1// <variant> -*- C++ -*-
2
3// Copyright (C) 2016-2022 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file variant
26 * This is the `<variant>` C++ Library header.
27 */
28
29#ifndef _GLIBCXX_VARIANT
30#define _GLIBCXX_VARIANT 1
31
32#pragma GCC system_header
33
34#if __cplusplus >= 201703L
35
36#include <initializer_list>
37#include <type_traits>
38#include <bits/enable_special_members.h>
39#include <bits/exception_defines.h>
40#include <bits/functional_hash.h>
41#include <bits/invoke.h>
42#include <bits/parse_numbers.h>
43#include <bits/stl_iterator_base_types.h>
44#include <bits/stl_iterator_base_funcs.h>
45#include <bits/stl_construct.h>
46#include <bits/utility.h> // in_place_index_t
47#if __cplusplus >= 202002L
48# include <compare>
49#endif
50
51#if __cpp_concepts >= 202002L && __cpp_constexpr >= 201811L
52// P2231R1 constexpr needs constexpr unions and constrained destructors.
53# define __cpp_lib_variant 202106L
54#else
55# include <ext/aligned_buffer.h> // Use __aligned_membuf instead of union.
56# define __cpp_lib_variant 202102L
57#endif
58
59namespace std _GLIBCXX_VISIBILITY(default)
60{
61_GLIBCXX_BEGIN_NAMESPACE_VERSION
62
63 template<typename... _Types> class tuple;
64 template<typename... _Types> class variant;
65 template <typename> struct hash;
66
67 template<typename _Variant>
68 struct variant_size;
69
70 template<typename _Variant>
71 struct variant_size<const _Variant> : variant_size<_Variant> {};
72
73 template<typename _Variant>
74 struct variant_size<volatile _Variant> : variant_size<_Variant> {};
75
76 template<typename _Variant>
77 struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
78
79 template<typename... _Types>
80 struct variant_size<variant<_Types...>>
81 : std::integral_constant<size_t, sizeof...(_Types)> {};
82
83 template<typename _Variant>
84 inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
85
86 template<typename... _Types>
87 inline constexpr size_t
88 variant_size_v<variant<_Types...>> = sizeof...(_Types);
89
90 template<typename... _Types>
91 inline constexpr size_t
92 variant_size_v<const variant<_Types...>> = sizeof...(_Types);
93
94 template<size_t _Np, typename _Variant>
95 struct variant_alternative;
96
97 template<size_t _Np, typename... _Types>
98 struct variant_alternative<_Np, variant<_Types...>>
99 {
100 static_assert(_Np < sizeof...(_Types));
101
102 using type = typename _Nth_type<_Np, _Types...>::type;
103 };
104
105 template<size_t _Np, typename _Variant>
106 using variant_alternative_t =
107 typename variant_alternative<_Np, _Variant>::type;
108
109 template<size_t _Np, typename _Variant>
110 struct variant_alternative<_Np, const _Variant>
111 { using type = add_const_t<variant_alternative_t<_Np, _Variant>>; };
112
113 template<size_t _Np, typename _Variant>
114 struct variant_alternative<_Np, volatile _Variant>
115 { using type = add_volatile_t<variant_alternative_t<_Np, _Variant>>; };
116
117 template<size_t _Np, typename _Variant>
118 struct variant_alternative<_Np, const volatile _Variant>
119 { using type = add_cv_t<variant_alternative_t<_Np, _Variant>>; };
120
121 inline constexpr size_t variant_npos = -1;
122
123 template<size_t _Np, typename... _Types>
124 constexpr variant_alternative_t<_Np, variant<_Types...>>&
125 get(variant<_Types...>&);
126
127 template<size_t _Np, typename... _Types>
128 constexpr variant_alternative_t<_Np, variant<_Types...>>&&
129 get(variant<_Types...>&&);
130
131 template<size_t _Np, typename... _Types>
132 constexpr variant_alternative_t<_Np, variant<_Types...>> const&
133 get(const variant<_Types...>&);
134
135 template<size_t _Np, typename... _Types>
136 constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
137 get(const variant<_Types...>&&);
138
139 template<typename _Result_type, typename _Visitor, typename... _Variants>
140 constexpr decltype(auto)
141 __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
142
143 template <typename... _Types, typename _Tp>
144 _GLIBCXX20_CONSTEXPR
145 decltype(auto)
146 __variant_cast(_Tp&& __rhs)
147 {
148 if constexpr (is_lvalue_reference_v<_Tp>)
149 {
150 if constexpr (is_const_v<remove_reference_t<_Tp>>)
151 return static_cast<const variant<_Types...>&>(__rhs);
152 else
153 return static_cast<variant<_Types...>&>(__rhs);
154 }
155 else
156 return static_cast<variant<_Types...>&&>(__rhs);
157 }
158
159namespace __detail
160{
161namespace __variant
162{
163 // used for raw visitation
164 struct __variant_cookie {};
165 // used for raw visitation with indices passed in
166 struct __variant_idx_cookie { using type = __variant_idx_cookie; };
167 // Used to enable deduction (and same-type checking) for std::visit:
168 template<typename _Tp> struct __deduce_visit_result { using type = _Tp; };
169
170 // Visit variants that might be valueless.
171 template<typename _Visitor, typename... _Variants>
172 constexpr void
173 __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
174 {
175 std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
176 std::forward<_Variants>(__variants)...);
177 }
178
179 // Visit variants that might be valueless, passing indices to the visitor.
180 template<typename _Visitor, typename... _Variants>
181 constexpr void
182 __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
183 {
184 std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
185 std::forward<_Variants>(__variants)...);
186 }
187
188 // The __as function templates implement the exposition-only "as-variant"
189
190 template<typename... _Types>
191 constexpr std::variant<_Types...>&
192 __as(std::variant<_Types...>& __v) noexcept
193 { return __v; }
194
195 template<typename... _Types>
196 constexpr const std::variant<_Types...>&
197 __as(const std::variant<_Types...>& __v) noexcept
198 { return __v; }
199
200 template<typename... _Types>
201 constexpr std::variant<_Types...>&&
202 __as(std::variant<_Types...>&& __v) noexcept
203 { return std::move(__v); }
204
205 template<typename... _Types>
206 constexpr const std::variant<_Types...>&&
207 __as(const std::variant<_Types...>&& __v) noexcept
208 { return std::move(__v); }
209
210 // For C++17:
211 // _Uninitialized<T> is guaranteed to be a trivially destructible type,
212 // even if T is not.
213 // For C++20:
214 // _Uninitialized<T> is trivially destructible iff T is, so _Variant_union
215 // needs a constrained non-trivial destructor.
216 template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
217 struct _Uninitialized;
218
219 template<typename _Type>
220 struct _Uninitialized<_Type, true>
221 {
222 template<typename... _Args>
223 constexpr
224 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
225 : _M_storage(std::forward<_Args>(__args)...)
226 { }
227
228 constexpr const _Type& _M_get() const & noexcept
229 { return _M_storage; }
230
231 constexpr _Type& _M_get() & noexcept
232 { return _M_storage; }
233
234 constexpr const _Type&& _M_get() const && noexcept
235 { return std::move(_M_storage); }
236
237 constexpr _Type&& _M_get() && noexcept
238 { return std::move(_M_storage); }
239
240 _Type _M_storage;
241 };
242
243 template<typename _Type>
244 struct _Uninitialized<_Type, false>
245 {
246#if __cpp_lib_variant >= 202106L
247 template<typename... _Args>
248 constexpr
249 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
250 : _M_storage(std::forward<_Args>(__args)...)
251 { }
252
253 constexpr ~_Uninitialized() { }
254
255 _Uninitialized(const _Uninitialized&) = default;
256 _Uninitialized(_Uninitialized&&) = default;
257 _Uninitialized& operator=(const _Uninitialized&) = default;
258 _Uninitialized& operator=(_Uninitialized&&) = default;
259
260 constexpr const _Type& _M_get() const & noexcept
261 { return _M_storage; }
262
263 constexpr _Type& _M_get() & noexcept
264 { return _M_storage; }
265
266 constexpr const _Type&& _M_get() const && noexcept
267 { return std::move(_M_storage); }
268
269 constexpr _Type&& _M_get() && noexcept
270 { return std::move(_M_storage); }
271
272 struct _Empty_byte { };
273
274 union {
275 _Empty_byte _M_empty;
276 _Type _M_storage;
277 };
278#else
279 template<typename... _Args>
280 constexpr
281 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
282 {
283 ::new ((void*)std::addressof(_M_storage))
284 _Type(std::forward<_Args>(__args)...);
285 }
286
287 const _Type& _M_get() const & noexcept
288 { return *_M_storage._M_ptr(); }
289
290 _Type& _M_get() & noexcept
291 { return *_M_storage._M_ptr(); }
292
293 const _Type&& _M_get() const && noexcept
294 { return std::move(*_M_storage._M_ptr()); }
295
296 _Type&& _M_get() && noexcept
297 { return std::move(*_M_storage._M_ptr()); }
298
299 __gnu_cxx::__aligned_membuf<_Type> _M_storage;
300#endif
301 };
302
303 template<size_t _Np, typename _Union>
304 constexpr decltype(auto)
305 __get_n(_Union&& __u) noexcept
306 {
307 if constexpr (_Np == 0)
308 return std::forward<_Union>(__u)._M_first._M_get();
309 else if constexpr (_Np == 1)
310 return std::forward<_Union>(__u)._M_rest._M_first._M_get();
311 else if constexpr (_Np == 2)
312 return std::forward<_Union>(__u)._M_rest._M_rest._M_first._M_get();
313 else
314 return __variant::__get_n<_Np - 3>(
315 std::forward<_Union>(__u)._M_rest._M_rest._M_rest);
316 }
317
318 // Returns the typed storage for __v.
319 template<size_t _Np, typename _Variant>
320 constexpr decltype(auto)
321 __get(_Variant&& __v) noexcept
322 { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); }
323
324 template<typename... _Types>
325 struct _Traits
326 {
327 static constexpr bool _S_default_ctor =
328 is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
329 static constexpr bool _S_copy_ctor =
330 (is_copy_constructible_v<_Types> && ...);
331 static constexpr bool _S_move_ctor =
332 (is_move_constructible_v<_Types> && ...);
333 static constexpr bool _S_copy_assign =
334 _S_copy_ctor
335 && (is_copy_assignable_v<_Types> && ...);
336 static constexpr bool _S_move_assign =
337 _S_move_ctor
338 && (is_move_assignable_v<_Types> && ...);
339
340 static constexpr bool _S_trivial_dtor =
341 (is_trivially_destructible_v<_Types> && ...);
342 static constexpr bool _S_trivial_copy_ctor =
343 (is_trivially_copy_constructible_v<_Types> && ...);
344 static constexpr bool _S_trivial_move_ctor =
345 (is_trivially_move_constructible_v<_Types> && ...);
346 static constexpr bool _S_trivial_copy_assign =
347 _S_trivial_dtor && _S_trivial_copy_ctor
348 && (is_trivially_copy_assignable_v<_Types> && ...);
349 static constexpr bool _S_trivial_move_assign =
350 _S_trivial_dtor && _S_trivial_move_ctor
351 && (is_trivially_move_assignable_v<_Types> && ...);
352
353 // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
354 // are always nothrow.
355 static constexpr bool _S_nothrow_default_ctor =
356 is_nothrow_default_constructible_v<
357 typename _Nth_type<0, _Types...>::type>;
358 static constexpr bool _S_nothrow_copy_ctor = false;
359 static constexpr bool _S_nothrow_move_ctor =
360 (is_nothrow_move_constructible_v<_Types> && ...);
361 static constexpr bool _S_nothrow_copy_assign = false;
362 static constexpr bool _S_nothrow_move_assign =
363 _S_nothrow_move_ctor
364 && (is_nothrow_move_assignable_v<_Types> && ...);
365 };
366
367 // Defines members and ctors.
368 template<typename... _Types>
369 union _Variadic_union
370 {
371 _Variadic_union() = default;
372
373 template<size_t _Np, typename... _Args>
374 _Variadic_union(in_place_index_t<_Np>, _Args&&...) = delete;
375 };
376
377 template<typename _First, typename... _Rest>
378 union _Variadic_union<_First, _Rest...>
379 {
380 constexpr _Variadic_union() : _M_rest() { }
381
382 template<typename... _Args>
383 constexpr
384 _Variadic_union(in_place_index_t<0>, _Args&&... __args)
385 : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
386 { }
387
388 template<size_t _Np, typename... _Args>
389 constexpr
390 _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
391 : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
392 { }
393
394#if __cpp_lib_variant >= 202106L
395 _Variadic_union(const _Variadic_union&) = default;
396 _Variadic_union(_Variadic_union&&) = default;
397 _Variadic_union& operator=(const _Variadic_union&) = default;
398 _Variadic_union& operator=(_Variadic_union&&) = default;
399
400 ~_Variadic_union() = default;
401
402 constexpr ~_Variadic_union()
403 requires (!__has_trivial_destructor(_First))
404 || (!__has_trivial_destructor(_Variadic_union<_Rest...>))
405 { }
406#endif
407
408 _Uninitialized<_First> _M_first;
409 _Variadic_union<_Rest...> _M_rest;
410 };
411
412 // _Never_valueless_alt is true for variant alternatives that can
413 // always be placed in a variant without it becoming valueless.
414
415 // For suitably-small, trivially copyable types we can create temporaries
416 // on the stack and then memcpy them into place.
417 template<typename _Tp>
418 struct _Never_valueless_alt
419 : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
420 { };
421
422 // Specialize _Never_valueless_alt for other types which have a
423 // non-throwing and cheap move construction and move assignment operator,
424 // so that emplacing the type will provide the strong exception-safety
425 // guarantee, by creating and moving a temporary.
426 // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
427 // variant using that alternative, so we can't change the value later!
428
429 // True if every alternative in _Types... can be emplaced in a variant
430 // without it becoming valueless. If this is true, variant<_Types...>
431 // can never be valueless, which enables some minor optimizations.
432 template <typename... _Types>
433 constexpr bool __never_valueless()
434 {
435 return _Traits<_Types...>::_S_move_assign
436 && (_Never_valueless_alt<_Types>::value && ...);
437 }
438
439 // Defines index and the dtor, possibly trivial.
440 template<bool __trivially_destructible, typename... _Types>
441 struct _Variant_storage;
442
443 template <typename... _Types>
444 using __select_index =
445 typename __select_int::_Select_int_base<sizeof...(_Types),
446 unsigned char,
447 unsigned short>::type::value_type;
448
449 template<typename... _Types>
450 struct _Variant_storage<false, _Types...>
451 {
452 constexpr
453 _Variant_storage()
454 : _M_index(static_cast<__index_type>(variant_npos))
455 { }
456
457 template<size_t _Np, typename... _Args>
458 constexpr
459 _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
460 : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
461 _M_index{_Np}
462 { }
463
464 constexpr void
465 _M_reset()
466 {
467 if (!_M_valid()) [[unlikely]]
468 return;
469
470 std::__do_visit<void>([](auto&& __this_mem) mutable
471 {
472 std::_Destroy(std::__addressof(__this_mem));
473 }, __variant_cast<_Types...>(*this));
474
475 _M_index = static_cast<__index_type>(variant_npos);
476 }
477
478 _GLIBCXX20_CONSTEXPR
479 ~_Variant_storage()
480 { _M_reset(); }
481
482 constexpr bool
483 _M_valid() const noexcept
484 {
485 if constexpr (__variant::__never_valueless<_Types...>())
486 return true;
487 return this->_M_index != __index_type(variant_npos);
488 }
489
490 _Variadic_union<_Types...> _M_u;
491 using __index_type = __select_index<_Types...>;
492 __index_type _M_index;
493 };
494
495 template<typename... _Types>
496 struct _Variant_storage<true, _Types...>
497 {
498 constexpr
499 _Variant_storage()
500 : _M_index(static_cast<__index_type>(variant_npos))
501 { }
502
503 template<size_t _Np, typename... _Args>
504 constexpr
505 _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
506 : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
507 _M_index{_Np}
508 { }
509
510 constexpr void
511 _M_reset() noexcept
512 { _M_index = static_cast<__index_type>(variant_npos); }
513
514 constexpr bool
515 _M_valid() const noexcept
516 {
517 if constexpr (__variant::__never_valueless<_Types...>())
518 return true;
519 // It would be nice if we could just return true for -fno-exceptions.
520 // It's possible (but inadvisable) that a std::variant could become
521 // valueless in a translation unit compiled with -fexceptions and then
522 // be passed to functions compiled with -fno-exceptions. We would need
523 // some #ifdef _GLIBCXX_NO_EXCEPTIONS_GLOBALLY property to elide all
524 // checks for valueless_by_exception().
525 return this->_M_index != static_cast<__index_type>(variant_npos);
526 }
527
528 _Variadic_union<_Types...> _M_u;
529 using __index_type = __select_index<_Types...>;
530 __index_type _M_index;
531 };
532
533 // Implementation of v.emplace<N>(args...).
534 template<size_t _Np, bool _Triv, typename... _Types, typename... _Args>
535 _GLIBCXX20_CONSTEXPR
536 inline void
537 __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args)
538 {
539 __v._M_reset();
540 auto* __addr = std::__addressof(__variant::__get_n<_Np>(__v._M_u));
541 std::_Construct(__addr, std::forward<_Args>(__args)...);
542 // Construction didn't throw, so can set the new index now:
543 __v._M_index = _Np;
544 }
545
546 template<typename... _Types>
547 using _Variant_storage_alias =
548 _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
549
550 // The following are (Copy|Move) (ctor|assign) layers for forwarding
551 // triviality and handling non-trivial SMF behaviors.
552
553 template<bool, typename... _Types>
554 struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
555 {
556 using _Base = _Variant_storage_alias<_Types...>;
557 using _Base::_Base;
558
559 _GLIBCXX20_CONSTEXPR
560 _Copy_ctor_base(const _Copy_ctor_base& __rhs)
561 noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
562 {
563 __variant::__raw_idx_visit(
564 [this](auto&& __rhs_mem, auto __rhs_index) mutable
565 {
566 constexpr size_t __j = __rhs_index;
567 if constexpr (__j != variant_npos)
568 std::_Construct(std::__addressof(this->_M_u),
569 in_place_index<__j>, __rhs_mem);
570 }, __variant_cast<_Types...>(__rhs));
571 this->_M_index = __rhs._M_index;
572 }
573
574 _Copy_ctor_base(_Copy_ctor_base&&) = default;
575 _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
576 _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
577 };
578
579 template<typename... _Types>
580 struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
581 {
582 using _Base = _Variant_storage_alias<_Types...>;
583 using _Base::_Base;
584 };
585
586 template<typename... _Types>
587 using _Copy_ctor_alias =
588 _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
589
590 template<bool, typename... _Types>
591 struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
592 {
593 using _Base = _Copy_ctor_alias<_Types...>;
594 using _Base::_Base;
595
596 _GLIBCXX20_CONSTEXPR
597 _Move_ctor_base(_Move_ctor_base&& __rhs)
598 noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
599 {
600 __variant::__raw_idx_visit(
601 [this](auto&& __rhs_mem, auto __rhs_index) mutable
602 {
603 constexpr size_t __j = __rhs_index;
604 if constexpr (__j != variant_npos)
605 std::_Construct(std::__addressof(this->_M_u),
606 in_place_index<__j>,
607 std::forward<decltype(__rhs_mem)>(__rhs_mem));
608 }, __variant_cast<_Types...>(std::move(__rhs)));
609 this->_M_index = __rhs._M_index;
610 }
611
612 _Move_ctor_base(const _Move_ctor_base&) = default;
613 _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
614 _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
615 };
616
617 template<typename... _Types>
618 struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
619 {
620 using _Base = _Copy_ctor_alias<_Types...>;
621 using _Base::_Base;
622 };
623
624 template<typename... _Types>
625 using _Move_ctor_alias =
626 _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
627
628 template<bool, typename... _Types>
629 struct _Copy_assign_base : _Move_ctor_alias<_Types...>
630 {
631 using _Base = _Move_ctor_alias<_Types...>;
632 using _Base::_Base;
633
634 _GLIBCXX20_CONSTEXPR
635 _Copy_assign_base&
636 operator=(const _Copy_assign_base& __rhs)
637 noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
638 {
639 __variant::__raw_idx_visit(
640 [this](auto&& __rhs_mem, auto __rhs_index) mutable
641 {
642 constexpr size_t __j = __rhs_index;
643 if constexpr (__j == variant_npos)
644 this->_M_reset(); // Make *this valueless.
645 else if (this->_M_index == __j)
646 __variant::__get<__j>(*this) = __rhs_mem;
647 else
648 {
649 using _Tj = typename _Nth_type<__j, _Types...>::type;
650 if constexpr (is_nothrow_copy_constructible_v<_Tj>
651 || !is_nothrow_move_constructible_v<_Tj>)
652 __variant::__emplace<__j>(*this, __rhs_mem);
653 else
654 {
655 using _Variant = variant<_Types...>;
656 _Variant& __self = __variant_cast<_Types...>(*this);
657 __self = _Variant(in_place_index<__j>, __rhs_mem);
658 }
659 }
660 }, __variant_cast<_Types...>(__rhs));
661 return *this;
662 }
663
664 _Copy_assign_base(const _Copy_assign_base&) = default;
665 _Copy_assign_base(_Copy_assign_base&&) = default;
666 _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
667 };
668
669 template<typename... _Types>
670 struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
671 {
672 using _Base = _Move_ctor_alias<_Types...>;
673 using _Base::_Base;
674 };
675
676 template<typename... _Types>
677 using _Copy_assign_alias =
678 _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
679
680 template<bool, typename... _Types>
681 struct _Move_assign_base : _Copy_assign_alias<_Types...>
682 {
683 using _Base = _Copy_assign_alias<_Types...>;
684 using _Base::_Base;
685
686 _GLIBCXX20_CONSTEXPR
687 _Move_assign_base&
688 operator=(_Move_assign_base&& __rhs)
689 noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
690 {
691 __variant::__raw_idx_visit(
692 [this](auto&& __rhs_mem, auto __rhs_index) mutable
693 {
694 constexpr size_t __j = __rhs_index;
695 if constexpr (__j != variant_npos)
696 {
697 if (this->_M_index == __j)
698 __variant::__get<__j>(*this) = std::move(__rhs_mem);
699 else
700 {
701 using _Tj = typename _Nth_type<__j, _Types...>::type;
702 if constexpr (is_nothrow_move_constructible_v<_Tj>)
703 __variant::__emplace<__j>(*this, std::move(__rhs_mem));
704 else
705 {
706 using _Variant = variant<_Types...>;
707 _Variant& __self = __variant_cast<_Types...>(*this);
708 __self.template emplace<__j>(std::move(__rhs_mem));
709 }
710 }
711 }
712 else
713 this->_M_reset();
714 }, __variant_cast<_Types...>(__rhs));
715 return *this;
716 }
717
718 _Move_assign_base(const _Move_assign_base&) = default;
719 _Move_assign_base(_Move_assign_base&&) = default;
720 _Move_assign_base& operator=(const _Move_assign_base&) = default;
721 };
722
723 template<typename... _Types>
724 struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
725 {
726 using _Base = _Copy_assign_alias<_Types...>;
727 using _Base::_Base;
728 };
729
730 template<typename... _Types>
731 using _Move_assign_alias =
732 _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
733
734 template<typename... _Types>
735 struct _Variant_base : _Move_assign_alias<_Types...>
736 {
737 using _Base = _Move_assign_alias<_Types...>;
738
739 constexpr
740 _Variant_base() noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
741 : _Variant_base(in_place_index<0>) { }
742
743 template<size_t _Np, typename... _Args>
744 constexpr explicit
745 _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
746 : _Base(__i, std::forward<_Args>(__args)...)
747 { }
748
749 _Variant_base(const _Variant_base&) = default;
750 _Variant_base(_Variant_base&&) = default;
751 _Variant_base& operator=(const _Variant_base&) = default;
752 _Variant_base& operator=(_Variant_base&&) = default;
753 };
754
755 template<typename _Tp, typename... _Types>
756 inline constexpr bool __exactly_once
757 = std::__find_uniq_type_in_pack<_Tp, _Types...>() < sizeof...(_Types);
758
759 // Helper used to check for valid conversions that don't involve narrowing.
760 template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
761
762 // "Build an imaginary function FUN(Ti) for each alternative type Ti"
763 template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
764 struct _Build_FUN
765 {
766 // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
767 // but only static functions will be considered in the call below.
768 void _S_fun();
769 };
770
771 // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
772 template<size_t _Ind, typename _Tp, typename _Ti>
773 struct _Build_FUN<_Ind, _Tp, _Ti,
774 void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
775 {
776 // This is the FUN function for type _Ti, with index _Ind
777 static integral_constant<size_t, _Ind> _S_fun(_Ti);
778 };
779
780 template<typename _Tp, typename _Variant,
781 typename = make_index_sequence<variant_size_v<_Variant>>>
782 struct _Build_FUNs;
783
784 template<typename _Tp, typename... _Ti, size_t... _Ind>
785 struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
786 : _Build_FUN<_Ind, _Tp, _Ti>...
787 {
788 using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
789 };
790
791 // The index j of the overload FUN(Tj) selected by overload resolution
792 // for FUN(std::forward<_Tp>(t))
793 template<typename _Tp, typename _Variant>
794 using _FUN_type
795 = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
796
797 // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
798 template<typename _Tp, typename _Variant, typename = void>
799 struct __accepted_index
800 : integral_constant<size_t, variant_npos>
801 { };
802
803 template<typename _Tp, typename _Variant>
804 struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
805 : _FUN_type<_Tp, _Variant>
806 { };
807
808 template <typename _Maybe_variant_cookie, typename _Variant>
809 struct _Extra_visit_slot_needed
810 {
811 template <typename> struct _Variant_never_valueless;
812
813 template <typename... _Types>
814 struct _Variant_never_valueless<variant<_Types...>>
815 : bool_constant<__variant::__never_valueless<_Types...>()> {};
816
817 static constexpr bool value =
818 (is_same_v<_Maybe_variant_cookie, __variant_cookie>
819 || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
820 && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
821 };
822
823 // Used for storing a multi-dimensional vtable.
824 template<typename _Tp, size_t... _Dimensions>
825 struct _Multi_array;
826
827 // Partial specialization with rank zero, stores a single _Tp element.
828 template<typename _Tp>
829 struct _Multi_array<_Tp>
830 {
831 template<typename>
832 struct __untag_result
833 : false_type
834 { using element_type = _Tp; };
835
836 template <typename... _Args>
837 struct __untag_result<const void(*)(_Args...)>
838 : false_type
839 { using element_type = void(*)(_Args...); };
840
841 template <typename... _Args>
842 struct __untag_result<__variant_cookie(*)(_Args...)>
843 : false_type
844 { using element_type = void(*)(_Args...); };
845
846 template <typename... _Args>
847 struct __untag_result<__variant_idx_cookie(*)(_Args...)>
848 : false_type
849 { using element_type = void(*)(_Args...); };
850
851 template <typename _Res, typename... _Args>
852 struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
853 : true_type
854 { using element_type = _Res(*)(_Args...); };
855
856 using __result_is_deduced = __untag_result<_Tp>;
857
858 constexpr const typename __untag_result<_Tp>::element_type&
859 _M_access() const
860 { return _M_data; }
861
862 typename __untag_result<_Tp>::element_type _M_data;
863 };
864
865 // Partial specialization with rank >= 1.
866 template<typename _Ret,
867 typename _Visitor,
868 typename... _Variants,
869 size_t __first, size_t... __rest>
870 struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
871 {
872 static constexpr size_t __index =
873 sizeof...(_Variants) - sizeof...(__rest) - 1;
874
875 using _Variant = typename _Nth_type<__index, _Variants...>::type;
876
877 static constexpr int __do_cookie =
878 _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
879
880 using _Tp = _Ret(*)(_Visitor, _Variants...);
881
882 template<typename... _Args>
883 constexpr decltype(auto)
884 _M_access(size_t __first_index, _Args... __rest_indices) const
885 {
886 return _M_arr[__first_index + __do_cookie]
887 ._M_access(__rest_indices...);
888 }
889
890 _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
891 };
892
893 // Creates a multi-dimensional vtable recursively.
894 //
895 // For example,
896 // visit([](auto, auto){},
897 // variant<int, char>(), // typedef'ed as V1
898 // variant<float, double, long double>()) // typedef'ed as V2
899 // will trigger instantiations of:
900 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
901 // tuple<V1&&, V2&&>, std::index_sequence<>>
902 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
903 // tuple<V1&&, V2&&>, std::index_sequence<0>>
904 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
905 // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
906 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
907 // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
908 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
909 // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
910 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
911 // tuple<V1&&, V2&&>, std::index_sequence<1>>
912 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
913 // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
914 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
915 // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
916 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
917 // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
918 // The returned multi-dimensional vtable can be fast accessed by the visitor
919 // using index calculation.
920 template<typename _Array_type, typename _Index_seq>
921 struct __gen_vtable_impl;
922
923 // Defines the _S_apply() member that returns a _Multi_array populated
924 // with function pointers that perform the visitation expressions e(m)
925 // for each valid pack of indexes into the variant types _Variants.
926 //
927 // This partial specialization builds up the index sequences by recursively
928 // calling _S_apply() on the next specialization of __gen_vtable_impl.
929 // The base case of the recursion defines the actual function pointers.
930 template<typename _Result_type, typename _Visitor, size_t... __dimensions,
931 typename... _Variants, size_t... __indices>
932 struct __gen_vtable_impl<
933 _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
934 std::index_sequence<__indices...>>
935 {
936 using _Next =
937 remove_reference_t<typename _Nth_type<sizeof...(__indices),
938 _Variants...>::type>;
939 using _Array_type =
940 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
941 __dimensions...>;
942
943 static constexpr _Array_type
944 _S_apply()
945 {
946 _Array_type __vtable{};
947 _S_apply_all_alts(
948 __vtable, make_index_sequence<variant_size_v<_Next>>());
949 return __vtable;
950 }
951
952 template<size_t... __var_indices>
953 static constexpr void
954 _S_apply_all_alts(_Array_type& __vtable,
955 std::index_sequence<__var_indices...>)
956 {
957 if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
958 (_S_apply_single_alt<true, __var_indices>(
959 __vtable._M_arr[__var_indices + 1],
960 &(__vtable._M_arr[0])), ...);
961 else
962 (_S_apply_single_alt<false, __var_indices>(
963 __vtable._M_arr[__var_indices]), ...);
964 }
965
966 template<bool __do_cookie, size_t __index, typename _Tp>
967 static constexpr void
968 _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
969 {
970 if constexpr (__do_cookie)
971 {
972 __element = __gen_vtable_impl<
973 _Tp,
974 std::index_sequence<__indices..., __index>>::_S_apply();
975 *__cookie_element = __gen_vtable_impl<
976 _Tp,
977 std::index_sequence<__indices..., variant_npos>>::_S_apply();
978 }
979 else
980 {
981 auto __tmp_element = __gen_vtable_impl<
982 remove_reference_t<decltype(__element)>,
983 std::index_sequence<__indices..., __index>>::_S_apply();
984 static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
985 "std::visit requires the visitor to have the same "
986 "return type for all alternatives of a variant");
987 __element = __tmp_element;
988 }
989 }
990 };
991
992 // This partial specialization is the base case for the recursion.
993 // It populates a _Multi_array element with the address of a function
994 // that invokes the visitor with the alternatives specified by __indices.
995 template<typename _Result_type, typename _Visitor, typename... _Variants,
996 size_t... __indices>
997 struct __gen_vtable_impl<
998 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
999 std::index_sequence<__indices...>>
1000 {
1001 using _Array_type =
1002 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
1003
1004 template<size_t __index, typename _Variant>
1005 static constexpr decltype(auto)
1006 __element_by_index_or_cookie(_Variant&& __var) noexcept
1007 {
1008 if constexpr (__index != variant_npos)
1009 return __variant::__get<__index>(std::forward<_Variant>(__var));
1010 else
1011 return __variant_cookie{};
1012 }
1013
1014 static constexpr decltype(auto)
1015 __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1016 {
1017 if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1018 // For raw visitation using indices, pass the indices to the visitor
1019 // and discard the return value:
1020 std::__invoke(std::forward<_Visitor>(__visitor),
1021 __element_by_index_or_cookie<__indices>(
1022 std::forward<_Variants>(__vars))...,
1023 integral_constant<size_t, __indices>()...);
1024 else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1025 // For raw visitation without indices, and discard the return value:
1026 std::__invoke(std::forward<_Visitor>(__visitor),
1027 __element_by_index_or_cookie<__indices>(
1028 std::forward<_Variants>(__vars))...);
1029 else if constexpr (_Array_type::__result_is_deduced::value)
1030 // For the usual std::visit case deduce the return value:
1031 return std::__invoke(std::forward<_Visitor>(__visitor),
1032 __element_by_index_or_cookie<__indices>(
1033 std::forward<_Variants>(__vars))...);
1034 else // for std::visit<R> use INVOKE<R>
1035 return std::__invoke_r<_Result_type>(
1036 std::forward<_Visitor>(__visitor),
1037 __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1038 }
1039
1040 static constexpr auto
1041 _S_apply()
1042 {
1043 if constexpr (_Array_type::__result_is_deduced::value)
1044 {
1045 constexpr bool __visit_ret_type_mismatch =
1046 !is_same_v<typename _Result_type::type,
1047 decltype(__visit_invoke(visitor: std::declval<_Visitor>(),
1048 vars: std::declval<_Variants>()...))>;
1049 if constexpr (__visit_ret_type_mismatch)
1050 {
1051 struct __cannot_match {};
1052 return __cannot_match{};
1053 }
1054 else
1055 return _Array_type{&__visit_invoke};
1056 }
1057 else
1058 return _Array_type{&__visit_invoke};
1059 }
1060 };
1061
1062 template<typename _Result_type, typename _Visitor, typename... _Variants>
1063 struct __gen_vtable
1064 {
1065 using _Array_type =
1066 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1067 variant_size_v<remove_reference_t<_Variants>>...>;
1068
1069 static constexpr _Array_type _S_vtable
1070 = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1071 };
1072
1073 template<size_t _Np, typename _Tp>
1074 struct _Base_dedup : public _Tp { };
1075
1076 template<typename _Variant, typename __indices>
1077 struct _Variant_hash_base;
1078
1079 template<typename... _Types, size_t... __indices>
1080 struct _Variant_hash_base<variant<_Types...>,
1081 std::index_sequence<__indices...>>
1082 : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1083
1084 // Equivalent to decltype(get<_Np>(as-variant(declval<_Variant>())))
1085 template<size_t _Np, typename _Variant,
1086 typename _AsV = decltype(__variant::__as(std::declval<_Variant>())),
1087 typename _Tp = variant_alternative_t<_Np, remove_reference_t<_AsV>>>
1088 using __get_t
1089 = __conditional_t<is_lvalue_reference_v<_Variant>, _Tp&, _Tp&&>;
1090
1091 // Return type of std::visit.
1092 template<typename _Visitor, typename... _Variants>
1093 using __visit_result_t
1094 = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1095
1096 template<typename _Tp, typename... _Types>
1097 constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
1098
1099 template <typename _Visitor, typename _Variant, size_t... _Idxs>
1100 constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
1101 {
1102 return __same_types<
1103 invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
1104 >;
1105 }
1106
1107} // namespace __variant
1108} // namespace __detail
1109
1110 template<typename _Tp, typename... _Types>
1111 constexpr bool
1112 holds_alternative(const variant<_Types...>& __v) noexcept
1113 {
1114 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1115 "T must occur exactly once in alternatives");
1116 return __v.index() == std::__find_uniq_type_in_pack<_Tp, _Types...>();
1117 }
1118
1119 template<typename _Tp, typename... _Types>
1120 constexpr _Tp&
1121 get(variant<_Types...>& __v)
1122 {
1123 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1124 "T must occur exactly once in alternatives");
1125 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1126 constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1127 return std::get<__n>(__v);
1128 }
1129
1130 template<typename _Tp, typename... _Types>
1131 constexpr _Tp&&
1132 get(variant<_Types...>&& __v)
1133 {
1134 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1135 "T must occur exactly once in alternatives");
1136 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1137 constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1138 return std::get<__n>(std::move(__v));
1139 }
1140
1141 template<typename _Tp, typename... _Types>
1142 constexpr const _Tp&
1143 get(const variant<_Types...>& __v)
1144 {
1145 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1146 "T must occur exactly once in alternatives");
1147 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1148 constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1149 return std::get<__n>(__v);
1150 }
1151
1152 template<typename _Tp, typename... _Types>
1153 constexpr const _Tp&&
1154 get(const variant<_Types...>&& __v)
1155 {
1156 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1157 "T must occur exactly once in alternatives");
1158 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1159 constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1160 return std::get<__n>(std::move(__v));
1161 }
1162
1163 template<size_t _Np, typename... _Types>
1164 constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1165 get_if(variant<_Types...>* __ptr) noexcept
1166 {
1167 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1168 static_assert(_Np < sizeof...(_Types),
1169 "The index must be in [0, number of alternatives)");
1170 static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1171 if (__ptr && __ptr->index() == _Np)
1172 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1173 return nullptr;
1174 }
1175
1176 template<size_t _Np, typename... _Types>
1177 constexpr
1178 add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1179 get_if(const variant<_Types...>* __ptr) noexcept
1180 {
1181 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1182 static_assert(_Np < sizeof...(_Types),
1183 "The index must be in [0, number of alternatives)");
1184 static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1185 if (__ptr && __ptr->index() == _Np)
1186 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1187 return nullptr;
1188 }
1189
1190 template<typename _Tp, typename... _Types>
1191 constexpr add_pointer_t<_Tp>
1192 get_if(variant<_Types...>* __ptr) noexcept
1193 {
1194 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1195 "T must occur exactly once in alternatives");
1196 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1197 constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1198 return std::get_if<__n>(__ptr);
1199 }
1200
1201 template<typename _Tp, typename... _Types>
1202 constexpr add_pointer_t<const _Tp>
1203 get_if(const variant<_Types...>* __ptr) noexcept
1204 {
1205 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1206 "T must occur exactly once in alternatives");
1207 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1208 constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1209 return std::get_if<__n>(__ptr);
1210 }
1211
1212 struct monostate { };
1213
1214#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1215 template<typename... _Types> \
1216 constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1217 const variant<_Types...>& __rhs) \
1218 { \
1219 bool __ret = true; \
1220 __detail::__variant::__raw_idx_visit( \
1221 [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1222 { \
1223 if constexpr (__rhs_index != variant_npos) \
1224 { \
1225 if (__lhs.index() == __rhs_index) \
1226 { \
1227 auto& __this_mem = std::get<__rhs_index>(__lhs); \
1228 __ret = __this_mem __OP __rhs_mem; \
1229 } \
1230 else \
1231 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1232 } \
1233 else \
1234 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1235 }, __rhs); \
1236 return __ret; \
1237 }
1238
1239 _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1240 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1241 _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1242 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1243 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1244 _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1245
1246#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1247
1248 constexpr bool operator==(monostate, monostate) noexcept { return true; }
1249
1250#ifdef __cpp_lib_three_way_comparison
1251 template<typename... _Types>
1252 requires (three_way_comparable<_Types> && ...)
1253 constexpr
1254 common_comparison_category_t<compare_three_way_result_t<_Types>...>
1255 operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1256 {
1257 common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1258 = strong_ordering::equal;
1259
1260 __detail::__variant::__raw_idx_visit(
1261 [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1262 {
1263 if constexpr (__w_index != variant_npos)
1264 {
1265 if (__v.index() == __w_index)
1266 {
1267 auto& __this_mem = std::get<__w_index>(__v);
1268 __ret = __this_mem <=> __w_mem;
1269 return;
1270 }
1271 }
1272 __ret = (__v.index() + 1) <=> (__w_index + 1);
1273 }, __w);
1274 return __ret;
1275 }
1276
1277 constexpr strong_ordering
1278 operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1279#else
1280 constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1281 constexpr bool operator<(monostate, monostate) noexcept { return false; }
1282 constexpr bool operator>(monostate, monostate) noexcept { return false; }
1283 constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1284 constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1285#endif
1286
1287 template<typename _Visitor, typename... _Variants>
1288 constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1289 visit(_Visitor&&, _Variants&&...);
1290
1291 template<typename... _Types>
1292 _GLIBCXX20_CONSTEXPR
1293 inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1294 && (is_swappable_v<_Types> && ...)>
1295 swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1296 noexcept(noexcept(__lhs.swap(__rhs)))
1297 { __lhs.swap(__rhs); }
1298
1299 template<typename... _Types>
1300 enable_if_t<!((is_move_constructible_v<_Types> && ...)
1301 && (is_swappable_v<_Types> && ...))>
1302 swap(variant<_Types...>&, variant<_Types...>&) = delete;
1303
1304 class bad_variant_access : public exception
1305 {
1306 public:
1307 bad_variant_access() noexcept { }
1308
1309 const char* what() const noexcept override
1310 { return _M_reason; }
1311
1312 private:
1313 bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1314
1315 // Must point to a string with static storage duration:
1316 const char* _M_reason = "bad variant access";
1317
1318 friend void __throw_bad_variant_access(const char* __what);
1319 };
1320
1321 // Must only be called with a string literal
1322 inline void
1323 __throw_bad_variant_access(const char* __what)
1324 { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1325
1326 inline void
1327 __throw_bad_variant_access(bool __valueless)
1328 {
1329 if (__valueless) [[__unlikely__]]
1330 __throw_bad_variant_access(what: "std::get: variant is valueless");
1331 else
1332 __throw_bad_variant_access(what: "std::get: wrong index for variant");
1333 }
1334
1335 template<typename... _Types>
1336 class variant
1337 : private __detail::__variant::_Variant_base<_Types...>,
1338 private _Enable_default_constructor<
1339 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1340 variant<_Types...>>,
1341 private _Enable_copy_move<
1342 __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1343 __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1344 __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1345 __detail::__variant::_Traits<_Types...>::_S_move_assign,
1346 variant<_Types...>>
1347 {
1348 private:
1349 template <typename... _UTypes, typename _Tp>
1350 friend _GLIBCXX20_CONSTEXPR decltype(auto)
1351 __variant_cast(_Tp&&);
1352
1353 static_assert(sizeof...(_Types) > 0,
1354 "variant must have at least one alternative");
1355 static_assert(!(std::is_reference_v<_Types> || ...),
1356 "variant must have no reference alternative");
1357 static_assert(!(std::is_void_v<_Types> || ...),
1358 "variant must have no void alternative");
1359
1360 using _Base = __detail::__variant::_Variant_base<_Types...>;
1361 using _Default_ctor_enabler =
1362 _Enable_default_constructor<
1363 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1364 variant<_Types...>>;
1365
1366 template<typename _Tp>
1367 static constexpr bool __not_self
1368 = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1369
1370 template<typename _Tp>
1371 static constexpr bool
1372 __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1373
1374 template<typename _Tp>
1375 static constexpr size_t __accepted_index
1376 = __detail::__variant::__accepted_index<_Tp, variant>::value;
1377
1378 template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1379 using __to_type = typename _Nth_type<_Np, _Types...>::type;
1380
1381 template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1382 using __accepted_type = __to_type<__accepted_index<_Tp>>;
1383
1384 template<typename _Tp>
1385 static constexpr size_t __index_of
1386 = std::__find_uniq_type_in_pack<_Tp, _Types...>();
1387
1388 using _Traits = __detail::__variant::_Traits<_Types...>;
1389
1390 template<typename _Tp>
1391 struct __is_in_place_tag : false_type { };
1392 template<typename _Tp>
1393 struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1394 template<size_t _Np>
1395 struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1396
1397 template<typename _Tp>
1398 static constexpr bool __not_in_place_tag
1399 = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1400
1401 public:
1402 variant() = default;
1403 variant(const variant& __rhs) = default;
1404 variant(variant&&) = default;
1405 variant& operator=(const variant&) = default;
1406 variant& operator=(variant&&) = default;
1407 _GLIBCXX20_CONSTEXPR ~variant() = default;
1408
1409 template<typename _Tp,
1410 typename = enable_if_t<sizeof...(_Types) != 0>,
1411 typename = enable_if_t<__not_in_place_tag<_Tp>>,
1412 typename _Tj = __accepted_type<_Tp&&>,
1413 typename = enable_if_t<__exactly_once<_Tj>
1414 && is_constructible_v<_Tj, _Tp>>>
1415 constexpr
1416 variant(_Tp&& __t)
1417 noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1418 : variant(in_place_index<__accepted_index<_Tp>>,
1419 std::forward<_Tp>(__t))
1420 { }
1421
1422 template<typename _Tp, typename... _Args,
1423 typename = enable_if_t<__exactly_once<_Tp>
1424 && is_constructible_v<_Tp, _Args...>>>
1425 constexpr explicit
1426 variant(in_place_type_t<_Tp>, _Args&&... __args)
1427 : variant(in_place_index<__index_of<_Tp>>,
1428 std::forward<_Args>(__args)...)
1429 { }
1430
1431 template<typename _Tp, typename _Up, typename... _Args,
1432 typename = enable_if_t<__exactly_once<_Tp>
1433 && is_constructible_v<_Tp,
1434 initializer_list<_Up>&, _Args...>>>
1435 constexpr explicit
1436 variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1437 _Args&&... __args)
1438 : variant(in_place_index<__index_of<_Tp>>, __il,
1439 std::forward<_Args>(__args)...)
1440 { }
1441
1442 template<size_t _Np, typename... _Args,
1443 typename _Tp = __to_type<_Np>,
1444 typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1445 constexpr explicit
1446 variant(in_place_index_t<_Np>, _Args&&... __args)
1447 : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1448 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1449 { }
1450
1451 template<size_t _Np, typename _Up, typename... _Args,
1452 typename _Tp = __to_type<_Np>,
1453 typename = enable_if_t<is_constructible_v<_Tp,
1454 initializer_list<_Up>&,
1455 _Args...>>>
1456 constexpr explicit
1457 variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1458 _Args&&... __args)
1459 : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1460 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1461 { }
1462
1463 template<typename _Tp>
1464 _GLIBCXX20_CONSTEXPR
1465 enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1466 && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1467 && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1468 variant&>
1469 operator=(_Tp&& __rhs)
1470 noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1471 && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1472 {
1473 constexpr auto __index = __accepted_index<_Tp>;
1474 if (index() == __index)
1475 std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1476 else
1477 {
1478 using _Tj = __accepted_type<_Tp&&>;
1479 if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1480 || !is_nothrow_move_constructible_v<_Tj>)
1481 this->emplace<__index>(std::forward<_Tp>(__rhs));
1482 else
1483 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1484 // 3585. converting assignment with immovable alternative
1485 this->emplace<__index>(_Tj(std::forward<_Tp>(__rhs)));
1486 }
1487 return *this;
1488 }
1489
1490 template<typename _Tp, typename... _Args>
1491 _GLIBCXX20_CONSTEXPR
1492 enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1493 _Tp&>
1494 emplace(_Args&&... __args)
1495 {
1496 constexpr size_t __index = __index_of<_Tp>;
1497 return this->emplace<__index>(std::forward<_Args>(__args)...);
1498 }
1499
1500 template<typename _Tp, typename _Up, typename... _Args>
1501 _GLIBCXX20_CONSTEXPR
1502 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1503 && __exactly_once<_Tp>,
1504 _Tp&>
1505 emplace(initializer_list<_Up> __il, _Args&&... __args)
1506 {
1507 constexpr size_t __index = __index_of<_Tp>;
1508 return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1509 }
1510
1511 template<size_t _Np, typename... _Args>
1512 _GLIBCXX20_CONSTEXPR
1513 enable_if_t<is_constructible_v<__to_type<_Np>, _Args...>,
1514 __to_type<_Np>&>
1515 emplace(_Args&&... __args)
1516 {
1517 namespace __variant = std::__detail::__variant;
1518 using type = typename _Nth_type<_Np, _Types...>::type;
1519 // Provide the strong exception-safety guarantee when possible,
1520 // to avoid becoming valueless.
1521 if constexpr (is_nothrow_constructible_v<type, _Args...>)
1522 {
1523 __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1524 }
1525 else if constexpr (is_scalar_v<type>)
1526 {
1527 // This might invoke a potentially-throwing conversion operator:
1528 const type __tmp(std::forward<_Args>(__args)...);
1529 // But this won't throw:
1530 __variant::__emplace<_Np>(*this, __tmp);
1531 }
1532 else if constexpr (__variant::_Never_valueless_alt<type>()
1533 && _Traits::_S_move_assign)
1534 {
1535 // This construction might throw:
1536 variant __tmp(in_place_index<_Np>,
1537 std::forward<_Args>(__args)...);
1538 // But _Never_valueless_alt<type> means this won't:
1539 *this = std::move(__tmp);
1540 }
1541 else
1542 {
1543 // This case only provides the basic exception-safety guarantee,
1544 // i.e. the variant can become valueless.
1545 __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
1546 }
1547 return std::get<_Np>(*this);
1548 }
1549
1550 template<size_t _Np, typename _Up, typename... _Args>
1551 _GLIBCXX20_CONSTEXPR
1552 enable_if_t<is_constructible_v<__to_type<_Np>,
1553 initializer_list<_Up>&, _Args...>,
1554 __to_type<_Np>&>
1555 emplace(initializer_list<_Up> __il, _Args&&... __args)
1556 {
1557 namespace __variant = std::__detail::__variant;
1558 using type = typename _Nth_type<_Np, _Types...>::type;
1559 // Provide the strong exception-safety guarantee when possible,
1560 // to avoid becoming valueless.
1561 if constexpr (is_nothrow_constructible_v<type,
1562 initializer_list<_Up>&,
1563 _Args...>)
1564 {
1565 __variant::__emplace<_Np>(*this, __il,
1566 std::forward<_Args>(__args)...);
1567 }
1568 else if constexpr (__variant::_Never_valueless_alt<type>()
1569 && _Traits::_S_move_assign)
1570 {
1571 // This construction might throw:
1572 variant __tmp(in_place_index<_Np>, __il,
1573 std::forward<_Args>(__args)...);
1574 // But _Never_valueless_alt<type> means this won't:
1575 *this = std::move(__tmp);
1576 }
1577 else
1578 {
1579 // This case only provides the basic exception-safety guarantee,
1580 // i.e. the variant can become valueless.
1581 __variant::__emplace<_Np>(*this, __il,
1582 std::forward<_Args>(__args)...);
1583 }
1584 return std::get<_Np>(*this);
1585 }
1586
1587 template<size_t _Np, typename... _Args>
1588 enable_if_t<!(_Np < sizeof...(_Types))> emplace(_Args&&...) = delete;
1589
1590 template<typename _Tp, typename... _Args>
1591 enable_if_t<!__exactly_once<_Tp>> emplace(_Args&&...) = delete;
1592
1593 constexpr bool valueless_by_exception() const noexcept
1594 { return !this->_M_valid(); }
1595
1596 constexpr size_t index() const noexcept
1597 {
1598 using __index_type = typename _Base::__index_type;
1599 if constexpr (__detail::__variant::__never_valueless<_Types...>())
1600 return this->_M_index;
1601 else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1602 return make_signed_t<__index_type>(this->_M_index);
1603 else
1604 return size_t(__index_type(this->_M_index + 1)) - 1;
1605 }
1606
1607 _GLIBCXX20_CONSTEXPR
1608 void
1609 swap(variant& __rhs)
1610 noexcept((__is_nothrow_swappable<_Types>::value && ...)
1611 && is_nothrow_move_constructible_v<variant>)
1612 {
1613 static_assert((is_move_constructible_v<_Types> && ...));
1614
1615 // Handle this here to simplify the visitation.
1616 if (__rhs.valueless_by_exception()) [[__unlikely__]]
1617 {
1618 if (!this->valueless_by_exception()) [[__likely__]]
1619 __rhs.swap(*this);
1620 return;
1621 }
1622
1623 namespace __variant = __detail::__variant;
1624
1625 __variant::__raw_idx_visit(
1626 [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1627 {
1628 constexpr size_t __j = __rhs_index;
1629 if constexpr (__j != variant_npos)
1630 {
1631 if (this->index() == __j)
1632 {
1633 using std::swap;
1634 swap(std::get<__j>(*this), __rhs_mem);
1635 }
1636 else
1637 {
1638 auto __tmp(std::move(__rhs_mem));
1639
1640 if constexpr (_Traits::_S_trivial_move_assign)
1641 __rhs = std::move(*this);
1642 else
1643 __variant::__raw_idx_visit(
1644 [&__rhs](auto&& __this_mem, auto __this_index) mutable
1645 {
1646 constexpr size_t __k = __this_index;
1647 if constexpr (__k != variant_npos)
1648 __variant::__emplace<__k>(__rhs,
1649 std::move(__this_mem));
1650 }, *this);
1651
1652 __variant::__emplace<__j>(*this, std::move(__tmp));
1653 }
1654 }
1655 }, __rhs);
1656 }
1657
1658#if defined(__clang__) && __clang_major__ <= 7
1659 public:
1660 using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1661#endif
1662
1663 private:
1664 template<size_t _Np, typename _Vp>
1665 friend constexpr decltype(auto)
1666 __detail::__variant::__get(_Vp&& __v) noexcept;
1667
1668#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1669 template<typename... _Tp> \
1670 friend constexpr bool \
1671 operator __OP(const variant<_Tp...>& __lhs, \
1672 const variant<_Tp...>& __rhs);
1673
1674 _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1675 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1676 _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1677 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1678 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1679 _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1680
1681#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1682 };
1683
1684 template<size_t _Np, typename... _Types>
1685 constexpr variant_alternative_t<_Np, variant<_Types...>>&
1686 get(variant<_Types...>& __v)
1687 {
1688 static_assert(_Np < sizeof...(_Types),
1689 "The index must be in [0, number of alternatives)");
1690 if (__v.index() != _Np)
1691 __throw_bad_variant_access(__v.valueless_by_exception());
1692 return __detail::__variant::__get<_Np>(__v);
1693 }
1694
1695 template<size_t _Np, typename... _Types>
1696 constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1697 get(variant<_Types...>&& __v)
1698 {
1699 static_assert(_Np < sizeof...(_Types),
1700 "The index must be in [0, number of alternatives)");
1701 if (__v.index() != _Np)
1702 __throw_bad_variant_access(__v.valueless_by_exception());
1703 return __detail::__variant::__get<_Np>(std::move(__v));
1704 }
1705
1706 template<size_t _Np, typename... _Types>
1707 constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1708 get(const variant<_Types...>& __v)
1709 {
1710 static_assert(_Np < sizeof...(_Types),
1711 "The index must be in [0, number of alternatives)");
1712 if (__v.index() != _Np)
1713 __throw_bad_variant_access(__v.valueless_by_exception());
1714 return __detail::__variant::__get<_Np>(__v);
1715 }
1716
1717 template<size_t _Np, typename... _Types>
1718 constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1719 get(const variant<_Types...>&& __v)
1720 {
1721 static_assert(_Np < sizeof...(_Types),
1722 "The index must be in [0, number of alternatives)");
1723 if (__v.index() != _Np)
1724 __throw_bad_variant_access(__v.valueless_by_exception());
1725 return __detail::__variant::__get<_Np>(std::move(__v));
1726 }
1727
1728 /// @cond undocumented
1729 template<typename _Result_type, typename _Visitor, typename... _Variants>
1730 constexpr decltype(auto)
1731 __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1732 {
1733 // Get the silly case of visiting no variants out of the way first.
1734 if constexpr (sizeof...(_Variants) == 0)
1735 {
1736 if constexpr (is_void_v<_Result_type>)
1737 return (void) std::forward<_Visitor>(__visitor)();
1738 else
1739 return std::forward<_Visitor>(__visitor)();
1740 }
1741 else
1742 {
1743 constexpr size_t __max = 11; // "These go to eleven."
1744
1745 // The type of the first variant in the pack.
1746 using _V0 = typename _Nth_type<0, _Variants...>::type;
1747 // The number of alternatives in that first variant.
1748 constexpr auto __n = variant_size_v<remove_reference_t<_V0>>;
1749
1750 if constexpr (sizeof...(_Variants) > 1 || __n > __max)
1751 {
1752 // Use a jump table for the general case.
1753 constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1754 _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1755
1756 auto __func_ptr = __vtable._M_access(__variants.index()...);
1757 return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1758 std::forward<_Variants>(__variants)...);
1759 }
1760 else // We have a single variant with a small number of alternatives.
1761 {
1762 // A name for the first variant in the pack.
1763 _V0& __v0
1764 = [](_V0& __v, ...) -> _V0& { return __v; }(__variants...);
1765
1766 using __detail::__variant::_Multi_array;
1767 using __detail::__variant::__gen_vtable_impl;
1768 using _Ma = _Multi_array<_Result_type (*)(_Visitor&&, _V0&&)>;
1769
1770#ifdef _GLIBCXX_DEBUG
1771# define _GLIBCXX_VISIT_UNREACHABLE __builtin_trap
1772#else
1773# define _GLIBCXX_VISIT_UNREACHABLE __builtin_unreachable
1774#endif
1775
1776#define _GLIBCXX_VISIT_CASE(N) \
1777 case N: \
1778 { \
1779 if constexpr (N < __n) \
1780 { \
1781 return __gen_vtable_impl<_Ma, index_sequence<N>>:: \
1782 __visit_invoke(std::forward<_Visitor>(__visitor), \
1783 std::forward<_V0>(__v0)); \
1784 } \
1785 else _GLIBCXX_VISIT_UNREACHABLE(); \
1786 }
1787
1788 switch (__v0.index())
1789 {
1790 _GLIBCXX_VISIT_CASE(0)
1791 _GLIBCXX_VISIT_CASE(1)
1792 _GLIBCXX_VISIT_CASE(2)
1793 _GLIBCXX_VISIT_CASE(3)
1794 _GLIBCXX_VISIT_CASE(4)
1795 _GLIBCXX_VISIT_CASE(5)
1796 _GLIBCXX_VISIT_CASE(6)
1797 _GLIBCXX_VISIT_CASE(7)
1798 _GLIBCXX_VISIT_CASE(8)
1799 _GLIBCXX_VISIT_CASE(9)
1800 _GLIBCXX_VISIT_CASE(10)
1801 case variant_npos:
1802 using __detail::__variant::__variant_idx_cookie;
1803 using __detail::__variant::__variant_cookie;
1804 if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
1805 || is_same_v<_Result_type, __variant_cookie>)
1806 {
1807 using _Npos = index_sequence<variant_npos>;
1808 return __gen_vtable_impl<_Ma, _Npos>::
1809 __visit_invoke(std::forward<_Visitor>(__visitor),
1810 std::forward<_V0>(__v0));
1811 }
1812 else
1813 _GLIBCXX_VISIT_UNREACHABLE();
1814 default:
1815 _GLIBCXX_VISIT_UNREACHABLE();
1816 }
1817#undef _GLIBCXX_VISIT_CASE
1818#undef _GLIBCXX_VISIT_UNREACHABLE
1819 }
1820 }
1821 }
1822 /// @endcond
1823
1824 template<typename _Visitor, typename... _Variants>
1825 constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1826 visit(_Visitor&& __visitor, _Variants&&... __variants)
1827 {
1828 namespace __variant = std::__detail::__variant;
1829
1830 if ((__variant::__as(__variants).valueless_by_exception() || ...))
1831 __throw_bad_variant_access(what: "std::visit: variant is valueless");
1832
1833 using _Result_type
1834 = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1835
1836 using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1837
1838 if constexpr (sizeof...(_Variants) == 1)
1839 {
1840 using _Vp = decltype(__variant::__as(std::declval<_Variants>()...));
1841
1842 constexpr bool __visit_rettypes_match = __detail::__variant::
1843 __check_visitor_results<_Visitor, _Vp>(
1844 make_index_sequence<variant_size_v<remove_reference_t<_Vp>>>());
1845 if constexpr (!__visit_rettypes_match)
1846 {
1847 static_assert(__visit_rettypes_match,
1848 "std::visit requires the visitor to have the same "
1849 "return type for all alternatives of a variant");
1850 return;
1851 }
1852 else
1853 return std::__do_visit<_Tag>(
1854 std::forward<_Visitor>(__visitor),
1855 static_cast<_Vp>(__variants)...);
1856 }
1857 else
1858 return std::__do_visit<_Tag>(
1859 std::forward<_Visitor>(__visitor),
1860 __variant::__as(std::forward<_Variants>(__variants))...);
1861 }
1862
1863#if __cplusplus > 201703L
1864 template<typename _Res, typename _Visitor, typename... _Variants>
1865 constexpr _Res
1866 visit(_Visitor&& __visitor, _Variants&&... __variants)
1867 {
1868 namespace __variant = std::__detail::__variant;
1869
1870 if ((__variant::__as(__variants).valueless_by_exception() || ...))
1871 __throw_bad_variant_access("std::visit<R>: variant is valueless");
1872
1873 return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1874 __variant::__as(std::forward<_Variants>(__variants))...);
1875 }
1876#endif
1877
1878 /// @cond undocumented
1879 template<bool, typename... _Types>
1880 struct __variant_hash_call_base_impl
1881 {
1882 size_t
1883 operator()(const variant<_Types...>& __t) const
1884 noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1885 {
1886 size_t __ret;
1887 __detail::__variant::__raw_visit(
1888 [&__t, &__ret](auto&& __t_mem) mutable
1889 {
1890 using _Type = __remove_cvref_t<decltype(__t_mem)>;
1891 if constexpr (!is_same_v<_Type,
1892 __detail::__variant::__variant_cookie>)
1893 __ret = std::hash<size_t>{}(__t.index())
1894 + std::hash<_Type>{}(__t_mem);
1895 else
1896 __ret = std::hash<size_t>{}(__t.index());
1897 }, __t);
1898 return __ret;
1899 }
1900 };
1901
1902 template<typename... _Types>
1903 struct __variant_hash_call_base_impl<false, _Types...> {};
1904
1905 template<typename... _Types>
1906 using __variant_hash_call_base =
1907 __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1908 __enable_hash_call &&...), _Types...>;
1909 /// @endcond
1910
1911 template<typename... _Types>
1912 struct hash<variant<_Types...>>
1913 : private __detail::__variant::_Variant_hash_base<
1914 variant<_Types...>, std::index_sequence_for<_Types...>>,
1915 public __variant_hash_call_base<_Types...>
1916 {
1917 using result_type [[__deprecated__]] = size_t;
1918 using argument_type [[__deprecated__]] = variant<_Types...>;
1919 };
1920
1921 template<>
1922 struct hash<monostate>
1923 {
1924 using result_type [[__deprecated__]] = size_t;
1925 using argument_type [[__deprecated__]] = monostate;
1926
1927 size_t
1928 operator()(const monostate&) const noexcept
1929 {
1930 constexpr size_t __magic_monostate_hash = -7777;
1931 return __magic_monostate_hash;
1932 }
1933 };
1934
1935 template<typename... _Types>
1936 struct __is_fast_hash<hash<variant<_Types...>>>
1937 : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1938 { };
1939
1940_GLIBCXX_END_NAMESPACE_VERSION
1941} // namespace std
1942
1943#endif // C++17
1944
1945#endif // _GLIBCXX_VARIANT
1946