libstdc++
variant
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1 // <variant> -*- C++ -*-
2 
3 // Copyright (C) 2016-2020 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file variant
26  * This is the <variant> C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_VARIANT
30 #define _GLIBCXX_VARIANT 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus >= 201703L
35 
36 #include <type_traits>
37 #include <utility>
38 #include <bits/enable_special_members.h>
39 #include <bits/functexcept.h>
40 #include <bits/move.h>
41 #include <bits/functional_hash.h>
42 #include <bits/invoke.h>
43 #include <ext/aligned_buffer.h>
44 #include <bits/parse_numbers.h>
45 #include <bits/stl_iterator_base_types.h>
46 #include <bits/stl_iterator_base_funcs.h>
47 #include <bits/stl_construct.h>
48 #if __cplusplus > 201703L
49 # include <compare>
50 #endif
51 
52 namespace std _GLIBCXX_VISIBILITY(default)
53 {
54 _GLIBCXX_BEGIN_NAMESPACE_VERSION
55 
56 namespace __detail
57 {
58 namespace __variant
59 {
60  template<size_t _Np, typename... _Types>
61  struct _Nth_type;
62 
63  template<size_t _Np, typename _First, typename... _Rest>
64  struct _Nth_type<_Np, _First, _Rest...>
65  : _Nth_type<_Np-1, _Rest...> { };
66 
67  template<typename _First, typename... _Rest>
68  struct _Nth_type<0, _First, _Rest...>
69  { using type = _First; };
70 
71 } // namespace __variant
72 } // namespace __detail
73 
74 #define __cpp_lib_variant 201606L
75 
76  template<typename... _Types> class tuple;
77  template<typename... _Types> class variant;
78  template <typename> struct hash;
79 
80  template<typename _Variant>
81  struct variant_size;
82 
83  template<typename _Variant>
84  struct variant_size<const _Variant> : variant_size<_Variant> {};
85 
86  template<typename _Variant>
87  struct variant_size<volatile _Variant> : variant_size<_Variant> {};
88 
89  template<typename _Variant>
90  struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
91 
92  template<typename... _Types>
93  struct variant_size<variant<_Types...>>
94  : std::integral_constant<size_t, sizeof...(_Types)> {};
95 
96  template<typename _Variant>
97  inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
98 
99  template<size_t _Np, typename _Variant>
100  struct variant_alternative;
101 
102  template<size_t _Np, typename _First, typename... _Rest>
103  struct variant_alternative<_Np, variant<_First, _Rest...>>
104  : variant_alternative<_Np-1, variant<_Rest...>> {};
105 
106  template<typename _First, typename... _Rest>
107  struct variant_alternative<0, variant<_First, _Rest...>>
108  { using type = _First; };
109 
110  template<size_t _Np, typename _Variant>
111  using variant_alternative_t =
112  typename variant_alternative<_Np, _Variant>::type;
113 
114  template<size_t _Np, typename _Variant>
115  struct variant_alternative<_Np, const _Variant>
116  { using type = add_const_t<variant_alternative_t<_Np, _Variant>>; };
117 
118  template<size_t _Np, typename _Variant>
119  struct variant_alternative<_Np, volatile _Variant>
120  { using type = add_volatile_t<variant_alternative_t<_Np, _Variant>>; };
121 
122  template<size_t _Np, typename _Variant>
123  struct variant_alternative<_Np, const volatile _Variant>
124  { using type = add_cv_t<variant_alternative_t<_Np, _Variant>>; };
125 
126  inline constexpr size_t variant_npos = -1;
127 
128  template<size_t _Np, typename... _Types>
129  constexpr variant_alternative_t<_Np, variant<_Types...>>&
130  get(variant<_Types...>&);
131 
132  template<size_t _Np, typename... _Types>
133  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
134  get(variant<_Types...>&&);
135 
136  template<size_t _Np, typename... _Types>
137  constexpr variant_alternative_t<_Np, variant<_Types...>> const&
138  get(const variant<_Types...>&);
139 
140  template<size_t _Np, typename... _Types>
141  constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
142  get(const variant<_Types...>&&);
143 
144  template<typename _Result_type, typename _Visitor, typename... _Variants>
145  constexpr decltype(auto)
146  __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
147 
148  template <typename... _Types, typename _Tp>
149  decltype(auto)
150  __variant_cast(_Tp&& __rhs)
151  {
152  if constexpr (is_lvalue_reference_v<_Tp>)
153  {
154  if constexpr (is_const_v<remove_reference_t<_Tp>>)
155  return static_cast<const variant<_Types...>&>(__rhs);
156  else
157  return static_cast<variant<_Types...>&>(__rhs);
158  }
159  else
160  return static_cast<variant<_Types...>&&>(__rhs);
161  }
162 
163 namespace __detail
164 {
165 namespace __variant
166 {
167  // Returns the first appearence of _Tp in _Types.
168  // Returns sizeof...(_Types) if _Tp is not in _Types.
169  template<typename _Tp, typename... _Types>
170  struct __index_of : std::integral_constant<size_t, 0> {};
171 
172  template<typename _Tp, typename... _Types>
173  inline constexpr size_t __index_of_v = __index_of<_Tp, _Types...>::value;
174 
175  template<typename _Tp, typename _First, typename... _Rest>
176  struct __index_of<_Tp, _First, _Rest...> :
177  std::integral_constant<size_t, is_same_v<_Tp, _First>
178  ? 0 : __index_of_v<_Tp, _Rest...> + 1> {};
179 
180  // used for raw visitation
181  struct __variant_cookie {};
182  // used for raw visitation with indices passed in
183  struct __variant_idx_cookie { using type = __variant_idx_cookie; };
184  // Used to enable deduction (and same-type checking) for std::visit:
185  template<typename> struct __deduce_visit_result { };
186 
187  // Visit variants that might be valueless.
188  template<typename _Visitor, typename... _Variants>
189  constexpr void
190  __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
191  {
192  std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
193  std::forward<_Variants>(__variants)...);
194  }
195 
196  // Visit variants that might be valueless, passing indices to the visitor.
197  template<typename _Visitor, typename... _Variants>
198  constexpr void
199  __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
200  {
201  std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
202  std::forward<_Variants>(__variants)...);
203  }
204 
205  // _Uninitialized<T> is guaranteed to be a literal type, even if T is not.
206  // We have to do this, because [basic.types]p10.5.3 (n4606) is not implemented
207  // yet. When it's implemented, _Uninitialized<T> can be changed to the alias
208  // to T, therefore equivalent to being removed entirely.
209  //
210  // Another reason we may not want to remove _Uninitialzied<T> may be that, we
211  // want _Uninitialized<T> to be trivially destructible, no matter whether T
212  // is; but we will see.
213  template<typename _Type, bool = std::is_literal_type_v<_Type>>
214  struct _Uninitialized;
215 
216  template<typename _Type>
217  struct _Uninitialized<_Type, true>
218  {
219  template<typename... _Args>
220  constexpr
221  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
222  : _M_storage(std::forward<_Args>(__args)...)
223  { }
224 
225  constexpr const _Type& _M_get() const & noexcept
226  { return _M_storage; }
227 
228  constexpr _Type& _M_get() & noexcept
229  { return _M_storage; }
230 
231  constexpr const _Type&& _M_get() const && noexcept
232  { return std::move(_M_storage); }
233 
234  constexpr _Type&& _M_get() && noexcept
235  { return std::move(_M_storage); }
236 
237  _Type _M_storage;
238  };
239 
240  template<typename _Type>
241  struct _Uninitialized<_Type, false>
242  {
243  template<typename... _Args>
244  constexpr
245  _Uninitialized(in_place_index_t<0>, _Args&&... __args)
246  {
247  ::new ((void*)std::addressof(_M_storage))
248  _Type(std::forward<_Args>(__args)...);
249  }
250 
251  const _Type& _M_get() const & noexcept
252  { return *_M_storage._M_ptr(); }
253 
254  _Type& _M_get() & noexcept
255  { return *_M_storage._M_ptr(); }
256 
257  const _Type&& _M_get() const && noexcept
258  { return std::move(*_M_storage._M_ptr()); }
259 
260  _Type&& _M_get() && noexcept
261  { return std::move(*_M_storage._M_ptr()); }
262 
263  __gnu_cxx::__aligned_membuf<_Type> _M_storage;
264  };
265 
266  template<typename _Union>
267  constexpr decltype(auto)
268  __get(in_place_index_t<0>, _Union&& __u) noexcept
269  { return std::forward<_Union>(__u)._M_first._M_get(); }
270 
271  template<size_t _Np, typename _Union>
272  constexpr decltype(auto)
273  __get(in_place_index_t<_Np>, _Union&& __u) noexcept
274  {
275  return __variant::__get(in_place_index<_Np-1>,
276  std::forward<_Union>(__u)._M_rest);
277  }
278 
279  // Returns the typed storage for __v.
280  template<size_t _Np, typename _Variant>
281  constexpr decltype(auto)
282  __get(_Variant&& __v) noexcept
283  {
284  return __variant::__get(std::in_place_index<_Np>,
285  std::forward<_Variant>(__v)._M_u);
286  }
287 
288  template<typename... _Types>
289  struct _Traits
290  {
291  static constexpr bool _S_default_ctor =
292  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
293  static constexpr bool _S_copy_ctor =
294  (is_copy_constructible_v<_Types> && ...);
295  static constexpr bool _S_move_ctor =
296  (is_move_constructible_v<_Types> && ...);
297  static constexpr bool _S_copy_assign =
298  _S_copy_ctor
299  && (is_copy_assignable_v<_Types> && ...);
300  static constexpr bool _S_move_assign =
301  _S_move_ctor
302  && (is_move_assignable_v<_Types> && ...);
303 
304  static constexpr bool _S_trivial_dtor =
305  (is_trivially_destructible_v<_Types> && ...);
306  static constexpr bool _S_trivial_copy_ctor =
307  (is_trivially_copy_constructible_v<_Types> && ...);
308  static constexpr bool _S_trivial_move_ctor =
309  (is_trivially_move_constructible_v<_Types> && ...);
310  static constexpr bool _S_trivial_copy_assign =
311  _S_trivial_dtor && _S_trivial_copy_ctor
312  && (is_trivially_copy_assignable_v<_Types> && ...);
313  static constexpr bool _S_trivial_move_assign =
314  _S_trivial_dtor && _S_trivial_move_ctor
315  && (is_trivially_move_assignable_v<_Types> && ...);
316 
317  // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
318  // are always nothrow.
319  static constexpr bool _S_nothrow_default_ctor =
320  is_nothrow_default_constructible_v<
321  typename _Nth_type<0, _Types...>::type>;
322  static constexpr bool _S_nothrow_copy_ctor = false;
323  static constexpr bool _S_nothrow_move_ctor =
324  (is_nothrow_move_constructible_v<_Types> && ...);
325  static constexpr bool _S_nothrow_copy_assign = false;
326  static constexpr bool _S_nothrow_move_assign =
327  _S_nothrow_move_ctor
328  && (is_nothrow_move_assignable_v<_Types> && ...);
329  };
330 
331  // Defines members and ctors.
332  template<typename... _Types>
333  union _Variadic_union { };
334 
335  template<typename _First, typename... _Rest>
336  union _Variadic_union<_First, _Rest...>
337  {
338  constexpr _Variadic_union() : _M_rest() { }
339 
340  template<typename... _Args>
341  constexpr _Variadic_union(in_place_index_t<0>, _Args&&... __args)
342  : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
343  { }
344 
345  template<size_t _Np, typename... _Args>
346  constexpr _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
347  : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
348  { }
349 
350  _Uninitialized<_First> _M_first;
351  _Variadic_union<_Rest...> _M_rest;
352  };
353 
354  // _Never_valueless_alt is true for variant alternatives that can
355  // always be placed in a variant without it becoming valueless.
356 
357  // For suitably-small, trivially copyable types we can create temporaries
358  // on the stack and then memcpy them into place.
359  template<typename _Tp>
360  struct _Never_valueless_alt
361  : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
362  { };
363 
364  // Specialize _Never_valueless_alt for other types which have a
365  // non-throwing and cheap move construction and move assignment operator,
366  // so that emplacing the type will provide the strong exception-safety
367  // guarantee, by creating and moving a temporary.
368  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
369  // variant using that alternative, so we can't change the value later!
370 
371  // True if every alternative in _Types... can be emplaced in a variant
372  // without it becoming valueless. If this is true, variant<_Types...>
373  // can never be valueless, which enables some minor optimizations.
374  template <typename... _Types>
375  constexpr bool __never_valueless()
376  {
377  return _Traits<_Types...>::_S_move_assign
378  && (_Never_valueless_alt<_Types>::value && ...);
379  }
380 
381  // Defines index and the dtor, possibly trivial.
382  template<bool __trivially_destructible, typename... _Types>
383  struct _Variant_storage;
384 
385  template <typename... _Types>
386  using __select_index =
387  typename __select_int::_Select_int_base<sizeof...(_Types),
388  unsigned char,
389  unsigned short>::type::value_type;
390 
391  template<typename... _Types>
392  struct _Variant_storage<false, _Types...>
393  {
394  constexpr _Variant_storage() : _M_index(variant_npos) { }
395 
396  template<size_t _Np, typename... _Args>
397  constexpr _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
398  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
399  _M_index(_Np)
400  { }
401 
402  void _M_reset()
403  {
404  if (!_M_valid()) [[unlikely]]
405  return;
406 
407  std::__do_visit<void>([](auto&& __this_mem) mutable
408  {
409  std::_Destroy(std::__addressof(__this_mem));
410  }, __variant_cast<_Types...>(*this));
411 
412  _M_index = variant_npos;
413  }
414 
415  ~_Variant_storage()
416  { _M_reset(); }
417 
418  void*
419  _M_storage() const noexcept
420  {
421  return const_cast<void*>(static_cast<const void*>(
422  std::addressof(_M_u)));
423  }
424 
425  constexpr bool
426  _M_valid() const noexcept
427  {
428  if constexpr (__variant::__never_valueless<_Types...>())
429  return true;
430  return this->_M_index != __index_type(variant_npos);
431  }
432 
433  _Variadic_union<_Types...> _M_u;
434  using __index_type = __select_index<_Types...>;
435  __index_type _M_index;
436  };
437 
438  template<typename... _Types>
439  struct _Variant_storage<true, _Types...>
440  {
441  constexpr _Variant_storage() : _M_index(variant_npos) { }
442 
443  template<size_t _Np, typename... _Args>
444  constexpr _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
445  : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
446  _M_index(_Np)
447  { }
448 
449  void _M_reset() noexcept
450  { _M_index = variant_npos; }
451 
452  void*
453  _M_storage() const noexcept
454  {
455  return const_cast<void*>(static_cast<const void*>(
456  std::addressof(_M_u)));
457  }
458 
459  constexpr bool
460  _M_valid() const noexcept
461  {
462  if constexpr (__variant::__never_valueless<_Types...>())
463  return true;
464  return this->_M_index != __index_type(variant_npos);
465  }
466 
467  _Variadic_union<_Types...> _M_u;
468  using __index_type = __select_index<_Types...>;
469  __index_type _M_index;
470  };
471 
472  template<typename... _Types>
473  using _Variant_storage_alias =
474  _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
475 
476  template<typename _Tp, typename _Up>
477  void __variant_construct_single(_Tp&& __lhs, _Up&& __rhs_mem)
478  {
479  void* __storage = std::addressof(__lhs._M_u);
480  using _Type = remove_reference_t<decltype(__rhs_mem)>;
481  if constexpr (!is_same_v<_Type, __variant_cookie>)
482  ::new (__storage)
483  _Type(std::forward<decltype(__rhs_mem)>(__rhs_mem));
484  }
485 
486  template<typename... _Types, typename _Tp, typename _Up>
487  void __variant_construct(_Tp&& __lhs, _Up&& __rhs)
488  {
489  __lhs._M_index = __rhs._M_index;
490  __variant::__raw_visit([&__lhs](auto&& __rhs_mem) mutable
491  {
492  __variant_construct_single(std::forward<_Tp>(__lhs),
493  std::forward<decltype(__rhs_mem)>(__rhs_mem));
494  }, __variant_cast<_Types...>(std::forward<_Up>(__rhs)));
495  }
496 
497  // The following are (Copy|Move) (ctor|assign) layers for forwarding
498  // triviality and handling non-trivial SMF behaviors.
499 
500  template<bool, typename... _Types>
501  struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
502  {
503  using _Base = _Variant_storage_alias<_Types...>;
504  using _Base::_Base;
505 
506  _Copy_ctor_base(const _Copy_ctor_base& __rhs)
507  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
508  {
509  __variant_construct<_Types...>(*this, __rhs);
510  }
511 
512  _Copy_ctor_base(_Copy_ctor_base&&) = default;
513  _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
514  _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
515  };
516 
517  template<typename... _Types>
518  struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
519  {
520  using _Base = _Variant_storage_alias<_Types...>;
521  using _Base::_Base;
522  };
523 
524  template<typename... _Types>
525  using _Copy_ctor_alias =
526  _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
527 
528  template<bool, typename... _Types>
529  struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
530  {
531  using _Base = _Copy_ctor_alias<_Types...>;
532  using _Base::_Base;
533 
534  _Move_ctor_base(_Move_ctor_base&& __rhs)
535  noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
536  {
537  __variant_construct<_Types...>(*this, std::move(__rhs));
538  }
539 
540  template<typename _Up>
541  void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
542  {
543  this->_M_reset();
544  __variant_construct_single(*this, std::forward<_Up>(__rhs));
545  this->_M_index = __rhs_index;
546  }
547 
548  template<typename _Up>
549  void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
550  {
551  this->_M_reset();
552  __variant_construct_single(*this, __rhs);
553  this->_M_index = __rhs_index;
554  }
555 
556  _Move_ctor_base(const _Move_ctor_base&) = default;
557  _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
558  _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
559  };
560 
561  template<typename... _Types>
562  struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
563  {
564  using _Base = _Copy_ctor_alias<_Types...>;
565  using _Base::_Base;
566 
567  template<typename _Up>
568  void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
569  {
570  this->_M_reset();
571  __variant_construct_single(*this, std::forward<_Up>(__rhs));
572  this->_M_index = __rhs_index;
573  }
574 
575  template<typename _Up>
576  void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
577  {
578  this->_M_reset();
579  __variant_construct_single(*this, __rhs);
580  this->_M_index = __rhs_index;
581  }
582  };
583 
584  template<typename... _Types>
585  using _Move_ctor_alias =
586  _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
587 
588  template<bool, typename... _Types>
589  struct _Copy_assign_base : _Move_ctor_alias<_Types...>
590  {
591  using _Base = _Move_ctor_alias<_Types...>;
592  using _Base::_Base;
593 
594  _Copy_assign_base&
595  operator=(const _Copy_assign_base& __rhs)
596  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
597  {
598  __variant::__raw_idx_visit(
599  [this](auto&& __rhs_mem, auto __rhs_index) mutable
600  {
601  if constexpr (__rhs_index != variant_npos)
602  {
603  if (this->_M_index == __rhs_index)
604  __variant::__get<__rhs_index>(*this) = __rhs_mem;
605  else
606  {
607  using __rhs_type = __remove_cvref_t<decltype(__rhs_mem)>;
608  if constexpr (is_nothrow_copy_constructible_v<__rhs_type>
609  || !is_nothrow_move_constructible_v<__rhs_type>)
610  // The standard says this->emplace<__rhs_type>(__rhs_mem)
611  // should be used here, but _M_destructive_copy is
612  // equivalent in this case. Either copy construction
613  // doesn't throw, so _M_destructive_copy gives strong
614  // exception safety guarantee, or both copy construction
615  // and move construction can throw, so emplace only gives
616  // basic exception safety anyway.
617  this->_M_destructive_copy(__rhs_index, __rhs_mem);
618  else
619  __variant_cast<_Types...>(*this)
620  = variant<_Types...>(__rhs_mem);
621  }
622  }
623  else
624  this->_M_reset();
625  }, __variant_cast<_Types...>(__rhs));
626  return *this;
627  }
628 
629  _Copy_assign_base(const _Copy_assign_base&) = default;
630  _Copy_assign_base(_Copy_assign_base&&) = default;
631  _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
632  };
633 
634  template<typename... _Types>
635  struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
636  {
637  using _Base = _Move_ctor_alias<_Types...>;
638  using _Base::_Base;
639  };
640 
641  template<typename... _Types>
642  using _Copy_assign_alias =
643  _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
644 
645  template<bool, typename... _Types>
646  struct _Move_assign_base : _Copy_assign_alias<_Types...>
647  {
648  using _Base = _Copy_assign_alias<_Types...>;
649  using _Base::_Base;
650 
651  _Move_assign_base&
652  operator=(_Move_assign_base&& __rhs)
653  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
654  {
655  __variant::__raw_idx_visit(
656  [this](auto&& __rhs_mem, auto __rhs_index) mutable
657  {
658  if constexpr (__rhs_index != variant_npos)
659  {
660  if (this->_M_index == __rhs_index)
661  __variant::__get<__rhs_index>(*this) = std::move(__rhs_mem);
662  else
663  __variant_cast<_Types...>(*this)
664  .template emplace<__rhs_index>(std::move(__rhs_mem));
665  }
666  else
667  this->_M_reset();
668  }, __variant_cast<_Types...>(__rhs));
669  return *this;
670  }
671 
672  _Move_assign_base(const _Move_assign_base&) = default;
673  _Move_assign_base(_Move_assign_base&&) = default;
674  _Move_assign_base& operator=(const _Move_assign_base&) = default;
675  };
676 
677  template<typename... _Types>
678  struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
679  {
680  using _Base = _Copy_assign_alias<_Types...>;
681  using _Base::_Base;
682  };
683 
684  template<typename... _Types>
685  using _Move_assign_alias =
686  _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
687 
688  template<typename... _Types>
689  struct _Variant_base : _Move_assign_alias<_Types...>
690  {
691  using _Base = _Move_assign_alias<_Types...>;
692 
693  constexpr
694  _Variant_base()
695  noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
696  : _Variant_base(in_place_index<0>) { }
697 
698  template<size_t _Np, typename... _Args>
699  constexpr explicit
700  _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
701  : _Base(__i, std::forward<_Args>(__args)...)
702  { }
703 
704  _Variant_base(const _Variant_base&) = default;
705  _Variant_base(_Variant_base&&) = default;
706  _Variant_base& operator=(const _Variant_base&) = default;
707  _Variant_base& operator=(_Variant_base&&) = default;
708  };
709 
710  // For how many times does _Tp appear in _Tuple?
711  template<typename _Tp, typename _Tuple>
712  struct __tuple_count;
713 
714  template<typename _Tp, typename _Tuple>
715  inline constexpr size_t __tuple_count_v =
716  __tuple_count<_Tp, _Tuple>::value;
717 
718  template<typename _Tp, typename... _Types>
719  struct __tuple_count<_Tp, tuple<_Types...>>
720  : integral_constant<size_t, 0> { };
721 
722  template<typename _Tp, typename _First, typename... _Rest>
723  struct __tuple_count<_Tp, tuple<_First, _Rest...>>
724  : integral_constant<
725  size_t,
726  __tuple_count_v<_Tp, tuple<_Rest...>> + is_same_v<_Tp, _First>> { };
727 
728  // TODO: Reuse this in <tuple> ?
729  template<typename _Tp, typename... _Types>
730  inline constexpr bool __exactly_once =
731  __tuple_count_v<_Tp, tuple<_Types...>> == 1;
732 
733  // Helper used to check for valid conversions that don't involve narrowing.
734  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
735 
736  // Build an imaginary function FUN(Ti) for each alternative type Ti
737  template<size_t _Ind, typename _Tp, typename _Ti,
738  bool _Ti_is_cv_bool = is_same_v<remove_cv_t<_Ti>, bool>,
739  typename = void>
740  struct _Build_FUN
741  {
742  // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
743  // but only static functions will be considered in the call below.
744  void _S_fun();
745  };
746 
747  // ... for which Ti x[] = {std::forward<T>(t)}; is well-formed,
748  template<size_t _Ind, typename _Tp, typename _Ti>
749  struct _Build_FUN<_Ind, _Tp, _Ti, false,
750  void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
751  {
752  // This is the FUN function for type _Ti, with index _Ind
753  static integral_constant<size_t, _Ind> _S_fun(_Ti);
754  };
755 
756  // ... and if Ti is cv bool, remove_cvref_t<T> is bool.
757  template<size_t _Ind, typename _Tp, typename _Ti>
758  struct _Build_FUN<_Ind, _Tp, _Ti, true,
759  enable_if_t<is_same_v<__remove_cvref_t<_Tp>, bool>>>
760  {
761  // This is the FUN function for when _Ti is cv bool, with index _Ind
762  static integral_constant<size_t, _Ind> _S_fun(_Ti);
763  };
764 
765  template<typename _Tp, typename _Variant,
766  typename = make_index_sequence<variant_size_v<_Variant>>>
767  struct _Build_FUNs;
768 
769  template<typename _Tp, typename... _Ti, size_t... _Ind>
770  struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
771  : _Build_FUN<_Ind, _Tp, _Ti>...
772  {
773  using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
774  };
775 
776  // The index j of the overload FUN(Tj) selected by overload resolution
777  // for FUN(std::forward<_Tp>(t))
778  template<typename _Tp, typename _Variant>
779  using _FUN_type
780  = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
781 
782  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
783  template<typename _Tp, typename _Variant, typename = void>
784  struct __accepted_index
785  : integral_constant<size_t, variant_npos>
786  { };
787 
788  template<typename _Tp, typename _Variant>
789  struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
790  : _FUN_type<_Tp, _Variant>
791  { };
792 
793  // Returns the raw storage for __v.
794  template<typename _Variant>
795  void* __get_storage(_Variant&& __v) noexcept
796  { return __v._M_storage(); }
797 
798  template <typename _Maybe_variant_cookie, typename _Variant>
799  struct _Extra_visit_slot_needed
800  {
801  template <typename> struct _Variant_never_valueless;
802 
803  template <typename... _Types>
804  struct _Variant_never_valueless<variant<_Types...>>
805  : bool_constant<__variant::__never_valueless<_Types...>()> {};
806 
807  static constexpr bool value =
808  (is_same_v<_Maybe_variant_cookie, __variant_cookie>
809  || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
810  && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
811  };
812 
813  // Used for storing a multi-dimensional vtable.
814  template<typename _Tp, size_t... _Dimensions>
815  struct _Multi_array;
816 
817  // Partial specialization with rank zero, stores a single _Tp element.
818  template<typename _Tp>
819  struct _Multi_array<_Tp>
820  {
821  template<typename>
822  struct __untag_result
823  : false_type
824  { using element_type = _Tp; };
825 
826  template <typename... _Args>
827  struct __untag_result<const void(*)(_Args...)>
828  : false_type
829  { using element_type = void(*)(_Args...); };
830 
831  template <typename... _Args>
832  struct __untag_result<__variant_cookie(*)(_Args...)>
833  : false_type
834  { using element_type = void(*)(_Args...); };
835 
836  template <typename... _Args>
837  struct __untag_result<__variant_idx_cookie(*)(_Args...)>
838  : false_type
839  { using element_type = void(*)(_Args...); };
840 
841  template <typename _Res, typename... _Args>
842  struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
843  : true_type
844  { using element_type = _Res(*)(_Args...); };
845 
846  using __result_is_deduced = __untag_result<_Tp>;
847 
848  constexpr const typename __untag_result<_Tp>::element_type&
849  _M_access() const
850  { return _M_data; }
851 
852  typename __untag_result<_Tp>::element_type _M_data;
853  };
854 
855  // Partial specialization with rank >= 1.
856  template<typename _Ret,
857  typename _Visitor,
858  typename... _Variants,
859  size_t __first, size_t... __rest>
860  struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
861  {
862  static constexpr size_t __index =
863  sizeof...(_Variants) - sizeof...(__rest) - 1;
864 
865  using _Variant = typename _Nth_type<__index, _Variants...>::type;
866 
867  static constexpr int __do_cookie =
868  _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
869 
870  using _Tp = _Ret(*)(_Visitor, _Variants...);
871 
872  template<typename... _Args>
873  constexpr decltype(auto)
874  _M_access(size_t __first_index, _Args... __rest_indices) const
875  {
876  return _M_arr[__first_index + __do_cookie]
877  ._M_access(__rest_indices...);
878  }
879 
880  _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
881  };
882 
883  // Creates a multi-dimensional vtable recursively.
884  //
885  // For example,
886  // visit([](auto, auto){},
887  // variant<int, char>(), // typedef'ed as V1
888  // variant<float, double, long double>()) // typedef'ed as V2
889  // will trigger instantiations of:
890  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
891  // tuple<V1&&, V2&&>, std::index_sequence<>>
892  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
893  // tuple<V1&&, V2&&>, std::index_sequence<0>>
894  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
895  // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
896  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
897  // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
898  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
899  // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
900  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
901  // tuple<V1&&, V2&&>, std::index_sequence<1>>
902  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
903  // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
904  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
905  // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
906  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
907  // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
908  // The returned multi-dimensional vtable can be fast accessed by the visitor
909  // using index calculation.
910  template<typename _Array_type, typename _Index_seq>
911  struct __gen_vtable_impl;
912 
913  // Defines the _S_apply() member that returns a _Multi_array populated
914  // with function pointers that perform the visitation expressions e(m)
915  // for each valid pack of indexes into the variant types _Variants.
916  //
917  // This partial specialization builds up the index sequences by recursively
918  // calling _S_apply() on the next specialization of __gen_vtable_impl.
919  // The base case of the recursion defines the actual function pointers.
920  template<typename _Result_type, typename _Visitor, size_t... __dimensions,
921  typename... _Variants, size_t... __indices>
922  struct __gen_vtable_impl<
923  _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
924  std::index_sequence<__indices...>>
925  {
926  using _Next =
927  remove_reference_t<typename _Nth_type<sizeof...(__indices),
928  _Variants...>::type>;
929  using _Array_type =
930  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
931  __dimensions...>;
932 
933  static constexpr _Array_type
934  _S_apply()
935  {
936  _Array_type __vtable{};
937  _S_apply_all_alts(
938  __vtable, make_index_sequence<variant_size_v<_Next>>());
939  return __vtable;
940  }
941 
942  template<size_t... __var_indices>
943  static constexpr void
944  _S_apply_all_alts(_Array_type& __vtable,
945  std::index_sequence<__var_indices...>)
946  {
947  if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
948  (_S_apply_single_alt<true, __var_indices>(
949  __vtable._M_arr[__var_indices + 1],
950  &(__vtable._M_arr[0])), ...);
951  else
952  (_S_apply_single_alt<false, __var_indices>(
953  __vtable._M_arr[__var_indices]), ...);
954  }
955 
956  template<bool __do_cookie, size_t __index, typename _Tp>
957  static constexpr void
958  _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
959  {
960  if constexpr (__do_cookie)
961  {
962  __element = __gen_vtable_impl<
963  _Tp,
964  std::index_sequence<__indices..., __index>>::_S_apply();
965  *__cookie_element = __gen_vtable_impl<
966  _Tp,
967  std::index_sequence<__indices..., variant_npos>>::_S_apply();
968  }
969  else
970  {
971  __element = __gen_vtable_impl<
972  remove_reference_t<decltype(__element)>,
973  std::index_sequence<__indices..., __index>>::_S_apply();
974  }
975  }
976  };
977 
978  // This partial specialization is the base case for the recursion.
979  // It populates a _Multi_array element with the address of a function
980  // that invokes the visitor with the alternatives specified by __indices.
981  template<typename _Result_type, typename _Visitor, typename... _Variants,
982  size_t... __indices>
983  struct __gen_vtable_impl<
984  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
985  std::index_sequence<__indices...>>
986  {
987  using _Array_type =
988  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
989 
990  template<size_t __index, typename _Variant>
991  static constexpr decltype(auto)
992  __element_by_index_or_cookie(_Variant&& __var) noexcept
993  {
994  if constexpr (__index != variant_npos)
995  return __variant::__get<__index>(std::forward<_Variant>(__var));
996  else
997  return __variant_cookie{};
998  }
999 
1000  static constexpr decltype(auto)
1001  __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1002  {
1003  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1004  // For raw visitation using indices, pass the indices to the visitor
1005  // and discard the return value:
1006  std::__invoke(std::forward<_Visitor>(__visitor),
1007  __element_by_index_or_cookie<__indices>(
1008  std::forward<_Variants>(__vars))...,
1009  integral_constant<size_t, __indices>()...);
1010  else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1011  // For raw visitation without indices, and discard the return value:
1012  std::__invoke(std::forward<_Visitor>(__visitor),
1013  __element_by_index_or_cookie<__indices>(
1014  std::forward<_Variants>(__vars))...);
1015  else if constexpr (_Array_type::__result_is_deduced::value)
1016  // For the usual std::visit case deduce the return value:
1017  return std::__invoke(std::forward<_Visitor>(__visitor),
1018  __element_by_index_or_cookie<__indices>(
1019  std::forward<_Variants>(__vars))...);
1020  else // for std::visit<R> use INVOKE<R>
1021  return std::__invoke_r<_Result_type>(
1022  std::forward<_Visitor>(__visitor),
1023  __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1024  }
1025 
1026  static constexpr auto
1027  _S_apply()
1028  { return _Array_type{&__visit_invoke}; }
1029  };
1030 
1031  template<typename _Result_type, typename _Visitor, typename... _Variants>
1032  struct __gen_vtable
1033  {
1034  using _Array_type =
1035  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1036  variant_size_v<remove_reference_t<_Variants>>...>;
1037 
1038  static constexpr _Array_type _S_vtable
1039  = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1040  };
1041 
1042  template<size_t _Np, typename _Tp>
1043  struct _Base_dedup : public _Tp { };
1044 
1045  template<typename _Variant, typename __indices>
1046  struct _Variant_hash_base;
1047 
1048  template<typename... _Types, size_t... __indices>
1049  struct _Variant_hash_base<variant<_Types...>,
1050  std::index_sequence<__indices...>>
1051  : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1052 
1053 } // namespace __variant
1054 } // namespace __detail
1055 
1056  template<size_t _Np, typename _Variant, typename... _Args>
1057  void __variant_construct_by_index(_Variant& __v, _Args&&... __args)
1058  {
1059  __v._M_index = _Np;
1060  auto&& __storage = __detail::__variant::__get<_Np>(__v);
1061  ::new ((void*)std::addressof(__storage))
1062  remove_reference_t<decltype(__storage)>
1063  (std::forward<_Args>(__args)...);
1064  }
1065 
1066  template<typename _Tp, typename... _Types>
1067  constexpr bool
1068  holds_alternative(const variant<_Types...>& __v) noexcept
1069  {
1070  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1071  "T must occur exactly once in alternatives");
1072  return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
1073  }
1074 
1075  template<typename _Tp, typename... _Types>
1076  constexpr _Tp& get(variant<_Types...>& __v)
1077  {
1078  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1079  "T must occur exactly once in alternatives");
1080  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1081  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1082  }
1083 
1084  template<typename _Tp, typename... _Types>
1085  constexpr _Tp&& get(variant<_Types...>&& __v)
1086  {
1087  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1088  "T must occur exactly once in alternatives");
1089  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1090  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1091  std::move(__v));
1092  }
1093 
1094  template<typename _Tp, typename... _Types>
1095  constexpr const _Tp& get(const variant<_Types...>& __v)
1096  {
1097  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1098  "T must occur exactly once in alternatives");
1099  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1100  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1101  }
1102 
1103  template<typename _Tp, typename... _Types>
1104  constexpr const _Tp&& get(const variant<_Types...>&& __v)
1105  {
1106  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1107  "T must occur exactly once in alternatives");
1108  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1109  return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1110  std::move(__v));
1111  }
1112 
1113  template<size_t _Np, typename... _Types>
1114  constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1115  get_if(variant<_Types...>* __ptr) noexcept
1116  {
1117  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1118  static_assert(_Np < sizeof...(_Types),
1119  "The index must be in [0, number of alternatives)");
1120  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1121  if (__ptr && __ptr->index() == _Np)
1122  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1123  return nullptr;
1124  }
1125 
1126  template<size_t _Np, typename... _Types>
1127  constexpr
1128  add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1129  get_if(const variant<_Types...>* __ptr) noexcept
1130  {
1131  using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1132  static_assert(_Np < sizeof...(_Types),
1133  "The index must be in [0, number of alternatives)");
1134  static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1135  if (__ptr && __ptr->index() == _Np)
1136  return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1137  return nullptr;
1138  }
1139 
1140  template<typename _Tp, typename... _Types>
1141  constexpr add_pointer_t<_Tp>
1142  get_if(variant<_Types...>* __ptr) noexcept
1143  {
1144  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1145  "T must occur exactly once in alternatives");
1146  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1147  return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1148  __ptr);
1149  }
1150 
1151  template<typename _Tp, typename... _Types>
1152  constexpr add_pointer_t<const _Tp>
1153  get_if(const variant<_Types...>* __ptr) noexcept
1154  {
1155  static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1156  "T must occur exactly once in alternatives");
1157  static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1158  return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1159  __ptr);
1160  }
1161 
1162  struct monostate { };
1163 
1164 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1165  template<typename... _Types> \
1166  constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1167  const variant<_Types...>& __rhs) \
1168  { \
1169  bool __ret = true; \
1170  __detail::__variant::__raw_idx_visit( \
1171  [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1172  { \
1173  if constexpr (__rhs_index != variant_npos) \
1174  { \
1175  if (__lhs.index() == __rhs_index) \
1176  { \
1177  auto& __this_mem = std::get<__rhs_index>(__lhs); \
1178  __ret = __this_mem __OP __rhs_mem; \
1179  } \
1180  else \
1181  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1182  } \
1183  else \
1184  __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1185  }, __rhs); \
1186  return __ret; \
1187  }
1188 
1189  _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1190  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1191  _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1192  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1193  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1194  _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1195 
1196 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1197 
1198  constexpr bool operator==(monostate, monostate) noexcept { return true; }
1199 
1200 #ifdef __cpp_lib_three_way_comparison
1201  template<typename... _Types>
1202  requires (three_way_comparable<_Types> && ...)
1203  constexpr
1204  common_comparison_category_t<compare_three_way_result_t<_Types>...>
1205  operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1206  {
1207  common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1208  = strong_ordering::equal;
1209 
1210  __detail::__variant::__raw_idx_visit(
1211  [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1212  {
1213  if constexpr (__w_index != variant_npos)
1214  {
1215  if (__v.index() == __w_index)
1216  {
1217  auto& __this_mem = std::get<__w_index>(__v);
1218  __ret = __this_mem <=> __w_mem;
1219  return;
1220  }
1221  }
1222  __ret = (__v.index() + 1) <=> (__w_index + 1);
1223  }, __w);
1224  return __ret;
1225  }
1226 
1227  constexpr strong_ordering
1228  operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1229 #else
1230  constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1231  constexpr bool operator<(monostate, monostate) noexcept { return false; }
1232  constexpr bool operator>(monostate, monostate) noexcept { return false; }
1233  constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1234  constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1235 #endif
1236 
1237  template<typename _Visitor, typename... _Variants>
1238  constexpr decltype(auto) visit(_Visitor&&, _Variants&&...);
1239 
1240  template<typename... _Types>
1241  inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1242  && (is_swappable_v<_Types> && ...)>
1243  swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1244  noexcept(noexcept(__lhs.swap(__rhs)))
1245  { __lhs.swap(__rhs); }
1246 
1247  template<typename... _Types>
1248  enable_if_t<!((is_move_constructible_v<_Types> && ...)
1249  && (is_swappable_v<_Types> && ...))>
1250  swap(variant<_Types...>&, variant<_Types...>&) = delete;
1251 
1252  class bad_variant_access : public exception
1253  {
1254  public:
1255  bad_variant_access() noexcept { }
1256 
1257  const char* what() const noexcept override
1258  { return _M_reason; }
1259 
1260  private:
1261  bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1262 
1263  // Must point to a string with static storage duration:
1264  const char* _M_reason = "bad variant access";
1265 
1266  friend void __throw_bad_variant_access(const char* __what);
1267  };
1268 
1269  // Must only be called with a string literal
1270  inline void
1271  __throw_bad_variant_access(const char* __what)
1272  { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1273 
1274  inline void
1275  __throw_bad_variant_access(bool __valueless)
1276  {
1277  if (__valueless) [[__unlikely__]]
1278  __throw_bad_variant_access("std::get: variant is valueless");
1279  else
1280  __throw_bad_variant_access("std::get: wrong index for variant");
1281  }
1282 
1283  template<typename... _Types>
1284  class variant
1285  : private __detail::__variant::_Variant_base<_Types...>,
1286  private _Enable_default_constructor<
1287  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1288  variant<_Types...>>,
1289  private _Enable_copy_move<
1290  __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1291  __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1292  __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1293  __detail::__variant::_Traits<_Types...>::_S_move_assign,
1294  variant<_Types...>>
1295  {
1296  private:
1297  template <typename... _UTypes, typename _Tp>
1298  friend decltype(auto) __variant_cast(_Tp&&);
1299  template<size_t _Np, typename _Variant, typename... _Args>
1300  friend void __variant_construct_by_index(_Variant& __v,
1301  _Args&&... __args);
1302 
1303  static_assert(sizeof...(_Types) > 0,
1304  "variant must have at least one alternative");
1305  static_assert(!(std::is_reference_v<_Types> || ...),
1306  "variant must have no reference alternative");
1307  static_assert(!(std::is_void_v<_Types> || ...),
1308  "variant must have no void alternative");
1309 
1310  using _Base = __detail::__variant::_Variant_base<_Types...>;
1311  using _Default_ctor_enabler =
1312  _Enable_default_constructor<
1313  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1314  variant<_Types...>>;
1315 
1316  template<typename _Tp>
1317  static constexpr bool __not_self
1318  = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1319 
1320  template<typename _Tp>
1321  static constexpr bool
1322  __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1323 
1324  template<typename _Tp>
1325  static constexpr size_t __accepted_index
1326  = __detail::__variant::__accepted_index<_Tp, variant>::value;
1327 
1328  template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1329  using __to_type = variant_alternative_t<_Np, variant>;
1330 
1331  template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1332  using __accepted_type = __to_type<__accepted_index<_Tp>>;
1333 
1334  template<typename _Tp>
1335  static constexpr size_t __index_of =
1336  __detail::__variant::__index_of_v<_Tp, _Types...>;
1337 
1338  using _Traits = __detail::__variant::_Traits<_Types...>;
1339 
1340  template<typename _Tp>
1341  struct __is_in_place_tag : false_type { };
1342  template<typename _Tp>
1343  struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1344  template<size_t _Np>
1345  struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1346 
1347  template<typename _Tp>
1348  static constexpr bool __not_in_place_tag
1349  = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1350 
1351  public:
1352  variant() = default;
1353  variant(const variant& __rhs) = default;
1354  variant(variant&&) = default;
1355  variant& operator=(const variant&) = default;
1356  variant& operator=(variant&&) = default;
1357  ~variant() = default;
1358 
1359  template<typename _Tp,
1360  typename = enable_if_t<sizeof...(_Types) != 0>,
1361  typename = enable_if_t<__not_in_place_tag<_Tp>>,
1362  typename _Tj = __accepted_type<_Tp&&>,
1363  typename = enable_if_t<__exactly_once<_Tj>
1364  && is_constructible_v<_Tj, _Tp>>>
1365  constexpr
1366  variant(_Tp&& __t)
1367  noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1368  : variant(in_place_index<__accepted_index<_Tp>>,
1369  std::forward<_Tp>(__t))
1370  { }
1371 
1372  template<typename _Tp, typename... _Args,
1373  typename = enable_if_t<__exactly_once<_Tp>
1374  && is_constructible_v<_Tp, _Args...>>>
1375  constexpr explicit
1376  variant(in_place_type_t<_Tp>, _Args&&... __args)
1377  : variant(in_place_index<__index_of<_Tp>>,
1378  std::forward<_Args>(__args)...)
1379  { }
1380 
1381  template<typename _Tp, typename _Up, typename... _Args,
1382  typename = enable_if_t<__exactly_once<_Tp>
1383  && is_constructible_v<_Tp,
1384  initializer_list<_Up>&, _Args...>>>
1385  constexpr explicit
1386  variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1387  _Args&&... __args)
1388  : variant(in_place_index<__index_of<_Tp>>, __il,
1389  std::forward<_Args>(__args)...)
1390  { }
1391 
1392  template<size_t _Np, typename... _Args,
1393  typename _Tp = __to_type<_Np>,
1394  typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1395  constexpr explicit
1396  variant(in_place_index_t<_Np>, _Args&&... __args)
1397  : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1398  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1399  { }
1400 
1401  template<size_t _Np, typename _Up, typename... _Args,
1402  typename _Tp = __to_type<_Np>,
1403  typename = enable_if_t<is_constructible_v<_Tp,
1404  initializer_list<_Up>&,
1405  _Args...>>>
1406  constexpr explicit
1407  variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1408  _Args&&... __args)
1409  : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1410  _Default_ctor_enabler(_Enable_default_constructor_tag{})
1411  { }
1412 
1413  template<typename _Tp>
1414  enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1415  && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1416  && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1417  variant&>
1418  operator=(_Tp&& __rhs)
1419  noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1420  && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1421  {
1422  constexpr auto __index = __accepted_index<_Tp>;
1423  if (index() == __index)
1424  std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1425  else
1426  {
1427  using _Tj = __accepted_type<_Tp&&>;
1428  if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1429  || !is_nothrow_move_constructible_v<_Tj>)
1430  this->emplace<__index>(std::forward<_Tp>(__rhs));
1431  else
1432  operator=(variant(std::forward<_Tp>(__rhs)));
1433  }
1434  return *this;
1435  }
1436 
1437  template<typename _Tp, typename... _Args>
1438  enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1439  _Tp&>
1440  emplace(_Args&&... __args)
1441  {
1442  constexpr size_t __index = __index_of<_Tp>;
1443  return this->emplace<__index>(std::forward<_Args>(__args)...);
1444  }
1445 
1446  template<typename _Tp, typename _Up, typename... _Args>
1447  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1448  && __exactly_once<_Tp>,
1449  _Tp&>
1450  emplace(initializer_list<_Up> __il, _Args&&... __args)
1451  {
1452  constexpr size_t __index = __index_of<_Tp>;
1453  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1454  }
1455 
1456  template<size_t _Np, typename... _Args>
1457  enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1458  _Args...>,
1459  variant_alternative_t<_Np, variant>&>
1460  emplace(_Args&&... __args)
1461  {
1462  static_assert(_Np < sizeof...(_Types),
1463  "The index must be in [0, number of alternatives)");
1464  using type = variant_alternative_t<_Np, variant>;
1465  // Provide the strong exception-safety guarantee when possible,
1466  // to avoid becoming valueless.
1467  if constexpr (is_nothrow_constructible_v<type, _Args...>)
1468  {
1469  this->_M_reset();
1470  __variant_construct_by_index<_Np>(*this,
1471  std::forward<_Args>(__args)...);
1472  }
1473  else if constexpr (is_scalar_v<type>)
1474  {
1475  // This might invoke a potentially-throwing conversion operator:
1476  const type __tmp(std::forward<_Args>(__args)...);
1477  // But these steps won't throw:
1478  this->_M_reset();
1479  __variant_construct_by_index<_Np>(*this, __tmp);
1480  }
1481  else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1482  && _Traits::_S_move_assign)
1483  {
1484  // This construction might throw:
1485  variant __tmp(in_place_index<_Np>,
1486  std::forward<_Args>(__args)...);
1487  // But _Never_valueless_alt<type> means this won't:
1488  *this = std::move(__tmp);
1489  }
1490  else
1491  {
1492  // This case only provides the basic exception-safety guarantee,
1493  // i.e. the variant can become valueless.
1494  this->_M_reset();
1495  __try
1496  {
1497  __variant_construct_by_index<_Np>(*this,
1498  std::forward<_Args>(__args)...);
1499  }
1500  __catch (...)
1501  {
1502  this->_M_index = variant_npos;
1503  __throw_exception_again;
1504  }
1505  }
1506  return std::get<_Np>(*this);
1507  }
1508 
1509  template<size_t _Np, typename _Up, typename... _Args>
1510  enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1511  initializer_list<_Up>&, _Args...>,
1512  variant_alternative_t<_Np, variant>&>
1513  emplace(initializer_list<_Up> __il, _Args&&... __args)
1514  {
1515  static_assert(_Np < sizeof...(_Types),
1516  "The index must be in [0, number of alternatives)");
1517  using type = variant_alternative_t<_Np, variant>;
1518  // Provide the strong exception-safety guarantee when possible,
1519  // to avoid becoming valueless.
1520  if constexpr (is_nothrow_constructible_v<type,
1521  initializer_list<_Up>&,
1522  _Args...>)
1523  {
1524  this->_M_reset();
1525  __variant_construct_by_index<_Np>(*this, __il,
1526  std::forward<_Args>(__args)...);
1527  }
1528  else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1529  && _Traits::_S_move_assign)
1530  {
1531  // This construction might throw:
1532  variant __tmp(in_place_index<_Np>, __il,
1533  std::forward<_Args>(__args)...);
1534  // But _Never_valueless_alt<type> means this won't:
1535  *this = std::move(__tmp);
1536  }
1537  else
1538  {
1539  // This case only provides the basic exception-safety guarantee,
1540  // i.e. the variant can become valueless.
1541  this->_M_reset();
1542  __try
1543  {
1544  __variant_construct_by_index<_Np>(*this, __il,
1545  std::forward<_Args>(__args)...);
1546  }
1547  __catch (...)
1548  {
1549  this->_M_index = variant_npos;
1550  __throw_exception_again;
1551  }
1552  }
1553  return std::get<_Np>(*this);
1554  }
1555 
1556  constexpr bool valueless_by_exception() const noexcept
1557  { return !this->_M_valid(); }
1558 
1559  constexpr size_t index() const noexcept
1560  {
1561  using __index_type = typename _Base::__index_type;
1562  if constexpr (__detail::__variant::__never_valueless<_Types...>())
1563  return this->_M_index;
1564  else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1565  return make_signed_t<__index_type>(this->_M_index);
1566  else
1567  return size_t(__index_type(this->_M_index + 1)) - 1;
1568  }
1569 
1570  void
1571  swap(variant& __rhs)
1572  noexcept((__is_nothrow_swappable<_Types>::value && ...)
1573  && is_nothrow_move_constructible_v<variant>)
1574  {
1575  __detail::__variant::__raw_idx_visit(
1576  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1577  {
1578  if constexpr (__rhs_index != variant_npos)
1579  {
1580  if (this->index() == __rhs_index)
1581  {
1582  auto& __this_mem =
1583  std::get<__rhs_index>(*this);
1584  using std::swap;
1585  swap(__this_mem, __rhs_mem);
1586  }
1587  else
1588  {
1589  if (!this->valueless_by_exception()) [[__likely__]]
1590  {
1591  auto __tmp(std::move(__rhs_mem));
1592  __rhs = std::move(*this);
1593  this->_M_destructive_move(__rhs_index,
1594  std::move(__tmp));
1595  }
1596  else
1597  {
1598  this->_M_destructive_move(__rhs_index,
1599  std::move(__rhs_mem));
1600  __rhs._M_reset();
1601  }
1602  }
1603  }
1604  else
1605  {
1606  if (!this->valueless_by_exception()) [[__likely__]]
1607  {
1608  __rhs = std::move(*this);
1609  this->_M_reset();
1610  }
1611  }
1612  }, __rhs);
1613  }
1614 
1615  private:
1616 
1617 #if defined(__clang__) && __clang_major__ <= 7
1618  public:
1619  using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1620  private:
1621 #endif
1622 
1623  template<size_t _Np, typename _Vp>
1624  friend constexpr decltype(auto)
1625  __detail::__variant::__get(_Vp&& __v) noexcept;
1626 
1627  template<typename _Vp>
1628  friend void*
1629  __detail::__variant::__get_storage(_Vp&& __v) noexcept;
1630 
1631 #define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1632  template<typename... _Tp> \
1633  friend constexpr bool \
1634  operator __OP(const variant<_Tp...>& __lhs, \
1635  const variant<_Tp...>& __rhs);
1636 
1637  _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1638  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1639  _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1640  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1641  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1642  _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1643 
1644 #undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1645  };
1646 
1647  template<size_t _Np, typename... _Types>
1648  constexpr variant_alternative_t<_Np, variant<_Types...>>&
1649  get(variant<_Types...>& __v)
1650  {
1651  static_assert(_Np < sizeof...(_Types),
1652  "The index must be in [0, number of alternatives)");
1653  if (__v.index() != _Np)
1654  __throw_bad_variant_access(__v.valueless_by_exception());
1655  return __detail::__variant::__get<_Np>(__v);
1656  }
1657 
1658  template<size_t _Np, typename... _Types>
1659  constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1660  get(variant<_Types...>&& __v)
1661  {
1662  static_assert(_Np < sizeof...(_Types),
1663  "The index must be in [0, number of alternatives)");
1664  if (__v.index() != _Np)
1665  __throw_bad_variant_access(__v.valueless_by_exception());
1666  return __detail::__variant::__get<_Np>(std::move(__v));
1667  }
1668 
1669  template<size_t _Np, typename... _Types>
1670  constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1671  get(const variant<_Types...>& __v)
1672  {
1673  static_assert(_Np < sizeof...(_Types),
1674  "The index must be in [0, number of alternatives)");
1675  if (__v.index() != _Np)
1676  __throw_bad_variant_access(__v.valueless_by_exception());
1677  return __detail::__variant::__get<_Np>(__v);
1678  }
1679 
1680  template<size_t _Np, typename... _Types>
1681  constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1682  get(const variant<_Types...>&& __v)
1683  {
1684  static_assert(_Np < sizeof...(_Types),
1685  "The index must be in [0, number of alternatives)");
1686  if (__v.index() != _Np)
1687  __throw_bad_variant_access(__v.valueless_by_exception());
1688  return __detail::__variant::__get<_Np>(std::move(__v));
1689  }
1690 
1691  template<typename _Result_type, typename _Visitor, typename... _Variants>
1692  constexpr decltype(auto)
1693  __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1694  {
1695  constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1696  _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1697 
1698  auto __func_ptr = __vtable._M_access(__variants.index()...);
1699  return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1700  std::forward<_Variants>(__variants)...);
1701  }
1702 
1703  template<typename _Visitor, typename... _Variants>
1704  constexpr decltype(auto)
1705  visit(_Visitor&& __visitor, _Variants&&... __variants)
1706  {
1707  if ((__variants.valueless_by_exception() || ...))
1708  __throw_bad_variant_access("std::visit: variant is valueless");
1709 
1710  using _Result_type = std::invoke_result_t<_Visitor,
1711  decltype(std::get<0>(std::declval<_Variants>()))...>;
1712 
1713  using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1714 
1715  return std::__do_visit<_Tag>(std::forward<_Visitor>(__visitor),
1716  std::forward<_Variants>(__variants)...);
1717  }
1718 
1719 #if __cplusplus > 201703L
1720  template<typename _Res, typename _Visitor, typename... _Variants>
1721  constexpr _Res
1722  visit(_Visitor&& __visitor, _Variants&&... __variants)
1723  {
1724  if ((__variants.valueless_by_exception() || ...))
1725  __throw_bad_variant_access("std::visit<R>: variant is valueless");
1726 
1727  return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1728  std::forward<_Variants>(__variants)...);
1729  }
1730 #endif
1731 
1732  template<bool, typename... _Types>
1733  struct __variant_hash_call_base_impl
1734  {
1735  size_t
1736  operator()(const variant<_Types...>& __t) const
1737  noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1738  {
1739  size_t __ret;
1740  __detail::__variant::__raw_visit(
1741  [&__t, &__ret](auto&& __t_mem) mutable
1742  {
1743  using _Type = __remove_cvref_t<decltype(__t_mem)>;
1744  if constexpr (!is_same_v<_Type,
1745  __detail::__variant::__variant_cookie>)
1746  __ret = std::hash<size_t>{}(__t.index())
1747  + std::hash<_Type>{}(__t_mem);
1748  else
1749  __ret = std::hash<size_t>{}(__t.index());
1750  }, __t);
1751  return __ret;
1752  }
1753  };
1754 
1755  template<typename... _Types>
1756  struct __variant_hash_call_base_impl<false, _Types...> {};
1757 
1758  template<typename... _Types>
1759  using __variant_hash_call_base =
1760  __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1761  __enable_hash_call &&...), _Types...>;
1762 
1763  template<typename... _Types>
1764  struct hash<variant<_Types...>>
1765  : private __detail::__variant::_Variant_hash_base<
1766  variant<_Types...>, std::index_sequence_for<_Types...>>,
1767  public __variant_hash_call_base<_Types...>
1768  {
1769  using result_type [[__deprecated__]] = size_t;
1770  using argument_type [[__deprecated__]] = variant<_Types...>;
1771  };
1772 
1773  template<>
1774  struct hash<monostate>
1775  {
1776  using result_type [[__deprecated__]] = size_t;
1777  using argument_type [[__deprecated__]] = monostate;
1778 
1779  size_t
1780  operator()(const monostate&) const noexcept
1781  {
1782  constexpr size_t __magic_monostate_hash = -7777;
1783  return __magic_monostate_hash;
1784  }
1785  };
1786 
1787  template<typename... _Types>
1788  struct __is_fast_hash<hash<variant<_Types...>>>
1789  : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1790  { };
1791 
1792 _GLIBCXX_END_NAMESPACE_VERSION
1793 } // namespace std
1794 
1795 #endif // C++17
1796 
1797 #endif // _GLIBCXX_VARIANT