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