libstdc++
tuple
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1 // <tuple> -*- C++ -*-
2 
3 // Copyright (C) 2007-2022 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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 <bits/stl_pair.h> // for std::pair
39 #include <bits/uses_allocator.h> // for std::allocator_arg_t
40 #include <bits/utility.h> // for std::get, std::tuple_size etc.
41 #include <bits/invoke.h> // for std::__invoke
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  = __conditional_t<__is_final(_Tp), false_type,
70  __is_empty_non_tuple<_Tp>>;
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, bool _NotEmpty = (sizeof...(_Elements) >= 1),
805  _ImplicitCtor<_NotEmpty, const _Elements&...> = true>
806  _GLIBCXX20_CONSTEXPR
807  tuple(allocator_arg_t __tag, const _Alloc& __a,
808  const _Elements&... __elements)
809  : _Inherited(__tag, __a, __elements...) { }
810 
811  template<typename _Alloc, bool _NotEmpty = (sizeof...(_Elements) >= 1),
812  _ExplicitCtor<_NotEmpty, const _Elements&...> = false>
813  _GLIBCXX20_CONSTEXPR
814  explicit
815  tuple(allocator_arg_t __tag, const _Alloc& __a,
816  const _Elements&... __elements)
817  : _Inherited(__tag, __a, __elements...) { }
818 
819  template<typename _Alloc, typename... _UElements,
820  bool _Valid = __valid_args<_UElements...>(),
821  _ImplicitCtor<_Valid, _UElements...> = true>
822  _GLIBCXX20_CONSTEXPR
823  tuple(allocator_arg_t __tag, const _Alloc& __a,
824  _UElements&&... __elements)
825  : _Inherited(__tag, __a, std::forward<_UElements>(__elements)...)
826  { }
827 
828  template<typename _Alloc, typename... _UElements,
829  bool _Valid = __valid_args<_UElements...>(),
830  _ExplicitCtor<_Valid, _UElements...> = false>
831  _GLIBCXX20_CONSTEXPR
832  explicit
833  tuple(allocator_arg_t __tag, const _Alloc& __a,
834  _UElements&&... __elements)
835  : _Inherited(__tag, __a, std::forward<_UElements>(__elements)...)
836  { }
837 
838  template<typename _Alloc>
839  _GLIBCXX20_CONSTEXPR
840  tuple(allocator_arg_t __tag, const _Alloc& __a, const tuple& __in)
841  : _Inherited(__tag, __a, static_cast<const _Inherited&>(__in)) { }
842 
843  template<typename _Alloc>
844  _GLIBCXX20_CONSTEXPR
845  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple&& __in)
846  : _Inherited(__tag, __a, static_cast<_Inherited&&>(__in)) { }
847 
848  template<typename _Alloc, typename... _UElements,
849  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
850  && !__use_other_ctor<const tuple<_UElements...>&>(),
851  _ImplicitCtor<_Valid, const _UElements&...> = true>
852  _GLIBCXX20_CONSTEXPR
853  tuple(allocator_arg_t __tag, const _Alloc& __a,
854  const tuple<_UElements...>& __in)
855  : _Inherited(__tag, __a,
856  static_cast<const _Tuple_impl<0, _UElements...>&>(__in))
857  { }
858 
859  template<typename _Alloc, typename... _UElements,
860  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
861  && !__use_other_ctor<const tuple<_UElements...>&>(),
862  _ExplicitCtor<_Valid, const _UElements&...> = false>
863  _GLIBCXX20_CONSTEXPR
864  explicit
865  tuple(allocator_arg_t __tag, const _Alloc& __a,
866  const tuple<_UElements...>& __in)
867  : _Inherited(__tag, __a,
868  static_cast<const _Tuple_impl<0, _UElements...>&>(__in))
869  { }
870 
871  template<typename _Alloc, typename... _UElements,
872  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
873  && !__use_other_ctor<tuple<_UElements...>&&>(),
874  _ImplicitCtor<_Valid, _UElements...> = true>
875  _GLIBCXX20_CONSTEXPR
876  tuple(allocator_arg_t __tag, const _Alloc& __a,
877  tuple<_UElements...>&& __in)
878  : _Inherited(__tag, __a,
879  static_cast<_Tuple_impl<0, _UElements...>&&>(__in))
880  { }
881 
882  template<typename _Alloc, typename... _UElements,
883  bool _Valid = (sizeof...(_Elements) == sizeof...(_UElements))
884  && !__use_other_ctor<tuple<_UElements...>&&>(),
885  _ExplicitCtor<_Valid, _UElements...> = false>
886  _GLIBCXX20_CONSTEXPR
887  explicit
888  tuple(allocator_arg_t __tag, const _Alloc& __a,
889  tuple<_UElements...>&& __in)
890  : _Inherited(__tag, __a,
891  static_cast<_Tuple_impl<0, _UElements...>&&>(__in))
892  { }
893 
894  // tuple assignment
895 
896  _GLIBCXX20_CONSTEXPR
897  tuple&
898  operator=(__conditional_t<__assignable<const _Elements&...>(),
899  const tuple&,
900  const __nonesuch&> __in)
901  noexcept(__nothrow_assignable<const _Elements&...>())
902  {
903  this->_M_assign(__in);
904  return *this;
905  }
906 
907  _GLIBCXX20_CONSTEXPR
908  tuple&
909  operator=(__conditional_t<__assignable<_Elements...>(),
910  tuple&&,
911  __nonesuch&&> __in)
912  noexcept(__nothrow_assignable<_Elements...>())
913  {
914  this->_M_assign(std::move(__in));
915  return *this;
916  }
917 
918  template<typename... _UElements>
919  _GLIBCXX20_CONSTEXPR
920  __enable_if_t<__assignable<const _UElements&...>(), tuple&>
921  operator=(const tuple<_UElements...>& __in)
922  noexcept(__nothrow_assignable<const _UElements&...>())
923  {
924  this->_M_assign(__in);
925  return *this;
926  }
927 
928  template<typename... _UElements>
929  _GLIBCXX20_CONSTEXPR
930  __enable_if_t<__assignable<_UElements...>(), tuple&>
931  operator=(tuple<_UElements...>&& __in)
932  noexcept(__nothrow_assignable<_UElements...>())
933  {
934  this->_M_assign(std::move(__in));
935  return *this;
936  }
937 
938  // tuple swap
939  _GLIBCXX20_CONSTEXPR
940  void
941  swap(tuple& __in)
942  noexcept(__and_<__is_nothrow_swappable<_Elements>...>::value)
943  { _Inherited::_M_swap(__in); }
944  };
945 
946 #if __cpp_deduction_guides >= 201606
947  template<typename... _UTypes>
948  tuple(_UTypes...) -> tuple<_UTypes...>;
949  template<typename _T1, typename _T2>
950  tuple(pair<_T1, _T2>) -> tuple<_T1, _T2>;
951  template<typename _Alloc, typename... _UTypes>
952  tuple(allocator_arg_t, _Alloc, _UTypes...) -> tuple<_UTypes...>;
953  template<typename _Alloc, typename _T1, typename _T2>
954  tuple(allocator_arg_t, _Alloc, pair<_T1, _T2>) -> tuple<_T1, _T2>;
955  template<typename _Alloc, typename... _UTypes>
956  tuple(allocator_arg_t, _Alloc, tuple<_UTypes...>) -> tuple<_UTypes...>;
957 #endif
958 
959  // Explicit specialization, zero-element tuple.
960  template<>
961  class tuple<>
962  {
963  public:
964  _GLIBCXX20_CONSTEXPR
965  void swap(tuple&) noexcept { /* no-op */ }
966  // We need the default since we're going to define no-op
967  // allocator constructors.
968  tuple() = default;
969  // No-op allocator constructors.
970  template<typename _Alloc>
971  _GLIBCXX20_CONSTEXPR
972  tuple(allocator_arg_t, const _Alloc&) noexcept { }
973  template<typename _Alloc>
974  _GLIBCXX20_CONSTEXPR
975  tuple(allocator_arg_t, const _Alloc&, const tuple&) noexcept { }
976  };
977 
978  /// Partial specialization, 2-element tuple.
979  /// Includes construction and assignment from a pair.
980  template<typename _T1, typename _T2>
981  class tuple<_T1, _T2> : public _Tuple_impl<0, _T1, _T2>
982  {
983  typedef _Tuple_impl<0, _T1, _T2> _Inherited;
984 
985  // Constraint for non-explicit default constructor
986  template<bool _Dummy, typename _U1, typename _U2>
987  using _ImplicitDefaultCtor = __enable_if_t<
988  _TupleConstraints<_Dummy, _U1, _U2>::
989  __is_implicitly_default_constructible(),
990  bool>;
991 
992  // Constraint for explicit default constructor
993  template<bool _Dummy, typename _U1, typename _U2>
994  using _ExplicitDefaultCtor = __enable_if_t<
995  _TupleConstraints<_Dummy, _U1, _U2>::
996  __is_explicitly_default_constructible(),
997  bool>;
998 
999  template<bool _Dummy>
1000  using _TCC = _TupleConstraints<_Dummy, _T1, _T2>;
1001 
1002  // Constraint for non-explicit constructors
1003  template<bool _Cond, typename _U1, typename _U2>
1004  using _ImplicitCtor = __enable_if_t<
1005  _TCC<_Cond>::template __is_implicitly_constructible<_U1, _U2>(),
1006  bool>;
1007 
1008  // Constraint for non-explicit constructors
1009  template<bool _Cond, typename _U1, typename _U2>
1010  using _ExplicitCtor = __enable_if_t<
1011  _TCC<_Cond>::template __is_explicitly_constructible<_U1, _U2>(),
1012  bool>;
1013 
1014  template<typename _U1, typename _U2>
1015  static constexpr bool __assignable()
1016  {
1017  return __and_<is_assignable<_T1&, _U1>,
1018  is_assignable<_T2&, _U2>>::value;
1019  }
1020 
1021  template<typename _U1, typename _U2>
1022  static constexpr bool __nothrow_assignable()
1023  {
1024  return __and_<is_nothrow_assignable<_T1&, _U1>,
1025  is_nothrow_assignable<_T2&, _U2>>::value;
1026  }
1027 
1028  template<typename _U1, typename _U2>
1029  static constexpr bool __nothrow_constructible()
1030  {
1031  return __and_<is_nothrow_constructible<_T1, _U1>,
1032  is_nothrow_constructible<_T2, _U2>>::value;
1033  }
1034 
1035  static constexpr bool __nothrow_default_constructible()
1036  {
1037  return __and_<is_nothrow_default_constructible<_T1>,
1038  is_nothrow_default_constructible<_T2>>::value;
1039  }
1040 
1041  template<typename _U1>
1042  static constexpr bool __is_alloc_arg()
1043  { return is_same<__remove_cvref_t<_U1>, allocator_arg_t>::value; }
1044 
1045  public:
1046  template<bool _Dummy = true,
1047  _ImplicitDefaultCtor<_Dummy, _T1, _T2> = true>
1048  constexpr
1049  tuple()
1050  noexcept(__nothrow_default_constructible())
1051  : _Inherited() { }
1052 
1053  template<bool _Dummy = true,
1054  _ExplicitDefaultCtor<_Dummy, _T1, _T2> = false>
1055  explicit constexpr
1056  tuple()
1057  noexcept(__nothrow_default_constructible())
1058  : _Inherited() { }
1059 
1060  template<bool _Dummy = true,
1061  _ImplicitCtor<_Dummy, const _T1&, const _T2&> = true>
1062  constexpr
1063  tuple(const _T1& __a1, const _T2& __a2)
1064  noexcept(__nothrow_constructible<const _T1&, const _T2&>())
1065  : _Inherited(__a1, __a2) { }
1066 
1067  template<bool _Dummy = true,
1068  _ExplicitCtor<_Dummy, const _T1&, const _T2&> = false>
1069  explicit constexpr
1070  tuple(const _T1& __a1, const _T2& __a2)
1071  noexcept(__nothrow_constructible<const _T1&, const _T2&>())
1072  : _Inherited(__a1, __a2) { }
1073 
1074  template<typename _U1, typename _U2,
1075  _ImplicitCtor<!__is_alloc_arg<_U1>(), _U1, _U2> = true>
1076  constexpr
1077  tuple(_U1&& __a1, _U2&& __a2)
1078  noexcept(__nothrow_constructible<_U1, _U2>())
1079  : _Inherited(std::forward<_U1>(__a1), std::forward<_U2>(__a2)) { }
1080 
1081  template<typename _U1, typename _U2,
1082  _ExplicitCtor<!__is_alloc_arg<_U1>(), _U1, _U2> = false>
1083  explicit 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  constexpr tuple(const tuple&) = default;
1089 
1090  constexpr tuple(tuple&&) = default;
1091 
1092  template<typename _U1, typename _U2,
1093  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1094  constexpr
1095  tuple(const tuple<_U1, _U2>& __in)
1096  noexcept(__nothrow_constructible<const _U1&, const _U2&>())
1097  : _Inherited(static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in)) { }
1098 
1099  template<typename _U1, typename _U2,
1100  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1101  explicit 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  _ImplicitCtor<true, _U1, _U2> = true>
1108  constexpr
1109  tuple(tuple<_U1, _U2>&& __in)
1110  noexcept(__nothrow_constructible<_U1, _U2>())
1111  : _Inherited(static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in)) { }
1112 
1113  template<typename _U1, typename _U2,
1114  _ExplicitCtor<true, _U1, _U2> = false>
1115  explicit 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  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1122  constexpr
1123  tuple(const pair<_U1, _U2>& __in)
1124  noexcept(__nothrow_constructible<const _U1&, const _U2&>())
1125  : _Inherited(__in.first, __in.second) { }
1126 
1127  template<typename _U1, typename _U2,
1128  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1129  explicit 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  _ImplicitCtor<true, _U1, _U2> = true>
1136  constexpr
1137  tuple(pair<_U1, _U2>&& __in)
1138  noexcept(__nothrow_constructible<_U1, _U2>())
1139  : _Inherited(std::forward<_U1>(__in.first),
1140  std::forward<_U2>(__in.second)) { }
1141 
1142  template<typename _U1, typename _U2,
1143  _ExplicitCtor<true, _U1, _U2> = false>
1144  explicit constexpr
1145  tuple(pair<_U1, _U2>&& __in)
1146  noexcept(__nothrow_constructible<_U1, _U2>())
1147  : _Inherited(std::forward<_U1>(__in.first),
1148  std::forward<_U2>(__in.second)) { }
1149 
1150  // Allocator-extended constructors.
1151 
1152  template<typename _Alloc,
1153  _ImplicitDefaultCtor<is_object<_Alloc>::value, _T1, _T2> = true>
1154  _GLIBCXX20_CONSTEXPR
1155  tuple(allocator_arg_t __tag, const _Alloc& __a)
1156  : _Inherited(__tag, __a) { }
1157 
1158  template<typename _Alloc, bool _Dummy = true,
1159  _ImplicitCtor<_Dummy, const _T1&, const _T2&> = true>
1160  _GLIBCXX20_CONSTEXPR
1161  tuple(allocator_arg_t __tag, const _Alloc& __a,
1162  const _T1& __a1, const _T2& __a2)
1163  : _Inherited(__tag, __a, __a1, __a2) { }
1164 
1165  template<typename _Alloc, bool _Dummy = true,
1166  _ExplicitCtor<_Dummy, const _T1&, const _T2&> = false>
1167  explicit
1168  _GLIBCXX20_CONSTEXPR
1169  tuple(allocator_arg_t __tag, const _Alloc& __a,
1170  const _T1& __a1, const _T2& __a2)
1171  : _Inherited(__tag, __a, __a1, __a2) { }
1172 
1173  template<typename _Alloc, typename _U1, typename _U2,
1174  _ImplicitCtor<true, _U1, _U2> = true>
1175  _GLIBCXX20_CONSTEXPR
1176  tuple(allocator_arg_t __tag, const _Alloc& __a, _U1&& __a1, _U2&& __a2)
1177  : _Inherited(__tag, __a, std::forward<_U1>(__a1),
1178  std::forward<_U2>(__a2)) { }
1179 
1180  template<typename _Alloc, typename _U1, typename _U2,
1181  _ExplicitCtor<true, _U1, _U2> = false>
1182  explicit
1183  _GLIBCXX20_CONSTEXPR
1184  tuple(allocator_arg_t __tag, const _Alloc& __a,
1185  _U1&& __a1, _U2&& __a2)
1186  : _Inherited(__tag, __a, std::forward<_U1>(__a1),
1187  std::forward<_U2>(__a2)) { }
1188 
1189  template<typename _Alloc>
1190  _GLIBCXX20_CONSTEXPR
1191  tuple(allocator_arg_t __tag, const _Alloc& __a, const tuple& __in)
1192  : _Inherited(__tag, __a, static_cast<const _Inherited&>(__in)) { }
1193 
1194  template<typename _Alloc>
1195  _GLIBCXX20_CONSTEXPR
1196  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple&& __in)
1197  : _Inherited(__tag, __a, static_cast<_Inherited&&>(__in)) { }
1198 
1199  template<typename _Alloc, typename _U1, typename _U2,
1200  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1201  _GLIBCXX20_CONSTEXPR
1202  tuple(allocator_arg_t __tag, const _Alloc& __a,
1203  const tuple<_U1, _U2>& __in)
1204  : _Inherited(__tag, __a,
1205  static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in))
1206  { }
1207 
1208  template<typename _Alloc, typename _U1, typename _U2,
1209  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1210  explicit
1211  _GLIBCXX20_CONSTEXPR
1212  tuple(allocator_arg_t __tag, const _Alloc& __a,
1213  const tuple<_U1, _U2>& __in)
1214  : _Inherited(__tag, __a,
1215  static_cast<const _Tuple_impl<0, _U1, _U2>&>(__in))
1216  { }
1217 
1218  template<typename _Alloc, typename _U1, typename _U2,
1219  _ImplicitCtor<true, _U1, _U2> = true>
1220  _GLIBCXX20_CONSTEXPR
1221  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple<_U1, _U2>&& __in)
1222  : _Inherited(__tag, __a, static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in))
1223  { }
1224 
1225  template<typename _Alloc, typename _U1, typename _U2,
1226  _ExplicitCtor<true, _U1, _U2> = false>
1227  explicit
1228  _GLIBCXX20_CONSTEXPR
1229  tuple(allocator_arg_t __tag, const _Alloc& __a, tuple<_U1, _U2>&& __in)
1230  : _Inherited(__tag, __a, static_cast<_Tuple_impl<0, _U1, _U2>&&>(__in))
1231  { }
1232 
1233  template<typename _Alloc, typename _U1, typename _U2,
1234  _ImplicitCtor<true, const _U1&, const _U2&> = true>
1235  _GLIBCXX20_CONSTEXPR
1236  tuple(allocator_arg_t __tag, const _Alloc& __a,
1237  const pair<_U1, _U2>& __in)
1238  : _Inherited(__tag, __a, __in.first, __in.second) { }
1239 
1240  template<typename _Alloc, typename _U1, typename _U2,
1241  _ExplicitCtor<true, const _U1&, const _U2&> = false>
1242  explicit
1243  _GLIBCXX20_CONSTEXPR
1244  tuple(allocator_arg_t __tag, const _Alloc& __a,
1245  const pair<_U1, _U2>& __in)
1246  : _Inherited(__tag, __a, __in.first, __in.second) { }
1247 
1248  template<typename _Alloc, typename _U1, typename _U2,
1249  _ImplicitCtor<true, _U1, _U2> = true>
1250  _GLIBCXX20_CONSTEXPR
1251  tuple(allocator_arg_t __tag, const _Alloc& __a, pair<_U1, _U2>&& __in)
1252  : _Inherited(__tag, __a, std::forward<_U1>(__in.first),
1253  std::forward<_U2>(__in.second)) { }
1254 
1255  template<typename _Alloc, typename _U1, typename _U2,
1256  _ExplicitCtor<true, _U1, _U2> = false>
1257  explicit
1258  _GLIBCXX20_CONSTEXPR
1259  tuple(allocator_arg_t __tag, const _Alloc& __a, pair<_U1, _U2>&& __in)
1260  : _Inherited(__tag, __a, std::forward<_U1>(__in.first),
1261  std::forward<_U2>(__in.second)) { }
1262 
1263  // Tuple assignment.
1264 
1265  _GLIBCXX20_CONSTEXPR
1266  tuple&
1267  operator=(__conditional_t<__assignable<const _T1&, const _T2&>(),
1268  const tuple&,
1269  const __nonesuch&> __in)
1270  noexcept(__nothrow_assignable<const _T1&, const _T2&>())
1271  {
1272  this->_M_assign(__in);
1273  return *this;
1274  }
1275 
1276  _GLIBCXX20_CONSTEXPR
1277  tuple&
1278  operator=(__conditional_t<__assignable<_T1, _T2>(),
1279  tuple&&,
1280  __nonesuch&&> __in)
1281  noexcept(__nothrow_assignable<_T1, _T2>())
1282  {
1283  this->_M_assign(std::move(__in));
1284  return *this;
1285  }
1286 
1287  template<typename _U1, typename _U2>
1288  _GLIBCXX20_CONSTEXPR
1289  __enable_if_t<__assignable<const _U1&, const _U2&>(), tuple&>
1290  operator=(const tuple<_U1, _U2>& __in)
1291  noexcept(__nothrow_assignable<const _U1&, const _U2&>())
1292  {
1293  this->_M_assign(__in);
1294  return *this;
1295  }
1296 
1297  template<typename _U1, typename _U2>
1298  _GLIBCXX20_CONSTEXPR
1299  __enable_if_t<__assignable<_U1, _U2>(), tuple&>
1300  operator=(tuple<_U1, _U2>&& __in)
1301  noexcept(__nothrow_assignable<_U1, _U2>())
1302  {
1303  this->_M_assign(std::move(__in));
1304  return *this;
1305  }
1306 
1307  template<typename _U1, typename _U2>
1308  _GLIBCXX20_CONSTEXPR
1309  __enable_if_t<__assignable<const _U1&, const _U2&>(), tuple&>
1310  operator=(const pair<_U1, _U2>& __in)
1311  noexcept(__nothrow_assignable<const _U1&, const _U2&>())
1312  {
1313  this->_M_head(*this) = __in.first;
1314  this->_M_tail(*this)._M_head(*this) = __in.second;
1315  return *this;
1316  }
1317 
1318  template<typename _U1, typename _U2>
1319  _GLIBCXX20_CONSTEXPR
1320  __enable_if_t<__assignable<_U1, _U2>(), tuple&>
1321  operator=(pair<_U1, _U2>&& __in)
1322  noexcept(__nothrow_assignable<_U1, _U2>())
1323  {
1324  this->_M_head(*this) = std::forward<_U1>(__in.first);
1325  this->_M_tail(*this)._M_head(*this) = std::forward<_U2>(__in.second);
1326  return *this;
1327  }
1328 
1329  _GLIBCXX20_CONSTEXPR
1330  void
1331  swap(tuple& __in)
1332  noexcept(__and_<__is_nothrow_swappable<_T1>,
1333  __is_nothrow_swappable<_T2>>::value)
1334  { _Inherited::_M_swap(__in); }
1335  };
1336 
1337 
1338  /// class tuple_size
1339  template<typename... _Elements>
1340  struct tuple_size<tuple<_Elements...>>
1341  : public integral_constant<size_t, sizeof...(_Elements)> { };
1342 
1343 #if __cplusplus >= 201703L
1344  template<typename... _Types>
1345  inline constexpr size_t tuple_size_v<tuple<_Types...>>
1346  = sizeof...(_Types);
1347 
1348  template<typename... _Types>
1349  inline constexpr size_t tuple_size_v<const tuple<_Types...>>
1350  = sizeof...(_Types);
1351 #endif
1352 
1353  /// Trait to get the Ith element type from a tuple.
1354  template<size_t __i, typename... _Types>
1355  struct tuple_element<__i, tuple<_Types...>>
1356  {
1357  static_assert(__i < sizeof...(_Types), "tuple index must be in range");
1358 
1359  using type = typename _Nth_type<__i, _Types...>::type;
1360  };
1361 
1362  template<size_t __i, typename _Head, typename... _Tail>
1363  constexpr _Head&
1364  __get_helper(_Tuple_impl<__i, _Head, _Tail...>& __t) noexcept
1365  { return _Tuple_impl<__i, _Head, _Tail...>::_M_head(__t); }
1366 
1367  template<size_t __i, typename _Head, typename... _Tail>
1368  constexpr const _Head&
1369  __get_helper(const _Tuple_impl<__i, _Head, _Tail...>& __t) noexcept
1370  { return _Tuple_impl<__i, _Head, _Tail...>::_M_head(__t); }
1371 
1372  // Deleted overload to improve diagnostics for invalid indices
1373  template<size_t __i, typename... _Types>
1374  __enable_if_t<(__i >= sizeof...(_Types))>
1375  __get_helper(const tuple<_Types...>&) = delete;
1376 
1377  /// Return a reference to the ith element of a tuple.
1378  template<size_t __i, typename... _Elements>
1379  constexpr __tuple_element_t<__i, tuple<_Elements...>>&
1380  get(tuple<_Elements...>& __t) noexcept
1381  { return std::__get_helper<__i>(__t); }
1382 
1383  /// Return a const reference to the ith element of a const tuple.
1384  template<size_t __i, typename... _Elements>
1385  constexpr const __tuple_element_t<__i, tuple<_Elements...>>&
1386  get(const tuple<_Elements...>& __t) noexcept
1387  { return std::__get_helper<__i>(__t); }
1388 
1389  /// Return an rvalue reference to the ith element of a tuple rvalue.
1390  template<size_t __i, typename... _Elements>
1391  constexpr __tuple_element_t<__i, tuple<_Elements...>>&&
1392  get(tuple<_Elements...>&& __t) noexcept
1393  {
1394  typedef __tuple_element_t<__i, tuple<_Elements...>> __element_type;
1395  return std::forward<__element_type>(std::__get_helper<__i>(__t));
1396  }
1397 
1398  /// Return a const rvalue reference to the ith element of a const tuple rvalue.
1399  template<size_t __i, typename... _Elements>
1400  constexpr const __tuple_element_t<__i, tuple<_Elements...>>&&
1401  get(const tuple<_Elements...>&& __t) noexcept
1402  {
1403  typedef __tuple_element_t<__i, tuple<_Elements...>> __element_type;
1404  return std::forward<const __element_type>(std::__get_helper<__i>(__t));
1405  }
1406 
1407  /// @cond undocumented
1408  // Deleted overload chosen for invalid indices.
1409  template<size_t __i, typename... _Elements>
1410  constexpr __enable_if_t<(__i >= sizeof...(_Elements))>
1411  get(const tuple<_Elements...>&) = delete;
1412  /// @endcond
1413 
1414 #if __cplusplus >= 201402L
1415 
1416 #define __cpp_lib_tuples_by_type 201304L
1417 
1418  /// Return a reference to the unique element of type _Tp of a tuple.
1419  template <typename _Tp, typename... _Types>
1420  constexpr _Tp&
1421  get(tuple<_Types...>& __t) noexcept
1422  {
1423  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1424  static_assert(__idx < sizeof...(_Types),
1425  "the type T in std::get<T> must occur exactly once in the tuple");
1426  return std::__get_helper<__idx>(__t);
1427  }
1428 
1429  /// Return a reference to the unique element of type _Tp of a tuple rvalue.
1430  template <typename _Tp, typename... _Types>
1431  constexpr _Tp&&
1432  get(tuple<_Types...>&& __t) noexcept
1433  {
1434  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1435  static_assert(__idx < sizeof...(_Types),
1436  "the type T in std::get<T> must occur exactly once in the tuple");
1437  return std::forward<_Tp>(std::__get_helper<__idx>(__t));
1438  }
1439 
1440  /// Return a const reference to the unique element of type _Tp of a tuple.
1441  template <typename _Tp, typename... _Types>
1442  constexpr const _Tp&
1443  get(const tuple<_Types...>& __t) noexcept
1444  {
1445  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1446  static_assert(__idx < sizeof...(_Types),
1447  "the type T in std::get<T> must occur exactly once in the tuple");
1448  return std::__get_helper<__idx>(__t);
1449  }
1450 
1451  /// Return a const reference to the unique element of type _Tp of
1452  /// a const tuple rvalue.
1453  template <typename _Tp, typename... _Types>
1454  constexpr const _Tp&&
1455  get(const tuple<_Types...>&& __t) noexcept
1456  {
1457  constexpr size_t __idx = __find_uniq_type_in_pack<_Tp, _Types...>();
1458  static_assert(__idx < sizeof...(_Types),
1459  "the type T in std::get<T> must occur exactly once in the tuple");
1460  return std::forward<const _Tp>(std::__get_helper<__idx>(__t));
1461  }
1462 #endif
1463 
1464  // This class performs the comparison operations on tuples
1465  template<typename _Tp, typename _Up, size_t __i, size_t __size>
1466  struct __tuple_compare
1467  {
1468  static constexpr bool
1469  __eq(const _Tp& __t, const _Up& __u)
1470  {
1471  return bool(std::get<__i>(__t) == std::get<__i>(__u))
1472  && __tuple_compare<_Tp, _Up, __i + 1, __size>::__eq(__t, __u);
1473  }
1474 
1475  static constexpr bool
1476  __less(const _Tp& __t, const _Up& __u)
1477  {
1478  return bool(std::get<__i>(__t) < std::get<__i>(__u))
1479  || (!bool(std::get<__i>(__u) < std::get<__i>(__t))
1480  && __tuple_compare<_Tp, _Up, __i + 1, __size>::__less(__t, __u));
1481  }
1482  };
1483 
1484  template<typename _Tp, typename _Up, size_t __size>
1485  struct __tuple_compare<_Tp, _Up, __size, __size>
1486  {
1487  static constexpr bool
1488  __eq(const _Tp&, const _Up&) { return true; }
1489 
1490  static constexpr bool
1491  __less(const _Tp&, const _Up&) { return false; }
1492  };
1493 
1494  template<typename... _TElements, typename... _UElements>
1495  constexpr bool
1496  operator==(const tuple<_TElements...>& __t,
1497  const tuple<_UElements...>& __u)
1498  {
1499  static_assert(sizeof...(_TElements) == sizeof...(_UElements),
1500  "tuple objects can only be compared if they have equal sizes.");
1501  using __compare = __tuple_compare<tuple<_TElements...>,
1502  tuple<_UElements...>,
1503  0, sizeof...(_TElements)>;
1504  return __compare::__eq(__t, __u);
1505  }
1506 
1507 #if __cpp_lib_three_way_comparison
1508  template<typename _Cat, typename _Tp, typename _Up>
1509  constexpr _Cat
1510  __tuple_cmp(const _Tp&, const _Up&, index_sequence<>)
1511  { return _Cat::equivalent; }
1512 
1513  template<typename _Cat, typename _Tp, typename _Up,
1514  size_t _Idx0, size_t... _Idxs>
1515  constexpr _Cat
1516  __tuple_cmp(const _Tp& __t, const _Up& __u,
1517  index_sequence<_Idx0, _Idxs...>)
1518  {
1519  auto __c
1520  = __detail::__synth3way(std::get<_Idx0>(__t), std::get<_Idx0>(__u));
1521  if (__c != 0)
1522  return __c;
1523  return std::__tuple_cmp<_Cat>(__t, __u, index_sequence<_Idxs...>());
1524  }
1525 
1526  template<typename... _Tps, typename... _Ups>
1527  constexpr
1528  common_comparison_category_t<__detail::__synth3way_t<_Tps, _Ups>...>
1529  operator<=>(const tuple<_Tps...>& __t, const tuple<_Ups...>& __u)
1530  {
1531  using _Cat
1532  = common_comparison_category_t<__detail::__synth3way_t<_Tps, _Ups>...>;
1533  return std::__tuple_cmp<_Cat>(__t, __u, index_sequence_for<_Tps...>());
1534  }
1535 #else
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::__less(__t, __u);
1547  }
1548 
1549  template<typename... _TElements, typename... _UElements>
1550  constexpr bool
1551  operator!=(const tuple<_TElements...>& __t,
1552  const tuple<_UElements...>& __u)
1553  { return !(__t == __u); }
1554 
1555  template<typename... _TElements, typename... _UElements>
1556  constexpr bool
1557  operator>(const tuple<_TElements...>& __t,
1558  const tuple<_UElements...>& __u)
1559  { return __u < __t; }
1560 
1561  template<typename... _TElements, typename... _UElements>
1562  constexpr bool
1563  operator<=(const tuple<_TElements...>& __t,
1564  const tuple<_UElements...>& __u)
1565  { return !(__u < __t); }
1566 
1567  template<typename... _TElements, typename... _UElements>
1568  constexpr bool
1569  operator>=(const tuple<_TElements...>& __t,
1570  const tuple<_UElements...>& __u)
1571  { return !(__t < __u); }
1572 #endif // three_way_comparison
1573 
1574  // NB: DR 705.
1575  template<typename... _Elements>
1576  constexpr tuple<typename __decay_and_strip<_Elements>::__type...>
1577  make_tuple(_Elements&&... __args)
1578  {
1579  typedef tuple<typename __decay_and_strip<_Elements>::__type...>
1580  __result_type;
1581  return __result_type(std::forward<_Elements>(__args)...);
1582  }
1583 
1584  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1585  // 2275. Why is forward_as_tuple not constexpr?
1586  /// std::forward_as_tuple
1587  template<typename... _Elements>
1588  constexpr tuple<_Elements&&...>
1589  forward_as_tuple(_Elements&&... __args) noexcept
1590  { return tuple<_Elements&&...>(std::forward<_Elements>(__args)...); }
1591 
1592  // Declarations of std::array and its std::get overloads, so that
1593  // std::tuple_cat can use them if <tuple> is included before <array>.
1594 
1595  template<typename _Tp, size_t _Nm> struct array;
1596 
1597  template<size_t _Int, typename _Tp, size_t _Nm>
1598  constexpr _Tp&
1599  get(array<_Tp, _Nm>&) noexcept;
1600 
1601  template<size_t _Int, typename _Tp, size_t _Nm>
1602  constexpr _Tp&&
1603  get(array<_Tp, _Nm>&&) noexcept;
1604 
1605  template<size_t _Int, typename _Tp, size_t _Nm>
1606  constexpr const _Tp&
1607  get(const array<_Tp, _Nm>&) noexcept;
1608 
1609  template<size_t _Int, typename _Tp, size_t _Nm>
1610  constexpr const _Tp&&
1611  get(const array<_Tp, _Nm>&&) noexcept;
1612 
1613 
1614  template<size_t, typename, typename, size_t>
1615  struct __make_tuple_impl;
1616 
1617  template<size_t _Idx, typename _Tuple, typename... _Tp, size_t _Nm>
1618  struct __make_tuple_impl<_Idx, tuple<_Tp...>, _Tuple, _Nm>
1619  : __make_tuple_impl<_Idx + 1,
1620  tuple<_Tp..., __tuple_element_t<_Idx, _Tuple>>,
1621  _Tuple, _Nm>
1622  { };
1623 
1624  template<size_t _Nm, typename _Tuple, typename... _Tp>
1625  struct __make_tuple_impl<_Nm, tuple<_Tp...>, _Tuple, _Nm>
1626  {
1627  typedef tuple<_Tp...> __type;
1628  };
1629 
1630  template<typename _Tuple>
1631  struct __do_make_tuple
1632  : __make_tuple_impl<0, tuple<>, _Tuple, tuple_size<_Tuple>::value>
1633  { };
1634 
1635  // Returns the std::tuple equivalent of a tuple-like type.
1636  template<typename _Tuple>
1637  struct __make_tuple
1638  : public __do_make_tuple<__remove_cvref_t<_Tuple>>
1639  { };
1640 
1641  // Combines several std::tuple's into a single one.
1642  template<typename...>
1643  struct __combine_tuples;
1644 
1645  template<>
1646  struct __combine_tuples<>
1647  {
1648  typedef tuple<> __type;
1649  };
1650 
1651  template<typename... _Ts>
1652  struct __combine_tuples<tuple<_Ts...>>
1653  {
1654  typedef tuple<_Ts...> __type;
1655  };
1656 
1657  template<typename... _T1s, typename... _T2s, typename... _Rem>
1658  struct __combine_tuples<tuple<_T1s...>, tuple<_T2s...>, _Rem...>
1659  {
1660  typedef typename __combine_tuples<tuple<_T1s..., _T2s...>,
1661  _Rem...>::__type __type;
1662  };
1663 
1664  // Computes the result type of tuple_cat given a set of tuple-like types.
1665  template<typename... _Tpls>
1666  struct __tuple_cat_result
1667  {
1668  typedef typename __combine_tuples
1669  <typename __make_tuple<_Tpls>::__type...>::__type __type;
1670  };
1671 
1672  // Helper to determine the index set for the first tuple-like
1673  // type of a given set.
1674  template<typename...>
1675  struct __make_1st_indices;
1676 
1677  template<>
1678  struct __make_1st_indices<>
1679  {
1680  typedef _Index_tuple<> __type;
1681  };
1682 
1683  template<typename _Tp, typename... _Tpls>
1684  struct __make_1st_indices<_Tp, _Tpls...>
1685  {
1686  typedef typename _Build_index_tuple<tuple_size<
1687  typename remove_reference<_Tp>::type>::value>::__type __type;
1688  };
1689 
1690  // Performs the actual concatenation by step-wise expanding tuple-like
1691  // objects into the elements, which are finally forwarded into the
1692  // result tuple.
1693  template<typename _Ret, typename _Indices, typename... _Tpls>
1694  struct __tuple_concater;
1695 
1696  template<typename _Ret, size_t... _Is, typename _Tp, typename... _Tpls>
1697  struct __tuple_concater<_Ret, _Index_tuple<_Is...>, _Tp, _Tpls...>
1698  {
1699  template<typename... _Us>
1700  static constexpr _Ret
1701  _S_do(_Tp&& __tp, _Tpls&&... __tps, _Us&&... __us)
1702  {
1703  typedef typename __make_1st_indices<_Tpls...>::__type __idx;
1704  typedef __tuple_concater<_Ret, __idx, _Tpls...> __next;
1705  return __next::_S_do(std::forward<_Tpls>(__tps)...,
1706  std::forward<_Us>(__us)...,
1707  std::get<_Is>(std::forward<_Tp>(__tp))...);
1708  }
1709  };
1710 
1711  template<typename _Ret>
1712  struct __tuple_concater<_Ret, _Index_tuple<>>
1713  {
1714  template<typename... _Us>
1715  static constexpr _Ret
1716  _S_do(_Us&&... __us)
1717  {
1718  return _Ret(std::forward<_Us>(__us)...);
1719  }
1720  };
1721 
1722  template<typename... _Tps>
1723  struct __is_tuple_like_impl<tuple<_Tps...>> : true_type
1724  { };
1725 
1726  /// tuple_cat
1727  template<typename... _Tpls, typename = typename
1728  enable_if<__and_<__is_tuple_like<_Tpls>...>::value>::type>
1729  constexpr auto
1730  tuple_cat(_Tpls&&... __tpls)
1731  -> typename __tuple_cat_result<_Tpls...>::__type
1732  {
1733  typedef typename __tuple_cat_result<_Tpls...>::__type __ret;
1734  typedef typename __make_1st_indices<_Tpls...>::__type __idx;
1735  typedef __tuple_concater<__ret, __idx, _Tpls...> __concater;
1736  return __concater::_S_do(std::forward<_Tpls>(__tpls)...);
1737  }
1738 
1739  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1740  // 2301. Why is tie not constexpr?
1741  /// tie
1742  template<typename... _Elements>
1743  constexpr tuple<_Elements&...>
1744  tie(_Elements&... __args) noexcept
1745  { return tuple<_Elements&...>(__args...); }
1746 
1747  /// swap
1748  template<typename... _Elements>
1749  _GLIBCXX20_CONSTEXPR
1750  inline
1751 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1752  // Constrained free swap overload, see p0185r1
1753  typename enable_if<__and_<__is_swappable<_Elements>...>::value
1754  >::type
1755 #else
1756  void
1757 #endif
1758  swap(tuple<_Elements...>& __x, tuple<_Elements...>& __y)
1759  noexcept(noexcept(__x.swap(__y)))
1760  { __x.swap(__y); }
1761 
1762 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
1763  template<typename... _Elements>
1764  _GLIBCXX20_CONSTEXPR
1765  typename enable_if<!__and_<__is_swappable<_Elements>...>::value>::type
1766  swap(tuple<_Elements...>&, tuple<_Elements...>&) = delete;
1767 #endif
1768 
1769  // A class (and instance) which can be used in 'tie' when an element
1770  // of a tuple is not required.
1771  // _GLIBCXX14_CONSTEXPR
1772  // 2933. PR for LWG 2773 could be clearer
1773  struct _Swallow_assign
1774  {
1775  template<class _Tp>
1776  _GLIBCXX14_CONSTEXPR const _Swallow_assign&
1777  operator=(const _Tp&) const
1778  { return *this; }
1779  };
1780 
1781  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1782  // 2773. Making std::ignore constexpr
1783  _GLIBCXX17_INLINE constexpr _Swallow_assign ignore{};
1784 
1785  /// Partial specialization for tuples
1786  template<typename... _Types, typename _Alloc>
1787  struct uses_allocator<tuple<_Types...>, _Alloc> : true_type { };
1788 
1789  // See stl_pair.h...
1790  /** "piecewise construction" using a tuple of arguments for each member.
1791  *
1792  * @param __first Arguments for the first member of the pair.
1793  * @param __second Arguments for the second member of the pair.
1794  *
1795  * The elements of each tuple will be used as the constructor arguments
1796  * for the data members of the pair.
1797  */
1798  template<class _T1, class _T2>
1799  template<typename... _Args1, typename... _Args2>
1800  _GLIBCXX20_CONSTEXPR
1801  inline
1802  pair<_T1, _T2>::
1803  pair(piecewise_construct_t,
1804  tuple<_Args1...> __first, tuple<_Args2...> __second)
1805  : pair(__first, __second,
1806  typename _Build_index_tuple<sizeof...(_Args1)>::__type(),
1807  typename _Build_index_tuple<sizeof...(_Args2)>::__type())
1808  { }
1809 
1810  template<class _T1, class _T2>
1811  template<typename... _Args1, size_t... _Indexes1,
1812  typename... _Args2, size_t... _Indexes2>
1813  _GLIBCXX20_CONSTEXPR inline
1814  pair<_T1, _T2>::
1815  pair(tuple<_Args1...>& __tuple1, tuple<_Args2...>& __tuple2,
1816  _Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>)
1817  : first(std::forward<_Args1>(std::get<_Indexes1>(__tuple1))...),
1818  second(std::forward<_Args2>(std::get<_Indexes2>(__tuple2))...)
1819  { }
1820 
1821 #if __cplusplus >= 201703L
1822 
1823  // Unpack a std::tuple into a type trait and use its value.
1824  // For cv std::tuple<_Up> the result is _Trait<_Tp, cv _Up...>::value.
1825  // For cv std::tuple<_Up>& the result is _Trait<_Tp, cv _Up&...>::value.
1826  // Otherwise the result is false (because we don't know if std::get throws).
1827  template<template<typename...> class _Trait, typename _Tp, typename _Tuple>
1828  inline constexpr bool __unpack_std_tuple = false;
1829 
1830  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1831  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, tuple<_Up...>>
1832  = _Trait<_Tp, _Up...>::value;
1833 
1834  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1835  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, tuple<_Up...>&>
1836  = _Trait<_Tp, _Up&...>::value;
1837 
1838  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1839  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, const tuple<_Up...>>
1840  = _Trait<_Tp, const _Up...>::value;
1841 
1842  template<template<typename...> class _Trait, typename _Tp, typename... _Up>
1843  inline constexpr bool __unpack_std_tuple<_Trait, _Tp, const tuple<_Up...>&>
1844  = _Trait<_Tp, const _Up&...>::value;
1845 
1846 # define __cpp_lib_apply 201603L
1847 
1848  template <typename _Fn, typename _Tuple, size_t... _Idx>
1849  constexpr decltype(auto)
1850  __apply_impl(_Fn&& __f, _Tuple&& __t, index_sequence<_Idx...>)
1851  {
1852  return std::__invoke(std::forward<_Fn>(__f),
1853  std::get<_Idx>(std::forward<_Tuple>(__t))...);
1854  }
1855 
1856  template <typename _Fn, typename _Tuple>
1857  constexpr decltype(auto)
1858  apply(_Fn&& __f, _Tuple&& __t)
1859  noexcept(__unpack_std_tuple<is_nothrow_invocable, _Fn, _Tuple>)
1860  {
1861  using _Indices
1862  = make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>;
1863  return std::__apply_impl(std::forward<_Fn>(__f),
1864  std::forward<_Tuple>(__t),
1865  _Indices{});
1866  }
1867 
1868 #define __cpp_lib_make_from_tuple 201606L
1869 
1870  template <typename _Tp, typename _Tuple, size_t... _Idx>
1871  constexpr _Tp
1872  __make_from_tuple_impl(_Tuple&& __t, index_sequence<_Idx...>)
1873  { return _Tp(std::get<_Idx>(std::forward<_Tuple>(__t))...); }
1874 
1875  template <typename _Tp, typename _Tuple>
1876  constexpr _Tp
1877  make_from_tuple(_Tuple&& __t)
1878  noexcept(__unpack_std_tuple<is_nothrow_constructible, _Tp, _Tuple>)
1879  {
1880  return __make_from_tuple_impl<_Tp>(
1881  std::forward<_Tuple>(__t),
1882  make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>{});
1883  }
1884 #endif // C++17
1885 
1886  /// @}
1887 
1888 _GLIBCXX_END_NAMESPACE_VERSION
1889 } // namespace std
1890 
1891 #endif // C++11
1892 
1893 #endif // _GLIBCXX_TUPLE