source: Daodan/MSYS2/mingw32/include/c++/11.2.0/variant@ 1186

Last change on this file since 1186 was 1166, checked in by rossy, 3 years ago

Daodan: Replace MinGW build env with an up-to-date MSYS2 env
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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 <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
52namespace std _GLIBCXX_VISIBILITY(default)
53{
54_GLIBCXX_BEGIN_NAMESPACE_VERSION
55
56namespace __detail
57{
58namespace __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
163namespace __detail
164{
165namespace __variant
166{
167 // Returns the first appearance 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 _Tp> struct __deduce_visit_result { using type = _Tp; };
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 trivially destructible type,
206 // even if T is not.
207 template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
208 struct _Uninitialized;
209
210 template<typename _Type>
211 struct _Uninitialized<_Type, true>
212 {
213 template<typename... _Args>
214 constexpr
215 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
216 : _M_storage(std::forward<_Args>(__args)...)
217 { }
218
219 constexpr const _Type& _M_get() const & noexcept
220 { return _M_storage; }
221
222 constexpr _Type& _M_get() & noexcept
223 { return _M_storage; }
224
225 constexpr const _Type&& _M_get() const && noexcept
226 { return std::move(_M_storage); }
227
228 constexpr _Type&& _M_get() && noexcept
229 { return std::move(_M_storage); }
230
231 _Type _M_storage;
232 };
233
234 template<typename _Type>
235 struct _Uninitialized<_Type, false>
236 {
237 template<typename... _Args>
238 constexpr
239 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
240 {
241 ::new ((void*)std::addressof(_M_storage))
242 _Type(std::forward<_Args>(__args)...);
243 }
244
245 const _Type& _M_get() const & noexcept
246 { return *_M_storage._M_ptr(); }
247
248 _Type& _M_get() & noexcept
249 { return *_M_storage._M_ptr(); }
250
251 const _Type&& _M_get() const && noexcept
252 { return std::move(*_M_storage._M_ptr()); }
253
254 _Type&& _M_get() && noexcept
255 { return std::move(*_M_storage._M_ptr()); }
256
257 __gnu_cxx::__aligned_membuf<_Type> _M_storage;
258 };
259
260 template<typename _Union>
261 constexpr decltype(auto)
262 __get(in_place_index_t<0>, _Union&& __u) noexcept
263 { return std::forward<_Union>(__u)._M_first._M_get(); }
264
265 template<size_t _Np, typename _Union>
266 constexpr decltype(auto)
267 __get(in_place_index_t<_Np>, _Union&& __u) noexcept
268 {
269 return __variant::__get(in_place_index<_Np-1>,
270 std::forward<_Union>(__u)._M_rest);
271 }
272
273 // Returns the typed storage for __v.
274 template<size_t _Np, typename _Variant>
275 constexpr decltype(auto)
276 __get(_Variant&& __v) noexcept
277 {
278 return __variant::__get(std::in_place_index<_Np>,
279 std::forward<_Variant>(__v)._M_u);
280 }
281
282 template<typename... _Types>
283 struct _Traits
284 {
285 static constexpr bool _S_default_ctor =
286 is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
287 static constexpr bool _S_copy_ctor =
288 (is_copy_constructible_v<_Types> && ...);
289 static constexpr bool _S_move_ctor =
290 (is_move_constructible_v<_Types> && ...);
291 static constexpr bool _S_copy_assign =
292 _S_copy_ctor
293 && (is_copy_assignable_v<_Types> && ...);
294 static constexpr bool _S_move_assign =
295 _S_move_ctor
296 && (is_move_assignable_v<_Types> && ...);
297
298 static constexpr bool _S_trivial_dtor =
299 (is_trivially_destructible_v<_Types> && ...);
300 static constexpr bool _S_trivial_copy_ctor =
301 (is_trivially_copy_constructible_v<_Types> && ...);
302 static constexpr bool _S_trivial_move_ctor =
303 (is_trivially_move_constructible_v<_Types> && ...);
304 static constexpr bool _S_trivial_copy_assign =
305 _S_trivial_dtor && _S_trivial_copy_ctor
306 && (is_trivially_copy_assignable_v<_Types> && ...);
307 static constexpr bool _S_trivial_move_assign =
308 _S_trivial_dtor && _S_trivial_move_ctor
309 && (is_trivially_move_assignable_v<_Types> && ...);
310
311 // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
312 // are always nothrow.
313 static constexpr bool _S_nothrow_default_ctor =
314 is_nothrow_default_constructible_v<
315 typename _Nth_type<0, _Types...>::type>;
316 static constexpr bool _S_nothrow_copy_ctor = false;
317 static constexpr bool _S_nothrow_move_ctor =
318 (is_nothrow_move_constructible_v<_Types> && ...);
319 static constexpr bool _S_nothrow_copy_assign = false;
320 static constexpr bool _S_nothrow_move_assign =
321 _S_nothrow_move_ctor
322 && (is_nothrow_move_assignable_v<_Types> && ...);
323 };
324
325 // Defines members and ctors.
326 template<typename... _Types>
327 union _Variadic_union { };
328
329 template<typename _First, typename... _Rest>
330 union _Variadic_union<_First, _Rest...>
331 {
332 constexpr _Variadic_union() : _M_rest() { }
333
334 template<typename... _Args>
335 constexpr _Variadic_union(in_place_index_t<0>, _Args&&... __args)
336 : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
337 { }
338
339 template<size_t _Np, typename... _Args>
340 constexpr _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
341 : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
342 { }
343
344 _Uninitialized<_First> _M_first;
345 _Variadic_union<_Rest...> _M_rest;
346 };
347
348 // _Never_valueless_alt is true for variant alternatives that can
349 // always be placed in a variant without it becoming valueless.
350
351 // For suitably-small, trivially copyable types we can create temporaries
352 // on the stack and then memcpy them into place.
353 template<typename _Tp>
354 struct _Never_valueless_alt
355 : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
356 { };
357
358 // Specialize _Never_valueless_alt for other types which have a
359 // non-throwing and cheap move construction and move assignment operator,
360 // so that emplacing the type will provide the strong exception-safety
361 // guarantee, by creating and moving a temporary.
362 // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
363 // variant using that alternative, so we can't change the value later!
364
365 // True if every alternative in _Types... can be emplaced in a variant
366 // without it becoming valueless. If this is true, variant<_Types...>
367 // can never be valueless, which enables some minor optimizations.
368 template <typename... _Types>
369 constexpr bool __never_valueless()
370 {
371 return _Traits<_Types...>::_S_move_assign
372 && (_Never_valueless_alt<_Types>::value && ...);
373 }
374
375 // Defines index and the dtor, possibly trivial.
376 template<bool __trivially_destructible, typename... _Types>
377 struct _Variant_storage;
378
379 template <typename... _Types>
380 using __select_index =
381 typename __select_int::_Select_int_base<sizeof...(_Types),
382 unsigned char,
383 unsigned short>::type::value_type;
384
385 template<typename... _Types>
386 struct _Variant_storage<false, _Types...>
387 {
388 constexpr
389 _Variant_storage()
390 : _M_index(static_cast<__index_type>(variant_npos))
391 { }
392
393 template<size_t _Np, typename... _Args>
394 constexpr
395 _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
396 : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
397 _M_index{_Np}
398 { }
399
400 void _M_reset()
401 {
402 if (!_M_valid()) [[unlikely]]
403 return;
404
405 std::__do_visit<void>([](auto&& __this_mem) mutable
406 {
407 std::_Destroy(std::__addressof(__this_mem));
408 }, __variant_cast<_Types...>(*this));
409
410 _M_index = static_cast<__index_type>(variant_npos);
411 }
412
413 ~_Variant_storage()
414 { _M_reset(); }
415
416 void*
417 _M_storage() const noexcept
418 {
419 return const_cast<void*>(static_cast<const void*>(
420 std::addressof(_M_u)));
421 }
422
423 constexpr bool
424 _M_valid() const noexcept
425 {
426 if constexpr (__variant::__never_valueless<_Types...>())
427 return true;
428 return this->_M_index != __index_type(variant_npos);
429 }
430
431 _Variadic_union<_Types...> _M_u;
432 using __index_type = __select_index<_Types...>;
433 __index_type _M_index;
434 };
435
436 template<typename... _Types>
437 struct _Variant_storage<true, _Types...>
438 {
439 constexpr
440 _Variant_storage()
441 : _M_index(static_cast<__index_type>(variant_npos))
442 { }
443
444 template<size_t _Np, typename... _Args>
445 constexpr
446 _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
447 : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
448 _M_index{_Np}
449 { }
450
451 void _M_reset() noexcept
452 { _M_index = static_cast<__index_type>(variant_npos); }
453
454 void*
455 _M_storage() const noexcept
456 {
457 return const_cast<void*>(static_cast<const void*>(
458 std::addressof(_M_u)));
459 }
460
461 constexpr bool
462 _M_valid() const noexcept
463 {
464 if constexpr (__variant::__never_valueless<_Types...>())
465 return true;
466 return this->_M_index != static_cast<__index_type>(variant_npos);
467 }
468
469 _Variadic_union<_Types...> _M_u;
470 using __index_type = __select_index<_Types...>;
471 __index_type _M_index;
472 };
473
474 template<typename... _Types>
475 using _Variant_storage_alias =
476 _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
477
478 template<typename _Tp, typename _Up>
479 void __variant_construct_single(_Tp&& __lhs, _Up&& __rhs_mem)
480 {
481 void* __storage = std::addressof(__lhs._M_u);
482 using _Type = remove_reference_t<decltype(__rhs_mem)>;
483 if constexpr (!is_same_v<_Type, __variant_cookie>)
484 ::new (__storage)
485 _Type(std::forward<decltype(__rhs_mem)>(__rhs_mem));
486 }
487
488 template<typename... _Types, typename _Tp, typename _Up>
489 void __variant_construct(_Tp&& __lhs, _Up&& __rhs)
490 {
491 __lhs._M_index = __rhs._M_index;
492 __variant::__raw_visit([&__lhs](auto&& __rhs_mem) mutable
493 {
494 __variant_construct_single(std::forward<_Tp>(__lhs),
495 std::forward<decltype(__rhs_mem)>(__rhs_mem));
496 }, __variant_cast<_Types...>(std::forward<_Up>(__rhs)));
497 }
498
499 // The following are (Copy|Move) (ctor|assign) layers for forwarding
500 // triviality and handling non-trivial SMF behaviors.
501
502 template<bool, typename... _Types>
503 struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
504 {
505 using _Base = _Variant_storage_alias<_Types...>;
506 using _Base::_Base;
507
508 _Copy_ctor_base(const _Copy_ctor_base& __rhs)
509 noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
510 {
511 __variant_construct<_Types...>(*this, __rhs);
512 }
513
514 _Copy_ctor_base(_Copy_ctor_base&&) = default;
515 _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
516 _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
517 };
518
519 template<typename... _Types>
520 struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
521 {
522 using _Base = _Variant_storage_alias<_Types...>;
523 using _Base::_Base;
524 };
525
526 template<typename... _Types>
527 using _Copy_ctor_alias =
528 _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
529
530 template<bool, typename... _Types>
531 struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
532 {
533 using _Base = _Copy_ctor_alias<_Types...>;
534 using _Base::_Base;
535
536 _Move_ctor_base(_Move_ctor_base&& __rhs)
537 noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
538 {
539 __variant_construct<_Types...>(*this, std::move(__rhs));
540 }
541
542 template<typename _Up>
543 void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
544 {
545 this->_M_reset();
546 __variant_construct_single(*this, std::forward<_Up>(__rhs));
547 this->_M_index = __rhs_index;
548 }
549
550 template<typename _Up>
551 void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
552 {
553 this->_M_reset();
554 __variant_construct_single(*this, __rhs);
555 this->_M_index = __rhs_index;
556 }
557
558 _Move_ctor_base(const _Move_ctor_base&) = default;
559 _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
560 _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
561 };
562
563 template<typename... _Types>
564 struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
565 {
566 using _Base = _Copy_ctor_alias<_Types...>;
567 using _Base::_Base;
568
569 template<typename _Up>
570 void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
571 {
572 this->_M_reset();
573 __variant_construct_single(*this, std::forward<_Up>(__rhs));
574 this->_M_index = __rhs_index;
575 }
576
577 template<typename _Up>
578 void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
579 {
580 this->_M_reset();
581 __variant_construct_single(*this, __rhs);
582 this->_M_index = __rhs_index;
583 }
584 };
585
586 template<typename... _Types>
587 using _Move_ctor_alias =
588 _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
589
590 template<bool, typename... _Types>
591 struct _Copy_assign_base : _Move_ctor_alias<_Types...>
592 {
593 using _Base = _Move_ctor_alias<_Types...>;
594 using _Base::_Base;
595
596 _Copy_assign_base&
597 operator=(const _Copy_assign_base& __rhs)
598 noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
599 {
600 __variant::__raw_idx_visit(
601 [this](auto&& __rhs_mem, auto __rhs_index) mutable
602 {
603 if constexpr (__rhs_index != variant_npos)
604 {
605 if (this->_M_index == __rhs_index)
606 __variant::__get<__rhs_index>(*this) = __rhs_mem;
607 else
608 {
609 using __rhs_type = __remove_cvref_t<decltype(__rhs_mem)>;
610 if constexpr (is_nothrow_copy_constructible_v<__rhs_type>
611 || !is_nothrow_move_constructible_v<__rhs_type>)
612 // The standard says this->emplace<__rhs_type>(__rhs_mem)
613 // should be used here, but _M_destructive_copy is
614 // equivalent in this case. Either copy construction
615 // doesn't throw, so _M_destructive_copy gives strong
616 // exception safety guarantee, or both copy construction
617 // and move construction can throw, so emplace only gives
618 // basic exception safety anyway.
619 this->_M_destructive_copy(__rhs_index, __rhs_mem);
620 else
621 __variant_cast<_Types...>(*this)
622 = variant<_Types...>(std::in_place_index<__rhs_index>,
623 __rhs_mem);
624 }
625 }
626 else
627 this->_M_reset();
628 }, __variant_cast<_Types...>(__rhs));
629 return *this;
630 }
631
632 _Copy_assign_base(const _Copy_assign_base&) = default;
633 _Copy_assign_base(_Copy_assign_base&&) = default;
634 _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
635 };
636
637 template<typename... _Types>
638 struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
639 {
640 using _Base = _Move_ctor_alias<_Types...>;
641 using _Base::_Base;
642 };
643
644 template<typename... _Types>
645 using _Copy_assign_alias =
646 _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
647
648 template<bool, typename... _Types>
649 struct _Move_assign_base : _Copy_assign_alias<_Types...>
650 {
651 using _Base = _Copy_assign_alias<_Types...>;
652 using _Base::_Base;
653
654 _Move_assign_base&
655 operator=(_Move_assign_base&& __rhs)
656 noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
657 {
658 __variant::__raw_idx_visit(
659 [this](auto&& __rhs_mem, auto __rhs_index) mutable
660 {
661 if constexpr (__rhs_index != variant_npos)
662 {
663 if (this->_M_index == __rhs_index)
664 __variant::__get<__rhs_index>(*this) = std::move(__rhs_mem);
665 else
666 __variant_cast<_Types...>(*this)
667 .template emplace<__rhs_index>(std::move(__rhs_mem));
668 }
669 else
670 this->_M_reset();
671 }, __variant_cast<_Types...>(__rhs));
672 return *this;
673 }
674
675 _Move_assign_base(const _Move_assign_base&) = default;
676 _Move_assign_base(_Move_assign_base&&) = default;
677 _Move_assign_base& operator=(const _Move_assign_base&) = default;
678 };
679
680 template<typename... _Types>
681 struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
682 {
683 using _Base = _Copy_assign_alias<_Types...>;
684 using _Base::_Base;
685 };
686
687 template<typename... _Types>
688 using _Move_assign_alias =
689 _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
690
691 template<typename... _Types>
692 struct _Variant_base : _Move_assign_alias<_Types...>
693 {
694 using _Base = _Move_assign_alias<_Types...>;
695
696 constexpr
697 _Variant_base()
698 noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
699 : _Variant_base(in_place_index<0>) { }
700
701 template<size_t _Np, typename... _Args>
702 constexpr explicit
703 _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
704 : _Base(__i, std::forward<_Args>(__args)...)
705 { }
706
707 _Variant_base(const _Variant_base&) = default;
708 _Variant_base(_Variant_base&&) = default;
709 _Variant_base& operator=(const _Variant_base&) = default;
710 _Variant_base& operator=(_Variant_base&&) = default;
711 };
712
713 // For how many times does _Tp appear in _Tuple?
714 template<typename _Tp, typename _Tuple>
715 struct __tuple_count;
716
717 template<typename _Tp, typename _Tuple>
718 inline constexpr size_t __tuple_count_v =
719 __tuple_count<_Tp, _Tuple>::value;
720
721 template<typename _Tp, typename... _Types>
722 struct __tuple_count<_Tp, tuple<_Types...>>
723 : integral_constant<size_t, 0> { };
724
725 template<typename _Tp, typename _First, typename... _Rest>
726 struct __tuple_count<_Tp, tuple<_First, _Rest...>>
727 : integral_constant<
728 size_t,
729 __tuple_count_v<_Tp, tuple<_Rest...>> + is_same_v<_Tp, _First>> { };
730
731 // TODO: Reuse this in <tuple> ?
732 template<typename _Tp, typename... _Types>
733 inline constexpr bool __exactly_once =
734 __tuple_count_v<_Tp, tuple<_Types...>> == 1;
735
736 // Helper used to check for valid conversions that don't involve narrowing.
737 template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
738
739 // "Build an imaginary function FUN(Ti) for each alternative type Ti"
740 template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
741 struct _Build_FUN
742 {
743 // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
744 // but only static functions will be considered in the call below.
745 void _S_fun();
746 };
747
748 // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
749 template<size_t _Ind, typename _Tp, typename _Ti>
750 struct _Build_FUN<_Ind, _Tp, _Ti,
751 void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
752 {
753 // This is the FUN function for type _Ti, with index _Ind
754 static integral_constant<size_t, _Ind> _S_fun(_Ti);
755 };
756
757 template<typename _Tp, typename _Variant,
758 typename = make_index_sequence<variant_size_v<_Variant>>>
759 struct _Build_FUNs;
760
761 template<typename _Tp, typename... _Ti, size_t... _Ind>
762 struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
763 : _Build_FUN<_Ind, _Tp, _Ti>...
764 {
765 using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
766 };
767
768 // The index j of the overload FUN(Tj) selected by overload resolution
769 // for FUN(std::forward<_Tp>(t))
770 template<typename _Tp, typename _Variant>
771 using _FUN_type
772 = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
773
774 // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
775 template<typename _Tp, typename _Variant, typename = void>
776 struct __accepted_index
777 : integral_constant<size_t, variant_npos>
778 { };
779
780 template<typename _Tp, typename _Variant>
781 struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
782 : _FUN_type<_Tp, _Variant>
783 { };
784
785 // Returns the raw storage for __v.
786 template<typename _Variant>
787 void* __get_storage(_Variant&& __v) noexcept
788 { return __v._M_storage(); }
789
790 template <typename _Maybe_variant_cookie, typename _Variant>
791 struct _Extra_visit_slot_needed
792 {
793 template <typename> struct _Variant_never_valueless;
794
795 template <typename... _Types>
796 struct _Variant_never_valueless<variant<_Types...>>
797 : bool_constant<__variant::__never_valueless<_Types...>()> {};
798
799 static constexpr bool value =
800 (is_same_v<_Maybe_variant_cookie, __variant_cookie>
801 || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
802 && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
803 };
804
805 // Used for storing a multi-dimensional vtable.
806 template<typename _Tp, size_t... _Dimensions>
807 struct _Multi_array;
808
809 // Partial specialization with rank zero, stores a single _Tp element.
810 template<typename _Tp>
811 struct _Multi_array<_Tp>
812 {
813 template<typename>
814 struct __untag_result
815 : false_type
816 { using element_type = _Tp; };
817
818 template <typename... _Args>
819 struct __untag_result<const void(*)(_Args...)>
820 : false_type
821 { using element_type = void(*)(_Args...); };
822
823 template <typename... _Args>
824 struct __untag_result<__variant_cookie(*)(_Args...)>
825 : false_type
826 { using element_type = void(*)(_Args...); };
827
828 template <typename... _Args>
829 struct __untag_result<__variant_idx_cookie(*)(_Args...)>
830 : false_type
831 { using element_type = void(*)(_Args...); };
832
833 template <typename _Res, typename... _Args>
834 struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
835 : true_type
836 { using element_type = _Res(*)(_Args...); };
837
838 using __result_is_deduced = __untag_result<_Tp>;
839
840 constexpr const typename __untag_result<_Tp>::element_type&
841 _M_access() const
842 { return _M_data; }
843
844 typename __untag_result<_Tp>::element_type _M_data;
845 };
846
847 // Partial specialization with rank >= 1.
848 template<typename _Ret,
849 typename _Visitor,
850 typename... _Variants,
851 size_t __first, size_t... __rest>
852 struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
853 {
854 static constexpr size_t __index =
855 sizeof...(_Variants) - sizeof...(__rest) - 1;
856
857 using _Variant = typename _Nth_type<__index, _Variants...>::type;
858
859 static constexpr int __do_cookie =
860 _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
861
862 using _Tp = _Ret(*)(_Visitor, _Variants...);
863
864 template<typename... _Args>
865 constexpr decltype(auto)
866 _M_access(size_t __first_index, _Args... __rest_indices) const
867 {
868 return _M_arr[__first_index + __do_cookie]
869 ._M_access(__rest_indices...);
870 }
871
872 _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
873 };
874
875 // Creates a multi-dimensional vtable recursively.
876 //
877 // For example,
878 // visit([](auto, auto){},
879 // variant<int, char>(), // typedef'ed as V1
880 // variant<float, double, long double>()) // typedef'ed as V2
881 // will trigger instantiations of:
882 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
883 // tuple<V1&&, V2&&>, std::index_sequence<>>
884 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
885 // tuple<V1&&, V2&&>, std::index_sequence<0>>
886 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
887 // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
888 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
889 // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
890 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
891 // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
892 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
893 // tuple<V1&&, V2&&>, std::index_sequence<1>>
894 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
895 // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
896 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
897 // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
898 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
899 // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
900 // The returned multi-dimensional vtable can be fast accessed by the visitor
901 // using index calculation.
902 template<typename _Array_type, typename _Index_seq>
903 struct __gen_vtable_impl;
904
905 // Defines the _S_apply() member that returns a _Multi_array populated
906 // with function pointers that perform the visitation expressions e(m)
907 // for each valid pack of indexes into the variant types _Variants.
908 //
909 // This partial specialization builds up the index sequences by recursively
910 // calling _S_apply() on the next specialization of __gen_vtable_impl.
911 // The base case of the recursion defines the actual function pointers.
912 template<typename _Result_type, typename _Visitor, size_t... __dimensions,
913 typename... _Variants, size_t... __indices>
914 struct __gen_vtable_impl<
915 _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
916 std::index_sequence<__indices...>>
917 {
918 using _Next =
919 remove_reference_t<typename _Nth_type<sizeof...(__indices),
920 _Variants...>::type>;
921 using _Array_type =
922 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
923 __dimensions...>;
924
925 static constexpr _Array_type
926 _S_apply()
927 {
928 _Array_type __vtable{};
929 _S_apply_all_alts(
930 __vtable, make_index_sequence<variant_size_v<_Next>>());
931 return __vtable;
932 }
933
934 template<size_t... __var_indices>
935 static constexpr void
936 _S_apply_all_alts(_Array_type& __vtable,
937 std::index_sequence<__var_indices...>)
938 {
939 if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
940 (_S_apply_single_alt<true, __var_indices>(
941 __vtable._M_arr[__var_indices + 1],
942 &(__vtable._M_arr[0])), ...);
943 else
944 (_S_apply_single_alt<false, __var_indices>(
945 __vtable._M_arr[__var_indices]), ...);
946 }
947
948 template<bool __do_cookie, size_t __index, typename _Tp>
949 static constexpr void
950 _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
951 {
952 if constexpr (__do_cookie)
953 {
954 __element = __gen_vtable_impl<
955 _Tp,
956 std::index_sequence<__indices..., __index>>::_S_apply();
957 *__cookie_element = __gen_vtable_impl<
958 _Tp,
959 std::index_sequence<__indices..., variant_npos>>::_S_apply();
960 }
961 else
962 {
963 auto __tmp_element = __gen_vtable_impl<
964 remove_reference_t<decltype(__element)>,
965 std::index_sequence<__indices..., __index>>::_S_apply();
966 static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
967 "std::visit requires the visitor to have the same "
968 "return type for all alternatives of a variant");
969 __element = __tmp_element;
970 }
971 }
972 };
973
974 // This partial specialization is the base case for the recursion.
975 // It populates a _Multi_array element with the address of a function
976 // that invokes the visitor with the alternatives specified by __indices.
977 template<typename _Result_type, typename _Visitor, typename... _Variants,
978 size_t... __indices>
979 struct __gen_vtable_impl<
980 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
981 std::index_sequence<__indices...>>
982 {
983 using _Array_type =
984 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
985
986 template<size_t __index, typename _Variant>
987 static constexpr decltype(auto)
988 __element_by_index_or_cookie(_Variant&& __var) noexcept
989 {
990 if constexpr (__index != variant_npos)
991 return __variant::__get<__index>(std::forward<_Variant>(__var));
992 else
993 return __variant_cookie{};
994 }
995
996 static constexpr decltype(auto)
997 __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
998 {
999 if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1000 // For raw visitation using indices, pass the indices to the visitor
1001 // and discard the return value:
1002 std::__invoke(std::forward<_Visitor>(__visitor),
1003 __element_by_index_or_cookie<__indices>(
1004 std::forward<_Variants>(__vars))...,
1005 integral_constant<size_t, __indices>()...);
1006 else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1007 // For raw visitation without indices, and discard the return value:
1008 std::__invoke(std::forward<_Visitor>(__visitor),
1009 __element_by_index_or_cookie<__indices>(
1010 std::forward<_Variants>(__vars))...);
1011 else if constexpr (_Array_type::__result_is_deduced::value)
1012 // For the usual std::visit case deduce the return value:
1013 return std::__invoke(std::forward<_Visitor>(__visitor),
1014 __element_by_index_or_cookie<__indices>(
1015 std::forward<_Variants>(__vars))...);
1016 else // for std::visit<R> use INVOKE<R>
1017 return std::__invoke_r<_Result_type>(
1018 std::forward<_Visitor>(__visitor),
1019 __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1020 }
1021
1022 static constexpr auto
1023 _S_apply()
1024 {
1025 if constexpr (_Array_type::__result_is_deduced::value)
1026 {
1027 constexpr bool __visit_ret_type_mismatch =
1028 !is_same_v<typename _Result_type::type,
1029 decltype(__visit_invoke(std::declval<_Visitor>(),
1030 std::declval<_Variants>()...))>;
1031 if constexpr (__visit_ret_type_mismatch)
1032 {
1033 struct __cannot_match {};
1034 return __cannot_match{};
1035 }
1036 else
1037 return _Array_type{&__visit_invoke};
1038 }
1039 else
1040 return _Array_type{&__visit_invoke};
1041 }
1042 };
1043
1044 template<typename _Result_type, typename _Visitor, typename... _Variants>
1045 struct __gen_vtable
1046 {
1047 using _Array_type =
1048 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1049 variant_size_v<remove_reference_t<_Variants>>...>;
1050
1051 static constexpr _Array_type _S_vtable
1052 = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1053 };
1054
1055 template<size_t _Np, typename _Tp>
1056 struct _Base_dedup : public _Tp { };
1057
1058 template<typename _Variant, typename __indices>
1059 struct _Variant_hash_base;
1060
1061 template<typename... _Types, size_t... __indices>
1062 struct _Variant_hash_base<variant<_Types...>,
1063 std::index_sequence<__indices...>>
1064 : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1065
1066 template<size_t _Np, typename _Variant>
1067 using __get_t = decltype(std::get<_Np>(std::declval<_Variant>()));
1068
1069 // Return type of std::visit.
1070 template<typename _Visitor, typename... _Variants>
1071 using __visit_result_t
1072 = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1073
1074 template<typename _Tp, typename... _Types>
1075 constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
1076
1077 template <typename _Visitor, typename _Variant, size_t... _Idxs>
1078 constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
1079 {
1080 return __same_types<
1081 invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
1082 >;
1083 }
1084
1085} // namespace __variant
1086} // namespace __detail
1087
1088 template<size_t _Np, typename _Variant, typename... _Args>
1089 void __variant_construct_by_index(_Variant& __v, _Args&&... __args)
1090 {
1091 __v._M_index = _Np;
1092 auto&& __storage = __detail::__variant::__get<_Np>(__v);
1093 ::new ((void*)std::addressof(__storage))
1094 remove_reference_t<decltype(__storage)>
1095 (std::forward<_Args>(__args)...);
1096 }
1097
1098 template<typename _Tp, typename... _Types>
1099 constexpr bool
1100 holds_alternative(const variant<_Types...>& __v) noexcept
1101 {
1102 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1103 "T must occur exactly once in alternatives");
1104 return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
1105 }
1106
1107 template<typename _Tp, typename... _Types>
1108 constexpr _Tp& get(variant<_Types...>& __v)
1109 {
1110 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1111 "T must occur exactly once in alternatives");
1112 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1113 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1114 }
1115
1116 template<typename _Tp, typename... _Types>
1117 constexpr _Tp&& get(variant<_Types...>&& __v)
1118 {
1119 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1120 "T must occur exactly once in alternatives");
1121 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1122 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1123 std::move(__v));
1124 }
1125
1126 template<typename _Tp, typename... _Types>
1127 constexpr const _Tp& get(const variant<_Types...>& __v)
1128 {
1129 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1130 "T must occur exactly once in alternatives");
1131 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1132 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1133 }
1134
1135 template<typename _Tp, typename... _Types>
1136 constexpr const _Tp&& get(const variant<_Types...>&& __v)
1137 {
1138 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1139 "T must occur exactly once in alternatives");
1140 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1141 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1142 std::move(__v));
1143 }
1144
1145 template<size_t _Np, typename... _Types>
1146 constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1147 get_if(variant<_Types...>* __ptr) noexcept
1148 {
1149 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1150 static_assert(_Np < sizeof...(_Types),
1151 "The index must be in [0, number of alternatives)");
1152 static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1153 if (__ptr && __ptr->index() == _Np)
1154 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1155 return nullptr;
1156 }
1157
1158 template<size_t _Np, typename... _Types>
1159 constexpr
1160 add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1161 get_if(const variant<_Types...>* __ptr) noexcept
1162 {
1163 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1164 static_assert(_Np < sizeof...(_Types),
1165 "The index must be in [0, number of alternatives)");
1166 static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1167 if (__ptr && __ptr->index() == _Np)
1168 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1169 return nullptr;
1170 }
1171
1172 template<typename _Tp, typename... _Types>
1173 constexpr add_pointer_t<_Tp>
1174 get_if(variant<_Types...>* __ptr) noexcept
1175 {
1176 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1177 "T must occur exactly once in alternatives");
1178 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1179 return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1180 __ptr);
1181 }
1182
1183 template<typename _Tp, typename... _Types>
1184 constexpr add_pointer_t<const _Tp>
1185 get_if(const variant<_Types...>* __ptr) noexcept
1186 {
1187 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1188 "T must occur exactly once in alternatives");
1189 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1190 return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1191 __ptr);
1192 }
1193
1194 struct monostate { };
1195
1196#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1197 template<typename... _Types> \
1198 constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1199 const variant<_Types...>& __rhs) \
1200 { \
1201 bool __ret = true; \
1202 __detail::__variant::__raw_idx_visit( \
1203 [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1204 { \
1205 if constexpr (__rhs_index != variant_npos) \
1206 { \
1207 if (__lhs.index() == __rhs_index) \
1208 { \
1209 auto& __this_mem = std::get<__rhs_index>(__lhs); \
1210 __ret = __this_mem __OP __rhs_mem; \
1211 } \
1212 else \
1213 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1214 } \
1215 else \
1216 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1217 }, __rhs); \
1218 return __ret; \
1219 }
1220
1221 _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1222 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1223 _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1224 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1225 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1226 _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1227
1228#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1229
1230 constexpr bool operator==(monostate, monostate) noexcept { return true; }
1231
1232#ifdef __cpp_lib_three_way_comparison
1233 template<typename... _Types>
1234 requires (three_way_comparable<_Types> && ...)
1235 constexpr
1236 common_comparison_category_t<compare_three_way_result_t<_Types>...>
1237 operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1238 {
1239 common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1240 = strong_ordering::equal;
1241
1242 __detail::__variant::__raw_idx_visit(
1243 [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1244 {
1245 if constexpr (__w_index != variant_npos)
1246 {
1247 if (__v.index() == __w_index)
1248 {
1249 auto& __this_mem = std::get<__w_index>(__v);
1250 __ret = __this_mem <=> __w_mem;
1251 return;
1252 }
1253 }
1254 __ret = (__v.index() + 1) <=> (__w_index + 1);
1255 }, __w);
1256 return __ret;
1257 }
1258
1259 constexpr strong_ordering
1260 operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1261#else
1262 constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1263 constexpr bool operator<(monostate, monostate) noexcept { return false; }
1264 constexpr bool operator>(monostate, monostate) noexcept { return false; }
1265 constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1266 constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1267#endif
1268
1269 template<typename _Visitor, typename... _Variants>
1270 constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1271 visit(_Visitor&&, _Variants&&...);
1272
1273 template<typename... _Types>
1274 inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1275 && (is_swappable_v<_Types> && ...)>
1276 swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1277 noexcept(noexcept(__lhs.swap(__rhs)))
1278 { __lhs.swap(__rhs); }
1279
1280 template<typename... _Types>
1281 enable_if_t<!((is_move_constructible_v<_Types> && ...)
1282 && (is_swappable_v<_Types> && ...))>
1283 swap(variant<_Types...>&, variant<_Types...>&) = delete;
1284
1285 class bad_variant_access : public exception
1286 {
1287 public:
1288 bad_variant_access() noexcept { }
1289
1290 const char* what() const noexcept override
1291 { return _M_reason; }
1292
1293 private:
1294 bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1295
1296 // Must point to a string with static storage duration:
1297 const char* _M_reason = "bad variant access";
1298
1299 friend void __throw_bad_variant_access(const char* __what);
1300 };
1301
1302 // Must only be called with a string literal
1303 inline void
1304 __throw_bad_variant_access(const char* __what)
1305 { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1306
1307 inline void
1308 __throw_bad_variant_access(bool __valueless)
1309 {
1310 if (__valueless) [[__unlikely__]]
1311 __throw_bad_variant_access("std::get: variant is valueless");
1312 else
1313 __throw_bad_variant_access("std::get: wrong index for variant");
1314 }
1315
1316 template<typename... _Types>
1317 class variant
1318 : private __detail::__variant::_Variant_base<_Types...>,
1319 private _Enable_default_constructor<
1320 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1321 variant<_Types...>>,
1322 private _Enable_copy_move<
1323 __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1324 __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1325 __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1326 __detail::__variant::_Traits<_Types...>::_S_move_assign,
1327 variant<_Types...>>
1328 {
1329 private:
1330 template <typename... _UTypes, typename _Tp>
1331 friend decltype(auto) __variant_cast(_Tp&&);
1332 template<size_t _Np, typename _Variant, typename... _Args>
1333 friend void __variant_construct_by_index(_Variant& __v,
1334 _Args&&... __args);
1335
1336 static_assert(sizeof...(_Types) > 0,
1337 "variant must have at least one alternative");
1338 static_assert(!(std::is_reference_v<_Types> || ...),
1339 "variant must have no reference alternative");
1340 static_assert(!(std::is_void_v<_Types> || ...),
1341 "variant must have no void alternative");
1342
1343 using _Base = __detail::__variant::_Variant_base<_Types...>;
1344 using _Default_ctor_enabler =
1345 _Enable_default_constructor<
1346 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1347 variant<_Types...>>;
1348
1349 template<typename _Tp>
1350 static constexpr bool __not_self
1351 = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1352
1353 template<typename _Tp>
1354 static constexpr bool
1355 __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1356
1357 template<typename _Tp>
1358 static constexpr size_t __accepted_index
1359 = __detail::__variant::__accepted_index<_Tp, variant>::value;
1360
1361 template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1362 using __to_type = variant_alternative_t<_Np, variant>;
1363
1364 template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1365 using __accepted_type = __to_type<__accepted_index<_Tp>>;
1366
1367 template<typename _Tp>
1368 static constexpr size_t __index_of =
1369 __detail::__variant::__index_of_v<_Tp, _Types...>;
1370
1371 using _Traits = __detail::__variant::_Traits<_Types...>;
1372
1373 template<typename _Tp>
1374 struct __is_in_place_tag : false_type { };
1375 template<typename _Tp>
1376 struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1377 template<size_t _Np>
1378 struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1379
1380 template<typename _Tp>
1381 static constexpr bool __not_in_place_tag
1382 = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1383
1384 public:
1385 variant() = default;
1386 variant(const variant& __rhs) = default;
1387 variant(variant&&) = default;
1388 variant& operator=(const variant&) = default;
1389 variant& operator=(variant&&) = default;
1390 ~variant() = default;
1391
1392 template<typename _Tp,
1393 typename = enable_if_t<sizeof...(_Types) != 0>,
1394 typename = enable_if_t<__not_in_place_tag<_Tp>>,
1395 typename _Tj = __accepted_type<_Tp&&>,
1396 typename = enable_if_t<__exactly_once<_Tj>
1397 && is_constructible_v<_Tj, _Tp>>>
1398 constexpr
1399 variant(_Tp&& __t)
1400 noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1401 : variant(in_place_index<__accepted_index<_Tp>>,
1402 std::forward<_Tp>(__t))
1403 { }
1404
1405 template<typename _Tp, typename... _Args,
1406 typename = enable_if_t<__exactly_once<_Tp>
1407 && is_constructible_v<_Tp, _Args...>>>
1408 constexpr explicit
1409 variant(in_place_type_t<_Tp>, _Args&&... __args)
1410 : variant(in_place_index<__index_of<_Tp>>,
1411 std::forward<_Args>(__args)...)
1412 { }
1413
1414 template<typename _Tp, typename _Up, typename... _Args,
1415 typename = enable_if_t<__exactly_once<_Tp>
1416 && is_constructible_v<_Tp,
1417 initializer_list<_Up>&, _Args...>>>
1418 constexpr explicit
1419 variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1420 _Args&&... __args)
1421 : variant(in_place_index<__index_of<_Tp>>, __il,
1422 std::forward<_Args>(__args)...)
1423 { }
1424
1425 template<size_t _Np, typename... _Args,
1426 typename _Tp = __to_type<_Np>,
1427 typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1428 constexpr explicit
1429 variant(in_place_index_t<_Np>, _Args&&... __args)
1430 : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1431 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1432 { }
1433
1434 template<size_t _Np, typename _Up, typename... _Args,
1435 typename _Tp = __to_type<_Np>,
1436 typename = enable_if_t<is_constructible_v<_Tp,
1437 initializer_list<_Up>&,
1438 _Args...>>>
1439 constexpr explicit
1440 variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1441 _Args&&... __args)
1442 : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1443 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1444 { }
1445
1446 template<typename _Tp>
1447 enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1448 && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1449 && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1450 variant&>
1451 operator=(_Tp&& __rhs)
1452 noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1453 && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1454 {
1455 constexpr auto __index = __accepted_index<_Tp>;
1456 if (index() == __index)
1457 std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1458 else
1459 {
1460 using _Tj = __accepted_type<_Tp&&>;
1461 if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1462 || !is_nothrow_move_constructible_v<_Tj>)
1463 this->emplace<__index>(std::forward<_Tp>(__rhs));
1464 else
1465 operator=(variant(std::forward<_Tp>(__rhs)));
1466 }
1467 return *this;
1468 }
1469
1470 template<typename _Tp, typename... _Args>
1471 enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1472 _Tp&>
1473 emplace(_Args&&... __args)
1474 {
1475 constexpr size_t __index = __index_of<_Tp>;
1476 return this->emplace<__index>(std::forward<_Args>(__args)...);
1477 }
1478
1479 template<typename _Tp, typename _Up, typename... _Args>
1480 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1481 && __exactly_once<_Tp>,
1482 _Tp&>
1483 emplace(initializer_list<_Up> __il, _Args&&... __args)
1484 {
1485 constexpr size_t __index = __index_of<_Tp>;
1486 return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1487 }
1488
1489 template<size_t _Np, typename... _Args>
1490 enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1491 _Args...>,
1492 variant_alternative_t<_Np, variant>&>
1493 emplace(_Args&&... __args)
1494 {
1495 static_assert(_Np < sizeof...(_Types),
1496 "The index must be in [0, number of alternatives)");
1497 using type = variant_alternative_t<_Np, variant>;
1498 // Provide the strong exception-safety guarantee when possible,
1499 // to avoid becoming valueless.
1500 if constexpr (is_nothrow_constructible_v<type, _Args...>)
1501 {
1502 this->_M_reset();
1503 __variant_construct_by_index<_Np>(*this,
1504 std::forward<_Args>(__args)...);
1505 }
1506 else if constexpr (is_scalar_v<type>)
1507 {
1508 // This might invoke a potentially-throwing conversion operator:
1509 const type __tmp(std::forward<_Args>(__args)...);
1510 // But these steps won't throw:
1511 this->_M_reset();
1512 __variant_construct_by_index<_Np>(*this, __tmp);
1513 }
1514 else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1515 && _Traits::_S_move_assign)
1516 {
1517 // This construction might throw:
1518 variant __tmp(in_place_index<_Np>,
1519 std::forward<_Args>(__args)...);
1520 // But _Never_valueless_alt<type> means this won't:
1521 *this = std::move(__tmp);
1522 }
1523 else
1524 {
1525 // This case only provides the basic exception-safety guarantee,
1526 // i.e. the variant can become valueless.
1527 this->_M_reset();
1528 __try
1529 {
1530 __variant_construct_by_index<_Np>(*this,
1531 std::forward<_Args>(__args)...);
1532 }
1533 __catch (...)
1534 {
1535 using __index_type = decltype(this->_M_index);
1536 this->_M_index = static_cast<__index_type>(variant_npos);
1537 __throw_exception_again;
1538 }
1539 }
1540 return std::get<_Np>(*this);
1541 }
1542
1543 template<size_t _Np, typename _Up, typename... _Args>
1544 enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1545 initializer_list<_Up>&, _Args...>,
1546 variant_alternative_t<_Np, variant>&>
1547 emplace(initializer_list<_Up> __il, _Args&&... __args)
1548 {
1549 static_assert(_Np < sizeof...(_Types),
1550 "The index must be in [0, number of alternatives)");
1551 using type = variant_alternative_t<_Np, variant>;
1552 // Provide the strong exception-safety guarantee when possible,
1553 // to avoid becoming valueless.
1554 if constexpr (is_nothrow_constructible_v<type,
1555 initializer_list<_Up>&,
1556 _Args...>)
1557 {
1558 this->_M_reset();
1559 __variant_construct_by_index<_Np>(*this, __il,
1560 std::forward<_Args>(__args)...);
1561 }
1562 else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1563 && _Traits::_S_move_assign)
1564 {
1565 // This construction might throw:
1566 variant __tmp(in_place_index<_Np>, __il,
1567 std::forward<_Args>(__args)...);
1568 // But _Never_valueless_alt<type> means this won't:
1569 *this = std::move(__tmp);
1570 }
1571 else
1572 {
1573 // This case only provides the basic exception-safety guarantee,
1574 // i.e. the variant can become valueless.
1575 this->_M_reset();
1576 __try
1577 {
1578 __variant_construct_by_index<_Np>(*this, __il,
1579 std::forward<_Args>(__args)...);
1580 }
1581 __catch (...)
1582 {
1583 using __index_type = decltype(this->_M_index);
1584 this->_M_index = static_cast<__index_type>(variant_npos);
1585 __throw_exception_again;
1586 }
1587 }
1588 return std::get<_Np>(*this);
1589 }
1590
1591 constexpr bool valueless_by_exception() const noexcept
1592 { return !this->_M_valid(); }
1593
1594 constexpr size_t index() const noexcept
1595 {
1596 using __index_type = typename _Base::__index_type;
1597 if constexpr (__detail::__variant::__never_valueless<_Types...>())
1598 return this->_M_index;
1599 else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1600 return make_signed_t<__index_type>(this->_M_index);
1601 else
1602 return size_t(__index_type(this->_M_index + 1)) - 1;
1603 }
1604
1605 void
1606 swap(variant& __rhs)
1607 noexcept((__is_nothrow_swappable<_Types>::value && ...)
1608 && is_nothrow_move_constructible_v<variant>)
1609 {
1610 __detail::__variant::__raw_idx_visit(
1611 [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1612 {
1613 if constexpr (__rhs_index != variant_npos)
1614 {
1615 if (this->index() == __rhs_index)
1616 {
1617 auto& __this_mem =
1618 std::get<__rhs_index>(*this);
1619 using std::swap;
1620 swap(__this_mem, __rhs_mem);
1621 }
1622 else
1623 {
1624 if (!this->valueless_by_exception()) [[__likely__]]
1625 {
1626 auto __tmp(std::move(__rhs_mem));
1627 __rhs = std::move(*this);
1628 this->_M_destructive_move(__rhs_index,
1629 std::move(__tmp));
1630 }
1631 else
1632 {
1633 this->_M_destructive_move(__rhs_index,
1634 std::move(__rhs_mem));
1635 __rhs._M_reset();
1636 }
1637 }
1638 }
1639 else
1640 {
1641 if (!this->valueless_by_exception()) [[__likely__]]
1642 {
1643 __rhs = std::move(*this);
1644 this->_M_reset();
1645 }
1646 }
1647 }, __rhs);
1648 }
1649
1650 private:
1651
1652#if defined(__clang__) && __clang_major__ <= 7
1653 public:
1654 using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1655 private:
1656#endif
1657
1658 template<size_t _Np, typename _Vp>
1659 friend constexpr decltype(auto)
1660 __detail::__variant::__get(_Vp&& __v) noexcept;
1661
1662 template<typename _Vp>
1663 friend void*
1664 __detail::__variant::__get_storage(_Vp&& __v) noexcept;
1665
1666#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1667 template<typename... _Tp> \
1668 friend constexpr bool \
1669 operator __OP(const variant<_Tp...>& __lhs, \
1670 const variant<_Tp...>& __rhs);
1671
1672 _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
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
1679#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1680 };
1681
1682 template<size_t _Np, typename... _Types>
1683 constexpr variant_alternative_t<_Np, variant<_Types...>>&
1684 get(variant<_Types...>& __v)
1685 {
1686 static_assert(_Np < sizeof...(_Types),
1687 "The index must be in [0, number of alternatives)");
1688 if (__v.index() != _Np)
1689 __throw_bad_variant_access(__v.valueless_by_exception());
1690 return __detail::__variant::__get<_Np>(__v);
1691 }
1692
1693 template<size_t _Np, typename... _Types>
1694 constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1695 get(variant<_Types...>&& __v)
1696 {
1697 static_assert(_Np < sizeof...(_Types),
1698 "The index must be in [0, number of alternatives)");
1699 if (__v.index() != _Np)
1700 __throw_bad_variant_access(__v.valueless_by_exception());
1701 return __detail::__variant::__get<_Np>(std::move(__v));
1702 }
1703
1704 template<size_t _Np, typename... _Types>
1705 constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1706 get(const variant<_Types...>& __v)
1707 {
1708 static_assert(_Np < sizeof...(_Types),
1709 "The index must be in [0, number of alternatives)");
1710 if (__v.index() != _Np)
1711 __throw_bad_variant_access(__v.valueless_by_exception());
1712 return __detail::__variant::__get<_Np>(__v);
1713 }
1714
1715 template<size_t _Np, typename... _Types>
1716 constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1717 get(const variant<_Types...>&& __v)
1718 {
1719 static_assert(_Np < sizeof...(_Types),
1720 "The index must be in [0, number of alternatives)");
1721 if (__v.index() != _Np)
1722 __throw_bad_variant_access(__v.valueless_by_exception());
1723 return __detail::__variant::__get<_Np>(std::move(__v));
1724 }
1725
1726 template<typename _Result_type, typename _Visitor, typename... _Variants>
1727 constexpr decltype(auto)
1728 __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1729 {
1730 constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1731 _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1732
1733 auto __func_ptr = __vtable._M_access(__variants.index()...);
1734 return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1735 std::forward<_Variants>(__variants)...);
1736 }
1737
1738 template<typename _Visitor, typename... _Variants>
1739 constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1740 visit(_Visitor&& __visitor, _Variants&&... __variants)
1741 {
1742 if ((__variants.valueless_by_exception() || ...))
1743 __throw_bad_variant_access("std::visit: variant is valueless");
1744
1745 using _Result_type
1746 = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1747
1748 using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1749
1750 if constexpr (sizeof...(_Variants) == 1)
1751 {
1752 constexpr bool __visit_rettypes_match = __detail::__variant::
1753 __check_visitor_results<_Visitor, _Variants...>(
1754 std::make_index_sequence<
1755 std::variant_size<remove_reference_t<_Variants>...>::value>());
1756 if constexpr (!__visit_rettypes_match)
1757 {
1758 static_assert(__visit_rettypes_match,
1759 "std::visit requires the visitor to have the same "
1760 "return type for all alternatives of a variant");
1761 return;
1762 }
1763 else
1764 return std::__do_visit<_Tag>(
1765 std::forward<_Visitor>(__visitor),
1766 std::forward<_Variants>(__variants)...);
1767 }
1768 else
1769 return std::__do_visit<_Tag>(
1770 std::forward<_Visitor>(__visitor),
1771 std::forward<_Variants>(__variants)...);
1772 }
1773
1774#if __cplusplus > 201703L
1775 template<typename _Res, typename _Visitor, typename... _Variants>
1776 constexpr _Res
1777 visit(_Visitor&& __visitor, _Variants&&... __variants)
1778 {
1779 if ((__variants.valueless_by_exception() || ...))
1780 __throw_bad_variant_access("std::visit<R>: variant is valueless");
1781
1782 return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1783 std::forward<_Variants>(__variants)...);
1784 }
1785#endif
1786
1787 template<bool, typename... _Types>
1788 struct __variant_hash_call_base_impl
1789 {
1790 size_t
1791 operator()(const variant<_Types...>& __t) const
1792 noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1793 {
1794 size_t __ret;
1795 __detail::__variant::__raw_visit(
1796 [&__t, &__ret](auto&& __t_mem) mutable
1797 {
1798 using _Type = __remove_cvref_t<decltype(__t_mem)>;
1799 if constexpr (!is_same_v<_Type,
1800 __detail::__variant::__variant_cookie>)
1801 __ret = std::hash<size_t>{}(__t.index())
1802 + std::hash<_Type>{}(__t_mem);
1803 else
1804 __ret = std::hash<size_t>{}(__t.index());
1805 }, __t);
1806 return __ret;
1807 }
1808 };
1809
1810 template<typename... _Types>
1811 struct __variant_hash_call_base_impl<false, _Types...> {};
1812
1813 template<typename... _Types>
1814 using __variant_hash_call_base =
1815 __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1816 __enable_hash_call &&...), _Types...>;
1817
1818 template<typename... _Types>
1819 struct hash<variant<_Types...>>
1820 : private __detail::__variant::_Variant_hash_base<
1821 variant<_Types...>, std::index_sequence_for<_Types...>>,
1822 public __variant_hash_call_base<_Types...>
1823 {
1824 using result_type [[__deprecated__]] = size_t;
1825 using argument_type [[__deprecated__]] = variant<_Types...>;
1826 };
1827
1828 template<>
1829 struct hash<monostate>
1830 {
1831 using result_type [[__deprecated__]] = size_t;
1832 using argument_type [[__deprecated__]] = monostate;
1833
1834 size_t
1835 operator()(const monostate&) const noexcept
1836 {
1837 constexpr size_t __magic_monostate_hash = -7777;
1838 return __magic_monostate_hash;
1839 }
1840 };
1841
1842 template<typename... _Types>
1843 struct __is_fast_hash<hash<variant<_Types...>>>
1844 : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1845 { };
1846
1847_GLIBCXX_END_NAMESPACE_VERSION
1848} // namespace std
1849
1850#endif // C++17
1851
1852#endif // _GLIBCXX_VARIANT
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