libstdc++
variant
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1 // <variant> -*- C++ -*-
2 
3 // Copyright (C) 2016-2023 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 <initializer_list>
37 #include <type_traits>
38 #include <bits/enable_special_members.h>
39 #include <bits/exception_defines.h>
40 #include <bits/functional_hash.h>
41 #include <bits/invoke.h>
42 #include <bits/parse_numbers.h>
43 #include <bits/stl_iterator_base_funcs.h>
44 #include <bits/stl_construct.h>
45 #include <bits/utility.h> // in_place_index_t
46 #if __cplusplus >= 202002L
47 # include <compare>
48 #endif
49 
50 #if __cpp_concepts >= 202002L && __cpp_constexpr >= 201811L
51 // P2231R1 constexpr needs constexpr unions and constrained destructors.
52 # define __cpp_lib_variant 202106L
53 #else
54 # include <ext/aligned_buffer.h> // Use __aligned_membuf instead of union.
55 # define __cpp_lib_variant 202102L
56 #endif
57 
58 namespace std _GLIBCXX_VISIBILITY(default)
59 {
60 _GLIBCXX_BEGIN_NAMESPACE_VERSION
61 
62  template<typename... _Types> class tuple;
63  template<typename... _Types> class variant;
64  template <typename> struct hash;
65 
66  template<typename _Variant>
67  struct variant_size;
68 
69  template<typename _Variant>
70  struct variant_size<const _Variant> : variant_size<_Variant> {};
71 
72  template<typename _Variant>
73  struct variant_size<volatile _Variant> : variant_size<_Variant> {};
74 
75  template<typename _Variant>
76  struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
77 
78  template<typename... _Types>
79  struct variant_size<variant<_Types...>>
80  : std::integral_constant<size_t, sizeof...(_Types)> {};
81 
82  template<typename _Variant>
83  inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
84 
85  template<typename... _Types>
86  inline constexpr size_t
87  variant_size_v<variant<_Types...>> = sizeof...(_Types);
88 
89  template<typename... _Types>
90  inline constexpr size_t
91  variant_size_v<const variant<_Types...>> = sizeof...(_Types);
92 
93  template<size_t _Np, typename _Variant>
94  struct variant_alternative;
95 
96  template<size_t _Np, typename... _Types>
97  struct variant_alternative<_Np, variant<_Types...>>
98  {
99  static_assert(_Np < sizeof...(_Types));
100 
101  using type = typename _Nth_type<_Np, _Types...>::type;
102  };
103 
104  template<size_t _Np, typename _Variant>
105  using variant_alternative_t =
106  typename variant_alternative<_Np, _Variant>::type;
107 
108  template<size_t _Np, typename _Variant>
109  struct variant_alternative<_Np, const _Variant>
110  { using type = const variant_alternative_t<_Np, _Variant>; };
111 
112  template<size_t _Np, typename _Variant>
113  struct variant_alternative<_Np, volatile _Variant>
114  { using type = volatile variant_alternative_t<_Np, _Variant>; };
115 
116  template<size_t _Np, typename _Variant>
117  struct variant_alternative<_Np, const volatile _Variant>
118  { using type = const volatile variant_alternative_t<_Np, _Variant>; };
119 
120  inline constexpr size_t variant_npos = -1;
121 
122  template<size_t _Np, typename... _Types>
123  constexpr variant_alternative_t<_Np, variant<_Types...>>&
124  get(variant<_Types...>&);
125 
126  template<size_t _Np, typename... _Types>
127  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
128  get(variant<_Types...>&&);
129 
130  template<size_t _Np, typename... _Types>
131  constexpr variant_alternative_t<_Np, variant<_Types...>> const&
132  get(const variant<_Types...>&);
133 
134  template<size_t _Np, typename... _Types>
135  constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
136  get(const variant<_Types...>&&);
137 
138  template<typename _Result_type, typename _Visitor, typename... _Variants>
139  constexpr decltype(auto)
140  __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
141 
142  template <typename... _Types, typename _Tp>
143  _GLIBCXX20_CONSTEXPR
144  decltype(auto)
145  __variant_cast(_Tp&& __rhs)
146  {
147  if constexpr (is_lvalue_reference_v<_Tp>)
148  {
149  if constexpr (is_const_v<remove_reference_t<_Tp>>)
150  return static_cast<const variant<_Types...>&>(__rhs);
151  else
152  return static_cast<variant<_Types...>&>(__rhs);
153  }
154  else
155  return static_cast<variant<_Types...>&&>(__rhs);
156  }
157 
158 namespace __detail
159 {
160 namespace __variant
161 {
162  // used for raw visitation
163  struct __variant_cookie {};
164  // used for raw visitation with indices passed in
165  struct __variant_idx_cookie { using type = __variant_idx_cookie; };
166  // Used to enable deduction (and same-type checking) for std::visit:
167  template<typename _Tp> struct __deduce_visit_result { using type = _Tp; };
168 
169  // Visit variants that might be valueless.
170  template<typename _Visitor, typename... _Variants>
171  constexpr void
172  __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
173  {
174  std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
175  std::forward<_Variants>(__variants)...);
176  }
177 
178  // Visit variants that might be valueless, passing indices to the visitor.
179  template<typename _Visitor, typename... _Variants>
180  constexpr void
181  __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
182  {
183  std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
184  std::forward<_Variants>(__variants)...);
185  }
186 
187  // The __as function templates implement the exposition-only "as-variant"
188 
189  template<typename... _Types>
190  constexpr std::variant<_Types...>&
191  __as(std::variant<_Types...>& __v) noexcept
192  { return __v; }
193 
194  template<typename... _Types>
195  constexpr const std::variant<_Types...>&
196  __as(const std::variant<_Types...>& __v) noexcept
197  { return __v; }
198 
199  template<typename... _Types>
200  constexpr std::variant<_Types...>&&
201  __as(std::variant<_Types...>&& __v) noexcept
202  { return std::move(__v); }
203 
204  template<typename... _Types>
205  constexpr const std::variant<_Types...>&&
206  __as(const std::variant<_Types...>&& __v) noexcept
207  { return std::move(__v); }
208 
209  // For C++17:
210  // _Uninitialized<T> is guaranteed to be a trivially destructible type,
211  // even if T is not.
212  // For C++20:
213  // _Uninitialized<T> is trivially destructible iff T is, so _Variant_union
214  // needs a constrained non-trivial destructor.
215  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
216  struct _Uninitialized;
217 
218  template<typename _Type>
219  struct _Uninitialized<_Type, true>
220  {
221  template<typename... _Args>
222  constexpr
223  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
224  : _M_storage(std::forward<_Args>(__args)...)
225  { }
226 
227  constexpr const _Type& _M_get() const & noexcept
228  { return _M_storage; }
229 
230  constexpr _Type& _M_get() & noexcept
231  { return _M_storage; }
232 
233  constexpr const _Type&& _M_get() const && noexcept
234  { return std::move(_M_storage); }
235 
236  constexpr _Type&& _M_get() && noexcept
237  { return std::move(_M_storage); }
238 
239  _Type _M_storage;
240  };
241 
242  template<typename _Type>
243  struct _Uninitialized<_Type, false>
244  {
245 #if __cpp_lib_variant >= 202106L
246  template<typename... _Args>
247  constexpr
248  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
249  : _M_storage(std::forward<_Args>(__args)...)
250  { }
251 
252  constexpr ~_Uninitialized() { }
253 
254  _Uninitialized(const _Uninitialized&) = default;
255  _Uninitialized(_Uninitialized&&) = default;
256  _Uninitialized& operator=(const _Uninitialized&) = default;
257  _Uninitialized& operator=(_Uninitialized&&) = default;
258 
259  constexpr const _Type& _M_get() const & noexcept
260  { return _M_storage; }
261 
262  constexpr _Type& _M_get() & noexcept
263  { return _M_storage; }
264 
265  constexpr const _Type&& _M_get() const && noexcept
266  { return std::move(_M_storage); }
267 
268  constexpr _Type&& _M_get() && noexcept
269  { return std::move(_M_storage); }
270 
271  struct _Empty_byte { };
272 
273  union {
274  _Empty_byte _M_empty;
275  _Type _M_storage;
276  };
277 #else
278  template<typename... _Args>
279  constexpr
280  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
281  {
282  ::new ((void*)std::addressof(_M_storage))
283  _Type(std::forward<_Args>(__args)...);
284  }
285 
286  const _Type& _M_get() const & noexcept
287  { return *_M_storage._M_ptr(); }
288 
289  _Type& _M_get() & noexcept
290  { return *_M_storage._M_ptr(); }
291 
292  const _Type&& _M_get() const && noexcept
293  { return std::move(*_M_storage._M_ptr()); }
294 
295  _Type&& _M_get() && noexcept
296  { return std::move(*_M_storage._M_ptr()); }
297 
298  __gnu_cxx::__aligned_membuf<_Type> _M_storage;
299 #endif
300  };
301 
302  template<size_t _Np, typename _Union>
303  constexpr decltype(auto)
304  __get_n(_Union&& __u) noexcept
305  {
306  if constexpr (_Np == 0)
307  return std::forward<_Union>(__u)._M_first._M_get();
308  else if constexpr (_Np == 1)
309  return std::forward<_Union>(__u)._M_rest._M_first._M_get();
310  else if constexpr (_Np == 2)
311  return std::forward<_Union>(__u)._M_rest._M_rest._M_first._M_get();
312  else
313  return __variant::__get_n<_Np - 3>(
314  std::forward<_Union>(__u)._M_rest._M_rest._M_rest);
315  }
316 
317  // Returns the typed storage for __v.
318  template<size_t _Np, typename _Variant>
319  constexpr decltype(auto)
320  __get(_Variant&& __v) noexcept
321  { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); }
322 
323  // Gets the _Uninitialized to construct into for __u.
324  template<size_t _Np, typename _Union>
325  constexpr decltype(auto)
326  __construct_n(_Union& __u) noexcept
327  {
328  if constexpr (_Np == 0)
329  return &__u._M_first;
330  else if constexpr (_Np == 1)
331  {
332  std::_Construct(&__u._M_rest);
333  return &__u._M_rest._M_first;
334  }
335  else if constexpr (_Np == 2)
336  {
337  std::_Construct(&__u._M_rest);
338  std::_Construct(&__u._M_rest._M_rest);
339  return &__u._M_rest._M_rest._M_first;
340  }
341  else
342  {
343  std::_Construct(&__u._M_rest);
344  std::_Construct(&__u._M_rest._M_rest);
345  std::_Construct(&__u._M_rest._M_rest._M_rest);
346  return __variant::__construct_n<_Np - 3>(__u._M_rest._M_rest._M_rest);
347  }
348  }
349 
350  template<typename... _Types>
351  struct _Traits
352  {
353  static constexpr bool _S_default_ctor =
354  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
355  static constexpr bool _S_copy_ctor =
356  (is_copy_constructible_v<_Types> && ...);
357  static constexpr bool _S_move_ctor =
358  (is_move_constructible_v<_Types> && ...);
359  static constexpr bool _S_copy_assign =
360  _S_copy_ctor
361  && (is_copy_assignable_v<_Types> && ...);
362  static constexpr bool _S_move_assign =
363  _S_move_ctor
364  && (is_move_assignable_v<_Types> && ...);
365 
366  static constexpr bool _S_trivial_dtor =
367  (is_trivially_destructible_v<_Types> && ...);
368  static constexpr bool _S_trivial_copy_ctor =
369  (is_trivially_copy_constructible_v<_Types> && ...);
370  static constexpr bool _S_trivial_move_ctor =
371  (is_trivially_move_constructible_v<_Types> && ...);
372  static constexpr bool _S_trivial_copy_assign =
373  _S_trivial_dtor && _S_trivial_copy_ctor
374  && (is_trivially_copy_assignable_v<_Types> && ...);
375  static constexpr bool _S_trivial_move_assign =
376  _S_trivial_dtor && _S_trivial_move_ctor
377  && (is_trivially_move_assignable_v<_Types> && ...);
378 
379  // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
380  // are always nothrow.
381  static constexpr bool _S_nothrow_default_ctor =
382  is_nothrow_default_constructible_v<
383  typename _Nth_type<0, _Types...>::type>;
384  static constexpr bool _S_nothrow_copy_ctor = false;
385  static constexpr bool _S_nothrow_move_ctor =
386  (is_nothrow_move_constructible_v<_Types> && ...);
387  static constexpr bool _S_nothrow_copy_assign = false;
388  static constexpr bool _S_nothrow_move_assign =
389  _S_nothrow_move_ctor
390  && (is_nothrow_move_assignable_v<_Types> && ...);
391  };
392 
393  // Defines members and ctors.
394  template<typename... _Types>
395  union _Variadic_union
396  {
397  _Variadic_union() = default;
398 
399  template<size_t _Np, typename... _Args>
400  _Variadic_union(in_place_index_t<_Np>, _Args&&...) = delete;
401  };
402 
403  template<typename _First, typename... _Rest>
404  union _Variadic_union<_First, _Rest...>
405  {
406  constexpr _Variadic_union() : _M_rest() { }
407 
408  template<typename... _Args>
409  constexpr
410  _Variadic_union(in_place_index_t<0>, _Args&&... __args)
411  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
412  { }
413 
414  template<size_t _Np, typename... _Args>
415  constexpr
416  _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
417  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
418  { }
419 
420 #if __cpp_lib_variant >= 202106L
421  _Variadic_union(const _Variadic_union&) = default;
422  _Variadic_union(_Variadic_union&&) = default;
423  _Variadic_union& operator=(const _Variadic_union&) = default;
424  _Variadic_union& operator=(_Variadic_union&&) = default;
425 
426  ~_Variadic_union() = default;
427 
428  constexpr ~_Variadic_union()
429  requires (!__has_trivial_destructor(_First))
430  || (!__has_trivial_destructor(_Variadic_union<_Rest...>))
431  { }
432 #endif
433 
434  _Uninitialized<_First> _M_first;
435  _Variadic_union<_Rest...> _M_rest;
436  };
437 
438  // _Never_valueless_alt is true for variant alternatives that can
439  // always be placed in a variant without it becoming valueless.
440 
441  // For suitably-small, trivially copyable types we can create temporaries
442  // on the stack and then memcpy them into place.
443  template<typename _Tp>
444  struct _Never_valueless_alt
445  : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
446  { };
447 
448  // Specialize _Never_valueless_alt for other types which have a
449  // non-throwing and cheap move construction and move assignment operator,
450  // so that emplacing the type will provide the strong exception-safety
451  // guarantee, by creating and moving a temporary.
452  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
453  // variant using that alternative, so we can't change the value later!
454 
455  // True if every alternative in _Types... can be emplaced in a variant
456  // without it becoming valueless. If this is true, variant<_Types...>
457  // can never be valueless, which enables some minor optimizations.
458  template <typename... _Types>
459  constexpr bool __never_valueless()
460  {
461  return _Traits<_Types...>::_S_move_assign
462  && (_Never_valueless_alt<_Types>::value && ...);
463  }
464 
465  // Defines index and the dtor, possibly trivial.
466  template<bool __trivially_destructible, typename... _Types>
467  struct _Variant_storage;
468 
469  template <typename... _Types>
470  using __select_index =
471  typename __select_int::_Select_int_base<sizeof...(_Types),
472  unsigned char,
473  unsigned short>::type::value_type;
474 
475  template<typename... _Types>
476  struct _Variant_storage<false, _Types...>
477  {
478  constexpr
479  _Variant_storage()
480  : _M_index(static_cast<__index_type>(variant_npos))
481  { }
482 
483  template<size_t _Np, typename... _Args>
484  constexpr
485  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
486  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
487  _M_index{_Np}
488  { }
489 
490  constexpr void
491  _M_reset()
492  {
493  if (!_M_valid()) [[unlikely]]
494  return;
495 
496  std::__do_visit<void>([](auto&& __this_mem) mutable
497  {
498  std::_Destroy(std::__addressof(__this_mem));
499  }, __variant_cast<_Types...>(*this));
500 
501  _M_index = static_cast<__index_type>(variant_npos);
502  }
503 
504  _GLIBCXX20_CONSTEXPR
505  ~_Variant_storage()
506  { _M_reset(); }
507 
508  constexpr bool
509  _M_valid() const noexcept
510  {
511  if constexpr (__variant::__never_valueless<_Types...>())
512  return true;
513  return this->_M_index != __index_type(variant_npos);
514  }
515 
516  _Variadic_union<_Types...> _M_u;
517  using __index_type = __select_index<_Types...>;
518  __index_type _M_index;
519  };
520 
521  template<typename... _Types>
522  struct _Variant_storage<true, _Types...>
523  {
524  constexpr
525  _Variant_storage()
526  : _M_index(static_cast<__index_type>(variant_npos))
527  { }
528 
529  template<size_t _Np, typename... _Args>
530  constexpr
531  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
532  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
533  _M_index{_Np}
534  { }
535 
536  constexpr void
537  _M_reset() noexcept
538  { _M_index = static_cast<__index_type>(variant_npos); }
539 
540  constexpr bool
541  _M_valid() const noexcept
542  {
543  if constexpr (__variant::__never_valueless<_Types...>())
544  return true;
545  // It would be nice if we could just return true for -fno-exceptions.
546  // It's possible (but inadvisable) that a std::variant could become
547  // valueless in a translation unit compiled with -fexceptions and then
548  // be passed to functions compiled with -fno-exceptions. We would need
549  // some #ifdef _GLIBCXX_NO_EXCEPTIONS_GLOBALLY property to elide all
550  // checks for valueless_by_exception().
551  return this->_M_index != static_cast<__index_type>(variant_npos);
552  }
553 
554  _Variadic_union<_Types...> _M_u;
555  using __index_type = __select_index<_Types...>;
556  __index_type _M_index;
557  };
558 
559  // Implementation of v.emplace<N>(args...).
560  template<size_t _Np, bool _Triv, typename... _Types, typename... _Args>
561  _GLIBCXX20_CONSTEXPR
562  inline void
563  __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args)
564  {
565  __v._M_reset();
566  auto* __addr = __variant::__construct_n<_Np>(__v._M_u);
567  std::_Construct(__addr, in_place_index<0>,
568  std::forward<_Args>(__args)...);
569  // Construction didn't throw, so can set the new index now:
570  __v._M_index = _Np;
571  }
572 
573  template<typename... _Types>
574  using _Variant_storage_alias =
575  _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
576 
577  // The following are (Copy|Move) (ctor|assign) layers for forwarding
578  // triviality and handling non-trivial SMF behaviors.
579 
580  template<bool, typename... _Types>
581  struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
582  {
583  using _Base = _Variant_storage_alias<_Types...>;
584  using _Base::_Base;
585 
586  _GLIBCXX20_CONSTEXPR
587  _Copy_ctor_base(const _Copy_ctor_base& __rhs)
588  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
589  {
590  __variant::__raw_idx_visit(
591  [this](auto&& __rhs_mem, auto __rhs_index) mutable
592  {
593  constexpr size_t __j = __rhs_index;
594  if constexpr (__j != variant_npos)
595  std::_Construct(std::__addressof(this->_M_u),
596  in_place_index<__j>, __rhs_mem);
597  }, __variant_cast<_Types...>(__rhs));
598  this->_M_index = __rhs._M_index;
599  }
600 
601  _Copy_ctor_base(_Copy_ctor_base&&) = default;
602  _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
603  _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
604  };
605 
606  template<typename... _Types>
607  struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
608  {
609  using _Base = _Variant_storage_alias<_Types...>;
610  using _Base::_Base;
611  };
612 
613  template<typename... _Types>
614  using _Copy_ctor_alias =
615  _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
616 
617  template<bool, typename... _Types>
618  struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
619  {
620  using _Base = _Copy_ctor_alias<_Types...>;
621  using _Base::_Base;
622 
623  _GLIBCXX20_CONSTEXPR
624  _Move_ctor_base(_Move_ctor_base&& __rhs)
625  noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
626  {
627  __variant::__raw_idx_visit(
628  [this](auto&& __rhs_mem, auto __rhs_index) mutable
629  {
630  constexpr size_t __j = __rhs_index;
631  if constexpr (__j != variant_npos)
632  std::_Construct(std::__addressof(this->_M_u),
633  in_place_index<__j>,
634  std::forward<decltype(__rhs_mem)>(__rhs_mem));
635  }, __variant_cast<_Types...>(std::move(__rhs)));
636  this->_M_index = __rhs._M_index;
637  }
638 
639  _Move_ctor_base(const _Move_ctor_base&) = default;
640  _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
641  _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
642  };
643 
644  template<typename... _Types>
645  struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
646  {
647  using _Base = _Copy_ctor_alias<_Types...>;
648  using _Base::_Base;
649  };
650 
651  template<typename... _Types>
652  using _Move_ctor_alias =
653  _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
654 
655  template<bool, typename... _Types>
656  struct _Copy_assign_base : _Move_ctor_alias<_Types...>
657  {
658  using _Base = _Move_ctor_alias<_Types...>;
659  using _Base::_Base;
660 
661  _GLIBCXX20_CONSTEXPR
662  _Copy_assign_base&
663  operator=(const _Copy_assign_base& __rhs)
664  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
665  {
666  __variant::__raw_idx_visit(
667  [this](auto&& __rhs_mem, auto __rhs_index) mutable
668  {
669  constexpr size_t __j = __rhs_index;
670  if constexpr (__j == variant_npos)
671  this->_M_reset(); // Make *this valueless.
672  else if (this->_M_index == __j)
673  __variant::__get<__j>(*this) = __rhs_mem;
674  else
675  {
676  using _Tj = typename _Nth_type<__j, _Types...>::type;
677  if constexpr (is_nothrow_copy_constructible_v<_Tj>
678  || !is_nothrow_move_constructible_v<_Tj>)
679  __variant::__emplace<__j>(*this, __rhs_mem);
680  else
681  {
682  using _Variant = variant<_Types...>;
683  _Variant& __self = __variant_cast<_Types...>(*this);
684  __self = _Variant(in_place_index<__j>, __rhs_mem);
685  }
686  }
687  }, __variant_cast<_Types...>(__rhs));
688  return *this;
689  }
690 
691  _Copy_assign_base(const _Copy_assign_base&) = default;
692  _Copy_assign_base(_Copy_assign_base&&) = default;
693  _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
694  };
695 
696  template<typename... _Types>
697  struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
698  {
699  using _Base = _Move_ctor_alias<_Types...>;
700  using _Base::_Base;
701  };
702 
703  template<typename... _Types>
704  using _Copy_assign_alias =
705  _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
706 
707  template<bool, typename... _Types>
708  struct _Move_assign_base : _Copy_assign_alias<_Types...>
709  {
710  using _Base = _Copy_assign_alias<_Types...>;
711  using _Base::_Base;
712 
713  _GLIBCXX20_CONSTEXPR
714  _Move_assign_base&
715  operator=(_Move_assign_base&& __rhs)
716  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
717  {
718  __variant::__raw_idx_visit(
719  [this](auto&& __rhs_mem, auto __rhs_index) mutable
720  {
721  constexpr size_t __j = __rhs_index;
722  if constexpr (__j != variant_npos)
723  {
724  if (this->_M_index == __j)
725  __variant::__get<__j>(*this) = std::move(__rhs_mem);
726  else
727  {
728  using _Tj = typename _Nth_type<__j, _Types...>::type;
729  if constexpr (is_nothrow_move_constructible_v<_Tj>)
730  __variant::__emplace<__j>(*this, std::move(__rhs_mem));
731  else
732  {
733  using _Variant = variant<_Types...>;
734  _Variant& __self = __variant_cast<_Types...>(*this);
735  __self.template emplace<__j>(std::move(__rhs_mem));
736  }
737  }
738  }
739  else
740  this->_M_reset();
741  }, __variant_cast<_Types...>(__rhs));
742  return *this;
743  }
744 
745  _Move_assign_base(const _Move_assign_base&) = default;
746  _Move_assign_base(_Move_assign_base&&) = default;
747  _Move_assign_base& operator=(const _Move_assign_base&) = default;
748  };
749 
750  template<typename... _Types>
751  struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
752  {
753  using _Base = _Copy_assign_alias<_Types...>;
754  using _Base::_Base;
755  };
756 
757  template<typename... _Types>
758  using _Move_assign_alias =
759  _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
760 
761  template<typename... _Types>
762  struct _Variant_base : _Move_assign_alias<_Types...>
763  {
764  using _Base = _Move_assign_alias<_Types...>;
765 
766  constexpr
767  _Variant_base() noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
768  : _Variant_base(in_place_index<0>) { }
769 
770  template<size_t _Np, typename... _Args>
771  constexpr explicit
772  _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
773  : _Base(__i, std::forward<_Args>(__args)...)
774  { }
775 
776  _Variant_base(const _Variant_base&) = default;
777  _Variant_base(_Variant_base&&) = default;
778  _Variant_base& operator=(const _Variant_base&) = default;
779  _Variant_base& operator=(_Variant_base&&) = default;
780  };
781 
782  template<typename _Tp, typename... _Types>
783  inline constexpr bool __exactly_once
784  = std::__find_uniq_type_in_pack<_Tp, _Types...>() < sizeof...(_Types);
785 
786  // Helper used to check for valid conversions that don't involve narrowing.
787  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
788 
789  // "Build an imaginary function FUN(Ti) for each alternative type Ti"
790  template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
791  struct _Build_FUN
792  {
793  // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
794  // but only static functions will be considered in the call below.
795  void _S_fun() = delete;
796  };
797 
798  // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
799  template<size_t _Ind, typename _Tp, typename _Ti>
800  struct _Build_FUN<_Ind, _Tp, _Ti,
801  void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
802  {
803  // This is the FUN function for type _Ti, with index _Ind
804  static integral_constant<size_t, _Ind> _S_fun(_Ti);
805  };
806 
807  template<typename _Tp, typename _Variant,
808  typename = make_index_sequence<variant_size_v<_Variant>>>
809  struct _Build_FUNs;
810 
811  template<typename _Tp, typename... _Ti, size_t... _Ind>
812  struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
813  : _Build_FUN<_Ind, _Tp, _Ti>...
814  {
815  using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
816  };
817 
818  // The index j of the overload FUN(Tj) selected by overload resolution
819  // for FUN(std::forward<_Tp>(t))
820  template<typename _Tp, typename _Variant>
821  using _FUN_type
822  = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
823 
824  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
825  template<typename _Tp, typename _Variant, typename = void>
826  inline constexpr size_t
827  __accepted_index = variant_npos;
828 
829  template<typename _Tp, typename _Variant>
830  inline constexpr size_t
831  __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
832  = _FUN_type<_Tp, _Variant>::value;
833 
834  template<typename _Maybe_variant_cookie, typename _Variant,
835  typename = __remove_cvref_t<_Variant>>
836  inline constexpr bool
837  __extra_visit_slot_needed = false;
838 
839  template<typename _Var, typename... _Types>
840  inline constexpr bool
841  __extra_visit_slot_needed<__variant_cookie, _Var, variant<_Types...>>
842  = !__variant::__never_valueless<_Types...>();
843 
844  template<typename _Var, typename... _Types>
845  inline constexpr bool
846  __extra_visit_slot_needed<__variant_idx_cookie, _Var, variant<_Types...>>
847  = !__variant::__never_valueless<_Types...>();
848 
849  // Used for storing a multi-dimensional vtable.
850  template<typename _Tp, size_t... _Dimensions>
851  struct _Multi_array;
852 
853  // Partial specialization with rank zero, stores a single _Tp element.
854  template<typename _Tp>
855  struct _Multi_array<_Tp>
856  {
857  template<typename>
858  struct __untag_result
859  : false_type
860  { using element_type = _Tp; };
861 
862 #pragma GCC diagnostic push
863 #pragma GCC diagnostic ignored "-Wignored-qualifiers"
864  template <typename... _Args>
865  struct __untag_result<const void(*)(_Args...)>
866  : false_type
867  { using element_type = void(*)(_Args...); };
868 #pragma GCC diagnostic pop
869 
870  template <typename... _Args>
871  struct __untag_result<__variant_cookie(*)(_Args...)>
872  : false_type
873  { using element_type = void(*)(_Args...); };
874 
875  template <typename... _Args>
876  struct __untag_result<__variant_idx_cookie(*)(_Args...)>
877  : false_type
878  { using element_type = void(*)(_Args...); };
879 
880  template <typename _Res, typename... _Args>
881  struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
882  : true_type
883  { using element_type = _Res(*)(_Args...); };
884 
885  using __result_is_deduced = __untag_result<_Tp>;
886 
887  constexpr const typename __untag_result<_Tp>::element_type&
888  _M_access() const
889  { return _M_data; }
890 
891  typename __untag_result<_Tp>::element_type _M_data;
892  };
893 
894  // Partial specialization with rank >= 1.
895  template<typename _Ret,
896  typename _Visitor,
897  typename... _Variants,
898  size_t __first, size_t... __rest>
899  struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
900  {
901  static constexpr size_t __index =
902  sizeof...(_Variants) - sizeof...(__rest) - 1;
903 
904  using _Variant = typename _Nth_type<__index, _Variants...>::type;
905 
906  static constexpr int __do_cookie =
907  __extra_visit_slot_needed<_Ret, _Variant> ? 1 : 0;
908 
909  using _Tp = _Ret(*)(_Visitor, _Variants...);
910 
911  template<typename... _Args>
912  constexpr decltype(auto)
913  _M_access(size_t __first_index, _Args... __rest_indices) const
914  {
915  return _M_arr[__first_index + __do_cookie]
916  ._M_access(__rest_indices...);
917  }
918 
919  _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
920  };
921 
922  // Creates a multi-dimensional vtable recursively.
923  //
924  // For example,
925  // visit([](auto, auto){},
926  // variant<int, char>(), // typedef'ed as V1
927  // variant<float, double, long double>()) // typedef'ed as V2
928  // will trigger instantiations of:
929  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
930  // tuple<V1&&, V2&&>, std::index_sequence<>>
931  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
932  // tuple<V1&&, V2&&>, std::index_sequence<0>>
933  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
934  // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
935  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
936  // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
937  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
938  // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
939  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
940  // tuple<V1&&, V2&&>, std::index_sequence<1>>
941  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
942  // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
943  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
944  // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
945  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
946  // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
947  // The returned multi-dimensional vtable can be fast accessed by the visitor
948  // using index calculation.
949  template<typename _Array_type, typename _Index_seq>
950  struct __gen_vtable_impl;
951 
952  // Defines the _S_apply() member that returns a _Multi_array populated
953  // with function pointers that perform the visitation expressions e(m)
954  // for each valid pack of indexes into the variant types _Variants.
955  //
956  // This partial specialization builds up the index sequences by recursively
957  // calling _S_apply() on the next specialization of __gen_vtable_impl.
958  // The base case of the recursion defines the actual function pointers.
959  template<typename _Result_type, typename _Visitor, size_t... __dimensions,
960  typename... _Variants, size_t... __indices>
961  struct __gen_vtable_impl<
962  _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
963  std::index_sequence<__indices...>>
964  {
965  using _Next =
966  remove_reference_t<typename _Nth_type<sizeof...(__indices),
967  _Variants...>::type>;
968  using _Array_type =
969  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
970  __dimensions...>;
971 
972  static constexpr _Array_type
973  _S_apply()
974  {
975  _Array_type __vtable{};
976  _S_apply_all_alts(
977  __vtable, make_index_sequence<variant_size_v<_Next>>());
978  return __vtable;
979  }
980 
981  template<size_t... __var_indices>
982  static constexpr void
983  _S_apply_all_alts(_Array_type& __vtable,
984  std::index_sequence<__var_indices...>)
985  {
986  if constexpr (__extra_visit_slot_needed<_Result_type, _Next>)
987  (_S_apply_single_alt<true, __var_indices>(
988  __vtable._M_arr[__var_indices + 1],
989  &(__vtable._M_arr[0])), ...);
990  else
991  (_S_apply_single_alt<false, __var_indices>(
992  __vtable._M_arr[__var_indices]), ...);
993  }
994 
995  template<bool __do_cookie, size_t __index, typename _Tp>
996  static constexpr void
997  _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
998  {
999  if constexpr (__do_cookie)
1000  {
1001  __element = __gen_vtable_impl<
1002  _Tp,
1003  std::index_sequence<__indices..., __index>>::_S_apply();
1004  *__cookie_element = __gen_vtable_impl<
1005  _Tp,
1006  std::index_sequence<__indices..., variant_npos>>::_S_apply();
1007  }
1008  else
1009  {
1010  auto __tmp_element = __gen_vtable_impl<
1011  remove_reference_t<decltype(__element)>,
1012  std::index_sequence<__indices..., __index>>::_S_apply();
1013  static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
1014  "std::visit requires the visitor to have the same "
1015  "return type for all alternatives of a variant");
1016  __element = __tmp_element;
1017  }
1018  }
1019  };
1020 
1021  // This partial specialization is the base case for the recursion.
1022  // It populates a _Multi_array element with the address of a function
1023  // that invokes the visitor with the alternatives specified by __indices.
1024  template<typename _Result_type, typename _Visitor, typename... _Variants,
1025  size_t... __indices>
1026  struct __gen_vtable_impl<
1027  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
1028  std::index_sequence<__indices...>>
1029  {
1030  using _Array_type =
1031  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
1032 
1033  template<size_t __index, typename _Variant>
1034  static constexpr decltype(auto)
1035  __element_by_index_or_cookie(_Variant&& __var) noexcept
1036  {
1037  if constexpr (__index != variant_npos)
1038  return __variant::__get<__index>(std::forward<_Variant>(__var));
1039  else
1040  return __variant_cookie{};
1041  }
1042 
1043  static constexpr decltype(auto)
1044  __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1045  {
1046  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1047  // For raw visitation using indices, pass the indices to the visitor
1048  // and discard the return value:
1049  std::__invoke(std::forward<_Visitor>(__visitor),
1050  __element_by_index_or_cookie<__indices>(
1051  std::forward<_Variants>(__vars))...,
1052  integral_constant<size_t, __indices>()...);
1053  else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1054  // For raw visitation without indices, and discard the return value:
1055  std::__invoke(std::forward<_Visitor>(__visitor),
1056  __element_by_index_or_cookie<__indices>(
1057  std::forward<_Variants>(__vars))...);
1058  else if constexpr (_Array_type::__result_is_deduced::value)
1059  // For the usual std::visit case deduce the return value:
1060  return std::__invoke(std::forward<_Visitor>(__visitor),
1061  __element_by_index_or_cookie<__indices>(
1062  std::forward<_Variants>(__vars))...);
1063  else // for std::visit<R> use INVOKE<R>
1064  return std::__invoke_r<_Result_type>(
1065  std::forward<_Visitor>(__visitor),
1066  __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1067  }
1068 
1069  static constexpr auto
1070  _S_apply()
1071  {
1072  if constexpr (_Array_type::__result_is_deduced::value)
1073  {
1074  constexpr bool __visit_ret_type_mismatch =
1075  !is_same_v<typename _Result_type::type,
1076  decltype(__visit_invoke(std::declval<_Visitor>(),
1077  std::declval<_Variants>()...))>;
1078  if constexpr (__visit_ret_type_mismatch)
1079  {
1080  struct __cannot_match {};
1081  return __cannot_match{};
1082  }
1083  else
1084  return _Array_type{&__visit_invoke};
1085  }
1086  else
1087  return _Array_type{&__visit_invoke};
1088  }
1089  };
1090 
1091  template<typename _Result_type, typename _Visitor, typename... _Variants>
1092  struct __gen_vtable
1093  {
1094  using _Array_type =
1095  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1096  variant_size_v<remove_reference_t<_Variants>>...>;
1097 
1098  static constexpr _Array_type _S_vtable
1099  = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1100  };
1101 
1102  template<size_t _Np, typename _Tp>
1103  struct _Base_dedup : public _Tp { };
1104 
1105  template<typename _Variant, typename __indices>
1106  struct _Variant_hash_base;
1107 
1108  template<typename... _Types, size_t... __indices>
1109  struct _Variant_hash_base<variant<_Types...>,
1110  std::index_sequence<__indices...>>
1111  : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1112 
1113  // Equivalent to decltype(get<_Np>(as-variant(declval<_Variant>())))
1114  template<size_t _Np, typename _Variant,
1115  typename _AsV = decltype(__variant::__as(std::declval<_Variant>())),
1116  typename _Tp = variant_alternative_t<_Np, remove_reference_t<_AsV>>>
1117  using __get_t
1118  = __conditional_t<is_lvalue_reference_v<_Variant>, _Tp&, _Tp&&>;
1119 
1120  // Return type of std::visit.
1121  template<typename _Visitor, typename... _Variants>
1122  using __visit_result_t
1123  = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1124 
1125  template<typename _Tp, typename... _Types>
1126  constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
1127 
1128  template <typename _Visitor, typename _Variant, size_t... _Idxs>
1129  constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
1130  {
1131  return __same_types<
1132  invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
1133  >;
1134  }
1135 
1136 } // namespace __variant
1137 } // namespace __detail
1138 
1139  template<typename _Tp, typename... _Types>
1140  constexpr bool
1141  holds_alternative(const variant<_Types...>& __v) noexcept
1142  {
1143  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1144  "T must occur exactly once in alternatives");
1145  return __v.index() == std::__find_uniq_type_in_pack<_Tp, _Types...>();
1146  }
1147 
1148  template<typename _Tp, typename... _Types>
1149  constexpr _Tp&
1150  get(variant<_Types...>& __v)
1151  {
1152  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1153  "T must occur exactly once in alternatives");
1154  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1155  return std::get<__n>(__v);
1156  }
1157 
1158  template<typename _Tp, typename... _Types>
1159  constexpr _Tp&&
1160  get(variant<_Types...>&& __v)
1161  {
1162  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1163  "T must occur exactly once in alternatives");
1164  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1165  return std::get<__n>(std::move(__v));
1166  }
1167 
1168  template<typename _Tp, typename... _Types>
1169  constexpr const _Tp&
1170  get(const variant<_Types...>& __v)
1171  {
1172  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1173  "T must occur exactly once in alternatives");
1174  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1175  return std::get<__n>(__v);
1176  }
1177 
1178  template<typename _Tp, typename... _Types>
1179  constexpr const _Tp&&
1180  get(const variant<_Types...>&& __v)
1181  {
1182  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1183  "T must occur exactly once in alternatives");
1184  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1185  return std::get<__n>(std::move(__v));
1186  }
1187 
1188  template<size_t _Np, typename... _Types>
1189  constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1190  get_if(variant<_Types...>* __ptr) noexcept
1191  {
1192  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1193  static_assert(_Np < sizeof...(_Types),
1194  "The index must be in [0, number of alternatives)");
1195  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1196  if (__ptr && __ptr->index() == _Np)
1197  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1198  return nullptr;
1199  }
1200 
1201  template<size_t _Np, typename... _Types>
1202  constexpr
1203  add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1204  get_if(const variant<_Types...>* __ptr) noexcept
1205  {
1206  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1207  static_assert(_Np < sizeof...(_Types),
1208  "The index must be in [0, number of alternatives)");
1209  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1210  if (__ptr && __ptr->index() == _Np)
1211  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1212  return nullptr;
1213  }
1214 
1215  template<typename _Tp, typename... _Types>
1216  constexpr add_pointer_t<_Tp>
1217  get_if(variant<_Types...>* __ptr) noexcept
1218  {
1219  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1220  "T must occur exactly once in alternatives");
1221  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1222  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1223  return std::get_if<__n>(__ptr);
1224  }
1225 
1226  template<typename _Tp, typename... _Types>
1227  constexpr add_pointer_t<const _Tp>
1228  get_if(const variant<_Types...>* __ptr) noexcept
1229  {
1230  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1231  "T must occur exactly once in alternatives");
1232  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1233  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1234  return std::get_if<__n>(__ptr);
1235  }
1236 
1237  struct monostate { };
1238 
1239 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1240  template<typename... _Types> \
1241  constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1242  const variant<_Types...>& __rhs) \
1243  { \
1244  bool __ret = true; \
1245  __detail::__variant::__raw_idx_visit( \
1246  [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1247  { \
1248  if constexpr (__rhs_index != variant_npos) \
1249  { \
1250  if (__lhs.index() == __rhs_index) \
1251  { \
1252  auto& __this_mem = std::get<__rhs_index>(__lhs); \
1253  __ret = __this_mem __OP __rhs_mem; \
1254  } \
1255  else \
1256  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1257  } \
1258  else \
1259  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1260  }, __rhs); \
1261  return __ret; \
1262  }
1263 
1264  _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1265  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1266  _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1267  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1268  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1269  _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1270 
1271 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1272 
1273  constexpr bool operator==(monostate, monostate) noexcept { return true; }
1274 
1275 #ifdef __cpp_lib_three_way_comparison
1276  template<typename... _Types>
1277  requires (three_way_comparable<_Types> && ...)
1278  constexpr
1279  common_comparison_category_t<compare_three_way_result_t<_Types>...>
1280  operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1281  {
1282  common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1283  = strong_ordering::equal;
1284 
1285  __detail::__variant::__raw_idx_visit(
1286  [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1287  {
1288  if constexpr (__w_index != variant_npos)
1289  {
1290  if (__v.index() == __w_index)
1291  {
1292  auto& __this_mem = std::get<__w_index>(__v);
1293  __ret = __this_mem <=> __w_mem;
1294  return;
1295  }
1296  }
1297  __ret = (__v.index() + 1) <=> (__w_index + 1);
1298  }, __w);
1299  return __ret;
1300  }
1301 
1302  constexpr strong_ordering
1303  operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1304 #else
1305  constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1306  constexpr bool operator<(monostate, monostate) noexcept { return false; }
1307  constexpr bool operator>(monostate, monostate) noexcept { return false; }
1308  constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1309  constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1310 #endif
1311 
1312  template<typename _Visitor, typename... _Variants>
1313  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1314  visit(_Visitor&&, _Variants&&...);
1315 
1316  template<typename... _Types>
1317  _GLIBCXX20_CONSTEXPR
1318  inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1319  && (is_swappable_v<_Types> && ...)>
1320  swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1321  noexcept(noexcept(__lhs.swap(__rhs)))
1322  { __lhs.swap(__rhs); }
1323 
1324  template<typename... _Types>
1325  enable_if_t<!((is_move_constructible_v<_Types> && ...)
1326  && (is_swappable_v<_Types> && ...))>
1327  swap(variant<_Types...>&, variant<_Types...>&) = delete;
1328 
1329  class bad_variant_access : public exception
1330  {
1331  public:
1332  bad_variant_access() noexcept { }
1333 
1334  const char* what() const noexcept override
1335  { return _M_reason; }
1336 
1337  private:
1338  bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1339 
1340  // Must point to a string with static storage duration:
1341  const char* _M_reason = "bad variant access";
1342 
1343  friend void __throw_bad_variant_access(const char* __what);
1344  };
1345 
1346  // Must only be called with a string literal
1347  inline void
1348  __throw_bad_variant_access(const char* __what)
1349  { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1350 
1351  inline void
1352  __throw_bad_variant_access(bool __valueless)
1353  {
1354  if (__valueless) [[__unlikely__]]
1355  __throw_bad_variant_access("std::get: variant is valueless");
1356  else
1357  __throw_bad_variant_access("std::get: wrong index for variant");
1358  }
1359 
1360  template<typename... _Types>
1361  class variant
1362  : private __detail::__variant::_Variant_base<_Types...>,
1363  private _Enable_default_constructor<
1364  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1365  variant<_Types...>>,
1366  private _Enable_copy_move<
1367  __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1368  __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1369  __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1370  __detail::__variant::_Traits<_Types...>::_S_move_assign,
1371  variant<_Types...>>
1372  {
1373  private:
1374  template <typename... _UTypes, typename _Tp>
1375  friend _GLIBCXX20_CONSTEXPR decltype(auto)
1376  __variant_cast(_Tp&&);
1377 
1378  static_assert(sizeof...(_Types) > 0,
1379  "variant must have at least one alternative");
1380  static_assert(!(std::is_reference_v<_Types> || ...),
1381  "variant must have no reference alternative");
1382  static_assert(!(std::is_void_v<_Types> || ...),
1383  "variant must have no void alternative");
1384 
1385  using _Base = __detail::__variant::_Variant_base<_Types...>;
1386  using _Default_ctor_enabler =
1387  _Enable_default_constructor<
1388  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1389  variant<_Types...>>;
1390 
1391  template<typename _Tp>
1392  static constexpr bool __not_self
1393  = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1394 
1395  template<typename _Tp>
1396  static constexpr bool
1397  __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1398 
1399  template<typename _Tp>
1400  static constexpr size_t __accepted_index
1401  = __detail::__variant::__accepted_index<_Tp, variant>;
1402 
1403  template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1404  using __to_type = typename _Nth_type<_Np, _Types...>::type;
1405 
1406  template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1407  using __accepted_type = __to_type<__accepted_index<_Tp>>;
1408 
1409  template<typename _Tp>
1410  static constexpr size_t __index_of
1411  = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1412 
1413  using _Traits = __detail::__variant::_Traits<_Types...>;
1414 
1415  template<typename _Tp>
1416  struct __is_in_place_tag : false_type { };
1417  template<typename _Tp>
1418  struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1419  template<size_t _Np>
1420  struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1421 
1422  template<typename _Tp>
1423  static constexpr bool __not_in_place_tag
1424  = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1425 
1426  public:
1427  variant() = default;
1428  variant(const variant& __rhs) = default;
1429  variant(variant&&) = default;
1430  variant& operator=(const variant&) = default;
1431  variant& operator=(variant&&) = default;
1432  _GLIBCXX20_CONSTEXPR ~variant() = default;
1433 
1434  template<typename _Tp,
1435  typename = enable_if_t<sizeof...(_Types) != 0>,
1436  typename = enable_if_t<__not_in_place_tag<_Tp>>,
1437  typename _Tj = __accepted_type<_Tp&&>,
1438  typename = enable_if_t<__exactly_once<_Tj>
1439  && is_constructible_v<_Tj, _Tp>>>
1440  constexpr
1441  variant(_Tp&& __t)
1442  noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1443  : variant(in_place_index<__accepted_index<_Tp>>,
1444  std::forward<_Tp>(__t))
1445  { }
1446 
1447  template<typename _Tp, typename... _Args,
1448  typename = enable_if_t<__exactly_once<_Tp>
1449  && is_constructible_v<_Tp, _Args...>>>
1450  constexpr explicit
1451  variant(in_place_type_t<_Tp>, _Args&&... __args)
1452  : variant(in_place_index<__index_of<_Tp>>,
1453  std::forward<_Args>(__args)...)
1454  { }
1455 
1456  template<typename _Tp, typename _Up, typename... _Args,
1457  typename = enable_if_t<__exactly_once<_Tp>
1458  && is_constructible_v<_Tp,
1459  initializer_list<_Up>&, _Args...>>>
1460  constexpr explicit
1461  variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1462  _Args&&... __args)
1463  : variant(in_place_index<__index_of<_Tp>>, __il,
1464  std::forward<_Args>(__args)...)
1465  { }
1466 
1467  template<size_t _Np, typename... _Args,
1468  typename _Tp = __to_type<_Np>,
1469  typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1470  constexpr explicit
1471  variant(in_place_index_t<_Np>, _Args&&... __args)
1472  : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1473  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1474  { }
1475 
1476  template<size_t _Np, typename _Up, typename... _Args,
1477  typename _Tp = __to_type<_Np>,
1478  typename = enable_if_t<is_constructible_v<_Tp,
1479  initializer_list<_Up>&,
1480  _Args...>>>
1481  constexpr explicit
1482  variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1483  _Args&&... __args)
1484  : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1485  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1486  { }
1487 
1488  template<typename _Tp>
1489  _GLIBCXX20_CONSTEXPR
1490  enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1491  && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1492  && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1493  variant&>
1494  operator=(_Tp&& __rhs)
1495  noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1496  && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1497  {
1498  constexpr auto __index = __accepted_index<_Tp>;
1499  if (index() == __index)
1500  std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1501  else
1502  {
1503  using _Tj = __accepted_type<_Tp&&>;
1504  if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1505  || !is_nothrow_move_constructible_v<_Tj>)
1506  this->emplace<__index>(std::forward<_Tp>(__rhs));
1507  else
1508  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1509  // 3585. converting assignment with immovable alternative
1510  this->emplace<__index>(_Tj(std::forward<_Tp>(__rhs)));
1511  }
1512  return *this;
1513  }
1514 
1515  template<typename _Tp, typename... _Args>
1516  _GLIBCXX20_CONSTEXPR
1517  enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1518  _Tp&>
1519  emplace(_Args&&... __args)
1520  {
1521  constexpr size_t __index = __index_of<_Tp>;
1522  return this->emplace<__index>(std::forward<_Args>(__args)...);
1523  }
1524 
1525  template<typename _Tp, typename _Up, typename... _Args>
1526  _GLIBCXX20_CONSTEXPR
1527  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1528  && __exactly_once<_Tp>,
1529  _Tp&>
1530  emplace(initializer_list<_Up> __il, _Args&&... __args)
1531  {
1532  constexpr size_t __index = __index_of<_Tp>;
1533  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1534  }
1535 
1536  template<size_t _Np, typename... _Args>
1537  _GLIBCXX20_CONSTEXPR
1538  enable_if_t<is_constructible_v<__to_type<_Np>, _Args...>,
1539  __to_type<_Np>&>
1540  emplace(_Args&&... __args)
1541  {
1542  namespace __variant = std::__detail::__variant;
1543  using type = typename _Nth_type<_Np, _Types...>::type;
1544  // Provide the strong exception-safety guarantee when possible,
1545  // to avoid becoming valueless.
1546  if constexpr (is_nothrow_constructible_v<type, _Args...>)
1547  {
1548  __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1549  }
1550  else if constexpr (is_scalar_v<type>)
1551  {
1552  // This might invoke a potentially-throwing conversion operator:
1553  const type __tmp(std::forward<_Args>(__args)...);
1554  // But this won't throw:
1555  __variant::__emplace<_Np>(*this, __tmp);
1556  }
1557  else if constexpr (__variant::_Never_valueless_alt<type>()
1558  && _Traits::_S_move_assign)
1559  {
1560  // This construction might throw:
1561  variant __tmp(in_place_index<_Np>,
1562  std::forward<_Args>(__args)...);
1563  // But _Never_valueless_alt<type> means this won't:
1564  *this = std::move(__tmp);
1565  }
1566  else
1567  {
1568  // This case only provides the basic exception-safety guarantee,
1569  // i.e. the variant can become valueless.
1570  __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1571  }
1572  return std::get<_Np>(*this);
1573  }
1574 
1575  template<size_t _Np, typename _Up, typename... _Args>
1576  _GLIBCXX20_CONSTEXPR
1577  enable_if_t<is_constructible_v<__to_type<_Np>,
1578  initializer_list<_Up>&, _Args...>,
1579  __to_type<_Np>&>
1580  emplace(initializer_list<_Up> __il, _Args&&... __args)
1581  {
1582  namespace __variant = std::__detail::__variant;
1583  using type = typename _Nth_type<_Np, _Types...>::type;
1584  // Provide the strong exception-safety guarantee when possible,
1585  // to avoid becoming valueless.
1586  if constexpr (is_nothrow_constructible_v<type,
1587  initializer_list<_Up>&,
1588  _Args...>)
1589  {
1590  __variant::__emplace<_Np>(*this, __il,
1591  std::forward<_Args>(__args)...);
1592  }
1593  else if constexpr (__variant::_Never_valueless_alt<type>()
1594  && _Traits::_S_move_assign)
1595  {
1596  // This construction might throw:
1597  variant __tmp(in_place_index<_Np>, __il,
1598  std::forward<_Args>(__args)...);
1599  // But _Never_valueless_alt<type> means this won't:
1600  *this = std::move(__tmp);
1601  }
1602  else
1603  {
1604  // This case only provides the basic exception-safety guarantee,
1605  // i.e. the variant can become valueless.
1606  __variant::__emplace<_Np>(*this, __il,
1607  std::forward<_Args>(__args)...);
1608  }
1609  return std::get<_Np>(*this);
1610  }
1611 
1612  template<size_t _Np, typename... _Args>
1613  enable_if_t<!(_Np < sizeof...(_Types))> emplace(_Args&&...) = delete;
1614 
1615  template<typename _Tp, typename... _Args>
1616  enable_if_t<!__exactly_once<_Tp>> emplace(_Args&&...) = delete;
1617 
1618  constexpr bool valueless_by_exception() const noexcept
1619  { return !this->_M_valid(); }
1620 
1621  constexpr size_t index() const noexcept
1622  {
1623  using __index_type = typename _Base::__index_type;
1624  if constexpr (__detail::__variant::__never_valueless<_Types...>())
1625  return this->_M_index;
1626  else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1627  return make_signed_t<__index_type>(this->_M_index);
1628  else
1629  return size_t(__index_type(this->_M_index + 1)) - 1;
1630  }
1631 
1632  _GLIBCXX20_CONSTEXPR
1633  void
1634  swap(variant& __rhs)
1635  noexcept((__is_nothrow_swappable<_Types>::value && ...)
1636  && is_nothrow_move_constructible_v<variant>)
1637  {
1638  static_assert((is_move_constructible_v<_Types> && ...));
1639 
1640  // Handle this here to simplify the visitation.
1641  if (__rhs.valueless_by_exception()) [[__unlikely__]]
1642  {
1643  if (!this->valueless_by_exception()) [[__likely__]]
1644  __rhs.swap(*this);
1645  return;
1646  }
1647 
1648  namespace __variant = __detail::__variant;
1649 
1650  __variant::__raw_idx_visit(
1651  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1652  {
1653  constexpr size_t __j = __rhs_index;
1654  if constexpr (__j != variant_npos)
1655  {
1656  if (this->index() == __j)
1657  {
1658  using std::swap;
1659  swap(std::get<__j>(*this), __rhs_mem);
1660  }
1661  else
1662  {
1663  auto __tmp(std::move(__rhs_mem));
1664 
1665  if constexpr (_Traits::_S_trivial_move_assign)
1666  __rhs = std::move(*this);
1667  else
1668  __variant::__raw_idx_visit(
1669  [&__rhs](auto&& __this_mem, auto __this_index) mutable
1670  {
1671  constexpr size_t __k = __this_index;
1672  if constexpr (__k != variant_npos)
1673  __variant::__emplace<__k>(__rhs,
1674  std::move(__this_mem));
1675  }, *this);
1676 
1677  __variant::__emplace<__j>(*this, std::move(__tmp));
1678  }
1679  }
1680  }, __rhs);
1681  }
1682 
1683 #if defined(__clang__) && __clang_major__ <= 7
1684  public:
1685  using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1686 #endif
1687 
1688  private:
1689  template<size_t _Np, typename _Vp>
1690  friend constexpr decltype(auto)
1691  __detail::__variant::__get(_Vp&& __v) noexcept;
1692 
1693 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1694  template<typename... _Tp> \
1695  friend constexpr bool \
1696  operator __OP(const variant<_Tp...>& __lhs, \
1697  const variant<_Tp...>& __rhs);
1698 
1699  _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1700  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1701  _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1702  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1703  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1704  _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1705 
1706 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1707  };
1708 
1709  template<size_t _Np, typename... _Types>
1710  constexpr variant_alternative_t<_Np, variant<_Types...>>&
1711  get(variant<_Types...>& __v)
1712  {
1713  static_assert(_Np < sizeof...(_Types),
1714  "The index must be in [0, number of alternatives)");
1715  if (__v.index() != _Np)
1716  __throw_bad_variant_access(__v.valueless_by_exception());
1717  return __detail::__variant::__get<_Np>(__v);
1718  }
1719 
1720  template<size_t _Np, typename... _Types>
1721  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1722  get(variant<_Types...>&& __v)
1723  {
1724  static_assert(_Np < sizeof...(_Types),
1725  "The index must be in [0, number of alternatives)");
1726  if (__v.index() != _Np)
1727  __throw_bad_variant_access(__v.valueless_by_exception());
1728  return __detail::__variant::__get<_Np>(std::move(__v));
1729  }
1730 
1731  template<size_t _Np, typename... _Types>
1732  constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1733  get(const variant<_Types...>& __v)
1734  {
1735  static_assert(_Np < sizeof...(_Types),
1736  "The index must be in [0, number of alternatives)");
1737  if (__v.index() != _Np)
1738  __throw_bad_variant_access(__v.valueless_by_exception());
1739  return __detail::__variant::__get<_Np>(__v);
1740  }
1741 
1742  template<size_t _Np, typename... _Types>
1743  constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1744  get(const variant<_Types...>&& __v)
1745  {
1746  static_assert(_Np < sizeof...(_Types),
1747  "The index must be in [0, number of alternatives)");
1748  if (__v.index() != _Np)
1749  __throw_bad_variant_access(__v.valueless_by_exception());
1750  return __detail::__variant::__get<_Np>(std::move(__v));
1751  }
1752 
1753  /// @cond undocumented
1754  template<typename _Result_type, typename _Visitor, typename... _Variants>
1755  constexpr decltype(auto)
1756  __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1757  {
1758  // Get the silly case of visiting no variants out of the way first.
1759  if constexpr (sizeof...(_Variants) == 0)
1760  {
1761  if constexpr (is_void_v<_Result_type>)
1762  return (void) std::forward<_Visitor>(__visitor)();
1763  else
1764  return std::forward<_Visitor>(__visitor)();
1765  }
1766  else
1767  {
1768  constexpr size_t __max = 11; // "These go to eleven."
1769 
1770  // The type of the first variant in the pack.
1771  using _V0 = typename _Nth_type<0, _Variants...>::type;
1772  // The number of alternatives in that first variant.
1773  constexpr auto __n = variant_size_v<remove_reference_t<_V0>>;
1774 
1775  if constexpr (sizeof...(_Variants) > 1 || __n > __max)
1776  {
1777  // Use a jump table for the general case.
1778  constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1779  _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1780 
1781  auto __func_ptr = __vtable._M_access(__variants.index()...);
1782  return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1783  std::forward<_Variants>(__variants)...);
1784  }
1785  else // We have a single variant with a small number of alternatives.
1786  {
1787  // A name for the first variant in the pack.
1788  _V0& __v0
1789  = [](_V0& __v, ...) -> _V0& { return __v; }(__variants...);
1790 
1791  using __detail::__variant::_Multi_array;
1792  using __detail::__variant::__gen_vtable_impl;
1793  using _Ma = _Multi_array<_Result_type (*)(_Visitor&&, _V0&&)>;
1794 
1795 #ifdef _GLIBCXX_DEBUG
1796 # define _GLIBCXX_VISIT_UNREACHABLE __builtin_trap
1797 #else
1798 # define _GLIBCXX_VISIT_UNREACHABLE __builtin_unreachable
1799 #endif
1800 
1801 #define _GLIBCXX_VISIT_CASE(N) \
1802  case N: \
1803  { \
1804  if constexpr (N < __n) \
1805  { \
1806  return __gen_vtable_impl<_Ma, index_sequence<N>>:: \
1807  __visit_invoke(std::forward<_Visitor>(__visitor), \
1808  std::forward<_V0>(__v0)); \
1809  } \
1810  else _GLIBCXX_VISIT_UNREACHABLE(); \
1811  }
1812 
1813  switch (__v0.index())
1814  {
1815  _GLIBCXX_VISIT_CASE(0)
1816  _GLIBCXX_VISIT_CASE(1)
1817  _GLIBCXX_VISIT_CASE(2)
1818  _GLIBCXX_VISIT_CASE(3)
1819  _GLIBCXX_VISIT_CASE(4)
1820  _GLIBCXX_VISIT_CASE(5)
1821  _GLIBCXX_VISIT_CASE(6)
1822  _GLIBCXX_VISIT_CASE(7)
1823  _GLIBCXX_VISIT_CASE(8)
1824  _GLIBCXX_VISIT_CASE(9)
1825  _GLIBCXX_VISIT_CASE(10)
1826  case variant_npos:
1827  using __detail::__variant::__variant_idx_cookie;
1828  using __detail::__variant::__variant_cookie;
1829  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
1830  || is_same_v<_Result_type, __variant_cookie>)
1831  {
1832  using _Npos = index_sequence<variant_npos>;
1833  return __gen_vtable_impl<_Ma, _Npos>::
1834  __visit_invoke(std::forward<_Visitor>(__visitor),
1835  std::forward<_V0>(__v0));
1836  }
1837  else
1838  _GLIBCXX_VISIT_UNREACHABLE();
1839  default:
1840  _GLIBCXX_VISIT_UNREACHABLE();
1841  }
1842 #undef _GLIBCXX_VISIT_CASE
1843 #undef _GLIBCXX_VISIT_UNREACHABLE
1844  }
1845  }
1846  }
1847  /// @endcond
1848 
1849  template<typename _Visitor, typename... _Variants>
1850  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1851  visit(_Visitor&& __visitor, _Variants&&... __variants)
1852  {
1853  namespace __variant = std::__detail::__variant;
1854 
1855  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1856  __throw_bad_variant_access("std::visit: variant is valueless");
1857 
1858  using _Result_type
1859  = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1860 
1861  using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1862 
1863  if constexpr (sizeof...(_Variants) == 1)
1864  {
1865  using _Vp = decltype(__variant::__as(std::declval<_Variants>()...));
1866 
1867  constexpr bool __visit_rettypes_match = __detail::__variant::
1868  __check_visitor_results<_Visitor, _Vp>(
1869  make_index_sequence<variant_size_v<remove_reference_t<_Vp>>>());
1870  if constexpr (!__visit_rettypes_match)
1871  {
1872  static_assert(__visit_rettypes_match,
1873  "std::visit requires the visitor to have the same "
1874  "return type for all alternatives of a variant");
1875  return;
1876  }
1877  else
1878  return std::__do_visit<_Tag>(
1879  std::forward<_Visitor>(__visitor),
1880  static_cast<_Vp>(__variants)...);
1881  }
1882  else
1883  return std::__do_visit<_Tag>(
1884  std::forward<_Visitor>(__visitor),
1885  __variant::__as(std::forward<_Variants>(__variants))...);
1886  }
1887 
1888 #if __cplusplus > 201703L
1889  template<typename _Res, typename _Visitor, typename... _Variants>
1890  constexpr _Res
1891  visit(_Visitor&& __visitor, _Variants&&... __variants)
1892  {
1893  namespace __variant = std::__detail::__variant;
1894 
1895  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1896  __throw_bad_variant_access("std::visit<R>: variant is valueless");
1897 
1898  return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1899  __variant::__as(std::forward<_Variants>(__variants))...);
1900  }
1901 #endif
1902 
1903  /// @cond undocumented
1904  template<bool, typename... _Types>
1905  struct __variant_hash_call_base_impl
1906  {
1907  size_t
1908  operator()(const variant<_Types...>& __t) const
1909  noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1910  {
1911  size_t __ret;
1912  __detail::__variant::__raw_visit(
1913  [&__t, &__ret](auto&& __t_mem) mutable
1914  {
1915  using _Type = __remove_cvref_t<decltype(__t_mem)>;
1916  if constexpr (!is_same_v<_Type,
1917  __detail::__variant::__variant_cookie>)
1918  __ret = std::hash<size_t>{}(__t.index())
1919  + std::hash<_Type>{}(__t_mem);
1920  else
1921  __ret = std::hash<size_t>{}(__t.index());
1922  }, __t);
1923  return __ret;
1924  }
1925  };
1926 
1927  template<typename... _Types>
1928  struct __variant_hash_call_base_impl<false, _Types...> {};
1929 
1930  template<typename... _Types>
1931  using __variant_hash_call_base =
1932  __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1933  __enable_hash_call &&...), _Types...>;
1934  /// @endcond
1935 
1936  template<typename... _Types>
1937  struct hash<variant<_Types...>>
1938  : private __detail::__variant::_Variant_hash_base<
1939  variant<_Types...>, std::index_sequence_for<_Types...>>,
1940  public __variant_hash_call_base<_Types...>
1941  {
1942  using result_type [[__deprecated__]] = size_t;
1943  using argument_type [[__deprecated__]] = variant<_Types...>;
1944  };
1945 
1946  template<>
1947  struct hash<monostate>
1948  {
1949  using result_type [[__deprecated__]] = size_t;
1950  using argument_type [[__deprecated__]] = monostate;
1951 
1952  size_t
1953  operator()(const monostate&) const noexcept
1954  {
1955  constexpr size_t __magic_monostate_hash = -7777;
1956  return __magic_monostate_hash;
1957  }
1958  };
1959 
1960  template<typename... _Types>
1961  struct __is_fast_hash<hash<variant<_Types...>>>
1962  : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1963  { };
1964 
1965 _GLIBCXX_END_NAMESPACE_VERSION
1966 } // namespace std
1967 
1968 #endif // C++17
1969 
1970 #endif // _GLIBCXX_VARIANT