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>
38 #include <bits/enable_special_members.h>
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>
45 #include <bits/stl_iterator_base_types.h>
46 #include <bits/stl_iterator_base_funcs.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 202102L
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  // The __as function templates implement the exposition-only "as-variant"
206 
207  template<typename... _Types>
208  constexpr std::variant<_Types...>&
209  __as(std::variant<_Types...>& __v) noexcept
210  { return __v; }
211 
212  template<typename... _Types>
213  constexpr const std::variant<_Types...>&
214  __as(const std::variant<_Types...>& __v) noexcept
215  { return __v; }
216 
217  template<typename... _Types>
218  constexpr std::variant<_Types...>&&
219  __as(std::variant<_Types...>&& __v) noexcept
220  { return std::move(__v); }
221 
222  template<typename... _Types>
223  constexpr const std::variant<_Types...>&&
224  __as(const std::variant<_Types...>&& __v) noexcept
225  { return std::move(__v); }
226 
227  // _Uninitialized<T> is guaranteed to be a trivially destructible type,
228  // even if T is not.
229  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
230  struct _Uninitialized;
231 
232  template<typename _Type>
233  struct _Uninitialized<_Type, true>
234  {
235  template<typename... _Args>
236  constexpr
237  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
238  : _M_storage(std::forward<_Args>(__args)...)
239  { }
240 
241  constexpr const _Type& _M_get() const & noexcept
242  { return _M_storage; }
243 
244  constexpr _Type& _M_get() & noexcept
245  { return _M_storage; }
246 
247  constexpr const _Type&& _M_get() const && noexcept
248  { return std::move(_M_storage); }
249 
250  constexpr _Type&& _M_get() && noexcept
251  { return std::move(_M_storage); }
252 
253  _Type _M_storage;
254  };
255 
256  template<typename _Type>
257  struct _Uninitialized<_Type, false>
258  {
259  template<typename... _Args>
260  constexpr
261  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
262  {
263  ::new ((void*)std::addressof(_M_storage))
264  _Type(std::forward<_Args>(__args)...);
265  }
266 
267  const _Type& _M_get() const & noexcept
268  { return *_M_storage._M_ptr(); }
269 
270  _Type& _M_get() & noexcept
271  { return *_M_storage._M_ptr(); }
272 
273  const _Type&& _M_get() const && noexcept
274  { return std::move(*_M_storage._M_ptr()); }
275 
276  _Type&& _M_get() && noexcept
277  { return std::move(*_M_storage._M_ptr()); }
278 
279  __gnu_cxx::__aligned_membuf<_Type> _M_storage;
280  };
281 
282  template<typename _Union>
283  constexpr decltype(auto)
284  __get(in_place_index_t<0>, _Union&& __u) noexcept
285  { return std::forward<_Union>(__u)._M_first._M_get(); }
286 
287  template<size_t _Np, typename _Union>
288  constexpr decltype(auto)
289  __get(in_place_index_t<_Np>, _Union&& __u) noexcept
290  {
291  return __variant::__get(in_place_index<_Np-1>,
292  std::forward<_Union>(__u)._M_rest);
293  }
294 
295  // Returns the typed storage for __v.
296  template<size_t _Np, typename _Variant>
297  constexpr decltype(auto)
298  __get(_Variant&& __v) noexcept
299  {
300  return __variant::__get(std::in_place_index<_Np>,
301  std::forward<_Variant>(__v)._M_u);
302  }
303 
304  template<typename... _Types>
305  struct _Traits
306  {
307  static constexpr bool _S_default_ctor =
308  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
309  static constexpr bool _S_copy_ctor =
310  (is_copy_constructible_v<_Types> && ...);
311  static constexpr bool _S_move_ctor =
312  (is_move_constructible_v<_Types> && ...);
313  static constexpr bool _S_copy_assign =
314  _S_copy_ctor
315  && (is_copy_assignable_v<_Types> && ...);
316  static constexpr bool _S_move_assign =
317  _S_move_ctor
318  && (is_move_assignable_v<_Types> && ...);
319 
320  static constexpr bool _S_trivial_dtor =
321  (is_trivially_destructible_v<_Types> && ...);
322  static constexpr bool _S_trivial_copy_ctor =
323  (is_trivially_copy_constructible_v<_Types> && ...);
324  static constexpr bool _S_trivial_move_ctor =
325  (is_trivially_move_constructible_v<_Types> && ...);
326  static constexpr bool _S_trivial_copy_assign =
327  _S_trivial_dtor && _S_trivial_copy_ctor
328  && (is_trivially_copy_assignable_v<_Types> && ...);
329  static constexpr bool _S_trivial_move_assign =
330  _S_trivial_dtor && _S_trivial_move_ctor
331  && (is_trivially_move_assignable_v<_Types> && ...);
332 
333  // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
334  // are always nothrow.
335  static constexpr bool _S_nothrow_default_ctor =
336  is_nothrow_default_constructible_v<
337  typename _Nth_type<0, _Types...>::type>;
338  static constexpr bool _S_nothrow_copy_ctor = false;
339  static constexpr bool _S_nothrow_move_ctor =
340  (is_nothrow_move_constructible_v<_Types> && ...);
341  static constexpr bool _S_nothrow_copy_assign = false;
342  static constexpr bool _S_nothrow_move_assign =
343  _S_nothrow_move_ctor
344  && (is_nothrow_move_assignable_v<_Types> && ...);
345  };
346 
347  // Defines members and ctors.
348  template<typename... _Types>
349  union _Variadic_union { };
350 
351  template<typename _First, typename... _Rest>
352  union _Variadic_union<_First, _Rest...>
353  {
354  constexpr _Variadic_union() : _M_rest() { }
355 
356  template<typename... _Args>
357  constexpr _Variadic_union(in_place_index_t<0>, _Args&&... __args)
358  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
359  { }
360 
361  template<size_t _Np, typename... _Args>
362  constexpr _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
363  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
364  { }
365 
366  _Uninitialized<_First> _M_first;
367  _Variadic_union<_Rest...> _M_rest;
368  };
369 
370  // _Never_valueless_alt is true for variant alternatives that can
371  // always be placed in a variant without it becoming valueless.
372 
373  // For suitably-small, trivially copyable types we can create temporaries
374  // on the stack and then memcpy them into place.
375  template<typename _Tp>
376  struct _Never_valueless_alt
377  : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
378  { };
379 
380  // Specialize _Never_valueless_alt for other types which have a
381  // non-throwing and cheap move construction and move assignment operator,
382  // so that emplacing the type will provide the strong exception-safety
383  // guarantee, by creating and moving a temporary.
384  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
385  // variant using that alternative, so we can't change the value later!
386 
387  // True if every alternative in _Types... can be emplaced in a variant
388  // without it becoming valueless. If this is true, variant<_Types...>
389  // can never be valueless, which enables some minor optimizations.
390  template <typename... _Types>
391  constexpr bool __never_valueless()
392  {
393  return _Traits<_Types...>::_S_move_assign
394  && (_Never_valueless_alt<_Types>::value && ...);
395  }
396 
397  // Defines index and the dtor, possibly trivial.
398  template<bool __trivially_destructible, typename... _Types>
399  struct _Variant_storage;
400 
401  template <typename... _Types>
402  using __select_index =
403  typename __select_int::_Select_int_base<sizeof...(_Types),
404  unsigned char,
405  unsigned short>::type::value_type;
406 
407  template<typename... _Types>
408  struct _Variant_storage<false, _Types...>
409  {
410  constexpr
411  _Variant_storage()
412  : _M_index(static_cast<__index_type>(variant_npos))
413  { }
414 
415  template<size_t _Np, typename... _Args>
416  constexpr
417  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
418  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
419  _M_index{_Np}
420  { }
421 
422  void _M_reset()
423  {
424  if (!_M_valid()) [[unlikely]]
425  return;
426 
427  std::__do_visit<void>([](auto&& __this_mem) mutable
428  {
429  std::_Destroy(std::__addressof(__this_mem));
430  }, __variant_cast<_Types...>(*this));
431 
432  _M_index = static_cast<__index_type>(variant_npos);
433  }
434 
435  ~_Variant_storage()
436  { _M_reset(); }
437 
438  constexpr bool
439  _M_valid() const noexcept
440  {
441  if constexpr (__variant::__never_valueless<_Types...>())
442  return true;
443  return this->_M_index != __index_type(variant_npos);
444  }
445 
446  _Variadic_union<_Types...> _M_u;
447  using __index_type = __select_index<_Types...>;
448  __index_type _M_index;
449  };
450 
451  template<typename... _Types>
452  struct _Variant_storage<true, _Types...>
453  {
454  constexpr
455  _Variant_storage()
456  : _M_index(static_cast<__index_type>(variant_npos))
457  { }
458 
459  template<size_t _Np, typename... _Args>
460  constexpr
461  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
462  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
463  _M_index{_Np}
464  { }
465 
466  void _M_reset() noexcept
467  { _M_index = static_cast<__index_type>(variant_npos); }
468 
469  constexpr bool
470  _M_valid() const noexcept
471  {
472  if constexpr (__variant::__never_valueless<_Types...>())
473  return true;
474  return this->_M_index != static_cast<__index_type>(variant_npos);
475  }
476 
477  _Variadic_union<_Types...> _M_u;
478  using __index_type = __select_index<_Types...>;
479  __index_type _M_index;
480  };
481 
482  template<typename... _Types>
483  using _Variant_storage_alias =
484  _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
485 
486  template<typename _Tp, typename _Up>
487  void __variant_construct_single(_Tp&& __lhs, _Up&& __rhs_mem)
488  {
489  void* __storage = std::addressof(__lhs._M_u);
490  using _Type = remove_reference_t<decltype(__rhs_mem)>;
491  if constexpr (!is_same_v<_Type, __variant_cookie>)
492  ::new (__storage)
493  _Type(std::forward<decltype(__rhs_mem)>(__rhs_mem));
494  }
495 
496  template<typename... _Types, typename _Tp, typename _Up>
497  void __variant_construct(_Tp&& __lhs, _Up&& __rhs)
498  {
499  __lhs._M_index = __rhs._M_index;
500  __variant::__raw_visit([&__lhs](auto&& __rhs_mem) mutable
501  {
502  __variant_construct_single(std::forward<_Tp>(__lhs),
503  std::forward<decltype(__rhs_mem)>(__rhs_mem));
504  }, __variant_cast<_Types...>(std::forward<_Up>(__rhs)));
505  }
506 
507  // The following are (Copy|Move) (ctor|assign) layers for forwarding
508  // triviality and handling non-trivial SMF behaviors.
509 
510  template<bool, typename... _Types>
511  struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
512  {
513  using _Base = _Variant_storage_alias<_Types...>;
514  using _Base::_Base;
515 
516  _Copy_ctor_base(const _Copy_ctor_base& __rhs)
517  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
518  {
519  __variant_construct<_Types...>(*this, __rhs);
520  }
521 
522  _Copy_ctor_base(_Copy_ctor_base&&) = default;
523  _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
524  _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
525  };
526 
527  template<typename... _Types>
528  struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
529  {
530  using _Base = _Variant_storage_alias<_Types...>;
531  using _Base::_Base;
532  };
533 
534  template<typename... _Types>
535  using _Copy_ctor_alias =
536  _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
537 
538  template<bool, typename... _Types>
539  struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
540  {
541  using _Base = _Copy_ctor_alias<_Types...>;
542  using _Base::_Base;
543 
544  _Move_ctor_base(_Move_ctor_base&& __rhs)
545  noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
546  {
547  __variant_construct<_Types...>(*this, std::move(__rhs));
548  }
549 
550  template<typename _Up>
551  void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
552  {
553  this->_M_reset();
554  __variant_construct_single(*this, std::forward<_Up>(__rhs));
555  this->_M_index = __rhs_index;
556  }
557 
558  template<typename _Up>
559  void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
560  {
561  this->_M_reset();
562  __variant_construct_single(*this, __rhs);
563  this->_M_index = __rhs_index;
564  }
565 
566  _Move_ctor_base(const _Move_ctor_base&) = default;
567  _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
568  _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
569  };
570 
571  template<typename... _Types>
572  struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
573  {
574  using _Base = _Copy_ctor_alias<_Types...>;
575  using _Base::_Base;
576 
577  template<typename _Up>
578  void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
579  {
580  this->_M_reset();
581  __variant_construct_single(*this, std::forward<_Up>(__rhs));
582  this->_M_index = __rhs_index;
583  }
584 
585  template<typename _Up>
586  void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
587  {
588  this->_M_reset();
589  __variant_construct_single(*this, __rhs);
590  this->_M_index = __rhs_index;
591  }
592  };
593 
594  template<typename... _Types>
595  using _Move_ctor_alias =
596  _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
597 
598  template<bool, typename... _Types>
599  struct _Copy_assign_base : _Move_ctor_alias<_Types...>
600  {
601  using _Base = _Move_ctor_alias<_Types...>;
602  using _Base::_Base;
603 
604  _Copy_assign_base&
605  operator=(const _Copy_assign_base& __rhs)
606  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
607  {
608  __variant::__raw_idx_visit(
609  [this](auto&& __rhs_mem, auto __rhs_index) mutable
610  {
611  if constexpr (__rhs_index != variant_npos)
612  {
613  if (this->_M_index == __rhs_index)
614  __variant::__get<__rhs_index>(*this) = __rhs_mem;
615  else
616  {
617  using __rhs_type = __remove_cvref_t<decltype(__rhs_mem)>;
618  if constexpr (is_nothrow_copy_constructible_v<__rhs_type>
619  || !is_nothrow_move_constructible_v<__rhs_type>)
620  // The standard says this->emplace<__rhs_type>(__rhs_mem)
621  // should be used here, but _M_destructive_copy is
622  // equivalent in this case. Either copy construction
623  // doesn't throw, so _M_destructive_copy gives strong
624  // exception safety guarantee, or both copy construction
625  // and move construction can throw, so emplace only gives
626  // basic exception safety anyway.
627  this->_M_destructive_copy(__rhs_index, __rhs_mem);
628  else
629  __variant_cast<_Types...>(*this)
630  = variant<_Types...>(std::in_place_index<__rhs_index>,
631  __rhs_mem);
632  }
633  }
634  else
635  this->_M_reset();
636  }, __variant_cast<_Types...>(__rhs));
637  return *this;
638  }
639 
640  _Copy_assign_base(const _Copy_assign_base&) = default;
641  _Copy_assign_base(_Copy_assign_base&&) = default;
642  _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
643  };
644 
645  template<typename... _Types>
646  struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
647  {
648  using _Base = _Move_ctor_alias<_Types...>;
649  using _Base::_Base;
650  };
651 
652  template<typename... _Types>
653  using _Copy_assign_alias =
654  _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
655 
656  template<bool, typename... _Types>
657  struct _Move_assign_base : _Copy_assign_alias<_Types...>
658  {
659  using _Base = _Copy_assign_alias<_Types...>;
660  using _Base::_Base;
661 
662  _Move_assign_base&
663  operator=(_Move_assign_base&& __rhs)
664  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
665  {
666  __variant::__raw_idx_visit(
667  [this](auto&& __rhs_mem, auto __rhs_index) mutable
668  {
669  if constexpr (__rhs_index != variant_npos)
670  {
671  if (this->_M_index == __rhs_index)
672  __variant::__get<__rhs_index>(*this) = std::move(__rhs_mem);
673  else
674  __variant_cast<_Types...>(*this)
675  .template emplace<__rhs_index>(std::move(__rhs_mem));
676  }
677  else
678  this->_M_reset();
679  }, __variant_cast<_Types...>(__rhs));
680  return *this;
681  }
682 
683  _Move_assign_base(const _Move_assign_base&) = default;
684  _Move_assign_base(_Move_assign_base&&) = default;
685  _Move_assign_base& operator=(const _Move_assign_base&) = default;
686  };
687 
688  template<typename... _Types>
689  struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
690  {
691  using _Base = _Copy_assign_alias<_Types...>;
692  using _Base::_Base;
693  };
694 
695  template<typename... _Types>
696  using _Move_assign_alias =
697  _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
698 
699  template<typename... _Types>
700  struct _Variant_base : _Move_assign_alias<_Types...>
701  {
702  using _Base = _Move_assign_alias<_Types...>;
703 
704  constexpr
705  _Variant_base()
706  noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
707  : _Variant_base(in_place_index<0>) { }
708 
709  template<size_t _Np, typename... _Args>
710  constexpr explicit
711  _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
712  : _Base(__i, std::forward<_Args>(__args)...)
713  { }
714 
715  _Variant_base(const _Variant_base&) = default;
716  _Variant_base(_Variant_base&&) = default;
717  _Variant_base& operator=(const _Variant_base&) = default;
718  _Variant_base& operator=(_Variant_base&&) = default;
719  };
720 
721  // For how many times does _Tp appear in _Tuple?
722  template<typename _Tp, typename _Tuple>
723  struct __tuple_count;
724 
725  template<typename _Tp, typename _Tuple>
726  inline constexpr size_t __tuple_count_v =
727  __tuple_count<_Tp, _Tuple>::value;
728 
729  template<typename _Tp, typename... _Types>
730  struct __tuple_count<_Tp, tuple<_Types...>>
731  : integral_constant<size_t, 0> { };
732 
733  template<typename _Tp, typename _First, typename... _Rest>
734  struct __tuple_count<_Tp, tuple<_First, _Rest...>>
735  : integral_constant<
736  size_t,
737  __tuple_count_v<_Tp, tuple<_Rest...>> + is_same_v<_Tp, _First>> { };
738 
739  // TODO: Reuse this in <tuple> ?
740  template<typename _Tp, typename... _Types>
741  inline constexpr bool __exactly_once =
742  __tuple_count_v<_Tp, tuple<_Types...>> == 1;
743 
744  // Helper used to check for valid conversions that don't involve narrowing.
745  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
746 
747  // "Build an imaginary function FUN(Ti) for each alternative type Ti"
748  template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
749  struct _Build_FUN
750  {
751  // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
752  // but only static functions will be considered in the call below.
753  void _S_fun();
754  };
755 
756  // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
757  template<size_t _Ind, typename _Tp, typename _Ti>
758  struct _Build_FUN<_Ind, _Tp, _Ti,
759  void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
760  {
761  // This is the FUN function for type _Ti, with index _Ind
762  static integral_constant<size_t, _Ind> _S_fun(_Ti);
763  };
764 
765  template<typename _Tp, typename _Variant,
766  typename = make_index_sequence<variant_size_v<_Variant>>>
767  struct _Build_FUNs;
768 
769  template<typename _Tp, typename... _Ti, size_t... _Ind>
770  struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
771  : _Build_FUN<_Ind, _Tp, _Ti>...
772  {
773  using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
774  };
775 
776  // The index j of the overload FUN(Tj) selected by overload resolution
777  // for FUN(std::forward<_Tp>(t))
778  template<typename _Tp, typename _Variant>
779  using _FUN_type
780  = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
781 
782  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
783  template<typename _Tp, typename _Variant, typename = void>
784  struct __accepted_index
785  : integral_constant<size_t, variant_npos>
786  { };
787 
788  template<typename _Tp, typename _Variant>
789  struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
790  : _FUN_type<_Tp, _Variant>
791  { };
792 
793  template <typename _Maybe_variant_cookie, typename _Variant>
794  struct _Extra_visit_slot_needed
795  {
796  template <typename> struct _Variant_never_valueless;
797 
798  template <typename... _Types>
799  struct _Variant_never_valueless<variant<_Types...>>
800  : bool_constant<__variant::__never_valueless<_Types...>()> {};
801 
802  static constexpr bool value =
803  (is_same_v<_Maybe_variant_cookie, __variant_cookie>
804  || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
805  && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
806  };
807 
808  // Used for storing a multi-dimensional vtable.
809  template<typename _Tp, size_t... _Dimensions>
810  struct _Multi_array;
811 
812  // Partial specialization with rank zero, stores a single _Tp element.
813  template<typename _Tp>
814  struct _Multi_array<_Tp>
815  {
816  template<typename>
817  struct __untag_result
818  : false_type
819  { using element_type = _Tp; };
820 
821  template <typename... _Args>
822  struct __untag_result<const void(*)(_Args...)>
823  : false_type
824  { using element_type = void(*)(_Args...); };
825 
826  template <typename... _Args>
827  struct __untag_result<__variant_cookie(*)(_Args...)>
828  : false_type
829  { using element_type = void(*)(_Args...); };
830 
831  template <typename... _Args>
832  struct __untag_result<__variant_idx_cookie(*)(_Args...)>
833  : false_type
834  { using element_type = void(*)(_Args...); };
835 
836  template <typename _Res, typename... _Args>
837  struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
838  : true_type
839  { using element_type = _Res(*)(_Args...); };
840 
841  using __result_is_deduced = __untag_result<_Tp>;
842 
843  constexpr const typename __untag_result<_Tp>::element_type&
844  _M_access() const
845  { return _M_data; }
846 
847  typename __untag_result<_Tp>::element_type _M_data;
848  };
849 
850  // Partial specialization with rank >= 1.
851  template<typename _Ret,
852  typename _Visitor,
853  typename... _Variants,
854  size_t __first, size_t... __rest>
855  struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
856  {
857  static constexpr size_t __index =
858  sizeof...(_Variants) - sizeof...(__rest) - 1;
859 
860  using _Variant = typename _Nth_type<__index, _Variants...>::type;
861 
862  static constexpr int __do_cookie =
863  _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
864 
865  using _Tp = _Ret(*)(_Visitor, _Variants...);
866 
867  template<typename... _Args>
868  constexpr decltype(auto)
869  _M_access(size_t __first_index, _Args... __rest_indices) const
870  {
871  return _M_arr[__first_index + __do_cookie]
872  ._M_access(__rest_indices...);
873  }
874 
875  _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
876  };
877 
878  // Creates a multi-dimensional vtable recursively.
879  //
880  // For example,
881  // visit([](auto, auto){},
882  // variant<int, char>(), // typedef'ed as V1
883  // variant<float, double, long double>()) // typedef'ed as V2
884  // will trigger instantiations of:
885  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
886  // tuple<V1&&, V2&&>, std::index_sequence<>>
887  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
888  // tuple<V1&&, V2&&>, std::index_sequence<0>>
889  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
890  // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
891  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
892  // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
893  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
894  // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
895  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
896  // tuple<V1&&, V2&&>, std::index_sequence<1>>
897  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
898  // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
899  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
900  // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
901  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
902  // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
903  // The returned multi-dimensional vtable can be fast accessed by the visitor
904  // using index calculation.
905  template<typename _Array_type, typename _Index_seq>
906  struct __gen_vtable_impl;
907 
908  // Defines the _S_apply() member that returns a _Multi_array populated
909  // with function pointers that perform the visitation expressions e(m)
910  // for each valid pack of indexes into the variant types _Variants.
911  //
912  // This partial specialization builds up the index sequences by recursively
913  // calling _S_apply() on the next specialization of __gen_vtable_impl.
914  // The base case of the recursion defines the actual function pointers.
915  template<typename _Result_type, typename _Visitor, size_t... __dimensions,
916  typename... _Variants, size_t... __indices>
917  struct __gen_vtable_impl<
918  _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
919  std::index_sequence<__indices...>>
920  {
921  using _Next =
922  remove_reference_t<typename _Nth_type<sizeof...(__indices),
923  _Variants...>::type>;
924  using _Array_type =
925  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
926  __dimensions...>;
927 
928  static constexpr _Array_type
929  _S_apply()
930  {
931  _Array_type __vtable{};
932  _S_apply_all_alts(
933  __vtable, make_index_sequence<variant_size_v<_Next>>());
934  return __vtable;
935  }
936 
937  template<size_t... __var_indices>
938  static constexpr void
939  _S_apply_all_alts(_Array_type& __vtable,
940  std::index_sequence<__var_indices...>)
941  {
942  if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
943  (_S_apply_single_alt<true, __var_indices>(
944  __vtable._M_arr[__var_indices + 1],
945  &(__vtable._M_arr[0])), ...);
946  else
947  (_S_apply_single_alt<false, __var_indices>(
948  __vtable._M_arr[__var_indices]), ...);
949  }
950 
951  template<bool __do_cookie, size_t __index, typename _Tp>
952  static constexpr void
953  _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
954  {
955  if constexpr (__do_cookie)
956  {
957  __element = __gen_vtable_impl<
958  _Tp,
959  std::index_sequence<__indices..., __index>>::_S_apply();
960  *__cookie_element = __gen_vtable_impl<
961  _Tp,
962  std::index_sequence<__indices..., variant_npos>>::_S_apply();
963  }
964  else
965  {
966  auto __tmp_element = __gen_vtable_impl<
967  remove_reference_t<decltype(__element)>,
968  std::index_sequence<__indices..., __index>>::_S_apply();
969  static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
970  "std::visit requires the visitor to have the same "
971  "return type for all alternatives of a variant");
972  __element = __tmp_element;
973  }
974  }
975  };
976 
977  // This partial specialization is the base case for the recursion.
978  // It populates a _Multi_array element with the address of a function
979  // that invokes the visitor with the alternatives specified by __indices.
980  template<typename _Result_type, typename _Visitor, typename... _Variants,
981  size_t... __indices>
982  struct __gen_vtable_impl<
983  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
984  std::index_sequence<__indices...>>
985  {
986  using _Array_type =
987  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
988 
989  template<size_t __index, typename _Variant>
990  static constexpr decltype(auto)
991  __element_by_index_or_cookie(_Variant&& __var) noexcept
992  {
993  if constexpr (__index != variant_npos)
994  return __variant::__get<__index>(std::forward<_Variant>(__var));
995  else
996  return __variant_cookie{};
997  }
998 
999  static constexpr decltype(auto)
1000  __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1001  {
1002  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1003  // For raw visitation using indices, pass the indices to the visitor
1004  // and discard the return value:
1005  std::__invoke(std::forward<_Visitor>(__visitor),
1006  __element_by_index_or_cookie<__indices>(
1007  std::forward<_Variants>(__vars))...,
1008  integral_constant<size_t, __indices>()...);
1009  else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1010  // For raw visitation without indices, and discard the return value:
1011  std::__invoke(std::forward<_Visitor>(__visitor),
1012  __element_by_index_or_cookie<__indices>(
1013  std::forward<_Variants>(__vars))...);
1014  else if constexpr (_Array_type::__result_is_deduced::value)
1015  // For the usual std::visit case deduce the return value:
1016  return std::__invoke(std::forward<_Visitor>(__visitor),
1017  __element_by_index_or_cookie<__indices>(
1018  std::forward<_Variants>(__vars))...);
1019  else // for std::visit<R> use INVOKE<R>
1020  return std::__invoke_r<_Result_type>(
1021  std::forward<_Visitor>(__visitor),
1022  __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1023  }
1024 
1025  static constexpr auto
1026  _S_apply()
1027  {
1028  if constexpr (_Array_type::__result_is_deduced::value)
1029  {
1030  constexpr bool __visit_ret_type_mismatch =
1031  !is_same_v<typename _Result_type::type,
1032  decltype(__visit_invoke(std::declval<_Visitor>(),
1033  std::declval<_Variants>()...))>;
1034  if constexpr (__visit_ret_type_mismatch)
1035  {
1036  struct __cannot_match {};
1037  return __cannot_match{};
1038  }
1039  else
1040  return _Array_type{&__visit_invoke};
1041  }
1042  else
1043  return _Array_type{&__visit_invoke};
1044  }
1045  };
1046 
1047  template<typename _Result_type, typename _Visitor, typename... _Variants>
1048  struct __gen_vtable
1049  {
1050  using _Array_type =
1051  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1052  variant_size_v<remove_reference_t<_Variants>>...>;
1053 
1054  static constexpr _Array_type _S_vtable
1055  = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1056  };
1057 
1058  template<size_t _Np, typename _Tp>
1059  struct _Base_dedup : public _Tp { };
1060 
1061  template<typename _Variant, typename __indices>
1062  struct _Variant_hash_base;
1063 
1064  template<typename... _Types, size_t... __indices>
1065  struct _Variant_hash_base<variant<_Types...>,
1066  std::index_sequence<__indices...>>
1067  : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1068 
1069  // Equivalent to decltype(get<_Np>(as-variant(declval<_Variant>())))
1070  template<size_t _Np, typename _Variant,
1071  typename _AsV = decltype(__variant::__as(std::declval<_Variant>())),
1072  typename _Tp = variant_alternative_t<_Np, remove_reference_t<_AsV>>>
1073  using __get_t
1074  = conditional_t<is_lvalue_reference_v<_Variant>, _Tp&, _Tp&&>;
1075 
1076  // Return type of std::visit.
1077  template<typename _Visitor, typename... _Variants>
1078  using __visit_result_t
1079  = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1080 
1081  template<typename _Tp, typename... _Types>
1082  constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
1083 
1084  template <typename _Visitor, typename _Variant, size_t... _Idxs>
1085  constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
1086  {
1087  return __same_types<
1088  invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
1089  >;
1090  }
1091 
1092  template<size_t _Np, typename _Variant, typename... _Args>
1093  inline void
1094  __construct_by_index(_Variant& __v, _Args&&... __args)
1095  {
1096  auto&& __storage = __detail::__variant::__get<_Np>(__v);
1097  ::new ((void*)std::addressof(__storage))
1098  remove_reference_t<decltype(__storage)>
1099  (std::forward<_Args>(__args)...);
1100  // Construction didn't throw, so can set the new index now:
1101  __v._M_index = _Np;
1102  }
1103 
1104 } // namespace __variant
1105 } // namespace __detail
1106 
1107  template<typename _Tp, typename... _Types>
1108  constexpr bool
1109  holds_alternative(const variant<_Types...>& __v) noexcept
1110  {
1111  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1112  "T must occur exactly once in alternatives");
1113  return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
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...>>(__v);
1123  }
1124 
1125  template<typename _Tp, typename... _Types>
1126  constexpr _Tp&& get(variant<_Types...>&& __v)
1127  {
1128  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1129  "T must occur exactly once in alternatives");
1130  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1131  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1132  std::move(__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...>>(__v);
1142  }
1143 
1144  template<typename _Tp, typename... _Types>
1145  constexpr const _Tp&& get(const variant<_Types...>&& __v)
1146  {
1147  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1148  "T must occur exactly once in alternatives");
1149  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1150  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1151  std::move(__v));
1152  }
1153 
1154  template<size_t _Np, typename... _Types>
1155  constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1156  get_if(variant<_Types...>* __ptr) noexcept
1157  {
1158  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1159  static_assert(_Np < sizeof...(_Types),
1160  "The index must be in [0, number of alternatives)");
1161  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1162  if (__ptr && __ptr->index() == _Np)
1163  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1164  return nullptr;
1165  }
1166 
1167  template<size_t _Np, typename... _Types>
1168  constexpr
1169  add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1170  get_if(const variant<_Types...>* __ptr) noexcept
1171  {
1172  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1173  static_assert(_Np < sizeof...(_Types),
1174  "The index must be in [0, number of alternatives)");
1175  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1176  if (__ptr && __ptr->index() == _Np)
1177  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1178  return nullptr;
1179  }
1180 
1181  template<typename _Tp, typename... _Types>
1182  constexpr add_pointer_t<_Tp>
1183  get_if(variant<_Types...>* __ptr) noexcept
1184  {
1185  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1186  "T must occur exactly once in alternatives");
1187  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1188  return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1189  __ptr);
1190  }
1191 
1192  template<typename _Tp, typename... _Types>
1193  constexpr add_pointer_t<const _Tp>
1194  get_if(const variant<_Types...>* __ptr) noexcept
1195  {
1196  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1197  "T must occur exactly once in alternatives");
1198  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1199  return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1200  __ptr);
1201  }
1202 
1203  struct monostate { };
1204 
1205 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1206  template<typename... _Types> \
1207  constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1208  const variant<_Types...>& __rhs) \
1209  { \
1210  bool __ret = true; \
1211  __detail::__variant::__raw_idx_visit( \
1212  [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1213  { \
1214  if constexpr (__rhs_index != variant_npos) \
1215  { \
1216  if (__lhs.index() == __rhs_index) \
1217  { \
1218  auto& __this_mem = std::get<__rhs_index>(__lhs); \
1219  __ret = __this_mem __OP __rhs_mem; \
1220  } \
1221  else \
1222  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1223  } \
1224  else \
1225  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1226  }, __rhs); \
1227  return __ret; \
1228  }
1229 
1230  _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1231  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1232  _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1233  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1234  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1235  _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1236 
1237 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1238 
1239  constexpr bool operator==(monostate, monostate) noexcept { return true; }
1240 
1241 #ifdef __cpp_lib_three_way_comparison
1242  template<typename... _Types>
1243  requires (three_way_comparable<_Types> && ...)
1244  constexpr
1245  common_comparison_category_t<compare_three_way_result_t<_Types>...>
1246  operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1247  {
1248  common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1249  = strong_ordering::equal;
1250 
1251  __detail::__variant::__raw_idx_visit(
1252  [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1253  {
1254  if constexpr (__w_index != variant_npos)
1255  {
1256  if (__v.index() == __w_index)
1257  {
1258  auto& __this_mem = std::get<__w_index>(__v);
1259  __ret = __this_mem <=> __w_mem;
1260  return;
1261  }
1262  }
1263  __ret = (__v.index() + 1) <=> (__w_index + 1);
1264  }, __w);
1265  return __ret;
1266  }
1267 
1268  constexpr strong_ordering
1269  operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1270 #else
1271  constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1272  constexpr bool operator<(monostate, monostate) noexcept { return false; }
1273  constexpr bool operator>(monostate, monostate) noexcept { return false; }
1274  constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1275  constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1276 #endif
1277 
1278  template<typename _Visitor, typename... _Variants>
1279  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1280  visit(_Visitor&&, _Variants&&...);
1281 
1282  template<typename... _Types>
1283  inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1284  && (is_swappable_v<_Types> && ...)>
1285  swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1286  noexcept(noexcept(__lhs.swap(__rhs)))
1287  { __lhs.swap(__rhs); }
1288 
1289  template<typename... _Types>
1290  enable_if_t<!((is_move_constructible_v<_Types> && ...)
1291  && (is_swappable_v<_Types> && ...))>
1292  swap(variant<_Types...>&, variant<_Types...>&) = delete;
1293 
1294  class bad_variant_access : public exception
1295  {
1296  public:
1297  bad_variant_access() noexcept { }
1298 
1299  const char* what() const noexcept override
1300  { return _M_reason; }
1301 
1302  private:
1303  bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1304 
1305  // Must point to a string with static storage duration:
1306  const char* _M_reason = "bad variant access";
1307 
1308  friend void __throw_bad_variant_access(const char* __what);
1309  };
1310 
1311  // Must only be called with a string literal
1312  inline void
1313  __throw_bad_variant_access(const char* __what)
1314  { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1315 
1316  inline void
1317  __throw_bad_variant_access(bool __valueless)
1318  {
1319  if (__valueless) [[__unlikely__]]
1320  __throw_bad_variant_access("std::get: variant is valueless");
1321  else
1322  __throw_bad_variant_access("std::get: wrong index for variant");
1323  }
1324 
1325  template<typename... _Types>
1326  class variant
1327  : private __detail::__variant::_Variant_base<_Types...>,
1328  private _Enable_default_constructor<
1329  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1330  variant<_Types...>>,
1331  private _Enable_copy_move<
1332  __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1333  __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1334  __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1335  __detail::__variant::_Traits<_Types...>::_S_move_assign,
1336  variant<_Types...>>
1337  {
1338  private:
1339  template <typename... _UTypes, typename _Tp>
1340  friend decltype(auto) __variant_cast(_Tp&&);
1341  template<size_t _Np, typename _Variant, typename... _Args>
1342  friend void
1343  __detail::__variant::__construct_by_index(_Variant& __v,
1344  _Args&&... __args);
1345 
1346  static_assert(sizeof...(_Types) > 0,
1347  "variant must have at least one alternative");
1348  static_assert(!(std::is_reference_v<_Types> || ...),
1349  "variant must have no reference alternative");
1350  static_assert(!(std::is_void_v<_Types> || ...),
1351  "variant must have no void alternative");
1352 
1353  using _Base = __detail::__variant::_Variant_base<_Types...>;
1354  using _Default_ctor_enabler =
1355  _Enable_default_constructor<
1356  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1357  variant<_Types...>>;
1358 
1359  template<typename _Tp>
1360  static constexpr bool __not_self
1361  = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1362 
1363  template<typename _Tp>
1364  static constexpr bool
1365  __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1366 
1367  template<typename _Tp>
1368  static constexpr size_t __accepted_index
1369  = __detail::__variant::__accepted_index<_Tp, variant>::value;
1370 
1371  template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1372  using __to_type = variant_alternative_t<_Np, variant>;
1373 
1374  template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1375  using __accepted_type = __to_type<__accepted_index<_Tp>>;
1376 
1377  template<typename _Tp>
1378  static constexpr size_t __index_of =
1379  __detail::__variant::__index_of_v<_Tp, _Types...>;
1380 
1381  using _Traits = __detail::__variant::_Traits<_Types...>;
1382 
1383  template<typename _Tp>
1384  struct __is_in_place_tag : false_type { };
1385  template<typename _Tp>
1386  struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1387  template<size_t _Np>
1388  struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1389 
1390  template<typename _Tp>
1391  static constexpr bool __not_in_place_tag
1392  = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1393 
1394  public:
1395  variant() = default;
1396  variant(const variant& __rhs) = default;
1397  variant(variant&&) = default;
1398  variant& operator=(const variant&) = default;
1399  variant& operator=(variant&&) = default;
1400  ~variant() = default;
1401 
1402  template<typename _Tp,
1403  typename = enable_if_t<sizeof...(_Types) != 0>,
1404  typename = enable_if_t<__not_in_place_tag<_Tp>>,
1405  typename _Tj = __accepted_type<_Tp&&>,
1406  typename = enable_if_t<__exactly_once<_Tj>
1407  && is_constructible_v<_Tj, _Tp>>>
1408  constexpr
1409  variant(_Tp&& __t)
1410  noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1411  : variant(in_place_index<__accepted_index<_Tp>>,
1412  std::forward<_Tp>(__t))
1413  { }
1414 
1415  template<typename _Tp, typename... _Args,
1416  typename = enable_if_t<__exactly_once<_Tp>
1417  && is_constructible_v<_Tp, _Args...>>>
1418  constexpr explicit
1419  variant(in_place_type_t<_Tp>, _Args&&... __args)
1420  : variant(in_place_index<__index_of<_Tp>>,
1421  std::forward<_Args>(__args)...)
1422  { }
1423 
1424  template<typename _Tp, typename _Up, typename... _Args,
1425  typename = enable_if_t<__exactly_once<_Tp>
1426  && is_constructible_v<_Tp,
1427  initializer_list<_Up>&, _Args...>>>
1428  constexpr explicit
1429  variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1430  _Args&&... __args)
1431  : variant(in_place_index<__index_of<_Tp>>, __il,
1432  std::forward<_Args>(__args)...)
1433  { }
1434 
1435  template<size_t _Np, typename... _Args,
1436  typename _Tp = __to_type<_Np>,
1437  typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1438  constexpr explicit
1439  variant(in_place_index_t<_Np>, _Args&&... __args)
1440  : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1441  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1442  { }
1443 
1444  template<size_t _Np, typename _Up, typename... _Args,
1445  typename _Tp = __to_type<_Np>,
1446  typename = enable_if_t<is_constructible_v<_Tp,
1447  initializer_list<_Up>&,
1448  _Args...>>>
1449  constexpr explicit
1450  variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1451  _Args&&... __args)
1452  : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1453  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1454  { }
1455 
1456  template<typename _Tp>
1457  enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1458  && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1459  && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1460  variant&>
1461  operator=(_Tp&& __rhs)
1462  noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1463  && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1464  {
1465  constexpr auto __index = __accepted_index<_Tp>;
1466  if (index() == __index)
1467  std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1468  else
1469  {
1470  using _Tj = __accepted_type<_Tp&&>;
1471  if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1472  || !is_nothrow_move_constructible_v<_Tj>)
1473  this->emplace<__index>(std::forward<_Tp>(__rhs));
1474  else
1475  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1476  // 3585. converting assignment with immovable alternative
1477  this->emplace<__index>(_Tj(std::forward<_Tp>(__rhs)));
1478  }
1479  return *this;
1480  }
1481 
1482  template<typename _Tp, typename... _Args>
1483  enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1484  _Tp&>
1485  emplace(_Args&&... __args)
1486  {
1487  constexpr size_t __index = __index_of<_Tp>;
1488  return this->emplace<__index>(std::forward<_Args>(__args)...);
1489  }
1490 
1491  template<typename _Tp, typename _Up, typename... _Args>
1492  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1493  && __exactly_once<_Tp>,
1494  _Tp&>
1495  emplace(initializer_list<_Up> __il, _Args&&... __args)
1496  {
1497  constexpr size_t __index = __index_of<_Tp>;
1498  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1499  }
1500 
1501  template<size_t _Np, typename... _Args>
1502  enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1503  _Args...>,
1504  variant_alternative_t<_Np, variant>&>
1505  emplace(_Args&&... __args)
1506  {
1507  static_assert(_Np < sizeof...(_Types),
1508  "The index must be in [0, number of alternatives)");
1509  using type = variant_alternative_t<_Np, variant>;
1510  namespace __variant = std::__detail::__variant;
1511  // Provide the strong exception-safety guarantee when possible,
1512  // to avoid becoming valueless.
1513  if constexpr (is_nothrow_constructible_v<type, _Args...>)
1514  {
1515  this->_M_reset();
1516  __variant::__construct_by_index<_Np>(*this,
1517  std::forward<_Args>(__args)...);
1518  }
1519  else if constexpr (is_scalar_v<type>)
1520  {
1521  // This might invoke a potentially-throwing conversion operator:
1522  const type __tmp(std::forward<_Args>(__args)...);
1523  // But these steps won't throw:
1524  this->_M_reset();
1525  __variant::__construct_by_index<_Np>(*this, __tmp);
1526  }
1527  else if constexpr (__variant::_Never_valueless_alt<type>()
1528  && _Traits::_S_move_assign)
1529  {
1530  // This construction might throw:
1531  variant __tmp(in_place_index<_Np>,
1532  std::forward<_Args>(__args)...);
1533  // But _Never_valueless_alt<type> means this won't:
1534  *this = std::move(__tmp);
1535  }
1536  else
1537  {
1538  // This case only provides the basic exception-safety guarantee,
1539  // i.e. the variant can become valueless.
1540  this->_M_reset();
1541  __variant::__construct_by_index<_Np>(*this,
1542  std::forward<_Args>(__args)...);
1543  }
1544  return std::get<_Np>(*this);
1545  }
1546 
1547  template<size_t _Np, typename _Up, typename... _Args>
1548  enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1549  initializer_list<_Up>&, _Args...>,
1550  variant_alternative_t<_Np, variant>&>
1551  emplace(initializer_list<_Up> __il, _Args&&... __args)
1552  {
1553  static_assert(_Np < sizeof...(_Types),
1554  "The index must be in [0, number of alternatives)");
1555  using type = variant_alternative_t<_Np, variant>;
1556  namespace __variant = std::__detail::__variant;
1557  // Provide the strong exception-safety guarantee when possible,
1558  // to avoid becoming valueless.
1559  if constexpr (is_nothrow_constructible_v<type,
1560  initializer_list<_Up>&,
1561  _Args...>)
1562  {
1563  this->_M_reset();
1564  __variant::__construct_by_index<_Np>(*this, __il,
1565  std::forward<_Args>(__args)...);
1566  }
1567  else if constexpr (__variant::_Never_valueless_alt<type>()
1568  && _Traits::_S_move_assign)
1569  {
1570  // This construction might throw:
1571  variant __tmp(in_place_index<_Np>, __il,
1572  std::forward<_Args>(__args)...);
1573  // But _Never_valueless_alt<type> means this won't:
1574  *this = std::move(__tmp);
1575  }
1576  else
1577  {
1578  // This case only provides the basic exception-safety guarantee,
1579  // i.e. the variant can become valueless.
1580  this->_M_reset();
1581  __variant::__construct_by_index<_Np>(*this, __il,
1582  std::forward<_Args>(__args)...);
1583  }
1584  return std::get<_Np>(*this);
1585  }
1586 
1587  constexpr bool valueless_by_exception() const noexcept
1588  { return !this->_M_valid(); }
1589 
1590  constexpr size_t index() const noexcept
1591  {
1592  using __index_type = typename _Base::__index_type;
1593  if constexpr (__detail::__variant::__never_valueless<_Types...>())
1594  return this->_M_index;
1595  else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1596  return make_signed_t<__index_type>(this->_M_index);
1597  else
1598  return size_t(__index_type(this->_M_index + 1)) - 1;
1599  }
1600 
1601  void
1602  swap(variant& __rhs)
1603  noexcept((__is_nothrow_swappable<_Types>::value && ...)
1604  && is_nothrow_move_constructible_v<variant>)
1605  {
1606  __detail::__variant::__raw_idx_visit(
1607  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1608  {
1609  if constexpr (__rhs_index != variant_npos)
1610  {
1611  if (this->index() == __rhs_index)
1612  {
1613  auto& __this_mem =
1614  std::get<__rhs_index>(*this);
1615  using std::swap;
1616  swap(__this_mem, __rhs_mem);
1617  }
1618  else
1619  {
1620  if (!this->valueless_by_exception()) [[__likely__]]
1621  {
1622  auto __tmp(std::move(__rhs_mem));
1623  __rhs = std::move(*this);
1624  this->_M_destructive_move(__rhs_index,
1625  std::move(__tmp));
1626  }
1627  else
1628  {
1629  this->_M_destructive_move(__rhs_index,
1630  std::move(__rhs_mem));
1631  __rhs._M_reset();
1632  }
1633  }
1634  }
1635  else
1636  {
1637  if (!this->valueless_by_exception()) [[__likely__]]
1638  {
1639  __rhs = std::move(*this);
1640  this->_M_reset();
1641  }
1642  }
1643  }, __rhs);
1644  }
1645 
1646  private:
1647 
1648 #if defined(__clang__) && __clang_major__ <= 7
1649  public:
1650  using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1651  private:
1652 #endif
1653 
1654  template<size_t _Np, typename _Vp>
1655  friend constexpr decltype(auto)
1656  __detail::__variant::__get(_Vp&& __v) noexcept;
1657 
1658 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1659  template<typename... _Tp> \
1660  friend constexpr bool \
1661  operator __OP(const variant<_Tp...>& __lhs, \
1662  const variant<_Tp...>& __rhs);
1663 
1664  _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1665  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1666  _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1667  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1668  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1669  _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1670 
1671 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1672  };
1673 
1674  template<size_t _Np, typename... _Types>
1675  constexpr variant_alternative_t<_Np, variant<_Types...>>&
1676  get(variant<_Types...>& __v)
1677  {
1678  static_assert(_Np < sizeof...(_Types),
1679  "The index must be in [0, number of alternatives)");
1680  if (__v.index() != _Np)
1681  __throw_bad_variant_access(__v.valueless_by_exception());
1682  return __detail::__variant::__get<_Np>(__v);
1683  }
1684 
1685  template<size_t _Np, typename... _Types>
1686  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1687  get(variant<_Types...>&& __v)
1688  {
1689  static_assert(_Np < sizeof...(_Types),
1690  "The index must be in [0, number of alternatives)");
1691  if (__v.index() != _Np)
1692  __throw_bad_variant_access(__v.valueless_by_exception());
1693  return __detail::__variant::__get<_Np>(std::move(__v));
1694  }
1695 
1696  template<size_t _Np, typename... _Types>
1697  constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1698  get(const variant<_Types...>& __v)
1699  {
1700  static_assert(_Np < sizeof...(_Types),
1701  "The index must be in [0, number of alternatives)");
1702  if (__v.index() != _Np)
1703  __throw_bad_variant_access(__v.valueless_by_exception());
1704  return __detail::__variant::__get<_Np>(__v);
1705  }
1706 
1707  template<size_t _Np, typename... _Types>
1708  constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1709  get(const variant<_Types...>&& __v)
1710  {
1711  static_assert(_Np < sizeof...(_Types),
1712  "The index must be in [0, number of alternatives)");
1713  if (__v.index() != _Np)
1714  __throw_bad_variant_access(__v.valueless_by_exception());
1715  return __detail::__variant::__get<_Np>(std::move(__v));
1716  }
1717 
1718  /// @cond undocumented
1719  template<typename _Result_type, typename _Visitor, typename... _Variants>
1720  constexpr decltype(auto)
1721  __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1722  {
1723  constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1724  _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1725 
1726  auto __func_ptr = __vtable._M_access(__variants.index()...);
1727  return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1728  std::forward<_Variants>(__variants)...);
1729  }
1730  /// @endcond
1731 
1732  template<typename _Visitor, typename... _Variants>
1733  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1734  visit(_Visitor&& __visitor, _Variants&&... __variants)
1735  {
1736  namespace __variant = std::__detail::__variant;
1737 
1738  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1739  __throw_bad_variant_access("std::visit: variant is valueless");
1740 
1741  using _Result_type
1742  = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1743 
1744  using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1745 
1746  if constexpr (sizeof...(_Variants) == 1)
1747  {
1748  using _Vp = decltype(__variant::__as(std::declval<_Variants>()...));
1749 
1750  constexpr bool __visit_rettypes_match = __detail::__variant::
1751  __check_visitor_results<_Visitor, _Vp>(
1752  make_index_sequence<variant_size_v<remove_reference_t<_Vp>>>());
1753  if constexpr (!__visit_rettypes_match)
1754  {
1755  static_assert(__visit_rettypes_match,
1756  "std::visit requires the visitor to have the same "
1757  "return type for all alternatives of a variant");
1758  return;
1759  }
1760  else
1761  return std::__do_visit<_Tag>(
1762  std::forward<_Visitor>(__visitor),
1763  static_cast<_Vp>(__variants)...);
1764  }
1765  else
1766  return std::__do_visit<_Tag>(
1767  std::forward<_Visitor>(__visitor),
1768  __variant::__as(std::forward<_Variants>(__variants))...);
1769  }
1770 
1771 #if __cplusplus > 201703L
1772  template<typename _Res, typename _Visitor, typename... _Variants>
1773  constexpr _Res
1774  visit(_Visitor&& __visitor, _Variants&&... __variants)
1775  {
1776  namespace __variant = std::__detail::__variant;
1777 
1778  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1779  __throw_bad_variant_access("std::visit<R>: variant is valueless");
1780 
1781  return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1782  __variant::__as(std::forward<_Variants>(__variants))...);
1783  }
1784 #endif
1785 
1786  /// @cond undocumented
1787  template<bool, typename... _Types>
1788  struct __variant_hash_call_base_impl
1789  {
1790  size_t
1791  operator()(const variant<_Types...>& __t) const
1792  noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1793  {
1794  size_t __ret;
1795  __detail::__variant::__raw_visit(
1796  [&__t, &__ret](auto&& __t_mem) mutable
1797  {
1798  using _Type = __remove_cvref_t<decltype(__t_mem)>;
1799  if constexpr (!is_same_v<_Type,
1800  __detail::__variant::__variant_cookie>)
1801  __ret = std::hash<size_t>{}(__t.index())
1802  + std::hash<_Type>{}(__t_mem);
1803  else
1804  __ret = std::hash<size_t>{}(__t.index());
1805  }, __t);
1806  return __ret;
1807  }
1808  };
1809 
1810  template<typename... _Types>
1811  struct __variant_hash_call_base_impl<false, _Types...> {};
1812 
1813  template<typename... _Types>
1814  using __variant_hash_call_base =
1815  __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1816  __enable_hash_call &&...), _Types...>;
1817  /// @endcond
1818 
1819  template<typename... _Types>
1820  struct hash<variant<_Types...>>
1821  : private __detail::__variant::_Variant_hash_base<
1822  variant<_Types...>, std::index_sequence_for<_Types...>>,
1823  public __variant_hash_call_base<_Types...>
1824  {
1825  using result_type [[__deprecated__]] = size_t;
1826  using argument_type [[__deprecated__]] = variant<_Types...>;
1827  };
1828 
1829  template<>
1830  struct hash<monostate>
1831  {
1832  using result_type [[__deprecated__]] = size_t;
1833  using argument_type [[__deprecated__]] = monostate;
1834 
1835  size_t
1836  operator()(const monostate&) const noexcept
1837  {
1838  constexpr size_t __magic_monostate_hash = -7777;
1839  return __magic_monostate_hash;
1840  }
1841  };
1842 
1843  template<typename... _Types>
1844  struct __is_fast_hash<hash<variant<_Types...>>>
1845  : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1846  { };
1847 
1848 _GLIBCXX_END_NAMESPACE_VERSION
1849 } // namespace std
1850 
1851 #endif // C++17
1852 
1853 #endif // _GLIBCXX_VARIANT