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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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
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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 #endif
67 
68 namespace 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 =
84 
85  /// @cond undocumented
86 
87  // Forward declarations.
88  template<typename...>
89  class tuple;
90 
91  template<std::size_t...>
92  struct _Index_tuple;
93 
94  // Concept utility functions, reused in conditionally-explicit
95  // constructors.
96  // See PR 70437, don't look at is_constructible or
97  // is_convertible if the types are the same to
98  // avoid querying those properties for incomplete types.
99  template <bool, typename _T1, typename _T2>
100  struct _PCC
101  {
102  template <typename _U1, typename _U2>
103  static constexpr bool _ConstructiblePair()
104  {
105  return __and_<is_constructible<_T1, const _U1&>,
107  }
108 
109  template <typename _U1, typename _U2>
110  static constexpr bool _ImplicitlyConvertiblePair()
111  {
112  return __and_<is_convertible<const _U1&, _T1>,
113  is_convertible<const _U2&, _T2>>::value;
114  }
115 
116  template <typename _U1, typename _U2>
117  static constexpr bool _MoveConstructiblePair()
118  {
119  return __and_<is_constructible<_T1, _U1&&>,
120  is_constructible<_T2, _U2&&>>::value;
121  }
122 
123  template <typename _U1, typename _U2>
124  static constexpr bool _ImplicitlyMoveConvertiblePair()
125  {
126  return __and_<is_convertible<_U1&&, _T1>,
127  is_convertible<_U2&&, _T2>>::value;
128  }
129 
130  template <bool __implicit, typename _U1, typename _U2>
131  static constexpr bool _CopyMovePair()
132  {
133  using __do_converts = __and_<is_convertible<const _U1&, _T1>,
134  is_convertible<_U2&&, _T2>>;
135  using __converts = typename conditional<__implicit,
136  __do_converts,
137  __not_<__do_converts>>::type;
138  return __and_<is_constructible<_T1, const _U1&>,
139  is_constructible<_T2, _U2&&>,
140  __converts
141  >::value;
142  }
143 
144  template <bool __implicit, typename _U1, typename _U2>
145  static constexpr bool _MoveCopyPair()
146  {
147  using __do_converts = __and_<is_convertible<_U1&&, _T1>,
148  is_convertible<const _U2&, _T2>>;
149  using __converts = typename conditional<__implicit,
150  __do_converts,
151  __not_<__do_converts>>::type;
152  return __and_<is_constructible<_T1, _U1&&>,
153  is_constructible<_T2, const _U2&&>,
154  __converts
155  >::value;
156  }
157  };
158 
159  template <typename _T1, typename _T2>
160  struct _PCC<false, _T1, _T2>
161  {
162  template <typename _U1, typename _U2>
163  static constexpr bool _ConstructiblePair()
164  {
165  return false;
166  }
167 
168  template <typename _U1, typename _U2>
169  static constexpr bool _ImplicitlyConvertiblePair()
170  {
171  return false;
172  }
173 
174  template <typename _U1, typename _U2>
175  static constexpr bool _MoveConstructiblePair()
176  {
177  return false;
178  }
179 
180  template <typename _U1, typename _U2>
181  static constexpr bool _ImplicitlyMoveConvertiblePair()
182  {
183  return false;
184  }
185  };
186 #endif // C++11
187 
188  template<typename _U1, typename _U2> class __pair_base
189  {
190 #if __cplusplus >= 201103L
191  template<typename _T1, typename _T2> friend struct pair;
192  __pair_base() = default;
193  ~__pair_base() = default;
194  __pair_base(const __pair_base&) = default;
195  __pair_base& operator=(const __pair_base&) = delete;
196 #endif // C++11
197  };
198 
199  /// @endcond
200 
201  /**
202  * @brief Struct holding two objects of arbitrary type.
203  *
204  * @tparam _T1 Type of first object.
205  * @tparam _T2 Type of second object.
206  *
207  * <https://gcc.gnu.org/onlinedocs/libstdc++/manual/utilities.html>
208  */
209  template<typename _T1, typename _T2>
210  struct pair
211  : private __pair_base<_T1, _T2>
212  {
213  typedef _T1 first_type; ///< The type of the `first` member
214  typedef _T2 second_type; ///< The type of the `second` member
215 
216  _T1 first; ///< The first member
217  _T2 second; ///< The second member
218 
219  // _GLIBCXX_RESOLVE_LIB_DEFECTS
220  // 265. std::pair::pair() effects overly restrictive
221  /** The default constructor creates @c first and @c second using their
222  * respective default constructors. */
223 #if __cplusplus >= 201103L
224  template <typename _U1 = _T1,
225  typename _U2 = _T2,
226  typename enable_if<__and_<
227  __is_implicitly_default_constructible<_U1>,
228  __is_implicitly_default_constructible<_U2>>
229  ::value, bool>::type = true>
230 #endif
231  _GLIBCXX_CONSTEXPR pair()
232  : first(), second() { }
233 
234 #if __cplusplus >= 201103L
235  template <typename _U1 = _T1,
236  typename _U2 = _T2,
237  typename enable_if<__and_<
240  __not_<
241  __and_<__is_implicitly_default_constructible<_U1>,
242  __is_implicitly_default_constructible<_U2>>>>
243  ::value, bool>::type = false>
244  explicit constexpr pair()
245  : first(), second() { }
246 #endif
247 
248 #if __cplusplus < 201103L
249  /// Two objects may be passed to a @c pair constructor to be copied.
250  pair(const _T1& __a, const _T2& __b)
251  : first(__a), second(__b) { }
252 #else
253  // Shortcut for constraining the templates that don't take pairs.
254  /// @cond undocumented
255  using _PCCP = _PCC<true, _T1, _T2>;
256  /// @endcond
257 
258  /// Construct from two const lvalues, allowing implicit conversions.
259  template<typename _U1 = _T1, typename _U2=_T2, typename
260  enable_if<_PCCP::template
261  _ConstructiblePair<_U1, _U2>()
262  && _PCCP::template
263  _ImplicitlyConvertiblePair<_U1, _U2>(),
264  bool>::type=true>
265  constexpr pair(const _T1& __a, const _T2& __b)
266  : first(__a), second(__b) { }
267 
268  /// Construct from two const lvalues, disallowing implicit conversions.
269  template<typename _U1 = _T1, typename _U2=_T2, typename
270  enable_if<_PCCP::template
271  _ConstructiblePair<_U1, _U2>()
272  && !_PCCP::template
273  _ImplicitlyConvertiblePair<_U1, _U2>(),
274  bool>::type=false>
275  explicit constexpr pair(const _T1& __a, const _T2& __b)
276  : first(__a), second(__b) { }
277 #endif
278 
279 #if __cplusplus < 201103L
280  /// There is also a templated constructor to convert from other pairs.
281  template<typename _U1, typename _U2>
282  pair(const pair<_U1, _U2>& __p)
283  : first(__p.first), second(__p.second) { }
284 #else
285  // Shortcut for constraining the templates that take pairs.
286  /// @cond undocumented
287  template <typename _U1, typename _U2>
288  using _PCCFP = _PCC<!is_same<_T1, _U1>::value
289  || !is_same<_T2, _U2>::value,
290  _T1, _T2>;
291  /// @endcond
292 
293  template<typename _U1, typename _U2, typename
294  enable_if<_PCCFP<_U1, _U2>::template
295  _ConstructiblePair<_U1, _U2>()
296  && _PCCFP<_U1, _U2>::template
297  _ImplicitlyConvertiblePair<_U1, _U2>(),
298  bool>::type=true>
299  constexpr pair(const pair<_U1, _U2>& __p)
300  : first(__p.first), second(__p.second) { }
301 
302  template<typename _U1, typename _U2, typename
303  enable_if<_PCCFP<_U1, _U2>::template
304  _ConstructiblePair<_U1, _U2>()
305  && !_PCCFP<_U1, _U2>::template
306  _ImplicitlyConvertiblePair<_U1, _U2>(),
307  bool>::type=false>
308  explicit constexpr pair(const pair<_U1, _U2>& __p)
309  : first(__p.first), second(__p.second) { }
310 #endif
311 
312 #if __cplusplus >= 201103L
313  constexpr pair(const pair&) = default; ///< Copy constructor
314  constexpr pair(pair&&) = default; ///< Move constructor
315 
316  // DR 811.
317  template<typename _U1, typename
318  enable_if<_PCCP::template
319  _MoveCopyPair<true, _U1, _T2>(),
320  bool>::type=true>
321  constexpr pair(_U1&& __x, const _T2& __y)
322  : first(std::forward<_U1>(__x)), second(__y) { }
323 
324  template<typename _U1, typename
325  enable_if<_PCCP::template
326  _MoveCopyPair<false, _U1, _T2>(),
327  bool>::type=false>
328  explicit constexpr pair(_U1&& __x, const _T2& __y)
329  : first(std::forward<_U1>(__x)), second(__y) { }
330 
331  template<typename _U2, typename
332  enable_if<_PCCP::template
333  _CopyMovePair<true, _T1, _U2>(),
334  bool>::type=true>
335  constexpr pair(const _T1& __x, _U2&& __y)
336  : first(__x), second(std::forward<_U2>(__y)) { }
337 
338  template<typename _U2, typename
339  enable_if<_PCCP::template
340  _CopyMovePair<false, _T1, _U2>(),
341  bool>::type=false>
342  explicit pair(const _T1& __x, _U2&& __y)
343  : first(__x), second(std::forward<_U2>(__y)) { }
344 
345  template<typename _U1, typename _U2, typename
346  enable_if<_PCCP::template
347  _MoveConstructiblePair<_U1, _U2>()
348  && _PCCP::template
349  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
350  bool>::type=true>
351  constexpr pair(_U1&& __x, _U2&& __y)
352  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
353 
354  template<typename _U1, typename _U2, typename
355  enable_if<_PCCP::template
356  _MoveConstructiblePair<_U1, _U2>()
357  && !_PCCP::template
358  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
359  bool>::type=false>
360  explicit constexpr pair(_U1&& __x, _U2&& __y)
361  : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
362 
363 
364  template<typename _U1, typename _U2, typename
365  enable_if<_PCCFP<_U1, _U2>::template
366  _MoveConstructiblePair<_U1, _U2>()
367  && _PCCFP<_U1, _U2>::template
368  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
369  bool>::type=true>
370  constexpr pair(pair<_U1, _U2>&& __p)
371  : first(std::forward<_U1>(__p.first)),
372  second(std::forward<_U2>(__p.second)) { }
373 
374  template<typename _U1, typename _U2, typename
375  enable_if<_PCCFP<_U1, _U2>::template
376  _MoveConstructiblePair<_U1, _U2>()
377  && !_PCCFP<_U1, _U2>::template
378  _ImplicitlyMoveConvertiblePair<_U1, _U2>(),
379  bool>::type=false>
380  explicit constexpr pair(pair<_U1, _U2>&& __p)
381  : first(std::forward<_U1>(__p.first)),
382  second(std::forward<_U2>(__p.second)) { }
383 
384  template<typename... _Args1, typename... _Args2>
385  _GLIBCXX20_CONSTEXPR
386  pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
387 
388  _GLIBCXX20_CONSTEXPR pair&
389  operator=(typename conditional<
390  __and_<is_copy_assignable<_T1>,
391  is_copy_assignable<_T2>>::value,
392  const pair&, const __nonesuch&>::type __p)
393  {
394  first = __p.first;
395  second = __p.second;
396  return *this;
397  }
398 
399  _GLIBCXX20_CONSTEXPR pair&
400  operator=(typename conditional<
401  __and_<is_move_assignable<_T1>,
402  is_move_assignable<_T2>>::value,
403  pair&&, __nonesuch&&>::type __p)
404  noexcept(__and_<is_nothrow_move_assignable<_T1>,
405  is_nothrow_move_assignable<_T2>>::value)
406  {
407  first = std::forward<first_type>(__p.first);
408  second = std::forward<second_type>(__p.second);
409  return *this;
410  }
411 
412  template<typename _U1, typename _U2>
413  _GLIBCXX20_CONSTEXPR
414  typename enable_if<__and_<is_assignable<_T1&, const _U1&>,
415  is_assignable<_T2&, const _U2&>>::value,
416  pair&>::type
417  operator=(const pair<_U1, _U2>& __p)
418  {
419  first = __p.first;
420  second = __p.second;
421  return *this;
422  }
423 
424  template<typename _U1, typename _U2>
425  _GLIBCXX20_CONSTEXPR
426  typename enable_if<__and_<is_assignable<_T1&, _U1&&>,
427  is_assignable<_T2&, _U2&&>>::value,
428  pair&>::type
429  operator=(pair<_U1, _U2>&& __p)
430  {
431  first = std::forward<_U1>(__p.first);
432  second = std::forward<_U2>(__p.second);
433  return *this;
434  }
435 
436  /// Swap the first members and then the second members.
437  _GLIBCXX20_CONSTEXPR void
438  swap(pair& __p)
439  noexcept(__and_<__is_nothrow_swappable<_T1>,
440  __is_nothrow_swappable<_T2>>::value)
441  {
442  using std::swap;
443  swap(first, __p.first);
444  swap(second, __p.second);
445  }
446 
447  private:
448  template<typename... _Args1, std::size_t... _Indexes1,
449  typename... _Args2, std::size_t... _Indexes2>
450  _GLIBCXX20_CONSTEXPR
452  _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
453 #endif // C++11
454  };
455 
456  /// @relates pair @{
457 
458 #if __cpp_deduction_guides >= 201606
459  template<typename _T1, typename _T2> pair(_T1, _T2) -> pair<_T1, _T2>;
460 #endif
461 
462  /// Two pairs of the same type are equal iff their members are equal.
463  template<typename _T1, typename _T2>
464  inline _GLIBCXX_CONSTEXPR bool
465  operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
466  { return __x.first == __y.first && __x.second == __y.second; }
467 
468 #if __cpp_lib_three_way_comparison && __cpp_lib_concepts
469  template<typename _T1, typename _T2>
470  constexpr common_comparison_category_t<__detail::__synth3way_t<_T1>,
471  __detail::__synth3way_t<_T2>>
472  operator<=>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
473  {
474  if (auto __c = __detail::__synth3way(__x.first, __y.first); __c != 0)
475  return __c;
476  return __detail::__synth3way(__x.second, __y.second);
477  }
478 #else
479  /** Defines a lexicographical order for pairs.
480  *
481  * For two pairs of the same type, `P` is ordered before `Q` if
482  * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
483  * are equivalent (neither is less than the other) and `P.second` is less
484  * than `Q.second`.
485  */
486  template<typename _T1, typename _T2>
487  inline _GLIBCXX_CONSTEXPR bool
488  operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
489  { return __x.first < __y.first
490  || (!(__y.first < __x.first) && __x.second < __y.second); }
491 
492  /// Uses @c operator== to find the result.
493  template<typename _T1, typename _T2>
494  inline _GLIBCXX_CONSTEXPR bool
495  operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
496  { return !(__x == __y); }
497 
498  /// Uses @c operator< to find the result.
499  template<typename _T1, typename _T2>
500  inline _GLIBCXX_CONSTEXPR bool
501  operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
502  { return __y < __x; }
503 
504  /// Uses @c operator< to find the result.
505  template<typename _T1, typename _T2>
506  inline _GLIBCXX_CONSTEXPR bool
507  operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
508  { return !(__y < __x); }
509 
510  /// Uses @c operator< to find the result.
511  template<typename _T1, typename _T2>
512  inline _GLIBCXX_CONSTEXPR bool
513  operator>=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
514  { return !(__x < __y); }
515 #endif // !(three_way_comparison && concepts)
516 
517 #if __cplusplus >= 201103L
518  /** Swap overload for pairs. Calls std::pair::swap().
519  *
520  * @note This std::swap overload is not declared in C++03 mode,
521  * which has performance implications, e.g. see https://gcc.gnu.org/PR38466
522  */
523  template<typename _T1, typename _T2>
524  _GLIBCXX20_CONSTEXPR inline
525 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
526  // Constrained free swap overload, see p0185r1
528  __is_swappable<_T2>>::value>::type
529 #else
530  void
531 #endif
533  noexcept(noexcept(__x.swap(__y)))
534  { __x.swap(__y); }
535 
536 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
537  template<typename _T1, typename _T2>
539  __is_swappable<_T2>>::value>::type
540  swap(pair<_T1, _T2>&, pair<_T1, _T2>&) = delete;
541 #endif
542 #endif // __cplusplus >= 201103L
543 
544  // @} relates pair
545 
546  /**
547  * @brief A convenience wrapper for creating a pair from two objects.
548  * @param __x The first object.
549  * @param __y The second object.
550  * @return A newly-constructed pair<> object of the appropriate type.
551  *
552  * The C++98 standard says the objects are passed by reference-to-const,
553  * but C++03 says they are passed by value (this was LWG issue #181).
554  *
555  * Since C++11 they have been passed by forwarding reference and then
556  * forwarded to the new members of the pair. To create a pair with a
557  * member of reference type, pass a `reference_wrapper` to this function.
558  */
559  // _GLIBCXX_RESOLVE_LIB_DEFECTS
560  // 181. make_pair() unintended behavior
561 #if __cplusplus >= 201103L
562  // NB: DR 706.
563  template<typename _T1, typename _T2>
565  typename __decay_and_strip<_T2>::__type>
566  make_pair(_T1&& __x, _T2&& __y)
567  {
568  typedef typename __decay_and_strip<_T1>::__type __ds_type1;
569  typedef typename __decay_and_strip<_T2>::__type __ds_type2;
570  typedef pair<__ds_type1, __ds_type2> __pair_type;
571  return __pair_type(std::forward<_T1>(__x), std::forward<_T2>(__y));
572  }
573 #else
574  template<typename _T1, typename _T2>
575  inline pair<_T1, _T2>
576  make_pair(_T1 __x, _T2 __y)
577  { return pair<_T1, _T2>(__x, __y); }
578 #endif
579 
580  /// @}
581 
582 _GLIBCXX_END_NAMESPACE_VERSION
583 } // namespace std
584 
585 #endif /* _STL_PAIR_H */
std::pair::pair
constexpr pair(const _T1 &__a, const _T2 &__b)
Construct from two const lvalues, disallowing implicit conversions.
Definition: stl_pair.h:275
std::pair::first
_T1 first
The first member.
Definition: stl_pair.h:216
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:438
std::piecewise_construct_t
Tag type for piecewise construction of std::pair objects.
Definition: stl_pair.h:79
std::tuple
Primary class template, tuple.
Definition: tuple:56
std::pair::second_type
_T2 second_type
The type of the second member.
Definition: stl_pair.h:214
std
ISO C++ entities toplevel namespace is std.
std::pair::pair
constexpr pair(const _T1 &__a, const _T2 &__b)
Construct from two const lvalues, allowing implicit conversions.
Definition: stl_pair.h:265
std::pair::pair
constexpr pair()
Definition: stl_pair.h:231
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:465
std::is_default_constructible
is_default_constructible
Definition: type_traits:915
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:501
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:76
move.h
std::pair::first_type
_T1 first_type
The type of the first member.
Definition: stl_pair.h:213
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:566
type_traits
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:513
std::enable_if
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2169
std::pair::second
_T2 second
The second member.
Definition: stl_pair.h:217
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:495
std::is_constructible
is_constructible
Definition: type_traits:906
compare
std::pair
Struct holding two objects of arbitrary type.
Definition: stl_pair.h:210
std::piecewise_construct
constexpr piecewise_construct_t piecewise_construct
Tag for piecewise construction of std::pair objects.
Definition: stl_pair.h:82
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:532