1// <variant> -*- C++ -*-
2
3// Copyright (C) 2016-2019 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
49namespace std _GLIBCXX_VISIBILITY(default)
50{
51_GLIBCXX_BEGIN_NAMESPACE_VERSION
52
53namespace __detail
54{
55namespace __variant
56{
57 template<size_t _Np, typename... _Types>
58 struct _Nth_type;
59
60 template<size_t _Np, typename _First, typename... _Rest>
61 struct _Nth_type<_Np, _First, _Rest...>
62 : _Nth_type<_Np-1, _Rest...> { };
63
64 template<typename _First, typename... _Rest>
65 struct _Nth_type<0, _First, _Rest...>
66 { using type = _First; };
67
68} // namespace __variant
69} // namespace __detail
70
71#define __cpp_lib_variant 201606L
72
73 template<typename... _Types> class tuple;
74 template<typename... _Types> class variant;
75 template <typename> struct hash;
76
77 template<typename _Variant>
78 struct variant_size;
79
80 template<typename _Variant>
81 struct variant_size<const _Variant> : variant_size<_Variant> {};
82
83 template<typename _Variant>
84 struct variant_size<volatile _Variant> : variant_size<_Variant> {};
85
86 template<typename _Variant>
87 struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
88
89 template<typename... _Types>
90 struct variant_size<variant<_Types...>>
91 : std::integral_constant<size_t, sizeof...(_Types)> {};
92
93 template<typename _Variant>
94 inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
95
96 template<size_t _Np, typename _Variant>
97 struct variant_alternative;
98
99 template<size_t _Np, typename _First, typename... _Rest>
100 struct variant_alternative<_Np, variant<_First, _Rest...>>
101 : variant_alternative<_Np-1, variant<_Rest...>> {};
102
103 template<typename _First, typename... _Rest>
104 struct variant_alternative<0, variant<_First, _Rest...>>
105 { using type = _First; };
106
107 template<size_t _Np, typename _Variant>
108 using variant_alternative_t =
109 typename variant_alternative<_Np, _Variant>::type;
110
111 template<size_t _Np, typename _Variant>
112 struct variant_alternative<_Np, const _Variant>
113 { using type = add_const_t<variant_alternative_t<_Np, _Variant>>; };
114
115 template<size_t _Np, typename _Variant>
116 struct variant_alternative<_Np, volatile _Variant>
117 { using type = add_volatile_t<variant_alternative_t<_Np, _Variant>>; };
118
119 template<size_t _Np, typename _Variant>
120 struct variant_alternative<_Np, const volatile _Variant>
121 { using type = add_cv_t<variant_alternative_t<_Np, _Variant>>; };
122
123 inline constexpr size_t variant_npos = -1;
124
125 template<size_t _Np, typename... _Types>
126 constexpr variant_alternative_t<_Np, variant<_Types...>>&
127 get(variant<_Types...>&);
128
129 template<size_t _Np, typename... _Types>
130 constexpr variant_alternative_t<_Np, variant<_Types...>>&&
131 get(variant<_Types...>&&);
132
133 template<size_t _Np, typename... _Types>
134 constexpr variant_alternative_t<_Np, variant<_Types...>> const&
135 get(const variant<_Types...>&);
136
137 template<size_t _Np, typename... _Types>
138 constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
139 get(const variant<_Types...>&&);
140
141 template<bool __use_index=false,
142 bool __same_return_types = true,
143 typename _Visitor, typename... _Variants>
144 constexpr decltype(auto)
145 __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
146
147 template <typename... _Types, typename _Tp>
148 decltype(auto)
149 __variant_cast(_Tp&& __rhs)
150 {
151 if constexpr (is_lvalue_reference_v<_Tp>)
152 {
153 if constexpr (is_const_v<remove_reference_t<_Tp>>)
154 return static_cast<const variant<_Types...>&>(__rhs);
155 else
156 return static_cast<variant<_Types...>&>(__rhs);
157 }
158 else
159 return static_cast<variant<_Types...>&&>(__rhs);
160 }
161
162namespace __detail
163{
164namespace __variant
165{
166 // Returns the first apparence of _Tp in _Types.
167 // Returns sizeof...(_Types) if _Tp is not in _Types.
168 template<typename _Tp, typename... _Types>
169 struct __index_of : std::integral_constant<size_t, 0> {};
170
171 template<typename _Tp, typename... _Types>
172 inline constexpr size_t __index_of_v = __index_of<_Tp, _Types...>::value;
173
174 template<typename _Tp, typename _First, typename... _Rest>
175 struct __index_of<_Tp, _First, _Rest...> :
176 std::integral_constant<size_t, is_same_v<_Tp, _First>
177 ? 0 : __index_of_v<_Tp, _Rest...> + 1> {};
178
179 // used for raw visitation
180 struct __variant_cookie {};
181 // used for raw visitation with indices passed in
182 struct __variant_idx_cookie { using type = __variant_idx_cookie; };
183 // a more explanatory name than 'true'
184 inline constexpr auto __visit_with_index = bool_constant<true>{};
185
186 // _Uninitialized<T> is guaranteed to be a literal type, even if T is not.
187 // We have to do this, because [basic.types]p10.5.3 (n4606) is not implemented
188 // yet. When it's implemented, _Uninitialized<T> can be changed to the alias
189 // to T, therefore equivalent to being removed entirely.
190 //
191 // Another reason we may not want to remove _Uninitialzied<T> may be that, we
192 // want _Uninitialized<T> to be trivially destructible, no matter whether T
193 // is; but we will see.
194 template<typename _Type, bool = std::is_literal_type_v<_Type>>
195 struct _Uninitialized;
196
197 template<typename _Type>
198 struct _Uninitialized<_Type, true>
199 {
200 template<typename... _Args>
201 constexpr
202 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
203 : _M_storage(std::forward<_Args>(__args)...)
204 { }
205
206 constexpr const _Type& _M_get() const & noexcept
207 { return _M_storage; }
208
209 constexpr _Type& _M_get() & noexcept
210 { return _M_storage; }
211
212 constexpr const _Type&& _M_get() const && noexcept
213 { return std::move(_M_storage); }
214
215 constexpr _Type&& _M_get() && noexcept
216 { return std::move(_M_storage); }
217
218 _Type _M_storage;
219 };
220
221 template<typename _Type>
222 struct _Uninitialized<_Type, false>
223 {
224 template<typename... _Args>
225 constexpr
226 _Uninitialized(in_place_index_t<0>, _Args&&... __args)
227 {
228 ::new ((void*)std::addressof(_M_storage))
229 _Type(std::forward<_Args>(__args)...);
230 }
231
232 const _Type& _M_get() const & noexcept
233 { return *_M_storage._M_ptr(); }
234
235 _Type& _M_get() & noexcept
236 { return *_M_storage._M_ptr(); }
237
238 const _Type&& _M_get() const && noexcept
239 { return std::move(*_M_storage._M_ptr()); }
240
241 _Type&& _M_get() && noexcept
242 { return std::move(*_M_storage._M_ptr()); }
243
244 __gnu_cxx::__aligned_membuf<_Type> _M_storage;
245 };
246
247 template<typename _Union>
248 constexpr decltype(auto)
249 __get(in_place_index_t<0>, _Union&& __u) noexcept
250 { return std::forward<_Union>(__u)._M_first._M_get(); }
251
252 template<size_t _Np, typename _Union>
253 constexpr decltype(auto)
254 __get(in_place_index_t<_Np>, _Union&& __u) noexcept
255 {
256 return __variant::__get(in_place_index<_Np-1>,
257 std::forward<_Union>(__u)._M_rest);
258 }
259
260 // Returns the typed storage for __v.
261 template<size_t _Np, typename _Variant>
262 constexpr decltype(auto)
263 __get(_Variant&& __v) noexcept
264 {
265 return __variant::__get(std::in_place_index<_Np>,
266 std::forward<_Variant>(__v)._M_u);
267 }
268
269 template<typename... _Types>
270 struct _Traits
271 {
272 static constexpr bool _S_default_ctor =
273 is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
274 static constexpr bool _S_copy_ctor =
275 (is_copy_constructible_v<_Types> && ...);
276 static constexpr bool _S_move_ctor =
277 (is_move_constructible_v<_Types> && ...);
278 static constexpr bool _S_copy_assign =
279 _S_copy_ctor
280 && (is_copy_assignable_v<_Types> && ...);
281 static constexpr bool _S_move_assign =
282 _S_move_ctor
283 && (is_move_assignable_v<_Types> && ...);
284
285 static constexpr bool _S_trivial_dtor =
286 (is_trivially_destructible_v<_Types> && ...);
287 static constexpr bool _S_trivial_copy_ctor =
288 (is_trivially_copy_constructible_v<_Types> && ...);
289 static constexpr bool _S_trivial_move_ctor =
290 (is_trivially_move_constructible_v<_Types> && ...);
291 static constexpr bool _S_trivial_copy_assign =
292 _S_trivial_dtor && _S_trivial_copy_ctor
293 && (is_trivially_copy_assignable_v<_Types> && ...);
294 static constexpr bool _S_trivial_move_assign =
295 _S_trivial_dtor && _S_trivial_move_ctor
296 && (is_trivially_move_assignable_v<_Types> && ...);
297
298 // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
299 // are always nothrow.
300 static constexpr bool _S_nothrow_default_ctor =
301 is_nothrow_default_constructible_v<
302 typename _Nth_type<0, _Types...>::type>;
303 static constexpr bool _S_nothrow_copy_ctor = false;
304 static constexpr bool _S_nothrow_move_ctor =
305 (is_nothrow_move_constructible_v<_Types> && ...);
306 static constexpr bool _S_nothrow_copy_assign = false;
307 static constexpr bool _S_nothrow_move_assign =
308 _S_nothrow_move_ctor
309 && (is_nothrow_move_assignable_v<_Types> && ...);
310 };
311
312 // Defines members and ctors.
313 template<typename... _Types>
314 union _Variadic_union { };
315
316 template<typename _First, typename... _Rest>
317 union _Variadic_union<_First, _Rest...>
318 {
319 constexpr _Variadic_union() : _M_rest() { }
320
321 template<typename... _Args>
322 constexpr _Variadic_union(in_place_index_t<0>, _Args&&... __args)
323 : _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
324 { }
325
326 template<size_t _Np, typename... _Args>
327 constexpr _Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
328 : _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
329 { }
330
331 _Uninitialized<_First> _M_first;
332 _Variadic_union<_Rest...> _M_rest;
333 };
334
335 // _Never_valueless_alt is true for variant alternatives that can
336 // always be placed in a variant without it becoming valueless.
337
338 // For suitably-small, trivially copyable types we can create temporaries
339 // on the stack and then memcpy them into place.
340 template<typename _Tp>
341 struct _Never_valueless_alt
342 : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
343 { };
344
345 // Specialize _Never_valueless_alt for other types which have a
346 // non-throwing and cheap move construction and move assignment operator,
347 // so that emplacing the type will provide the strong exception-safety
348 // guarantee, by creating and moving a temporary.
349 // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
350 // variant using that alternative, so we can't change the value later!
351
352 // True if every alternative in _Types... can be emplaced in a variant
353 // without it becoming valueless. If this is true, variant<_Types...>
354 // can never be valueless, which enables some minor optimizations.
355 template <typename... _Types>
356 constexpr bool __never_valueless()
357 {
358 return _Traits<_Types...>::_S_move_assign
359 && (_Never_valueless_alt<_Types>::value && ...);
360 }
361
362 // Defines index and the dtor, possibly trivial.
363 template<bool __trivially_destructible, typename... _Types>
364 struct _Variant_storage;
365
366 template <typename... _Types>
367 using __select_index =
368 typename __select_int::_Select_int_base<sizeof...(_Types),
369 unsigned char,
370 unsigned short>::type::value_type;
371
372 template<typename... _Types>
373 struct _Variant_storage<false, _Types...>
374 {
375 constexpr
376 _Variant_storage()
377 : _M_index(static_cast<__index_type>(variant_npos))
378 { }
379
380 template<size_t _Np, typename... _Args>
381 constexpr
382 _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
383 : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
384 _M_index{_Np}
385 { }
386
387 constexpr void _M_reset_impl()
388 {
389 __do_visit([](auto&& __this_mem) mutable
390 -> __detail::__variant::__variant_cookie
391 {
392 if constexpr (!is_same_v<remove_reference_t<decltype(__this_mem)>,
393 __variant_cookie>)
394 std::_Destroy(std::__addressof(__this_mem));
395 return {};
396 }, __variant_cast<_Types...>(*this));
397 }
398
399 void _M_reset()
400 {
401 _M_reset_impl();
402 _M_index = static_cast<__index_type>(variant_npos);
403 }
404
405 ~_Variant_storage()
406 { _M_reset(); }
407
408 void*
409 _M_storage() const
410 {
411 return const_cast<void*>(static_cast<const void*>(
412 std::addressof(_M_u)));
413 }
414
415 constexpr bool
416 _M_valid() const noexcept
417 {
418 if constexpr (__never_valueless<_Types...>())
419 return true;
420 return this->_M_index != __index_type(variant_npos);
421 }
422
423 _Variadic_union<_Types...> _M_u;
424 using __index_type = __select_index<_Types...>;
425 __index_type _M_index;
426 };
427
428 template<typename... _Types>
429 struct _Variant_storage<true, _Types...>
430 {
431 constexpr
432 _Variant_storage()
433 : _M_index(static_cast<__index_type>(variant_npos))
434 { }
435
436 template<size_t _Np, typename... _Args>
437 constexpr
438 _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
439 : _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
440 _M_index{_Np}
441 { }
442
443 void _M_reset()
444 { _M_index = static_cast<__index_type>(variant_npos); }
445
446 void*
447 _M_storage() const
448 {
449 return const_cast<void*>(static_cast<const void*>(
450 std::addressof(_M_u)));
451 }
452
453 constexpr bool
454 _M_valid() const noexcept
455 {
456 if constexpr (__never_valueless<_Types...>())
457 return true;
458 return this->_M_index != static_cast<__index_type>(variant_npos);
459 }
460
461 _Variadic_union<_Types...> _M_u;
462 using __index_type = __select_index<_Types...>;
463 __index_type _M_index;
464 };
465
466 template<typename... _Types>
467 using _Variant_storage_alias =
468 _Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
469
470 template<typename _Tp, typename _Up>
471 void __variant_construct_single(_Tp&& __lhs, _Up&& __rhs_mem)
472 {
473 void* __storage = std::addressof(__lhs._M_u);
474 using _Type = remove_reference_t<decltype(__rhs_mem)>;
475 if constexpr (!is_same_v<_Type, __variant_cookie>)
476 ::new (__storage)
477 _Type(std::forward<decltype(__rhs_mem)>(__rhs_mem));
478 }
479
480 template<typename... _Types, typename _Tp, typename _Up>
481 void __variant_construct(_Tp&& __lhs, _Up&& __rhs)
482 {
483 __lhs._M_index = __rhs._M_index;
484 __do_visit([&__lhs](auto&& __rhs_mem) mutable
485 -> __detail::__variant::__variant_cookie
486 {
487 __variant_construct_single(std::forward<_Tp>(__lhs),
488 std::forward<decltype(__rhs_mem)>(__rhs_mem));
489 return {};
490 }, __variant_cast<_Types...>(std::forward<_Up>(__rhs)));
491 }
492
493 // The following are (Copy|Move) (ctor|assign) layers for forwarding
494 // triviality and handling non-trivial SMF behaviors.
495
496 template<bool, typename... _Types>
497 struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
498 {
499 using _Base = _Variant_storage_alias<_Types...>;
500 using _Base::_Base;
501
502 _Copy_ctor_base(const _Copy_ctor_base& __rhs)
503 noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
504 {
505 __variant_construct<_Types...>(*this, __rhs);
506 }
507
508 _Copy_ctor_base(_Copy_ctor_base&&) = default;
509 _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
510 _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
511 };
512
513 template<typename... _Types>
514 struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
515 {
516 using _Base = _Variant_storage_alias<_Types...>;
517 using _Base::_Base;
518 };
519
520 template<typename... _Types>
521 using _Copy_ctor_alias =
522 _Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
523
524 template<bool, typename... _Types>
525 struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
526 {
527 using _Base = _Copy_ctor_alias<_Types...>;
528 using _Base::_Base;
529
530 _Move_ctor_base(_Move_ctor_base&& __rhs)
531 noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
532 {
533 __variant_construct<_Types...>(*this, std::move(__rhs));
534 }
535
536 template<typename _Up>
537 void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
538 {
539 this->_M_reset();
540 __variant_construct_single(*this, std::forward<_Up>(__rhs));
541 this->_M_index = __rhs_index;
542 }
543
544 template<typename _Up>
545 void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
546 {
547 this->_M_reset();
548 __variant_construct_single(*this, __rhs);
549 this->_M_index = __rhs_index;
550 }
551
552 _Move_ctor_base(const _Move_ctor_base&) = default;
553 _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
554 _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
555 };
556
557 template<typename... _Types>
558 struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
559 {
560 using _Base = _Copy_ctor_alias<_Types...>;
561 using _Base::_Base;
562
563 template<typename _Up>
564 void _M_destructive_move(unsigned short __rhs_index, _Up&& __rhs)
565 {
566 this->_M_reset();
567 __variant_construct_single(*this, std::forward<_Up>(__rhs));
568 this->_M_index = __rhs_index;
569 }
570
571 template<typename _Up>
572 void _M_destructive_copy(unsigned short __rhs_index, const _Up& __rhs)
573 {
574 this->_M_reset();
575 __variant_construct_single(*this, __rhs);
576 this->_M_index = __rhs_index;
577 }
578 };
579
580 template<typename... _Types>
581 using _Move_ctor_alias =
582 _Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
583
584 template<bool, typename... _Types>
585 struct _Copy_assign_base : _Move_ctor_alias<_Types...>
586 {
587 using _Base = _Move_ctor_alias<_Types...>;
588 using _Base::_Base;
589
590 _Copy_assign_base&
591 operator=(const _Copy_assign_base& __rhs)
592 noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
593 {
594 __do_visit<__visit_with_index>([this](auto&& __rhs_mem,
595 auto __rhs_index) mutable
596 -> __detail::__variant::__variant_idx_cookie
597 {
598 if constexpr (__rhs_index != variant_npos)
599 {
600 if (this->_M_index == __rhs_index)
601 __variant::__get<__rhs_index>(*this) = __rhs_mem;
602 else
603 {
604 using __rhs_type = __remove_cvref_t<decltype(__rhs_mem)>;
605 if constexpr (is_nothrow_copy_constructible_v<__rhs_type>
606 || !is_nothrow_move_constructible_v<__rhs_type>)
607 // The standard says this->emplace<__rhs_type>(__rhs_mem)
608 // should be used here, but _M_destructive_copy is
609 // equivalent in this case. Either copy construction
610 // doesn't throw, so _M_destructive_copy gives strong
611 // exception safety guarantee, or both copy construction
612 // and move construction can throw, so emplace only gives
613 // basic exception safety anyway.
614 this->_M_destructive_copy(__rhs_index, __rhs_mem);
615 else
616 __variant_cast<_Types...>(*this)
617 = variant<_Types...>(std::in_place_index<__rhs_index>,
618 __rhs_mem);
619 }
620 }
621 else
622 this->_M_reset();
623 return {};
624 }, __variant_cast<_Types...>(__rhs));
625 return *this;
626 }
627
628 _Copy_assign_base(const _Copy_assign_base&) = default;
629 _Copy_assign_base(_Copy_assign_base&&) = default;
630 _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
631 };
632
633 template<typename... _Types>
634 struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
635 {
636 using _Base = _Move_ctor_alias<_Types...>;
637 using _Base::_Base;
638 };
639
640 template<typename... _Types>
641 using _Copy_assign_alias =
642 _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
643
644 template<bool, typename... _Types>
645 struct _Move_assign_base : _Copy_assign_alias<_Types...>
646 {
647 using _Base = _Copy_assign_alias<_Types...>;
648 using _Base::_Base;
649
650 _Move_assign_base&
651 operator=(_Move_assign_base&& __rhs)
652 noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
653 {
654 __do_visit<__visit_with_index>([this](auto&& __rhs_mem,
655 auto __rhs_index) mutable
656 -> __detail::__variant::__variant_idx_cookie
657 {
658 if constexpr (__rhs_index != variant_npos)
659 {
660 if (this->_M_index == __rhs_index)
661 __variant::__get<__rhs_index>(*this) = std::move(__rhs_mem);
662 else
663 __variant_cast<_Types...>(*this)
664 .template emplace<__rhs_index>(std::move(__rhs_mem));
665 }
666 else
667 this->_M_reset();
668 return {};
669 }, __variant_cast<_Types...>(__rhs));
670 return *this;
671 }
672
673 _Move_assign_base(const _Move_assign_base&) = default;
674 _Move_assign_base(_Move_assign_base&&) = default;
675 _Move_assign_base& operator=(const _Move_assign_base&) = default;
676 };
677
678 template<typename... _Types>
679 struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
680 {
681 using _Base = _Copy_assign_alias<_Types...>;
682 using _Base::_Base;
683 };
684
685 template<typename... _Types>
686 using _Move_assign_alias =
687 _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
688
689 template<typename... _Types>
690 struct _Variant_base : _Move_assign_alias<_Types...>
691 {
692 using _Base = _Move_assign_alias<_Types...>;
693
694 constexpr
695 _Variant_base()
696 noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
697 : _Variant_base(in_place_index<0>) { }
698
699 template<size_t _Np, typename... _Args>
700 constexpr explicit
701 _Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
702 : _Base(__i, std::forward<_Args>(__args)...)
703 { }
704
705 _Variant_base(const _Variant_base&) = default;
706 _Variant_base(_Variant_base&&) = default;
707 _Variant_base& operator=(const _Variant_base&) = default;
708 _Variant_base& operator=(_Variant_base&&) = default;
709 };
710
711 // For how many times does _Tp appear in _Tuple?
712 template<typename _Tp, typename _Tuple>
713 struct __tuple_count;
714
715 template<typename _Tp, typename _Tuple>
716 inline constexpr size_t __tuple_count_v =
717 __tuple_count<_Tp, _Tuple>::value;
718
719 template<typename _Tp, typename... _Types>
720 struct __tuple_count<_Tp, tuple<_Types...>>
721 : integral_constant<size_t, 0> { };
722
723 template<typename _Tp, typename _First, typename... _Rest>
724 struct __tuple_count<_Tp, tuple<_First, _Rest...>>
725 : integral_constant<
726 size_t,
727 __tuple_count_v<_Tp, tuple<_Rest...>> + is_same_v<_Tp, _First>> { };
728
729 // TODO: Reuse this in <tuple> ?
730 template<typename _Tp, typename... _Types>
731 inline constexpr bool __exactly_once =
732 __tuple_count_v<_Tp, tuple<_Types...>> == 1;
733
734 // Takes _Types and create an overloaded _S_fun for each type.
735 // If a type appears more than once in _Types, create only one overload.
736 template<typename... _Types>
737 struct __overload_set
738 { static void _S_fun(); };
739
740 template<typename _First, typename... _Rest>
741 struct __overload_set<_First, _Rest...> : __overload_set<_Rest...>
742 {
743 using __overload_set<_Rest...>::_S_fun;
744 static integral_constant<size_t, sizeof...(_Rest)> _S_fun(_First);
745 };
746
747 template<typename... _Rest>
748 struct __overload_set<void, _Rest...> : __overload_set<_Rest...>
749 {
750 using __overload_set<_Rest...>::_S_fun;
751 };
752
753 // Helper for variant(_Tp&&) and variant::operator=(_Tp&&).
754 // __accepted_index maps an arbitrary _Tp to an alternative type in _Variant
755 // (or to variant_npos).
756 template<typename _Tp, typename _Variant, typename = void>
757 struct __accepted_index
758 { static constexpr size_t value = variant_npos; };
759
760 template<typename _Tp, typename... _Types>
761 struct __accepted_index<
762 _Tp, variant<_Types...>,
763 void_t<decltype(__overload_set<_Types...>::_S_fun(std::declval<_Tp>()))>>
764 {
765 static constexpr size_t value = sizeof...(_Types) - 1
766 - decltype(__overload_set<_Types...>::
767 _S_fun(std::declval<_Tp>()))::value;
768 };
769
770 // Returns the raw storage for __v.
771 template<typename _Variant>
772 void* __get_storage(_Variant&& __v)
773 { return __v._M_storage(); }
774
775 template <typename _Maybe_variant_cookie, typename _Variant>
776 struct _Extra_visit_slot_needed
777 {
778 template <typename> struct _Variant_never_valueless;
779
780 template <typename... _Types>
781 struct _Variant_never_valueless<variant<_Types...>>
782 : bool_constant<__never_valueless<_Types...>()> {};
783
784 static constexpr bool value =
785 (is_same_v<_Maybe_variant_cookie, __variant_cookie>
786 || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
787 && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
788 };
789
790 // Used for storing a multi-dimensional vtable.
791 template<typename _Tp, size_t... _Dimensions>
792 struct _Multi_array;
793
794 // Partial specialization with rank zero, stores a single _Tp element.
795 template<typename _Tp>
796 struct _Multi_array<_Tp>
797 {
798 constexpr const _Tp&
799 _M_access() const
800 { return _M_data; }
801
802 _Tp _M_data;
803 };
804
805 // Partial specialization with rank >= 1.
806 template<typename _Ret,
807 typename _Visitor,
808 typename... _Variants,
809 size_t __first, size_t... __rest>
810 struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
811 {
812 static constexpr size_t __index =
813 sizeof...(_Variants) - sizeof...(__rest) - 1;
814
815 using _Variant = typename _Nth_type<__index, _Variants...>::type;
816
817 static constexpr int __do_cookie =
818 _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
819
820 using _Tp = _Ret(*)(_Visitor, _Variants...);
821
822 template<typename... _Args>
823 constexpr const _Tp&
824 _M_access(size_t __first_index, _Args... __rest_indices) const
825 {
826 return _M_arr[__first_index + __do_cookie]
827 ._M_access(__rest_indices...);
828 }
829
830 _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
831 };
832
833 // Creates a multi-dimensional vtable recursively.
834 //
835 // The __same_return_types non-type template parameter specifies whether
836 // to enforce that all visitor invocations return the same type. This is
837 // required by std::visit but not std::visit<R>.
838 //
839 // For example,
840 // visit([](auto, auto){},
841 // variant<int, char>(), // typedef'ed as V1
842 // variant<float, double, long double>()) // typedef'ed as V2
843 // will trigger instantiations of:
844 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&), 2, 3>,
845 // tuple<V1&&, V2&&>, std::index_sequence<>>
846 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&), 3>,
847 // tuple<V1&&, V2&&>, std::index_sequence<0>>
848 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&)>,
849 // tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
850 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&)>,
851 // tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
852 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&)>,
853 // tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
854 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&), 3>,
855 // tuple<V1&&, V2&&>, std::index_sequence<1>>
856 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&)>,
857 // tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
858 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&)>,
859 // tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
860 // __gen_vtable_impl<true, _Multi_array<void(*)(V1&&, V2&&)>,
861 // tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
862 // The returned multi-dimensional vtable can be fast accessed by the visitor
863 // using index calculation.
864 template<bool __same_return_types,
865 typename _Array_type, typename _Variant_tuple, typename _Index_seq>
866 struct __gen_vtable_impl;
867
868 // Defines the _S_apply() member that returns a _Multi_array populated
869 // with function pointers that perform the visitation expressions e(m)
870 // for each valid pack of indexes into the variant types _Variants.
871 //
872 // This partial specialization builds up the index sequences by recursively
873 // calling _S_apply() on the next specialization of __gen_vtable_impl.
874 // The base case of the recursion defines the actual function pointers.
875 template<bool __same_return_types,
876 typename _Result_type, typename _Visitor, size_t... __dimensions,
877 typename... _Variants, size_t... __indices>
878 struct __gen_vtable_impl<
879 __same_return_types,
880 _Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
881 tuple<_Variants...>, std::index_sequence<__indices...>>
882 {
883 using _Next =
884 remove_reference_t<typename _Nth_type<sizeof...(__indices),
885 _Variants...>::type>;
886 using _Array_type =
887 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
888 __dimensions...>;
889
890 static constexpr _Array_type
891 _S_apply()
892 {
893 _Array_type __vtable{};
894 _S_apply_all_alts(
895 __vtable, make_index_sequence<variant_size_v<_Next>>());
896 return __vtable;
897 }
898
899 template<size_t... __var_indices>
900 static constexpr void
901 _S_apply_all_alts(_Array_type& __vtable,
902 std::index_sequence<__var_indices...>)
903 {
904 if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
905 (_S_apply_single_alt<true, __var_indices>(
906 __vtable._M_arr[__var_indices + 1],
907 &(__vtable._M_arr[0])), ...);
908 else
909 (_S_apply_single_alt<false, __var_indices>(
910 __vtable._M_arr[__var_indices]), ...);
911 }
912
913 template<bool __do_cookie, size_t __index, typename _Tp>
914 static constexpr void
915 _S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
916 {
917 using _Alternative = variant_alternative_t<__index, _Next>;
918 if constexpr (__do_cookie)
919 {
920 __element = __gen_vtable_impl<
921 __same_return_types,
922 _Tp,
923 tuple<_Variants...>,
924 std::index_sequence<__indices..., __index>>::_S_apply();
925 *__cookie_element = __gen_vtable_impl<
926 __same_return_types,
927 _Tp,
928 tuple<_Variants...>,
929 std::index_sequence<__indices..., variant_npos>>::_S_apply();
930 }
931 else
932 {
933 __element = __gen_vtable_impl<
934 __same_return_types,
935 remove_reference_t<decltype(__element)>, tuple<_Variants...>,
936 std::index_sequence<__indices..., __index>>::_S_apply();
937 }
938 }
939 };
940
941 // This partial specialization is the base case for the recursion.
942 // It populates a _Multi_array element with the address of a function
943 // that invokes the visitor with the alternatives specified by __indices.
944 template<bool __same_return_types,
945 typename _Result_type, typename _Visitor, typename... _Variants,
946 size_t... __indices>
947 struct __gen_vtable_impl<
948 __same_return_types,
949 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
950 tuple<_Variants...>, std::index_sequence<__indices...>>
951 {
952 using _Array_type =
953 _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
954
955 template<size_t __index, typename _Variant>
956 static constexpr decltype(auto)
957 __element_by_index_or_cookie(_Variant&& __var) noexcept
958 {
959 if constexpr (__index != variant_npos)
960 return __variant::__get<__index>(std::forward<_Variant>(__var));
961 else
962 return __variant_cookie{};
963 }
964
965 static constexpr decltype(auto)
966 __visit_invoke_impl(_Visitor&& __visitor, _Variants... __vars)
967 {
968 // For raw visitation using indices, pass the indices to the visitor:
969 if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
970 return std::__invoke(std::forward<_Visitor>(__visitor),
971 __element_by_index_or_cookie<__indices>(
972 std::forward<_Variants>(__vars))...,
973 integral_constant<size_t, __indices>()...);
974 // For std::visit<cv void>, cast the result to void:
975 else if constexpr (!__same_return_types &&
976 std::is_void_v<_Result_type>)
977 return (void)std::__invoke(std::forward<_Visitor>(__visitor),
978 __element_by_index_or_cookie<__indices>(
979 std::forward<_Variants>(__vars))...);
980 else
981 return std::__invoke(std::forward<_Visitor>(__visitor),
982 __element_by_index_or_cookie<__indices>(
983 std::forward<_Variants>(__vars))...);
984 }
985
986 static constexpr decltype(auto)
987 __do_visit_invoke(_Visitor&& __visitor, _Variants... __vars)
988 {
989 return __visit_invoke_impl(visitor: std::forward<_Visitor>(__visitor),
990 vars: std::forward<_Variants>(__vars)...);
991 }
992
993 // Perform the implicit conversion to _Result_type for std::visit<R>.
994 static constexpr _Result_type
995 __do_visit_invoke_r(_Visitor&& __visitor, _Variants... __vars)
996 {
997 return __visit_invoke_impl(visitor: std::forward<_Visitor>(__visitor),
998 vars: std::forward<_Variants>(__vars)...);
999 }
1000
1001 static constexpr decltype(auto)
1002 __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
1003 {
1004 if constexpr (__same_return_types)
1005 return __do_visit_invoke(visitor: std::forward<_Visitor>(__visitor),
1006 vars: std::forward<_Variants>(__vars)...);
1007 else
1008 return __do_visit_invoke_r(visitor: std::forward<_Visitor>(__visitor),
1009 vars: std::forward<_Variants>(__vars)...);
1010 }
1011
1012 static constexpr auto
1013 _S_apply()
1014 { return _Array_type{&__visit_invoke}; }
1015 };
1016
1017 template<bool __same_return_types,
1018 typename _Result_type, typename _Visitor, typename... _Variants>
1019 struct __gen_vtable
1020 {
1021 using _Array_type =
1022 _Multi_array<_Result_type (*)(_Visitor, _Variants...),
1023 variant_size_v<remove_reference_t<_Variants>>...>;
1024
1025 static constexpr _Array_type _S_vtable
1026 = __gen_vtable_impl<__same_return_types,
1027 _Array_type, tuple<_Variants...>,
1028 std::index_sequence<>>::_S_apply();
1029 };
1030
1031 template<size_t _Np, typename _Tp>
1032 struct _Base_dedup : public _Tp { };
1033
1034 template<typename _Variant, typename __indices>
1035 struct _Variant_hash_base;
1036
1037 template<typename... _Types, size_t... __indices>
1038 struct _Variant_hash_base<variant<_Types...>,
1039 std::index_sequence<__indices...>>
1040 : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
1041
1042} // namespace __variant
1043} // namespace __detail
1044
1045 template<size_t _Np, typename _Variant, typename... _Args>
1046 void __variant_construct_by_index(_Variant& __v, _Args&&... __args)
1047 {
1048 __v._M_index = _Np;
1049 auto&& __storage = __detail::__variant::__get<_Np>(__v);
1050 ::new ((void*)std::addressof(__storage))
1051 remove_reference_t<decltype(__storage)>
1052 (std::forward<_Args>(__args)...);
1053 }
1054
1055 template<typename _Tp, typename... _Types>
1056 constexpr bool
1057 holds_alternative(const variant<_Types...>& __v) noexcept
1058 {
1059 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1060 "T should occur for exactly once in alternatives");
1061 return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
1062 }
1063
1064 template<typename _Tp, typename... _Types>
1065 constexpr _Tp& get(variant<_Types...>& __v)
1066 {
1067 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1068 "T should occur for exactly once in alternatives");
1069 static_assert(!is_void_v<_Tp>, "_Tp should not be void");
1070 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1071 }
1072
1073 template<typename _Tp, typename... _Types>
1074 constexpr _Tp&& get(variant<_Types...>&& __v)
1075 {
1076 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1077 "T should occur for exactly once in alternatives");
1078 static_assert(!is_void_v<_Tp>, "_Tp should not be void");
1079 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1080 std::move(__v));
1081 }
1082
1083 template<typename _Tp, typename... _Types>
1084 constexpr const _Tp& get(const variant<_Types...>& __v)
1085 {
1086 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1087 "T should occur for exactly once in alternatives");
1088 static_assert(!is_void_v<_Tp>, "_Tp should not be void");
1089 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
1090 }
1091
1092 template<typename _Tp, typename... _Types>
1093 constexpr const _Tp&& get(const variant<_Types...>&& __v)
1094 {
1095 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1096 "T should occur for exactly once in alternatives");
1097 static_assert(!is_void_v<_Tp>, "_Tp should not be void");
1098 return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1099 std::move(__v));
1100 }
1101
1102 template<size_t _Np, typename... _Types>
1103 constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
1104 get_if(variant<_Types...>* __ptr) noexcept
1105 {
1106 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1107 static_assert(_Np < sizeof...(_Types),
1108 "The index should be in [0, number of alternatives)");
1109 static_assert(!is_void_v<_Alternative_type>, "_Tp should not be void");
1110 if (__ptr && __ptr->index() == _Np)
1111 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1112 return nullptr;
1113 }
1114
1115 template<size_t _Np, typename... _Types>
1116 constexpr
1117 add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
1118 get_if(const variant<_Types...>* __ptr) noexcept
1119 {
1120 using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
1121 static_assert(_Np < sizeof...(_Types),
1122 "The index should be in [0, number of alternatives)");
1123 static_assert(!is_void_v<_Alternative_type>, "_Tp should not be void");
1124 if (__ptr && __ptr->index() == _Np)
1125 return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
1126 return nullptr;
1127 }
1128
1129 template<typename _Tp, typename... _Types>
1130 constexpr add_pointer_t<_Tp>
1131 get_if(variant<_Types...>* __ptr) noexcept
1132 {
1133 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1134 "T should occur for exactly once in alternatives");
1135 static_assert(!is_void_v<_Tp>, "_Tp should not be void");
1136 return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1137 __ptr);
1138 }
1139
1140 template<typename _Tp, typename... _Types>
1141 constexpr add_pointer_t<const _Tp>
1142 get_if(const variant<_Types...>* __ptr) noexcept
1143 {
1144 static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
1145 "T should occur for exactly once in alternatives");
1146 static_assert(!is_void_v<_Tp>, "_Tp should not be void");
1147 return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
1148 __ptr);
1149 }
1150
1151 struct monostate { };
1152
1153#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
1154 template<typename... _Types> \
1155 constexpr bool operator __OP(const variant<_Types...>& __lhs, \
1156 const variant<_Types...>& __rhs) \
1157 { \
1158 bool __ret = true; \
1159 __do_visit<__detail::__variant::__visit_with_index>( \
1160 [&__ret, &__lhs] \
1161 (auto&& __rhs_mem, auto __rhs_index) mutable \
1162 -> __detail::__variant::__variant_idx_cookie \
1163 { \
1164 if constexpr (__rhs_index != variant_npos) \
1165 { \
1166 if (__lhs.index() == __rhs_index) \
1167 { \
1168 auto& __this_mem = std::get<__rhs_index>(__lhs); \
1169 __ret = __this_mem __OP __rhs_mem; \
1170 } \
1171 else \
1172 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1173 } \
1174 else \
1175 __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
1176 return {}; \
1177 }, __rhs); \
1178 return __ret; \
1179 } \
1180\
1181 constexpr bool operator __OP(monostate, monostate) noexcept \
1182 { return 0 __OP 0; }
1183
1184 _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
1185 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
1186 _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
1187 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
1188 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
1189 _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
1190
1191#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1192
1193 template<typename _Visitor, typename... _Variants>
1194 constexpr decltype(auto) visit(_Visitor&&, _Variants&&...);
1195
1196 template<typename... _Types>
1197 inline enable_if_t<(is_move_constructible_v<_Types> && ...)
1198 && (is_swappable_v<_Types> && ...)>
1199 swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
1200 noexcept(noexcept(__lhs.swap(__rhs)))
1201 { __lhs.swap(__rhs); }
1202
1203 template<typename... _Types>
1204 enable_if_t<!((is_move_constructible_v<_Types> && ...)
1205 && (is_swappable_v<_Types> && ...))>
1206 swap(variant<_Types...>&, variant<_Types...>&) = delete;
1207
1208 class bad_variant_access : public exception
1209 {
1210 public:
1211 bad_variant_access() noexcept : _M_reason("Unknown reason") { }
1212 const char* what() const noexcept override
1213 { return _M_reason; }
1214
1215 private:
1216 bad_variant_access(const char* __reason) : _M_reason(__reason) { }
1217
1218 const char* _M_reason;
1219
1220 friend void __throw_bad_variant_access(const char* __what);
1221 };
1222
1223 inline void
1224 __throw_bad_variant_access(const char* __what)
1225 { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
1226
1227 template<typename... _Types>
1228 class variant
1229 : private __detail::__variant::_Variant_base<_Types...>,
1230 private _Enable_default_constructor<
1231 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1232 variant<_Types...>>,
1233 private _Enable_copy_move<
1234 __detail::__variant::_Traits<_Types...>::_S_copy_ctor,
1235 __detail::__variant::_Traits<_Types...>::_S_copy_assign,
1236 __detail::__variant::_Traits<_Types...>::_S_move_ctor,
1237 __detail::__variant::_Traits<_Types...>::_S_move_assign,
1238 variant<_Types...>>
1239 {
1240 private:
1241 template <typename... _UTypes, typename _Tp>
1242 friend decltype(auto) __variant_cast(_Tp&&);
1243 template<size_t _Np, typename _Variant, typename... _Args>
1244 friend void __variant_construct_by_index(_Variant& __v,
1245 _Args&&... __args);
1246
1247 static_assert(sizeof...(_Types) > 0,
1248 "variant must have at least one alternative");
1249 static_assert(!(std::is_reference_v<_Types> || ...),
1250 "variant must have no reference alternative");
1251 static_assert(!(std::is_void_v<_Types> || ...),
1252 "variant must have no void alternative");
1253
1254 using _Base = __detail::__variant::_Variant_base<_Types...>;
1255 using _Default_ctor_enabler =
1256 _Enable_default_constructor<
1257 __detail::__variant::_Traits<_Types...>::_S_default_ctor,
1258 variant<_Types...>>;
1259
1260 template<typename _Tp>
1261 static constexpr bool __not_self
1262 = !is_same_v<__remove_cvref_t<_Tp>, variant>;
1263
1264 template<typename _Tp>
1265 static constexpr bool
1266 __exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
1267
1268 template<typename _Tp>
1269 static constexpr size_t __accepted_index =
1270 __detail::__variant::__accepted_index<_Tp&&, variant>::value;
1271
1272 template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
1273 using __to_type = variant_alternative_t<_Np, variant>;
1274
1275 template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
1276 using __accepted_type = __to_type<__accepted_index<_Tp>>;
1277
1278 template<typename _Tp>
1279 static constexpr size_t __index_of =
1280 __detail::__variant::__index_of_v<_Tp, _Types...>;
1281
1282 using _Traits = __detail::__variant::_Traits<_Types...>;
1283
1284 template<typename _Tp>
1285 struct __is_in_place_tag : false_type { };
1286 template<typename _Tp>
1287 struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
1288 template<size_t _Np>
1289 struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
1290
1291 template<typename _Tp>
1292 static constexpr bool __not_in_place_tag
1293 = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
1294
1295 public:
1296 variant() = default;
1297 variant(const variant& __rhs) = default;
1298 variant(variant&&) = default;
1299 variant& operator=(const variant&) = default;
1300 variant& operator=(variant&&) = default;
1301 ~variant() = default;
1302
1303 template<typename _Tp,
1304 typename = enable_if_t<sizeof...(_Types) != 0>,
1305 typename = enable_if_t<__not_in_place_tag<_Tp>>,
1306 typename _Tj = __accepted_type<_Tp&&>,
1307 typename = enable_if_t<__exactly_once<_Tj>
1308 && is_constructible_v<_Tj, _Tp>>>
1309 constexpr
1310 variant(_Tp&& __t)
1311 noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
1312 : variant(in_place_index<__accepted_index<_Tp&&>>,
1313 std::forward<_Tp>(__t))
1314 { }
1315
1316 template<typename _Tp, typename... _Args,
1317 typename = enable_if_t<__exactly_once<_Tp>
1318 && is_constructible_v<_Tp, _Args...>>>
1319 constexpr explicit
1320 variant(in_place_type_t<_Tp>, _Args&&... __args)
1321 : variant(in_place_index<__index_of<_Tp>>,
1322 std::forward<_Args>(__args)...)
1323 { }
1324
1325 template<typename _Tp, typename _Up, typename... _Args,
1326 typename = enable_if_t<__exactly_once<_Tp>
1327 && is_constructible_v<_Tp,
1328 initializer_list<_Up>&, _Args...>>>
1329 constexpr explicit
1330 variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
1331 _Args&&... __args)
1332 : variant(in_place_index<__index_of<_Tp>>, __il,
1333 std::forward<_Args>(__args)...)
1334 { }
1335
1336 template<size_t _Np, typename... _Args,
1337 typename _Tp = __to_type<_Np>,
1338 typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
1339 constexpr explicit
1340 variant(in_place_index_t<_Np>, _Args&&... __args)
1341 : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
1342 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1343 { }
1344
1345 template<size_t _Np, typename _Up, typename... _Args,
1346 typename _Tp = __to_type<_Np>,
1347 typename = enable_if_t<is_constructible_v<_Tp,
1348 initializer_list<_Up>&,
1349 _Args...>>>
1350 constexpr explicit
1351 variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
1352 _Args&&... __args)
1353 : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
1354 _Default_ctor_enabler(_Enable_default_constructor_tag{})
1355 { }
1356
1357 template<typename _Tp>
1358 enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
1359 && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
1360 && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
1361 variant&>
1362 operator=(_Tp&& __rhs)
1363 noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
1364 && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
1365 {
1366 constexpr auto __index = __accepted_index<_Tp&&>;
1367 if (index() == __index)
1368 std::get<__index>(*this) = std::forward<_Tp>(__rhs);
1369 else
1370 {
1371 using _Tj = __accepted_type<_Tp&&>;
1372 if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
1373 || !is_nothrow_move_constructible_v<_Tj>)
1374 this->emplace<__index>(std::forward<_Tp>(__rhs));
1375 else
1376 operator=(variant(std::forward<_Tp>(__rhs)));
1377 }
1378 return *this;
1379 }
1380
1381 template<typename _Tp, typename... _Args>
1382 enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
1383 _Tp&>
1384 emplace(_Args&&... __args)
1385 {
1386 constexpr size_t __index = __index_of<_Tp>;
1387 return this->emplace<__index>(std::forward<_Args>(__args)...);
1388 }
1389
1390 template<typename _Tp, typename _Up, typename... _Args>
1391 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
1392 && __exactly_once<_Tp>,
1393 _Tp&>
1394 emplace(initializer_list<_Up> __il, _Args&&... __args)
1395 {
1396 constexpr size_t __index = __index_of<_Tp>;
1397 return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
1398 }
1399
1400 template<size_t _Np, typename... _Args>
1401 enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1402 _Args...>,
1403 variant_alternative_t<_Np, variant>&>
1404 emplace(_Args&&... __args)
1405 {
1406 static_assert(_Np < sizeof...(_Types),
1407 "The index should be in [0, number of alternatives)");
1408 using type = variant_alternative_t<_Np, variant>;
1409 // Provide the strong exception-safety guarantee when possible,
1410 // to avoid becoming valueless.
1411 if constexpr (is_nothrow_constructible_v<type, _Args...>)
1412 {
1413 this->_M_reset();
1414 __variant_construct_by_index<_Np>(*this,
1415 std::forward<_Args>(__args)...);
1416 }
1417 else if constexpr (is_scalar_v<type>)
1418 {
1419 // This might invoke a potentially-throwing conversion operator:
1420 const type __tmp(std::forward<_Args>(__args)...);
1421 // But these steps won't throw:
1422 this->_M_reset();
1423 __variant_construct_by_index<_Np>(*this, __tmp);
1424 }
1425 else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1426 && _Traits::_S_move_assign)
1427 {
1428 // This construction might throw:
1429 variant __tmp(in_place_index<_Np>,
1430 std::forward<_Args>(__args)...);
1431 // But _Never_valueless_alt<type> means this won't:
1432 *this = std::move(__tmp);
1433 }
1434 else
1435 {
1436 // This case only provides the basic exception-safety guarantee,
1437 // i.e. the variant can become valueless.
1438 this->_M_reset();
1439 __try
1440 {
1441 __variant_construct_by_index<_Np>(*this,
1442 std::forward<_Args>(__args)...);
1443 }
1444 __catch (...)
1445 {
1446 this->_M_index = variant_npos;
1447 __throw_exception_again;
1448 }
1449 }
1450 return std::get<_Np>(*this);
1451 }
1452
1453 template<size_t _Np, typename _Up, typename... _Args>
1454 enable_if_t<is_constructible_v<variant_alternative_t<_Np, variant>,
1455 initializer_list<_Up>&, _Args...>,
1456 variant_alternative_t<_Np, variant>&>
1457 emplace(initializer_list<_Up> __il, _Args&&... __args)
1458 {
1459 static_assert(_Np < sizeof...(_Types),
1460 "The index should be in [0, number of alternatives)");
1461 using type = variant_alternative_t<_Np, variant>;
1462 // Provide the strong exception-safety guarantee when possible,
1463 // to avoid becoming valueless.
1464 if constexpr (is_nothrow_constructible_v<type,
1465 initializer_list<_Up>&,
1466 _Args...>)
1467 {
1468 this->_M_reset();
1469 __variant_construct_by_index<_Np>(*this, __il,
1470 std::forward<_Args>(__args)...);
1471 }
1472 else if constexpr (__detail::__variant::_Never_valueless_alt<type>()
1473 && _Traits::_S_move_assign)
1474 {
1475 // This construction might throw:
1476 variant __tmp(in_place_index<_Np>, __il,
1477 std::forward<_Args>(__args)...);
1478 // But _Never_valueless_alt<type> means this won't:
1479 *this = std::move(__tmp);
1480 }
1481 else
1482 {
1483 // This case only provides the basic exception-safety guarantee,
1484 // i.e. the variant can become valueless.
1485 this->_M_reset();
1486 __try
1487 {
1488 __variant_construct_by_index<_Np>(*this, __il,
1489 std::forward<_Args>(__args)...);
1490 }
1491 __catch (...)
1492 {
1493 this->_M_index = variant_npos;
1494 __throw_exception_again;
1495 }
1496 }
1497 return std::get<_Np>(*this);
1498 }
1499
1500 constexpr bool valueless_by_exception() const noexcept
1501 { return !this->_M_valid(); }
1502
1503 constexpr size_t index() const noexcept
1504 {
1505 if (this->_M_index ==
1506 typename _Base::__index_type(variant_npos))
1507 return variant_npos;
1508 return this->_M_index;
1509 }
1510
1511 void
1512 swap(variant& __rhs)
1513 noexcept((__is_nothrow_swappable<_Types>::value && ...)
1514 && is_nothrow_move_constructible_v<variant>)
1515 {
1516 __do_visit<__detail::__variant::__visit_with_index>(
1517 [this, &__rhs](auto&& __rhs_mem,
1518 auto __rhs_index) mutable
1519 -> __detail::__variant::__variant_idx_cookie
1520 {
1521 if constexpr (__rhs_index != variant_npos)
1522 {
1523 if (this->index() == __rhs_index)
1524 {
1525 auto& __this_mem =
1526 std::get<__rhs_index>(*this);
1527 using std::swap;
1528 swap(__this_mem, __rhs_mem);
1529 }
1530 else
1531 {
1532 if (this->index() != variant_npos)
1533 {
1534 auto __tmp(std::move(__rhs_mem));
1535 __rhs = std::move(*this);
1536 this->_M_destructive_move(__rhs_index,
1537 std::move(__tmp));
1538 }
1539 else
1540 {
1541 this->_M_destructive_move(__rhs_index,
1542 std::move(__rhs_mem));
1543 __rhs._M_reset();
1544 }
1545 }
1546 }
1547 else
1548 {
1549 if (this->index() != variant_npos)
1550 {
1551 __rhs = std::move(*this);
1552 this->_M_reset();
1553 }
1554 }
1555 return {};
1556 }, __rhs);
1557 }
1558
1559 private:
1560
1561#if defined(__clang__) && __clang_major__ <= 7
1562 public:
1563 using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
1564 private:
1565#endif
1566
1567 template<size_t _Np, typename _Vp>
1568 friend constexpr decltype(auto)
1569 __detail::__variant::__get(_Vp&& __v) noexcept;
1570
1571 template<typename _Vp>
1572 friend void* __detail::__variant::__get_storage(_Vp&& __v);
1573
1574#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
1575 template<typename... _Tp> \
1576 friend constexpr bool \
1577 operator __OP(const variant<_Tp...>& __lhs, \
1578 const variant<_Tp...>& __rhs);
1579
1580 _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
1581 _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
1582 _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
1583 _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
1584 _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
1585 _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
1586
1587#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
1588 };
1589
1590 template<size_t _Np, typename... _Types>
1591 constexpr variant_alternative_t<_Np, variant<_Types...>>&
1592 get(variant<_Types...>& __v)
1593 {
1594 static_assert(_Np < sizeof...(_Types),
1595 "The index should be in [0, number of alternatives)");
1596 if (__v.index() != _Np)
1597 __throw_bad_variant_access(what: "Unexpected index");
1598 return __detail::__variant::__get<_Np>(__v);
1599 }
1600
1601 template<size_t _Np, typename... _Types>
1602 constexpr variant_alternative_t<_Np, variant<_Types...>>&&
1603 get(variant<_Types...>&& __v)
1604 {
1605 static_assert(_Np < sizeof...(_Types),
1606 "The index should be in [0, number of alternatives)");
1607 if (__v.index() != _Np)
1608 __throw_bad_variant_access(what: "Unexpected index");
1609 return __detail::__variant::__get<_Np>(std::move(__v));
1610 }
1611
1612 template<size_t _Np, typename... _Types>
1613 constexpr const variant_alternative_t<_Np, variant<_Types...>>&
1614 get(const variant<_Types...>& __v)
1615 {
1616 static_assert(_Np < sizeof...(_Types),
1617 "The index should be in [0, number of alternatives)");
1618 if (__v.index() != _Np)
1619 __throw_bad_variant_access(what: "Unexpected index");
1620 return __detail::__variant::__get<_Np>(__v);
1621 }
1622
1623 template<size_t _Np, typename... _Types>
1624 constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
1625 get(const variant<_Types...>&& __v)
1626 {
1627 static_assert(_Np < sizeof...(_Types),
1628 "The index should be in [0, number of alternatives)");
1629 if (__v.index() != _Np)
1630 __throw_bad_variant_access(what: "Unexpected index");
1631 return __detail::__variant::__get<_Np>(std::move(__v));
1632 }
1633
1634 template<bool __use_index,
1635 bool __same_return_types,
1636 typename _Visitor, typename... _Variants>
1637 constexpr decltype(auto)
1638 __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
1639 {
1640 using _Deduced_type = std::invoke_result<_Visitor,
1641 decltype(std::get<0>(std::declval<_Variants>()))...>;
1642
1643 using _Result_type = typename std::conditional_t<__use_index,
1644 __detail::__variant::__variant_idx_cookie,
1645 _Deduced_type>::type;
1646
1647 constexpr auto& __vtable = __detail::__variant::__gen_vtable<
1648 __same_return_types,
1649 _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
1650
1651 auto __func_ptr = __vtable._M_access(__variants.index()...);
1652 return (*__func_ptr)(std::forward<_Visitor>(__visitor),
1653 std::forward<_Variants>(__variants)...);
1654 }
1655
1656 template<typename _Visitor, typename... _Variants>
1657 constexpr decltype(auto)
1658 visit(_Visitor&& __visitor, _Variants&&... __variants)
1659 {
1660 if ((__variants.valueless_by_exception() || ...))
1661 __throw_bad_variant_access(what: "Unexpected index");
1662
1663 return __do_visit(std::forward<_Visitor>(__visitor),
1664 std::forward<_Variants>(__variants)...);
1665 }
1666
1667#if __cplusplus > 201703L
1668 template<typename _Res, typename _Visitor, typename... _Variants>
1669 constexpr _Res
1670 visit(_Visitor&& __visitor, _Variants&&... __variants)
1671 {
1672 if ((__variants.valueless_by_exception() || ...))
1673 __throw_bad_variant_access("Unexpected index");
1674
1675 if constexpr (std::is_void_v<_Res>)
1676 (void) __do_visit<false, false>(std::forward<_Visitor>(__visitor),
1677 std::forward<_Variants>(__variants)...);
1678 else
1679 return __do_visit<false, false>(std::forward<_Visitor>(__visitor),
1680 std::forward<_Variants>(__variants)...);
1681 }
1682#endif
1683
1684 template<bool, typename... _Types>
1685 struct __variant_hash_call_base_impl
1686 {
1687 size_t
1688 operator()(const variant<_Types...>& __t) const
1689 noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
1690 {
1691 size_t __ret;
1692 __do_visit([&__t, &__ret](auto&& __t_mem) mutable
1693 -> __detail::__variant::__variant_cookie
1694 {
1695 using _Type = __remove_cvref_t<decltype(__t_mem)>;
1696 if constexpr (!is_same_v<_Type,
1697 __detail::__variant::__variant_cookie>)
1698 __ret = std::hash<size_t>{}(__t.index())
1699 + std::hash<_Type>{}(__t_mem);
1700 else
1701 __ret = std::hash<size_t>{}(__t.index());
1702 return {};
1703 }, __t);
1704 return __ret;
1705 }
1706 };
1707
1708 template<typename... _Types>
1709 struct __variant_hash_call_base_impl<false, _Types...> {};
1710
1711 template<typename... _Types>
1712 using __variant_hash_call_base =
1713 __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
1714 __enable_hash_call &&...), _Types...>;
1715
1716 template<typename... _Types>
1717 struct hash<variant<_Types...>>
1718 : private __detail::__variant::_Variant_hash_base<
1719 variant<_Types...>, std::index_sequence_for<_Types...>>,
1720 public __variant_hash_call_base<_Types...>
1721 {
1722 using result_type [[__deprecated__]] = size_t;
1723 using argument_type [[__deprecated__]] = variant<_Types...>;
1724 };
1725
1726 template<>
1727 struct hash<monostate>
1728 {
1729 using result_type [[__deprecated__]] = size_t;
1730 using argument_type [[__deprecated__]] = monostate;
1731
1732 size_t
1733 operator()(const monostate& __t) const noexcept
1734 {
1735 constexpr size_t __magic_monostate_hash = -7777;
1736 return __magic_monostate_hash;
1737 }
1738 };
1739
1740 template<typename... _Types>
1741 struct __is_fast_hash<hash<variant<_Types...>>>
1742 : bool_constant<(__is_fast_hash<_Types>::value && ...)>
1743 { };
1744
1745_GLIBCXX_END_NAMESPACE_VERSION
1746} // namespace std
1747
1748#endif // C++17
1749
1750#endif // _GLIBCXX_VARIANT
1751