicit constexpr pair(pair<_U1, _U2>&& __p)
564  : first(std::forward<_U1>(__p.first)),
565  second(std::forward<_U2>(__p.second)) { }
566 
567  pair&
568  operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
569  is_copy_assignable<_T2>>::value,
570  const pair&, const __nonesuch&> __p)
571  {
572  first = __p.first;
573  second = __p.second;
574  return *this;
575  }
576 
577  pair&
578  operator=(__conditional_t<__and_<is_move_assignable<_T1>,
579  is_move_assignable<_T2>>::value,
580  pair&&, __nonesuch&&> __p)
581  noexcept(__and_<is_nothrow_move_assignable<_T1>,
582  is_nothrow_move_assignable<_T2>>::value)
583  {
584  first = std::forward<first_type>(__p.first);
585  second = std::forward<second_type>(__p.second);
586  return *this;
587  }
588 
589  template<typename _U1, typename _U2>
590  typename enable_if<__and_<is_assignable<_T1&, const _U1&>,
591  is_assignable<_T2&, const _U2&>>::value,
592  pair&>::type
593  operator=(const pair<_U1, _U2>& __p)
594  {
595  first = __p.first;
596  second = __p.second;
597  return *this;
598  }
599 
600  template<typename _U1, typename _U2>
601  typename enable_if<__and_<is_assignable<_T1&, _U1&&>,
602  is_assignable<_T2&, _U2&&>>::value,
603  pair&>::type
604  operator=(pair<_U1, _U2>&& __p)
605  {
606  first = std::forward<_U1>(__p.first);
607  second = std::forward<_U2>(__p.second);
608  return *this;
609  }
610 #endif // lib concepts
611 #else
612  // C++03 implementation
613 
614  // _GLIBCXX_RESOLVE_LIB_DEFECTS
615  // 265. std::pair::pair() effects overly restrictive
616  /** The default constructor creates @c first and @c second using their
617  * respective default constructors. */
618  pair() : first(), second() { }
619 
620  /// Two objects may be passed to a `pair` constructor to be copied.
621  pair(const _T1& __a, const _T2& __b)
622  : first(__a), second(__b) { }
623 
624  /// Templated constructor to convert from other pairs.
625  template<typename _U1, typename _U2>
626  pair(const pair<_U1, _U2>& __p)
627  : first(__p.first), second(__p.second) { }
628 #endif // C++11
629  };
630 
631  /// @relates pair @{
632 
633 #if __cpp_deduction_guides >= 201606
634  template<typename _T1, typename _T2> pair(_T1, _T2) -> pair<_T1, _T2>;
635 #endif
636 
637  /// Two pairs of the same type are equal iff their members are equal.
638  template<typename _T1, typename _T2>
639  inline _GLIBCXX_CONSTEXPR bool
640  operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
641  { return __x.first == __y.first && __x.second == __y.second; }
642 
643 #if __cpp_lib_three_way_comparison && __cpp_lib_concepts
644  template<typename _T1, typename _T2>
645  constexpr common_comparison_category_t<__detail::__synth3way_t<_T1>,
646  __detail::__synth3way_t<_T2>>
647  operator<=>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
648  {
649  if (auto __c = __detail::__synth3way(__x.first, __y.first); __c != 0)
650  return __c;
651  return __detail::__synth3way(__x.second, __y.second);
652  }
653 #else
654  /** Defines a lexicographical order for pairs.
655  *
656  * For two pairs of the same type, `P` is ordered before `Q` if
657  * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
658  * are equivalent (neither is less than the other) and `P.second` is less
659  * than `Q.second`.
660  */
661  template<typename _T1, typename _T2>
662  inline _GLIBCXX_CONSTEXPR bool
663  operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
664  { return __x.first < __y.first
665  || (!(__y.first < __x.first) && __x.second < __y.second); }
666 
667  /// Uses @c operator== to find the result.
668  template<typename _T1, typename _T2>
669  inline _GLIBCXX_CONSTEXPR bool
670  operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
671  { return !(__x == __y); }
672 
673  /// Uses @c operator< to find the result.
674  template<typename _T1, typename _T2>
675  inline _GLIBCXX_CONSTEXPR bool
676  operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
677  { return __y < __x; }
678 
679  /// Uses @c operator< to find the result.
680  template<typename _T1, typename _T2>
681  inline _GLIBCXX_CONSTEXPR bool
682  operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
683  { return !(__y < __x); }
684 
685  /// Uses @c operator< to find the result.
686  template<typename _T1, typename _T2>
687  inline _GLIBCXX_CONSTEXPR bool
688  operator>=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
689  { return !(__x < __y); }
690 #endif // !(three_way_comparison && concepts)
691 
692 #if __cplusplus >= 201103L
693  /** Swap overload for pairs. Calls std::pair::swap().
694  *
695  * @note This std::swap overload is not declared in C++03 mode,
696  * which has performance implications, e.g. see https://gcc.gnu.org/PR38466
697  */
698  template<typename _T1, typename _T2>
699  _GLIBCXX20_CONSTEXPR inline
700 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
701  // Constrained free swap overload, see p0185r1
702  typename enable_if<__and_<__is_swappable<_T1>,
703  __is_swappable<_T2>>::value>::type
704 #else
705  void
706 #endif
707  swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
708  noexcept(noexcept(__x.swap(__y)))
709  { __x.swap(__y); }
710 
711 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
712  template<typename _T1, typename _T2>
713  typename enable_if<!__and_<__is_swappable<_T1>,
714  __is_swappable<_T2>>::value>::type
715  swap(pair<_T1, _T2>&, pair<_T1, _T2>&) = delete;
716 #endif
717 #endif // __cplusplus >= 201103L
718 
719  /// @} relates pair
720 
721  /**
722  * @brief A convenience wrapper for creating a pair from two objects.
723  * @param __x The first object.
724  * @param __y The second object.
725  * @return A newly-constructed pair<> object of the appropriate type.
726  *
727  * The C++98 standard says the objects are passed by reference-to-const,
728  * but C++03 says they are passed by value (this was LWG issue #181).
729  *
730  * Since C++11 they have been passed by forwarding reference and then
731  * forwarded to the new members of the pair. To create a pair with a
732  * member of reference type, pass a `reference_wrapper` to this function.
733  */
734  // _GLIBCXX_RESOLVE_LIB_DEFECTS
735  // 181. make_pair() unintended behavior
736 #if __cplusplus >= 201103L
737  // NB: DR 706.
738  template<typename _T1, typename _T2>
739  constexpr pair<typename __decay_and_strip<_T1>::__type,
740  typename __decay_and_strip<_T2>::__type>
741  make_pair(_T1&& __x, _T2&& __y)
742  {
743  typedef typename __decay_and_strip<_T1>::__type __ds_type1;
744  typedef typename __decay_and_strip<_T2>::__type __ds_type2;
745  typedef pair<__ds_type1, __ds_type2> __pair_type;
746  return __pair_type(std::forward<_T1>(__x), std::forward<_T2>(__y));
747  }
748 #else
749  template<typename _T1, typename _T2>
750  inline pair<_T1, _T2>
751  make_pair(_T1 __x, _T2 __y)
752  { return pair<_T1, _T2>(__x, __y); }
753 #endif
754 
755  /// @}
756 
757 #if __cplusplus >= 201103L
758  // Various functions which give std::pair a tuple-like interface.
759 
760  template<typename _T1, typename _T2>
761  struct __is_tuple_like_impl<pair<_T1, _T2>> : true_type
762  { };
763 
764  /// Partial specialization for std::pair
765  template<class _Tp1, class _Tp2>
766  struct tuple_size<pair<_Tp1, _Tp2>>
767  : public integral_constant<size_t, 2> { };
768 
769  /// Partial specialization for std::pair
770  template<class _Tp1, class _Tp2>
771  struct tuple_element<0, pair<_Tp1, _Tp2>>
772  { typedef _Tp1 type; };
773 
774  /// Partial specialization for std::pair
775  template<class _Tp1, class _Tp2>
776  struct tuple_element<1, pair<_Tp1, _Tp2>>
777  { typedef _Tp2 type; };
778 
779 #if __cplusplus >= 201703L
780  template<typename _Tp1, typename _Tp2>
781  inline constexpr size_t tuple_size_v<pair<_Tp1, _Tp2>> = 2;
782 
783  template<typename _Tp1, typename _Tp2>
784  inline constexpr size_t tuple_size_v<const pair<_Tp1, _Tp2>> = 2;
785 
786  template<typename _Tp>
787  inline constexpr bool __is_pair = false;
788 
789  template<typename _Tp, typename _Up>
790  inline constexpr bool __is_pair<pair<_Tp, _Up>> = true;
791 
792  template<typename _Tp, typename _Up>
793  inline constexpr bool __is_pair<const pair<_Tp, _Up>> = true;
794 #endif
795 
796  /// @cond undocumented
797  template<size_t _Int>
798  struct __pair_get;
799 
800  template<>
801  struct __pair_get<0>
802  {
803  template<typename _Tp1, typename _Tp2>
804  static constexpr _Tp1&
805  __get(pair<_Tp1, _Tp2>& __pair) noexcept
806  { return __pair.first; }
807 
808  template<typename _Tp1, typename _Tp2>
809  static constexpr _Tp1&&
810  __move_get(pair<_Tp1, _Tp2>&& __pair) noexcept
811  { return std::forward<_Tp1>(__pair.first); }
812 
813  template<typename _Tp1, typename _Tp2>
814  static constexpr const _Tp1&
815  __const_get(const pair<_Tp1, _Tp2>& __pair) noexcept
816  { return __pair.first; }
817 
818  template<typename _Tp1, typename _Tp2>
819  static constexpr const _Tp1&&
820  __const_move_get(const pair<_Tp1, _Tp2>&& __pair) noexcept
821  { return std::forward<const _Tp1>(__pair.first); }
822  };
823 
824  template<>
825  struct __pair_get<1>
826  {
827  template<typename _Tp1, typename _Tp2>
828  static constexpr _Tp2&
829  __get(pair<_Tp1, _Tp2>& __pair) noexcept
830  { return __pair.second; }
831 
832  template<typename _Tp1, typename _Tp2>
833  static constexpr _Tp2&&
834  __move_get(pair<_Tp1, _Tp2>&& __pair) noexcept
835  { return std::forward<_Tp2>(__pair.second); }
836 
837  template<typename _Tp1, typename _Tp2>
838  static constexpr const _Tp2&
839  __const_get(const pair<_Tp1, _Tp2>& __pair) noexcept
840  { return __pair.second; }
841 
842  template<typename _Tp1, typename _Tp2>
843  static constexpr const _Tp2&&
844  __const_move_get(const pair<_Tp1, _Tp2>&& __pair) noexcept
845  { return std::forward<const _Tp2>(__pair.second); }
846  };
847  /// @endcond
848 
849  /** @{
850  * std::get overloads for accessing members of std::pair
851  */
852 
853  template<size_t _Int, class _Tp1, class _Tp2>
854  constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
855  get(pair<_Tp1, _Tp2>& __in) noexcept
856  { return __pair_get<_Int>::__get(__in); }
857 
858  template<size_t _Int, class _Tp1, class _Tp2>
859  constexpr typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
860  get(pair<_Tp1, _Tp2>&& __in) noexcept
861  { return __pair_get<_Int>::__move_get(std::move(__in)); }
862 
863  template<size_t _Int, class _Tp1, class _Tp2>
864  constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&
865  get(const pair<_Tp1, _Tp2>& __in) noexcept
866  { return __pair_get<_Int>::__const_get(__in); }
867 
868  template<size_t _Int, class _Tp1, class _Tp2>
869  constexpr const typename tuple_element<_Int, pair<_Tp1, _Tp2>>::type&&
870  get(const pair<_Tp1, _Tp2>&& __in) noexcept
871  { return __pair_get<_Int>::__const_move_get(std::move(__in)); }
872 
873 #if __cplusplus >= 201402L
874 
875 #define __cpp_lib_tuples_by_type 201304L
876 
877  template <typename _Tp, typename _Up>
878  constexpr _Tp&
879  get(pair<_Tp, _Up>& __p) noexcept
880  { return __p.first; }
881 
882  template <typename _Tp, typename _Up>
883  constexpr const _Tp&
884  get(const pair<_Tp, _Up>& __p) noexcept
885  { return __p.first; }
886 
887  template <typename _Tp, typename _Up>
888  constexpr _Tp&&
889  get(pair<_Tp, _Up>&& __p) noexcept
890  { return std::move(__p.first); }
891 
892  template <typename _Tp, typename _Up>
893  constexpr const _Tp&&
894  get(const pair<_Tp, _Up>&& __p) noexcept
895  { return std::move(__p.first); }
896 
897  template <typename _Tp, typename _Up>
898  constexpr _Tp&
899  get(pair<_Up, _Tp>& __p) noexcept
900  { return __p.second; }
901 
902  template <typename _Tp, typename _Up>
903  constexpr const _Tp&
904  get(const pair<_Up, _Tp>& __p) noexcept
905  { return __p.second; }
906 
907  template <typename _Tp, typename _Up>
908  constexpr _Tp&&
909  get(pair<_Up, _Tp>&& __p) noexcept
910  { return std::move(__p.second); }
911 
912  template <typename _Tp, typename _Up>
913  constexpr const _Tp&&
914  get(const pair<_Up, _Tp>&& __p) noexcept
915  { return std::move(__p.second); }
916 
917 #endif // C++14
918  /// @}
919 #endif // C++11
920 
921 _GLIBCXX_END_NAMESPACE_VERSION
922 } // namespace std
923 
924 #endif /* _STL_PAIR_H */
std::true_type
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:82
std::pair::pair
pair(_T1, _T2) -> pair< _T1, _T2 >
Two pairs of the same type are equal iff their members are equal.
std::pair::operator>
constexpr bool operator>(const pair< _T1, _T2 > &__x, const pair< _T1, _T2 > &__y)
Uses operator< to find the result.
Definition: stl_pair.h:676
std::pair::operator!=
constexpr bool operator!=(const pair< _T1, _T2 > &__x, const pair< _T1, _T2 > &__y)
Uses operator== to find the result.
Definition: stl_pair.h:670
std::pair::operator==
constexpr bool operator==(const pair< _T1, _T2 > &__x, const pair< _T1, _T2 > &__y)
Two pairs of the same type are equal iff their members are equal.
Definition: stl_pair.h:640
std::pair::operator>=
constexpr bool operator>=(const pair< _T1, _T2 > &__x, const pair< _T1, _T2 > &__y)
Uses operator< to find the result.
Definition: stl_pair.h:688
std::pair::swap
constexpr enable_if< __and_< __is_swappable< _T1 >, __is_swappable< _T2 > >::value >::type swap(pair< _T1, _T2 > &__x, pair< _T1, _T2 > &__y) noexcept(noexcept(__x.swap(__y)))
Definition: stl_pair.h:707
std::piecewise_construct
constexpr piecewise_construct_t piecewise_construct
Tag for piecewise construction of std::pair objects.
Definition: stl_pair.h:83
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
std::pair::make_pair
constexpr pair< typename __decay_and_strip< _T1 >::__type, typename __decay_and_strip< _T2 >::__type > make_pair(_T1 &&__x, _T2 &&__y)
A convenience wrapper for creating a pair from two objects.
Definition: stl_pair.h:741
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:77
std::swap
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:429
std
ISO C++ entities toplevel namespace is std.
std::tuple
Primary class template, tuple.
Definition: tuple:610
std::integral_constant
integral_constant
Definition: type_traits:63
std::is_same
is_same
Definition: type_traits:1435
std::is_constructible
is_constructible
Definition: type_traits:979
std::is_default_constructible
is_default_constructible
Definition: type_traits:988
std::enable_if
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2229
std::pair
Struct holding two objects of arbitrary type.
Definition: stl_pair.h:187
std::pair::pair
constexpr pair(const _T1 &__a, const _T2 &__b)
Construct from two const lvalues, allowing implicit conversions.
Definition: stl_pair.h:411
std::pair::first
_T1 first
The first member.
Definition: stl_pair.h:191
std::pair::first_type
_T1 first_type
The type of the first member.
Definition: stl_pair.h:188
std::pair::swap
constexpr void swap(pair &__p) noexcept(__and_< __is_nothrow_swappable< _T1 >, __is_nothrow_swappable< _T2 >>::value)
Swap the first members and then the second members.
Definition: stl_pair.h:204
std::pair::pair
constexpr pair(const pair &)=default
Copy constructor.
std::pair::pair
constexpr pair()
Definition: stl_pair.h:384
std::pair::second_type
_T2 second_type
The type of the second member.
Definition: stl_pair.h:189
std::pair::pair
constexpr pair(pair &&)=default
Move constructor.
std::pair::second
_T2 second
The second member.
Definition: stl_pair.h:192
std::piecewise_construct_t
Tag type for piecewise construction of std::pair objects.
Definition: stl_pair.h:80
std::tuple_size
Finds the size of a given tuple type.
Definition: utility.h:49
std::tuple_element
Gives the type of the ith element of a given tuple type.
Definition: utility.h:80