1// -*- C++ -*-
2//===------------------------------ variant -------------------------------===//
3//
4//                     The LLVM Compiler Infrastructure
5//
6// This file is dual licensed under the MIT and the University of Illinois Open
7// Source Licenses. See LICENSE.TXT for details.
8//
9//===----------------------------------------------------------------------===//
10
11#ifndef _LIBCPP_VARIANT
12#define _LIBCPP_VARIANT
13
14/*
15   variant synopsis
16
17namespace std {
18
19  // 20.7.2, class template variant
20  template <class... Types>
21  class variant {
22  public:
23
24    // 20.7.2.1, constructors
25    constexpr variant() noexcept(see below);
26    variant(const variant&);
27    variant(variant&&) noexcept(see below);
28
29    template <class T> constexpr variant(T&&) noexcept(see below);
30
31    template <class T, class... Args>
32    constexpr explicit variant(in_place_type_t<T>, Args&&...);
33
34    template <class T, class U, class... Args>
35    constexpr explicit variant(
36        in_place_type_t<T>, initializer_list<U>, Args&&...);
37
38    template <size_t I, class... Args>
39    constexpr explicit variant(in_place_index_t<I>, Args&&...);
40
41    template <size_t I, class U, class... Args>
42    constexpr explicit variant(
43        in_place_index_t<I>, initializer_list<U>, Args&&...);
44
45    // 20.7.2.2, destructor
46    ~variant();
47
48    // 20.7.2.3, assignment
49    variant& operator=(const variant&);
50    variant& operator=(variant&&) noexcept(see below);
51
52    template <class T> variant& operator=(T&&) noexcept(see below);
53
54    // 20.7.2.4, modifiers
55    template <class T, class... Args>
56    T& emplace(Args&&...);
57
58    template <class T, class U, class... Args>
59    T& emplace(initializer_list<U>, Args&&...);
60
61    template <size_t I, class... Args>
62    variant_alternative_t<I, variant>& emplace(Args&&...);
63
64    template <size_t I, class U, class...  Args>
65    variant_alternative_t<I, variant>& emplace(initializer_list<U>, Args&&...);
66
67    // 20.7.2.5, value status
68    constexpr bool valueless_by_exception() const noexcept;
69    constexpr size_t index() const noexcept;
70
71    // 20.7.2.6, swap
72    void swap(variant&) noexcept(see below);
73  };
74
75  // 20.7.3, variant helper classes
76  template <class T> struct variant_size; // undefined
77
78  template <class T>
79  inline constexpr size_t variant_size_v = variant_size<T>::value;
80
81  template <class T> struct variant_size<const T>;
82  template <class T> struct variant_size<volatile T>;
83  template <class T> struct variant_size<const volatile T>;
84
85  template <class... Types>
86  struct variant_size<variant<Types...>>;
87
88  template <size_t I, class T> struct variant_alternative; // undefined
89
90  template <size_t I, class T>
91  using variant_alternative_t = typename variant_alternative<I, T>::type;
92
93  template <size_t I, class T> struct variant_alternative<I, const T>;
94  template <size_t I, class T> struct variant_alternative<I, volatile T>;
95  template <size_t I, class T> struct variant_alternative<I, const volatile T>;
96
97  template <size_t I, class... Types>
98  struct variant_alternative<I, variant<Types...>>;
99
100  inline constexpr size_t variant_npos = -1;
101
102  // 20.7.4, value access
103  template <class T, class... Types>
104  constexpr bool holds_alternative(const variant<Types...>&) noexcept;
105
106  template <size_t I, class... Types>
107  constexpr variant_alternative_t<I, variant<Types...>>&
108  get(variant<Types...>&);
109
110  template <size_t I, class... Types>
111  constexpr variant_alternative_t<I, variant<Types...>>&&
112  get(variant<Types...>&&);
113
114  template <size_t I, class... Types>
115  constexpr variant_alternative_t<I, variant<Types...>> const&
116  get(const variant<Types...>&);
117
118  template <size_t I, class... Types>
119  constexpr variant_alternative_t<I, variant<Types...>> const&&
120  get(const variant<Types...>&&);
121
122  template <class T, class...  Types>
123  constexpr T& get(variant<Types...>&);
124
125  template <class T, class... Types>
126  constexpr T&& get(variant<Types...>&&);
127
128  template <class T, class... Types>
129  constexpr const T& get(const variant<Types...>&);
130
131  template <class T, class... Types>
132  constexpr const T&& get(const variant<Types...>&&);
133
134  template <size_t I, class... Types>
135  constexpr add_pointer_t<variant_alternative_t<I, variant<Types...>>>
136  get_if(variant<Types...>*) noexcept;
137
138  template <size_t I, class... Types>
139  constexpr add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
140  get_if(const variant<Types...>*) noexcept;
141
142  template <class T, class... Types>
143  constexpr add_pointer_t<T>
144  get_if(variant<Types...>*) noexcept;
145
146  template <class T, class... Types>
147  constexpr add_pointer_t<const T>
148  get_if(const variant<Types...>*) noexcept;
149
150  // 20.7.5, relational operators
151  template <class... Types>
152  constexpr bool operator==(const variant<Types...>&, const variant<Types...>&);
153
154  template <class... Types>
155  constexpr bool operator!=(const variant<Types...>&, const variant<Types...>&);
156
157  template <class... Types>
158  constexpr bool operator<(const variant<Types...>&, const variant<Types...>&);
159
160  template <class... Types>
161  constexpr bool operator>(const variant<Types...>&, const variant<Types...>&);
162
163  template <class... Types>
164  constexpr bool operator<=(const variant<Types...>&, const variant<Types...>&);
165
166  template <class... Types>
167  constexpr bool operator>=(const variant<Types...>&, const variant<Types...>&);
168
169  // 20.7.6, visitation
170  template <class Visitor, class... Variants>
171  constexpr see below visit(Visitor&&, Variants&&...);
172
173  // 20.7.7, class monostate
174  struct monostate;
175
176  // 20.7.8, monostate relational operators
177  constexpr bool operator<(monostate, monostate) noexcept;
178  constexpr bool operator>(monostate, monostate) noexcept;
179  constexpr bool operator<=(monostate, monostate) noexcept;
180  constexpr bool operator>=(monostate, monostate) noexcept;
181  constexpr bool operator==(monostate, monostate) noexcept;
182  constexpr bool operator!=(monostate, monostate) noexcept;
183
184  // 20.7.9, specialized algorithms
185  template <class... Types>
186  void swap(variant<Types...>&, variant<Types...>&) noexcept(see below);
187
188  // 20.7.10, class bad_variant_access
189  class bad_variant_access;
190
191  // 20.7.11, hash support
192  template <class T> struct hash;
193  template <class... Types> struct hash<variant<Types...>>;
194  template <> struct hash<monostate>;
195
196} // namespace std
197
198*/
199
200#include <__config>
201#include <__tuple>
202#include <array>
203#include <exception>
204#include <functional>
205#include <initializer_list>
206#include <new>
207#include <tuple>
208#include <type_traits>
209#include <utility>
210#include <limits>
211#include <version>
212
213#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
214#pragma GCC system_header
215#endif
216
217_LIBCPP_PUSH_MACROS
218#include <__undef_macros>
219
220namespace std { // explicitly not using versioning namespace
221
222class _LIBCPP_EXCEPTION_ABI bad_variant_access : public exception {
223public:
224  virtual const char* what() const _NOEXCEPT;
225};
226
227} // namespace std
228
229_LIBCPP_BEGIN_NAMESPACE_STD
230
231#if _LIBCPP_STD_VER > 14
232
233_LIBCPP_NORETURN
234inline _LIBCPP_INLINE_VISIBILITY
235void __throw_bad_variant_access() {
236#ifndef _LIBCPP_NO_EXCEPTIONS
237        throw bad_variant_access();
238#else
239        _VSTD::abort();
240#endif
241}
242
243template <class... _Types>
244class _LIBCPP_TEMPLATE_VIS variant;
245
246template <class _Tp>
247struct _LIBCPP_TEMPLATE_VIS variant_size;
248
249template <class _Tp>
250_LIBCPP_INLINE_VAR constexpr size_t variant_size_v = variant_size<_Tp>::value;
251
252template <class _Tp>
253struct _LIBCPP_TEMPLATE_VIS variant_size<const _Tp> : variant_size<_Tp> {};
254
255template <class _Tp>
256struct _LIBCPP_TEMPLATE_VIS variant_size<volatile _Tp> : variant_size<_Tp> {};
257
258template <class _Tp>
259struct _LIBCPP_TEMPLATE_VIS variant_size<const volatile _Tp>
260    : variant_size<_Tp> {};
261
262template <class... _Types>
263struct _LIBCPP_TEMPLATE_VIS variant_size<variant<_Types...>>
264    : integral_constant<size_t, sizeof...(_Types)> {};
265
266template <size_t _Ip, class _Tp>
267struct _LIBCPP_TEMPLATE_VIS variant_alternative;
268
269template <size_t _Ip, class _Tp>
270using variant_alternative_t = typename variant_alternative<_Ip, _Tp>::type;
271
272template <size_t _Ip, class _Tp>
273struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, const _Tp>
274    : add_const<variant_alternative_t<_Ip, _Tp>> {};
275
276template <size_t _Ip, class _Tp>
277struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, volatile _Tp>
278    : add_volatile<variant_alternative_t<_Ip, _Tp>> {};
279
280template <size_t _Ip, class _Tp>
281struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, const volatile _Tp>
282    : add_cv<variant_alternative_t<_Ip, _Tp>> {};
283
284template <size_t _Ip, class... _Types>
285struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, variant<_Types...>> {
286  static_assert(_Ip < sizeof...(_Types), "Index out of bounds in std::variant_alternative<>");
287  using type = __type_pack_element<_Ip, _Types...>;
288};
289
290_LIBCPP_INLINE_VAR constexpr size_t variant_npos = static_cast<size_t>(-1);
291
292constexpr int __choose_index_type(unsigned int __num_elem) {
293  if (__num_elem < std::numeric_limits<unsigned char>::max())
294    return 0;
295  if (__num_elem < std::numeric_limits<unsigned short>::max())
296    return 1;
297  return 2;
298}
299
300template <size_t _NumAlts>
301using __variant_index_t =
302#ifndef _LIBCPP_ABI_VARIANT_INDEX_TYPE_OPTIMIZATION
303  unsigned int;
304#else
305  std::tuple_element_t<
306      __choose_index_type(_NumAlts),
307      std::tuple<unsigned char, unsigned short, unsigned int>
308  >;
309#endif
310
311template <class _IndexType>
312constexpr _IndexType __variant_npos = static_cast<_IndexType>(-1);
313
314namespace __find_detail {
315
316template <class _Tp, class... _Types>
317inline _LIBCPP_INLINE_VISIBILITY
318constexpr size_t __find_index() {
319  constexpr bool __matches[] = {is_same_v<_Tp, _Types>...};
320  size_t __result = __not_found;
321  for (size_t __i = 0; __i < sizeof...(_Types); ++__i) {
322    if (__matches[__i]) {
323      if (__result != __not_found) {
324        return __ambiguous;
325      }
326      __result = __i;
327    }
328  }
329  return __result;
330}
331
332template <size_t _Index>
333struct __find_unambiguous_index_sfinae_impl
334    : integral_constant<size_t, _Index> {};
335
336template <>
337struct __find_unambiguous_index_sfinae_impl<__not_found> {};
338
339template <>
340struct __find_unambiguous_index_sfinae_impl<__ambiguous> {};
341
342template <class _Tp, class... _Types>
343struct __find_unambiguous_index_sfinae
344    : __find_unambiguous_index_sfinae_impl<__find_index<_Tp, _Types...>()> {};
345
346} // namespace __find_detail
347
348namespace __variant_detail {
349
350struct __valueless_t {};
351
352enum class _Trait { _TriviallyAvailable, _Available, _Unavailable };
353
354template <typename _Tp,
355          template <typename> class _IsTriviallyAvailable,
356          template <typename> class _IsAvailable>
357constexpr _Trait __trait =
358    _IsTriviallyAvailable<_Tp>::value
359        ? _Trait::_TriviallyAvailable
360        : _IsAvailable<_Tp>::value ? _Trait::_Available : _Trait::_Unavailable;
361
362inline _LIBCPP_INLINE_VISIBILITY
363constexpr _Trait __common_trait(initializer_list<_Trait> __traits) {
364  _Trait __result = _Trait::_TriviallyAvailable;
365  for (_Trait __t : __traits) {
366    if (static_cast<int>(__t) > static_cast<int>(__result)) {
367      __result = __t;
368    }
369  }
370  return __result;
371}
372
373template <typename... _Types>
374struct __traits {
375  static constexpr _Trait __copy_constructible_trait =
376      __common_trait({__trait<_Types,
377                              is_trivially_copy_constructible,
378                              is_copy_constructible>...});
379
380  static constexpr _Trait __move_constructible_trait =
381      __common_trait({__trait<_Types,
382                              is_trivially_move_constructible,
383                              is_move_constructible>...});
384
385  static constexpr _Trait __copy_assignable_trait = __common_trait(
386      {__copy_constructible_trait,
387       __trait<_Types, is_trivially_copy_assignable, is_copy_assignable>...});
388
389  static constexpr _Trait __move_assignable_trait = __common_trait(
390      {__move_constructible_trait,
391       __trait<_Types, is_trivially_move_assignable, is_move_assignable>...});
392
393  static constexpr _Trait __destructible_trait = __common_trait(
394      {__trait<_Types, is_trivially_destructible, is_destructible>...});
395};
396
397namespace __access {
398
399struct __union {
400  template <class _Vp>
401  inline _LIBCPP_INLINE_VISIBILITY
402  static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<0>) {
403    return _VSTD::forward<_Vp>(__v).__head;
404  }
405
406  template <class _Vp, size_t _Ip>
407  inline _LIBCPP_INLINE_VISIBILITY
408  static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<_Ip>) {
409    return __get_alt(_VSTD::forward<_Vp>(__v).__tail, in_place_index<_Ip - 1>);
410  }
411};
412
413struct __base {
414  template <size_t _Ip, class _Vp>
415  inline _LIBCPP_INLINE_VISIBILITY
416  static constexpr auto&& __get_alt(_Vp&& __v) {
417    return __union::__get_alt(_VSTD::forward<_Vp>(__v).__data,
418                              in_place_index<_Ip>);
419  }
420};
421
422struct __variant {
423  template <size_t _Ip, class _Vp>
424  inline _LIBCPP_INLINE_VISIBILITY
425  static constexpr auto&& __get_alt(_Vp&& __v) {
426    return __base::__get_alt<_Ip>(_VSTD::forward<_Vp>(__v).__impl);
427  }
428};
429
430} // namespace __access
431
432namespace __visitation {
433
434struct __base {
435  template <class _Visitor, class... _Vs>
436  inline _LIBCPP_INLINE_VISIBILITY
437  static constexpr decltype(auto)
438  __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
439    constexpr auto __fdiagonal =
440        __make_fdiagonal<_Visitor&&,
441                         decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
442    return __fdiagonal[__index](_VSTD::forward<_Visitor>(__visitor),
443                                _VSTD::forward<_Vs>(__vs).__as_base()...);
444  }
445
446  template <class _Visitor, class... _Vs>
447  inline _LIBCPP_INLINE_VISIBILITY
448  static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor,
449                                              _Vs&&... __vs) {
450    constexpr auto __fmatrix =
451        __make_fmatrix<_Visitor&&,
452                       decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
453    return __at(__fmatrix, __vs.index()...)(
454        _VSTD::forward<_Visitor>(__visitor),
455        _VSTD::forward<_Vs>(__vs).__as_base()...);
456  }
457
458private:
459  template <class _Tp>
460  inline _LIBCPP_INLINE_VISIBILITY
461  static constexpr const _Tp& __at(const _Tp& __elem) { return __elem; }
462
463  template <class _Tp, size_t _Np, typename... _Indices>
464  inline _LIBCPP_INLINE_VISIBILITY
465  static constexpr auto&& __at(const array<_Tp, _Np>& __elems,
466                               size_t __index, _Indices... __indices) {
467    return __at(__elems[__index], __indices...);
468  }
469
470  template <class _Fp, class... _Fs>
471  static constexpr void __std_visit_visitor_return_type_check() {
472    static_assert(
473        __all<is_same_v<_Fp, _Fs>...>::value,
474        "`std::visit` requires the visitor to have a single return type.");
475  }
476
477  template <class... _Fs>
478  inline _LIBCPP_INLINE_VISIBILITY
479  static constexpr auto __make_farray(_Fs&&... __fs) {
480    __std_visit_visitor_return_type_check<__uncvref_t<_Fs>...>();
481    using __result = array<common_type_t<__uncvref_t<_Fs>...>, sizeof...(_Fs)>;
482    return __result{{_VSTD::forward<_Fs>(__fs)...}};
483  }
484
485  template <std::size_t... _Is>
486  struct __dispatcher {
487    template <class _Fp, class... _Vs>
488    inline _LIBCPP_INLINE_VISIBILITY
489    static constexpr decltype(auto) __dispatch(_Fp __f, _Vs... __vs) {
490        return __invoke_constexpr(
491            static_cast<_Fp>(__f),
492            __access::__base::__get_alt<_Is>(static_cast<_Vs>(__vs))...);
493    }
494  };
495
496  template <class _Fp, class... _Vs, size_t... _Is>
497  inline _LIBCPP_INLINE_VISIBILITY
498  static constexpr auto __make_dispatch(index_sequence<_Is...>) {
499    return __dispatcher<_Is...>::template __dispatch<_Fp, _Vs...>;
500  }
501
502  template <size_t _Ip, class _Fp, class... _Vs>
503  inline _LIBCPP_INLINE_VISIBILITY
504  static constexpr auto __make_fdiagonal_impl() {
505    return __make_dispatch<_Fp, _Vs...>(
506        index_sequence<(__identity<_Vs>{}, _Ip)...>{});
507  }
508
509  template <class _Fp, class... _Vs, size_t... _Is>
510  inline _LIBCPP_INLINE_VISIBILITY
511  static constexpr auto __make_fdiagonal_impl(index_sequence<_Is...>) {
512    return __base::__make_farray(__make_fdiagonal_impl<_Is, _Fp, _Vs...>()...);
513  }
514
515  template <class _Fp, class _Vp, class... _Vs>
516  inline _LIBCPP_INLINE_VISIBILITY
517  static constexpr auto __make_fdiagonal() {
518    constexpr size_t _Np = __uncvref_t<_Vp>::__size();
519    static_assert(__all<(_Np == __uncvref_t<_Vs>::__size())...>::value);
520    return __make_fdiagonal_impl<_Fp, _Vp, _Vs...>(make_index_sequence<_Np>{});
521  }
522
523  template <class _Fp, class... _Vs, size_t... _Is>
524  inline _LIBCPP_INLINE_VISIBILITY
525  static constexpr auto __make_fmatrix_impl(index_sequence<_Is...> __is) {
526    return __make_dispatch<_Fp, _Vs...>(__is);
527  }
528
529  template <class _Fp, class... _Vs, size_t... _Is, size_t... _Js, class... _Ls>
530  inline _LIBCPP_INLINE_VISIBILITY
531  static constexpr auto __make_fmatrix_impl(index_sequence<_Is...>,
532                                            index_sequence<_Js...>,
533                                            _Ls... __ls) {
534    return __base::__make_farray(__make_fmatrix_impl<_Fp, _Vs...>(
535        index_sequence<_Is..., _Js>{}, __ls...)...);
536  }
537
538  template <class _Fp, class... _Vs>
539  inline _LIBCPP_INLINE_VISIBILITY
540  static constexpr auto __make_fmatrix() {
541    return __make_fmatrix_impl<_Fp, _Vs...>(
542        index_sequence<>{}, make_index_sequence<__uncvref_t<_Vs>::__size()>{}...);
543  }
544};
545
546struct __variant {
547  template <class _Visitor, class... _Vs>
548  inline _LIBCPP_INLINE_VISIBILITY
549  static constexpr decltype(auto)
550  __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
551    return __base::__visit_alt_at(__index,
552                                  _VSTD::forward<_Visitor>(__visitor),
553                                  _VSTD::forward<_Vs>(__vs).__impl...);
554  }
555
556  template <class _Visitor, class... _Vs>
557  inline _LIBCPP_INLINE_VISIBILITY
558  static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor,
559                                              _Vs&&... __vs) {
560    return __base::__visit_alt(_VSTD::forward<_Visitor>(__visitor),
561                               _VSTD::forward<_Vs>(__vs).__impl...);
562  }
563
564  template <class _Visitor, class... _Vs>
565  inline _LIBCPP_INLINE_VISIBILITY
566  static constexpr decltype(auto)
567  __visit_value_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
568    return __visit_alt_at(
569        __index,
570        __make_value_visitor(_VSTD::forward<_Visitor>(__visitor)),
571        _VSTD::forward<_Vs>(__vs)...);
572  }
573
574  template <class _Visitor, class... _Vs>
575  inline _LIBCPP_INLINE_VISIBILITY
576  static constexpr decltype(auto) __visit_value(_Visitor&& __visitor,
577                                                _Vs&&... __vs) {
578    return __visit_alt(
579        __make_value_visitor(_VSTD::forward<_Visitor>(__visitor)),
580        _VSTD::forward<_Vs>(__vs)...);
581  }
582
583private:
584  template <class _Visitor, class... _Values>
585  static constexpr void __std_visit_exhaustive_visitor_check() {
586    static_assert(is_invocable_v<_Visitor, _Values...>,
587                  "`std::visit` requires the visitor to be exhaustive.");
588  }
589
590  template <class _Visitor>
591  struct __value_visitor {
592    template <class... _Alts>
593    inline _LIBCPP_INLINE_VISIBILITY
594    constexpr decltype(auto) operator()(_Alts&&... __alts) const {
595      __std_visit_exhaustive_visitor_check<
596          _Visitor,
597          decltype((_VSTD::forward<_Alts>(__alts).__value))...>();
598      return __invoke_constexpr(_VSTD::forward<_Visitor>(__visitor),
599                                _VSTD::forward<_Alts>(__alts).__value...);
600    }
601    _Visitor&& __visitor;
602  };
603
604  template <class _Visitor>
605  inline _LIBCPP_INLINE_VISIBILITY
606  static constexpr auto __make_value_visitor(_Visitor&& __visitor) {
607    return __value_visitor<_Visitor>{_VSTD::forward<_Visitor>(__visitor)};
608  }
609};
610
611} // namespace __visitation
612
613template <size_t _Index, class _Tp>
614struct _LIBCPP_TEMPLATE_VIS __alt {
615  using __value_type = _Tp;
616
617  template <class... _Args>
618  inline _LIBCPP_INLINE_VISIBILITY
619  explicit constexpr __alt(in_place_t, _Args&&... __args)
620      : __value(_VSTD::forward<_Args>(__args)...) {}
621
622  __value_type __value;
623};
624
625template <_Trait _DestructibleTrait, size_t _Index, class... _Types>
626union _LIBCPP_TEMPLATE_VIS __union;
627
628template <_Trait _DestructibleTrait, size_t _Index>
629union _LIBCPP_TEMPLATE_VIS __union<_DestructibleTrait, _Index> {};
630
631#define _LIBCPP_VARIANT_UNION(destructible_trait, destructor)                  \
632  template <size_t _Index, class _Tp, class... _Types>                         \
633  union _LIBCPP_TEMPLATE_VIS __union<destructible_trait,                      \
634                                      _Index,                                  \
635                                      _Tp,                                     \
636                                      _Types...> {                             \
637  public:                                                                      \
638    inline _LIBCPP_INLINE_VISIBILITY                                           \
639    explicit constexpr __union(__valueless_t) noexcept : __dummy{} {}          \
640                                                                               \
641    template <class... _Args>                                                  \
642    inline _LIBCPP_INLINE_VISIBILITY                                           \
643    explicit constexpr __union(in_place_index_t<0>, _Args&&... __args)         \
644        : __head(in_place, _VSTD::forward<_Args>(__args)...) {}                \
645                                                                               \
646    template <size_t _Ip, class... _Args>                                      \
647    inline _LIBCPP_INLINE_VISIBILITY                                           \
648    explicit constexpr __union(in_place_index_t<_Ip>, _Args&&... __args)       \
649        : __tail(in_place_index<_Ip - 1>, _VSTD::forward<_Args>(__args)...) {} \
650                                                                               \
651    __union(const __union&) = default;                                         \
652    __union(__union&&) = default;                                              \
653                                                                               \
654    destructor                                                                 \
655                                                                               \
656    __union& operator=(const __union&) = default;                              \
657    __union& operator=(__union&&) = default;                                   \
658                                                                               \
659  private:                                                                     \
660    char __dummy;                                                              \
661    __alt<_Index, _Tp> __head;                                                 \
662    __union<destructible_trait, _Index + 1, _Types...> __tail;                 \
663                                                                               \
664    friend struct __access::__union;                                           \
665  }
666
667_LIBCPP_VARIANT_UNION(_Trait::_TriviallyAvailable, ~__union() = default;);
668_LIBCPP_VARIANT_UNION(_Trait::_Available, ~__union() {});
669_LIBCPP_VARIANT_UNION(_Trait::_Unavailable, ~__union() = delete;);
670
671#undef _LIBCPP_VARIANT_UNION
672
673template <_Trait _DestructibleTrait, class... _Types>
674class _LIBCPP_TEMPLATE_VIS __base {
675public:
676  using __index_t = __variant_index_t<sizeof...(_Types)>;
677
678  inline _LIBCPP_INLINE_VISIBILITY
679  explicit constexpr __base(__valueless_t tag) noexcept
680      : __data(tag), __index(__variant_npos<__index_t>) {}
681
682  template <size_t _Ip, class... _Args>
683  inline _LIBCPP_INLINE_VISIBILITY
684  explicit constexpr __base(in_place_index_t<_Ip>, _Args&&... __args)
685      :
686        __data(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...),
687        __index(_Ip) {}
688
689  inline _LIBCPP_INLINE_VISIBILITY
690  constexpr bool valueless_by_exception() const noexcept {
691    return index() == variant_npos;
692  }
693
694  inline _LIBCPP_INLINE_VISIBILITY
695  constexpr size_t index() const noexcept {
696    return __index == __variant_npos<__index_t> ? variant_npos : __index;
697  }
698
699protected:
700  inline _LIBCPP_INLINE_VISIBILITY
701  constexpr auto&& __as_base() & { return *this; }
702
703  inline _LIBCPP_INLINE_VISIBILITY
704  constexpr auto&& __as_base() && { return _VSTD::move(*this); }
705
706  inline _LIBCPP_INLINE_VISIBILITY
707  constexpr auto&& __as_base() const & { return *this; }
708
709  inline _LIBCPP_INLINE_VISIBILITY
710  constexpr auto&& __as_base() const && { return _VSTD::move(*this); }
711
712  inline _LIBCPP_INLINE_VISIBILITY
713  static constexpr size_t __size() { return sizeof...(_Types); }
714
715  __union<_DestructibleTrait, 0, _Types...> __data;
716  __index_t __index;
717
718  friend struct __access::__base;
719  friend struct __visitation::__base;
720};
721
722template <class _Traits, _Trait = _Traits::__destructible_trait>
723class _LIBCPP_TEMPLATE_VIS __destructor;
724
725#define _LIBCPP_VARIANT_DESTRUCTOR(destructible_trait, destructor, destroy)    \
726  template <class... _Types>                                                   \
727  class _LIBCPP_TEMPLATE_VIS __destructor<__traits<_Types...>,                 \
728                                           destructible_trait>                 \
729      : public __base<destructible_trait, _Types...> {                         \
730    using __base_type = __base<destructible_trait, _Types...>;                 \
731    using __index_t = typename __base_type::__index_t;                         \
732                                                                               \
733  public:                                                                      \
734    using __base_type::__base_type;                                            \
735    using __base_type::operator=;                                              \
736                                                                               \
737    __destructor(const __destructor&) = default;                               \
738    __destructor(__destructor&&) = default;                                    \
739    destructor                                                                 \
740    __destructor& operator=(const __destructor&) = default;                    \
741    __destructor& operator=(__destructor&&) = default;                         \
742                                                                               \
743  protected:                                                                   \
744    inline _LIBCPP_INLINE_VISIBILITY                                           \
745    destroy                                                                    \
746  }
747
748_LIBCPP_VARIANT_DESTRUCTOR(
749    _Trait::_TriviallyAvailable,
750    ~__destructor() = default;,
751    void __destroy() noexcept { this->__index = __variant_npos<__index_t>; });
752
753_LIBCPP_VARIANT_DESTRUCTOR(
754    _Trait::_Available,
755    ~__destructor() { __destroy(); },
756    void __destroy() noexcept {
757      if (!this->valueless_by_exception()) {
758        __visitation::__base::__visit_alt(
759            [](auto& __alt) noexcept {
760              using __alt_type = __uncvref_t<decltype(__alt)>;
761              __alt.~__alt_type();
762            },
763            *this);
764      }
765      this->__index = __variant_npos<__index_t>;
766    });
767
768_LIBCPP_VARIANT_DESTRUCTOR(
769    _Trait::_Unavailable,
770    ~__destructor() = delete;,
771    void __destroy() noexcept = delete;);
772
773#undef _LIBCPP_VARIANT_DESTRUCTOR
774
775template <class _Traits>
776class _LIBCPP_TEMPLATE_VIS __constructor : public __destructor<_Traits> {
777  using __base_type = __destructor<_Traits>;
778
779public:
780  using __base_type::__base_type;
781  using __base_type::operator=;
782
783protected:
784  template <size_t _Ip, class _Tp, class... _Args>
785  inline _LIBCPP_INLINE_VISIBILITY
786  static _Tp& __construct_alt(__alt<_Ip, _Tp>& __a, _Args&&... __args) {
787    ::new ((void*)_VSTD::addressof(__a))
788        __alt<_Ip, _Tp>(in_place, _VSTD::forward<_Args>(__args)...);
789    return __a.__value;
790  }
791
792  template <class _Rhs>
793  inline _LIBCPP_INLINE_VISIBILITY
794  static void __generic_construct(__constructor& __lhs, _Rhs&& __rhs) {
795    __lhs.__destroy();
796    if (!__rhs.valueless_by_exception()) {
797      __visitation::__base::__visit_alt_at(
798          __rhs.index(),
799          [](auto& __lhs_alt, auto&& __rhs_alt) {
800            __construct_alt(
801                __lhs_alt,
802                _VSTD::forward<decltype(__rhs_alt)>(__rhs_alt).__value);
803          },
804          __lhs, _VSTD::forward<_Rhs>(__rhs));
805      __lhs.__index = __rhs.index();
806    }
807  }
808};
809
810template <class _Traits, _Trait = _Traits::__move_constructible_trait>
811class _LIBCPP_TEMPLATE_VIS __move_constructor;
812
813#define _LIBCPP_VARIANT_MOVE_CONSTRUCTOR(move_constructible_trait,             \
814                                         move_constructor)                     \
815  template <class... _Types>                                                   \
816  class _LIBCPP_TEMPLATE_VIS __move_constructor<__traits<_Types...>,          \
817                                                 move_constructible_trait>     \
818      : public __constructor<__traits<_Types...>> {                            \
819    using __base_type = __constructor<__traits<_Types...>>;                    \
820                                                                               \
821  public:                                                                      \
822    using __base_type::__base_type;                                            \
823    using __base_type::operator=;                                              \
824                                                                               \
825    __move_constructor(const __move_constructor&) = default;                   \
826    move_constructor                                                           \
827    ~__move_constructor() = default;                                           \
828    __move_constructor& operator=(const __move_constructor&) = default;        \
829    __move_constructor& operator=(__move_constructor&&) = default;             \
830  }
831
832_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
833    _Trait::_TriviallyAvailable,
834    __move_constructor(__move_constructor&& __that) = default;);
835
836_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
837    _Trait::_Available,
838    __move_constructor(__move_constructor&& __that) noexcept(
839        __all<is_nothrow_move_constructible_v<_Types>...>::value)
840        : __move_constructor(__valueless_t{}) {
841      this->__generic_construct(*this, _VSTD::move(__that));
842    });
843
844_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
845    _Trait::_Unavailable,
846    __move_constructor(__move_constructor&&) = delete;);
847
848#undef _LIBCPP_VARIANT_MOVE_CONSTRUCTOR
849
850template <class _Traits, _Trait = _Traits::__copy_constructible_trait>
851class _LIBCPP_TEMPLATE_VIS __copy_constructor;
852
853#define _LIBCPP_VARIANT_COPY_CONSTRUCTOR(copy_constructible_trait,             \
854                                         copy_constructor)                     \
855  template <class... _Types>                                                   \
856  class _LIBCPP_TEMPLATE_VIS __copy_constructor<__traits<_Types...>,          \
857                                                 copy_constructible_trait>     \
858      : public __move_constructor<__traits<_Types...>> {                       \
859    using __base_type = __move_constructor<__traits<_Types...>>;               \
860                                                                               \
861  public:                                                                      \
862    using __base_type::__base_type;                                            \
863    using __base_type::operator=;                                              \
864                                                                               \
865    copy_constructor                                                           \
866    __copy_constructor(__copy_constructor&&) = default;                        \
867    ~__copy_constructor() = default;                                           \
868    __copy_constructor& operator=(const __copy_constructor&) = default;        \
869    __copy_constructor& operator=(__copy_constructor&&) = default;             \
870  }
871
872_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
873    _Trait::_TriviallyAvailable,
874    __copy_constructor(const __copy_constructor& __that) = default;);
875
876_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
877    _Trait::_Available,
878    __copy_constructor(const __copy_constructor& __that)
879        : __copy_constructor(__valueless_t{}) {
880      this->__generic_construct(*this, __that);
881    });
882
883_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
884    _Trait::_Unavailable,
885    __copy_constructor(const __copy_constructor&) = delete;);
886
887#undef _LIBCPP_VARIANT_COPY_CONSTRUCTOR
888
889template <class _Traits>
890class _LIBCPP_TEMPLATE_VIS __assignment : public __copy_constructor<_Traits> {
891  using __base_type = __copy_constructor<_Traits>;
892
893public:
894  using __base_type::__base_type;
895  using __base_type::operator=;
896
897  template <size_t _Ip, class... _Args>
898  inline _LIBCPP_INLINE_VISIBILITY
899  auto& __emplace(_Args&&... __args) {
900    this->__destroy();
901    auto& __res = this->__construct_alt(__access::__base::__get_alt<_Ip>(*this),
902                          _VSTD::forward<_Args>(__args)...);
903    this->__index = _Ip;
904    return __res;
905  }
906
907protected:
908  template <size_t _Ip, class _Tp, class _Arg>
909  inline _LIBCPP_INLINE_VISIBILITY
910  void __assign_alt(__alt<_Ip, _Tp>& __a, _Arg&& __arg) {
911    if (this->index() == _Ip) {
912      __a.__value = _VSTD::forward<_Arg>(__arg);
913    } else {
914      struct {
915        void operator()(true_type) const {
916          __this->__emplace<_Ip>(_VSTD::forward<_Arg>(__arg));
917        }
918        void operator()(false_type) const {
919          __this->__emplace<_Ip>(_Tp(_VSTD::forward<_Arg>(__arg)));
920        }
921        __assignment* __this;
922        _Arg&& __arg;
923      } __impl{this, _VSTD::forward<_Arg>(__arg)};
924      __impl(bool_constant<is_nothrow_constructible_v<_Tp, _Arg> ||
925                           !is_nothrow_move_constructible_v<_Tp>>{});
926    }
927  }
928
929  template <class _That>
930  inline _LIBCPP_INLINE_VISIBILITY
931  void __generic_assign(_That&& __that) {
932    if (this->valueless_by_exception() && __that.valueless_by_exception()) {
933      // do nothing.
934    } else if (__that.valueless_by_exception()) {
935      this->__destroy();
936    } else {
937      __visitation::__base::__visit_alt_at(
938          __that.index(),
939          [this](auto& __this_alt, auto&& __that_alt) {
940            this->__assign_alt(
941                __this_alt,
942                _VSTD::forward<decltype(__that_alt)>(__that_alt).__value);
943          },
944          *this, _VSTD::forward<_That>(__that));
945    }
946  }
947};
948
949template <class _Traits, _Trait = _Traits::__move_assignable_trait>
950class _LIBCPP_TEMPLATE_VIS __move_assignment;
951
952#define _LIBCPP_VARIANT_MOVE_ASSIGNMENT(move_assignable_trait,                 \
953                                        move_assignment)                       \
954  template <class... _Types>                                                   \
955  class _LIBCPP_TEMPLATE_VIS __move_assignment<__traits<_Types...>,           \
956                                                move_assignable_trait>         \
957      : public __assignment<__traits<_Types...>> {                             \
958    using __base_type = __assignment<__traits<_Types...>>;                     \
959                                                                               \
960  public:                                                                      \
961    using __base_type::__base_type;                                            \
962    using __base_type::operator=;                                              \
963                                                                               \
964    __move_assignment(const __move_assignment&) = default;                     \
965    __move_assignment(__move_assignment&&) = default;                          \
966    ~__move_assignment() = default;                                            \
967    __move_assignment& operator=(const __move_assignment&) = default;          \
968    move_assignment                                                            \
969  }
970
971_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
972    _Trait::_TriviallyAvailable,
973    __move_assignment& operator=(__move_assignment&& __that) = default;);
974
975_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
976    _Trait::_Available,
977    __move_assignment& operator=(__move_assignment&& __that) noexcept(
978        __all<(is_nothrow_move_constructible_v<_Types> &&
979               is_nothrow_move_assignable_v<_Types>)...>::value) {
980      this->__generic_assign(_VSTD::move(__that));
981      return *this;
982    });
983
984_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
985    _Trait::_Unavailable,
986    __move_assignment& operator=(__move_assignment&&) = delete;);
987
988#undef _LIBCPP_VARIANT_MOVE_ASSIGNMENT
989
990template <class _Traits, _Trait = _Traits::__copy_assignable_trait>
991class _LIBCPP_TEMPLATE_VIS __copy_assignment;
992
993#define _LIBCPP_VARIANT_COPY_ASSIGNMENT(copy_assignable_trait,                 \
994                                        copy_assignment)                       \
995  template <class... _Types>                                                   \
996  class _LIBCPP_TEMPLATE_VIS __copy_assignment<__traits<_Types...>,           \
997                                                copy_assignable_trait>         \
998      : public __move_assignment<__traits<_Types...>> {                        \
999    using __base_type = __move_assignment<__traits<_Types...>>;                \
1000                                                                               \
1001  public:                                                                      \
1002    using __base_type::__base_type;                                            \
1003    using __base_type::operator=;                                              \
1004                                                                               \
1005    __copy_assignment(const __copy_assignment&) = default;                     \
1006    __copy_assignment(__copy_assignment&&) = default;                          \
1007    ~__copy_assignment() = default;                                            \
1008    copy_assignment                                                            \
1009    __copy_assignment& operator=(__copy_assignment&&) = default;               \
1010  }
1011
1012_LIBCPP_VARIANT_COPY_ASSIGNMENT(
1013    _Trait::_TriviallyAvailable,
1014    __copy_assignment& operator=(const __copy_assignment& __that) = default;);
1015
1016_LIBCPP_VARIANT_COPY_ASSIGNMENT(
1017    _Trait::_Available,
1018    __copy_assignment& operator=(const __copy_assignment& __that) {
1019      this->__generic_assign(__that);
1020      return *this;
1021    });
1022
1023_LIBCPP_VARIANT_COPY_ASSIGNMENT(
1024    _Trait::_Unavailable,
1025    __copy_assignment& operator=(const __copy_assignment&) = delete;);
1026
1027#undef _LIBCPP_VARIANT_COPY_ASSIGNMENT
1028
1029template <class... _Types>
1030class _LIBCPP_TEMPLATE_VIS __impl
1031    : public __copy_assignment<__traits<_Types...>> {
1032  using __base_type = __copy_assignment<__traits<_Types...>>;
1033
1034public:
1035  using __base_type::__base_type;
1036  using __base_type::operator=;
1037
1038  template <size_t _Ip, class _Arg>
1039  inline _LIBCPP_INLINE_VISIBILITY
1040  void __assign(_Arg&& __arg) {
1041    this->__assign_alt(__access::__base::__get_alt<_Ip>(*this),
1042                       _VSTD::forward<_Arg>(__arg));
1043  }
1044
1045  inline _LIBCPP_INLINE_VISIBILITY
1046  void __swap(__impl& __that)  {
1047    if (this->valueless_by_exception() && __that.valueless_by_exception()) {
1048      // do nothing.
1049    } else if (this->index() == __that.index()) {
1050      __visitation::__base::__visit_alt_at(
1051          this->index(),
1052          [](auto& __this_alt, auto& __that_alt) {
1053            using _VSTD::swap;
1054            swap(__this_alt.__value, __that_alt.__value);
1055          },
1056          *this,
1057          __that);
1058    } else {
1059      __impl* __lhs = this;
1060      __impl* __rhs = _VSTD::addressof(__that);
1061      if (__lhs->__move_nothrow() && !__rhs->__move_nothrow()) {
1062        _VSTD::swap(__lhs, __rhs);
1063      }
1064      __impl __tmp(_VSTD::move(*__rhs));
1065#ifndef _LIBCPP_NO_EXCEPTIONS
1066      // EXTENSION: When the move construction of `__lhs` into `__rhs` throws
1067      // and `__tmp` is nothrow move constructible then we move `__tmp` back
1068      // into `__rhs` and provide the strong exception safety guarentee.
1069      try {
1070        this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
1071      } catch (...) {
1072        if (__tmp.__move_nothrow()) {
1073          this->__generic_construct(*__rhs, _VSTD::move(__tmp));
1074        }
1075        throw;
1076      }
1077#else
1078      this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
1079#endif
1080      this->__generic_construct(*__lhs, _VSTD::move(__tmp));
1081    }
1082  }
1083
1084private:
1085  inline _LIBCPP_INLINE_VISIBILITY
1086  bool __move_nothrow() const {
1087    constexpr bool __results[] = {is_nothrow_move_constructible_v<_Types>...};
1088    return this->valueless_by_exception() || __results[this->index()];
1089  }
1090};
1091
1092template <class... _Types>
1093struct __overload;
1094
1095template <>
1096struct __overload<> { void operator()() const; };
1097
1098template <class _Tp, class... _Types>
1099struct __overload<_Tp, _Types...> : __overload<_Types...> {
1100  using __overload<_Types...>::operator();
1101  __identity<_Tp> operator()(_Tp) const;
1102};
1103
1104template <class _Tp, class... _Types>
1105using __best_match_t = typename result_of_t<__overload<_Types...>(_Tp&&)>::type;
1106
1107} // __variant_detail
1108
1109template <class... _Types>
1110class _LIBCPP_TEMPLATE_VIS variant
1111    : private __sfinae_ctor_base<
1112          __all<is_copy_constructible_v<_Types>...>::value,
1113          __all<is_move_constructible_v<_Types>...>::value>,
1114      private __sfinae_assign_base<
1115          __all<(is_copy_constructible_v<_Types> &&
1116                 is_copy_assignable_v<_Types>)...>::value,
1117          __all<(is_move_constructible_v<_Types> &&
1118                 is_move_assignable_v<_Types>)...>::value> {
1119  static_assert(0 < sizeof...(_Types),
1120                "variant must consist of at least one alternative.");
1121
1122  static_assert(__all<!is_array_v<_Types>...>::value,
1123                "variant can not have an array type as an alternative.");
1124
1125  static_assert(__all<!is_reference_v<_Types>...>::value,
1126                "variant can not have a reference type as an alternative.");
1127
1128  static_assert(__all<!is_void_v<_Types>...>::value,
1129                "variant can not have a void type as an alternative.");
1130
1131  using __first_type = variant_alternative_t<0, variant>;
1132
1133public:
1134  template <bool _Dummy = true,
1135            enable_if_t<__dependent_type<is_default_constructible<__first_type>,
1136                                         _Dummy>::value,
1137                        int> = 0>
1138  inline _LIBCPP_INLINE_VISIBILITY
1139  constexpr variant() noexcept(is_nothrow_default_constructible_v<__first_type>)
1140      : __impl(in_place_index<0>) {}
1141
1142  variant(const variant&) = default;
1143  variant(variant&&) = default;
1144
1145  template <
1146      class _Arg,
1147      enable_if_t<!is_same_v<__uncvref_t<_Arg>, variant>, int> = 0,
1148      enable_if_t<!__is_inplace_type<__uncvref_t<_Arg>>::value, int> = 0,
1149      enable_if_t<!__is_inplace_index<__uncvref_t<_Arg>>::value, int> = 0,
1150      class _Tp = __variant_detail::__best_match_t<_Arg, _Types...>,
1151      size_t _Ip =
1152          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
1153      enable_if_t<is_constructible_v<_Tp, _Arg>, int> = 0>
1154  inline _LIBCPP_INLINE_VISIBILITY
1155  constexpr variant(_Arg&& __arg) noexcept(
1156      is_nothrow_constructible_v<_Tp, _Arg>)
1157      : __impl(in_place_index<_Ip>, _VSTD::forward<_Arg>(__arg)) {}
1158
1159  template <size_t _Ip, class... _Args,
1160            class = enable_if_t<(_Ip < sizeof...(_Types)), int>,
1161            class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
1162            enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
1163  inline _LIBCPP_INLINE_VISIBILITY
1164  explicit constexpr variant(
1165      in_place_index_t<_Ip>,
1166      _Args&&... __args) noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
1167      : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}
1168
1169  template <
1170      size_t _Ip,
1171      class _Up,
1172      class... _Args,
1173      enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
1174      class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
1175      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1176                  int> = 0>
1177  inline _LIBCPP_INLINE_VISIBILITY
1178  explicit constexpr variant(
1179      in_place_index_t<_Ip>,
1180      initializer_list<_Up> __il,
1181      _Args&&... __args) noexcept(
1182      is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
1183      : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}
1184
1185  template <
1186      class _Tp,
1187      class... _Args,
1188      size_t _Ip =
1189          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
1190      enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
1191  inline _LIBCPP_INLINE_VISIBILITY
1192  explicit constexpr variant(in_place_type_t<_Tp>, _Args&&... __args) noexcept(
1193      is_nothrow_constructible_v<_Tp, _Args...>)
1194      : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}
1195
1196  template <
1197      class _Tp,
1198      class _Up,
1199      class... _Args,
1200      size_t _Ip =
1201          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
1202      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1203                  int> = 0>
1204  inline _LIBCPP_INLINE_VISIBILITY
1205  explicit constexpr variant(
1206      in_place_type_t<_Tp>,
1207      initializer_list<_Up> __il,
1208      _Args&&... __args) noexcept(
1209      is_nothrow_constructible_v<_Tp, initializer_list< _Up>&, _Args...>)
1210      : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}
1211
1212  ~variant() = default;
1213
1214  variant& operator=(const variant&) = default;
1215  variant& operator=(variant&&) = default;
1216
1217  template <
1218      class _Arg,
1219      enable_if_t<!is_same_v<__uncvref_t<_Arg>, variant>, int> = 0,
1220      class _Tp = __variant_detail::__best_match_t<_Arg, _Types...>,
1221      size_t _Ip =
1222          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
1223      enable_if_t<is_assignable_v<_Tp&, _Arg> && is_constructible_v<_Tp, _Arg>,
1224                  int> = 0>
1225  inline _LIBCPP_INLINE_VISIBILITY
1226  variant& operator=(_Arg&& __arg) noexcept(
1227      is_nothrow_assignable_v<_Tp&, _Arg> &&
1228      is_nothrow_constructible_v<_Tp, _Arg>) {
1229    __impl.template __assign<_Ip>(_VSTD::forward<_Arg>(__arg));
1230    return *this;
1231  }
1232
1233  template <
1234      size_t _Ip,
1235      class... _Args,
1236      enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
1237      class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
1238      enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
1239  inline _LIBCPP_INLINE_VISIBILITY
1240  _Tp& emplace(_Args&&... __args) {
1241    return __impl.template __emplace<_Ip>(_VSTD::forward<_Args>(__args)...);
1242  }
1243
1244  template <
1245      size_t _Ip,
1246      class _Up,
1247      class... _Args,
1248      enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
1249      class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
1250      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1251                  int> = 0>
1252  inline _LIBCPP_INLINE_VISIBILITY
1253  _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
1254    return __impl.template __emplace<_Ip>(__il, _VSTD::forward<_Args>(__args)...);
1255  }
1256
1257  template <
1258      class _Tp,
1259      class... _Args,
1260      size_t _Ip =
1261          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
1262      enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
1263  inline _LIBCPP_INLINE_VISIBILITY
1264  _Tp& emplace(_Args&&... __args) {
1265    return __impl.template __emplace<_Ip>(_VSTD::forward<_Args>(__args)...);
1266  }
1267
1268  template <
1269      class _Tp,
1270      class _Up,
1271      class... _Args,
1272      size_t _Ip =
1273          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
1274      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1275                  int> = 0>
1276  inline _LIBCPP_INLINE_VISIBILITY
1277  _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
1278    return __impl.template __emplace<_Ip>(__il, _VSTD::forward<_Args>(__args)...);
1279  }
1280
1281  inline _LIBCPP_INLINE_VISIBILITY
1282  constexpr bool valueless_by_exception() const noexcept {
1283    return __impl.valueless_by_exception();
1284  }
1285
1286  inline _LIBCPP_INLINE_VISIBILITY
1287  constexpr size_t index() const noexcept { return __impl.index(); }
1288
1289  template <
1290      bool _Dummy = true,
1291      enable_if_t<
1292          __all<(
1293              __dependent_type<is_move_constructible<_Types>, _Dummy>::value &&
1294              __dependent_type<is_swappable<_Types>, _Dummy>::value)...>::value,
1295          int> = 0>
1296  inline _LIBCPP_INLINE_VISIBILITY
1297  void swap(variant& __that) noexcept(
1298      __all<(is_nothrow_move_constructible_v<_Types> &&
1299             is_nothrow_swappable_v<_Types>)...>::value) {
1300    __impl.__swap(__that.__impl);
1301  }
1302
1303private:
1304  __variant_detail::__impl<_Types...> __impl;
1305
1306  friend struct __variant_detail::__access::__variant;
1307  friend struct __variant_detail::__visitation::__variant;
1308};
1309
1310template <size_t _Ip, class... _Types>
1311inline _LIBCPP_INLINE_VISIBILITY
1312constexpr bool __holds_alternative(const variant<_Types...>& __v) noexcept {
1313  return __v.index() == _Ip;
1314}
1315
1316template <class _Tp, class... _Types>
1317inline _LIBCPP_INLINE_VISIBILITY
1318constexpr bool holds_alternative(const variant<_Types...>& __v) noexcept {
1319  return __holds_alternative<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
1320}
1321
1322template <size_t _Ip, class _Vp>
1323inline _LIBCPP_INLINE_VISIBILITY
1324constexpr auto&& __generic_get(_Vp&& __v) {
1325  using __variant_detail::__access::__variant;
1326  if (!__holds_alternative<_Ip>(__v)) {
1327    __throw_bad_variant_access();
1328  }
1329  return __variant::__get_alt<_Ip>(_VSTD::forward<_Vp>(__v)).__value;
1330}
1331
1332template <size_t _Ip, class... _Types>
1333inline _LIBCPP_INLINE_VISIBILITY
1334constexpr variant_alternative_t<_Ip, variant<_Types...>>& get(
1335    variant<_Types...>& __v) {
1336  static_assert(_Ip < sizeof...(_Types));
1337  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
1338  return __generic_get<_Ip>(__v);
1339}
1340
1341template <size_t _Ip, class... _Types>
1342inline _LIBCPP_INLINE_VISIBILITY
1343constexpr variant_alternative_t<_Ip, variant<_Types...>>&& get(
1344    variant<_Types...>&& __v) {
1345  static_assert(_Ip < sizeof...(_Types));
1346  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
1347  return __generic_get<_Ip>(_VSTD::move(__v));
1348}
1349
1350template <size_t _Ip, class... _Types>
1351inline _LIBCPP_INLINE_VISIBILITY
1352constexpr const variant_alternative_t<_Ip, variant<_Types...>>& get(
1353    const variant<_Types...>& __v) {
1354  static_assert(_Ip < sizeof...(_Types));
1355  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
1356  return __generic_get<_Ip>(__v);
1357}
1358
1359template <size_t _Ip, class... _Types>
1360inline _LIBCPP_INLINE_VISIBILITY
1361constexpr const variant_alternative_t<_Ip, variant<_Types...>>&& get(
1362    const variant<_Types...>&& __v) {
1363  static_assert(_Ip < sizeof...(_Types));
1364  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
1365  return __generic_get<_Ip>(_VSTD::move(__v));
1366}
1367
1368template <class _Tp, class... _Types>
1369inline _LIBCPP_INLINE_VISIBILITY
1370constexpr _Tp& get(variant<_Types...>& __v) {
1371  static_assert(!is_void_v<_Tp>);
1372  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
1373}
1374
1375template <class _Tp, class... _Types>
1376inline _LIBCPP_INLINE_VISIBILITY
1377constexpr _Tp&& get(variant<_Types...>&& __v) {
1378  static_assert(!is_void_v<_Tp>);
1379  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(
1380      _VSTD::move(__v));
1381}
1382
1383template <class _Tp, class... _Types>
1384inline _LIBCPP_INLINE_VISIBILITY
1385constexpr const _Tp& get(const variant<_Types...>& __v) {
1386  static_assert(!is_void_v<_Tp>);
1387  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
1388}
1389
1390template <class _Tp, class... _Types>
1391inline _LIBCPP_INLINE_VISIBILITY
1392constexpr const _Tp&& get(const variant<_Types...>&& __v) {
1393  static_assert(!is_void_v<_Tp>);
1394  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(
1395      _VSTD::move(__v));
1396}
1397
1398template <size_t _Ip, class _Vp>
1399inline _LIBCPP_INLINE_VISIBILITY
1400constexpr auto* __generic_get_if(_Vp* __v) noexcept {
1401  using __variant_detail::__access::__variant;
1402  return __v && __holds_alternative<_Ip>(*__v)
1403             ? _VSTD::addressof(__variant::__get_alt<_Ip>(*__v).__value)
1404             : nullptr;
1405}
1406
1407template <size_t _Ip, class... _Types>
1408inline _LIBCPP_INLINE_VISIBILITY
1409constexpr add_pointer_t<variant_alternative_t<_Ip, variant<_Types...>>>
1410get_if(variant<_Types...>* __v) noexcept {
1411  static_assert(_Ip < sizeof...(_Types));
1412  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
1413  return __generic_get_if<_Ip>(__v);
1414}
1415
1416template <size_t _Ip, class... _Types>
1417inline _LIBCPP_INLINE_VISIBILITY
1418constexpr add_pointer_t<const variant_alternative_t<_Ip, variant<_Types...>>>
1419get_if(const variant<_Types...>* __v) noexcept {
1420  static_assert(_Ip < sizeof...(_Types));
1421  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
1422  return __generic_get_if<_Ip>(__v);
1423}
1424
1425template <class _Tp, class... _Types>
1426inline _LIBCPP_INLINE_VISIBILITY
1427constexpr add_pointer_t<_Tp>
1428get_if(variant<_Types...>* __v) noexcept {
1429  static_assert(!is_void_v<_Tp>);
1430  return _VSTD::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
1431}
1432
1433template <class _Tp, class... _Types>
1434inline _LIBCPP_INLINE_VISIBILITY
1435constexpr add_pointer_t<const _Tp>
1436get_if(const variant<_Types...>* __v) noexcept {
1437  static_assert(!is_void_v<_Tp>);
1438  return _VSTD::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
1439}
1440
1441template <class _Operator>
1442struct __convert_to_bool {
1443  template <class _T1, class _T2>
1444  _LIBCPP_INLINE_VISIBILITY constexpr bool operator()(_T1 && __t1, _T2&& __t2) const {
1445    static_assert(std::is_convertible<decltype(_Operator{}(_VSTD::forward<_T1>(__t1), _VSTD::forward<_T2>(__t2))), bool>::value,
1446        "the relational operator does not return a type which is implicitly convertible to bool");
1447    return _Operator{}(_VSTD::forward<_T1>(__t1), _VSTD::forward<_T2>(__t2));
1448  }
1449};
1450
1451template <class... _Types>
1452inline _LIBCPP_INLINE_VISIBILITY
1453constexpr bool operator==(const variant<_Types...>& __lhs,
1454                          const variant<_Types...>& __rhs) {
1455  using __variant_detail::__visitation::__variant;
1456  if (__lhs.index() != __rhs.index()) return false;
1457  if (__lhs.valueless_by_exception()) return true;
1458  return __variant::__visit_value_at(__lhs.index(), __convert_to_bool<equal_to<>>{}, __lhs, __rhs);
1459}
1460
1461template <class... _Types>
1462inline _LIBCPP_INLINE_VISIBILITY
1463constexpr bool operator!=(const variant<_Types...>& __lhs,
1464                          const variant<_Types...>& __rhs) {
1465  using __variant_detail::__visitation::__variant;
1466  if (__lhs.index() != __rhs.index()) return true;
1467  if (__lhs.valueless_by_exception()) return false;
1468  return __variant::__visit_value_at(
1469      __lhs.index(), __convert_to_bool<not_equal_to<>>{}, __lhs, __rhs);
1470}
1471
1472template <class... _Types>
1473inline _LIBCPP_INLINE_VISIBILITY
1474constexpr bool operator<(const variant<_Types...>& __lhs,
1475                         const variant<_Types...>& __rhs) {
1476  using __variant_detail::__visitation::__variant;
1477  if (__rhs.valueless_by_exception()) return false;
1478  if (__lhs.valueless_by_exception()) return true;
1479  if (__lhs.index() < __rhs.index()) return true;
1480  if (__lhs.index() > __rhs.index()) return false;
1481  return __variant::__visit_value_at(__lhs.index(), __convert_to_bool<less<>>{}, __lhs, __rhs);
1482}
1483
1484template <class... _Types>
1485inline _LIBCPP_INLINE_VISIBILITY
1486constexpr bool operator>(const variant<_Types...>& __lhs,
1487                         const variant<_Types...>& __rhs) {
1488  using __variant_detail::__visitation::__variant;
1489  if (__lhs.valueless_by_exception()) return false;
1490  if (__rhs.valueless_by_exception()) return true;
1491  if (__lhs.index() > __rhs.index()) return true;
1492  if (__lhs.index() < __rhs.index()) return false;
1493  return __variant::__visit_value_at(__lhs.index(), __convert_to_bool<greater<>>{}, __lhs, __rhs);
1494}
1495
1496template <class... _Types>
1497inline _LIBCPP_INLINE_VISIBILITY
1498constexpr bool operator<=(const variant<_Types...>& __lhs,
1499                          const variant<_Types...>& __rhs) {
1500  using __variant_detail::__visitation::__variant;
1501  if (__lhs.valueless_by_exception()) return true;
1502  if (__rhs.valueless_by_exception()) return false;
1503  if (__lhs.index() < __rhs.index()) return true;
1504  if (__lhs.index() > __rhs.index()) return false;
1505  return __variant::__visit_value_at(
1506      __lhs.index(), __convert_to_bool<less_equal<>>{}, __lhs, __rhs);
1507}
1508
1509template <class... _Types>
1510inline _LIBCPP_INLINE_VISIBILITY
1511constexpr bool operator>=(const variant<_Types...>& __lhs,
1512                          const variant<_Types...>& __rhs) {
1513  using __variant_detail::__visitation::__variant;
1514  if (__rhs.valueless_by_exception()) return true;
1515  if (__lhs.valueless_by_exception()) return false;
1516  if (__lhs.index() > __rhs.index()) return true;
1517  if (__lhs.index() < __rhs.index()) return false;
1518  return __variant::__visit_value_at(
1519      __lhs.index(), __convert_to_bool<greater_equal<>>{}, __lhs, __rhs);
1520}
1521
1522template <class _Visitor, class... _Vs>
1523inline _LIBCPP_INLINE_VISIBILITY
1524constexpr decltype(auto) visit(_Visitor&& __visitor, _Vs&&... __vs) {
1525  using __variant_detail::__visitation::__variant;
1526  bool __results[] = {__vs.valueless_by_exception()...};
1527  for (bool __result : __results) {
1528    if (__result) {
1529      __throw_bad_variant_access();
1530    }
1531  }
1532  return __variant::__visit_value(_VSTD::forward<_Visitor>(__visitor),
1533                                  _VSTD::forward<_Vs>(__vs)...);
1534}
1535
1536struct _LIBCPP_TEMPLATE_VIS monostate {};
1537
1538inline _LIBCPP_INLINE_VISIBILITY
1539constexpr bool operator<(monostate, monostate) noexcept { return false; }
1540
1541inline _LIBCPP_INLINE_VISIBILITY
1542constexpr bool operator>(monostate, monostate) noexcept { return false; }
1543
1544inline _LIBCPP_INLINE_VISIBILITY
1545constexpr bool operator<=(monostate, monostate) noexcept { return true; }
1546
1547inline _LIBCPP_INLINE_VISIBILITY
1548constexpr bool operator>=(monostate, monostate) noexcept { return true; }
1549
1550inline _LIBCPP_INLINE_VISIBILITY
1551constexpr bool operator==(monostate, monostate) noexcept { return true; }
1552
1553inline _LIBCPP_INLINE_VISIBILITY
1554constexpr bool operator!=(monostate, monostate) noexcept { return false; }
1555
1556template <class... _Types>
1557inline _LIBCPP_INLINE_VISIBILITY
1558auto swap(variant<_Types...>& __lhs,
1559          variant<_Types...>& __rhs) noexcept(noexcept(__lhs.swap(__rhs)))
1560    -> decltype(__lhs.swap(__rhs)) {
1561  __lhs.swap(__rhs);
1562}
1563
1564template <class... _Types>
1565struct _LIBCPP_TEMPLATE_VIS hash<
1566    __enable_hash_helper<variant<_Types...>, remove_const_t<_Types>...>> {
1567  using argument_type = variant<_Types...>;
1568  using result_type = size_t;
1569
1570  inline _LIBCPP_INLINE_VISIBILITY
1571  result_type operator()(const argument_type& __v) const {
1572    using __variant_detail::__visitation::__variant;
1573    size_t __res =
1574        __v.valueless_by_exception()
1575               ? 299792458 // Random value chosen by the universe upon creation
1576               : __variant::__visit_alt(
1577                     [](const auto& __alt) {
1578                       using __alt_type = __uncvref_t<decltype(__alt)>;
1579                       using __value_type = remove_const_t<
1580                         typename __alt_type::__value_type>;
1581                       return hash<__value_type>{}(__alt.__value);
1582                     },
1583                     __v);
1584    return __hash_combine(__res, hash<size_t>{}(__v.index()));
1585  }
1586};
1587
1588template <>
1589struct _LIBCPP_TEMPLATE_VIS hash<monostate> {
1590  using argument_type = monostate;
1591  using result_type = size_t;
1592
1593  inline _LIBCPP_INLINE_VISIBILITY
1594  result_type operator()(const argument_type&) const _NOEXCEPT {
1595    return 66740831; // return a fundamentally attractive random value.
1596  }
1597};
1598
1599#endif  // _LIBCPP_STD_VER > 14
1600
1601_LIBCPP_END_NAMESPACE_STD
1602
1603_LIBCPP_POP_MACROS
1604
1605#endif  // _LIBCPP_VARIANT
1606