libstdc++
stl_pair.h
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1 // Pair implementation -*- C++ -*-
2 
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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,
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33  * that both that copyright notice and this permission notice appear
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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
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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 #include <bits/move.h> // for std::move / std::forward, and std::swap
60 
61 #if __cplusplus >= 201103L
62 # include <type_traits> // for std::__decay_and_strip, std::is_reference_v
63 #endif
64 #if __cplusplus > 201703L
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<std::size_t...>
93  struct _Index_tuple;
94 
95  // Concept utility functions, reused in conditionally-explicit
96  // constructors.
97  // See PR 70437, don't look at is_constructible or
98  // is_convertible if the types are the same to
99  // avoid querying those properties for incomplete types.
100  template <bool, typename _T1, typename _T2>
101  struct _PCC
102  {
103  template <typename _U1, typename _U2>
104  static constexpr bool _ConstructiblePair()
105  {
106  return __and_<is_constructible<_T1, const _U1&>,
107  is_constructible<_T2, const _U2&>>::value;
108  }
109 
110  template <typename _U1, typename _U2>
111  static constexpr bool _ImplicitlyConvertiblePair()
112  {
113  return __and_<is_convertible<const _U1&, _T1>,
114  is_convertible<const _U2&, _T2>>::value;
115  }
116 
117  template <typename _U1, typename _U2>
118  static constexpr bool _MoveConstructiblePair()
119  {
120  return __and_<is_constructible<_T1, _U1&&>,
121  is_constructible<_T2, _U2&&>>::value;
122  }
123 
124  template <typename _U1, typename _U2>
125  static constexpr bool _ImplicitlyMoveConvertiblePair()
126  {
127  return __and_<is_convertible<_U1&&, _T1>,
128  is_convertible<_U2&&, _T2>>::value;
129  }
130 
131  template <bool __implicit, typename _U1, typename _U2>
132  static constexpr bool _CopyMovePair()
133  {
134  using __do_converts = __and_<is_convertible<const _U1&, _T1>,
135  is_convertible<_U2&&, _T2>>;
136  using __converts = typename conditional<__implicit,
137  __do_converts,
138  __not_<__do_converts>>::type;
139  return __and_<is_constructible<_T1, const _U1&>,
140  is_constructible<_T2, _U2&&>,
141  __converts
142  >::value;
143  }
144 
145  template <bool __implicit, typename _U1, typename _U2>
146  static constexpr bool _MoveCopyPair()
147  {
148  using __do_converts = __and_<is_convertible<_U1&&, _T1>,
149  is_convertible<const _U2&, _T2>>;
150  using __converts = typename conditional<__implicit,
151  __do_converts,
152  __not_<__do_converts>>::type;
153  return __and_<is_constructible<_T1, _U1&&>,
154  is_constructible<_T2, const _U2&&>,
155  __converts
156  >::value;
157  }
158  };
159 
160  template <typename _T1, typename _T2>
161  struct _PCC<false, _T1, _T2>
162  {
163  template <typename _U1, typename _U2>
164  static constexpr bool _ConstructiblePair()
165  {
166  return false;
167  }
168 
169  template <typename _U1, typename _U2>
170  static constexpr bool _ImplicitlyConvertiblePair()
171  {
172  return false;
173  }
174 
175  template <typename _U1, typename _U2>
176  static constexpr bool _MoveConstructiblePair()
177  {
178  return false;
179  }
180 
181  template <typename _U1, typename _U2>
182  static constexpr bool _ImplicitlyMoveConvertiblePair()
183  {
184  return false;
185  }
186  };
187 #endif // C++11
188 
189  template<typename _U1, typename _U2> class __pair_base
190  {
191 #if __cplusplus >= 201103L
192  template<typename _T1, typename _T2> friend struct pair;
193  __pair_base() = default;
194  ~__pair_base() = default;
195  __pair_base(const __pair_base&) = default;
196  __pair_base& operator=(const __pair_base&) = delete;
197 #endif // C++11
198  };
199 
200  /// @endcond
201 
202  /**
203  * @brief Struct holding two objects of arbitrary type.
204  *
205  * @tparam _T1 Type of first object.
206  * @tparam _T2 Type of second object.
207  *
208  * <https://gcc.gnu.org/onlinedocs/libstdc++/manual/utilities.html>
209  */
210  template<typename _T1, typename _T2>
211  struct pair
212  : private __pair_base<_T1, _T2>
213  {
214  typedef _T1 first_type; ///< The type of the `first` member
215  typedef _T2 second_type; ///< The type of the `second` member
216 
217  _T1 first; ///< The first member
218  _T2 second; ///< The second member
219 
220  // _GLIBCXX_RESOLVE_LIB_DEFECTS
221  // 265. std::pair::pair() effects overly restrictive
222  /** The default constructor creates @c first and @c second using their
223  * respective default constructors. */
224 #if __cplusplus >= 201103L
225  template <typename _U1 = _T1,
226  typename _U2 = _T2,
227  typename enable_if<__and_<
228  __is_implicitly_default_constructible<_U1>,
229  __is_implicitly_default_constructible<_U2>>
230  ::value, bool>::type = true>
231 #endif
232  _GLIBCXX_CONSTEXPR pair()
233  : first(), second() { }
234 
235 #if __cplusplus >= 201103L
236  template <typename _U1 = _T1,
237  typename _U2 = _T2,
238  typename enable_if<__and_<
239  is_default_constructible<_U1>,
240  is_default_constructible<_U2>,
241  __not_<
242  __and_<__is_implicitly_default_constructible<_U1>,
243  __is_implicitly_default_constructible<_U2>>>>
244  ::value, bool>::type = false>
245  explicit constexpr pair()
246  : first(), second() { }
247 #endif
248 
249 #if __cplusplus < 201103L
250  /// Two objects may be passed to a @c pair constructor to be copied.
251  pair(const _T1& __a, const _T2& __b)
252  : first(__a), second(__b) { }
253 #else
254  // Shortcut for constraining the templates that don't take pairs.
255  /// @cond undocumented
256  using _PCCP = _PCC<true, _T1, _T2>;
257  /// @endcond
258 
259  /// Construct from two const lvalues, allowing implicit conversions.
260  template<typename _U1 = _T1, typename _U2=_T2, typename
261  enable_if<_PCCP::template
262  _ConstructiblePair<_U1, _U2>()
263  && _PCCP::template
264  _ImplicitlyConvertiblePair<_U1, _U2>(),
265  bool>::type=true>
266  constexpr pair(const _T1& __a, const _T2& __b)
267  : first(__a), second(__b) { }
268 
269  /// Construct from two const lvalues, disallowing implicit conversions.
270  template<typename _U1 = _T1, typename _U2=_T2, typename
271  enable_if<_PCCP::template
272  _ConstructiblePair<_U1, _U2>()
273  && !_PCCP::template
274  _ImplicitlyConvertiblePair<_U1, _U2>(),
275  bool>::type=false>
276  explicit constexpr pair(const _T1& __a, const _T2& __b)
277  : first(__a), second(__b) { }
278 #endif
279 
280 #if __cplusplus < 201103L
281  /// There is also a templated constructor to convert from other pairs.
282  template<typename _U1, typename _U2>
283  pair(const pair<_U1, _U2>& __p)
284  : first(__p.first), second(__p.second) { }
285 #else
286  // Shortcut for constraining the templates that take pairs.
287  /// @cond undocumented
288  template <typename _U1, typename _U2>
289  using _PCCFP = _PCC<!is_same<_T1, _U1>::value
290  || !is_same<_T2, _U2>::value,
291  _T1, _T2>;
292  /// @endcond
293 
294  template<typename _U1, typename _U2, typename
295  enable_if<_PCCFP<_U1, _U2>::template
296  _ConstructiblePair<_U1, _U2>()
297  && _PCCFP<_U1, _U2>::template
298  _ImplicitlyConvertiblePair<_U1, _U2>(),
299  bool>::type=true>
300  constexpr pair(const pair<_U1, _U2>& __p)
301  : first(__p.first), second(__p.second) { }
302 
303  template<typename _U1, typename _U2, typename
304  enable_if<_PCCFP<_U1, _U2>::template
305  _ConstructiblePair<_U1, _U2>()
306  && !_PCCFP<_U1, _U2>::template
307  _ImplicitlyConvertiblePair<_U1, _U2>(),
308  bool>::type=false>
309  explicit constexpr pair(const pair<_U1, _U2>& __p)
310  : first(__p.first), second(__p.second) { }
311 #endif
312 
313 #if __cplusplus >= 201103L
314  constexpr pair(const pair&) = default; ///< Copy constructor
315  constexpr pair(pair&&) = default; ///< Move constructor
316 
317  // DR 811.
318  template<typename _U1, typename
319  enable_if<_PCCP::template
320  _MoveCopyPair<true, _U1, _T2>(),
321  bool>::type=true>
322  constexpr pair(_U1&& __x, const _T2& __y)
323  : first(std::forward<_U1>(__x)), second(__y) { }
324 
325  template<typename _U1, typename
326  enable_if<_PCCP::template
327  _MoveCopyPair<false, _U1, _T2>(),
328  bool>::type=false>
329  explicit constexpr pair(_U1&& __x, const _T2& __y)
330  : first(std::forward<_U1>(__x)), second(__y) { }
331 
332  template<typename _U2, typename
333  enable_if<_PCCP::template
334  _CopyMovePair<true, _T1, _U2>(),
335  bool>::type=true>
336  constexpr pair(const _T1& __x, _U2&& __y)
337  : first(__x), second(std::forward<_U2>(__y)) { }
338 
339  template<typename _U2, typename
340  enable_if<_PCCP::template
341  _CopyMovePair<false, _T1, _U2>(),
342  bool>::type=false>
343  explicit pair(const _T1& __x, _U2&& __y)
344  : first(__x), second(std::forward<_U2>(__y)) { }
345 
346  template<typename _U1, typename _U2, typename
347  enable_if<_PCCP::template
348  _MoveConstructiblePair<_U1, _U2>()
349  && _PCCP::template
350  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
351  bool>::type=true>
352  constexpr pair(_U1&& __x, _U2&& __y)
353  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
354 
355  template<typename _U1, typename _U2, typename
356  enable_if<_PCCP::template
357  _MoveConstructiblePair<_U1, _U2>()
358  && !_PCCP::template
359  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
360  bool>::type=false>
361  explicit constexpr pair(_U1&& __x, _U2&& __y)
362  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
363 
364 
365  template<typename _U1, typename _U2, typename
366  enable_if<_PCCFP<_U1, _U2>::template
367  _MoveConstructiblePair<_U1, _U2>()
368  && _PCCFP<_U1, _U2>::template
369  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
370  bool>::type=true>
371  constexpr pair(pair<_U1, _U2>&& __p)
372  : first(std::forward<_U1>(__p.first)),
373  second(std::forward<_U2>(__p.second)) { }
374 
375  template<typename _U1, typename _U2, typename
376  enable_if<_PCCFP<_U1, _U2>::template
377  _MoveConstructiblePair<_U1, _U2>()
378  && !_PCCFP<_U1, _U2>::template
379  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
380  bool>::type=false>
381  explicit constexpr pair(pair<_U1, _U2>&& __p)
382  : first(std::forward<_U1>(__p.first)),
383  second(std::forward<_U2>(__p.second)) { }
384 
385  template<typename... _Args1, typename... _Args2>
386  _GLIBCXX20_CONSTEXPR
387  pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
388 
389  _GLIBCXX20_CONSTEXPR pair&
390  operator=(typename conditional<
391  __and_<is_copy_assignable<_T1>,
392  is_copy_assignable<_T2>>::value,
393  const pair&, const __nonesuch&>::type __p)
394  {
395  first = __p.first;
396  second = __p.second;
397  return *this;
398  }
399 
400  _GLIBCXX20_CONSTEXPR pair&
401  operator=(typename conditional<
402  __and_<is_move_assignable<_T1>,
403  is_move_assignable<_T2>>::value,
404  pair&&, __nonesuch&&>::type __p)
405  noexcept(__and_<is_nothrow_move_assignable<_T1>,
406  is_nothrow_move_assignable<_T2>>::value)
407  {
408  first = std::forward<first_type>(__p.first);
409  second = std::forward<second_type>(__p.second);
410  return *this;
411  }
412 
413  template<typename _U1, typename _U2>
414  _GLIBCXX20_CONSTEXPR
415  typename enable_if<__and_<is_assignable<_T1&, const _U1&>,
416  is_assignable<_T2&, const _U2&>>::value,
417  pair&>::type
418  operator=(const pair<_U1, _U2>& __p)
419  {
420  first = __p.first;
421  second = __p.second;
422  return *this;
423  }
424 
425  template<typename _U1, typename _U2>
426  _GLIBCXX20_CONSTEXPR
427  typename enable_if<__and_<is_assignable<_T1&, _U1&&>,
428  is_assignable<_T2&, _U2&&>>::value,
429  pair&>::type
430  operator=(pair<_U1, _U2>&& __p)
431  {
432  first = std::forward<_U1>(__p.first);
433  second = std::forward<_U2>(__p.second);
434  return *this;
435  }
436 
437  /// Swap the first members and then the second members.
438  _GLIBCXX20_CONSTEXPR void
439  swap(pair& __p)
440  noexcept(__and_<__is_nothrow_swappable<_T1>,
441  __is_nothrow_swappable<_T2>>::value)
442  {
443  using std::swap;
444  swap(first, __p.first);
445  swap(second, __p.second);
446  }
447 
448  private:
449  template<typename... _Args1, std::size_t... _Indexes1,
450  typename... _Args2, std::size_t... _Indexes2>
451  _GLIBCXX20_CONSTEXPR
452  pair(tuple<_Args1...>&, tuple<_Args2...>&,
453  _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
454 #endif // C++11
455  };
456 
457  /// @relates pair @{
458 
459 #if __cpp_deduction_guides >= 201606
460  template<typename _T1, typename _T2> pair(_T1, _T2) -> pair<_T1, _T2>;
461 #endif
462 
463  /// Two pairs of the same type are equal iff their members are equal.
464  template<typename _T1, typename _T2>
465  inline _GLIBCXX_CONSTEXPR bool
466  operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
467  { return __x.first == __y.first && __x.second == __y.second; }
468 
469 #if __cpp_lib_three_way_comparison && __cpp_lib_concepts
470  template<typename _T1, typename _T2>
471  constexpr common_comparison_category_t<__detail::__synth3way_t<_T1>,
472  __detail::__synth3way_t<_T2>>
473  operator<=>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
474  {
475  if (auto __c = __detail::__synth3way(__x.first, __y.first); __c != 0)
476  return __c;
477  return __detail::__synth3way(__x.second, __y.second);
478  }
479 #else
480  /** Defines a lexicographical order for pairs.
481  *
482  * For two pairs of the same type, `P` is ordered before `Q` if
483  * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
484  * are equivalent (neither is less than the other) and `P.second` is less
485  * than `Q.second`.
486  */
487  template<typename _T1, typename _T2>
488  inline _GLIBCXX_CONSTEXPR bool
489  operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
490  { return __x.first < __y.first
491  || (!(__y.first < __x.first) && __x.second < __y.second); }
492 
493  /// Uses @c operator== to find the result.
494  template<typename _T1, typename _T2>
495  inline _GLIBCXX_CONSTEXPR bool
496  operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
497  { return !(__x == __y); }
498 
499  /// Uses @c operator< to find the result.
500  template<typename _T1, typename _T2>
501  inline _GLIBCXX_CONSTEXPR bool
502  operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
503  { return __y < __x; }
504 
505  /// Uses @c operator< to find the result.
506  template<typename _T1, typename _T2>
507  inline _GLIBCXX_CONSTEXPR bool
508  operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
509  { return !(__y < __x); }
510 
511  /// Uses @c operator< to find the result.
512  template<typename _T1, typename _T2>
513  inline _GLIBCXX_CONSTEXPR bool
514  operator>=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
515  { return !(__x < __y); }
516 #endif // !(three_way_comparison && concepts)
517 
518 #if __cplusplus >= 201103L
519  /** Swap overload for pairs. Calls std::pair::swap().
520  *
521  * @note This std::swap overload is not declared in C++03 mode,
522  * which has performance implications, e.g. see https://gcc.gnu.org/PR38466
523  */
524  template<typename _T1, typename _T2>
525  _GLIBCXX20_CONSTEXPR inline
526 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
527  // Constrained free swap overload, see p0185r1
528  typename enable_if<__and_<__is_swappable<_T1>,
529  __is_swappable<_T2>>::value>::type
530 #else
531  void
532 #endif
533  swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
534  noexcept(noexcept(__x.swap(__y)))
535  { __x.swap(__y); }
536 
537 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
538  template<typename _T1, typename _T2>
539  typename enable_if<!__and_<__is_swappable<_T1>,
540  __is_swappable<_T2>>::value>::type
541  swap(pair<_T1, _T2>&, pair<_T1, _T2>&) = delete;
542 #endif
543 #endif // __cplusplus >= 201103L
544 
545  /// @} relates pair
546 
547  /**
548  * @brief A convenience wrapper for creating a pair from two objects.
549  * @param __x The first object.
550  * @param __y The second object.
551  * @return A newly-constructed pair<> object of the appropriate type.
552  *
553  * The C++98 standard says the objects are passed by reference-to-const,
554  * but C++03 says they are passed by value (this was LWG issue #181).
555  *
556  * Since C++11 they have been passed by forwarding reference and then
557  * forwarded to the new members of the pair. To create a pair with a
558  * member of reference type, pass a `reference_wrapper` to this function.
559  */
560  // _GLIBCXX_RESOLVE_LIB_DEFECTS
561  // 181. make_pair() unintended behavior
562 #if __cplusplus >= 201103L
563  // NB: DR 706.
564  template<typename _T1, typename _T2>
565  constexpr pair<typename __decay_and_strip<_T1>::__type,
566  typename __decay_and_strip<_T2>::__type>
567  make_pair(_T1&& __x, _T2&& __y)
568  {
569  typedef typename __decay_and_strip<_T1>::__type __ds_type1;
570  typedef typename __decay_and_strip<_T2>::__type __ds_type2;
571  typedef pair<__ds_type1, __ds_type2> __pair_type;
572  return __pair_type(std::forward<_T1>(__x), std::forward<_T2>(__y));
573  }
574 #else
575  template<typename _T1, typename _T2>
576  inline pair<_T1, _T2>
577  make_pair(_T1 __x, _T2 __y)
578  { return pair<_T1, _T2>(__x, __y); }
579 #endif
580 
581  /// @}
582 
583 _GLIBCXX_END_NAMESPACE_VERSION
584 } // namespace std
585 
586 #endif /* _STL_PAIR_H */
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:502
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:496
std::pair::operator==
constexpr bool operator==(const pair< _T1, _T2 > &__x, const pair< _T1, _T2 > &__y)
Definition: stl_pair.h:466
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:514
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:533
std::piecewise_construct
constexpr piecewise_construct_t piecewise_construct
Tag for piecewise construction of std::pair objects.
Definition: stl_pair.h:83
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:567
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:76
std
ISO C++ entities toplevel namespace is std.
std::tuple
Primary class template, tuple.
Definition: tuple:533
std::is_constructible
is_constructible
Definition: type_traits:908
std::is_default_constructible
is_default_constructible
Definition: type_traits:917
std::enable_if
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2183
std::piecewise_construct_t
Tag type for piecewise construction of std::pair objects.
Definition: stl_pair.h:80
std::pair
Struct holding two objects of arbitrary type.
Definition: stl_pair.h:213
std::pair::pair
constexpr pair(const _T1 &__a, const _T2 &__b)
Construct from two const lvalues, allowing implicit conversions.
Definition: stl_pair.h:266
std::pair::first
_T1 first
The first member.
Definition: stl_pair.h:217
std::pair::first_type
_T1 first_type
The type of the first member.
Definition: stl_pair.h:214
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:439
std::pair::pair
constexpr pair(const pair &)=default
Copy constructor.
std::pair::pair
constexpr pair()
Definition: stl_pair.h:232
std::pair::second_type
_T2 second_type
The type of the second member.
Definition: stl_pair.h:215
std::pair::pair
constexpr pair(pair &&)=default
Move constructor.
std::pair::second
_T2 second
The second member.
Definition: stl_pair.h:218