libstdc++
variant
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1 // <variant> -*- C++ -*-
2 
3 // Copyright (C) 2016-2021 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 variant
26  * This is the `<variant>` C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_VARIANT
30 #define _GLIBCXX_VARIANT 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus >= 201703L
35 
36 #include <type_traits>
37 #include <utility>
39 #include <bits/functexcept.h>
40 #include <bits/move.h>
41 #include <bits/functional_hash.h>
42 #include <bits/invoke.h>
43 #include <ext/aligned_buffer.h>
44 #include <bits/parse_numbers.h>
47 #include <bits/stl_construct.h>
48 #if __cplusplus > 201703L
49 # include <compare>
50 #endif
51 
52 namespace std _GLIBCXX_VISIBILITY(default)
53 {
54 _GLIBCXX_BEGIN_NAMESPACE_VERSION
55 
56 namespace __detail
57 {
58 namespace __variant
59 {
60  template<size_t _Np, typename... _Types>
61  struct _Nth_type;
62 
63  template<size_t _Np, typename _First, typename... _Rest>
64  struct _Nth_type<_Np, _First, _Rest...>
65  : _Nth_type<_Np-1, _Rest...> { };
66 
67  template<typename _First, typename... _Rest>
68  struct _Nth_type<0, _First, _Rest...>
69  { using type = _First; };
70 
71 } // namespace __variant
72 } // namespace __detail
73 
74 #define __cpp_lib_variant 201606L
75 
76  template<typename... _Types> class tuple;
77  template<typename... _Types> class variant;
78  template <typename> struct hash;
79 
80  template<typename _Variant>
81  struct variant_size;
82 
83  template<typename _Variant>
84  struct variant_size<const _Variant> : variant_size<_Variant> {};
85 
86  template<typename _Variant>
87  struct variant_size<volatile _Variant> : variant_size<_Variant> {};
88 
89  template<typename _Variant>
90  struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
91 
92  template<typename... _Types>
93  struct variant_size<variant<_Types...>>
94  : std::integral_constant<size_t, sizeof...(_Types)> {};
95 
96  template<typename _Variant>
97  inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
98 
99  template<size_t _Np, typename _Variant>
100  struct variant_alternative;
101 
102  template<size_t _Np, typename _First, typename... _Rest>
103  struct variant_alternative<_Np, variant<_First, _Rest...>>
104  : variant_alternative<_Np-1, variant<_Rest...>> {};
105 
106  template<typename _First, typename... _Rest>
107  struct variant_alternative<0, variant<_First, _Rest...>>
108  { using type = _First; };
109 
110  template<size_t _Np, typename _Variant>
111  using variant_alternative_t =
112  typename variant_alternative<_Np, _Variant>::type;
113 
114  template<size_t _Np, typename _Variant>
115  struct variant_alternative<_Np, const _Variant>
116  { using type = add_const_t<variant_alternative_t<_Np, _Variant>>; };
117 
118  template<size_t _Np, typename _Variant>
119  struct variant_alternative<_Np, volatile _Variant>
120  { using type = add_volatile_t<variant_alternative_t<_Np, _Variant>>; };
121 
122  template<size_t _Np, typename _Variant>
123  struct variant_alternative<_Np, const volatile _Variant>
124  { using type = add_cv_t<variant_alternative_t<_Np, _Variant>>; };
125 
126  inline constexpr size_t variant_npos = -1;
127 
128  template<size_t _Np, typename... _Types>
129  constexpr variant_alternative_t<_Np, variant<_Types...>>&
130  get(variant<_Types...>&);
131 
132  template<size_t _Np, typename... _Types>
133  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
134  get(variant<_Types...>&&);
135 
136  template<size_t _Np, typename... _Types>
137  constexpr variant_alternative_t<_Np, variant<_Types...>> const&
138  get(const variant<_Types...>&);
139 
140  template<size_t _Np, typename... _Types>
141  constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
142  get(const variant<_Types...>&&);
143 
144  template<typename _Result_type, typename _Visitor, typename... _Variants>
145  constexpr decltype(auto)
146  __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
147 
148  template <typename... _Types, typename _Tp>
149  decltype(auto)
150  __variant_cast(_Tp&& __rhs)
151  {
152  if constexpr (is_lvalue_reference_v<_Tp>)
153  {
154  if constexpr (is_const_v<remove_reference_t<_Tp>>)
155  return static_cast<const variant<_Types...>&>(__rhs);
156  else
157  return static_cast<variant<_Types...>&>(__rhs);
158  }
159  else
160  return static_cast<variant<_Types...>&&>(__rhs);
161  }
162 
163 namespace __detail
164 {
165 namespace __variant
166 {
167  // Returns the first appearance of _Tp in _Types.
168  // Returns sizeof...(_Types) if _Tp is not in _Types.
169  template<typename _Tp, typename... _Types>
170  struct __index_of : std::integral_constant<size_t, 0> {};
171 
172  template<typename _Tp, typename... _Types>
173  inline constexpr size_t __index_of_v = __index_of<_Tp, _Types...>::value;
174 
175  template<typename _Tp, typename _First, typename... _Rest>
176  struct __index_of<_Tp, _First, _Rest...> :
177  std::integral_constant<size_t, is_same_v<_Tp, _First>
178  ? 0 : __index_of_v<_Tp, _Rest...> + 1> {};
179 
180  // used for raw visitation
181  struct __variant_cookie {};
182  // used for raw visitation with indices passed in
183  struct __variant_idx_cookie { using type = __variant_idx_cookie; };
184  // Used to enable deduction (and same-type checking) for std::visit:
185  template<typename _Tp> struct __deduce_visit_result { using type = _Tp; };
186 
187  // Visit variants that might be valueless.
188  template<typename _Visitor, typename... _Variants>
189  constexpr void
190  __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
191  {
192  std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
193  std::forward<_Variants>(__variants)...);
194  }
195 
196  // Visit variants that might be valueless, passing indices to the visitor.
197  template<typename _Visitor, typename... _Variants>
198  constexpr void
199  __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
200  {
201  std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
202  std::forward<_Variants>(__variants)...);
203  }
204 
205  // _Uninitialized<T> is guaranteed to be a trivially destructible type,
206  // even if T is not.
207  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
208  struct _Uninitialized;
209 
210  template<typename _Type>
211  struct _Uninitialized<_Type, true>
212  {
213  template<typename... _Args>
214  constexpr
215  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
216  : _M_storage(std::forward<_Args>(__args)...)
217  { }
218 
219  constexpr const _Type& _M_get() const & noexcept
220  { return _M_storage; }
221 
222  constexpr _Type& _M_get() & noexcept
223  { return _M_storage; }
224 
225  constexpr const _Type&& _M_get() const && noexcept
226  { return std::move(_M_storage); }
227 
228  constexpr _Type&& _M_get() && noexcept
229  { return std::move(_M_storage); }
230 
231  _Type _M_storage;
232  };
233 
234  template<typename _Type>
235  struct _Uninitialized<_Type, false>
236  {
237  template<typename... _Args>
238  constexpr
239  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
240  {
241  ::new ((void*)std::addressof(_M_storage))
242  _Type(std::forward<_Args>(__args)...);
243  }
244 
245  const _Type& _M_get() const & noexcept
246  { return *_M_storage._M_ptr(); }
247 
248  _Type& _M_get() & noexcept
249  { return *_M_storage._M_ptr(); }
250 
251  const _Type&& _M_get() const && noexcept
252  { return std::move(*_M_storage._M_ptr()); }
253 
254  _Type&& _M_get() && noexcept
255  { return std::move(*_M_storage._M_ptr()); }
256 
257  __gnu_cxx::__aligned_membuf<_Type> _M_storage;
258  };
259 
260  template<typename _Union>
261  constexpr decltype(auto)
262  __get(in_place_index_t<0>, _Union&& __u) noexcept
263  { return std::forward<_Union>(__u)._M_first._M_get(); }
264 
265  template<size_t _Np, typename _Union>
266  constexpr decltype(auto)
267  __get(in_place_index_t<_Np>, _Union&& __u) noexcept
268  {
269  return __variant::__get(in_place_index<_Np-1>,
270  std::forward<_Union>(__u)._M_rest);
271  }
272 
273  // Returns the typed storage for __v.
274  template<size_t _Np, typename _Variant>
275  constexpr decltype(auto)
276  __get(_Variant&& __v) noexcept
277  {
278  return __variant::__get(std::in_place_index<_Np>,
279  std::forward<_Variant>(__v)._M_u);
280  }
281 
282  template<typename... _Types>
283  struct _Traits
284  {
285  static constexpr bool _S_default_ctor =
286  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
287  static constexpr bool _S_copy_ctor =
288  (is_copy_constructible_v<_Types> && ...);
289  static constexpr bool _S_move_ctor =
290  (is_move_constructible_v<_Types> && ...);
291  static constexpr bool _S_copy_assign =
292  _S_copy_ctor
293  && (is_copy_assignable_v<_Types> && ...);
294  static constexpr bool _S_move_assign =
295  _S_move_ctor
296  && (is_move_assignable_v<_Types> && ...);
297 
298  static constexpr bool _S_trivial_dtor =
299  (is_trivially_destructible_v<_Types> && ...);
300  static constexpr bool _S_trivial_copy_ctor =
301  (is_trivially_copy_constructible_v<_Types> && ...);
302  static constexpr bool _S_trivial_move_ctor =
303  (is_trivially_move_constructible_v<_Types> && ...);
304  static constexpr bool _S_trivial_copy_assign =
305  _S_trivial_dtor && _S_trivial_copy_ctor
306  && (is_trivially_copy_assignable_v<_Types> && ...);
307  static constexpr bool _S_trivial_move_assign =
308  _S_trivial_dtor && _S_trivial_move_ctor
309  && (is_trivially_move_assignable_v<_Types> && ...);
310 
311  // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
312  // are always nothrow.
313  static constexpr bool _S_nothrow_default_ctor =
314  is_nothrow_default_constructible_v<
315  typename _Nth_type<0, _Types...>::type>;
316  static constexpr bool _S_nothrow_copy_ctor = false;
317  static constexpr bool _S_nothrow_move_ctor =
318  (is_nothrow_move_constructible_v<_Types> && ...);
319  static constexpr bool _S_nothrow_copy_assign = false;
320  static constexpr bool _S_nothrow_move_assign =
321  _S_nothrow_move_ctor
322  && (is_nothrow_move_assignable_v<_Types> && ...);
323  };
324 
325  // Defines members and ctors.
326  template<typename... _Types>
327  union _Variadic_union { };
328 
329  template<typename _First, typename... _Rest>
330  union _Variadic_union<_First, _Rest...>
331  {
332  constexpr _Variadic_union() : _M_rest() { }
333 
334  template<typename... _Args>
335  constexpr _Variadic_union(in_place_index_t<0>, _Args&&... __args)
336  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
337  { }
338 
339  template<size_t _Np, typename... _Args>
340  constexpr _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
341  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
342  { }
343 
344  _Uninitialized<_First> _M_first;
345  _Variadic_union<_Rest...> _M_rest;
346  };
347 
348  // _Never_valueless_alt is true for variant alternatives that can
349  // always be placed in a variant without it becoming valueless.
350 
351  // For suitably-small, trivially copyable types we can create temporaries
352  // on the stack and then memcpy them into place.
353  template<typename _Tp>
354  struct _Never_valueless_alt
355  : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
356  { };
357 
358  // Specialize _Never_valueless_alt for other types which have a
359  // non-throwing and cheap move construction and move assignment operator,
360  // so that emplacing the type will provide the strong exception-safety
361  // guarantee, by creating and moving a temporary.
362  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
363  // variant using that alternative, so we can't change the value later!
364 
365  // True if every alternative in _Types... can be emplaced in a variant
366  // without it becoming valueless. If this is true, variant<_Types...>
367  // can never be valueless, which enables some minor optimizations.
368  template <typename... _Types>
369  constexpr bool __never_valueless()
370  {
371  return _Traits<_Types...>::_S_move_assign
372  && (_Never_valueless_alt<_Types>::value && ...);
373  }
374 
375  // Defines index and the dtor, possibly trivial.
376  template<bool __trivially_destructible, typename... _Types>
377  struct _Variant_storage;
378 
379  template <typename... _Types>
380  using __select_index =
381  typename __select_int::_Select_int_base<sizeof...(_Types),
382  unsigned char,
383  unsigned short>::type::value_type;
384 
385  template<typename... _Types>
386  struct _Variant_storage<false, _Types...>
387  {
388  constexpr
389  _Variant_storage()
390  : _M_index(static_cast<__index_type>(variant_npos))
391  { }
392 
393  template<size_t _Np, typename... _Args>
394  constexpr
395  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
396  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
397  _M_index{_Np}
398  { }
399 
400  void _M_reset()
401  {
402  if (!_M_valid()) [[unlikely]]
403  return;
404 
405  std::__do_visit<void>([](auto&& __this_mem) mutable
406  {
407  std::_Destroy(std::__addressof(__this_mem));
408  }, __variant_cast<_Types...>(*this));
409 
410  _M_index = static_cast<__index_type>(variant_npos);
411  }
412 
413  ~_Variant_storage()
414  { _M_reset(); }
415 
416  void*
417  _M_storage() const noexcept
418  {
419  return const_cast<void*>(static_cast<const void*>(
420  std::addressof(_M_u)));
421  }
422 
423  constexpr bool
424  _M_valid() const noexcept
425  {
426  if constexpr (__variant::__never_valueless<_Types...>())
427  return true;
428  return this->_M_index != __index_type(variant_npos);
429  }
430 
431  _Variadic_union<_Types...> _M_u;
432  using __index_type = __select_index<_Types...>;
433  __index_type _M_index;
434  };
435 
436  template<typename... _Types>
437  struct _Variant_storage<true, _Types...>
438  {
439  constexpr
440  _Variant_storage()
441  : _M_index(static_cast<__index_type>(variant_npos))
442  { }
443 
444  template<size_t _Np, typename... _Args>
445  constexpr
446  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
447  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
448  _M_index{_Np}
449  { }
450 
451  void _M_reset() noexcept
452  { _M_index = static_cast<__index_type>(variant_npos); }
453 
454  void*
455  _M_storage() const noexcept
456  {
457  return const_cast<void*>(static_cast<const void*>(
458  std::addressof(_M_u)));
459  }
460 
461  constexpr bool
462  _M_valid() const noexcept
463  {
464  if constexpr (__variant::__never_valueless<_Types...>())
465  return true;
466  return this->_M_index != static_cast<__index_type>(variant_npos);
467  }
468 
469  _Variadic_union<_Types...> _M_u;
470  using __index_type = __select_index<_Types...>;
471  __index_type _M_index;
472  };
473 
474  template<typename... _Types>
475  using _Variant_storage_alias =
476  _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
477 
478  template<typename _Tp, typename _Up>
479  void __variant_construct_single(_Tp&& __lhs, _Up&& __rhs_mem)
480  {
481  void* __storage = std::addressof(__lhs._M_u);
482  using _Type = remove_reference_t<decltype(__rhs_mem)>;
483  if constexpr (!is_same_v<_Type, __variant_cookie>)
484  ::new (__storage)
485  _Type(std::forward<decltype(__rhs_mem)>(__rhs_mem));
486  }
487 
488  template<typename... _Types, typename _Tp, typename _Up>
489  void __variant_construct(_Tp&& __lhs, _Up&& __rhs)
490  {
491  __lhs._M_index = __rhs._M_index;
492  __variant::__raw_visit([&__lhs](auto&& __rhs_mem) mutable
493  {
494  __variant_construct_single(std::forward<_Tp>(__lhs),
495  std::forward<decltype(__rhs_mem)>(__rhs_mem));
496  }, __variant_cast<_Types...>(std::forward<_Up>(__rhs)));
497  }
498 
499  // The following are (Copy|Move) (ctor|assign) layers for forwarding
500  // triviality and handling non-trivial SMF behaviors.
501 
502  template<bool, typename... _Types>
503  struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
504  {
505  using _Base = _Variant_storage_alias<_Types...>;
506  using _Base::_Base;
507 
508  _Copy_ctor_base(const _Copy_ctor_base& __rhs)
509  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
510  {
511  __variant_construct<_Types...>(*this, __rhs);
512  }
513 
514  _Copy_ctor_base(_Copy_ctor_base&&) = default;
515  _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
516  _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
517  };
518 
519  template<typename... _Types>
520  struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
521  {
522  using _Base = _Variant_storage_alias<_Types...>;
523  using _Base::_Base;
524  };
525 
526  template<typename... _Types>
527  using _Copy_ctor_alias =
528  _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
529 
530  template<bool, typename... _Types>
531  struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
532  {
533  using _Base = _Copy_ctor_alias<_Types...>;
534  using _Base::_Base;
535 
536  _Move_ctor_base(_Move_ctor_base&& __rhs)
537  noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
538  {
539  __variant_construct<_Types...>(*this, std::move(__rhs));
540  }
541 
542  template<typename _Up>
543  void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
544  {
545  this->_M_reset();
546  __variant_construct_single(*this, std::forward<_Up>(__rhs));
547  this->_M_index = __rhs_index;
548  }
549 
550  template<typename _Up>
551  void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
552  {
553  this->_M_reset();
554  __variant_construct_single(*this, __rhs);
555  this->_M_index = __rhs_index;
556  }
557 
558  _Move_ctor_base(const _Move_ctor_base&) = default;
559  _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
560  _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
561  };
562 
563  template<typename... _Types>
564  struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
565  {
566  using _Base = _Copy_ctor_alias<_Types...>;
567  using _Base::_Base;
568 
569  template<typename _Up>
570  void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
571  {
572  this->_M_reset();
573  __variant_construct_single(*this, std::forward<_Up>(__rhs));
574  this->_M_index = __rhs_index;
575  }
576 
577  template<typename _Up>
578  void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
579  {
580  this->_M_reset();
581  __variant_construct_single(*this, __rhs);
582  this->_M_index = __rhs_index;
583  }
584  };
585 
586  template<typename... _Types>
587  using _Move_ctor_alias =
588  _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
589 
590  template<bool, typename... _Types>
591  struct _Copy_assign_base : _Move_ctor_alias<_Types...>
592  {
593  using _Base = _Move_ctor_alias<_Types...>;
594  using _Base::_Base;
595 
596  _Copy_assign_base&
597  operator=(const _Copy_assign_base& __rhs)
598  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
599  {
600  __variant::__raw_idx_visit(
601  [this](auto&& __rhs_mem, auto __rhs_index) mutable
602  {
603  if constexpr (__rhs_index != variant_npos)
604  {
605  if (this->_M_index == __rhs_index)
606  __variant::__get<__rhs_index>(*this) = __rhs_mem;
607  else
608  {
609  using __rhs_type = __remove_cvref_t<decltype(__rhs_mem)>;
610  if constexpr (is_nothrow_copy_constructible_v<__rhs_type>
611  || !is_nothrow_move_constructible_v<__rhs_type>)
612  // The standard says this->emplace<__rhs_type>(__rhs_mem)
613  // should be used here, but _M_destructive_copy is
614  // equivalent in this case. Either copy construction
615  // doesn't throw, so _M_destructive_copy gives strong
616  // exception safety guarantee, or both copy construction
617  // and move construction can throw, so emplace only gives
618  // basic exception safety anyway.
619  this->_M_destructive_copy(__rhs_index, __rhs_mem);
620  else
621  __variant_cast<_Types...>(*this)
622  = variant<_Types...>(std::in_place_index<__rhs_index>,
623  __rhs_mem);
624  }
625  }
626  else
627  this->_M_reset();
628  }, __variant_cast<_Types...>(__rhs));
629  return *this;
630  }
631 
632  _Copy_assign_base(const _Copy_assign_base&) = default;
633  _Copy_assign_base(_Copy_assign_base&&) = default;
634  _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
635  };
636 
637  template<typename... _Types>
638  struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
639  {
640  using _Base = _Move_ctor_alias<_Types...>;
641  using _Base::_Base;
642  };
643 
644  template<typename... _Types>
645  using _Copy_assign_alias =
646  _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
647 
648  template<bool, typename... _Types>
649  struct _Move_assign_base : _Copy_assign_alias<_Types...>
650  {
651  using _Base = _Copy_assign_alias<_Types...>;
652  using _Base::_Base;
653 
654  _Move_assign_base&
655  operator=(_Move_assign_base&& __rhs)
656  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
657  {
658  __variant::__raw_idx_visit(
659  [this](auto&& __rhs_mem, auto __rhs_index) mutable
660  {
661  if constexpr (__rhs_index != variant_npos)
662  {
663  if (this->_M_index == __rhs_index)
664  __variant::__get<__rhs_index>(*this) = std::move(__rhs_mem);
665  else
666  __variant_cast<_Types...>(*this)
667  .template emplace<__rhs_index>(std::move(__rhs_mem));
668  }
669  else
670  this->_M_reset();
671  }, __variant_cast<_Types...>(__rhs));
672  return *this;
673  }
674 
675  _Move_assign_base(const _Move_assign_base&) = default;
676  _Move_assign_base(_Move_assign_base&&) = default;
677  _Move_assign_base& operator=(const _Move_assign_base&) = default;
678  };
679 
680  template<typename... _Types>
681  struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
682  {
683  using _Base = _Copy_assign_alias<_Types...>;
684  using _Base::_Base;
685  };
686 
687  template<typename... _Types>
688  using _Move_assign_alias =
689  _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
690 
691  template<typename... _Types>
692  struct _Variant_base : _Move_assign_alias<_Types...>
693  {
694  using _Base = _Move_assign_alias<_Types...>;
695 
696  constexpr
697  _Variant_base()
698  noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
699  : _Variant_base(in_place_index<0>) { }
700 
701  template<size_t _Np, typename... _Args>
702  constexpr explicit
703  _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
704  : _Base(__i, std::forward<_Args>(__args)...)
705  { }
706 
707  _Variant_base(const _Variant_base&) = default;
708  _Variant_base(_Variant_base&&) = default;
709  _Variant_base& operator=(const _Variant_base&) = default;
710  _Variant_base& operator=(_Variant_base&&) = default;
711  };
712 
713  // For how many times does _Tp appear in _Tuple?
714  template<typename _Tp, typename _Tuple>
715  struct __tuple_count;
716 
717  template<typename _Tp, typename _Tuple>
718  inline constexpr size_t __tuple_count_v =
719  __tuple_count<_Tp, _Tuple>::value;
720 
721  template<typename _Tp, typename... _Types>
722  struct __tuple_count<_Tp, tuple<_Types...>>
723  : integral_constant<size_t, 0> { };
724 
725  template<typename _Tp, typename _First, typename... _Rest>
726  struct __tuple_count<_Tp, tuple<_First, _Rest...>>
727  : integral_constant<
728  size_t,
729  __tuple_count_v<_Tp, tuple<_Rest...>> + is_same_v<_Tp, _First>> { };
730 
731  // TODO: Reuse this in <tuple> ?
732  template<typename _Tp, typename... _Types>
733  inline constexpr bool __exactly_once =
734  __tuple_count_v<_Tp, tuple<_Types...>> == 1;
735 
736  // Helper used to check for valid conversions that don't involve narrowing.
737  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
738 
739  // "Build an imaginary function FUN(Ti) for each alternative type Ti"
740  template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
741  struct _Build_FUN
742  {
743  // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
744  // but only static functions will be considered in the call below.
745  void _S_fun();
746  };
747 
748  // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
749  template<size_t _Ind, typename _Tp, typename _Ti>
750  struct _Build_FUN<_Ind, _Tp, _Ti,
751  void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
752  {
753  // This is the FUN function for type _Ti, with index _Ind
754  static integral_constant<size_t, _Ind> _S_fun(_Ti);
755  };
756 
757  template<typename _Tp, typename _Variant,
758  typename = make_index_sequence<variant_size_v<_Variant>>>
759  struct _Build_FUNs;
760 
761  template<typename _Tp, typename... _Ti, size_t... _Ind>
762  struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
763  : _Build_FUN<_Ind, _Tp, _Ti>...
764  {
765  using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
766  };
767 
768  // The index j of the overload FUN(Tj) selected by overload resolution
769  // for FUN(std::forward<_Tp>(t))
770  template<typename _Tp, typename _Variant>
771  using _FUN_type
772  = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
773 
774  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
775  template<typename _Tp, typename _Variant, typename = void>
776  struct __accepted_index
777  : integral_constant<size_t, variant_npos>
778  { };
779 
780  template<typename _Tp, typename _Variant>
781  struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
782  : _FUN_type<_Tp, _Variant>
783  { };
784 
785  // Returns the raw storage for __v.
786  template<typename _Variant>
787  void* __get_storage(_Variant&& __v) noexcept
788  { return __v._M_storage(); }
789 
790  template <typename _Maybe_variant_cookie, typename _Variant>
791  struct _Extra_visit_slot_needed
792  {
793  template <typename> struct _Variant_never_valueless;
794 
795  template <typename... _Types>
796  struct _Variant_never_valueless<variant<_Types...>>
797  : bool_constant<__variant::__never_valueless<_Types...>()> {};
798 
799  static constexpr bool value =
800  (is_same_v<_Maybe_variant_cookie, __variant_cookie>
801  || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
802  && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
803  };
804 
805  // Used for storing a multi-dimensional vtable.
806  template<typename _Tp, size_t... _Dimensions>
807  struct _Multi_array;
808 
809  // Partial specialization with rank zero, stores a single _Tp element.
810  template<typename _Tp>
811  struct _Multi_array<_Tp>
812  {
813  template<typename>
814  struct __untag_result
815  : false_type
816  { using element_type = _Tp; };
817 
818  template <typename... _Args>
819  struct __untag_result<const void(*)(_Args...)>
820  : false_type
821  { using element_type = void(*)(_Args...); };
822 
823  template <typename... _Args>
824  struct __untag_result<__variant_cookie(*)(_Args...)>
825  : false_type
826  { using element_type = void(*)(_Args...); };
827 
828  template <typename... _Args>
829  struct __untag_result<__variant_idx_cookie(*)(_Args...)>
830  : false_type
831  { using element_type = void(*)(_Args...); };
832 
833  template <typename _Res, typename... _Args>
834  struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
835  : true_type
836  { using element_type = _Res(*)(_Args...); };
837 
838  using __result_is_deduced = __untag_result<_Tp>;
839 
840  constexpr const typename __untag_result<_Tp>::element_type&
841  _M_access() const
842  { return _M_data; }
843 
844  typename __untag_result<_Tp>::element_type _M_data;
845  };
846 
847  // Partial specialization with rank >= 1.
848  template<typename _Ret,
849  typename _Visitor,
850  typename... _Variants,
851  size_t __first, size_t... __rest>
852  struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
853  {
854  static constexpr size_t __index =
855  sizeof...(_Variants) - sizeof...(__rest) - 1;
856 
857  using _Variant = typename _Nth_type<__index, _Variants...>::type;
858 
859  static constexpr int __do_cookie =
860  _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
861 
862  using _Tp = _Ret(*)(_Visitor, _Variants...);
863 
864  template<typename... _Args>
865  constexpr decltype(auto)
866  _M_access(size_t __first_index, _Args... __rest_indices) const
867  {
868  return _M_arr[__first_index + __do_cookie]
869  ._M_access(__rest_indices...);
870  }
871 
872  _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
873  };
874 
875  // Creates a multi-dimensional vtable recursively.
876  //
877  // For example,
878  // visit([](auto, auto){},
879  // variant<int, char>(), // typedef'ed as V1
880  // variant<float, double, long double>()) // typedef'ed as V2
881  // will trigger instantiations of:
882  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
883  // tuple<V1&&, V2&&>, std::index_sequence<>>
884  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
885  // tuple<V1&&, V2&&>, std::index_sequence<0>>
886  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
887  // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
888  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
889  // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
890  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
891  // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
892  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
893  // tuple<V1&&, V2&&>, std::index_sequence<1>>
894  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
895  // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
896  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
897  // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
898  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
899  // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
900  // The returned multi-dimensional vtable can be fast accessed by the visitor
901  // using index calculation.
902  template<typename _Array_type, typename _Index_seq>
903  struct __gen_vtable_impl;
904 
905  // Defines the _S_apply() member that returns a _Multi_array populated
906  // with function pointers that perform the visitation expressions e(m)
907  // for each valid pack of indexes into the variant types _Variants.
908  //
909  // This partial specialization builds up the index sequences by recursively
910  // calling _S_apply() on the next specialization of __gen_vtable_impl.
911  // The base case of the recursion defines the actual function pointers.
912  template<typename _Result_type, typename _Visitor, size_t... __dimensions,
913  typename... _Variants, size_t... __indices>
914  struct __gen_vtable_impl<
915  _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
916  std::index_sequence<__indices...>>
917  {
918  using _Next =
919  remove_reference_t<typename _Nth_type<sizeof...(__indices),
920  _Variants...>::type>;
921  using _Array_type =
922  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
923  __dimensions...>;
924 
925  static constexpr _Array_type
926  _S_apply()
927  {
928  _Array_type __vtable{};
929  _S_apply_all_alts(
930  __vtable, make_index_sequence<variant_size_v<_Next>>());
931  return __vtable;
932  }
933 
934  template<size_t... __var_indices>
935  static constexpr void
936  _S_apply_all_alts(_Array_type& __vtable,
938  {
939  if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
940  (_S_apply_single_alt<true, __var_indices>(
941  __vtable._M_arr[__var_indices + 1],
942  &(__vtable._M_arr[0])), ...);
943  else
944  (_S_apply_single_alt<false, __var_indices>(
945  __vtable._M_arr[__var_indices]), ...);
946  }
947 
948  template<bool __do_cookie, size_t __index, typename _Tp>
949  static constexpr void
950  _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
951  {
952  if constexpr (__do_cookie)
953  {
954  __element = __gen_vtable_impl<
955  _Tp,
956  std::index_sequence<__indices..., __index>>::_S_apply();
957  *__cookie_element = __gen_vtable_impl<
958  _Tp,
959  std::index_sequence<__indices..., variant_npos>>::_S_apply();
960  }
961  else
962  {
963  auto __tmp_element = __gen_vtable_impl<
964  remove_reference_t<decltype(__element)>,
965  std::index_sequence<__indices..., __index>>::_S_apply();
966  static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
967  "std::visit requires the visitor to have the same "
968  "return type for all alternatives of a variant");
969  __element = __tmp_element;
970  }
971  }
972  };
973 
974  // This partial specialization is the base case for the recursion.
975  // It populates a _Multi_array element with the address of a function
976  // that invokes the visitor with the alternatives specified by __indices.
977  template<typename _Result_type, typename _Visitor, typename... _Variants,
978  size_t... __indices>
979  struct __gen_vtable_impl<
980  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
981  std::index_sequence<__indices...>>
982  {
983  using _Array_type =
984  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
985 
986  template<size_t __index, typename _Variant>
987  static constexpr decltype(auto)
988  __element_by_index_or_cookie(_Variant&& __var) noexcept
989  {
990  if constexpr (__index != variant_npos)
991  return __variant::__get<__index>(std::forward<_Variant>(__var));
992  else
993  return __variant_cookie{};
994  }
995 
996  static constexpr decltype(auto)
997  __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
998  {
999  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1000  // For raw visitation using indices, pass the indices to the visitor
1001  // and discard the return value:
1002  std::__invoke(std::forward<_Visitor>(__visitor),
1003  __element_by_index_or_cookie<__indices>(
1004  std::forward<_Variants>(__vars))...,
1005  integral_constant<size_t, __indices>()...);
1006  else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1007  // For raw visitation without indices, and discard the return value:
1008  std::__invoke(std::forward<_Visitor>(__visitor),
1009  __element_by_index_or_cookie<__indices>(
1010  std::forward<_Variants>(__vars))...);
1011  else if constexpr (_Array_type::__result_is_deduced::value)
1012  // For the usual std::visit case deduce the return value:
1013  return std::__invoke(std::forward<_Visitor>(__visitor),
1014  __element_by_index_or_cookie<__indices>(
1015  std::forward<_Variants>(__vars))...);
1016  else // for std::visit<R> use INVOKE<R>
1017  return std::__invoke_r<_Result_type>(
1018  std::forward<_Visitor>(__visitor),
1019  __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1020  }
1021 
1022  static constexpr auto
1023  _S_apply()
1024  {
1025  if constexpr (_Array_type::__result_is_deduced::value)
1026  {
1027  constexpr bool __visit_ret_type_mismatch =
1028  !is_same_v<typename _Result_type::type,
1029  decltype(__visit_invoke(std::declval<_Visitor>(),
1030  std::declval<_Variants>()...))>;
1031  if constexpr (__visit_ret_type_mismatch)
1032  {
1033  struct __cannot_match {};
1034  return __cannot_match{};
1035  }
1036  else
1037  return _Array_type{&__visit_invoke};
1038  }
1039  else
1040  return _Array_type{&__visit_invoke};
1041  }
1042  };
1043 
1044  template<typename _Result_type, typename _Visitor, typename... _Variants>
1045  struct __gen_vtable
1046  {
1047  using _Array_type =
1048  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1049  variant_size_v<remove_reference_t<_Variants>>...>;
1050 
1051  static constexpr _Array_type _S_vtable
1052  = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1053  };
1054 
1055  template<size_t _Np, typename _Tp>
1056  struct _Base_dedup : public _Tp { };
1057 
1058  template<typename _Variant, typename __indices>
1059  struct _Variant_hash_base;
1060 
1061  template<typename... _Types, size_t... __indices>
1062  struct _Variant_hash_base<variant<_Types...>,
1063  std::index_sequence<__indices...>>
1064  : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1065 
1066  template<size_t _Np, typename _Variant>
1067  using __get_t = decltype(std::get<_Np>(std::declval<_Variant>()));
1068 
1069  // Return type of std::visit.
1070  template<typename _Visitor, typename... _Variants>
1071  using __visit_result_t
1072  = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1073 
1074  template<typename _Tp, typename... _Types>
1075  constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
1076 
1077  template <typename _Visitor, typename _Variant, size_t... _Idxs>
1078  constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
1079  {
1080  return __same_types<
1081  invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
1082  >;
1083  }
1084 
1085 } // namespace __variant
1086 } // namespace __detail
1087 
1088  template<size_t _Np, typename _Variant, typename... _Args>
1089  void __variant_construct_by_index(_Variant& __v, _Args&&... __args)
1090  {
1091  __v._M_index = _Np;
1092  auto&& __storage = __detail::__variant::__get<_Np>(__v);
1093  ::new ((void*)std::addressof(__storage))
1094  remove_reference_t<decltype(__storage)>
1095  (std::forward<_Args>(__args)...);
1096  }
1097 
1098  template<typename _Tp, typename... _Types>
1099  constexpr bool
1100  holds_alternative(const variant<_Types...>& __v) noexcept
1101  {
1102  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1103  "T must occur exactly once in alternatives");
1104  return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
1105  }
1106 
1107  template<typename _Tp, typename... _Types>
1108  constexpr _Tp& get(variant<_Types...>& __v)
1109  {
1110  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1111  "T must occur exactly once in alternatives");
1112  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1113  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1114  }
1115 
1116  template<typename _Tp, typename... _Types>
1117  constexpr _Tp&& get(variant<_Types...>&& __v)
1118  {
1119  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1120  "T must occur exactly once in alternatives");
1121  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1122  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1123  std::move(__v));
1124  }
1125 
1126  template<typename _Tp, typename... _Types>
1127  constexpr const _Tp& get(const variant<_Types...>& __v)
1128  {
1129  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1130  "T must occur exactly once in alternatives");
1131  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1132  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1133  }
1134 
1135  template<typename _Tp, typename... _Types>
1136  constexpr const _Tp&& get(const variant<_Types...>&& __v)
1137  {
1138  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1139  "T must occur exactly once in alternatives");
1140  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1141  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1142  std::move(__v));
1143  }
1144 
1145  template<size_t _Np, typename... _Types>
1146  constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1147  get_if(variant<_Types...>* __ptr) noexcept
1148  {
1149  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1150  static_assert(_Np < sizeof...(_Types),
1151  "The index must be in [0, number of alternatives)");
1152  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1153  if (__ptr && __ptr->index() == _Np)
1154  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1155  return nullptr;
1156  }
1157 
1158  template<size_t _Np, typename... _Types>
1159  constexpr
1160  add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1161  get_if(const variant<_Types...>* __ptr) noexcept
1162  {
1163  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1164  static_assert(_Np < sizeof...(_Types),
1165  "The index must be in [0, number of alternatives)");
1166  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1167  if (__ptr && __ptr->index() == _Np)
1168  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1169  return nullptr;
1170  }
1171 
1172  template<typename _Tp, typename... _Types>
1173  constexpr add_pointer_t<_Tp>
1174  get_if(variant<_Types...>* __ptr) noexcept
1175  {
1176  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1177  "T must occur exactly once in alternatives");
1178  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1179  return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1180  __ptr);
1181  }
1182 
1183  template<typename _Tp, typename... _Types>
1184  constexpr add_pointer_t<const _Tp>
1185  get_if(const variant<_Types...>* __ptr) noexcept
1186  {
1187  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1188  "T must occur exactly once in alternatives");
1189  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1190  return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1191  __ptr);
1192  }
1193 
1194  struct monostate { };
1195 
1196 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1197  template<typename... _Types> \
1198  constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1199  const variant<_Types...>& __rhs) \
1200  { \
1201  bool __ret = true; \
1202  __detail::__variant::__raw_idx_visit( \
1203  [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1204  { \
1205  if constexpr (__rhs_index != variant_npos) \
1206  { \
1207  if (__lhs.index() == __rhs_index) \
1208  { \
1209  auto& __this_mem = std::get<__rhs_index>(__lhs); \
1210  __ret = __this_mem __OP __rhs_mem; \
1211  } \
1212  else \
1213  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1214  } \
1215  else \
1216  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1217  }, __rhs); \
1218  return __ret; \
1219  }
1220 
1221  _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1222  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1223  _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1224  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1225  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1226  _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1227 
1228 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1229 
1230  constexpr bool operator==(monostate, monostate) noexcept { return true; }
1231 
1232 #ifdef __cpp_lib_three_way_comparison
1233  template<typename... _Types>
1234  requires (three_way_comparable<_Types> && ...)
1235  constexpr
1236  common_comparison_category_t<compare_three_way_result_t<_Types>...>
1237  operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1238  {
1239  common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1240  = strong_ordering::equal;
1241 
1242  __detail::__variant::__raw_idx_visit(
1243  [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1244  {
1245  if constexpr (__w_index != variant_npos)
1246  {
1247  if (__v.index() == __w_index)
1248  {
1249  auto& __this_mem = std::get<__w_index>(__v);
1250  __ret = __this_mem <=> __w_mem;
1251  return;
1252  }
1253  }
1254  __ret = (__v.index() + 1) <=> (__w_index + 1);
1255  }, __w);
1256  return __ret;
1257  }
1258 
1259  constexpr strong_ordering
1260  operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1261 #else
1262  constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1263  constexpr bool operator<(monostate, monostate) noexcept { return false; }
1264  constexpr bool operator>(monostate, monostate) noexcept { return false; }
1265  constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1266  constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1267 #endif
1268 
1269  template<typename _Visitor, typename... _Variants>
1270  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1271  visit(_Visitor&&, _Variants&&...);
1272 
1273  template<typename... _Types>
1274  inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1275  && (is_swappable_v<_Types> && ...)>
1276  swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1277  noexcept(noexcept(__lhs.swap(__rhs)))
1278  { __lhs.swap(__rhs); }
1279 
1280  template<typename... _Types>
1281  enable_if_t<!((is_move_constructible_v<_Types> && ...)
1282  && (is_swappable_v<_Types> && ...))>
1283  swap(variant<_Types...>&, variant<_Types...>&) = delete;
1284 
1285  class bad_variant_access : public exception
1286  {
1287  public:
1288  bad_variant_access() noexcept { }
1289 
1290  const char* what() const noexcept override
1291  { return _M_reason; }
1292 
1293  private:
1294  bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1295 
1296  // Must point to a string with static storage duration:
1297  const char* _M_reason = "bad variant access";
1298 
1299  friend void __throw_bad_variant_access(const char* __what);
1300  };
1301 
1302  // Must only be called with a string literal
1303  inline void
1304  __throw_bad_variant_access(const char* __what)
1305  { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1306 
1307  inline void
1308  __throw_bad_variant_access(bool __valueless)
1309  {
1310  if (__valueless) [[__unlikely__]]
1311  __throw_bad_variant_access("std::get: variant is valueless");
1312  else
1313  __throw_bad_variant_access("std::get: wrong index for variant");
1314  }
1315 
1316  template<typename... _Types>
1317  class variant
1318  : private __detail::__variant::_Variant_base<_Types...>,
1319  private _Enable_default_constructor<
1320  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1321  variant<_Types...>>,
1322  private _Enable_copy_move<
1323  __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1324  __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1325  __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1326  __detail::__variant::_Traits<_Types...>::_S_move_assign,
1327  variant<_Types...>>
1328  {
1329  private:
1330  template <typename... _UTypes, typename _Tp>
1331  friend decltype(auto) __variant_cast(_Tp&&);
1332  template<size_t _Np, typename _Variant, typename... _Args>
1333  friend void __variant_construct_by_index(_Variant& __v,
1334  _Args&&... __args);
1335 
1336  static_assert(sizeof...(_Types) > 0,
1337  "variant must have at least one alternative");
1338  static_assert(!(std::is_reference_v<_Types> || ...),
1339  "variant must have no reference alternative");
1340  static_assert(!(std::is_void_v<_Types> || ...),
1341  "variant must have no void alternative");
1342 
1343  using _Base = __detail::__variant::_Variant_base<_Types...>;
1344  using _Default_ctor_enabler =
1345  _Enable_default_constructor<
1346  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1347  variant<_Types...>>;
1348 
1349  template<typename _Tp>
1350  static constexpr bool __not_self
1351  = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1352 
1353  template<typename _Tp>
1354  static constexpr bool
1355  __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1356 
1357  template<typename _Tp>
1358  static constexpr size_t __accepted_index
1359  = __detail::__variant::__accepted_index<_Tp, variant>::value;
1360 
1361  template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1362  using __to_type = variant_alternative_t<_Np, variant>;
1363 
1364  template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1365  using __accepted_type = __to_type<__accepted_index<_Tp>>;
1366 
1367  template<typename _Tp>
1368  static constexpr size_t __index_of =
1369  __detail::__variant::__index_of_v<_Tp, _Types...>;
1370 
1371  using _Traits = __detail::__variant::_Traits<_Types...>;
1372 
1373  template<typename _Tp>
1374  struct __is_in_place_tag : false_type { };
1375  template<typename _Tp>
1376  struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1377  template<size_t _Np>
1378  struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1379 
1380  template<typename _Tp>
1381  static constexpr bool __not_in_place_tag
1382  = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1383 
1384  public:
1385  variant() = default;
1386  variant(const variant& __rhs) = default;
1387  variant(variant&&) = default;
1388  variant& operator=(const variant&) = default;
1389  variant& operator=(variant&&) = default;
1390  ~variant() = default;
1391 
1392  template<typename _Tp,
1393  typename = enable_if_t<sizeof...(_Types) != 0>,
1394  typename = enable_if_t<__not_in_place_tag<_Tp>>,
1395  typename _Tj = __accepted_type<_Tp&&>,
1396  typename = enable_if_t<__exactly_once<_Tj>
1397  && is_constructible_v<_Tj, _Tp>>>
1398  constexpr
1399  variant(_Tp&& __t)
1400  noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1401  : variant(in_place_index<__accepted_index<_Tp>>,
1402  std::forward<_Tp>(__t))
1403  { }
1404 
1405  template<typename _Tp, typename... _Args,
1406  typename = enable_if_t<__exactly_once<_Tp>
1407  && is_constructible_v<_Tp, _Args...>>>
1408  constexpr explicit
1409  variant(in_place_type_t<_Tp>, _Args&&... __args)
1410  : variant(in_place_index<__index_of<_Tp>>,
1411  std::forward<_Args>(__args)...)
1412  { }
1413 
1414  template<typename _Tp, typename _Up, typename... _Args,
1415  typename = enable_if_t<__exactly_once<_Tp>
1416  && is_constructible_v<_Tp,
1417  initializer_list<_Up>&, _Args...>>>
1418  constexpr explicit
1419  variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1420  _Args&&... __args)
1421  : variant(in_place_index<__index_of<_Tp>>, __il,
1422  std::forward<_Args>(__args)...)
1423  { }
1424 
1425  template<size_t _Np, typename... _Args,
1426  typename _Tp = __to_type<_Np>,
1427  typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1428  constexpr explicit
1429  variant(in_place_index_t<_Np>, _Args&&... __args)
1430  : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1431  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1432  { }
1433 
1434  template<size_t _Np, typename _Up, typename... _Args,
1435  typename _Tp = __to_type<_Np>,
1436  typename = enable_if_t<is_constructible_v<_Tp,
1437  initializer_list<_Up>&,
1438  _Args...>>>
1439  constexpr explicit
1440  variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1441  _Args&&... __args)
1442  : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1443  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1444  { }
1445 
1446  template<typename _Tp>
1447  enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1448  && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1449  && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1450  variant&>
1451  operator=(_Tp&& __rhs)
1452  noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1453  && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1454  {
1455  constexpr auto __index = __accepted_index<_Tp>;
1456  if (index() == __index)
1457  std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1458  else
1459  {
1460  using _Tj = __accepted_type<_Tp&&>;
1461  if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1462  || !is_nothrow_move_constructible_v<_Tj>)
1463  this->emplace<__index>(std::forward<_Tp>(__rhs));
1464  else
1465  operator=(variant(std::forward<_Tp>(__rhs)));
1466  }
1467  return *this;
1468  }
1469 
1470  template<typename _Tp, typename... _Args>
1471  enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1472  _Tp&>
1473  emplace(_Args&&... __args)
1474  {
1475  constexpr size_t __index = __index_of<_Tp>;
1476  return this->emplace<__index>(std::forward<_Args>(__args)...);
1477  }
1478 
1479  template<typename _Tp, typename _Up, typename... _Args>
1480  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1481  && __exactly_once<_Tp>,
1482  _Tp&>
1483  emplace(initializer_list<_Up> __il, _Args&&... __args)
1484  {
1485  constexpr size_t __index = __index_of<_Tp>;
1486  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1487  }
1488 
1489  template<size_t _Np, typename... _Args>
1490  enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1491  _Args...>,
1492  variant_alternative_t<_Np, variant>&>
1493  emplace(_Args&&... __args)
1494  {
1495  static_assert(_Np < sizeof...(_Types),
1496  "The index must be in [0, number of alternatives)");
1497  using type = variant_alternative_t<_Np, variant>;
1498  // Provide the strong exception-safety guarantee when possible,
1499  // to avoid becoming valueless.
1500  if constexpr (is_nothrow_constructible_v<type, _Args...>)
1501  {
1502  this->_M_reset();
1503  __variant_construct_by_index<_Np>(*this,
1504  std::forward<_Args>(__args)...);
1505  }
1506  else if constexpr (is_scalar_v<type>)
1507  {
1508  // This might invoke a potentially-throwing conversion operator:
1509  const type __tmp(std::forward<_Args>(__args)...);
1510  // But these steps won't throw:
1511  this->_M_reset();
1512  __variant_construct_by_index<_Np>(*this, __tmp);
1513  }
1514  else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1515  && _Traits::_S_move_assign)
1516  {
1517  // This construction might throw:
1518  variant __tmp(in_place_index<_Np>,
1519  std::forward<_Args>(__args)...);
1520  // But _Never_valueless_alt<type> means this won't:
1521  *this = std::move(__tmp);
1522  }
1523  else
1524  {
1525  // This case only provides the basic exception-safety guarantee,
1526  // i.e. the variant can become valueless.
1527  this->_M_reset();
1528  __try
1529  {
1530  __variant_construct_by_index<_Np>(*this,
1531  std::forward<_Args>(__args)...);
1532  }
1533  __catch (...)
1534  {
1535  using __index_type = decltype(this->_M_index);
1536  this->_M_index = static_cast<__index_type>(variant_npos);
1537  __throw_exception_again;
1538  }
1539  }
1540  return std::get<_Np>(*this);
1541  }
1542 
1543  template<size_t _Np, typename _Up, typename... _Args>
1544  enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1545  initializer_list<_Up>&, _Args...>,
1546  variant_alternative_t<_Np, variant>&>
1547  emplace(initializer_list<_Up> __il, _Args&&... __args)
1548  {
1549  static_assert(_Np < sizeof...(_Types),
1550  "The index must be in [0, number of alternatives)");
1551  using type = variant_alternative_t<_Np, variant>;
1552  // Provide the strong exception-safety guarantee when possible,
1553  // to avoid becoming valueless.
1554  if constexpr (is_nothrow_constructible_v<type,
1555  initializer_list<_Up>&,
1556  _Args...>)
1557  {
1558  this->_M_reset();
1559  __variant_construct_by_index<_Np>(*this, __il,
1560  std::forward<_Args>(__args)...);
1561  }
1562  else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1563  && _Traits::_S_move_assign)
1564  {
1565  // This construction might throw:
1566  variant __tmp(in_place_index<_Np>, __il,
1567  std::forward<_Args>(__args)...);
1568  // But _Never_valueless_alt<type> means this won't:
1569  *this = std::move(__tmp);
1570  }
1571  else
1572  {
1573  // This case only provides the basic exception-safety guarantee,
1574  // i.e. the variant can become valueless.
1575  this->_M_reset();
1576  __try
1577  {
1578  __variant_construct_by_index<_Np>(*this, __il,
1579  std::forward<_Args>(__args)...);
1580  }
1581  __catch (...)
1582  {
1583  using __index_type = decltype(this->_M_index);
1584  this->_M_index = static_cast<__index_type>(variant_npos);
1585  __throw_exception_again;
1586  }
1587  }
1588  return std::get<_Np>(*this);
1589  }
1590 
1591  constexpr bool valueless_by_exception() const noexcept
1592  { return !this->_M_valid(); }
1593 
1594  constexpr size_t index() const noexcept
1595  {
1596  using __index_type = typename _Base::__index_type;
1597  if constexpr (__detail::__variant::__never_valueless<_Types...>())
1598  return this->_M_index;
1599  else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1600  return make_signed_t<__index_type>(this->_M_index);
1601  else
1602  return size_t(__index_type(this->_M_index + 1)) - 1;
1603  }
1604 
1605  void
1606  swap(variant& __rhs)
1607  noexcept((__is_nothrow_swappable<_Types>::value && ...)
1608  && is_nothrow_move_constructible_v<variant>)
1609  {
1610  __detail::__variant::__raw_idx_visit(
1611  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1612  {
1613  if constexpr (__rhs_index != variant_npos)
1614  {
1615  if (this->index() == __rhs_index)
1616  {
1617  auto& __this_mem =
1618  std::get<__rhs_index>(*this);
1619  using std::swap;
1620  swap(__this_mem, __rhs_mem);
1621  }
1622  else
1623  {
1624  if (!this->valueless_by_exception()) [[__likely__]]
1625  {
1626  auto __tmp(std::move(__rhs_mem));
1627  __rhs = std::move(*this);
1628  this->_M_destructive_move(__rhs_index,
1629  std::move(__tmp));
1630  }
1631  else
1632  {
1633  this->_M_destructive_move(__rhs_index,
1634  std::move(__rhs_mem));
1635  __rhs._M_reset();
1636  }
1637  }
1638  }
1639  else
1640  {
1641  if (!this->valueless_by_exception()) [[__likely__]]
1642  {
1643  __rhs = std::move(*this);
1644  this->_M_reset();
1645  }
1646  }
1647  }, __rhs);
1648  }
1649 
1650  private:
1651 
1652 #if defined(__clang__) && __clang_major__ <= 7
1653  public:
1654  using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1655  private:
1656 #endif
1657 
1658  template<size_t _Np, typename _Vp>
1659  friend constexpr decltype(auto)
1660  __detail::__variant::__get(_Vp&& __v) noexcept;
1661 
1662  template<typename _Vp>
1663  friend void*
1664  __detail::__variant::__get_storage(_Vp&& __v) noexcept;
1665 
1666 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1667  template<typename... _Tp> \
1668  friend constexpr bool \
1669  operator __OP(const variant<_Tp...>& __lhs, \
1670  const variant<_Tp...>& __rhs);
1671 
1672  _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1673  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1674  _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1675  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1676  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1677  _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1678 
1679 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1680  };
1681 
1682  template<size_t _Np, typename... _Types>
1683  constexpr variant_alternative_t<_Np, variant<_Types...>>&
1684  get(variant<_Types...>& __v)
1685  {
1686  static_assert(_Np < sizeof...(_Types),
1687  "The index must be in [0, number of alternatives)");
1688  if (__v.index() != _Np)
1689  __throw_bad_variant_access(__v.valueless_by_exception());
1690  return __detail::__variant::__get<_Np>(__v);
1691  }
1692 
1693  template<size_t _Np, typename... _Types>
1694  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1695  get(variant<_Types...>&& __v)
1696  {
1697  static_assert(_Np < sizeof...(_Types),
1698  "The index must be in [0, number of alternatives)");
1699  if (__v.index() != _Np)
1700  __throw_bad_variant_access(__v.valueless_by_exception());
1701  return __detail::__variant::__get<_Np>(std::move(__v));
1702  }
1703 
1704  template<size_t _Np, typename... _Types>
1705  constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1706  get(const variant<_Types...>& __v)
1707  {
1708  static_assert(_Np < sizeof...(_Types),
1709  "The index must be in [0, number of alternatives)");
1710  if (__v.index() != _Np)
1711  __throw_bad_variant_access(__v.valueless_by_exception());
1712  return __detail::__variant::__get<_Np>(__v);
1713  }
1714 
1715  template<size_t _Np, typename... _Types>
1716  constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1717  get(const variant<_Types...>&& __v)
1718  {
1719  static_assert(_Np < sizeof...(_Types),
1720  "The index must be in [0, number of alternatives)");
1721  if (__v.index() != _Np)
1722  __throw_bad_variant_access(__v.valueless_by_exception());
1723  return __detail::__variant::__get<_Np>(std::move(__v));
1724  }
1725 
1726  /// @cond undocumented
1727  template<typename _Result_type, typename _Visitor, typename... _Variants>
1728  constexpr decltype(auto)
1729  __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1730  {
1731  constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1732  _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1733 
1734  auto __func_ptr = __vtable._M_access(__variants.index()...);
1735  return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1736  std::forward<_Variants>(__variants)...);
1737  }
1738  /// @endcond
1739 
1740  template<typename _Visitor, typename... _Variants>
1741  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1742  visit(_Visitor&& __visitor, _Variants&&... __variants)
1743  {
1744  if ((__variants.valueless_by_exception() || ...))
1745  __throw_bad_variant_access("std::visit: variant is valueless");
1746 
1747  using _Result_type
1748  = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1749 
1750  using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1751 
1752  if constexpr (sizeof...(_Variants) == 1)
1753  {
1754  constexpr bool __visit_rettypes_match = __detail::__variant::
1755  __check_visitor_results<_Visitor, _Variants...>(
1757  std::variant_size<remove_reference_t<_Variants>...>::value>());
1758  if constexpr (!__visit_rettypes_match)
1759  {
1760  static_assert(__visit_rettypes_match,
1761  "std::visit requires the visitor to have the same "
1762  "return type for all alternatives of a variant");
1763  return;
1764  }
1765  else
1766  return std::__do_visit<_Tag>(
1767  std::forward<_Visitor>(__visitor),
1768  std::forward<_Variants>(__variants)...);
1769  }
1770  else
1771  return std::__do_visit<_Tag>(
1772  std::forward<_Visitor>(__visitor),
1773  std::forward<_Variants>(__variants)...);
1774  }
1775 
1776 #if __cplusplus > 201703L
1777  template<typename _Res, typename _Visitor, typename... _Variants>
1778  constexpr _Res
1779  visit(_Visitor&& __visitor, _Variants&&... __variants)
1780  {
1781  if ((__variants.valueless_by_exception() || ...))
1782  __throw_bad_variant_access("std::visit<R>: variant is valueless");
1783 
1784  return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1785  std::forward<_Variants>(__variants)...);
1786  }
1787 #endif
1788 
1789  /// @cond undocumented
1790  template<bool, typename... _Types>
1791  struct __variant_hash_call_base_impl
1792  {
1793  size_t
1794  operator()(const variant<_Types...>& __t) const
1795  noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1796  {
1797  size_t __ret;
1798  __detail::__variant::__raw_visit(
1799  [&__t, &__ret](auto&& __t_mem) mutable
1800  {
1801  using _Type = __remove_cvref_t<decltype(__t_mem)>;
1802  if constexpr (!is_same_v<_Type,
1803  __detail::__variant::__variant_cookie>)
1804  __ret = std::hash<size_t>{}(__t.index())
1805  + std::hash<_Type>{}(__t_mem);
1806  else
1807  __ret = std::hash<size_t>{}(__t.index());
1808  }, __t);
1809  return __ret;
1810  }
1811  };
1812 
1813  template<typename... _Types>
1814  struct __variant_hash_call_base_impl<false, _Types...> {};
1815 
1816  template<typename... _Types>
1817  using __variant_hash_call_base =
1818  __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1819  __enable_hash_call &&...), _Types...>;
1820  /// @endcond
1821 
1822  template<typename... _Types>
1823  struct hash<variant<_Types...>>
1824  : private __detail::__variant::_Variant_hash_base<
1825  variant<_Types...>, std::index_sequence_for<_Types...>>,
1826  public __variant_hash_call_base<_Types...>
1827  {
1828  using result_type [[__deprecated__]] = size_t;
1829  using argument_type [[__deprecated__]] = variant<_Types...>;
1830  };
1831 
1832  template<>
1833  struct hash<monostate>
1834  {
1835  using result_type [[__deprecated__]] = size_t;
1836  using argument_type [[__deprecated__]] = monostate;
1837 
1838  size_t
1839  operator()(const monostate&) const noexcept
1840  {
1841  constexpr size_t __magic_monostate_hash = -7777;
1842  return __magic_monostate_hash;
1843  }
1844  };
1845 
1846  template<typename... _Types>
1847  struct __is_fast_hash<hash<variant<_Types...>>>
1848  : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1849  { };
1850 
1851 _GLIBCXX_END_NAMESPACE_VERSION
1852 } // namespace std
1853 
1854 #endif // C++17
1855 
1856 #endif // _GLIBCXX_VARIANT
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition: type_traits:1645
integral_constant< bool, __v > bool_constant
Alias template for compile-time boolean constant types.
Definition: type_traits:99
void void_t
A metafunction that always yields void, used for detecting valid types.
Definition: type_traits:2607
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:83
integral_constant< bool, false > false_type
The type used as a compile-time boolean with false value.
Definition: type_traits:86
typename add_pointer< _Tp >::type add_pointer_t
Alias template for add_pointer.
Definition: type_traits:2059
typename make_signed< _Tp >::type make_signed_t
Alias template for make_signed.
Definition: type_traits:1976
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition: type_traits:2585
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition: invoke.h:90
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:77
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:422
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:145
ISO C++ entities toplevel namespace is std.
make_integer_sequence< size_t, _Num > make_index_sequence
Alias template make_index_sequence.
Definition: utility:343
integer_sequence< size_t, _Idx... > index_sequence
Alias template index_sequence.
Definition: utility:339
Primary class template hash.
integral_constant
Definition: type_traits:66
Class template integer_sequence.
Definition: utility:323