libstdc++
variant
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1// <variant> -*- C++ -*-
2
3// Copyright (C) 2016-2020 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file variant
26 * This is the `<variant>` C++ Library header.
27 */
28
29#ifndef _GLIBCXX_VARIANT
30#define _GLIBCXX_VARIANT 1
31
32#pragma GCC system_header
33
34#if __cplusplus >= 201703L
35
36#include <type_traits>
37#include <utility>
38#include <bits/enable_special_members.h>
39#include <bits/functexcept.h>
40#include <bits/move.h>
41#include <bits/functional_hash.h>
42#include <bits/invoke.h>
43#include <ext/aligned_buffer.h>
44#include <bits/parse_numbers.h>
45#include <bits/stl_iterator_base_types.h>
46#include <bits/stl_iterator_base_funcs.h>
47#include <bits/stl_construct.h>
48#if __cplusplus > 201703L
49# include <compare>
50#endif
51
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 appearence of _Tp in _Types.
168 // Returns sizeof...(_Types) if _Tp is not in _Types.
169 template<typename _Tp, typename... _Types>
170 struct __index_of : std::integral_constant<size_t, 0> {};
171
172 template<typename _Tp, typename... _Types>
173 inline constexpr size_t __index_of_v = __index_of<_Tp, _Types...>::value;
174
175 template<typename _Tp, typename _First, typename... _Rest>
176 struct __index_of<_Tp, _First, _Rest...> :
177 std::integral_constant<size_t, is_same_v<_Tp, _First>
178 ? 0 : __index_of_v<_Tp, _Rest...> + 1> {};
179
180 // used for raw visitation
181 struct __variant_cookie {};
182 // used for raw visitation with indices passed in
183 struct __variant_idx_cookie { using type = __variant_idx_cookie; };
184 // Used to enable deduction (and same-type checking) for std::visit:
185 template<typename> struct __deduce_visit_result { };
186
187 // Visit variants that might be valueless.
188 template<typename _Visitor, typename... _Variants>
189 constexpr void
190 __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
191 {
192 std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
193 std::forward<_Variants>(__variants)...);
194 }
195
196 // Visit variants that might be valueless, passing indices to the visitor.
197 template<typename _Visitor, typename... _Variants>
198 constexpr void
199 __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
200 {
201 std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
202 std::forward<_Variants>(__variants)...);
203 }
204
205 // _Uninitialized<T> is guaranteed to be a 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,
741 bool _Ti_is_cv_bool = is_same_v<remove_cv_t<_Ti>, bool>,
742 typename = void>
743 struct _Build_FUN
744 {
745 // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
746 // but only static functions will be considered in the call below.
747 void _S_fun();
748 };
749
750 // ... for which Ti x[] = {std::forward<T>(t)}; is well-formed,
751 template<size_t _Ind, typename _Tp, typename _Ti>
752 struct _Build_FUN<_Ind, _Tp, _Ti, false,
753 void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
754 {
755 // This is the FUN function for type _Ti, with index _Ind
756 static integral_constant<size_t, _Ind> _S_fun(_Ti);
757 };
758
759 // ... and if Ti is cv bool, remove_cvref_t<T> is bool.
760 template<size_t _Ind, typename _Tp, typename _Ti>
761 struct _Build_FUN<_Ind, _Tp, _Ti, true,
762 enable_if_t<is_same_v<__remove_cvref_t<_Tp>, bool>>>
763 {
764 // This is the FUN function for when _Ti is cv bool, with index _Ind
765 static integral_constant<size_t, _Ind> _S_fun(_Ti);
766 };
767
768 template<typename _Tp, typename _Variant,
769 typename = make_index_sequence<variant_size_v<_Variant>>>
770 struct _Build_FUNs;
771
772 template<typename _Tp, typename... _Ti, size_t... _Ind>
773 struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
774 : _Build_FUN<_Ind, _Tp, _Ti>...
775 {
776 using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
777 };
778
779 // The index j of the overload FUN(Tj) selected by overload resolution
780 // for FUN(std::forward<_Tp>(t))
781 template<typename _Tp, typename _Variant>
782 using _FUN_type
783 = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
784
785 // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
786 template<typename _Tp, typename _Variant, typename = void>
787 struct __accepted_index
788 : integral_constant<size_t, variant_npos>
789 { };
790
791 template<typename _Tp, typename _Variant>
792 struct __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
793 : _FUN_type<_Tp, _Variant>
794 { };
795
796 // Returns the raw storage for __v.
797 template<typename _Variant>
798 void* __get_storage(_Variant&& __v) noexcept
799 { return __v._M_storage(); }
800
801 template <typename _Maybe_variant_cookie, typename _Variant>
802 struct _Extra_visit_slot_needed
803 {
804 template <typename> struct _Variant_never_valueless;
805
806 template <typename... _Types>
807 struct _Variant_never_valueless<variant<_Types...>>
808 : bool_constant<__variant::__never_valueless<_Types...>()> {};
809
810 static constexpr bool value =
811 (is_same_v<_Maybe_variant_cookie, __variant_cookie>
812 || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
813 && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
814 };
815
816 // Used for storing a multi-dimensional vtable.
817 template<typename _Tp, size_t... _Dimensions>
818 struct _Multi_array;
819
820 // Partial specialization with rank zero, stores a single _Tp element.
821 template<typename _Tp>
822 struct _Multi_array<_Tp>
823 {
824 template<typename>
825 struct __untag_result
826 : false_type
827 { using element_type = _Tp; };
828
829 template <typename... _Args>
830 struct __untag_result<const void(*)(_Args...)>
831 : false_type
832 { using element_type = void(*)(_Args...); };
833
834 template <typename... _Args>
835 struct __untag_result<__variant_cookie(*)(_Args...)>
836 : false_type
837 { using element_type = void(*)(_Args...); };
838
839 template <typename... _Args>
840 struct __untag_result<__variant_idx_cookie(*)(_Args...)>
841 : false_type
842 { using element_type = void(*)(_Args...); };
843
844 template <typename _Res, typename... _Args>
845 struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
846 : true_type
847 { using element_type = _Res(*)(_Args...); };
848
849 using __result_is_deduced = __untag_result<_Tp>;
850
851 constexpr const typename __untag_result<_Tp>::element_type&
852 _M_access() const
853 { return _M_data; }
854
855 typename __untag_result<_Tp>::element_type _M_data;
856 };
857
858 // Partial specialization with rank >= 1.
859 template<typename _Ret,
860 typename _Visitor,
861 typename... _Variants,
862 size_t __first, size_t... __rest>
863 struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
864 {
865 static constexpr size_t __index =
866 sizeof...(_Variants) - sizeof...(__rest) - 1;
867
868 using _Variant = typename _Nth_type<__index, _Variants...>::type;
869
870 static constexpr int __do_cookie =
871 _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
872
873 using _Tp = _Ret(*)(_Visitor, _Variants...);
874
875 template<typename... _Args>
876 constexpr decltype(auto)
877 _M_access(size_t __first_index, _Args... __rest_indices) const
878 {
879 return _M_arr[__first_index + __do_cookie]
880 ._M_access(__rest_indices...);
881 }
882
883 _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
884 };
885
886 // Creates a multi-dimensional vtable recursively.
887 //
888 // For example,
889 // visit([](auto, auto){},
890 // variant<int, char>(), // typedef'ed as V1
891 // variant<float, double, long double>()) // typedef'ed as V2
892 // will trigger instantiations of:
893 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
894 // tuple<V1&&, V2&&>, std::index_sequence<>>
895 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
896 // tuple<V1&&, V2&&>, std::index_sequence<0>>
897 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
898 // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
899 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
900 // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
901 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
902 // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
903 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
904 // tuple<V1&&, V2&&>, std::index_sequence<1>>
905 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
906 // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
907 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
908 // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
909 // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
910 // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
911 // The returned multi-dimensional vtable can be fast accessed by the visitor
912 // using index calculation.
913 template<typename _Array_type, typename _Index_seq>
914 struct __gen_vtable_impl;
915
916 // Defines the _S_apply() member that returns a _Multi_array populated
917 // with function pointers that perform the visitation expressions e(m)
918 // for each valid pack of indexes into the variant types _Variants.
919 //
920 // This partial specialization builds up the index sequences by recursively
921 // calling _S_apply() on the next specialization of __gen_vtable_impl.
922 // The base case of the recursion defines the actual function pointers.
923 template<typename _Result_type, typename _Visitor, size_t... __dimensions,
924 typename... _Variants, size_t... __indices>
925 struct __gen_vtable_impl<
926 _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
927 std::index_sequence<__indices...>>
928 {
929 using _Next =
930 remove_reference_t<typename _Nth_type<sizeof...(__indices),
931 _Variants...>::type>;
932 using _Array_type =
933 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
934 __dimensions...>;
935
936 static constexpr _Array_type
937 _S_apply()
938 {
939 _Array_type __vtable{};
940 _S_apply_all_alts(
941 __vtable, make_index_sequence<variant_size_v<_Next>>());
942 return __vtable;
943 }
944
945 template<size_t... __var_indices>
946 static constexpr void
947 _S_apply_all_alts(_Array_type& __vtable,
948 std::index_sequence<__var_indices...>)
949 {
950 if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
951 (_S_apply_single_alt<true, __var_indices>(
952 __vtable._M_arr[__var_indices + 1],
953 &(__vtable._M_arr[0])), ...);
954 else
955 (_S_apply_single_alt<false, __var_indices>(
956 __vtable._M_arr[__var_indices]), ...);
957 }
958
959 template<bool __do_cookie, size_t __index, typename _Tp>
960 static constexpr void
961 _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
962 {
963 if constexpr (__do_cookie)
964 {
965 __element = __gen_vtable_impl<
966 _Tp,
967 std::index_sequence<__indices..., __index>>::_S_apply();
968 *__cookie_element = __gen_vtable_impl<
969 _Tp,
970 std::index_sequence<__indices..., variant_npos>>::_S_apply();
971 }
972 else
973 {
974 __element = __gen_vtable_impl<
975 remove_reference_t<decltype(__element)>,
976 std::index_sequence<__indices..., __index>>::_S_apply();
977 }
978 }
979 };
980
981 // This partial specialization is the base case for the recursion.
982 // It populates a _Multi_array element with the address of a function
983 // that invokes the visitor with the alternatives specified by __indices.
984 template<typename _Result_type, typename _Visitor, typename... _Variants,
985 size_t... __indices>
986 struct __gen_vtable_impl<
987 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
988 std::index_sequence<__indices...>>
989 {
990 using _Array_type =
991 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
992
993 template<size_t __index, typename _Variant>
994 static constexpr decltype(auto)
995 __element_by_index_or_cookie(_Variant&& __var) noexcept
996 {
997 if constexpr (__index != variant_npos)
998 return __variant::__get<__index>(std::forward<_Variant>(__var));
999 else
1000 return __variant_cookie{};
1001 }
1002
1003 static constexpr decltype(auto)
1004 __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1005 {
1006 if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
1007 // For raw visitation using indices, pass the indices to the visitor
1008 // and discard the return value:
1009 std::__invoke(std::forward<_Visitor>(__visitor),
1010 __element_by_index_or_cookie<__indices>(
1011 std::forward<_Variants>(__vars))...,
1012 integral_constant<size_t, __indices>()...);
1013 else if constexpr (is_same_v<_Result_type, __variant_cookie>)
1014 // For raw visitation without indices, and discard the return value:
1015 std::__invoke(std::forward<_Visitor>(__visitor),
1016 __element_by_index_or_cookie<__indices>(
1017 std::forward<_Variants>(__vars))...);
1018 else if constexpr (_Array_type::__result_is_deduced::value)
1019 // For the usual std::visit case deduce the return value:
1020 return std::__invoke(std::forward<_Visitor>(__visitor),
1021 __element_by_index_or_cookie<__indices>(
1022 std::forward<_Variants>(__vars))...);
1023 else // for std::visit<R> use INVOKE<R>
1024 return std::__invoke_r<_Result_type>(
1025 std::forward<_Visitor>(__visitor),
1026 __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
1027 }
1028
1029 static constexpr auto
1030 _S_apply()
1031 { return _Array_type{&__visit_invoke}; }
1032 };
1033
1034 template<typename _Result_type, typename _Visitor, typename... _Variants>
1035 struct __gen_vtable
1036 {
1037 using _Array_type =
1038 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1039 variant_size_v<remove_reference_t<_Variants>>...>;
1040
1041 static constexpr _Array_type _S_vtable
1042 = __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
1043 };
1044
1045 template<size_t _Np, typename _Tp>
1046 struct _Base_dedup : public _Tp { };
1047
1048 template<typename _Variant, typename __indices>
1049 struct _Variant_hash_base;
1050
1051 template<typename... _Types, size_t... __indices>
1052 struct _Variant_hash_base<variant<_Types...>,
1053 std::index_sequence<__indices...>>
1054 : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1055
1056 template<size_t _Np, typename _Variant>
1057 using __get_t = decltype(std::get<_Np>(std::declval<_Variant>()));
1058
1059 // Return type of std::visit.
1060 template<typename _Visitor, typename... _Variants>
1061 using __visit_result_t
1062 = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
1063
1064} // namespace __variant
1065} // namespace __detail
1066
1067 template<size_t _Np, typename _Variant, typename... _Args>
1068 void __variant_construct_by_index(_Variant& __v, _Args&&... __args)
1069 {
1070 __v._M_index = _Np;
1071 auto&& __storage = __detail::__variant::__get<_Np>(__v);
1072 ::new ((void*)std::addressof(__storage))
1073 remove_reference_t<decltype(__storage)>
1074 (std::forward<_Args>(__args)...);
1075 }
1076
1077 template<typename _Tp, typename... _Types>
1078 constexpr bool
1079 holds_alternative(const variant<_Types...>& __v) noexcept
1080 {
1081 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1082 "T must occur exactly once in alternatives");
1083 return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
1084 }
1085
1086 template<typename _Tp, typename... _Types>
1087 constexpr _Tp& get(variant<_Types...>& __v)
1088 {
1089 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1090 "T must occur exactly once in alternatives");
1091 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1092 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1093 }
1094
1095 template<typename _Tp, typename... _Types>
1096 constexpr _Tp&& get(variant<_Types...>&& __v)
1097 {
1098 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1099 "T must occur exactly once in alternatives");
1100 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1101 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1102 std::move(__v));
1103 }
1104
1105 template<typename _Tp, typename... _Types>
1106 constexpr const _Tp& get(const variant<_Types...>& __v)
1107 {
1108 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1109 "T must occur exactly once in alternatives");
1110 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1111 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1112 }
1113
1114 template<typename _Tp, typename... _Types>
1115 constexpr const _Tp&& get(const variant<_Types...>&& __v)
1116 {
1117 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1118 "T must occur exactly once in alternatives");
1119 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1120 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1121 std::move(__v));
1122 }
1123
1124 template<size_t _Np, typename... _Types>
1125 constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1126 get_if(variant<_Types...>* __ptr) noexcept
1127 {
1128 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1129 static_assert(_Np < sizeof...(_Types),
1130 "The index must be in [0, number of alternatives)");
1131 static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1132 if (__ptr && __ptr->index() == _Np)
1133 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1134 return nullptr;
1135 }
1136
1137 template<size_t _Np, typename... _Types>
1138 constexpr
1139 add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1140 get_if(const variant<_Types...>* __ptr) noexcept
1141 {
1142 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1143 static_assert(_Np < sizeof...(_Types),
1144 "The index must be in [0, number of alternatives)");
1145 static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
1146 if (__ptr && __ptr->index() == _Np)
1147 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1148 return nullptr;
1149 }
1150
1151 template<typename _Tp, typename... _Types>
1152 constexpr add_pointer_t<_Tp>
1153 get_if(variant<_Types...>* __ptr) noexcept
1154 {
1155 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1156 "T must occur exactly once in alternatives");
1157 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1158 return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1159 __ptr);
1160 }
1161
1162 template<typename _Tp, typename... _Types>
1163 constexpr add_pointer_t<const _Tp>
1164 get_if(const variant<_Types...>* __ptr) noexcept
1165 {
1166 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1167 "T must occur exactly once in alternatives");
1168 static_assert(!is_void_v<_Tp>, "_Tp must not be void");
1169 return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1170 __ptr);
1171 }
1172
1173 struct monostate { };
1174
1175#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1176 template<typename... _Types> \
1177 constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1178 const variant<_Types...>& __rhs) \
1179 { \
1180 bool __ret = true; \
1181 __detail::__variant::__raw_idx_visit( \
1182 [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
1183 { \
1184 if constexpr (__rhs_index != variant_npos) \
1185 { \
1186 if (__lhs.index() == __rhs_index) \
1187 { \
1188 auto& __this_mem = std::get<__rhs_index>(__lhs); \
1189 __ret = __this_mem __OP __rhs_mem; \
1190 } \
1191 else \
1192 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1193 } \
1194 else \
1195 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1196 }, __rhs); \
1197 return __ret; \
1198 }
1199
1200 _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1201 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1202 _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1203 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1204 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1205 _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1206
1207#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1208
1209 constexpr bool operator==(monostate, monostate) noexcept { return true; }
1210
1211#ifdef __cpp_lib_three_way_comparison
1212 template<typename... _Types>
1213 requires (three_way_comparable<_Types> && ...)
1214 constexpr
1215 common_comparison_category_t<compare_three_way_result_t<_Types>...>
1216 operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
1217 {
1218 common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
1219 = strong_ordering::equal;
1220
1221 __detail::__variant::__raw_idx_visit(
1222 [&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
1223 {
1224 if constexpr (__w_index != variant_npos)
1225 {
1226 if (__v.index() == __w_index)
1227 {
1228 auto& __this_mem = std::get<__w_index>(__v);
1229 __ret = __this_mem <=> __w_mem;
1230 return;
1231 }
1232 }
1233 __ret = (__v.index() + 1) <=> (__w_index + 1);
1234 }, __w);
1235 return __ret;
1236 }
1237
1238 constexpr strong_ordering
1239 operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
1240#else
1241 constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1242 constexpr bool operator<(monostate, monostate) noexcept { return false; }
1243 constexpr bool operator>(monostate, monostate) noexcept { return false; }
1244 constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1245 constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1246#endif
1247
1248 template<typename _Visitor, typename... _Variants>
1249 constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1250 visit(_Visitor&&, _Variants&&...);
1251
1252 template<typename... _Types>
1253 inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1254 && (is_swappable_v<_Types> && ...)>
1255 swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1256 noexcept(noexcept(__lhs.swap(__rhs)))
1257 { __lhs.swap(__rhs); }
1258
1259 template<typename... _Types>
1260 enable_if_t<!((is_move_constructible_v<_Types> && ...)
1261 && (is_swappable_v<_Types> && ...))>
1262 swap(variant<_Types...>&, variant<_Types...>&) = delete;
1263
1264 class bad_variant_access : public exception
1265 {
1266 public:
1267 bad_variant_access() noexcept { }
1268
1269 const char* what() const noexcept override
1270 { return _M_reason; }
1271
1272 private:
1273 bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
1274
1275 // Must point to a string with static storage duration:
1276 const char* _M_reason = "bad variant access";
1277
1278 friend void __throw_bad_variant_access(const char* __what);
1279 };
1280
1281 // Must only be called with a string literal
1282 inline void
1283 __throw_bad_variant_access(const char* __what)
1284 { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1285
1286 inline void
1287 __throw_bad_variant_access(bool __valueless)
1288 {
1289 if (__valueless) [[__unlikely__]]
1290 __throw_bad_variant_access("std::get: variant is valueless");
1291 else
1292 __throw_bad_variant_access("std::get: wrong index for variant");
1293 }
1294
1295 template<typename... _Types>
1296 class variant
1297 : private __detail::__variant::_Variant_base<_Types...>,
1298 private _Enable_default_constructor<
1299 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1300 variant<_Types...>>,
1301 private _Enable_copy_move<
1302 __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1303 __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1304 __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1305 __detail::__variant::_Traits<_Types...>::_S_move_assign,
1306 variant<_Types...>>
1307 {
1308 private:
1309 template <typename... _UTypes, typename _Tp>
1310 friend decltype(auto) __variant_cast(_Tp&&);
1311 template<size_t _Np, typename _Variant, typename... _Args>
1312 friend void __variant_construct_by_index(_Variant& __v,
1313 _Args&&... __args);
1314
1315 static_assert(sizeof...(_Types) > 0,
1316 "variant must have at least one alternative");
1317 static_assert(!(std::is_reference_v<_Types> || ...),
1318 "variant must have no reference alternative");
1319 static_assert(!(std::is_void_v<_Types> || ...),
1320 "variant must have no void alternative");
1321
1322 using _Base = __detail::__variant::_Variant_base<_Types...>;
1323 using _Default_ctor_enabler =
1324 _Enable_default_constructor<
1325 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1326 variant<_Types...>>;
1327
1328 template<typename _Tp>
1329 static constexpr bool __not_self
1330 = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1331
1332 template<typename _Tp>
1333 static constexpr bool
1334 __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1335
1336 template<typename _Tp>
1337 static constexpr size_t __accepted_index
1338 = __detail::__variant::__accepted_index<_Tp, variant>::value;
1339
1340 template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1341 using __to_type = variant_alternative_t<_Np, variant>;
1342
1343 template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1344 using __accepted_type = __to_type<__accepted_index<_Tp>>;
1345
1346 template<typename _Tp>
1347 static constexpr size_t __index_of =
1348 __detail::__variant::__index_of_v<_Tp, _Types...>;
1349
1350 using _Traits = __detail::__variant::_Traits<_Types...>;
1351
1352 template<typename _Tp>
1353 struct __is_in_place_tag : false_type { };
1354 template<typename _Tp>
1355 struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1356 template<size_t _Np>
1357 struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1358
1359 template<typename _Tp>
1360 static constexpr bool __not_in_place_tag
1361 = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1362
1363 public:
1364 variant() = default;
1365 variant(const variant& __rhs) = default;
1366 variant(variant&&) = default;
1367 variant& operator=(const variant&) = default;
1368 variant& operator=(variant&&) = default;
1369 ~variant() = default;
1370
1371 template<typename _Tp,
1372 typename = enable_if_t<sizeof...(_Types) != 0>,
1373 typename = enable_if_t<__not_in_place_tag<_Tp>>,
1374 typename _Tj = __accepted_type<_Tp&&>,
1375 typename = enable_if_t<__exactly_once<_Tj>
1376 && is_constructible_v<_Tj, _Tp>>>
1377 constexpr
1378 variant(_Tp&& __t)
1379 noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1380 : variant(in_place_index<__accepted_index<_Tp>>,
1381 std::forward<_Tp>(__t))
1382 { }
1383
1384 template<typename _Tp, typename... _Args,
1385 typename = enable_if_t<__exactly_once<_Tp>
1386 && is_constructible_v<_Tp, _Args...>>>
1387 constexpr explicit
1388 variant(in_place_type_t<_Tp>, _Args&&... __args)
1389 : variant(in_place_index<__index_of<_Tp>>,
1390 std::forward<_Args>(__args)...)
1391 { }
1392
1393 template<typename _Tp, typename _Up, typename... _Args,
1394 typename = enable_if_t<__exactly_once<_Tp>
1395 && is_constructible_v<_Tp,
1396 initializer_list<_Up>&, _Args...>>>
1397 constexpr explicit
1398 variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1399 _Args&&... __args)
1400 : variant(in_place_index<__index_of<_Tp>>, __il,
1401 std::forward<_Args>(__args)...)
1402 { }
1403
1404 template<size_t _Np, typename... _Args,
1405 typename _Tp = __to_type<_Np>,
1406 typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1407 constexpr explicit
1408 variant(in_place_index_t<_Np>, _Args&&... __args)
1409 : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1410 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1411 { }
1412
1413 template<size_t _Np, typename _Up, typename... _Args,
1414 typename _Tp = __to_type<_Np>,
1415 typename = enable_if_t<is_constructible_v<_Tp,
1416 initializer_list<_Up>&,
1417 _Args...>>>
1418 constexpr explicit
1419 variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1420 _Args&&... __args)
1421 : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1422 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1423 { }
1424
1425 template<typename _Tp>
1426 enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1427 && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1428 && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1429 variant&>
1430 operator=(_Tp&& __rhs)
1431 noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1432 && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1433 {
1434 constexpr auto __index = __accepted_index<_Tp>;
1435 if (index() == __index)
1436 std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1437 else
1438 {
1439 using _Tj = __accepted_type<_Tp&&>;
1440 if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1441 || !is_nothrow_move_constructible_v<_Tj>)
1442 this->emplace<__index>(std::forward<_Tp>(__rhs));
1443 else
1444 operator=(variant(std::forward<_Tp>(__rhs)));
1445 }
1446 return *this;
1447 }
1448
1449 template<typename _Tp, typename... _Args>
1450 enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1451 _Tp&>
1452 emplace(_Args&&... __args)
1453 {
1454 constexpr size_t __index = __index_of<_Tp>;
1455 return this->emplace<__index>(std::forward<_Args>(__args)...);
1456 }
1457
1458 template<typename _Tp, typename _Up, typename... _Args>
1459 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1460 && __exactly_once<_Tp>,
1461 _Tp&>
1462 emplace(initializer_list<_Up> __il, _Args&&... __args)
1463 {
1464 constexpr size_t __index = __index_of<_Tp>;
1465 return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1466 }
1467
1468 template<size_t _Np, typename... _Args>
1469 enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1470 _Args...>,
1471 variant_alternative_t<_Np, variant>&>
1472 emplace(_Args&&... __args)
1473 {
1474 static_assert(_Np < sizeof...(_Types),
1475 "The index must be in [0, number of alternatives)");
1476 using type = variant_alternative_t<_Np, variant>;
1477 // Provide the strong exception-safety guarantee when possible,
1478 // to avoid becoming valueless.
1479 if constexpr (is_nothrow_constructible_v<type, _Args...>)
1480 {
1481 this->_M_reset();
1482 __variant_construct_by_index<_Np>(*this,
1483 std::forward<_Args>(__args)...);
1484 }
1485 else if constexpr (is_scalar_v<type>)
1486 {
1487 // This might invoke a potentially-throwing conversion operator:
1488 const type __tmp(std::forward<_Args>(__args)...);
1489 // But these steps won't throw:
1490 this->_M_reset();
1491 __variant_construct_by_index<_Np>(*this, __tmp);
1492 }
1493 else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1494 && _Traits::_S_move_assign)
1495 {
1496 // This construction might throw:
1497 variant __tmp(in_place_index<_Np>,
1498 std::forward<_Args>(__args)...);
1499 // But _Never_valueless_alt<type> means this won't:
1500 *this = std::move(__tmp);
1501 }
1502 else
1503 {
1504 // This case only provides the basic exception-safety guarantee,
1505 // i.e. the variant can become valueless.
1506 this->_M_reset();
1507 __try
1508 {
1509 __variant_construct_by_index<_Np>(*this,
1510 std::forward<_Args>(__args)...);
1511 }
1512 __catch (...)
1513 {
1514 this->_M_index = variant_npos;
1515 __throw_exception_again;
1516 }
1517 }
1518 return std::get<_Np>(*this);
1519 }
1520
1521 template<size_t _Np, typename _Up, typename... _Args>
1522 enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1523 initializer_list<_Up>&, _Args...>,
1524 variant_alternative_t<_Np, variant>&>
1525 emplace(initializer_list<_Up> __il, _Args&&... __args)
1526 {
1527 static_assert(_Np < sizeof...(_Types),
1528 "The index must be in [0, number of alternatives)");
1529 using type = variant_alternative_t<_Np, variant>;
1530 // Provide the strong exception-safety guarantee when possible,
1531 // to avoid becoming valueless.
1532 if constexpr (is_nothrow_constructible_v<type,
1533 initializer_list<_Up>&,
1534 _Args...>)
1535 {
1536 this->_M_reset();
1537 __variant_construct_by_index<_Np>(*this, __il,
1538 std::forward<_Args>(__args)...);
1539 }
1540 else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1541 && _Traits::_S_move_assign)
1542 {
1543 // This construction might throw:
1544 variant __tmp(in_place_index<_Np>, __il,
1545 std::forward<_Args>(__args)...);
1546 // But _Never_valueless_alt<type> means this won't:
1547 *this = std::move(__tmp);
1548 }
1549 else
1550 {
1551 // This case only provides the basic exception-safety guarantee,
1552 // i.e. the variant can become valueless.
1553 this->_M_reset();
1554 __try
1555 {
1556 __variant_construct_by_index<_Np>(*this, __il,
1557 std::forward<_Args>(__args)...);
1558 }
1559 __catch (...)
1560 {
1561 this->_M_index = variant_npos;
1562 __throw_exception_again;
1563 }
1564 }
1565 return std::get<_Np>(*this);
1566 }
1567
1568 constexpr bool valueless_by_exception() const noexcept
1569 { return !this->_M_valid(); }
1570
1571 constexpr size_t index() const noexcept
1572 {
1573 using __index_type = typename _Base::__index_type;
1574 if constexpr (__detail::__variant::__never_valueless<_Types...>())
1575 return this->_M_index;
1576 else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
1577 return make_signed_t<__index_type>(this->_M_index);
1578 else
1579 return size_t(__index_type(this->_M_index + 1)) - 1;
1580 }
1581
1582 void
1583 swap(variant& __rhs)
1584 noexcept((__is_nothrow_swappable<_Types>::value && ...)
1585 && is_nothrow_move_constructible_v<variant>)
1586 {
1587 __detail::__variant::__raw_idx_visit(
1588 [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
1589 {
1590 if constexpr (__rhs_index != variant_npos)
1591 {
1592 if (this->index() == __rhs_index)
1593 {
1594 auto& __this_mem =
1595 std::get<__rhs_index>(*this);
1596 using std::swap;
1597 swap(__this_mem, __rhs_mem);
1598 }
1599 else
1600 {
1601 if (!this->valueless_by_exception()) [[__likely__]]
1602 {
1603 auto __tmp(std::move(__rhs_mem));
1604 __rhs = std::move(*this);
1605 this->_M_destructive_move(__rhs_index,
1606 std::move(__tmp));
1607 }
1608 else
1609 {
1610 this->_M_destructive_move(__rhs_index,
1611 std::move(__rhs_mem));
1612 __rhs._M_reset();
1613 }
1614 }
1615 }
1616 else
1617 {
1618 if (!this->valueless_by_exception()) [[__likely__]]
1619 {
1620 __rhs = std::move(*this);
1621 this->_M_reset();
1622 }
1623 }
1624 }, __rhs);
1625 }
1626
1627 private:
1628
1629#if defined(__clang__) && __clang_major__ <= 7
1630 public:
1631 using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1632 private:
1633#endif
1634
1635 template<size_t _Np, typename _Vp>
1636 friend constexpr decltype(auto)
1637 __detail::__variant::__get(_Vp&& __v) noexcept;
1638
1639 template<typename _Vp>
1640 friend void*
1641 __detail::__variant::__get_storage(_Vp&& __v) noexcept;
1642
1643#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1644 template<typename... _Tp> \
1645 friend constexpr bool \
1646 operator __OP(const variant<_Tp...>& __lhs, \
1647 const variant<_Tp...>& __rhs);
1648
1649 _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1650 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1651 _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1652 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1653 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1654 _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1655
1656#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1657 };
1658
1659 template<size_t _Np, typename... _Types>
1660 constexpr variant_alternative_t<_Np, variant<_Types...>>&
1661 get(variant<_Types...>& __v)
1662 {
1663 static_assert(_Np < sizeof...(_Types),
1664 "The index must be in [0, number of alternatives)");
1665 if (__v.index() != _Np)
1666 __throw_bad_variant_access(__v.valueless_by_exception());
1667 return __detail::__variant::__get<_Np>(__v);
1668 }
1669
1670 template<size_t _Np, typename... _Types>
1671 constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1672 get(variant<_Types...>&& __v)
1673 {
1674 static_assert(_Np < sizeof...(_Types),
1675 "The index must be in [0, number of alternatives)");
1676 if (__v.index() != _Np)
1677 __throw_bad_variant_access(__v.valueless_by_exception());
1678 return __detail::__variant::__get<_Np>(std::move(__v));
1679 }
1680
1681 template<size_t _Np, typename... _Types>
1682 constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1683 get(const variant<_Types...>& __v)
1684 {
1685 static_assert(_Np < sizeof...(_Types),
1686 "The index must be in [0, number of alternatives)");
1687 if (__v.index() != _Np)
1688 __throw_bad_variant_access(__v.valueless_by_exception());
1689 return __detail::__variant::__get<_Np>(__v);
1690 }
1691
1692 template<size_t _Np, typename... _Types>
1693 constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1694 get(const variant<_Types...>&& __v)
1695 {
1696 static_assert(_Np < sizeof...(_Types),
1697 "The index must be in [0, number of alternatives)");
1698 if (__v.index() != _Np)
1699 __throw_bad_variant_access(__v.valueless_by_exception());
1700 return __detail::__variant::__get<_Np>(std::move(__v));
1701 }
1702
1703 template<typename _Result_type, typename _Visitor, typename... _Variants>
1704 constexpr decltype(auto)
1705 __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1706 {
1707 constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1708 _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1709
1710 auto __func_ptr = __vtable._M_access(__variants.index()...);
1711 return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1712 std::forward<_Variants>(__variants)...);
1713 }
1714
1715 template<typename _Visitor, typename... _Variants>
1716 constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
1717 visit(_Visitor&& __visitor, _Variants&&... __variants)
1718 {
1719 if ((__variants.valueless_by_exception() || ...))
1720 __throw_bad_variant_access("std::visit: variant is valueless");
1721
1722 using _Result_type
1723 = __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
1724
1725 using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
1726
1727 return std::__do_visit<_Tag>(std::forward<_Visitor>(__visitor),
1728 std::forward<_Variants>(__variants)...);
1729 }
1730
1731#if __cplusplus > 201703L
1732 template<typename _Res, typename _Visitor, typename... _Variants>
1733 constexpr _Res
1734 visit(_Visitor&& __visitor, _Variants&&... __variants)
1735 {
1736 if ((__variants.valueless_by_exception() || ...))
1737 __throw_bad_variant_access("std::visit<R>: variant is valueless");
1738
1739 return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
1740 std::forward<_Variants>(__variants)...);
1741 }
1742#endif
1743
1744 template<bool, typename... _Types>
1745 struct __variant_hash_call_base_impl
1746 {
1747 size_t
1748 operator()(const variant<_Types...>& __t) const
1749 noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1750 {
1751 size_t __ret;
1752 __detail::__variant::__raw_visit(
1753 [&__t, &__ret](auto&& __t_mem) mutable
1754 {
1755 using _Type = __remove_cvref_t<decltype(__t_mem)>;
1756 if constexpr (!is_same_v<_Type,
1757 __detail::__variant::__variant_cookie>)
1758 __ret = std::hash<size_t>{}(__t.index())
1759 + std::hash<_Type>{}(__t_mem);
1760 else
1761 __ret = std::hash<size_t>{}(__t.index());
1762 }, __t);
1763 return __ret;
1764 }
1765 };
1766
1767 template<typename... _Types>
1768 struct __variant_hash_call_base_impl<false, _Types...> {};
1769
1770 template<typename... _Types>
1771 using __variant_hash_call_base =
1772 __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1773 __enable_hash_call &&...), _Types...>;
1774
1775 template<typename... _Types>
1776 struct hash<variant<_Types...>>
1777 : private __detail::__variant::_Variant_hash_base<
1778 variant<_Types...>, std::index_sequence_for<_Types...>>,
1779 public __variant_hash_call_base<_Types...>
1780 {
1781 using result_type [[__deprecated__]] = size_t;
1782 using argument_type [[__deprecated__]] = variant<_Types...>;
1783 };
1784
1785 template<>
1786 struct hash<monostate>
1787 {
1788 using result_type [[__deprecated__]] = size_t;
1789 using argument_type [[__deprecated__]] = monostate;
1790
1791 size_t
1792 operator()(const monostate&) const noexcept
1793 {
1794 constexpr size_t __magic_monostate_hash = -7777;
1795 return __magic_monostate_hash;
1796 }
1797 };
1798
1799 template<typename... _Types>
1800 struct __is_fast_hash<hash<variant<_Types...>>>
1801 : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1802 { };
1803
1804_GLIBCXX_END_NAMESPACE_VERSION
1805} // namespace std
1806
1807#endif // C++17
1808
1809#endif // _GLIBCXX_VARIANT