libstdc++
variant
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1 // <variant> -*- C++ -*-
2 
3 // Copyright (C) 2016-2021 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file variant
26  * This is the `<variant>` C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_VARIANT
30 #define _GLIBCXX_VARIANT 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus >= 201703L
35 
36 #include <initializer_list>
37 #include <type_traits>
39 #include <bits/exception_defines.h>
40 #include <bits/functional_hash.h>
41 #include <bits/invoke.h>
42 #include <bits/parse_numbers.h>
45 #include <bits/stl_construct.h>
46 #include <bits/utility.h> // in_place_index_t
47 #if __cplusplus == 201703L
48 # include <ext/aligned_buffer.h>
49 #else
50 # include <compare>
51 #endif
52 
53 namespace std _GLIBCXX_VISIBILITY(default)
54 {
55 _GLIBCXX_BEGIN_NAMESPACE_VERSION
56 
57 #if __cplusplus >= 202002L && __cpp_concepts
58 // P2231R1 constexpr needs constexpr unions and constrained destructors.
59 # define __cpp_lib_variant 202106L
60 #else
61 # define __cpp_lib_variant 202102L
62 #endif
63 
64  template<typename... _Types> class tuple;
65  template<typename... _Types> class variant;
66  template <typename> struct hash;
67 
68  template<typename _Variant>
69  struct variant_size;
70 
71  template<typename _Variant>
72  struct variant_size<const _Variant> : variant_size<_Variant> {};
73 
74  template<typename _Variant>
75  struct variant_size<volatile _Variant> : variant_size<_Variant> {};
76 
77  template<typename _Variant>
78  struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
79 
80  template<typename... _Types>
81  struct variant_size<variant<_Types...>>
82  : std::integral_constant<size_t, sizeof...(_Types)> {};
83 
84  template<typename _Variant>
85  inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
86 
87  template<typename... _Types>
88  inline constexpr size_t
89  variant_size_v<variant<_Types...>> = sizeof...(_Types);
90 
91  template<typename... _Types>
92  inline constexpr size_t
93  variant_size_v<const variant<_Types...>> = sizeof...(_Types);
94 
95  template<size_t _Np, typename _Variant>
96  struct variant_alternative;
97 
98  template<size_t _Np, typename... _Types>
99  struct variant_alternative<_Np, variant<_Types...>>
100  {
101  static_assert(_Np < sizeof...(_Types));
102 
103  using type = typename _Nth_type<_Np, _Types...>::type;
104  };
105 
106  template<size_t _Np, typename _Variant>
107  using variant_alternative_t =
108  typename variant_alternative<_Np, _Variant>::type;
109 
110  template<size_t _Np, typename _Variant>
111  struct variant_alternative<_Np, const _Variant>
112  { using type = add_const_t<variant_alternative_t<_Np, _Variant>>; };
113 
114  template<size_t _Np, typename _Variant>
115  struct variant_alternative<_Np, volatile _Variant>
116  { using type = add_volatile_t<variant_alternative_t<_Np, _Variant>>; };
117 
118  template<size_t _Np, typename _Variant>
119  struct variant_alternative<_Np, const volatile _Variant>
120  { using type = add_cv_t<variant_alternative_t<_Np, _Variant>>; };
121 
122  inline constexpr size_t variant_npos = -1;
123 
124  template<size_t _Np, typename... _Types>
125  constexpr variant_alternative_t<_Np, variant<_Types...>>&
126  get(variant<_Types...>&);
127 
128  template<size_t _Np, typename... _Types>
129  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
130  get(variant<_Types...>&&);
131 
132  template<size_t _Np, typename... _Types>
133  constexpr variant_alternative_t<_Np, variant<_Types...>> const&
134  get(const variant<_Types...>&);
135 
136  template<size_t _Np, typename... _Types>
137  constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
138  get(const variant<_Types...>&&);
139 
140  template<typename _Result_type, typename _Visitor, typename... _Variants>
141  constexpr decltype(auto)
142  __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
143 
144  template <typename... _Types, typename _Tp>
145  _GLIBCXX20_CONSTEXPR
146  decltype(auto)
147  __variant_cast(_Tp&& __rhs)
148  {
149  if constexpr (is_lvalue_reference_v<_Tp>)
150  {
151  if constexpr (is_const_v<remove_reference_t<_Tp>>)
152  return static_cast<const variant<_Types...>&>(__rhs);
153  else
154  return static_cast<variant<_Types...>&>(__rhs);
155  }
156  else
157  return static_cast<variant<_Types...>&&>(__rhs);
158  }
159 
160 namespace __detail
161 {
162 namespace __variant
163 {
164  // used for raw visitation
165  struct __variant_cookie {};
166  // used for raw visitation with indices passed in
167  struct __variant_idx_cookie { using type = __variant_idx_cookie; };
168  // Used to enable deduction (and same-type checking) for std::visit:
169  template<typename _Tp> struct __deduce_visit_result { using type = _Tp; };
170 
171  // Visit variants that might be valueless.
172  template<typename _Visitor, typename... _Variants>
173  constexpr void
174  __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
175  {
176  std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
177  std::forward<_Variants>(__variants)...);
178  }
179 
180  // Visit variants that might be valueless, passing indices to the visitor.
181  template<typename _Visitor, typename... _Variants>
182  constexpr void
183  __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
184  {
185  std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
186  std::forward<_Variants>(__variants)...);
187  }
188 
189  // The __as function templates implement the exposition-only "as-variant"
190 
191  template<typename... _Types>
192  constexpr std::variant<_Types...>&
193  __as(std::variant<_Types...>& __v) noexcept
194  { return __v; }
195 
196  template<typename... _Types>
197  constexpr const std::variant<_Types...>&
198  __as(const std::variant<_Types...>& __v) noexcept
199  { return __v; }
200 
201  template<typename... _Types>
202  constexpr std::variant<_Types...>&&
203  __as(std::variant<_Types...>&& __v) noexcept
204  { return std::move(__v); }
205 
206  template<typename... _Types>
207  constexpr const std::variant<_Types...>&&
208  __as(const std::variant<_Types...>&& __v) noexcept
209  { return std::move(__v); }
210 
211  // For C++17:
212  // _Uninitialized<T> is guaranteed to be a trivially destructible type,
213  // even if T is not.
214  // For C++20:
215  // _Uninitialized<T> is trivially destructible iff T is, so _Variant_union
216  // needs a constrained non-trivial destructor.
217  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
218  struct _Uninitialized;
219 
220  template<typename _Type>
221  struct _Uninitialized<_Type, true>
222  {
223  template<typename... _Args>
224  constexpr
225  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
226  : _M_storage(std::forward<_Args>(__args)...)
227  { }
228 
229  constexpr const _Type& _M_get() const & noexcept
230  { return _M_storage; }
231 
232  constexpr _Type& _M_get() & noexcept
233  { return _M_storage; }
234 
235  constexpr const _Type&& _M_get() const && noexcept
236  { return std::move(_M_storage); }
237 
238  constexpr _Type&& _M_get() && noexcept
239  { return std::move(_M_storage); }
240 
241  _Type _M_storage;
242  };
243 
244  template<typename _Type>
245  struct _Uninitialized<_Type, false>
246  {
247 #if __cpp_lib_variant >= 202106L
248  template<typename... _Args>
249  constexpr
250  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
251  : _M_storage(std::forward<_Args>(__args)...)
252  { }
253 
254  constexpr ~_Uninitialized() { }
255 
256  _Uninitialized(const _Uninitialized&) = default;
257  _Uninitialized(_Uninitialized&&) = default;
258  _Uninitialized& operator=(const _Uninitialized&) = default;
259  _Uninitialized& operator=(_Uninitialized&&) = default;
260 
261  constexpr const _Type& _M_get() const & noexcept
262  { return _M_storage; }
263 
264  constexpr _Type& _M_get() & noexcept
265  { return _M_storage; }
266 
267  constexpr const _Type&& _M_get() const && noexcept
268  { return std::move(_M_storage); }
269 
270  constexpr _Type&& _M_get() && noexcept
271  { return std::move(_M_storage); }
272 
273  struct _Empty_byte { };
274 
275  union {
276  _Empty_byte _M_empty;
277  _Type _M_storage;
278  };
279 #else
280  template<typename... _Args>
281  constexpr
282  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
283  {
284  ::new ((void*)std::addressof(_M_storage))
285  _Type(std::forward<_Args>(__args)...);
286  }
287 
288  const _Type& _M_get() const & noexcept
289  { return *_M_storage._M_ptr(); }
290 
291  _Type& _M_get() & noexcept
292  { return *_M_storage._M_ptr(); }
293 
294  const _Type&& _M_get() const && noexcept
295  { return std::move(*_M_storage._M_ptr()); }
296 
297  _Type&& _M_get() && noexcept
298  { return std::move(*_M_storage._M_ptr()); }
299 
300  __gnu_cxx::__aligned_membuf<_Type> _M_storage;
301 #endif
302  };
303 
304  template<size_t _Np, typename _Union>
305  constexpr decltype(auto)
306  __get_n(_Union&& __u) noexcept
307  {
308  if constexpr (_Np == 0)
309  return std::forward<_Union>(__u)._M_first._M_get();
310  else if constexpr (_Np == 1)
311  return std::forward<_Union>(__u)._M_rest._M_first._M_get();
312  else if constexpr (_Np == 2)
313  return std::forward<_Union>(__u)._M_rest._M_rest._M_first._M_get();
314  else
315  return __variant::__get_n<_Np - 3>(
316  std::forward<_Union>(__u)._M_rest._M_rest._M_rest);
317  }
318 
319  // Returns the typed storage for __v.
320  template<size_t _Np, typename _Variant>
321  constexpr decltype(auto)
322  __get(_Variant&& __v) noexcept
323  { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); }
324 
325  template<typename... _Types>
326  struct _Traits
327  {
328  static constexpr bool _S_default_ctor =
329  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
330  static constexpr bool _S_copy_ctor =
331  (is_copy_constructible_v<_Types> && ...);
332  static constexpr bool _S_move_ctor =
333  (is_move_constructible_v<_Types> && ...);
334  static constexpr bool _S_copy_assign =
335  _S_copy_ctor
336  && (is_copy_assignable_v<_Types> && ...);
337  static constexpr bool _S_move_assign =
338  _S_move_ctor
339  && (is_move_assignable_v<_Types> && ...);
340 
341  static constexpr bool _S_trivial_dtor =
342  (is_trivially_destructible_v<_Types> && ...);
343  static constexpr bool _S_trivial_copy_ctor =
344  (is_trivially_copy_constructible_v<_Types> && ...);
345  static constexpr bool _S_trivial_move_ctor =
346  (is_trivially_move_constructible_v<_Types> && ...);
347  static constexpr bool _S_trivial_copy_assign =
348  _S_trivial_dtor && _S_trivial_copy_ctor
349  && (is_trivially_copy_assignable_v<_Types> && ...);
350  static constexpr bool _S_trivial_move_assign =
351  _S_trivial_dtor && _S_trivial_move_ctor
352  && (is_trivially_move_assignable_v<_Types> && ...);
353 
354  // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
355  // are always nothrow.
356  static constexpr bool _S_nothrow_default_ctor =
357  is_nothrow_default_constructible_v<
358  typename _Nth_type<0, _Types...>::type>;
359  static constexpr bool _S_nothrow_copy_ctor = false;
360  static constexpr bool _S_nothrow_move_ctor =
361  (is_nothrow_move_constructible_v<_Types> && ...);
362  static constexpr bool _S_nothrow_copy_assign = false;
363  static constexpr bool _S_nothrow_move_assign =
364  _S_nothrow_move_ctor
365  && (is_nothrow_move_assignable_v<_Types> && ...);
366  };
367 
368  // Defines members and ctors.
369  template<typename... _Types>
370  union _Variadic_union
371  {
372  _Variadic_union() = default;
373 
374  template<size_t _Np, typename... _Args>
375  _Variadic_union(in_place_index_t<_Np>, _Args&&...) = delete;
376  };
377 
378  template<typename _First, typename... _Rest>
379  union _Variadic_union<_First, _Rest...>
380  {
381  constexpr _Variadic_union() : _M_rest() { }
382 
383  template<typename... _Args>
384  constexpr
385  _Variadic_union(in_place_index_t<0>, _Args&&... __args)
386  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
387  { }
388 
389  template<size_t _Np, typename... _Args>
390  constexpr
391  _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
392  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
393  { }
394 
395 #if __cpp_lib_variant >= 202106L
396  _Variadic_union(const _Variadic_union&) = default;
397  _Variadic_union(_Variadic_union&&) = default;
398  _Variadic_union& operator=(const _Variadic_union&) = default;
399  _Variadic_union& operator=(_Variadic_union&&) = default;
400 
401  ~_Variadic_union() = default;
402 
403  constexpr ~_Variadic_union()
404  requires (!__has_trivial_destructor(_First))
405  || (!__has_trivial_destructor(_Variadic_union<_Rest...>))
406  { }
407 #endif
408 
409  _Uninitialized<_First> _M_first;
410  _Variadic_union<_Rest...> _M_rest;
411  };
412 
413  // _Never_valueless_alt is true for variant alternatives that can
414  // always be placed in a variant without it becoming valueless.
415 
416  // For suitably-small, trivially copyable types we can create temporaries
417  // on the stack and then memcpy them into place.
418  template<typename _Tp>
419  struct _Never_valueless_alt
420  : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
421  { };
422 
423  // Specialize _Never_valueless_alt for other types which have a
424  // non-throwing and cheap move construction and move assignment operator,
425  // so that emplacing the type will provide the strong exception-safety
426  // guarantee, by creating and moving a temporary.
427  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
428  // variant using that alternative, so we can't change the value later!
429 
430  // True if every alternative in _Types... can be emplaced in a variant
431  // without it becoming valueless. If this is true, variant<_Types...>
432  // can never be valueless, which enables some minor optimizations.
433  template <typename... _Types>
434  constexpr bool __never_valueless()
435  {
436  return _Traits<_Types...>::_S_move_assign
437  && (_Never_valueless_alt<_Types>::value && ...);
438  }
439 
440  // Defines index and the dtor, possibly trivial.
441  template<bool __trivially_destructible, typename... _Types>
442  struct _Variant_storage;
443 
444  template <typename... _Types>
445  using __select_index =
446  typename __select_int::_Select_int_base<sizeof...(_Types),
447  unsigned char,
448  unsigned short>::type::value_type;
449 
450  template<typename... _Types>
451  struct _Variant_storage<false, _Types...>
452  {
453  constexpr
454  _Variant_storage()
455  : _M_index(static_cast<__index_type>(variant_npos))
456  { }
457 
458  template<size_t _Np, typename... _Args>
459  constexpr
460  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
461  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
462  _M_index{_Np}
463  { }
464 
465  constexpr void
466  _M_reset()
467  {
468  if (!_M_valid()) [[unlikely]]
469  return;
470 
471  std::__do_visit<void>([](auto&& __this_mem) mutable
472  {
473  std::_Destroy(std::__addressof(__this_mem));
474  }, __variant_cast<_Types...>(*this));
475 
476  _M_index = static_cast<__index_type>(variant_npos);
477  }
478 
479  _GLIBCXX20_CONSTEXPR
480  ~_Variant_storage()
481  { _M_reset(); }
482 
483  constexpr bool
484  _M_valid() const noexcept
485  {
486  if constexpr (__variant::__never_valueless<_Types...>())
487  return true;
488  return this->_M_index != __index_type(variant_npos);
489  }
490 
491  _Variadic_union<_Types...> _M_u;
492  using __index_type = __select_index<_Types...>;
493  __index_type _M_index;
494  };
495 
496  template<typename... _Types>
497  struct _Variant_storage<true, _Types...>
498  {
499  constexpr
500  _Variant_storage()
501  : _M_index(static_cast<__index_type>(variant_npos))
502  { }
503 
504  template<size_t _Np, typename... _Args>
505  constexpr
506  _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
507  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
508  _M_index{_Np}
509  { }
510 
511  constexpr void
512  _M_reset() noexcept
513  { _M_index = static_cast<__index_type>(variant_npos); }
514 
515  constexpr bool
516  _M_valid() const noexcept
517  {
518  if constexpr (__variant::__never_valueless<_Types...>())
519  return true;
520  // It would be nice if we could just return true for -fno-exceptions.
521  // It's possible (but inadvisable) that a std::variant could become
522  // valueless in a translation unit compiled with -fexceptions and then
523  // be passed to functions compiled with -fno-exceptions. We would need
524  // some #ifdef _GLIBCXX_NO_EXCEPTIONS_GLOBALLY property to elide all
525  // checks for valueless_by_exception().
526  return this->_M_index != static_cast<__index_type>(variant_npos);
527  }
528 
529  _Variadic_union<_Types...> _M_u;
530  using __index_type = __select_index<_Types...>;
531  __index_type _M_index;
532  };
533 
534  // Implementation of v.emplace<N>(args...).
535  template<size_t _Np, bool _Triv, typename... _Types, typename... _Args>
536  _GLIBCXX20_CONSTEXPR
537  inline void
538  __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args)
539  {
540  __v._M_reset();
541  auto* __addr = std::__addressof(__variant::__get_n<_Np>(__v._M_u));
542  std::_Construct(__addr, std::forward<_Args>(__args)...);
543  // Construction didn't throw, so can set the new index now:
544  __v._M_index = _Np;
545  }
546 
547  template<typename... _Types>
548  using _Variant_storage_alias =
549  _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
550 
551  // The following are (Copy|Move) (ctor|assign) layers for forwarding
552  // triviality and handling non-trivial SMF behaviors.
553 
554  template<bool, typename... _Types>
555  struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
556  {
557  using _Base = _Variant_storage_alias<_Types...>;
558  using _Base::_Base;
559 
560  _GLIBCXX20_CONSTEXPR
561  _Copy_ctor_base(const _Copy_ctor_base& __rhs)
562  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
563  {
564  __variant::__raw_idx_visit(
565  [this](auto&& __rhs_mem, auto __rhs_index) mutable
566  {
567  constexpr size_t __j = __rhs_index;
568  if constexpr (__j != variant_npos)
569  std::_Construct(std::__addressof(this->_M_u),
570  in_place_index<__j>, __rhs_mem);
571  }, __variant_cast<_Types...>(__rhs));
572  this->_M_index = __rhs._M_index;
573  }
574 
575  _Copy_ctor_base(_Copy_ctor_base&&) = default;
576  _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
577  _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
578  };
579 
580  template<typename... _Types>
581  struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
582  {
583  using _Base = _Variant_storage_alias<_Types...>;
584  using _Base::_Base;
585  };
586 
587  template<typename... _Types>
588  using _Copy_ctor_alias =
589  _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
590 
591  template<bool, typename... _Types>
592  struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
593  {
594  using _Base = _Copy_ctor_alias<_Types...>;
595  using _Base::_Base;
596 
597  _GLIBCXX20_CONSTEXPR
598  _Move_ctor_base(_Move_ctor_base&& __rhs)
599  noexcept(_Traits<_Types...>::_S_nothrow_move_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>,
608  std::forward<decltype(__rhs_mem)>(__rhs_mem));
609  }, __variant_cast<_Types...>(std::move(__rhs)));
610  this->_M_index = __rhs._M_index;
611  }
612 
613  _Move_ctor_base(const _Move_ctor_base&) = default;
614  _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
615  _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
616  };
617 
618  template<typename... _Types>
619  struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
620  {
621  using _Base = _Copy_ctor_alias<_Types...>;
622  using _Base::_Base;
623  };
624 
625  template<typename... _Types>
626  using _Move_ctor_alias =
627  _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
628 
629  template<bool, typename... _Types>
630  struct _Copy_assign_base : _Move_ctor_alias<_Types...>
631  {
632  using _Base = _Move_ctor_alias<_Types...>;
633  using _Base::_Base;
634 
635  _GLIBCXX20_CONSTEXPR
636  _Copy_assign_base&
637  operator=(const _Copy_assign_base& __rhs)
638  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
639  {
640  __variant::__raw_idx_visit(
641  [this](auto&& __rhs_mem, auto __rhs_index) mutable
642  {
643  constexpr size_t __j = __rhs_index;
644  if constexpr (__j == variant_npos)
645  this->_M_reset(); // Make *this valueless.
646  else if (this->_M_index == __j)
647  __variant::__get<__j>(*this) = __rhs_mem;
648  else
649  {
650  using _Tj = typename _Nth_type<__j, _Types...>::type;
651  if constexpr (is_nothrow_copy_constructible_v<_Tj>
652  || !is_nothrow_move_constructible_v<_Tj>)
653  __variant::__emplace<__j>(*this, __rhs_mem);
654  else
655  {
656  using _Variant = variant<_Types...>;
657  _Variant& __self = __variant_cast<_Types...>(*this);
658  __self = _Variant(in_place_index<__j>, __rhs_mem);
659  }
660  }
661  }, __variant_cast<_Types...>(__rhs));
662  return *this;
663  }
664 
665  _Copy_assign_base(const _Copy_assign_base&) = default;
666  _Copy_assign_base(_Copy_assign_base&&) = default;
667  _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
668  };
669 
670  template<typename... _Types>
671  struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
672  {
673  using _Base = _Move_ctor_alias<_Types...>;
674  using _Base::_Base;
675  };
676 
677  template<typename... _Types>
678  using _Copy_assign_alias =
679  _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
680 
681  template<bool, typename... _Types>
682  struct _Move_assign_base : _Copy_assign_alias<_Types...>
683  {
684  using _Base = _Copy_assign_alias<_Types...>;
685  using _Base::_Base;
686 
687  _GLIBCXX20_CONSTEXPR
688  _Move_assign_base&
689  operator=(_Move_assign_base&& __rhs)
690  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
691  {
692  __variant::__raw_idx_visit(
693  [this](auto&& __rhs_mem, auto __rhs_index) mutable
694  {
695  constexpr size_t __j = __rhs_index;
696  if constexpr (__j != variant_npos)
697  {
698  if (this->_M_index == __j)
699  __variant::__get<__j>(*this) = std::move(__rhs_mem);
700  else
701  {
702  using _Tj = typename _Nth_type<__j, _Types...>::type;
703  if constexpr (is_nothrow_move_constructible_v<_Tj>)
704  __variant::__emplace<__j>(*this, std::move(__rhs_mem));
705  else
706  {
707  using _Variant = variant<_Types...>;
708  _Variant& __self = __variant_cast<_Types...>(*this);
709  __self.template emplace<__j>(std::move(__rhs_mem));
710  }
711  }
712  }
713  else
714  this->_M_reset();
715  }, __variant_cast<_Types...>(__rhs));
716  return *this;
717  }
718 
719  _Move_assign_base(const _Move_assign_base&) = default;
720  _Move_assign_base(_Move_assign_base&&) = default;
721  _Move_assign_base& operator=(const _Move_assign_base&) = default;
722  };
723 
724  template<typename... _Types>
725  struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
726  {
727  using _Base = _Copy_assign_alias<_Types...>;
728  using _Base::_Base;
729  };
730 
731  template<typename... _Types>
732  using _Move_assign_alias =
733  _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
734 
735  template<typename... _Types>
736  struct _Variant_base : _Move_assign_alias<_Types...>
737  {
738  using _Base = _Move_assign_alias<_Types...>;
739 
740  constexpr
741  _Variant_base() noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
742  : _Variant_base(in_place_index<0>) { }
743 
744  template<size_t _Np, typename... _Args>
745  constexpr explicit
746  _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
747  : _Base(__i, std::forward<_Args>(__args)...)
748  { }
749 
750  _Variant_base(const _Variant_base&) = default;
751  _Variant_base(_Variant_base&&) = default;
752  _Variant_base& operator=(const _Variant_base&) = default;
753  _Variant_base& operator=(_Variant_base&&) = default;
754  };
755 
756  template<typename _Tp, typename... _Types>
757  inline constexpr bool __exactly_once
758  = std::__find_uniq_type_in_pack<_Tp, _Types...>() < sizeof...(_Types);
759 
760  // Helper used to check for valid conversions that don't involve narrowing.
761  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
762 
763  // "Build an imaginary function FUN(Ti) for each alternative type Ti"
764  template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
765  struct _Build_FUN
766  {
767  // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
768  // but only static functions will be considered in the call below.
769  void _S_fun();
770  };
771 
772  // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
773  template<size_t _Ind, typename _Tp, typename _Ti>
774  struct _Build_FUN<_Ind, _Tp, _Ti,
775  void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
776  {
777  // This is the FUN function for type _Ti, with index _Ind
778  static integral_constant<size_t, _Ind> _S_fun(_Ti);
779  };
780 
781  template<typename _Tp, typename _Variant,
782  typename = make_index_sequence<variant_size_v<_Variant>>>
783  struct _Build_FUNs;
784 
785  template<typename _Tp, typename... _Ti, size_t... _Ind>
786  struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
787  : _Build_FUN<_Ind, _Tp, _Ti>...
788  {
789  using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
790  };
791 
792  // The index j of the overload FUN(Tj) selected by overload resolution
793  // for FUN(std::forward<_Tp>(t))
794  template<typename _Tp, typename _Variant>
795  using _FUN_type
796  = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
797 
798  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
799  template<typename _Tp, typename _Variant, typename = void>
800  struct __accepted_index
801  : integral_constant<size_t, variant_npos>
802  { };
803 
804  template<typename _Tp, typename _Variant>
805  struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
806  : _FUN_type<_Tp, _Variant>
807  { };
808 
809  template <typename _Maybe_variant_cookie, typename _Variant>
810  struct _Extra_visit_slot_needed
811  {
812  template <typename> struct _Variant_never_valueless;
813 
814  template <typename... _Types>
815  struct _Variant_never_valueless<variant<_Types...>>
816  : bool_constant<__variant::__never_valueless<_Types...>()> {};
817 
818  static constexpr bool value =
819  (is_same_v<_Maybe_variant_cookie, __variant_cookie>
820  || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
821  && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
822  };
823 
824  // Used for storing a multi-dimensional vtable.
825  template<typename _Tp, size_t... _Dimensions>
826  struct _Multi_array;
827 
828  // Partial specialization with rank zero, stores a single _Tp element.
829  template<typename _Tp>
830  struct _Multi_array<_Tp>
831  {
832  template<typename>
833  struct __untag_result
834  : false_type
835  { using element_type = _Tp; };
836 
837  template <typename... _Args>
838  struct __untag_result<const void(*)(_Args...)>
839  : false_type
840  { using element_type = void(*)(_Args...); };
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>::value ? 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,
957  {
958  if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
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>::value;
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  operator=(variant(std::forward<_Tp>(__rhs)));
1485  }
1486  return *this;
1487  }
1488 
1489  template<typename _Tp, typename... _Args>
1490  _GLIBCXX20_CONSTEXPR
1491  enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1492  _Tp&>
1493  emplace(_Args&&... __args)
1494  {
1495  constexpr size_t __index = __index_of<_Tp>;
1496  return this->emplace<__index>(std::forward<_Args>(__args)...);
1497  }
1498 
1499  template<typename _Tp, typename _Up, typename... _Args>
1500  _GLIBCXX20_CONSTEXPR
1501  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1502  && __exactly_once<_Tp>,
1503  _Tp&>
1504  emplace(initializer_list<_Up> __il, _Args&&... __args)
1505  {
1506  constexpr size_t __index = __index_of<_Tp>;
1507  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1508  }
1509 
1510  template<size_t _Np, typename... _Args>
1511  _GLIBCXX20_CONSTEXPR
1512  enable_if_t<is_constructible_v<__to_type<_Np>, _Args...>,
1513  __to_type<_Np>&>
1514  emplace(_Args&&... __args)
1515  {
1516  namespace __variant = std::__detail::__variant;
1517  using type = typename _Nth_type<_Np, _Types...>::type;
1518  // Provide the strong exception-safety guarantee when possible,
1519  // to avoid becoming valueless.
1520  if constexpr (is_nothrow_constructible_v<type, _Args...>)
1521  {
1522  __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1523  }
1524  else if constexpr (is_scalar_v<type>)
1525  {
1526  // This might invoke a potentially-throwing conversion operator:
1527  const type __tmp(std::forward<_Args>(__args)...);
1528  // But this won't throw:
1529  __variant::__emplace<_Np>(*this, __tmp);
1530  }
1531  else if constexpr (__variant::_Never_valueless_alt<type>()
1532  && _Traits::_S_move_assign)
1533  {
1534  // This construction might throw:
1535  variant __tmp(in_place_index<_Np>,
1536  std::forward<_Args>(__args)...);
1537  // But _Never_valueless_alt<type> means this won't:
1538  *this = std::move(__tmp);
1539  }
1540  else
1541  {
1542  // This case only provides the basic exception-safety guarantee,
1543  // i.e. the variant can become valueless.
1544  __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1545  }
1546  return std::get<_Np>(*this);
1547  }
1548 
1549  template<size_t _Np, typename _Up, typename... _Args>
1550  _GLIBCXX20_CONSTEXPR
1551  enable_if_t<is_constructible_v<__to_type<_Np>,
1552  initializer_list<_Up>&, _Args...>,
1553  __to_type<_Np>&>
1554  emplace(initializer_list<_Up> __il, _Args&&... __args)
1555  {
1556  namespace __variant = std::__detail::__variant;
1557  using type = typename _Nth_type<_Np, _Types...>::type;
1558  // Provide the strong exception-safety guarantee when possible,
1559  // to avoid becoming valueless.
1560  if constexpr (is_nothrow_constructible_v<type,
1561  initializer_list<_Up>&,
1562  _Args...>)
1563  {
1564  __variant::__emplace<_Np>(*this, __il,
1565  std::forward<_Args>(__args)...);
1566  }
1567  else if constexpr (__variant::_Never_valueless_alt<type>()
1568  && _Traits::_S_move_assign)
1569  {
1570  // This construction might throw:
1571  variant __tmp(in_place_index<_Np>, __il,
1572  std::forward<_Args>(__args)...);
1573  // But _Never_valueless_alt<type> means this won't:
1574  *this = std::move(__tmp);
1575  }
1576  else
1577  {
1578  // This case only provides the basic exception-safety guarantee,
1579  // i.e. the variant can become valueless.
1580  __variant::__emplace<_Np>(*this, __il,
1581  std::forward<_Args>(__args)...);
1582  }
1583  return std::get<_Np>(*this);
1584  }
1585 
1586  template<size_t _Np, typename... _Args>
1587  enable_if_t<!(_Np < sizeof...(_Types))> emplace(_Args&&...) = delete;
1588 
1589  template<typename _Tp, typename... _Args>
1590  enable_if_t<!__exactly_once<_Tp>> emplace(_Args&&...) = delete;
1591 
1592  constexpr bool valueless_by_exception() const noexcept
1593  { return !this->_M_valid(); }
1594 
1595  constexpr size_t index() const noexcept
1596  {
1597  using __index_type = typename _Base::__index_type;
1598  if constexpr (__detail::__variant::__never_valueless<_Types...>())
1599  return this->_M_index;
1600  else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1601  return make_signed_t<__index_type>(this->_M_index);
1602  else
1603  return size_t(__index_type(this->_M_index + 1)) - 1;
1604  }
1605 
1606  _GLIBCXX20_CONSTEXPR
1607  void
1608  swap(variant& __rhs)
1609  noexcept((__is_nothrow_swappable<_Types>::value && ...)
1610  && is_nothrow_move_constructible_v<variant>)
1611  {
1612  static_assert((is_move_constructible_v<_Types> && ...));
1613 
1614  // Handle this here to simplify the visitation.
1615  if (__rhs.valueless_by_exception()) [[__unlikely__]]
1616  {
1617  if (!this->valueless_by_exception()) [[__likely__]]
1618  __rhs.swap(*this);
1619  return;
1620  }
1621 
1622  namespace __variant = __detail::__variant;
1623 
1624  __variant::__raw_idx_visit(
1625  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1626  {
1627  constexpr size_t __j = __rhs_index;
1628  if constexpr (__j != variant_npos)
1629  {
1630  if (this->index() == __j)
1631  {
1632  using std::swap;
1633  swap(std::get<__j>(*this), __rhs_mem);
1634  }
1635  else
1636  {
1637  auto __tmp(std::move(__rhs_mem));
1638 
1639  if constexpr (_Traits::_S_trivial_move_assign)
1640  __rhs = std::move(*this);
1641  else
1642  __variant::__raw_idx_visit(
1643  [&__rhs](auto&& __this_mem, auto __this_index) mutable
1644  {
1645  constexpr size_t __k = __this_index;
1646  if constexpr (__k != variant_npos)
1647  __variant::__emplace<__k>(__rhs,
1648  std::move(__this_mem));
1649  }, *this);
1650 
1651  __variant::__emplace<__j>(*this, std::move(__tmp));
1652  }
1653  }
1654  }, __rhs);
1655  }
1656 
1657 #if defined(__clang__) && __clang_major__ <= 7
1658  public:
1659  using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1660 #endif
1661 
1662  private:
1663  template<size_t _Np, typename _Vp>
1664  friend constexpr decltype(auto)
1665  __detail::__variant::__get(_Vp&& __v) noexcept;
1666 
1667 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1668  template<typename... _Tp> \
1669  friend constexpr bool \
1670  operator __OP(const variant<_Tp...>& __lhs, \
1671  const variant<_Tp...>& __rhs);
1672 
1673  _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1674  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1675  _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1676  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1677  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1678  _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1679 
1680 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1681  };
1682 
1683  template<size_t _Np, typename... _Types>
1684  constexpr variant_alternative_t<_Np, variant<_Types...>>&
1685  get(variant<_Types...>& __v)
1686  {
1687  static_assert(_Np < sizeof...(_Types),
1688  "The index must be in [0, number of alternatives)");
1689  if (__v.index() != _Np)
1690  __throw_bad_variant_access(__v.valueless_by_exception());
1691  return __detail::__variant::__get<_Np>(__v);
1692  }
1693 
1694  template<size_t _Np, typename... _Types>
1695  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1696  get(variant<_Types...>&& __v)
1697  {
1698  static_assert(_Np < sizeof...(_Types),
1699  "The index must be in [0, number of alternatives)");
1700  if (__v.index() != _Np)
1701  __throw_bad_variant_access(__v.valueless_by_exception());
1702  return __detail::__variant::__get<_Np>(std::move(__v));
1703  }
1704 
1705  template<size_t _Np, typename... _Types>
1706  constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1707  get(const variant<_Types...>& __v)
1708  {
1709  static_assert(_Np < sizeof...(_Types),
1710  "The index must be in [0, number of alternatives)");
1711  if (__v.index() != _Np)
1712  __throw_bad_variant_access(__v.valueless_by_exception());
1713  return __detail::__variant::__get<_Np>(__v);
1714  }
1715 
1716  template<size_t _Np, typename... _Types>
1717  constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1718  get(const variant<_Types...>&& __v)
1719  {
1720  static_assert(_Np < sizeof...(_Types),
1721  "The index must be in [0, number of alternatives)");
1722  if (__v.index() != _Np)
1723  __throw_bad_variant_access(__v.valueless_by_exception());
1724  return __detail::__variant::__get<_Np>(std::move(__v));
1725  }
1726 
1727  /// @cond undocumented
1728  template<typename _Result_type, typename _Visitor, typename... _Variants>
1729  constexpr decltype(auto)
1730  __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1731  {
1732  // Get the silly case of visiting no variants out of the way first.
1733  if constexpr (sizeof...(_Variants) == 0)
1734  return std::forward<_Visitor>(__visitor)();
1735  else
1736  {
1737  constexpr size_t __max = 11; // "These go to eleven."
1738 
1739  // The type of the first variant in the pack.
1740  using _V0 = typename _Nth_type<0, _Variants...>::type;
1741  // The number of alternatives in that first variant.
1742  constexpr auto __n = variant_size_v<remove_reference_t<_V0>>;
1743 
1744  if constexpr (sizeof...(_Variants) > 1 || __n > __max)
1745  {
1746  // Use a jump table for the general case.
1747  constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1748  _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1749 
1750  auto __func_ptr = __vtable._M_access(__variants.index()...);
1751  return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1752  std::forward<_Variants>(__variants)...);
1753  }
1754  else // We have a single variant with a small number of alternatives.
1755  {
1756  // A name for the first variant in the pack.
1757  _V0& __v0
1758  = [](_V0& __v, ...) -> _V0& { return __v; }(__variants...);
1759 
1760  using __detail::__variant::_Multi_array;
1761  using __detail::__variant::__gen_vtable_impl;
1762  using _Ma = _Multi_array<_Result_type (*)(_Visitor&&, _V0&&)>;
1763 
1764 #ifdef _GLIBCXX_DEBUG
1765 # define _GLIBCXX_VISIT_UNREACHABLE __builtin_trap
1766 #else
1767 # define _GLIBCXX_VISIT_UNREACHABLE __builtin_unreachable
1768 #endif
1769 
1770 #define _GLIBCXX_VISIT_CASE(N) \
1771  case N: \
1772  { \
1773  if constexpr (N < __n) \
1774  { \
1775  return __gen_vtable_impl<_Ma, index_sequence<N>>:: \
1776  __visit_invoke(std::forward<_Visitor>(__visitor), \
1777  std::forward<_V0>(__v0)); \
1778  } \
1779  else _GLIBCXX_VISIT_UNREACHABLE(); \
1780  }
1781 
1782  switch (__v0.index())
1783  {
1784  _GLIBCXX_VISIT_CASE(0)
1785  _GLIBCXX_VISIT_CASE(1)
1786  _GLIBCXX_VISIT_CASE(2)
1787  _GLIBCXX_VISIT_CASE(3)
1788  _GLIBCXX_VISIT_CASE(4)
1789  _GLIBCXX_VISIT_CASE(5)
1790  _GLIBCXX_VISIT_CASE(6)
1791  _GLIBCXX_VISIT_CASE(7)
1792  _GLIBCXX_VISIT_CASE(8)
1793  _GLIBCXX_VISIT_CASE(9)
1794  _GLIBCXX_VISIT_CASE(10)
1795  case variant_npos:
1796  using __detail::__variant::__variant_idx_cookie;
1797  using __detail::__variant::__variant_cookie;
1798  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
1799  || is_same_v<_Result_type, __variant_cookie>)
1800  {
1801  using _Npos = index_sequence<variant_npos>;
1802  return __gen_vtable_impl<_Ma, _Npos>::
1803  __visit_invoke(std::forward<_Visitor>(__visitor),
1804  std::forward<_V0>(__v0));
1805  }
1806  else
1807  _GLIBCXX_VISIT_UNREACHABLE();
1808  default:
1809  _GLIBCXX_VISIT_UNREACHABLE();
1810  }
1811 #undef _GLIBCXX_VISIT_CASE
1812 #undef _GLIBCXX_VISIT_UNREACHABLE
1813  }
1814  }
1815  }
1816  /// @endcond
1817 
1818  template<typename _Visitor, typename... _Variants>
1819  constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1820  visit(_Visitor&& __visitor, _Variants&&... __variants)
1821  {
1822  namespace __variant = std::__detail::__variant;
1823 
1824  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1825  __throw_bad_variant_access("std::visit: variant is valueless");
1826 
1827  using _Result_type
1828  = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1829 
1830  using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1831 
1832  if constexpr (sizeof...(_Variants) == 1)
1833  {
1834  using _Vp = decltype(__variant::__as(std::declval<_Variants>()...));
1835 
1836  constexpr bool __visit_rettypes_match = __detail::__variant::
1837  __check_visitor_results<_Visitor, _Vp>(
1838  make_index_sequence<variant_size_v<remove_reference_t<_Vp>>>());
1839  if constexpr (!__visit_rettypes_match)
1840  {
1841  static_assert(__visit_rettypes_match,
1842  "std::visit requires the visitor to have the same "
1843  "return type for all alternatives of a variant");
1844  return;
1845  }
1846  else
1847  return std::__do_visit<_Tag>(
1848  std::forward<_Visitor>(__visitor),
1849  static_cast<_Vp>(__variants)...);
1850  }
1851  else
1852  return std::__do_visit<_Tag>(
1853  std::forward<_Visitor>(__visitor),
1854  __variant::__as(std::forward<_Variants>(__variants))...);
1855  }
1856 
1857 #if __cplusplus > 201703L
1858  template<typename _Res, typename _Visitor, typename... _Variants>
1859  constexpr _Res
1860  visit(_Visitor&& __visitor, _Variants&&... __variants)
1861  {
1862  namespace __variant = std::__detail::__variant;
1863 
1864  if ((__variant::__as(__variants).valueless_by_exception() || ...))
1865  __throw_bad_variant_access("std::visit<R>: variant is valueless");
1866 
1867  return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1868  __variant::__as(std::forward<_Variants>(__variants))...);
1869  }
1870 #endif
1871 
1872  /// @cond undocumented
1873  template<bool, typename... _Types>
1874  struct __variant_hash_call_base_impl
1875  {
1876  size_t
1877  operator()(const variant<_Types...>& __t) const
1878  noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1879  {
1880  size_t __ret;
1881  __detail::__variant::__raw_visit(
1882  [&__t, &__ret](auto&& __t_mem) mutable
1883  {
1884  using _Type = __remove_cvref_t<decltype(__t_mem)>;
1885  if constexpr (!is_same_v<_Type,
1886  __detail::__variant::__variant_cookie>)
1887  __ret = std::hash<size_t>{}(__t.index())
1888  + std::hash<_Type>{}(__t_mem);
1889  else
1890  __ret = std::hash<size_t>{}(__t.index());
1891  }, __t);
1892  return __ret;
1893  }
1894  };
1895 
1896  template<typename... _Types>
1897  struct __variant_hash_call_base_impl<false, _Types...> {};
1898 
1899  template<typename... _Types>
1900  using __variant_hash_call_base =
1901  __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1902  __enable_hash_call &&...), _Types...>;
1903  /// @endcond
1904 
1905  template<typename... _Types>
1906  struct hash<variant<_Types...>>
1907  : private __detail::__variant::_Variant_hash_base<
1908  variant<_Types...>, std::index_sequence_for<_Types...>>,
1909  public __variant_hash_call_base<_Types...>
1910  {
1911  using result_type [[__deprecated__]] = size_t;
1912  using argument_type [[__deprecated__]] = variant<_Types...>;
1913  };
1914 
1915  template<>
1916  struct hash<monostate>
1917  {
1918  using result_type [[__deprecated__]] = size_t;
1919  using argument_type [[__deprecated__]] = monostate;
1920 
1921  size_t
1922  operator()(const monostate&) const noexcept
1923  {
1924  constexpr size_t __magic_monostate_hash = -7777;
1925  return __magic_monostate_hash;
1926  }
1927  };
1928 
1929  template<typename... _Types>
1930  struct __is_fast_hash<hash<variant<_Types...>>>
1931  : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1932  { };
1933 
1934 _GLIBCXX_END_NAMESPACE_VERSION
1935 } // namespace std
1936 
1937 #endif // C++17
1938 
1939 #endif // _GLIBCXX_VARIANT
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition: type_traits:1670
integral_constant< bool, __v > bool_constant
Alias template for compile-time boolean constant types.
Definition: type_traits:98
void void_t
A metafunction that always yields void, used for detecting valid types.
Definition: type_traits:2636
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:82
integral_constant< bool, false > false_type
The type used as a compile-time boolean with false value.
Definition: type_traits:85
typename add_pointer< _Tp >::type add_pointer_t
Alias template for add_pointer.
Definition: type_traits:2088
typename make_signed< _Tp >::type make_signed_t
Alias template for make_signed.
Definition: type_traits:2005
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition: type_traits:2614
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition: invoke.h:90
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:77
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:429
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:145
ISO C++ entities toplevel namespace is std.
make_integer_sequence< size_t, _Num > make_index_sequence
Alias template make_index_sequence.
Definition: utility.h:185
constexpr void _Construct(_Tp *__p, _Args &&... __args)
integer_sequence< size_t, _Idx... > index_sequence
Alias template index_sequence.
Definition: utility.h:181
typename __detail::__cmp3way_res_impl< _Tp, _Up >::type compare_three_way_result_t
[cmp.result], result of three-way comparison
Definition: compare:522
Primary class template hash.
integral_constant
Definition: type_traits:63
Class template integer_sequence.
Definition: utility.h:165