libstdc++
variant
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1 // <variant> -*- C++ -*-
2 
3 // Copyright (C) 2016-2026 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 #ifdef _GLIBCXX_SYSHDR
33 #pragma GCC system_header
34 #endif
35 
36 #define __glibcxx_want_freestanding_variant
37 #define __glibcxx_want_variant
38 #define __glibcxx_want_constrained_equality
39 #define __glibcxx_want_constexpr_exceptions
40 #include <bits/version.h>
41 
42 #ifdef __cpp_lib_variant // C++ >= 17
43 #include <initializer_list>
44 #include <type_traits>
45 #include <bits/enable_special_members.h>
46 #include <bits/exception_defines.h>
47 #include <bits/functional_hash.h>
48 #include <bits/invoke.h>
49 #include <bits/monostate.h>
50 #include <bits/parse_numbers.h> // _Select_int
51 #include <bits/stl_iterator_base_funcs.h>
52 #include <bits/stl_construct.h>
53 #include <bits/utility.h> // in_place_index_t
54 #if __cplusplus >= 202002L
55 # include <concepts>
56 # include <compare>
57 #endif
58 
59 // C++ < 20 || __cpp_concepts < 202002L || __cpp_constexpr < 201811L
60 #if __cpp_lib_variant < 202106L
61 # include <ext/aligned_buffer.h> // Use __aligned_membuf for storage.
62 #endif
63 
64 namespace std _GLIBCXX_VISIBILITY(default)
65 {
66 _GLIBCXX_BEGIN_NAMESPACE_VERSION
67 
68  template<typename... _Types> class tuple;
69  template<typename... _Types> class variant;
70 
71  template<typename _Variant>
72  struct variant_size;
73 
74  template<typename _Variant>
75  struct variant_size<const _Variant> : variant_size<_Variant> {};
76 
77  template<typename _Variant>
78  struct variant_size<volatile _Variant> : variant_size<_Variant> {};
79 
80  template<typename _Variant>
81  struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
82 
83  template<typename... _Types>
84  struct variant_size<variant<_Types...>>
85  : std::integral_constant<size_t, sizeof...(_Types)> {};
86 
87  template<typename _Variant>
88  inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
89 
90  template<typename... _Types>
91  inline constexpr size_t
92  variant_size_v<variant<_Types...>> = sizeof...(_Types);
93 
94  template<typename... _Types>
95  inline constexpr size_t
96  variant_size_v<const variant<_Types...>> = sizeof...(_Types);
97 
98  template<size_t _Np, typename _Variant>
99  struct variant_alternative;
100 
101  template<size_t _Np, typename... _Types>
102  struct variant_alternative<_Np, variant<_Types...>>
103  {
104  static_assert(_Np < sizeof...(_Types));
105 
106  using type = typename _Nth_type<_Np, _Types...>::type;
107  };
108 
109  template<size_t _Np, typename _Variant>
110  using variant_alternative_t =
111  typename variant_alternative<_Np, _Variant>::type;
112 
113  template<size_t _Np, typename _Variant>
114  struct variant_alternative<_Np, const _Variant>
115  { using type = const variant_alternative_t<_Np, _Variant>; };
116 
117  template<size_t _Np, typename _Variant>
118  struct variant_alternative<_Np, volatile _Variant>
119  { using type = volatile variant_alternative_t<_Np, _Variant>; };
120 
121  template<size_t _Np, typename _Variant>
122  struct variant_alternative<_Np, const volatile _Variant>
123  { using type = const volatile variant_alternative_t<_Np, _Variant>; };
124 
125  inline constexpr size_t variant_npos = -1;
126 
127  template<size_t _Np, typename... _Types>
128  constexpr variant_alternative_t<_Np, variant<_Types...>>&
129  get(variant<_Types...>&);
130 
131  template<size_t _Np, typename... _Types>
132  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
133  get(variant<_Types...>&&);
134 
135  template<size_t _Np, typename... _Types>
136  constexpr variant_alternative_t<_Np, variant<_Types...>> const&
137  get(const variant<_Types...>&);
138 
139  template<size_t _Np, typename... _Types>
140  constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
141  get(const variant<_Types...>&&);
142 
143  template<typename _Result_type, typename _Visitor, typename... _Variants>
144  constexpr decltype(auto)
145  __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
146 
147  template <typename... _Types, typename _Tp>
148  _GLIBCXX20_CONSTEXPR
149  decltype(auto)
150  __variant_cast(_Tp&& __rhs)
151  {
152  if constexpr (is_lvalue_reference_v<_Tp>)
153  {
154  if constexpr (is_const_v<remove_reference_t<_Tp>>)
155  return static_cast<const variant<_Types...>&>(__rhs);
156  else
157  return static_cast<variant<_Types...>&>(__rhs);
158  }
159  else
160  return static_cast<variant<_Types...>&&>(__rhs);
161  }
162 
163 namespace __detail
164 {
165 namespace __variant
166 {
167  // used for raw visitation
168  struct __variant_cookie {};
169  // used for raw visitation with indices passed in
170  struct __variant_idx_cookie { using type = __variant_idx_cookie; };
171  // Used to enable deduction (and same-type checking) for std::visit:
172  template<typename _Tp> struct __deduce_visit_result { using type = _Tp; };
173 
174  // Visit variants that might be valueless.
175  template<typename _Visitor, typename... _Variants>
176  constexpr void
177  __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
178  {
179  std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
180  std::forward<_Variants>(__variants)...);
181  }
182 
183  // Visit variants that might be valueless, passing indices to the visitor.
184  template<typename _Visitor, typename... _Variants>
185  constexpr void
186  __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
187  {
188  std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
189  std::forward<_Variants>(__variants)...);
190  }
191 
192  // The __as function templates implement the exposition-only "as-variant"
193 
194  template<typename... _Types>
195  constexpr std::variant<_Types...>&
196  __as(std::variant<_Types...>& __v) noexcept
197  { return __v; }
198 
199  template<typename... _Types>
200  constexpr const std::variant<_Types...>&
201  __as(const std::variant<_Types...>& __v) noexcept
202  { return __v; }
203 
204  template<typename... _Types>
205  constexpr std::variant<_Types...>&&
206  __as(std::variant<_Types...>&& __v) noexcept
207  { return std::move(__v); }
208 
209  template<typename... _Types>
210  constexpr const std::variant<_Types...>&&
211  __as(const std::variant<_Types...>&& __v) noexcept
212  { return std::move(__v); }
213 
214 #if (__cpp_lib_variant < 202106L) && defined(_GLIBCXX_USE_VARIANT_CXX17_OLD_ABI)
215  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
216  struct _Uninitialized;
217 #else
218  template<typename _Type, bool /* unused */ = true>
219  struct _Uninitialized;
220 #endif
221 
222  // The primary template is used for trivially destructible types in C++17,
223  // and for all types in C++20.
224  template<typename _Type, bool>
225  struct _Uninitialized
226  {
227  template<typename... _Args>
228  constexpr
229  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
230  : _M_storage(std::forward<_Args>(__args)...)
231  { }
232 
233 #if (__cpp_lib_variant < 202106L) && defined(_GLIBCXX_USE_VARIANT_CXX17_OLD_ABI)
234  constexpr const _Type& _M_get() const & noexcept
235  { return _M_storage; }
236 
237  constexpr _Type& _M_get() & noexcept
238  { return _M_storage; }
239 
240  constexpr const _Type&& _M_get() const && noexcept
241  { return std::move(_M_storage); }
242 
243  constexpr _Type&& _M_get() && noexcept
244  { return std::move(_M_storage); }
245 #endif
246 
247  _Type _M_storage;
248  };
249 
250 #if (__cpp_lib_variant < 202106L) && defined(_GLIBCXX_USE_VARIANT_CXX17_OLD_ABI)
251  // This partial specialization is used for non-trivially destructible types
252  // in C++17.
253  template<typename _Type>
254  struct _Uninitialized<_Type, false>
255  {
256  template<typename... _Args>
257  constexpr
258  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
259  {
260  ::new ((void*)std::addressof(_M_storage))
261  _Type(std::forward<_Args>(__args)...);
262  }
263 
264  const _Type& _M_get() const & noexcept
265  { return *_M_storage._M_ptr(); }
266 
267  _Type& _M_get() & noexcept
268  { return *_M_storage._M_ptr(); }
269 
270  const _Type&& _M_get() const && noexcept
271  { return std::move(*_M_storage._M_ptr()); }
272 
273  _Type&& _M_get() && noexcept
274  { return std::move(*_M_storage._M_ptr()); }
275 
276  __gnu_cxx::__aligned_membuf<_Type> _M_storage;
277  };
278 
279  template<size_t _Np, typename _Union>
280  constexpr decltype(auto)
281  __get_n(_Union&& __u) noexcept
282  {
283  if constexpr (_Np == 0)
284  return std::forward<_Union>(__u)._M_first._M_get();
285  else if constexpr (_Np == 1)
286  return std::forward<_Union>(__u)._M_rest._M_first._M_get();
287  else if constexpr (_Np == 2)
288  return std::forward<_Union>(__u)._M_rest._M_rest._M_first._M_get();
289  else
290  return __variant::__get_n<_Np - 3>(
291  std::forward<_Union>(__u)._M_rest._M_rest._M_rest);
292  }
293 #else // !_GLIBCXX_USE_VARIANT_CXX17_OLD_ABI
294  template<size_t _Np, typename _Union>
295  constexpr auto&&
296  __get_n(_Union&& __u) noexcept
297  {
298  if constexpr (_Np == 0)
299  return std::forward<_Union>(__u)._M_first._M_storage;
300  else if constexpr (_Np == 1)
301  return std::forward<_Union>(__u)._M_rest._M_first._M_storage;
302  else if constexpr (_Np == 2)
303  return std::forward<_Union>(__u)._M_rest._M_rest._M_first._M_storage;
304  else
305  return __variant::__get_n<_Np - 3>(
306  std::forward<_Union>(__u)._M_rest._M_rest._M_rest);
307  }
308 #endif // !_GLIBCXX_USE_VARIANT_CXX17_OLD_ABI
309 
310  // Returns the typed storage for __v.
311  template<size_t _Np, typename _Variant>
312  constexpr decltype(auto)
313  __get(_Variant&& __v) noexcept
314  { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); }
315 
316  // Gets the _Uninitialized to construct into for __u.
317  template<size_t _Np, typename _Union>
318  constexpr decltype(auto)
319  __construct_n(_Union& __u) noexcept
320  {
321  if constexpr (_Np == 0)
322  return &__u._M_first;
323  else if constexpr (_Np == 1)
324  {
325  std::_Construct(&__u._M_rest);
326  return &__u._M_rest._M_first;
327  }
328  else if constexpr (_Np == 2)
329  {
330  std::_Construct(&__u._M_rest);
331  std::_Construct(&__u._M_rest._M_rest);
332  return &__u._M_rest._M_rest._M_first;
333  }
334  else
335  {
336  std::_Construct(&__u._M_rest);
337  std::_Construct(&__u._M_rest._M_rest);
338  std::_Construct(&__u._M_rest._M_rest._M_rest);
339  return __variant::__construct_n<_Np - 3>(__u._M_rest._M_rest._M_rest);
340  }
341  }
342 
343  template<typename... _Types>
344  struct _Traits
345  {
346  static constexpr bool _S_default_ctor =
347  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
348  static constexpr bool _S_copy_ctor =
349  (is_copy_constructible_v<_Types> && ...);
350  static constexpr bool _S_move_ctor =
351  (is_move_constructible_v<_Types> && ...);
352  static constexpr bool _S_copy_assign =
353  _S_copy_ctor
354  && (is_copy_assignable_v<_Types> && ...);
355  static constexpr bool _S_move_assign =
356  _S_move_ctor
357  && (is_move_assignable_v<_Types> && ...);
358 
359  static constexpr bool _S_trivial_dtor =
360  (is_trivially_destructible_v<_Types> && ...);
361  static constexpr bool _S_trivial_copy_ctor =
362  (is_trivially_copy_constructible_v<_Types> && ...);
363  static constexpr bool _S_trivial_move_ctor =
364  (is_trivially_move_constructible_v<_Types> && ...);
365  static constexpr bool _S_trivial_copy_assign =
366  _S_trivial_dtor && _S_trivial_copy_ctor
367  && (is_trivially_copy_assignable_v<_Types> && ...);
368  static constexpr bool _S_trivial_move_assign =
369  _S_trivial_dtor && _S_trivial_move_ctor
370  && (is_trivially_move_assignable_v<_Types> && ...);
371 
372  // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
373  // are always nothrow.
374  static constexpr bool _S_nothrow_default_ctor =
375  is_nothrow_default_constructible_v<
376  typename _Nth_type<0, _Types...>::type>;
377  static constexpr bool _S_nothrow_copy_ctor = false;
378  static constexpr bool _S_nothrow_move_ctor =
379  (is_nothrow_move_constructible_v<_Types> && ...);
380  static constexpr bool _S_nothrow_copy_assign = false;
381  static constexpr bool _S_nothrow_move_assign =
382  _S_nothrow_move_ctor
383  && (is_nothrow_move_assignable_v<_Types> && ...);
384  };
385 
386  // Defines members and ctors.
387  template<bool __trivially_destructible, typename... _Types>
388  union _Variadic_union
389  {
390  _Variadic_union() = default;
391 
392  template<size_t _Np, typename... _Args>
393  _Variadic_union(in_place_index_t<_Np>, _Args&&...) = delete;
394  };
395 
396  template<typename _First, typename... _Rest>
397  union _Variadic_union<true, _First, _Rest...>
398  {
399  constexpr _Variadic_union() : _M_rest() { }
400 
401  template<typename... _Args>
402  constexpr
403  _Variadic_union(in_place_index_t<0>, _Args&&... __args)
404  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
405  { }
406 
407  template<size_t _Np, typename... _Args>
408  constexpr
409  _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
410  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
411  { }
412 
413  _Uninitialized<_First> _M_first;
414  _Variadic_union<true, _Rest...> _M_rest;
415  };
416 
417  template<typename _First, typename... _Rest>
418  union _Variadic_union<false, _First, _Rest...>
419  {
420  constexpr _Variadic_union() : _M_rest() { }
421 
422  template<typename... _Args>
423  constexpr
424  _Variadic_union(in_place_index_t<0>, _Args&&... __args)
425  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
426  { }
427 
428  template<size_t _Np, typename... _Args>
429  constexpr
430  _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
431  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
432  { }
433 
434  _Variadic_union(const _Variadic_union&) = default;
435  _Variadic_union(_Variadic_union&&) = default;
436  _Variadic_union& operator=(const _Variadic_union&) = default;
437  _Variadic_union& operator=(_Variadic_union&&) = default;
438 
439  // If any alternative type is not trivially destructible then we need a
440  // user-provided destructor that does nothing. The active alternative
441  // will be destroyed by _Variant_storage::_M_reset() instead of here.
442  _GLIBCXX20_CONSTEXPR ~_Variadic_union()
443  { }
444 
445  _Uninitialized<_First> _M_first;
446  _Variadic_union<(is_trivially_destructible_v<_Rest> && ...), _Rest...> _M_rest;
447  };
448 
449  // _Never_valueless_alt is true for variant alternatives that can
450  // always be placed in a variant without it becoming valueless.
451 
452  // For suitably-small, trivially copyable types we can create temporaries
453  // on the stack and then memcpy them into place.
454  template<typename _Tp>
455  struct _Never_valueless_alt
456  : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
457  { };
458 
459  // Specialize _Never_valueless_alt for other types which have a
460  // non-throwing and cheap move construction and move assignment operator,
461  // so that emplacing the type will provide the strong exception-safety
462  // guarantee, by creating and moving a temporary.
463  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
464  // variant using that alternative, so we can't change the value later!
465 
466  // True if every alternative in _Types... can be emplaced in a variant
467  // without it becoming valueless. If this is true, variant<_Types...>
468  // can never be valueless, which enables some minor optimizations.
469  template <typename... _Types>
470  constexpr bool __never_valueless()
471  {
472  return _Traits<_Types...>::_S_move_assign
473  && (_Never_valueless_alt<_Types>::value && ...);
474  }
475 
476  // Defines index and the dtor, possibly trivial.
477  template<bool __trivially_destructible, typename... _Types>
478  struct _Variant_storage;
479 
480  template <typename... _Types>
481  using __select_index =
482  typename __select_int::_Select_int_base<sizeof...(_Types),
483  unsigned char,
484  unsigned short>::type::value_type;
485 
486  template<typename... _Types>
487  struct _Variant_storage<false, _Types...>
488  {
489  constexpr
490  _Variant_storage()
491  : _M_index(static_cast<__index_type>(variant_npos))
492  { }
493 
494  template<size_t _Np, typename... _Args>
495  constexpr
496  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
497  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
498  _M_index{_Np}
499  { }
500 
501  constexpr void
502  _M_reset()
503  {
504  if (!_M_valid()) [[__unlikely__]]
505  return;
506 
507  std::__do_visit<void>([](auto&& __this_mem) mutable
508  {
509  std::_Destroy(std::__addressof(__this_mem));
510  }, __variant_cast<_Types...>(*this));
511 
512  _M_index = static_cast<__index_type>(variant_npos);
513  }
514 
515  _GLIBCXX20_CONSTEXPR
516  ~_Variant_storage()
517  { _M_reset(); }
518 
519  constexpr bool
520  _M_valid() const noexcept
521  {
522  if constexpr (__variant::__never_valueless<_Types...>())
523  return true;
524  return this->_M_index != __index_type(variant_npos);
525  }
526 
527  _Variadic_union<false, _Types...> _M_u;
528  using __index_type = __select_index<_Types...>;
529  __index_type _M_index;
530  };
531 
532  template<typename... _Types>
533  struct _Variant_storage<true, _Types...>
534  {
535  constexpr
536  _Variant_storage()
537  : _M_index(static_cast<__index_type>(variant_npos))
538  { }
539 
540  template<size_t _Np, typename... _Args>
541  constexpr
542  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
543  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
544  _M_index{_Np}
545  { }
546 
547  constexpr void
548  _M_reset() noexcept
549  { _M_index = static_cast<__index_type>(variant_npos); }
550 
551  constexpr bool
552  _M_valid() const noexcept
553  {
554  if constexpr (__variant::__never_valueless<_Types...>())
555  return true;
556  // It would be nice if we could just return true for -fno-exceptions.
557  // It's possible (but inadvisable) that a std::variant could become
558  // valueless in a translation unit compiled with -fexceptions and then
559  // be passed to functions compiled with -fno-exceptions. We would need
560  // some #ifdef _GLIBCXX_NO_EXCEPTIONS_GLOBALLY property to elide all
561  // checks for valueless_by_exception().
562  return this->_M_index != static_cast<__index_type>(variant_npos);
563  }
564 
565  _Variadic_union<true, _Types...> _M_u;
566  using __index_type = __select_index<_Types...>;
567  __index_type _M_index;
568  };
569 
570  // Implementation of v.emplace<N>(args...).
571  template<size_t _Np, bool _Triv, typename... _Types, typename... _Args>
572  _GLIBCXX20_CONSTEXPR
573  inline void
574  __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args)
575  {
576  __v._M_reset();
577  auto* __addr = __variant::__construct_n<_Np>(__v._M_u);
578  std::_Construct(__addr, in_place_index<0>,
579  std::forward<_Args>(__args)...);
580  // Construction didn't throw, so can set the new index now:
581  __v._M_index = _Np;
582  }
583 
584  template<typename... _Types>
585  using _Variant_storage_alias =
586  _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
587 
588  // The following are (Copy|Move) (ctor|assign) layers for forwarding
589  // triviality and handling non-trivial SMF behaviors.
590 
591  template<bool, typename... _Types>
592  struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
593  {
594  using _Base = _Variant_storage_alias<_Types...>;
595  using _Base::_Base;
596 
597  _GLIBCXX20_CONSTEXPR
598  _Copy_ctor_base(const _Copy_ctor_base& __rhs)
599  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
600  {
601  __variant::__raw_idx_visit(
602  [this](auto&& __rhs_mem, auto __rhs_index) mutable
603  {
604  constexpr size_t __j = __rhs_index;
605  if constexpr (__j != variant_npos)
606  std::_Construct(std::__addressof(this->_M_u),
607  in_place_index<__j>, __rhs_mem);
608  }, __variant_cast<_Types...>(__rhs));
609  this->_M_index = __rhs._M_index;
610  }
611 
612  _Copy_ctor_base(_Copy_ctor_base&&) = default;
613  _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
614  _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
615  };
616 
617  template<typename... _Types>
618  struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
619  {
620  using _Base = _Variant_storage_alias<_Types...>;
621  using _Base::_Base;
622  };
623 
624  template<typename... _Types>
625  using _Copy_ctor_alias =
626  _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
627 
628  template<bool, typename... _Types>
629  struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
630  {
631  using _Base = _Copy_ctor_alias<_Types...>;
632  using _Base::_Base;
633 
634  _GLIBCXX20_CONSTEXPR
635  _Move_ctor_base(_Move_ctor_base&& __rhs)
636  noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
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  std::_Construct(std::__addressof(this->_M_u),
644  in_place_index<__j>,
645  std::forward<decltype(__rhs_mem)>(__rhs_mem));
646  }, __variant_cast<_Types...>(std::move(__rhs)));
647  this->_M_index = __rhs._M_index;
648  }
649 
650  _Move_ctor_base(const _Move_ctor_base&) = default;
651  _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
652  _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
653  };
654 
655  template<typename... _Types>
656  struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
657  {
658  using _Base = _Copy_ctor_alias<_Types...>;
659  using _Base::_Base;
660  };
661 
662  template<typename... _Types>
663  using _Move_ctor_alias =
664  _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
665 
666  template<bool, typename... _Types>
667  struct _Copy_assign_base : _Move_ctor_alias<_Types...>
668  {
669  using _Base = _Move_ctor_alias<_Types...>;
670  using _Base::_Base;
671 
672  _GLIBCXX20_CONSTEXPR
673  _Copy_assign_base&
674  operator=(const _Copy_assign_base& __rhs)
675  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
676  {
677  __variant::__raw_idx_visit(
678  [this](auto&& __rhs_mem, auto __rhs_index) mutable
679  {
680  constexpr size_t __j = __rhs_index;
681  if constexpr (__j == variant_npos)
682  this->_M_reset(); // Make *this valueless.
683  else if (this->_M_index == __j)
684  __variant::__get<__j>(*this) = __rhs_mem;
685  else
686  {
687  using _Tj = typename _Nth_type<__j, _Types...>::type;
688  if constexpr (is_nothrow_copy_constructible_v<_Tj>
689  || !is_nothrow_move_constructible_v<_Tj>)
690  __variant::__emplace<__j>(*this, __rhs_mem);
691  else
692  {
693  using _Variant = variant<_Types...>;
694  _Variant& __self = __variant_cast<_Types...>(*this);
695  __self = _Variant(in_place_index<__j>, __rhs_mem);
696  }
697  }
698  }, __variant_cast<_Types...>(__rhs));
699  return *this;
700  }
701 
702  _Copy_assign_base(const _Copy_assign_base&) = default;
703  _Copy_assign_base(_Copy_assign_base&&) = default;
704  _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
705  };
706 
707  template<typename... _Types>
708  struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
709  {
710  using _Base = _Move_ctor_alias<_Types...>;
711  using _Base::_Base;
712  };
713 
714  template<typename... _Types>
715  using _Copy_assign_alias =
716  _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
717 
718  template<bool, typename... _Types>
719  struct _Move_assign_base : _Copy_assign_alias<_Types...>
720  {
721  using _Base = _Copy_assign_alias<_Types...>;
722  using _Base::_Base;
723 
724  _GLIBCXX20_CONSTEXPR
725  _Move_assign_base&
726  operator=(_Move_assign_base&& __rhs)
727  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
728  {
729  __variant::__raw_idx_visit(
730  [this](auto&& __rhs_mem, auto __rhs_index) mutable
731  {
732  constexpr size_t __j = __rhs_index;
733  if constexpr (__j != variant_npos)
734  {
735  if (this->_M_index == __j)
736  __variant::__get<__j>(*this) = std::move(__rhs_mem);
737  else
738  {
739  using _Tj = typename _Nth_type<__j, _Types...>::type;
740  if constexpr (is_nothrow_move_constructible_v<_Tj>)
741  __variant::__emplace<__j>(*this, std::move(__rhs_mem));
742  else
743  {
744  using _Variant = variant<_Types...>;
745  _Variant& __self = __variant_cast<_Types...>(*this);
746  __self.template emplace<__j>(std::move(__rhs_mem));
747  }
748  }
749  }
750  else
751  this->_M_reset();
752  }, __variant_cast<_Types...>(__rhs));
753  return *this;
754  }
755 
756  _Move_assign_base(const _Move_assign_base&) = default;
757  _Move_assign_base(_Move_assign_base&&) = default;
758  _Move_assign_base& operator=(const _Move_assign_base&) = default;
759  };
760 
761  template<typename... _Types>
762  struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
763  {
764  using _Base = _Copy_assign_alias<_Types...>;
765  using _Base::_Base;
766  };
767 
768  template<typename... _Types>
769  using _Move_assign_alias =
770  _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
771 
772  template<typename... _Types>
773  struct _Variant_base : _Move_assign_alias<_Types...>
774  {
775  using _Base = _Move_assign_alias<_Types...>;
776 
777  constexpr
778  _Variant_base() noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
779  : _Variant_base(in_place_index<0>) { }
780 
781  template<size_t _Np, typename... _Args>
782  constexpr explicit
783  _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
784  : _Base(__i, std::forward<_Args>(__args)...)
785  { }
786 
787  _Variant_base(const _Variant_base&) = default;
788  _Variant_base(_Variant_base&&) = default;
789  _Variant_base& operator=(const _Variant_base&) = default;
790  _Variant_base& operator=(_Variant_base&&) = default;
791  };
792 
793  template<typename _Tp, typename... _Types>
794  inline constexpr bool __exactly_once
795  = std::__find_uniq_type_in_pack<_Tp, _Types...>() < sizeof...(_Types);
796 
797  // Helper used to check for valid conversions that don't involve narrowing.
798  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
799 
800  // "Build an imaginary function FUN(Ti) for each alternative type Ti"
801  template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
802  struct _Build_FUN
803  {
804  // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
805  // but only static functions will be considered in the call below.
806  void _S_fun() = delete;
807  };
808 
809  // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
810  template<size_t _Ind, typename _Tp, typename _Ti>
811  struct _Build_FUN<_Ind, _Tp, _Ti,
812  void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
813  {
814  // This is the FUN function for type _Ti, with index _Ind
815  static integral_constant<size_t, _Ind> _S_fun(_Ti);
816  };
817 
818  template<typename _Tp, typename _Variant,
819  typename = make_index_sequence<variant_size_v<_Variant>>>
820  struct _Build_FUNs;
821 
822  template<typename _Tp, typename... _Ti, size_t... _Ind>
823  struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
824  : _Build_FUN<_Ind, _Tp, _Ti>...
825  {
826  using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
827  };
828 
829  // The index j of the overload FUN(Tj) selected by overload resolution
830  // for FUN(std::forward<_Tp>(t))
831  template<typename _Tp, typename _Variant>
832  using _FUN_type
833  = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
834 
835  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
836  template<typename _Tp, typename _Variant, typename = void>
837  inline constexpr size_t
838  __accepted_index = variant_npos;
839 
840  template<typename _Tp, typename _Variant>
841  inline constexpr size_t
842  __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
843  = _FUN_type<_Tp, _Variant>::value;
844 
845  template<typename _Maybe_variant_cookie, typename _Variant,
846  typename = __remove_cvref_t<_Variant>>
847  inline constexpr bool
848  __extra_visit_slot_needed = false;
849 
850  template<typename _Var, typename... _Types>
851  inline constexpr bool
852  __extra_visit_slot_needed<__variant_cookie, _Var, variant<_Types...>>
853  = !__variant::__never_valueless<_Types...>();
854 
855  template<typename _Var, typename... _Types>
856  inline constexpr bool
857  __extra_visit_slot_needed<__variant_idx_cookie, _Var, variant<_Types...>>
858  = !__variant::__never_valueless<_Types...>();
859 
860  // Used for storing a multi-dimensional vtable.
861  template<typename _Tp, size_t... _Dimensions>
862  struct _Multi_array;
863 
864  // Partial specialization with rank zero, stores a single _Tp element.
865  template<typename _Tp>
866  struct _Multi_array<_Tp>
867  {
868  template<typename>
869  struct __untag_result
870  : false_type
871  { using element_type = _Tp; };
872 
873 #pragma GCC diagnostic push
874 #pragma GCC diagnostic ignored "-Wignored-qualifiers"
875  template <typename... _Args>
876  struct __untag_result<const void(*)(_Args...)>
877  : false_type
878  { using element_type = void(*)(_Args...); };
879 #pragma GCC diagnostic pop
880 
881  template <typename... _Args>
882  struct __untag_result<__variant_cookie(*)(_Args...)>
883  : false_type
884  { using element_type = void(*)(_Args...); };
885 
886  template <typename... _Args>
887  struct __untag_result<__variant_idx_cookie(*)(_Args...)>
888  : false_type
889  { using element_type = void(*)(_Args...); };
890 
891  template <typename _Res, typename... _Args>
892  struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
893  : true_type
894  { using element_type = _Res(*)(_Args...); };
895 
896  using __result_is_deduced = __untag_result<_Tp>;
897 
898  constexpr const typename __untag_result<_Tp>::element_type&
899  _M_access() const
900  { return _M_data; }
901 
902  typename __untag_result<_Tp>::element_type _M_data;
903  };
904 
905  // Partial specialization with rank >= 1.
906  template<typename _Ret,
907  typename _Visitor,
908  typename... _Variants,
909  size_t __first, size_t... __rest>
910  struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
911  {
912  static constexpr size_t __index =
913  sizeof...(_Variants) - sizeof...(__rest) - 1;
914 
915  using _Variant = typename _Nth_type<__index, _Variants...>::type;
916 
917  static constexpr int __do_cookie =
918  __extra_visit_slot_needed<_Ret, _Variant> ? 1 : 0;
919 
920  using _Tp = _Ret(*)(_Visitor, _Variants...);
921 
922  template<typename... _Args>
923  constexpr decltype(auto)
924  _M_access(size_t __first_index, _Args... __rest_indices) const
925  {
926  return _M_arr[__first_index + __do_cookie]
927  ._M_access(__rest_indices...);
928  }
929 
930  _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
931  };
932 
933  // Creates a multi-dimensional vtable recursively.
934  //
935  // For example,
936  // visit([](auto, auto){},
937  // variant<int, char>(), // typedef'ed as V1
938  // variant<float, double, long double>()) // typedef'ed as V2
939  // will trigger instantiations of:
940  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
941  // tuple<V1&&, V2&&>, std::index_sequence<>>
942  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
943  // tuple<V1&&, V2&&>, std::index_sequence<0>>
944  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
945  // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
946  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
947  // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
948  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
949  // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
950  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
951  // tuple<V1&&, V2&&>, std::index_sequence<1>>
952  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
953  // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
954  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
955  // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
956  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
957  // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
958  // The returned multi-dimensional vtable can be fast accessed by the visitor
959  // using index calculation.
960  template<typename _Array_type, typename _Index_seq>
961  struct __gen_vtable_impl;
962 
963  // Defines the _S_apply() member that returns a _Multi_array populated
964  // with function pointers that perform the visitation expressions e(m)
965  // for each valid pack of indexes into the variant types _Variants.
966  //
967  // This partial specialization builds up the index sequences by recursively
968  // calling _S_apply() on the next specialization of __gen_vtable_impl.
969  // The base case of the recursion defines the actual function pointers.
970  template<typename _Result_type, typename _Visitor, size_t... __dimensions,
971  typename... _Variants, size_t... __indices>
972  struct __gen_vtable_impl<
973  _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
974  std::index_sequence<__indices...>>
975  {
976  using _Next =
977  remove_reference_t<typename _Nth_type<sizeof...(__indices),
978  _Variants...>::type>;
979  using _Array_type =
980  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
981  __dimensions...>;
982 
983  static constexpr _Array_type
984  _S_apply()
985  {
986  _Array_type __vtable{};
987  _S_apply_all_alts(
988  __vtable, make_index_sequence<variant_size_v<_Next>>());
989  return __vtable;
990  }
991 
992  template<size_t... __var_indices>
993  static constexpr void
994  _S_apply_all_alts(_Array_type& __vtable,
995  std::index_sequence<__var_indices...>)
996  {
997  if constexpr (__extra_visit_slot_needed<_Result_type, _Next>)
998  (_S_apply_single_alt<true, __var_indices>(
999  __vtable._M_arr[__var_indices + 1],
1000  &(__vtable._M_arr[0])), ...);
1001  else
1002  (_S_apply_single_alt<false, __var_indices>(
1003  __vtable._M_arr[__var_indices]), ...);
1004  }
1005 
1006  template<bool __do_cookie, size_t __index, typename _Tp>
1007  static constexpr void
1008  _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
1009  {
1010  if constexpr (__do_cookie)
1011  {
1012  __element = __gen_vtable_impl<
1013  _Tp,
1014  std::index_sequence<__indices..., __index>>::_S_apply();
1015  *__cookie_element = __gen_vtable_impl<
1016  _Tp,
1017  std::index_sequence<__indices..., variant_npos>>::_S_apply();
1018  }
1019  else
1020  {
1021  auto __tmp_element = __gen_vtable_impl<
1022  remove_reference_t<decltype(__element)>,
1023  std::index_sequence<__indices..., __index>>::_S_apply();
1024  static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
1025  "std::visit requires the visitor to have the same "
1026  "return type for all alternatives of a variant");
1027  __element = __tmp_element;
1028  }
1029  }
1030  };
1031 
1032  // This partial specialization is the base case for the recursion.
1033  // It populates a _Multi_array element with the address of a function
1034  // that invokes the visitor with the alternatives specified by __indices.
1035  template<typename _Result_type, typename _Visitor, typename... _Variants,
1036  size_t... __indices>
1037  struct __gen_vtable_impl<
1038  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
1039  std::index_sequence<__indices...>>
1040  {
1041  using _Array_type =
1042  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
1043 
1044  template<size_t __index, typename _Variant>
1045  static constexpr decltype(auto)
1046  __element_by_index_or_cookie(_Variant&& __var) noexcept
1047  {
1048  if constexpr (__index != variant_npos)
1049  return __variant::__get<__index>(std::forward<_Variant>(__var));
1050  else
1051  return __variant_cookie{};
1052  }
1053 
1054  static constexpr decltype(auto)
1055  __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1056  {
1057  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1058  // For raw visitation using indices, pass the indices to the visitor
1059  // and discard the return value:
1060  std::__invoke(std::forward<_Visitor>(__visitor),
1061  __element_by_index_or_cookie<__indices>(
1062  std::forward<_Variants>(__vars))...,
1063  integral_constant<size_t, __indices>()...);
1064  else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1065  // For raw visitation without indices, and discard the return value:
1066  std::__invoke(std::forward<_Visitor>(__visitor),
1067  __element_by_index_or_cookie<__indices>(
1068  std::forward<_Variants>(__vars))...);
1069  else if constexpr (_Array_type::__result_is_deduced::value)
1070  // For the usual std::visit case deduce the return value:
1071  return std::__invoke(std::forward<_Visitor>(__visitor),
1072  __element_by_index_or_cookie<__indices>(
1073  std::forward<_Variants>(__vars))...);
1074  else // for std::visit<R> use INVOKE<R>
1075  return std::__invoke_r<_Result_type>(
1076  std::forward<_Visitor>(__visitor),
1077  __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1078  }
1079 
1080  static constexpr auto
1081  _S_apply()
1082  {
1083  if constexpr (_Array_type::__result_is_deduced::value)
1084  {
1085  constexpr bool __visit_ret_type_mismatch =
1086  !is_same_v<typename _Result_type::type,
1087  decltype(__visit_invoke(std::declval<_Visitor>(),
1088  std::declval<_Variants>()...))>;
1089  if constexpr (__visit_ret_type_mismatch)
1090  {
1091  struct __cannot_match {};
1092  return __cannot_match{};
1093  }
1094  else
1095  return _Array_type{&__visit_invoke};
1096  }
1097  else
1098  return _Array_type{&__visit_invoke};
1099  }
1100  };
1101 
1102  template<typename _Result_type, typename _Visitor, typename... _Variants>
1103  struct __gen_vtable
1104  {
1105  using _Array_type =
1106  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1107  variant_size_v<remove_reference_t<_Variants>>...>;
1108 
1109  static constexpr _Array_type _S_vtable
1110  = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1111  };
1112 
1113 #if ! _GLIBCXX_INLINE_VERSION
1114  template<size_t _Nm, typename _Tp>
1115  struct _Base_dedup : public _Tp { };
1116 
1117  template<typename _Variant, typename __indices>
1118  struct _Variant_hash_base;
1119 
1120  template<typename... _Types, size_t... __indices>
1121  struct _Variant_hash_base<variant<_Types...>,
1122  std::index_sequence<__indices...>>
1123  : _Base_dedup<__indices, __hash_empty_base<remove_const_t<_Types>>>...
1124  { };
1125 #endif
1126 
1127  // Equivalent to decltype(get<_Np>(as-variant(declval<_Variant>())))
1128  template<size_t _Np, typename _Variant,
1129  typename _AsV = decltype(__variant::__as(std::declval<_Variant>())),
1130  typename _Tp = variant_alternative_t<_Np, remove_reference_t<_AsV>>>
1131  using __get_t
1132  = __conditional_t<is_lvalue_reference_v<_Variant>, _Tp&, _Tp&&>;
1133 
1134  // Return type of std::visit.
1135  template<typename _Visitor, typename... _Variants>
1136  using __visit_result_t
1137  = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1138 
1139  template<typename _Tp, typename... _Types>
1140  constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
1141 
1142  template <typename _Visitor, typename _Variant, size_t... _Idxs>
1143  constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
1144  {
1145  return __same_types<
1146  invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
1147  >;
1148  }
1149 
1150 } // namespace __variant
1151 } // namespace __detail
1152 
1153  template<typename _Tp, typename... _Types>
1154  constexpr bool
1155  holds_alternative(const variant<_Types...>& __v) noexcept
1156  {
1157  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1158  "T must occur exactly once in alternatives");
1159  return __v.index() == std::__find_uniq_type_in_pack<_Tp, _Types...>();
1160  }
1161 
1162  template<typename _Tp, typename... _Types>
1163  constexpr _Tp&
1164  get(variant<_Types...>& __v)
1165  {
1166  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1167  "T must occur exactly once in alternatives");
1168  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1169  return std::get<__n>(__v);
1170  }
1171 
1172  template<typename _Tp, typename... _Types>
1173  constexpr _Tp&&
1174  get(variant<_Types...>&& __v)
1175  {
1176  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1177  "T must occur exactly once in alternatives");
1178  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1179  return std::get<__n>(std::move(__v));
1180  }
1181 
1182  template<typename _Tp, typename... _Types>
1183  constexpr const _Tp&
1184  get(const variant<_Types...>& __v)
1185  {
1186  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1187  "T must occur exactly once in alternatives");
1188  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1189  return std::get<__n>(__v);
1190  }
1191 
1192  template<typename _Tp, typename... _Types>
1193  constexpr const _Tp&&
1194  get(const variant<_Types...>&& __v)
1195  {
1196  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1197  "T must occur exactly once in alternatives");
1198  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1199  return std::get<__n>(std::move(__v));
1200  }
1201 
1202  template<size_t _Np, typename... _Types>
1203  constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1204  get_if(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<size_t _Np, typename... _Types>
1216  constexpr
1217  add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1218  get_if(const variant<_Types...>* __ptr) noexcept
1219  {
1220  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1221  static_assert(_Np < sizeof...(_Types),
1222  "The index must be in [0, number of alternatives)");
1223  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1224  if (__ptr && __ptr->index() == _Np)
1225  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1226  return nullptr;
1227  }
1228 
1229  template<typename _Tp, typename... _Types>
1230  constexpr add_pointer_t<_Tp>
1231  get_if(variant<_Types...>* __ptr) noexcept
1232  {
1233  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1234  "T must occur exactly once in alternatives");
1235  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1236  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1237  return std::get_if<__n>(__ptr);
1238  }
1239 
1240  template<typename _Tp, typename... _Types>
1241  constexpr add_pointer_t<const _Tp>
1242  get_if(const variant<_Types...>* __ptr) noexcept
1243  {
1244  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1245  "T must occur exactly once in alternatives");
1246  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1247  constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1248  return std::get_if<__n>(__ptr);
1249  }
1250 
1251 namespace __detail::__variant
1252 {
1253  template<typename _Ret, typename _Vp, typename _Op>
1254  constexpr _Ret
1255  __compare(_Ret __ret, const _Vp& __lhs, const _Vp& __rhs, _Op __op)
1256  {
1257  __variant::__raw_idx_visit(
1258  [&__ret, &__lhs, __op] (auto&& __rhs_mem, auto __rhs_index) mutable
1259  {
1260  if constexpr (__rhs_index != variant_npos)
1261  {
1262  if (__lhs.index() == __rhs_index.value)
1263  {
1264  auto& __this_mem = std::get<__rhs_index>(__lhs);
1265  __ret = __op(__this_mem, __rhs_mem);
1266  return;
1267  }
1268  }
1269  __ret = __op(__lhs.index() + 1, __rhs_index + 1);
1270  }, __rhs);
1271  return __ret;
1272  }
1273 } // namespace __detail::__variant
1274 
1275  template<typename... _Types>
1276 #if __cpp_lib_concepts
1277  requires ((requires (const _Types& __t) {
1278  { __t == __t } -> convertible_to<bool>; }) && ...)
1279 #endif
1280  constexpr bool
1281  operator== [[nodiscard]] (const variant<_Types...>& __lhs,
1282  const variant<_Types...>& __rhs)
1283  {
1284  namespace __variant = __detail::__variant;
1285  return __variant::__compare(true, __lhs, __rhs,
1286  [](auto&& __l, auto&& __r) -> bool {
1287  return __l == __r;
1288  });
1289  }
1290 
1291  template<typename... _Types>
1292 #if __cpp_lib_concepts
1293  requires ((requires (const _Types& __t) {
1294  { __t != __t } -> convertible_to<bool>; }) && ...)
1295 #endif
1296  constexpr bool
1297  operator!= [[nodiscard]] (const variant<_Types...>& __lhs,
1298  const variant<_Types...>& __rhs)
1299  {
1300  namespace __variant = __detail::__variant;
1301  return __variant::__compare(true, __lhs, __rhs,
1302  [](auto&& __l, auto&& __r) -> bool {
1303  return __l != __r;
1304  });
1305  }
1306 
1307  template<typename... _Types>
1308 #if __cpp_lib_concepts
1309  requires ((requires (const _Types& __t) {
1310  { __t < __t } -> convertible_to<bool>; }) && ...)
1311 #endif
1312  constexpr bool
1313  operator< [[nodiscard]] (const variant<_Types...>& __lhs,
1314  const variant<_Types...>& __rhs)
1315  {
1316  namespace __variant = __detail::__variant;
1317  return __variant::__compare(true, __lhs, __rhs,
1318  [](auto&& __l, auto&& __r) -> bool {
1319  return __l < __r;
1320  });
1321  }
1322 
1323  template<typename... _Types>
1324 #if __cpp_lib_concepts
1325  requires ((requires (const _Types& __t) {
1326  { __t <= __t } -> convertible_to<bool>; }) && ...)
1327 #endif
1328  constexpr bool
1329  operator<= [[nodiscard]] (const variant<_Types...>& __lhs,
1330  const variant<_Types...>& __rhs)
1331  {
1332  namespace __variant = __detail::__variant;
1333  return __variant::__compare(true, __lhs, __rhs,
1334  [](auto&& __l, auto&& __r) -> bool {
1335  return __l <= __r;
1336  });
1337  }
1338 
1339  template<typename... _Types>
1340 #if __cpp_lib_concepts
1341  requires ((requires (const _Types& __t) {
1342  { __t > __t } -> convertible_to<bool>; }) && ...)
1343 #endif
1344  constexpr bool
1345  operator> [[nodiscard]] (const variant<_Types...>& __lhs,
1346  const variant<_Types...>& __rhs)
1347  {
1348  namespace __variant = __detail::__variant;
1349  return __variant::__compare(true, __lhs, __rhs,
1350  [](auto&& __l, auto&& __r) -> bool {
1351  return __l > __r;
1352  });
1353  }
1354 
1355  template<typename... _Types>
1356 #if __cpp_lib_concepts
1357  requires ((requires (const _Types& __t) {
1358  { __t >= __t } -> convertible_to<bool>; }) && ...)
1359 #endif
1360  constexpr bool
1361  operator>= [[nodiscard]] (const variant<_Types...>& __lhs,
1362  const variant<_Types...>& __rhs)
1363  {
1364  namespace __variant = __detail::__variant;
1365  return __variant::__compare(true, __lhs, __rhs,
1366  [](auto&& __l, auto&& __r) -> bool {
1367  return __l >= __r;
1368  });
1369  }
1370 
1371 #ifdef __cpp_lib_three_way_comparison
1372  template<typename... _Types>
1373  requires (three_way_comparable<_Types> && ...)
1374  constexpr
1375  common_comparison_category_t<compare_three_way_result_t<_Types>...>
1376  operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1377  {
1378  common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1379  = strong_ordering::equal;
1380  namespace __variant = __detail::__variant;
1381  return __variant::__compare(__ret, __v, __w,
1382  [](auto&& __l, auto&& __r) {
1383  return __l <=> __r;
1384  });
1385  }
1386 #endif
1387 
1388  template<typename _Visitor, typename... _Variants>
1389  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1390  visit(_Visitor&&, _Variants&&...);
1391 
1392 #if __cplusplus > 201703L
1393  template<typename _Res, typename _Visitor, typename... _Variants>
1394  constexpr _Res
1395  visit(_Visitor&&, _Variants&&...);
1396 #endif
1397 
1398  template<typename... _Types>
1399  _GLIBCXX20_CONSTEXPR
1400  inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1401  && (is_swappable_v<_Types> && ...)>
1402  swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1403  noexcept(noexcept(__lhs.swap(__rhs)))
1404  { __lhs.swap(__rhs); }
1405 
1406  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1407  // 2766. Swapping non-swappable types
1408  template<typename... _Types>
1409  enable_if_t<!((is_move_constructible_v<_Types> && ...)
1410  && (is_swappable_v<_Types> && ...))>
1411  swap(variant<_Types...>&, variant<_Types...>&) = delete;
1412 
1413 #if __cpp_lib_constexpr_exceptions >= 202502L
1414 #define _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS constexpr
1415 #else
1416 #define _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS
1417 #endif
1418  [[noreturn]] _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS void
1419  __throw_bad_variant_access(unsigned);
1420 
1421  class bad_variant_access : public exception
1422  {
1423  public:
1424  _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS bad_variant_access() noexcept { }
1425 
1426  _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS const char* what()
1427  const noexcept override
1428  { return _M_reason; }
1429 
1430  private:
1431  // Must only be called with a string literal
1432  _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS
1433  bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1434 
1435  // Must point to a string with static storage duration:
1436  const char* _M_reason = "bad variant access";
1437 
1438  friend _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS void
1439  __throw_bad_variant_access([[maybe_unused]] unsigned __n)
1440  {
1441  [[maybe_unused]] static constexpr const char* __reasons[] = {
1442  "std::get: wrong index for variant",
1443  "std::get: variant is valueless",
1444  "std::visit: variant is valueless",
1445  "std::visit<R>: variant is valueless",
1446  };
1447  _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__reasons[__n % 4u]));
1448  }
1449 #undef _GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS
1450  };
1451 
1452  template<typename... _Types>
1453  class variant
1454  : private __detail::__variant::_Variant_base<_Types...>,
1455  private _Enable_copy_move<
1456  __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1457  __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1458  __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1459  __detail::__variant::_Traits<_Types...>::_S_move_assign,
1460  variant<_Types...>>
1461  {
1462  private:
1463  template <typename... _UTypes, typename _Tp>
1464  friend _GLIBCXX20_CONSTEXPR decltype(auto)
1465  __variant_cast(_Tp&&);
1466 
1467  static_assert(sizeof...(_Types) > 0,
1468  "variant must have at least one alternative");
1469  static_assert(((std::is_object_v<_Types> && !is_array_v<_Types>) && ...),
1470  "variant alternatives must be non-array object types");
1471 
1472  using _Base = __detail::__variant::_Variant_base<_Types...>;
1473 
1474  template<typename _Tp>
1475  static constexpr bool __not_self
1476  = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1477 
1478  template<typename _Tp>
1479  static constexpr bool
1480  __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1481 
1482  template<typename _Tp>
1483  static constexpr size_t __accepted_index
1484  = __detail::__variant::__accepted_index<_Tp, variant>;
1485 
1486  template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1487  using __to_type = typename _Nth_type<_Np, _Types...>::type;
1488 
1489  template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1490  using __accepted_type = __to_type<__accepted_index<_Tp>>;
1491 
1492  template<typename _Tp>
1493  static constexpr size_t __index_of
1494  = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1495 
1496  using _Traits = __detail::__variant::_Traits<_Types...>;
1497 
1498  template<typename _Tp>
1499  static constexpr bool __not_in_place_tag
1500  = !__is_in_place_type_v<__remove_cvref_t<_Tp>>
1501  && !__is_in_place_index_v<__remove_cvref_t<_Tp>>;
1502 
1503  public:
1504 #if __cpp_concepts
1505  variant() requires is_default_constructible_v<__to_type<0>> = default;
1506 #else
1507  template<typename _Tp0 = __to_type<0>,
1508  typename = enable_if_t<is_default_constructible_v<_Tp0>>>
1509  constexpr
1510  variant() noexcept(is_nothrow_default_constructible_v<__to_type<0>>)
1511  { }
1512 #endif
1513 
1514  variant(const variant& __rhs) = default;
1515  variant(variant&&) = default;
1516  variant& operator=(const variant&) = default;
1517  variant& operator=(variant&&) = default;
1518  _GLIBCXX20_CONSTEXPR ~variant() = default;
1519 
1520  template<typename _Tp,
1521  typename = enable_if_t<sizeof...(_Types) != 0>,
1522  typename = enable_if_t<__not_in_place_tag<_Tp>>,
1523  typename _Tj = __accepted_type<_Tp&&>,
1524  typename = enable_if_t<__exactly_once<_Tj>
1525  && is_constructible_v<_Tj, _Tp>>>
1526  constexpr
1527  variant(_Tp&& __t)
1528  noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1529  : variant(in_place_index<__accepted_index<_Tp>>,
1530  std::forward<_Tp>(__t))
1531  { }
1532 
1533  template<typename _Tp, typename... _Args,
1534  typename = enable_if_t<__exactly_once<_Tp>
1535  && is_constructible_v<_Tp, _Args...>>>
1536  constexpr explicit
1537  variant(in_place_type_t<_Tp>, _Args&&... __args)
1538  : variant(in_place_index<__index_of<_Tp>>,
1539  std::forward<_Args>(__args)...)
1540  { }
1541 
1542  template<typename _Tp, typename _Up, typename... _Args,
1543  typename = enable_if_t<__exactly_once<_Tp>
1544  && is_constructible_v<_Tp,
1545  initializer_list<_Up>&, _Args...>>>
1546  constexpr explicit
1547  variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1548  _Args&&... __args)
1549  : variant(in_place_index<__index_of<_Tp>>, __il,
1550  std::forward<_Args>(__args)...)
1551  { }
1552 
1553  template<size_t _Np, typename... _Args,
1554  typename _Tp = __to_type<_Np>,
1555  typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1556  constexpr explicit
1557  variant(in_place_index_t<_Np>, _Args&&... __args)
1558  : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...)
1559  { }
1560 
1561  template<size_t _Np, typename _Up, typename... _Args,
1562  typename _Tp = __to_type<_Np>,
1563  typename = enable_if_t<is_constructible_v<_Tp,
1564  initializer_list<_Up>&,
1565  _Args...>>>
1566  constexpr explicit
1567  variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1568  _Args&&... __args)
1569  : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...)
1570  { }
1571 
1572  template<typename _Tp>
1573  _GLIBCXX20_CONSTEXPR
1574  enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1575  && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1576  && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1577  variant&>
1578  operator=(_Tp&& __rhs)
1579  noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1580  && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1581  {
1582  constexpr auto __index = __accepted_index<_Tp>;
1583  if (index() == __index)
1584  std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1585  else
1586  {
1587  using _Tj = __accepted_type<_Tp&&>;
1588  if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1589  || !is_nothrow_move_constructible_v<_Tj>)
1590  this->emplace<__index>(std::forward<_Tp>(__rhs));
1591  else
1592  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1593  // 3585. converting assignment with immovable alternative
1594  this->emplace<__index>(_Tj(std::forward<_Tp>(__rhs)));
1595  }
1596  return *this;
1597  }
1598 
1599  template<typename _Tp, typename... _Args>
1600  _GLIBCXX20_CONSTEXPR
1601  enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1602  _Tp&>
1603  emplace(_Args&&... __args)
1604  {
1605  constexpr size_t __index = __index_of<_Tp>;
1606  return this->emplace<__index>(std::forward<_Args>(__args)...);
1607  }
1608 
1609  template<typename _Tp, typename _Up, typename... _Args>
1610  _GLIBCXX20_CONSTEXPR
1611  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1612  && __exactly_once<_Tp>,
1613  _Tp&>
1614  emplace(initializer_list<_Up> __il, _Args&&... __args)
1615  {
1616  constexpr size_t __index = __index_of<_Tp>;
1617  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1618  }
1619 
1620  template<size_t _Np, typename... _Args>
1621  _GLIBCXX20_CONSTEXPR
1622  enable_if_t<is_constructible_v<__to_type<_Np>, _Args...>,
1623  __to_type<_Np>&>
1624  emplace(_Args&&... __args)
1625  {
1626  namespace __variant = std::__detail::__variant;
1627  using type = typename _Nth_type<_Np, _Types...>::type;
1628  // Provide the strong exception-safety guarantee when possible,
1629  // to avoid becoming valueless.
1630  if constexpr (is_nothrow_constructible_v<type, _Args...>)
1631  {
1632  __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1633  }
1634  else if constexpr (is_scalar_v<type>)
1635  {
1636  // This might invoke a potentially-throwing conversion operator:
1637  const type __tmp(std::forward<_Args>(__args)...);
1638  // But this won't throw:
1639  __variant::__emplace<_Np>(*this, __tmp);
1640  }
1641  else if constexpr (__variant::_Never_valueless_alt<type>()
1642  && _Traits::_S_move_assign)
1643  {
1644  // This construction might throw:
1645  variant __tmp(in_place_index<_Np>,
1646  std::forward<_Args>(__args)...);
1647  // But _Never_valueless_alt<type> means this won't:
1648  *this = std::move(__tmp);
1649  }
1650  else
1651  {
1652  // This case only provides the basic exception-safety guarantee,
1653  // i.e. the variant can become valueless.
1654  __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1655  }
1656  return std::get<_Np>(*this);
1657  }
1658 
1659  template<size_t _Np, typename _Up, typename... _Args>
1660  _GLIBCXX20_CONSTEXPR
1661  enable_if_t<is_constructible_v<__to_type<_Np>,
1662  initializer_list<_Up>&, _Args...>,
1663  __to_type<_Np>&>
1664  emplace(initializer_list<_Up> __il, _Args&&... __args)
1665  {
1666  namespace __variant = std::__detail::__variant;
1667  using type = typename _Nth_type<_Np, _Types...>::type;
1668  // Provide the strong exception-safety guarantee when possible,
1669  // to avoid becoming valueless.
1670  if constexpr (is_nothrow_constructible_v<type,
1671  initializer_list<_Up>&,
1672  _Args...>)
1673  {
1674  __variant::__emplace<_Np>(*this, __il,
1675  std::forward<_Args>(__args)...);
1676  }
1677  else if constexpr (__variant::_Never_valueless_alt<type>()
1678  && _Traits::_S_move_assign)
1679  {
1680  // This construction might throw:
1681  variant __tmp(in_place_index<_Np>, __il,
1682  std::forward<_Args>(__args)...);
1683  // But _Never_valueless_alt<type> means this won't:
1684  *this = std::move(__tmp);
1685  }
1686  else
1687  {
1688  // This case only provides the basic exception-safety guarantee,
1689  // i.e. the variant can become valueless.
1690  __variant::__emplace<_Np>(*this, __il,
1691  std::forward<_Args>(__args)...);
1692  }
1693  return std::get<_Np>(*this);
1694  }
1695 
1696  template<size_t _Np, typename... _Args>
1697  enable_if_t<!(_Np < sizeof...(_Types))> emplace(_Args&&...) = delete;
1698 
1699  template<typename _Tp, typename... _Args>
1700  enable_if_t<!__exactly_once<_Tp>> emplace(_Args&&...) = delete;
1701 
1702  constexpr bool valueless_by_exception() const noexcept
1703  { return !this->_M_valid(); }
1704 
1705  constexpr size_t index() const noexcept
1706  {
1707  using __index_type = typename _Base::__index_type;
1708  if constexpr (__detail::__variant::__never_valueless<_Types...>())
1709  return this->_M_index;
1710  else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1711  return make_signed_t<__index_type>(this->_M_index);
1712  else
1713  return size_t(__index_type(this->_M_index + 1)) - 1;
1714  }
1715 
1716  _GLIBCXX20_CONSTEXPR
1717  void
1718  swap(variant& __rhs)
1719  noexcept((__is_nothrow_swappable<_Types>::value && ...)
1720  && is_nothrow_move_constructible_v<variant>)
1721  {
1722  static_assert((is_move_constructible_v<_Types> && ...));
1723 
1724  // Handle this here to simplify the visitation.
1725  if (__rhs.valueless_by_exception()) [[__unlikely__]]
1726  {
1727  if (!this->valueless_by_exception()) [[__likely__]]
1728  __rhs.swap(*this);
1729  return;
1730  }
1731 
1732  namespace __variant = __detail::__variant;
1733 
1734  __variant::__raw_idx_visit(
1735  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1736  {
1737  constexpr size_t __j = __rhs_index;
1738  if constexpr (__j != variant_npos)
1739  {
1740  if (this->index() == __j)
1741  {
1742  using std::swap;
1743  swap(std::get<__j>(*this), __rhs_mem);
1744  }
1745  else
1746  {
1747  auto __tmp(std::move(__rhs_mem));
1748 
1749  if constexpr (_Traits::_S_trivial_move_assign)
1750  __rhs = std::move(*this);
1751  else
1752  __variant::__raw_idx_visit(
1753  [&__rhs](auto&& __this_mem, auto __this_index) mutable
1754  {
1755  constexpr size_t __k = __this_index;
1756  if constexpr (__k != variant_npos)
1757  __variant::__emplace<__k>(__rhs,
1758  std::move(__this_mem));
1759  }, *this);
1760 
1761  __variant::__emplace<__j>(*this, std::move(__tmp));
1762  }
1763  }
1764  }, __rhs);
1765  }
1766 
1767 #if __cpp_lib_variant >= 202306L // >= C++26
1768  // [variant.visit], visitation
1769 
1770  /** Simple visitation for a single variant
1771  *
1772  * To visit a single variant you can use `var.visit(visitor)`
1773  * instead of `std::visit(visitor, var)`.
1774  *
1775  * @since C++26
1776  */
1777  template<int = 0, typename _Self, typename _Visitor>
1778  constexpr decltype(auto)
1779  visit(this _Self&& __self, _Visitor&& __vis)
1780  {
1781  using _CVar = __conditional_t<is_const_v<remove_reference_t<_Self>>,
1782  const variant, variant>;
1783  using _Var = __conditional_t<is_rvalue_reference_v<_Self&&>,
1784  _CVar&&, _CVar&>;
1785  return std::visit(std::forward<_Visitor>(__vis), (_Var)__self);
1786  }
1787 
1788  /** Simple visitation for a single variant, with explicit return type
1789  *
1790  * To visit a single variant you can use `var.visit<R>(visitor)`
1791  * instead of `std::visit<R>(visitor, var)`.
1792  *
1793  * @since C++26
1794  */
1795  template<typename _Res, typename _Self, typename _Visitor>
1796  constexpr _Res
1797  visit(this _Self&& __self, _Visitor&& __vis)
1798  {
1799  using _CVar = __conditional_t<is_const_v<remove_reference_t<_Self>>,
1800  const variant, variant>;
1801  using _Var = __conditional_t<is_rvalue_reference_v<_Self&&>,
1802  _CVar&&, _CVar&>;
1803  return std::visit<_Res>(std::forward<_Visitor>(__vis), (_Var)__self);
1804  }
1805 #endif
1806 
1807  private:
1808  template<size_t _Np, typename _Vp>
1809  friend constexpr decltype(auto)
1810  __detail::__variant::__get(_Vp&& __v) noexcept;
1811  };
1812 
1813  template<size_t _Np, typename... _Types>
1814  constexpr variant_alternative_t<_Np, variant<_Types...>>&
1815  get(variant<_Types...>& __v)
1816  {
1817  static_assert(_Np < sizeof...(_Types),
1818  "The index must be in [0, number of alternatives)");
1819  if (__v.index() != _Np)
1820  __throw_bad_variant_access(__v.valueless_by_exception());
1821  return __detail::__variant::__get<_Np>(__v);
1822  }
1823 
1824  template<size_t _Np, typename... _Types>
1825  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1826  get(variant<_Types...>&& __v)
1827  {
1828  static_assert(_Np < sizeof...(_Types),
1829  "The index must be in [0, number of alternatives)");
1830  if (__v.index() != _Np)
1831  __throw_bad_variant_access(__v.valueless_by_exception());
1832  return __detail::__variant::__get<_Np>(std::move(__v));
1833  }
1834 
1835  template<size_t _Np, typename... _Types>
1836  constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1837  get(const variant<_Types...>& __v)
1838  {
1839  static_assert(_Np < sizeof...(_Types),
1840  "The index must be in [0, number of alternatives)");
1841  if (__v.index() != _Np)
1842  __throw_bad_variant_access(__v.valueless_by_exception());
1843  return __detail::__variant::__get<_Np>(__v);
1844  }
1845 
1846  template<size_t _Np, typename... _Types>
1847  constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1848  get(const variant<_Types...>&& __v)
1849  {
1850  static_assert(_Np < sizeof...(_Types),
1851  "The index must be in [0, number of alternatives)");
1852  if (__v.index() != _Np)
1853  __throw_bad_variant_access(__v.valueless_by_exception());
1854  return __detail::__variant::__get<_Np>(std::move(__v));
1855  }
1856 
1857  /// @cond undocumented
1858  template<typename _Result_type, typename _Visitor, typename... _Variants>
1859  constexpr decltype(auto)
1860  __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1861  {
1862  // Get the silly case of visiting no variants out of the way first.
1863  if constexpr (sizeof...(_Variants) == 0)
1864  {
1865  if constexpr (is_void_v<_Result_type>)
1866  return (void) std::forward<_Visitor>(__visitor)();
1867  else
1868  return std::forward<_Visitor>(__visitor)();
1869  }
1870  else
1871  {
1872  constexpr size_t __max = 11; // "These go to eleven."
1873 
1874  // The type of the first variant in the pack.
1875  using _V0 = typename _Nth_type<0, _Variants...>::type;
1876  // The number of alternatives in that first variant.
1877  constexpr auto __n = variant_size_v<remove_reference_t<_V0>>;
1878 
1879  if constexpr (sizeof...(_Variants) > 1 || __n > __max)
1880  {
1881  // Use a jump table for the general case.
1882  constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1883  _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1884 
1885  auto __func_ptr = __vtable._M_access(__variants.index()...);
1886  return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1887  std::forward<_Variants>(__variants)...);
1888  }
1889  else // We have a single variant with a small number of alternatives.
1890  {
1891  // A name for the first variant in the pack.
1892  _V0& __v0
1893  = [](_V0& __v, ...) -> _V0& { return __v; }(__variants...);
1894 
1895  using __detail::__variant::_Multi_array;
1896  using __detail::__variant::__gen_vtable_impl;
1897  using _Ma = _Multi_array<_Result_type (*)(_Visitor&&, _V0&&)>;
1898 
1899 #ifdef _GLIBCXX_DEBUG
1900 # define _GLIBCXX_VISIT_UNREACHABLE __builtin_trap
1901 #else
1902 # define _GLIBCXX_VISIT_UNREACHABLE __builtin_unreachable
1903 #endif
1904 
1905 #define _GLIBCXX_VISIT_CASE(N) \
1906  case N: \
1907  { \
1908  if constexpr (N < __n) \
1909  { \
1910  return __gen_vtable_impl<_Ma, index_sequence<N>>:: \
1911  __visit_invoke(std::forward<_Visitor>(__visitor), \
1912  std::forward<_V0>(__v0)); \
1913  } \
1914  else _GLIBCXX_VISIT_UNREACHABLE(); \
1915  }
1916 
1917  switch (__v0.index())
1918  {
1919  _GLIBCXX_VISIT_CASE(0)
1920  _GLIBCXX_VISIT_CASE(1)
1921  _GLIBCXX_VISIT_CASE(2)
1922  _GLIBCXX_VISIT_CASE(3)
1923  _GLIBCXX_VISIT_CASE(4)
1924  _GLIBCXX_VISIT_CASE(5)
1925  _GLIBCXX_VISIT_CASE(6)
1926  _GLIBCXX_VISIT_CASE(7)
1927  _GLIBCXX_VISIT_CASE(8)
1928  _GLIBCXX_VISIT_CASE(9)
1929  _GLIBCXX_VISIT_CASE(10)
1930  case variant_npos:
1931  using __detail::__variant::__variant_idx_cookie;
1932  using __detail::__variant::__variant_cookie;
1933  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
1934  || is_same_v<_Result_type, __variant_cookie>)
1935  {
1936  using _Npos = index_sequence<variant_npos>;
1937  return __gen_vtable_impl<_Ma, _Npos>::
1938  __visit_invoke(std::forward<_Visitor>(__visitor),
1939  std::forward<_V0>(__v0));
1940  }
1941  else
1942  _GLIBCXX_VISIT_UNREACHABLE();
1943  default:
1944  _GLIBCXX_VISIT_UNREACHABLE();
1945  }
1946 #undef _GLIBCXX_VISIT_CASE
1947 #undef _GLIBCXX_VISIT_UNREACHABLE
1948  }
1949  }
1950  }
1951  /// @endcond
1952 
1953  template<typename _Visitor, typename... _Variants>
1954  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1955  visit(_Visitor&& __visitor, _Variants&&... __variants)
1956  {
1957  namespace __variant = std::__detail::__variant;
1958 
1959  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1960  __throw_bad_variant_access(2);
1961 
1962  using _Result_type
1963  = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1964 
1965  using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1966 
1967  if constexpr (sizeof...(_Variants) == 1)
1968  {
1969  using _Vp = decltype(__variant::__as(std::declval<_Variants>()...));
1970 
1971  constexpr bool __visit_rettypes_match = __detail::__variant::
1972  __check_visitor_results<_Visitor, _Vp>(
1973  make_index_sequence<variant_size_v<remove_reference_t<_Vp>>>());
1974  if constexpr (!__visit_rettypes_match)
1975  {
1976  static_assert(__visit_rettypes_match,
1977  "std::visit requires the visitor to have the same "
1978  "return type for all alternatives of a variant");
1979  return;
1980  }
1981  else
1982  return std::__do_visit<_Tag>(
1983  std::forward<_Visitor>(__visitor),
1984  static_cast<_Vp>(__variants)...);
1985  }
1986  else
1987  return std::__do_visit<_Tag>(
1988  std::forward<_Visitor>(__visitor),
1989  __variant::__as(std::forward<_Variants>(__variants))...);
1990  }
1991 
1992 #if __cplusplus > 201703L
1993  template<typename _Res, typename _Visitor, typename... _Variants>
1994  constexpr _Res
1995  visit(_Visitor&& __visitor, _Variants&&... __variants)
1996  {
1997  namespace __variant = std::__detail::__variant;
1998 
1999  if ((__variant::__as(__variants).valueless_by_exception() || ...))
2000  __throw_bad_variant_access(3);
2001 
2002  return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
2003  __variant::__as(std::forward<_Variants>(__variants))...);
2004  }
2005 #endif
2006 
2007  /// @cond undocumented
2008  template<typename... _Types>
2009  struct __variant_hash
2010  {
2011 #if __cplusplus < 202002L
2012  using result_type [[__deprecated__]] = size_t;
2013  using argument_type [[__deprecated__]] = variant<_Types...>;
2014 #endif
2015 
2016  size_t
2017  operator()(const variant<_Types...>& __t) const
2018  noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
2019  {
2020  size_t __ret;
2021  __detail::__variant::__raw_visit(
2022  [&__t, &__ret](auto&& __t_mem) mutable
2023  {
2024  using _Type = __remove_cvref_t<decltype(__t_mem)>;
2025  if constexpr (!is_same_v<_Type,
2026  __detail::__variant::__variant_cookie>)
2027  __ret = std::hash<size_t>{}(__t.index())
2028  + std::hash<_Type>{}(__t_mem);
2029  else
2030  __ret = std::hash<size_t>{}(__t.index());
2031  }, __t);
2032  return __ret;
2033  }
2034  };
2035  /// @endcond
2036 
2037  template<typename... _Types>
2038  struct hash<variant<_Types...>>
2039  : __conditional_t<(__is_hash_enabled_for<remove_const_t<_Types>> && ...),
2040  __variant_hash<_Types...>,
2041  __hash_not_enabled<variant<_Types...>>>
2042 #if ! _GLIBCXX_INLINE_VERSION
2043  , __detail::__variant::_Variant_hash_base<variant<_Types...>,
2044  index_sequence_for<_Types...>>
2045 #endif
2046  { };
2047 
2048  template<typename... _Types>
2049  struct __is_fast_hash<hash<variant<_Types...>>>
2050  : bool_constant<(__is_fast_hash<_Types>::value && ...)>
2051  { };
2052 
2053 _GLIBCXX_END_NAMESPACE_VERSION
2054 } // namespace std
2055 
2056 #endif // __cpp_lib_variant
2057 #endif // _GLIBCXX_VARIANT
std::compare_three_way_result_t
typename __detail::__cmp3way_res_impl< _Tp, _Up >::type compare_three_way_result_t
[cmp.result], result of three-way comparison
Definition: compare:549
std::make_index_sequence
make_integer_sequence< size_t, _Num > make_index_sequence
Alias template make_index_sequence.
Definition: utility.h:168
std::integer_sequence
Class template integer_sequence.
Definition: utility.h:144
std::enable_if_t
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition: type_traits:2942
std::add_pointer_t
typename add_pointer< _Tp >::type add_pointer_t
Alias template for add_pointer.
Definition: type_traits:2358
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:119
std::_Construct
constexpr void _Construct(_Tp *__p, _Args &&... __args)
Definition: stl_construct.h:122
std
ISO C++ entities toplevel namespace is std.
std::false_type
__bool_constant< false > false_type
The type used as a compile-time boolean with false value.
Definition: type_traits:122
std::make_signed_t
typename make_signed< _Tp >::type make_signed_t
Alias template for make_signed.
Definition: type_traits:2244
__detail
Definition: simd.h:306
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:138
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:72
std::hash
Primary class template hash.
Definition: string_view:796
std::addressof
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:176
std::remove_reference_t
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition: type_traits:1888
std::experimental::fundamentals_v2::void_t
void void_t
A metafunction that always yields void, used for detecting valid types.
Definition: experimental/type_traits:262
std::integral_constant
integral_constant
Definition: type_traits:95
std::__invoke
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition: invoke.h:92
std::index_sequence
integer_sequence< size_t, _Idx... > index_sequence
Alias template index_sequence.
Definition: utility.h:164