libstdc++
tuple
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1 // <tuple> -*- C++ -*-
2 
3 // Copyright (C) 2007-2021 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 /** @file include/tuple
26  * This is a Standard C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_TUPLE
30 #define _GLIBCXX_TUPLE 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus < 201103L
35 # include <bits/c++0x_warning.h>
36 #else
37 
38 #include <utility>
39 #include <array>
40 #include <bits/uses_allocator.h>
41 #include <bits/invoke.h>
42 #if __cplusplus > 201703L
43 # include <compare>
44 # define __cpp_lib_constexpr_tuple 201811L
45 #endif
46 
47 namespace std _GLIBCXX_VISIBILITY(default)
48 {
49 _GLIBCXX_BEGIN_NAMESPACE_VERSION
50 
51  /**
52  * @addtogroup utilities
53  * @{
54  */
55 
56  template<typename... _Elements>
57  class tuple;
58 
59  template<typename _Tp>
60  struct __is_empty_non_tuple : is_empty<_Tp> { };
61 
62  // Using EBO for elements that are tuples causes ambiguous base errors.
63  template<typename _El0, typename... _El>
64  struct __is_empty_non_tuple<tuple<_El0, _El...>> : false_type { };
65 
66  // Use the Empty Base-class Optimization for empty, non-final types.
67  template<typename _Tp>
68  using __empty_not_final
69  = typename conditional<__is_final(_Tp), false_type,
70  __is_empty_non_tuple<_Tp>>::type;
71 
72  template<size_t _Idx, typename _Head,
73  bool = __empty_not_final<_Head>::value>
74  struct _Head_base;
75 
76 #if __has_cpp_attribute(__no_unique_address__)
77  template<size_t _Idx, typename _Head>
78  struct _Head_base<_Idx, _Head, true>
79  {
80  constexpr _Head_base()
81  : _M_head_impl() { }
82 
83  constexpr _Head_base(const _Head& __h)
84  : _M_head_impl(__h) { }
85 
86  constexpr _Head_base(const _Head_base&) = default;
87  constexpr _Head_base(_Head_base&&) = default;
88 
89  template<typename _UHead>
90  constexpr _Head_base(_UHead&& __h)
91  : _M_head_impl(std::forward<_UHead>(__h)) { }
92 
93  _GLIBCXX20_CONSTEXPR
94  _Head_base(allocator_arg_t, __uses_alloc0)
95  : _M_head_impl() { }
96 
97  template<typename _Alloc>
98  _GLIBCXX20_CONSTEXPR
99  _Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
100  : _M_head_impl(allocator_arg, *__a._M_a) { }
101 
102  template<typename _Alloc>
103  _GLIBCXX20_CONSTEXPR
104  _Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
105  : _M_head_impl(*__a._M_a) { }
106 
107  template<typename _UHead>
108  _GLIBCXX20_CONSTEXPR
109  _Head_base(__uses_alloc0, _UHead&& __uhead)
110  : _M_head_impl(std::forward<_UHead>(__uhead)) { }
111 
112  template<typename _Alloc, typename _UHead>
113  _GLIBCXX20_CONSTEXPR
114  _Head_base(__uses_alloc1<_Alloc> __a, _UHead&& __uhead)
115  : _M_head_impl(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead))
116  { }
117 
118  template<typename _Alloc, typename _UHead>
119  _GLIBCXX20_CONSTEXPR
120  _Head_base(__uses_alloc2<_Alloc> __a, _UHead&& __uhead)
121  : _M_head_impl(std::forward<_UHead>(__uhead), *__a._M_a) { }
122 
123  static constexpr _Head&
124  _M_head(_Head_base& __b) noexcept { return __b._M_head_impl; }
125 
126  static constexpr const _Head&
127  _M_head(const _Head_base& __b) noexcept { return __b._M_head_impl; }
128 
129  [[__no_unique_address__]] _Head _M_head_impl;
130  };
131 #else
132  template<size_t _Idx, typename _Head>
133  struct _Head_base<_Idx, _Head, true>
134  : public _Head
135  {
136  constexpr _Head_base()
137  : _Head() { }
138 
139  constexpr _Head_base(const _Head& __h)
140  : _Head(__h) { }
141 
142  constexpr _Head_base(const _Head_base&) = default;
143  constexpr _Head_base(_Head_base&&) = default;
144 
145  template<typename _UHead>
146  constexpr _Head_base(_UHead&& __h)
147  : _Head(std::forward<_UHead>(__h)) { }
148 
149  _GLIBCXX20_CONSTEXPR
150  _Head_base(allocator_arg_t, __uses_alloc0)
151  : _Head() { }
152 
153  template<typename _Alloc>
154  _GLIBCXX20_CONSTEXPR
155  _Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
156  : _Head(allocator_arg, *__a._M_a) { }
157 
158  template<typename _Alloc>
159  _GLIBCXX20_CONSTEXPR
160  _Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
161  : _Head(*__a._M_a) { }
162 
163  template<typename _UHead>
164  _GLIBCXX20_CONSTEXPR
165  _Head_base(__uses_alloc0, _UHead&& __uhead)
166  : _Head(std::forward<_UHead>(__uhead)) { }
167 
168  template<typename _Alloc, typename _UHead>
169  _GLIBCXX20_CONSTEXPR
170  _Head_base(__uses_alloc1<_Alloc> __a, _UHead&& __uhead)
171  : _Head(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead)) { }
172 
173  template<typename _Alloc, typename _UHead>
174  _GLIBCXX20_CONSTEXPR
175  _Head_base(__uses_alloc2<_Alloc> __a, _UHead&& __uhead)
176  : _Head(std::forward<_UHead>(__uhead), *__a._M_a) { }
177 
178  static constexpr _Head&
179  _M_head(_Head_base& __b) noexcept { return __b; }
180 
181  static constexpr const _Head&
182  _M_head(const _Head_base& __b) noexcept { return __b; }
183  };
184 #endif
185 
186  template<size_t _Idx, typename _Head>
187  struct _Head_base<_Idx, _Head, false>
188  {
189  constexpr _Head_base()
190  : _M_head_impl() { }
191 
192  constexpr _Head_base(const _Head& __h)
193  : _M_head_impl(__h) { }
194 
195  constexpr _Head_base(const _Head_base&) = default;
196  constexpr _Head_base(_Head_base&&) = default;
197 
198  template<typename _UHead>
199  constexpr _Head_base(_UHead&& __h)
200  : _M_head_impl(std::forward<_UHead>(__h)) { }
201 
202  _GLIBCXX20_CONSTEXPR
203  _Head_base(allocator_arg_t, __uses_alloc0)
204  : _M_head_impl() { }
205 
206  template<typename _Alloc>
207  _GLIBCXX20_CONSTEXPR
208  _Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
209  : _M_head_impl(allocator_arg, *__a._M_a) { }
210 
211  template<typename _Alloc>
212  _GLIBCXX20_CONSTEXPR
213  _Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
214  : _M_head_impl(*__a._M_a) { }
215 
216  template<typename _UHead>
217  _GLIBCXX20_CONSTEXPR
218  _Head_base(__uses_alloc0, _UHead&& __uhead)
219  : _M_head_impl(std::forward<_UHead>(__uhead)) { }
220 
221  template<typename _Alloc, typename _UHead>
222  _GLIBCXX20_CONSTEXPR
223  _Head_base(__uses_alloc1<_Alloc> __a, _UHead&& __uhead)
224  : _M_head_impl(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead))
225  { }
226 
227  template<typename _Alloc, typename _UHead>
228  _GLIBCXX20_CONSTEXPR
229  _Head_base(__uses_alloc2<_Alloc> __a, _UHead&& __uhead)
230  : _M_head_impl(std::forward<_UHead>(__uhead), *__a._M_a) { }
231 
232  static constexpr _Head&
233  _M_head(_Head_base& __b) noexcept { return __b._M_head_impl; }
234 
235  static constexpr const _Head&
236  _M_head(const _Head_base& __b) noexcept { return __b._M_head_impl; }
237 
238  _Head _M_head_impl;
239  };
240 
241  /**
242  * Contains the actual implementation of the @c tuple template, stored
243  * as a recursive inheritance hierarchy from the first element (most
244  * derived class) to the last (least derived class). The @c Idx
245  * parameter gives the 0-based index of the element stored at this
246  * point in the hierarchy; we use it to implement a constant-time
247  * get() operation.
248  */
249  template<size_t _Idx, typename... _Elements>
250  struct _Tuple_impl;
251 
252  /**
253  * Recursive tuple implementation. Here we store the @c Head element
254  * and derive from a @c Tuple_impl containing the remaining elements
255  * (which contains the @c Tail).
256  */
257  template<size_t _Idx, typename _Head, typename... _Tail>
258  struct _Tuple_impl<_Idx, _Head, _Tail...>
259  : public _Tuple_impl<_Idx + 1, _Tail...>,
260  private _Head_base<_Idx, _Head>
261  {
262  template<size_t, typename...> friend struct _Tuple_impl;
263 
264  typedef _Tuple_impl<_Idx + 1, _Tail...> _Inherited;
265  typedef _Head_base<_Idx, _Head> _Base;
266 
267  static constexpr _Head&
268  _M_head(_Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
269 
270  static constexpr const _Head&
271  _M_head(const _Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
272 
273  static constexpr _Inherited&
274  _M_tail(_Tuple_impl& __t) noexcept { return __t; }
275 
276  static constexpr const _Inherited&
277  _M_tail(const _Tuple_impl& __t) noexcept { return __t; }
278 
279  constexpr _Tuple_impl()
280  : _Inherited(), _Base() { }
281 
282  explicit constexpr
283  _Tuple_impl(const _Head& __head, const _Tail&... __tail)
284  : _Inherited(__tail...), _Base(__head)
285  { }
286 
287  template<typename _UHead, typename... _UTail,
288  typename = __enable_if_t<sizeof...(_Tail) == sizeof...(_UTail)>>
289  explicit constexpr
290  _Tuple_impl(_UHead&& __head, _UTail&&... __tail)
291  : _Inherited(std::forward<_UTail>(__tail)...),
292  _Base(std::forward<_UHead>(__head))
293  { }
294 
295  constexpr _Tuple_impl(const _Tuple_impl&) = default;
296 
297  // _GLIBCXX_RESOLVE_LIB_DEFECTS
298  // 2729. Missing SFINAE on std::pair::operator=
299  _Tuple_impl& operator=(const _Tuple_impl&) = delete;
300 
301  _Tuple_impl(_Tuple_impl&&) = default;
302 
303  template<typename... _UElements>
304  constexpr
305  _Tuple_impl(const _Tuple_impl<_Idx, _UElements...>& __in)
306  : _Inherited(_Tuple_impl<_Idx, _UElements...>::_M_tail(__in)),
307  _Base(_Tuple_impl<_Idx, _UElements...>::_M_head(__in))
308  { }
309 
310  template<typename _UHead, typename... _UTails>
311  constexpr
312  _Tuple_impl(_Tuple_impl<_Idx, _UHead, _UTails...>&& __in)
313  : _Inherited(std::move
314  (_Tuple_impl<_Idx, _UHead, _UTails...>::_M_tail(__in))),
315  _Base(std::forward<_UHead>
316  (_Tuple_impl<_Idx, _UHead, _UTails...>::_M_head(__in)))
317  { }
318 
319  template<typename _Alloc>
320  _GLIBCXX20_CONSTEXPR
321  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a)
322  : _Inherited(__tag, __a),
323  _Base(__tag, __use_alloc<_Head>(__a))
324  { }
325 
326  template<typename _Alloc>
327  _GLIBCXX20_CONSTEXPR
328  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
329  const _Head& __head, const _Tail&... __tail)
330  : _Inherited(__tag, __a, __tail...),
331  _Base(__use_alloc<_Head, _Alloc, _Head>(__a), __head)
332  { }
333 
334  template<typename _Alloc, typename _UHead, typename... _UTail,
335  typename = __enable_if_t<sizeof...(_Tail) == sizeof...(_UTail)>>
336  _GLIBCXX20_CONSTEXPR
337  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
338  _UHead&& __head, _UTail&&... __tail)
339  : _Inherited(__tag, __a, std::forward<_UTail>(__tail)...),
340  _Base(__use_alloc<_Head, _Alloc, _UHead>(__a),
341  std::forward<_UHead>(__head))
342  { }
343 
344  template<typename _Alloc>
345  _GLIBCXX20_CONSTEXPR
346  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
347  const _Tuple_impl& __in)
348  : _Inherited(__tag, __a, _M_tail(__in)),
349  _Base(__use_alloc<_Head, _Alloc, _Head>(__a), _M_head(__in))
350  { }
351 
352  template<typename _Alloc>
353  _GLIBCXX20_CONSTEXPR
354  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
355  _Tuple_impl&& __in)
356  : _Inherited(__tag, __a, std::move(_M_tail(__in))),
357  _Base(__use_alloc<_Head, _Alloc, _Head>(__a),
358  std::forward<_Head>(_M_head(__in)))
359  { }
360 
361  template<typename _Alloc, typename _UHead, typename... _UTails>
362  _GLIBCXX20_CONSTEXPR
363  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
364  const _Tuple_impl<_Idx, _UHead, _UTails...>& __in)
365  : _Inherited(__tag, __a,
366  _Tuple_impl<_Idx, _UHead, _UTails...>::_M_tail(__in)),
367  _Base(__use_alloc<_Head, _Alloc, const _UHead&>(__a),
368  _Tuple_impl<_Idx, _UHead, _UTails...>::_M_head(__in))
369  { }
370 
371  template<typename _Alloc, typename _UHead, typename... _UTails>
372  _GLIBCXX20_CONSTEXPR
373  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
374  _Tuple_impl<_Idx, _UHead, _UTails...>&& __in)
375  : _Inherited(__tag, __a, std::move
376  (_Tuple_impl<_Idx, _UHead, _UTails...>::_M_tail(__in))),
377  _Base(__use_alloc<_Head, _Alloc, _UHead>(__a),
378  std::forward<_UHead>
379  (_Tuple_impl<_Idx, _UHead, _UTails...>::_M_head(__in)))
380  { }
381 
382  template<typename... _UElements>
383  _GLIBCXX20_CONSTEXPR
384  void
385  _M_assign(const _Tuple_impl<_Idx, _UElements...>& __in)
386  {
387  _M_head(*this) = _Tuple_impl<_Idx, _UElements...>::_M_head(__in);
388  _M_tail(*this)._M_assign(
389  _Tuple_impl<_Idx, _UElements...>::_M_tail(__in));
390  }
391 
392  template<typename _UHead, typename... _UTails>
393  _GLIBCXX20_CONSTEXPR
394  void
395  _M_assign(_Tuple_impl<_Idx, _UHead, _UTails...>&& __in)
396  {
397  _M_head(*this) = std::forward<_UHead>
398  (_Tuple_impl<_Idx, _UHead, _UTails...>::_M_head(__in));
399  _M_tail(*this)._M_assign(
400  std::move(_Tuple_impl<_Idx, _UHead, _UTails...>::_M_tail(__in)));
401  }
402 
403  protected:
404  _GLIBCXX20_CONSTEXPR
405  void
406  _M_swap(_Tuple_impl& __in)
407  {
408  using std::swap;
409  swap(_M_head(*this), _M_head(__in));
410  _Inherited::_M_swap(_M_tail(__in));
411  }
412  };
413 
414  // Basis case of inheritance recursion.
415  template<size_t _Idx, typename _Head>
416  struct _Tuple_impl<_Idx, _Head>
417  : private _Head_base<_Idx, _Head>
418  {
419  template<size_t, typename...> friend struct _Tuple_impl;
420 
421  typedef _Head_base<_Idx, _Head> _Base;
422 
423  static constexpr _Head&
424  _M_head(_Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
425 
426  static constexpr const _Head&
427  _M_head(const _Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
428 
429  constexpr
430  _Tuple_impl()
431  : _Base() { }
432 
433  explicit constexpr
434  _Tuple_impl(const _Head& __head)
435  : _Base(__head)
436  { }
437 
438  template<typename _UHead>
439  explicit constexpr
440  _Tuple_impl(_UHead&& __head)
441  : _Base(std::forward<_UHead>(__head))
442  { }
443 
444  constexpr _Tuple_impl(const _Tuple_impl&) = default;
445 
446  // _GLIBCXX_RESOLVE_LIB_DEFECTS
447  // 2729. Missing SFINAE on std::pair::operator=
448  _Tuple_impl& operator=(const _Tuple_impl&) = delete;
449 
450 #if _GLIBCXX_INLINE_VERSION
451  _Tuple_impl(_Tuple_impl&&) = default;
452 #else
453  constexpr
454  _Tuple_impl(_Tuple_impl&& __in)
455  noexcept(is_nothrow_move_constructible<_Head>::value)
456  : _Base(static_cast<_Base&&>(__in))
457  { }
458 #endif
459 
460  template<typename _UHead>
461  constexpr
462  _Tuple_impl(const _Tuple_impl<_Idx, _UHead>& __in)
463  : _Base(_Tuple_impl<_Idx, _UHead>::_M_head(__in))
464  { }
465 
466  template<typename _UHead>
467  constexpr
468  _Tuple_impl(_Tuple_impl<_Idx, _UHead>&& __in)
469  : _Base(std::forward<_UHead>(_Tuple_impl<_Idx, _UHead>::_M_head(__in)))
470  { }
471 
472  template<typename _Alloc>
473  _GLIBCXX20_CONSTEXPR
474  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a)
475  : _Base(__tag, __use_alloc<_Head>(__a))
476  { }
477 
478  template<typename _Alloc>
479  _GLIBCXX20_CONSTEXPR
480  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
481  const _Head& __head)
482  : _Base(__use_alloc<_Head, _Alloc, const _Head&>(__a), __head)
483  { }
484 
485  template<typename _Alloc, typename _UHead>
486  _GLIBCXX20_CONSTEXPR
487  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
488  _UHead&& __head)
489  : _Base(__use_alloc<_Head, _Alloc, _UHead>(__a),
490  std::forward<_UHead>(__head))
491  { }
492 
493  template<typename _Alloc>
494  _GLIBCXX20_CONSTEXPR
495  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
496  const _Tuple_impl& __in)
497  : _Base(__use_alloc<_Head, _Alloc, const _Head&>(__a), _M_head(__in))
498  { }
499 
500  template<typename _Alloc>
501  _GLIBCXX20_CONSTEXPR
502  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
503  _Tuple_impl&& __in)
504  : _Base(__use_alloc<_Head, _Alloc, _Head>(__a),
505  std::forward<_Head>(_M_head(__in)))
506  { }
507 
508  template<typename _Alloc, typename _UHead>
509  _GLIBCXX20_CONSTEXPR
510  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
511  const _Tuple_impl<_Idx, _UHead>& __in)
512  : _Base(__use_alloc<_Head, _Alloc, const _UHead&>(__a),
513  _Tuple_impl<_Idx, _UHead>::_M_head(__in))
514  { }
515 
516  template<typename _Alloc, typename _UHead>
517  _GLIBCXX20_CONSTEXPR
518  _Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
519  _Tuple_impl<_Idx, _UHead>&& __in)
520  : _Base(__use_alloc<_Head, _Alloc, _UHead>(__a),
521  std::forward<_UHead>(_Tuple_impl<_Idx, _UHead>::_M_head(__in)))
522  { }
523 
524  template<typename _UHead>
525  _GLIBCXX20_CONSTEXPR
526  void
527  _M_assign(const _Tuple_impl<_Idx, _UHead>& __in)
528  {
529  _M_head(*this) = _Tuple_impl<_Idx, _UHead>::_M_head(__in);
530  }
531 
532  template<typename _UHead>
533  _GLIBCXX20_CONSTEXPR
534  void
535  _M_assign(_Tuple_impl<_Idx, _UHead>&& __in)
536  {
537  _M_head(*this)
538  = std::forward<_UHead>(_Tuple_impl<_Idx, _UHead>::_M_head(__in));
539  }
540 
541  protected:
542  _GLIBCXX20_CONSTEXPR
543  void
544  _M_swap(_Tuple_impl& __in)
545  {
546  using std::swap;
547  swap(_M_head(*this), _M_head(__in));
548  }
549  };
550 
551  // Concept utility functions, reused in conditionally-explicit
552  // constructors.
553  template<bool, typename... _Types>
554  struct _TupleConstraints
555  {
556  // Constraint for a non-explicit constructor.
557  // True iff each Ti in _Types... can be constructed from Ui in _UTypes...
558  // and every Ui is implicitly convertible to Ti.
559  template<typename... _UTypes>
560  static constexpr bool __is_implicitly_constructible()
561  {
562  return __and_<is_constructible<_Types, _UTypes>...,
563  is_convertible<_UTypes, _Types>...
564  >::value;
565  }
566 
567  // Constraint for a non-explicit constructor.
568  // True iff each Ti in _Types... can be constructed from Ui in _UTypes...
569  // but not every Ui is implicitly convertible to Ti.
570  template<typename... _UTypes>
571  static constexpr bool __is_explicitly_constructible()
572  {
573  return __and_<is_constructible<_Types, _UTypes>...,
574  __not_<__and_<is_convertible<_UTypes, _Types>...>>
575  >::value;
576  }
577 
578  static constexpr bool __is_implicitly_default_constructible()
579  {
580  return __and_<std::__is_implicitly_default_constructible<_Types>...
581  >::value;
582  }
583 
584  static constexpr bool __is_explicitly_default_constructible()
585  {
586  return __and_<is_default_constructible<_Types>...,
587  __not_<__and_<
588  std::__is_implicitly_default_constructible<_Types>...>
589  >>::value;
590  }
591  };
592 
593  // Partial specialization used when a required precondition isn't met,
594  // e.g. when sizeof...(_Types) != sizeof...(_UTypes).
595  template<typename... _Types>
596  struct _TupleConstraints<false, _Types...>
597  {
598  template<typename... _UTypes>
599  static constexpr bool __is_implicitly_constructible()
600  { return false; }
601 
602  template<typename... _UTypes>
603  static constexpr bool __is_explicitly_constructible()
604  { return false; }
605  };
606 
607  /// Primary class template, tuple
608  template<typename... _Elements>
609  class tuple : public _Tuple_impl<0, _Elements...>
610  {
611  typedef _Tuple_impl<0, _Elements...> _Inherited;
612 
613  template<bool _Cond>
614  using _TCC = _TupleConstraints<_Cond, _Elements...>;
615 
616  // Constraint for non-explicit default constructor
617  template<bool _Dummy>
618  using _ImplicitDefaultCtor = __enable_if_t<
619  _TCC<_Dummy>::__is_implicitly_default_constructible(),
620  bool>;
621 
622  // Constraint for explicit default constructor
623  template<bool _Dummy>
624  using _ExplicitDefaultCtor = __enable_if_t<
625  _TCC<_Dummy>::__is_explicitly_default_constructible(),
626  bool>;
627 
628  // Constraint for non-explicit constructors
629  template<bool _Cond, typename... _Args>
630  using _ImplicitCtor = __enable_if_t<
631  _TCC<_Cond>::template __is_implicitly_constructible<_Args...>(),
632  bool>;
633 
634  // Constraint for non-explicit constructors
635  template<bool _Cond, typename... _Args>
636  using _ExplicitCtor = __enable_if_t<
637  _TCC<_Cond>::template __is_explicitly_constructible<_Args...>(),
638  bool>;
639 
640  template<typename... _UElements>
641  static constexpr
642  __enable_if_t<sizeof...(_UElements) == sizeof...(_Elements), bool>
643  __assignable()
644  { return __and_<is_assignable<_Elements&, _UElements>...>::value; }
645 
646  // Condition for noexcept-specifier of an assignment operator.
647  template<typename... _UElements>
648  static constexpr bool __nothrow_assignable()
649  {
650  return
651  __and_<is_nothrow_assignable<_Elements&, _UElements>...>::value;
652  }
653 
654  // Condition for noexcept-specifier of a constructor.
655  template<typename... _UElements>
656  static constexpr bool __nothrow_constructible()
657  {
658  return
659  __and_<is_nothrow_constructible<_Elements, _UElements>...>::value;
660  }
661 
662  // Constraint for tuple(_UTypes&&...) where sizeof...(_UTypes) == 1.
663  template<typename _Up>
664  static constexpr bool __valid_args()
665  {
666  return sizeof...(_Elements) == 1
667  && !is_same<tuple, __remove_cvref_t<_Up>>::value;
668  }
669 
670  // Constraint for tuple(_UTypes&&...) where sizeof...(_UTypes) > 1.
671  template<typename, typename, typename... _Tail>
672  static constexpr bool __valid_args()
673  { return (sizeof...(_Tail) + 2) == sizeof...(_Elements); }
674 
675  /* Constraint for constructors with a tuple<UTypes...> parameter ensures
676  * that the constructor is only viable when it would not interfere with
677  * tuple(UTypes&&...) or tuple(const tuple&) or tuple(tuple&&).
678  * Such constructors are only viable if:
679  * either sizeof...(Types) != 1,
680  * or (when Types... expands to T and UTypes... expands to U)
681  * is_convertible_v<TUPLE, T>, is_constructible_v<T, TUPLE>,
682  * and is_same_v<T, U> are all false.
683  */
684  template<typename _Tuple, typename = tuple,
685  typename = __remove_cvref_t<_Tuple>>
686  struct _UseOtherCtor
687  : false_type
688  { };
689  // If TUPLE is convertible to the single element in *this,
690  // then TUPLE should match tuple(UTypes&&...) instead.
691  template<typename _Tuple, typename _Tp, typename _Up>
692  struct _UseOtherCtor<_Tuple, tuple<_Tp>, tuple<_Up>>
693  : __or_<is_convertible<_Tuple, _Tp>, is_constructible<_Tp, _Tuple>>
694  { };
695  // If TUPLE and *this each have a single element of the same type,
696  // then TUPLE should match a copy/move constructor instead.
697  template<typename _Tuple, typename _Tp>
698  struct _UseOtherCtor<_Tuple, tuple<_Tp>, tuple<_Tp>>
699  : true_type
700  { };
701 
702  // Return true iff sizeof...(Types) == 1 && tuple_size_v<TUPLE> == 1
703  // and the single element in Types can be initialized from TUPLE,
704  // or is the same type as tuple_element_t<0, TUPLE>.
705  template<typename _Tuple>
706  static constexpr bool __use_other_ctor()
707  { return _UseOtherCtor<_Tuple>::value; }
708 
709  public:
710  template<typename _Dummy = void,
711  _ImplicitDefaultCtor<is_void<_Dummy>::value> = true>
712  constexpr
713  tuple()
714  noexcept(__and_<is_nothrow_default_constructible<_Elements>...>::value)
715  : _Inherited() { }
716 
717  template<typename _Dummy = void,
718  _ExplicitDefaultCtor<is_void<_Dummy>::value> = false>
719  explicit constexpr
720  tuple()
721  noexcept(__and_<is_nothrow_default_constructible<_Elements>...>::value)
722  : _Inherited() { }
723 
724  template<bool _NotEmpty = (sizeof...(_Elements) >= 1),
725  _ImplicitCtor<_NotEmpty, const _Elements&...> = true>
726  constexpr
727  tuple(const _Elements&... __elements)
728  noexcept(__nothrow_constructible<const _Elements&...>())
729  : _Inherited(__elements...) { }
730 
731  template<bool _NotEmpty = (sizeof...(_Elements) >= 1),
732  _ExplicitCtor<_NotEmpty, const _Elements&...> = false>
733  explicit constexpr
734  tuple(const _Elements&... __elements)
735  noexcept(__nothrow_constructible<const _Elements&...>())
736  : _Inherited(__elements...) { }
737 
738  template<typename... _UElements,
739  bool _Valid = __valid_args<_UElements...>(),
740  _ImplicitCtor<_Valid, _UElements...> = true>
741  constexpr
742  tuple(_UElements&&... __elements)
743  noexcept(__nothrow_constructible<_UElements...>())
744  : _Inherited(std::forward<_UElements>(__elements)...) { }
745 
746  template<typename... _UElements,
747  bool _Valid = __valid_args<_UElements...>(),
748  _ExplicitCtor<_Valid, _UElements...> = false>
749  explicit constexpr
750  tuple(_UElements&&... __elements)
751  noexcept(__nothrow_constructible<_UElements...>())
752  : _Inherited(std::forward<_UElements>(__elements)...) { }
753 
754  constexpr tuple(const tuple&) = default;
755 
756  constexpr tuple(tuple&&) = default;
757 
758  template<typename... _UElements,
759  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
760  && !__use_other_ctor<const tuple<_UElements...>&>(),
761  _ImplicitCtor<_Valid, const _UElements&...> = true>
762  constexpr
763  tuple(const tuple<_UElements...>& __in)
764  noexcept(__nothrow_constructible<const _UElements&...>())
765  : _Inherited(static_cast<const _Tuple_impl<0, _UElements...>&>(__in))
766  { }
767 
768  template<typename... _UElements,
769  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
770  && !__use_other_ctor<const tuple<_UElements...>&>(),
771  _ExplicitCtor<_Valid, const _UElements&...> = false>
772  explicit constexpr
773  tuple(const tuple<_UElements...>& __in)
774  noexcept(__nothrow_constructible<const _UElements&...>())
775  : _Inherited(static_cast<const _Tuple_impl<0, _UElements...>&>(__in))
776  { }
777 
778  template<typename... _UElements,
779  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
780  && !__use_other_ctor<tuple<_UElements...>&&>(),
781  _ImplicitCtor<_Valid, _UElements...> = true>
782  constexpr
783  tuple(tuple<_UElements...>&& __in)
784  noexcept(__nothrow_constructible<_UElements...>())
785  : _Inherited(static_cast<_Tuple_impl<0, _UElements...>&&>(__in)) { }
786 
787  template<typename... _UElements,
788  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
789  && !__use_other_ctor<tuple<_UElements...>&&>(),
790  _ExplicitCtor<_Valid, _UElements...> = false>
791  explicit constexpr
792  tuple(tuple<_UElements...>&& __in)
793  noexcept(__nothrow_constructible<_UElements...>())
794  : _Inherited(static_cast<_Tuple_impl<0, _UElements...>&&>(__in)) { }
795 
796  // Allocator-extended constructors.
797 
798  template<typename _Alloc,
799  _ImplicitDefaultCtor<is_object<_Alloc>::value> = true>
800  _GLIBCXX20_CONSTEXPR
801  tuple(allocator_arg_t __tag, const _Alloc& __a)
802  : _Inherited(__tag, __a) { }
803 
804  template<typename _Alloc,
805  _ExplicitDefaultCtor<is_object<_Alloc>::value> = false>
806  _GLIBCXX20_CONSTEXPR
807  explicit
808  tuple(allocator_arg_t __tag, const _Alloc& __a)
809  : _Inherited(__tag, __a) { }
810 
811  template<typename _Alloc, bool _NotEmpty = (sizeof...(_Elements) >= 1),
812  _ImplicitCtor<_NotEmpty, const _Elements&...> = true>
813  _GLIBCXX20_CONSTEXPR
814  tuple(allocator_arg_t __tag, const _Alloc& __a,
815  const _Elements&... __elements)
816  : _Inherited(__tag, __a, __elements...) { }
817 
818  template<typename _Alloc, bool _NotEmpty = (sizeof...(_Elements) >= 1),
819  _ExplicitCtor<_NotEmpty, const _Elements&...> = false>
820  _GLIBCXX20_CONSTEXPR
821  explicit
822  tuple(allocator_arg_t __tag, const _Alloc& __a,
823  const _Elements&... __elements)
824  : _Inherited(__tag, __a, __elements...) { }
825 
826  template<typename _Alloc, typename... _UElements,
827  bool _Valid = __valid_args<_UElements...>(),
828  _ImplicitCtor<_Valid, _UElements...> = true>
829  _GLIBCXX20_CONSTEXPR
830  tuple(allocator_arg_t __tag, const _Alloc& __a,
831  _UElements&&... __elements)
832  : _Inherited(__tag, __a, std::forward<_UElements>(__elements)...)
833  { }
834 
835  template<typename _Alloc, typename... _UElements,
836  bool _Valid = __valid_args<_UElements...>(),
837  _ExplicitCtor<_Valid, _UElements...> = false>
838  _GLIBCXX20_CONSTEXPR
839  explicit
840  tuple(allocator_arg_t __tag, const _Alloc& __a,
841  _UElements&&... __elements)
842  : _Inherited(__tag, __a, std::forward<_UElements>(__elements)...)
843  { }
844 
845  template<typename _Alloc>
846  _GLIBCXX20_CONSTEXPR
847  tuple(allocator_arg_t __tag, const _Alloc& __a, const tuple& __in)
848  : _Inherited(__tag, __a, static_cast<const _Inherited&>(__in)) { }
849 
850  template<typename _Alloc>
851  _GLIBCXX20_CONSTEXPR
852  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple&& __in)
853  : _Inherited(__tag, __a, static_cast<_Inherited&&>(__in)) { }
854 
855  template<typename _Alloc, typename... _UElements,
856  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
857  && !__use_other_ctor<const tuple<_UElements...>&>(),
858  _ImplicitCtor<_Valid, const _UElements&...> = true>
859  _GLIBCXX20_CONSTEXPR
860  tuple(allocator_arg_t __tag, const _Alloc& __a,
861  const tuple<_UElements...>& __in)
862  : _Inherited(__tag, __a,
863  static_cast<const _Tuple_impl<0, _UElements...>&>(__in))
864  { }
865 
866  template<typename _Alloc, typename... _UElements,
867  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
868  && !__use_other_ctor<const tuple<_UElements...>&>(),
869  _ExplicitCtor<_Valid, const _UElements&...> = false>
870  _GLIBCXX20_CONSTEXPR
871  explicit
872  tuple(allocator_arg_t __tag, const _Alloc& __a,
873  const tuple<_UElements...>& __in)
874  : _Inherited(__tag, __a,
875  static_cast<const _Tuple_impl<0, _UElements...>&>(__in))
876  { }
877 
878  template<typename _Alloc, typename... _UElements,
879  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
880  && !__use_other_ctor<tuple<_UElements...>&&>(),
881  _ImplicitCtor<_Valid, _UElements...> = true>
882  _GLIBCXX20_CONSTEXPR
883  tuple(allocator_arg_t __tag, const _Alloc& __a,
884  tuple<_UElements...>&& __in)
885  : _Inherited(__tag, __a,
886  static_cast<_Tuple_impl<0, _UElements...>&&>(__in))
887  { }
888 
889  template<typename _Alloc, typename... _UElements,
890  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
891  && !__use_other_ctor<tuple<_UElements...>&&>(),
892  _ExplicitCtor<_Valid, _UElements...> = false>
893  _GLIBCXX20_CONSTEXPR
894  explicit
895  tuple(allocator_arg_t __tag, const _Alloc& __a,
896  tuple<_UElements...>&& __in)
897  : _Inherited(__tag, __a,
898  static_cast<_Tuple_impl<0, _UElements...>&&>(__in))
899  { }
900 
901  // tuple assignment
902 
903  _GLIBCXX20_CONSTEXPR
904  tuple&
905  operator=(typename conditional<__assignable<const _Elements&...>(),
906  const tuple&,
907  const __nonesuch&>::type __in)
908  noexcept(__nothrow_assignable<const _Elements&...>())
909  {
910  this->_M_assign(__in);
911  return *this;
912  }
913 
914  _GLIBCXX20_CONSTEXPR
915  tuple&
916  operator=(typename conditional<__assignable<_Elements...>(),
917  tuple&&,
918  __nonesuch&&>::type __in)
919  noexcept(__nothrow_assignable<_Elements...>())
920  {
921  this->_M_assign(std::move(__in));
922  return *this;
923  }
924 
925  template<typename... _UElements>
926  _GLIBCXX20_CONSTEXPR
927  __enable_if_t<__assignable<const _UElements&...>(), tuple&>
928  operator=(const tuple<_UElements...>& __in)
929  noexcept(__nothrow_assignable<const _UElements&...>())
930  {
931  this->_M_assign(__in);
932  return *this;
933  }
934 
935  template<typename... _UElements>
936  _GLIBCXX20_CONSTEXPR
937  __enable_if_t<__assignable<_UElements...>(), tuple&>
938  operator=(tuple<_UElements...>&& __in)
939  noexcept(__nothrow_assignable<_UElements...>())
940  {
941  this->_M_assign(std::move(__in));
942  return *this;
943  }
944 
945  // tuple swap
946  _GLIBCXX20_CONSTEXPR
947  void
948  swap(tuple& __in)
949  noexcept(__and_<__is_nothrow_swappable<_Elements>...>::value)
950  { _Inherited::_M_swap(__in); }
951  };
952 
953 #if __cpp_deduction_guides >= 201606
954  template<typename... _UTypes>
955  tuple(_UTypes...) -> tuple<_UTypes...>;
956  template<typename _T1, typename _T2>
957  tuple(pair<_T1, _T2>) -> tuple<_T1, _T2>;
958  template<typename _Alloc, typename... _UTypes>
959  tuple(allocator_arg_t, _Alloc, _UTypes...) -> tuple<_UTypes...>;
960  template<typename _Alloc, typename _T1, typename _T2>
961  tuple(allocator_arg_t, _Alloc, pair<_T1, _T2>) -> tuple<_T1, _T2>;
962  template<typename _Alloc, typename... _UTypes>
963  tuple(allocator_arg_t, _Alloc, tuple<_UTypes...>) -> tuple<_UTypes...>;
964 #endif
965 
966  // Explicit specialization, zero-element tuple.
967  template<>
968  class tuple<>
969  {
970  public:
971  _GLIBCXX20_CONSTEXPR
972  void swap(tuple&) noexcept { /* no-op */ }
973  // We need the default since we're going to define no-op
974  // allocator constructors.
975  tuple() = default;
976  // No-op allocator constructors.
977  template<typename _Alloc>
978  _GLIBCXX20_CONSTEXPR
979  tuple(allocator_arg_t, const _Alloc&) noexcept { }
980  template<typename _Alloc>
981  _GLIBCXX20_CONSTEXPR
982  tuple(allocator_arg_t, const _Alloc&, const tuple&) noexcept { }
983  };
984 
985  /// Partial specialization, 2-element tuple.
986  /// Includes construction and assignment from a pair.
987  template<typename _T1, typename _T2>
988  class tuple<_T1, _T2> : public _Tuple_impl<0, _T1, _T2>
989  {
990  typedef _Tuple_impl<0, _T1, _T2> _Inherited;
991 
992  // Constraint for non-explicit default constructor
993  template<bool _Dummy, typename _U1, typename _U2>
994  using _ImplicitDefaultCtor = __enable_if_t<
995  _TupleConstraints<_Dummy, _U1, _U2>::
996  __is_implicitly_default_constructible(),
997  bool>;
998 
999  // Constraint for explicit default constructor
1000  template<bool _Dummy, typename _U1, typename _U2>
1001  using _ExplicitDefaultCtor = __enable_if_t<
1002  _TupleConstraints<_Dummy, _U1, _U2>::
1003  __is_explicitly_default_constructible(),
1004  bool>;
1005 
1006  template<bool _Dummy>
1007  using _TCC = _TupleConstraints<_Dummy, _T1, _T2>;
1008 
1009  // Constraint for non-explicit constructors
1010  template<bool _Cond, typename _U1, typename _U2>
1011  using _ImplicitCtor = __enable_if_t<
1012  _TCC<_Cond>::template __is_implicitly_constructible<_U1, _U2>(),
1013  bool>;
1014 
1015  // Constraint for non-explicit constructors
1016  template<bool _Cond, typename _U1, typename _U2>
1017  using _ExplicitCtor = __enable_if_t<
1018  _TCC<_Cond>::template __is_explicitly_constructible<_U1, _U2>(),
1019  bool>;
1020 
1021  template<typename _U1, typename _U2>
1022  static constexpr bool __assignable()
1023  {
1024  return __and_<is_assignable<_T1&, _U1>,
1025  is_assignable<_T2&, _U2>>::value;
1026  }
1027 
1028  template<typename _U1, typename _U2>
1029  static constexpr bool __nothrow_assignable()
1030  {
1031  return __and_<is_nothrow_assignable<_T1&, _U1>,
1032  is_nothrow_assignable<_T2&, _U2>>::value;
1033  }
1034 
1035  template<typename _U1, typename _U2>
1036  static constexpr bool __nothrow_constructible()
1037  {
1038  return __and_<is_nothrow_constructible<_T1, _U1>,
1039  is_nothrow_constructible<_T2, _U2>>::value;
1040  }
1041 
1042  static constexpr bool __nothrow_default_constructible()
1043  {
1044  return __and_<is_nothrow_default_constructible<_T1>,
1045  is_nothrow_default_constructible<_T2>>::value;
1046  }
1047 
1048  template<typename _U1>
1049  static constexpr bool __is_alloc_arg()
1050  { return is_same<__remove_cvref_t<_U1>, allocator_arg_t>::value; }
1051 
1052  public:
1053  template<bool _Dummy = true,
1054  _ImplicitDefaultCtor<_Dummy, _T1, _T2> = true>
1055  constexpr
1056  tuple()
1057  noexcept(__nothrow_default_constructible())
1058  : _Inherited() { }
1059 
1060  template<bool _Dummy = true,
1061  _ExplicitDefaultCtor<_Dummy, _T1, _T2> = false>
1062  explicit constexpr
1063  tuple()
1064  noexcept(__nothrow_default_constructible())
1065  : _Inherited() { }
1066 
1067  template<bool _Dummy = true,
1068  _ImplicitCtor<_Dummy, const _T1&, const _T2&> = true>
1069  constexpr
1070  tuple(const _T1& __a1, const _T2& __a2)
1071  noexcept(__nothrow_constructible<const _T1&, const _T2&>())
1072  : _Inherited(__a1, __a2) { }
1073 
1074  template<bool _Dummy = true,
1075  _ExplicitCtor<_Dummy, const _T1&, const _T2&> = false>
1076  explicit constexpr
1077  tuple(const _T1& __a1, const _T2& __a2)
1078  noexcept(__nothrow_constructible<const _T1&, const _T2&>())
1079  : _Inherited(__a1, __a2) { }
1080 
1081  template<typename _U1, typename _U2,
1082  _ImplicitCtor<!__is_alloc_arg<_U1>(), _U1, _U2> = true>
1083  constexpr
1084  tuple(_U1&& __a1, _U2&& __a2)
1085  noexcept(__nothrow_constructible<_U1, _U2>())
1086  : _Inherited(std::forward<_U1>(__a1), std::forward<_U2>(__a2)) { }
1087 
1088  template<typename _U1, typename _U2,
1089  _ExplicitCtor<!__is_alloc_arg<_U1>(), _U1, _U2> = false>
1090  explicit constexpr
1091  tuple(_U1&& __a1, _U2&& __a2)
1092  noexcept(__nothrow_constructible<_U1, _U2>())
1093  : _Inherited(std::forward<_U1>(__a1), std::forward<_U2>(__a2)) { }
1094 
1095  constexpr tuple(const tuple&) = default;
1096 
1097  constexpr tuple(tuple&&) = default;
1098 
1099  template<typename _U1, typename _U2,
1100  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1101  constexpr
1102  tuple(const tuple<_U1, _U2>& __in)
1103  noexcept(__nothrow_constructible<const _U1&, const _U2&>())
1104  : _Inherited(static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in)) { }
1105 
1106  template<typename _U1, typename _U2,
1107  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1108  explicit constexpr
1109  tuple(const tuple<_U1, _U2>& __in)
1110  noexcept(__nothrow_constructible<const _U1&, const _U2&>())
1111  : _Inherited(static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in)) { }
1112 
1113  template<typename _U1, typename _U2,
1114  _ImplicitCtor<true, _U1, _U2> = true>
1115  constexpr
1116  tuple(tuple<_U1, _U2>&& __in)
1117  noexcept(__nothrow_constructible<_U1, _U2>())
1118  : _Inherited(static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in)) { }
1119 
1120  template<typename _U1, typename _U2,
1121  _ExplicitCtor<true, _U1, _U2> = false>
1122  explicit constexpr
1123  tuple(tuple<_U1, _U2>&& __in)
1124  noexcept(__nothrow_constructible<_U1, _U2>())
1125  : _Inherited(static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in)) { }
1126 
1127  template<typename _U1, typename _U2,
1128  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1129  constexpr
1130  tuple(const pair<_U1, _U2>& __in)
1131  noexcept(__nothrow_constructible<const _U1&, const _U2&>())
1132  : _Inherited(__in.first, __in.second) { }
1133 
1134  template<typename _U1, typename _U2,
1135  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1136  explicit constexpr
1137  tuple(const pair<_U1, _U2>& __in)
1138  noexcept(__nothrow_constructible<const _U1&, const _U2&>())
1139  : _Inherited(__in.first, __in.second) { }
1140 
1141  template<typename _U1, typename _U2,
1142  _ImplicitCtor<true, _U1, _U2> = true>
1143  constexpr
1144  tuple(pair<_U1, _U2>&& __in)
1145  noexcept(__nothrow_constructible<_U1, _U2>())
1146  : _Inherited(std::forward<_U1>(__in.first),
1147  std::forward<_U2>(__in.second)) { }
1148 
1149  template<typename _U1, typename _U2,
1150  _ExplicitCtor<true, _U1, _U2> = false>
1151  explicit constexpr
1152  tuple(pair<_U1, _U2>&& __in)
1153  noexcept(__nothrow_constructible<_U1, _U2>())
1154  : _Inherited(std::forward<_U1>(__in.first),
1155  std::forward<_U2>(__in.second)) { }
1156 
1157  // Allocator-extended constructors.
1158 
1159  template<typename _Alloc,
1160  _ImplicitDefaultCtor<is_object<_Alloc>::value, _T1, _T2> = true>
1161  _GLIBCXX20_CONSTEXPR
1162  tuple(allocator_arg_t __tag, const _Alloc& __a)
1163  : _Inherited(__tag, __a) { }
1164 
1165  template<typename _Alloc,
1166  _ExplicitDefaultCtor<is_object<_Alloc>::value, _T1, _T2> = false>
1167  _GLIBCXX20_CONSTEXPR
1168  explicit
1169  tuple(allocator_arg_t __tag, const _Alloc& __a)
1170  : _Inherited(__tag, __a) { }
1171 
1172  template<typename _Alloc, bool _Dummy = true,
1173  _ImplicitCtor<_Dummy, const _T1&, const _T2&> = true>
1174  _GLIBCXX20_CONSTEXPR
1175  tuple(allocator_arg_t __tag, const _Alloc& __a,
1176  const _T1& __a1, const _T2& __a2)
1177  : _Inherited(__tag, __a, __a1, __a2) { }
1178 
1179  template<typename _Alloc, bool _Dummy = true,
1180  _ExplicitCtor<_Dummy, const _T1&, const _T2&> = false>
1181  explicit
1182  _GLIBCXX20_CONSTEXPR
1183  tuple(allocator_arg_t __tag, const _Alloc& __a,
1184  const _T1& __a1, const _T2& __a2)
1185  : _Inherited(__tag, __a, __a1, __a2) { }
1186 
1187  template<typename _Alloc, typename _U1, typename _U2,
1188  _ImplicitCtor<true, _U1, _U2> = true>
1189  _GLIBCXX20_CONSTEXPR
1190  tuple(allocator_arg_t __tag, const _Alloc& __a, _U1&& __a1, _U2&& __a2)
1191  : _Inherited(__tag, __a, std::forward<_U1>(__a1),
1192  std::forward<_U2>(__a2)) { }
1193 
1194  template<typename _Alloc, typename _U1, typename _U2,
1195  _ExplicitCtor<true, _U1, _U2> = false>
1196  explicit
1197  _GLIBCXX20_CONSTEXPR
1198  tuple(allocator_arg_t __tag, const _Alloc& __a,
1199  _U1&& __a1, _U2&& __a2)
1200  : _Inherited(__tag, __a, std::forward<_U1>(__a1),
1201  std::forward<_U2>(__a2)) { }
1202 
1203  template<typename _Alloc>
1204  _GLIBCXX20_CONSTEXPR
1205  tuple(allocator_arg_t __tag, const _Alloc& __a, const tuple& __in)
1206  : _Inherited(__tag, __a, static_cast<const _Inherited&>(__in)) { }
1207 
1208  template<typename _Alloc>
1209  _GLIBCXX20_CONSTEXPR
1210  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple&& __in)
1211  : _Inherited(__tag, __a, static_cast<_Inherited&&>(__in)) { }
1212 
1213  template<typename _Alloc, typename _U1, typename _U2,
1214  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1215  _GLIBCXX20_CONSTEXPR
1216  tuple(allocator_arg_t __tag, const _Alloc& __a,
1217  const tuple<_U1, _U2>& __in)
1218  : _Inherited(__tag, __a,
1219  static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in))
1220  { }
1221 
1222  template<typename _Alloc, typename _U1, typename _U2,
1223  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1224  explicit
1225  _GLIBCXX20_CONSTEXPR
1226  tuple(allocator_arg_t __tag, const _Alloc& __a,
1227  const tuple<_U1, _U2>& __in)
1228  : _Inherited(__tag, __a,
1229  static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in))
1230  { }
1231 
1232  template<typename _Alloc, typename _U1, typename _U2,
1233  _ImplicitCtor<true, _U1, _U2> = true>
1234  _GLIBCXX20_CONSTEXPR
1235  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple<_U1, _U2>&& __in)
1236  : _Inherited(__tag, __a, static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in))
1237  { }
1238 
1239  template<typename _Alloc, typename _U1, typename _U2,
1240  _ExplicitCtor<true, _U1, _U2> = false>
1241  explicit
1242  _GLIBCXX20_CONSTEXPR
1243  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple<_U1, _U2>&& __in)
1244  : _Inherited(__tag, __a, static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in))
1245  { }
1246 
1247  template<typename _Alloc, typename _U1, typename _U2,
1248  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1249  _GLIBCXX20_CONSTEXPR
1250  tuple(allocator_arg_t __tag, const _Alloc& __a,
1251  const pair<_U1, _U2>& __in)
1252  : _Inherited(__tag, __a, __in.first, __in.second) { }
1253 
1254  template<typename _Alloc, typename _U1, typename _U2,
1255  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1256  explicit
1257  _GLIBCXX20_CONSTEXPR
1258  tuple(allocator_arg_t __tag, const _Alloc& __a,
1259  const pair<_U1, _U2>& __in)
1260  : _Inherited(__tag, __a, __in.first, __in.second) { }
1261 
1262  template<typename _Alloc, typename _U1, typename _U2,
1263  _ImplicitCtor<true, _U1, _U2> = true>
1264  _GLIBCXX20_CONSTEXPR
1265  tuple(allocator_arg_t __tag, const _Alloc& __a, pair<_U1, _U2>&& __in)
1266  : _Inherited(__tag, __a, std::forward<_U1>(__in.first),
1267  std::forward<_U2>(__in.second)) { }
1268 
1269  template<typename _Alloc, typename _U1, typename _U2,
1270  _ExplicitCtor<true, _U1, _U2> = false>
1271  explicit
1272  _GLIBCXX20_CONSTEXPR
1273  tuple(allocator_arg_t __tag, const _Alloc& __a, pair<_U1, _U2>&& __in)
1274  : _Inherited(__tag, __a, std::forward<_U1>(__in.first),
1275  std::forward<_U2>(__in.second)) { }
1276 
1277  // Tuple assignment.
1278 
1279  _GLIBCXX20_CONSTEXPR
1280  tuple&
1281  operator=(typename conditional<__assignable<const _T1&, const _T2&>(),
1282  const tuple&,
1283  const __nonesuch&>::type __in)
1284  noexcept(__nothrow_assignable<const _T1&, const _T2&>())
1285  {
1286  this->_M_assign(__in);
1287  return *this;
1288  }
1289 
1290  _GLIBCXX20_CONSTEXPR
1291  tuple&
1292  operator=(typename conditional<__assignable<_T1, _T2>(),
1293  tuple&&,
1294  __nonesuch&&>::type __in)
1295  noexcept(__nothrow_assignable<_T1, _T2>())
1296  {
1297  this->_M_assign(std::move(__in));
1298  return *this;
1299  }
1300 
1301  template<typename _U1, typename _U2>
1302  _GLIBCXX20_CONSTEXPR
1303  __enable_if_t<__assignable<const _U1&, const _U2&>(), tuple&>
1304  operator=(const tuple<_U1, _U2>& __in)
1305  noexcept(__nothrow_assignable<const _U1&, const _U2&>())
1306  {
1307  this->_M_assign(__in);
1308  return *this;
1309  }
1310 
1311  template<typename _U1, typename _U2>
1312  _GLIBCXX20_CONSTEXPR
1313  __enable_if_t<__assignable<_U1, _U2>(), tuple&>
1314  operator=(tuple<_U1, _U2>&& __in)
1315  noexcept(__nothrow_assignable<_U1, _U2>())
1316  {
1317  this->_M_assign(std::move(__in));
1318  return *this;
1319  }
1320 
1321  template<typename _U1, typename _U2>
1322  _GLIBCXX20_CONSTEXPR
1323  __enable_if_t<__assignable<const _U1&, const _U2&>(), tuple&>
1324  operator=(const pair<_U1, _U2>& __in)
1325  noexcept(__nothrow_assignable<const _U1&, const _U2&>())
1326  {
1327  this->_M_head(*this) = __in.first;
1328  this->_M_tail(*this)._M_head(*this) = __in.second;
1329  return *this;
1330  }
1331 
1332  template<typename _U1, typename _U2>
1333  _GLIBCXX20_CONSTEXPR
1334  __enable_if_t<__assignable<_U1, _U2>(), tuple&>
1335  operator=(pair<_U1, _U2>&& __in)
1336  noexcept(__nothrow_assignable<_U1, _U2>())
1337  {
1338  this->_M_head(*this) = std::forward<_U1>(__in.first);
1339  this->_M_tail(*this)._M_head(*this) = std::forward<_U2>(__in.second);
1340  return *this;
1341  }
1342 
1343  _GLIBCXX20_CONSTEXPR
1344  void
1345  swap(tuple& __in)
1346  noexcept(__and_<__is_nothrow_swappable<_T1>,
1347  __is_nothrow_swappable<_T2>>::value)
1348  { _Inherited::_M_swap(__in); }
1349  };
1350 
1351 
1352  /// class tuple_size
1353  template<typename... _Elements>
1354  struct tuple_size<tuple<_Elements...>>
1355  : public integral_constant<size_t, sizeof...(_Elements)> { };
1356 
1357 #if __cplusplus > 201402L
1358  template <typename _Tp>
1359  inline constexpr size_t tuple_size_v = tuple_size<_Tp>::value;
1360 #endif
1361 
1362  /**
1363  * Recursive case for tuple_element: strip off the first element in
1364  * the tuple and retrieve the (i-1)th element of the remaining tuple.
1365  */
1366  template<size_t __i, typename _Head, typename... _Tail>
1367  struct tuple_element<__i, tuple<_Head, _Tail...> >
1368  : tuple_element<__i - 1, tuple<_Tail...> > { };
1369 
1370  /**
1371  * Basis case for tuple_element: The first element is the one we're seeking.
1372  */
1373  template<typename _Head, typename... _Tail>
1374  struct tuple_element<0, tuple<_Head, _Tail...> >
1375  {
1376  typedef _Head type;
1377  };
1378 
1379  /**
1380  * Error case for tuple_element: invalid index.
1381  */
1382  template<size_t __i>
1383  struct tuple_element<__i, tuple<>>
1384  {
1385  static_assert(__i < tuple_size<tuple<>>::value,
1386  "tuple index must be in range");
1387  };
1388 
1389  template<size_t __i, typename _Head, typename... _Tail>
1390  constexpr _Head&
1391  __get_helper(_Tuple_impl<__i, _Head, _Tail...>& __t) noexcept
1392  { return _Tuple_impl<__i, _Head, _Tail...>::_M_head(__t); }
1393 
1394  template<size_t __i, typename _Head, typename... _Tail>
1395  constexpr const _Head&
1396  __get_helper(const _Tuple_impl<__i, _Head, _Tail...>& __t) noexcept
1397  { return _Tuple_impl<__i, _Head, _Tail...>::_M_head(__t); }
1398 
1399  // Deleted overload to improve diagnostics for invalid indices
1400  template<size_t __i, typename... _Types>
1401  __enable_if_t<(__i >= sizeof...(_Types))>
1402  __get_helper(const tuple<_Types...>&) = delete;
1403 
1404  /// Return a reference to the ith element of a tuple.
1405  template<size_t __i, typename... _Elements>
1406  constexpr __tuple_element_t<__i, tuple<_Elements...>>&
1407  get(tuple<_Elements...>& __t) noexcept
1408  { return std::__get_helper<__i>(__t); }
1409 
1410  /// Return a const reference to the ith element of a const tuple.
1411  template<size_t __i, typename... _Elements>
1412  constexpr const __tuple_element_t<__i, tuple<_Elements...>>&
1413  get(const tuple<_Elements...>& __t) noexcept
1414  { return std::__get_helper<__i>(__t); }
1415 
1416  /// Return an rvalue reference to the ith element of a tuple rvalue.
1417  template<size_t __i, typename... _Elements>
1418  constexpr __tuple_element_t<__i, tuple<_Elements...>>&&
1419  get(tuple<_Elements...>&& __t) noexcept
1420  {
1421  typedef __tuple_element_t<__i, tuple<_Elements...>> __element_type;
1422  return std::forward<__element_type>(std::__get_helper<__i>(__t));
1423  }
1424 
1425  /// Return a const rvalue reference to the ith element of a const tuple rvalue.
1426  template<size_t __i, typename... _Elements>
1427  constexpr const __tuple_element_t<__i, tuple<_Elements...>>&&
1428  get(const tuple<_Elements...>&& __t) noexcept
1429  {
1430  typedef __tuple_element_t<__i, tuple<_Elements...>> __element_type;
1431  return std::forward<const __element_type>(std::__get_helper<__i>(__t));
1432  }
1433 
1434 #if __cplusplus >= 201402L
1435 
1436 #define __cpp_lib_tuples_by_type 201304
1437 
1438  // Return the index of _Tp in _Types, if it occurs exactly once.
1439  // Otherwise, return sizeof...(_Types).
1440  // TODO reuse this for __detail::__variant::__exactly_once.
1441  template<typename _Tp, typename... _Types>
1442  constexpr size_t
1443  __find_uniq_type_in_pack()
1444  {
1445  constexpr size_t __sz = sizeof...(_Types);
1446  constexpr bool __found[__sz] = { __is_same(_Tp, _Types) ... };
1447  size_t __n = __sz;
1448  for (size_t __i = 0; __i < __sz; ++__i)
1449  {
1450  if (__found[__i])
1451  {
1452  if (__n < __sz) // more than one _Tp found
1453  return __sz;
1454  __n = __i;
1455  }
1456  }
1457  return __n;
1458  }
1459 
1460  /// Return a reference to the unique element of type _Tp of a tuple.
1461  template <typename _Tp, typename... _Types>
1462  constexpr _Tp&
1463  get(tuple<_Types...>& __t) noexcept
1464  {
1465  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1466  static_assert(__idx < sizeof...(_Types),
1467  "the type T in std::get<T> must occur exactly once in the tuple");
1468  return std::__get_helper<__idx>(__t);
1469  }
1470 
1471  /// Return a reference to the unique element of type _Tp of a tuple rvalue.
1472  template <typename _Tp, typename... _Types>
1473  constexpr _Tp&&
1474  get(tuple<_Types...>&& __t) noexcept
1475  {
1476  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1477  static_assert(__idx < sizeof...(_Types),
1478  "the type T in std::get<T> must occur exactly once in the tuple");
1479  return std::forward<_Tp>(std::__get_helper<__idx>(__t));
1480  }
1481 
1482  /// Return a const reference to the unique element of type _Tp of a tuple.
1483  template <typename _Tp, typename... _Types>
1484  constexpr const _Tp&
1485  get(const tuple<_Types...>& __t) noexcept
1486  {
1487  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1488  static_assert(__idx < sizeof...(_Types),
1489  "the type T in std::get<T> must occur exactly once in the tuple");
1490  return std::__get_helper<__idx>(__t);
1491  }
1492 
1493  /// Return a const reference to the unique element of type _Tp of
1494  /// a const tuple rvalue.
1495  template <typename _Tp, typename... _Types>
1496  constexpr const _Tp&&
1497  get(const tuple<_Types...>&& __t) noexcept
1498  {
1499  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1500  static_assert(__idx < sizeof...(_Types),
1501  "the type T in std::get<T> must occur exactly once in the tuple");
1502  return std::forward<const _Tp>(std::__get_helper<__idx>(__t));
1503  }
1504 #endif
1505 
1506  // This class performs the comparison operations on tuples
1507  template<typename _Tp, typename _Up, size_t __i, size_t __size>
1508  struct __tuple_compare
1509  {
1510  static constexpr bool
1511  __eq(const _Tp& __t, const _Up& __u)
1512  {
1513  return bool(std::get<__i>(__t) == std::get<__i>(__u))
1514  && __tuple_compare<_Tp, _Up, __i + 1, __size>::__eq(__t, __u);
1515  }
1516 
1517  static constexpr bool
1518  __less(const _Tp& __t, const _Up& __u)
1519  {
1520  return bool(std::get<__i>(__t) < std::get<__i>(__u))
1521  || (!bool(std::get<__i>(__u) < std::get<__i>(__t))
1522  && __tuple_compare<_Tp, _Up, __i + 1, __size>::__less(__t, __u));
1523  }
1524  };
1525 
1526  template<typename _Tp, typename _Up, size_t __size>
1527  struct __tuple_compare<_Tp, _Up, __size, __size>
1528  {
1529  static constexpr bool
1530  __eq(const _Tp&, const _Up&) { return true; }
1531 
1532  static constexpr bool
1533  __less(const _Tp&, const _Up&) { return false; }
1534  };
1535 
1536  template<typename... _TElements, typename... _UElements>
1537  constexpr bool
1538  operator==(const tuple<_TElements...>& __t,
1539  const tuple<_UElements...>& __u)
1540  {
1541  static_assert(sizeof...(_TElements) == sizeof...(_UElements),
1542  "tuple objects can only be compared if they have equal sizes.");
1543  using __compare = __tuple_compare<tuple<_TElements...>,
1544  tuple<_UElements...>,
1545  0, sizeof...(_TElements)>;
1546  return __compare::__eq(__t, __u);
1547  }
1548 
1549 #if __cpp_lib_three_way_comparison
1550  template<typename _Cat, typename _Tp, typename _Up>
1551  constexpr _Cat
1552  __tuple_cmp(const _Tp&, const _Up&, index_sequence<>)
1553  { return _Cat::equivalent; }
1554 
1555  template<typename _Cat, typename _Tp, typename _Up,
1556  size_t _Idx0, size_t... _Idxs>
1557  constexpr _Cat
1558  __tuple_cmp(const _Tp& __t, const _Up& __u,
1559  index_sequence<_Idx0, _Idxs...>)
1560  {
1561  auto __c
1562  = __detail::__synth3way(std::get<_Idx0>(__t), std::get<_Idx0>(__u));
1563  if (__c != 0)
1564  return __c;
1565  return std::__tuple_cmp<_Cat>(__t, __u, index_sequence<_Idxs...>());
1566  }
1567 
1568  template<typename... _Tps, typename... _Ups>
1569  constexpr
1570  common_comparison_category_t<__detail::__synth3way_t<_Tps, _Ups>...>
1571  operator<=>(const tuple<_Tps...>& __t, const tuple<_Ups...>& __u)
1572  {
1573  using _Cat
1574  = common_comparison_category_t<__detail::__synth3way_t<_Tps, _Ups>...>;
1575  return std::__tuple_cmp<_Cat>(__t, __u, index_sequence_for<_Tps...>());
1576  }
1577 #else
1578  template<typename... _TElements, typename... _UElements>
1579  constexpr bool
1580  operator<(const tuple<_TElements...>& __t,
1581  const tuple<_UElements...>& __u)
1582  {
1583  static_assert(sizeof...(_TElements) == sizeof...(_UElements),
1584  "tuple objects can only be compared if they have equal sizes.");
1585  using __compare = __tuple_compare<tuple<_TElements...>,
1586  tuple<_UElements...>,
1587  0, sizeof...(_TElements)>;
1588  return __compare::__less(__t, __u);
1589  }
1590 
1591  template<typename... _TElements, typename... _UElements>
1592  constexpr bool
1593  operator!=(const tuple<_TElements...>& __t,
1594  const tuple<_UElements...>& __u)
1595  { return !(__t == __u); }
1596 
1597  template<typename... _TElements, typename... _UElements>
1598  constexpr bool
1599  operator>(const tuple<_TElements...>& __t,
1600  const tuple<_UElements...>& __u)
1601  { return __u < __t; }
1602 
1603  template<typename... _TElements, typename... _UElements>
1604  constexpr bool
1605  operator<=(const tuple<_TElements...>& __t,
1606  const tuple<_UElements...>& __u)
1607  { return !(__u < __t); }
1608 
1609  template<typename... _TElements, typename... _UElements>
1610  constexpr bool
1611  operator>=(const tuple<_TElements...>& __t,
1612  const tuple<_UElements...>& __u)
1613  { return !(__t < __u); }
1614 #endif // three_way_comparison
1615 
1616  // NB: DR 705.
1617  template<typename... _Elements>
1618  constexpr tuple<typename __decay_and_strip<_Elements>::__type...>
1619  make_tuple(_Elements&&... __args)
1620  {
1621  typedef tuple<typename __decay_and_strip<_Elements>::__type...>
1622  __result_type;
1623  return __result_type(std::forward<_Elements>(__args)...);
1624  }
1625 
1626  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1627  // 2275. Why is forward_as_tuple not constexpr?
1628  /// std::forward_as_tuple
1629  template<typename... _Elements>
1630  constexpr tuple<_Elements&&...>
1631  forward_as_tuple(_Elements&&... __args) noexcept
1632  { return tuple<_Elements&&...>(std::forward<_Elements>(__args)...); }
1633 
1634  template<size_t, typename, typename, size_t>
1635  struct __make_tuple_impl;
1636 
1637  template<size_t _Idx, typename _Tuple, typename... _Tp, size_t _Nm>
1638  struct __make_tuple_impl<_Idx, tuple<_Tp...>, _Tuple, _Nm>
1639  : __make_tuple_impl<_Idx + 1,
1640  tuple<_Tp..., __tuple_element_t<_Idx, _Tuple>>,
1641  _Tuple, _Nm>
1642  { };
1643 
1644  template<size_t _Nm, typename _Tuple, typename... _Tp>
1645  struct __make_tuple_impl<_Nm, tuple<_Tp...>, _Tuple, _Nm>
1646  {
1647  typedef tuple<_Tp...> __type;
1648  };
1649 
1650  template<typename _Tuple>
1651  struct __do_make_tuple
1652  : __make_tuple_impl<0, tuple<>, _Tuple, tuple_size<_Tuple>::value>
1653  { };
1654 
1655  // Returns the std::tuple equivalent of a tuple-like type.
1656  template<typename _Tuple>
1657  struct __make_tuple
1658  : public __do_make_tuple<__remove_cvref_t<_Tuple>>
1659  { };
1660 
1661  // Combines several std::tuple's into a single one.
1662  template<typename...>
1663  struct __combine_tuples;
1664 
1665  template<>
1666  struct __combine_tuples<>
1667  {
1668  typedef tuple<> __type;
1669  };
1670 
1671  template<typename... _Ts>
1672  struct __combine_tuples<tuple<_Ts...>>
1673  {
1674  typedef tuple<_Ts...> __type;
1675  };
1676 
1677  template<typename... _T1s, typename... _T2s, typename... _Rem>
1678  struct __combine_tuples<tuple<_T1s...>, tuple<_T2s...>, _Rem...>
1679  {
1680  typedef typename __combine_tuples<tuple<_T1s..., _T2s...>,
1681  _Rem...>::__type __type;
1682  };
1683 
1684  // Computes the result type of tuple_cat given a set of tuple-like types.
1685  template<typename... _Tpls>
1686  struct __tuple_cat_result
1687  {
1688  typedef typename __combine_tuples
1689  <typename __make_tuple<_Tpls>::__type...>::__type __type;
1690  };
1691 
1692  // Helper to determine the index set for the first tuple-like
1693  // type of a given set.
1694  template<typename...>
1695  struct __make_1st_indices;
1696 
1697  template<>
1698  struct __make_1st_indices<>
1699  {
1700  typedef _Index_tuple<> __type;
1701  };
1702 
1703  template<typename _Tp, typename... _Tpls>
1704  struct __make_1st_indices<_Tp, _Tpls...>
1705  {
1706  typedef typename _Build_index_tuple<tuple_size<
1707  typename remove_reference<_Tp>::type>::value>::__type __type;
1708  };
1709 
1710  // Performs the actual concatenation by step-wise expanding tuple-like
1711  // objects into the elements, which are finally forwarded into the
1712  // result tuple.
1713  template<typename _Ret, typename _Indices, typename... _Tpls>
1714  struct __tuple_concater;
1715 
1716  template<typename _Ret, size_t... _Is, typename _Tp, typename... _Tpls>
1717  struct __tuple_concater<_Ret, _Index_tuple<_Is...>, _Tp, _Tpls...>
1718  {
1719  template<typename... _Us>
1720  static constexpr _Ret
1721  _S_do(_Tp&& __tp, _Tpls&&... __tps, _Us&&... __us)
1722  {
1723  typedef typename __make_1st_indices<_Tpls...>::__type __idx;
1724  typedef __tuple_concater<_Ret, __idx, _Tpls...> __next;
1725  return __next::_S_do(std::forward<_Tpls>(__tps)...,
1726  std::forward<_Us>(__us)...,
1727  std::get<_Is>(std::forward<_Tp>(__tp))...);
1728  }
1729  };
1730 
1731  template<typename _Ret>
1732  struct __tuple_concater<_Ret, _Index_tuple<>>
1733  {
1734  template<typename... _Us>
1735  static constexpr _Ret
1736  _S_do(_Us&&... __us)
1737  {
1738  return _Ret(std::forward<_Us>(__us)...);
1739  }
1740  };
1741 
1742  /// tuple_cat
1743  template<typename... _Tpls, typename = typename
1744  enable_if<__and_<__is_tuple_like<_Tpls>...>::value>::type>
1745  constexpr auto
1746  tuple_cat(_Tpls&&... __tpls)
1747  -> typename __tuple_cat_result<_Tpls...>::__type
1748  {
1749  typedef typename __tuple_cat_result<_Tpls...>::__type __ret;
1750  typedef typename __make_1st_indices<_Tpls...>::__type __idx;
1751  typedef __tuple_concater<__ret, __idx, _Tpls...> __concater;
1752  return __concater::_S_do(std::forward<_Tpls>(__tpls)...);
1753  }
1754 
1755  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1756  // 2301. Why is tie not constexpr?
1757  /// tie
1758  template<typename... _Elements>
1759  constexpr tuple<_Elements&...>
1760  tie(_Elements&... __args) noexcept
1761  { return tuple<_Elements&...>(__args...); }
1762 
1763  /// swap
1764  template<typename... _Elements>
1765  _GLIBCXX20_CONSTEXPR
1766  inline
1767 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1768  // Constrained free swap overload, see p0185r1
1769  typename enable_if<__and_<__is_swappable<_Elements>...>::value
1770  >::type
1771 #else
1772  void
1773 #endif
1774  swap(tuple<_Elements...>& __x, tuple<_Elements...>& __y)
1775  noexcept(noexcept(__x.swap(__y)))
1776  { __x.swap(__y); }
1777 
1778 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1779  template<typename... _Elements>
1780  _GLIBCXX20_CONSTEXPR
1781  typename enable_if<!__and_<__is_swappable<_Elements>...>::value>::type
1782  swap(tuple<_Elements...>&, tuple<_Elements...>&) = delete;
1783 #endif
1784 
1785  // A class (and instance) which can be used in 'tie' when an element
1786  // of a tuple is not required.
1787  // _GLIBCXX14_CONSTEXPR
1788  // 2933. PR for LWG 2773 could be clearer
1789  struct _Swallow_assign
1790  {
1791  template<class _Tp>
1792  _GLIBCXX14_CONSTEXPR const _Swallow_assign&
1793  operator=(const _Tp&) const
1794  { return *this; }
1795  };
1796 
1797  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1798  // 2773. Making std::ignore constexpr
1799  _GLIBCXX17_INLINE constexpr _Swallow_assign ignore{};
1800 
1801  /// Partial specialization for tuples
1802  template<typename... _Types, typename _Alloc>
1803  struct uses_allocator<tuple<_Types...>, _Alloc> : true_type { };
1804 
1805  // See stl_pair.h...
1806  /** "piecewise construction" using a tuple of arguments for each member.
1807  *
1808  * @param __first Arguments for the first member of the pair.
1809  * @param __second Arguments for the second member of the pair.
1810  *
1811  * The elements of each tuple will be used as the constructor arguments
1812  * for the data members of the pair.
1813  */
1814  template<class _T1, class _T2>
1815  template<typename... _Args1, typename... _Args2>
1816  _GLIBCXX20_CONSTEXPR
1817  inline
1818  pair<_T1, _T2>::
1819  pair(piecewise_construct_t,
1820  tuple<_Args1...> __first, tuple<_Args2...> __second)
1821  : pair(__first, __second,
1822  typename _Build_index_tuple<sizeof...(_Args1)>::__type(),
1823  typename _Build_index_tuple<sizeof...(_Args2)>::__type())
1824  { }
1825 
1826  template<class _T1, class _T2>
1827  template<typename... _Args1, size_t... _Indexes1,
1828  typename... _Args2, size_t... _Indexes2>
1829  _GLIBCXX20_CONSTEXPR inline
1830  pair<_T1, _T2>::
1831  pair(tuple<_Args1...>& __tuple1, tuple<_Args2...>& __tuple2,
1832  _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>)
1833  : first(std::forward<_Args1>(std::get<_Indexes1>(__tuple1))...),
1834  second(std::forward<_Args2>(std::get<_Indexes2>(__tuple2))...)
1835  { }
1836 
1837 #if __cplusplus >= 201703L
1838 
1839  // Unpack a std::tuple into a type trait and use its value.
1840  // For cv std::tuple<_Up> the result is _Trait<_Tp, cv _Up...>::value.
1841  // For cv std::tuple<_Up>& the result is _Trait<_Tp, cv _Up&...>::value.
1842  // Otherwise the result is false (because we don't know if std::get throws).
1843  template<template<typename...> class _Trait, typename _Tp, typename _Tuple>
1844  inline constexpr bool __unpack_std_tuple = false;
1845 
1846  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1847  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, tuple<_Up...>>
1848  = _Trait<_Tp, _Up...>::value;
1849 
1850  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1851  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, tuple<_Up...>&>
1852  = _Trait<_Tp, _Up&...>::value;
1853 
1854  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1855  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, const tuple<_Up...>>
1856  = _Trait<_Tp, const _Up...>::value;
1857 
1858  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1859  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, const tuple<_Up...>&>
1860  = _Trait<_Tp, const _Up&...>::value;
1861 
1862 # define __cpp_lib_apply 201603
1863 
1864  template <typename _Fn, typename _Tuple, size_t... _Idx>
1865  constexpr decltype(auto)
1866  __apply_impl(_Fn&& __f, _Tuple&& __t, index_sequence<_Idx...>)
1867  {
1868  return std::__invoke(std::forward<_Fn>(__f),
1869  std::get<_Idx>(std::forward<_Tuple>(__t))...);
1870  }
1871 
1872  template <typename _Fn, typename _Tuple>
1873  constexpr decltype(auto)
1874  apply(_Fn&& __f, _Tuple&& __t)
1875  noexcept(__unpack_std_tuple<is_nothrow_invocable, _Fn, _Tuple>)
1876  {
1877  using _Indices
1878  = make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>;
1879  return std::__apply_impl(std::forward<_Fn>(__f),
1880  std::forward<_Tuple>(__t),
1881  _Indices{});
1882  }
1883 
1884 #define __cpp_lib_make_from_tuple 201606
1885 
1886  template <typename _Tp, typename _Tuple, size_t... _Idx>
1887  constexpr _Tp
1888  __make_from_tuple_impl(_Tuple&& __t, index_sequence<_Idx...>)
1889  { return _Tp(std::get<_Idx>(std::forward<_Tuple>(__t))...); }
1890 
1891  template <typename _Tp, typename _Tuple>
1892  constexpr _Tp
1893  make_from_tuple(_Tuple&& __t)
1894  noexcept(__unpack_std_tuple<is_nothrow_constructible, _Tp, _Tuple>)
1895  {
1896  return __make_from_tuple_impl<_Tp>(
1897  std::forward<_Tuple>(__t),
1898  make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>{});
1899  }
1900 #endif // C++17
1901 
1902  /// @}
1903 
1904 _GLIBCXX_END_NAMESPACE_VERSION
1905 } // namespace std
1906 
1907 #endif // C++11
1908 
1909 #endif // _GLIBCXX_TUPLE