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// -*- C++ -*-
//===------------------------------ variant -------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_VARIANT
#define _LIBCPP_VARIANT

/*
   variant synopsis

namespace std {

// 20.7.2, class template variant
 template <class... Types>
 class variant {
 public:

// 20.7.2.1, constructors
    constexpr variant() noexcept(see below);
    variant(const variant&);                // constexpr in C++20
    variant(variant&&) noexcept(see below); // constexpr in C++20

template <class T> constexpr variant(T&&) noexcept(see below);

template <class T, class... Args>
 constexpr explicit variant(in_place_type_t<T>, Args&&...);

template <class T, class U, class... Args>
 constexpr explicit variant(
 in_place_type_t<T>, initializer_list, Args&&...);

template <size_t I, class... Args>
 constexpr explicit variant(in_place_index_t, Args&&...);

template <size_t I, class U, class... Args>
 constexpr explicit variant(
 in_place_index_t, initializer_list, Args&&...);

// 20.7.2.2, destructor
    ~variant();

// 20.7.2.3, assignment
    variant& operator=(const variant&);                // constexpr in C++20
    variant& operator=(variant&&) noexcept(see below); // constexpr in C++20

template <class T> variant& operator=(T&&) noexcept(see below);

// 20.7.2.4, modifiers
 template <class T, class... Args>
 T& emplace(Args&&...);

template <class T, class U, class... Args>
 T& emplace(initializer_list, Args&&...);

template <size_t I, class... Args>
 variant_alternative_t<I, variant>& emplace(Args&&...);

template <size_t I, class U, class... Args>
 variant_alternative_t<I, variant>& emplace(initializer_list, Args&&...);

// 20.7.2.5, value status
    constexpr bool valueless_by_exception() const noexcept;
    constexpr size_t index() const noexcept;

// 20.7.2.6, swap
    void swap(variant&) noexcept(see below);
  };

// 20.7.3, variant helper classes
 template <class T> struct variant_size; // undefined

template <class T>
 inline constexpr size_t variant_size_v = variant_size<T>::value;

template <class T> struct variant_size<const T>;
 template <class T> struct variant_size<volatile T>;
 template <class T> struct variant_size<const volatile T>;

template <class... Types>
 struct variant_size<variant<Types...>>;

template <size_t I, class T> struct variant_alternative; // undefined

template <size_t I, class T>
 using variant_alternative_t = typename variant_alternative<I, T>::type;

template <size_t I, class T> struct variant_alternative<I, const T>;
 template <size_t I, class T> struct variant_alternative<I, volatile T>;
 template <size_t I, class T> struct variant_alternative<I, const volatile T>;

template <size_t I, class... Types>
 struct variant_alternative<I, variant<Types...>>;

inline constexpr size_t variant_npos = -1;

// 20.7.4, value access
 template <class T, class... Types>
 constexpr bool holds_alternative(const variant<Types...>&) noexcept;

template <size_t I, class... Types>
 constexpr variant_alternative_t<I, variant<Types...>>&
 get(variant<Types...>&);

template <size_t I, class... Types>
 constexpr variant_alternative_t<I, variant<Types...>>&&
 get(variant<Types...>&&);

template <size_t I, class... Types>
 constexpr variant_alternative_t<I, variant<Types...>> const&
 get(const variant<Types...>&);

template <size_t I, class... Types>
 constexpr variant_alternative_t<I, variant<Types...>> const&&
 get(const variant<Types...>&&);

template <class T, class... Types>
 constexpr T& get(variant<Types...>&);

template <class T, class... Types>
 constexpr T&& get(variant<Types...>&&);

template <class T, class... Types>
 constexpr const T& get(const variant<Types...>&);

template <class T, class... Types>
 constexpr const T&& get(const variant<Types...>&&);

template <size_t I, class... Types>
 constexpr add_pointer_t<variant_alternative_t<I, variant<Types...>>>
 get_if(variant<Types...>*) noexcept;

template <size_t I, class... Types>
 constexpr add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
 get_if(const variant<Types...>*) noexcept;

template <class T, class... Types>
 constexpr add_pointer_t<T>
 get_if(variant<Types...>*) noexcept;

template <class T, class... Types>
 constexpr add_pointer_t<const T>
 get_if(const variant<Types...>*) noexcept;

// 20.7.5, relational operators
 template <class... Types>
 constexpr bool operator==(const variant<Types...>&, const variant<Types...>&);

template <class... Types>
 constexpr bool operator!=(const variant<Types...>&, const variant<Types...>&);

template <class... Types>
 constexpr bool operator<(const variant<Types...>&, const variant<Types...>&);

template <class... Types>
 constexpr bool operator>(const variant<Types...>&, const variant<Types...>&);

template <class... Types>
 constexpr bool operator<=(const variant<Types...>&, const variant<Types...>&);

template <class... Types>
 constexpr bool operator>=(const variant<Types...>&, const variant<Types...>&);

// 20.7.6, visitation
 template <class Visitor, class... Variants>
 constexpr see below visit(Visitor&&, Variants&&...);

// 20.7.7, class monostate
  struct monostate;

// 20.7.8, monostate relational operators
 constexpr bool operator<(monostate, monostate) noexcept;
 constexpr bool operator>(monostate, monostate) noexcept;
 constexpr bool operator<=(monostate, monostate) noexcept;
 constexpr bool operator>=(monostate, monostate) noexcept;
 constexpr bool operator==(monostate, monostate) noexcept;
 constexpr bool operator!=(monostate, monostate) noexcept;

// 20.7.9, specialized algorithms
 template <class... Types>
 void swap(variant<Types...>&, variant<Types...>&) noexcept(see below);

// 20.7.10, class bad_variant_access
  class bad_variant_access;

// 20.7.11, hash support
 template <class T> struct hash;
 template <class... Types> struct hash<variant<Types...>>;
 template <> struct hash<monostate>;

} // namespace std

#include <__config>
#include <__tuple>
#include <array>
#include <exception>
#include <functional>
#include <initializer_list>
#include <new>
#include <tuple>
#include <type_traits>
#include <utility>
#include <limits>
#include <version>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

namespace std { // explicitly not using versioning namespace

class _LIBCPP_EXCEPTION_ABI _LIBCPP_AVAILABILITY_BAD_VARIANT_ACCESS bad_variant_access : public exception {
public:
  virtual const char* what() const _NOEXCEPT;
};

} // namespace std

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER > 14

_LIBCPP_NORETURN
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
void __throw_bad_variant_access() {
#ifndef _LIBCPP_NO_EXCEPTIONS
        throw bad_variant_access();
#else
        _VSTD::abort();
#endif
}

template <class... _Types>
class _LIBCPP_TEMPLATE_VIS variant;

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_size;

template <class _Tp>
_LIBCPP_INLINE_VAR constexpr size_t variant_size_v = variant_size<_Tp>::value;

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_size<const _Tp> : variant_size<_Tp> {};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_size<volatile _Tp> : variant_size<_Tp> {};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_size<const volatile _Tp>
 : variant_size<_Tp> {};

template <class... _Types>
struct _LIBCPP_TEMPLATE_VIS variant_size<variant<_Types...>>
 : integral_constant<size_t, sizeof...(_Types)> {};

template <size_t _Ip, class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_alternative;

template <size_t _Ip, class _Tp>
using variant_alternative_t = typename variant_alternative<_Ip, _Tp>::type;

template <size_t _Ip, class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, const _Tp>
 : add_const<variant_alternative_t<_Ip, _Tp>> {};

template <size_t _Ip, class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, volatile _Tp>
 : add_volatile<variant_alternative_t<_Ip, _Tp>> {};

template <size_t _Ip, class _Tp>
struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, const volatile _Tp>
 : add_cv<variant_alternative_t<_Ip, _Tp>> {};

template <size_t _Ip, class... _Types>
struct _LIBCPP_TEMPLATE_VIS variant_alternative<_Ip, variant<_Types...>> {
 static_assert(_Ip < sizeof...(_Types), "Index out of bounds in std::variant_alternative<>");
 using type = __type_pack_element<_Ip, _Types...>;
};

_LIBCPP_INLINE_VAR constexpr size_t variant_npos = static_cast<size_t>(-1);

constexpr int __choose_index_type(unsigned int __num_elem) {
 if (__num_elem < std::numeric_limits<unsigned char>::max())
 return 0;
 if (__num_elem < std::numeric_limits<unsigned short>::max())
 return 1;
 return 2;
}

template <size_t _NumAlts>
using __variant_index_t =
#ifndef _LIBCPP_ABI_VARIANT_INDEX_TYPE_OPTIMIZATION
 unsigned int;
#else
 std::tuple_element_t<
 __choose_index_type(_NumAlts),
 std::tuple<unsigned char, unsigned short, unsigned int>
 >;
#endif

template <class _IndexType>
constexpr _IndexType __variant_npos = static_cast<_IndexType>(-1);

namespace __find_detail {

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr size_t __find_index() {
 constexpr bool __matches[] = {is_same_v<_Tp, _Types>...};
 size_t __result = __not_found;
 for (size_t __i = 0; __i < sizeof...(_Types); ++__i) {
 if (__matches[__i]) {
 if (__result != __not_found) {
 return __ambiguous;
 }
 __result = __i;
 }
 }
 return __result;
}

template <size_t _Index>
struct __find_unambiguous_index_sfinae_impl
 : integral_constant<size_t, _Index> {};

template <>
struct __find_unambiguous_index_sfinae_impl<__not_found> {};

template <>
struct __find_unambiguous_index_sfinae_impl<__ambiguous> {};

template <class _Tp, class... _Types>
struct __find_unambiguous_index_sfinae
 : __find_unambiguous_index_sfinae_impl<__find_index<_Tp, _Types...>()> {};

} // namespace __find_detail

namespace __variant_detail {

struct __valueless_t {};

enum class _Trait { _TriviallyAvailable, _Available, _Unavailable };

template <typename _Tp,
 template <typename> class _IsTriviallyAvailable,
 template <typename> class _IsAvailable>
constexpr _Trait __trait =
 _IsTriviallyAvailable<_Tp>::value
 ? _Trait::_TriviallyAvailable
 : _IsAvailable<_Tp>::value ? _Trait::_Available : _Trait::_Unavailable;

inline _LIBCPP_INLINE_VISIBILITY
constexpr _Trait __common_trait(initializer_list<_Trait> __traits) {
 _Trait __result = _Trait::_TriviallyAvailable;
 for (_Trait __t : __traits) {
 if (static_cast<int>(__t) > static_cast<int>(__result)) {
 __result = __t;
 }
 }
 return __result;
}

template <typename... _Types>
struct __traits {
 static constexpr _Trait __copy_constructible_trait =
 __common_trait({__trait<_Types,
 is_trivially_copy_constructible,
 is_copy_constructible>...});

static constexpr _Trait __move_constructible_trait =
 __common_trait({__trait<_Types,
 is_trivially_move_constructible,
 is_move_constructible>...});

static constexpr _Trait __copy_assignable_trait = __common_trait(
 {__copy_constructible_trait,
 __trait<_Types, is_trivially_copy_assignable, is_copy_assignable>...});

static constexpr _Trait __move_assignable_trait = __common_trait(
 {__move_constructible_trait,
 __trait<_Types, is_trivially_move_assignable, is_move_assignable>...});

static constexpr _Trait __destructible_trait = __common_trait(
 {__trait<_Types, is_trivially_destructible, is_destructible>...});
};

namespace __access {

struct __union {
 template <class _Vp>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<0>) {
 return _VSTD::forward<_Vp>(__v).__head;
 }

template <class _Vp, size_t _Ip>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<_Ip>) {
 return __get_alt(_VSTD::forward<_Vp>(__v).__tail, in_place_index<_Ip - 1>);
 }
};

struct __base {
 template <size_t _Ip, class _Vp>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto&& __get_alt(_Vp&& __v) {
 return __union::__get_alt(_VSTD::forward<_Vp>(__v).__data,
 in_place_index<_Ip>);
 }
};

struct __variant {
 template <size_t _Ip, class _Vp>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto&& __get_alt(_Vp&& __v) {
 return __base::__get_alt<_Ip>(_VSTD::forward<_Vp>(__v).__impl);
 }
};

} // namespace __access

namespace __visitation {

struct __base {
 template <class _Visitor, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto)
 __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
 constexpr auto __fdiagonal =
 __make_fdiagonal<_Visitor&&,
 decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
 return __fdiagonal[__index](_VSTD::forward<_Visitor>(__visitor),
 _VSTD::forward<_Vs>(__vs).__as_base()...);
 }

template <class _Visitor, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor,
 _Vs&&... __vs) {
 constexpr auto __fmatrix =
 __make_fmatrix<_Visitor&&,
 decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
 return __at(__fmatrix, __vs.index()...)(
 _VSTD::forward<_Visitor>(__visitor),
 _VSTD::forward<_Vs>(__vs).__as_base()...);
 }

private:
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr const _Tp& __at(const _Tp& __elem) { return __elem; }

template <class _Tp, size_t _Np, typename... _Indices>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto&& __at(const array<_Tp, _Np>& __elems,
 size_t __index, _Indices... __indices) {
 return __at(__elems[__index], __indices...);
 }

template <class _Fp, class... _Fs>
 static constexpr void __std_visit_visitor_return_type_check() {
 static_assert(
 __all<is_same_v<_Fp, _Fs>...>::value,
 "`std::visit` requires the visitor to have a single return type.");
 }

template <class... _Fs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_farray(_Fs&&... __fs) {
 __std_visit_visitor_return_type_check<__uncvref_t<_Fs>...>();
 using __result = array<common_type_t<__uncvref_t<_Fs>...>, sizeof...(_Fs)>;
 return __result{{_VSTD::forward<_Fs>(__fs)...}};
 }

template <std::size_t... _Is>
 struct __dispatcher {
 template <class _Fp, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto) __dispatch(_Fp __f, _Vs... __vs) {
 return __invoke_constexpr(
 static_cast<_Fp>(__f),
 __access::__base::__get_alt<_Is>(static_cast<_Vs>(__vs))...);
 }
 };

template <class _Fp, class... _Vs, size_t... _Is>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_dispatch(index_sequence<_Is...>) {
 return __dispatcher<_Is...>::template __dispatch<_Fp, _Vs...>;
 }

template <size_t _Ip, class _Fp, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_fdiagonal_impl() {
 return __make_dispatch<_Fp, _Vs...>(
 index_sequence<(__identity<_Vs>{}, _Ip)...>{});
 }

template <class _Fp, class... _Vs, size_t... _Is>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_fdiagonal_impl(index_sequence<_Is...>) {
 return __base::__make_farray(__make_fdiagonal_impl<_Is, _Fp, _Vs...>()...);
 }

template <class _Fp, class _Vp, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_fdiagonal() {
 constexpr size_t _Np = __uncvref_t<_Vp>::__size();
 static_assert(__all<(_Np == __uncvref_t<_Vs>::__size())...>::value);
 return __make_fdiagonal_impl<_Fp, _Vp, _Vs...>(make_index_sequence<_Np>{});
 }

template <class _Fp, class... _Vs, size_t... _Is>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_fmatrix_impl(index_sequence<_Is...> __is) {
 return __make_dispatch<_Fp, _Vs...>(__is);
 }

template <class _Fp, class... _Vs, size_t... _Is, size_t... _Js, class... _Ls>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_fmatrix_impl(index_sequence<_Is...>,
 index_sequence<_Js...>,
 _Ls... __ls) {
 return __base::__make_farray(__make_fmatrix_impl<_Fp, _Vs...>(
 index_sequence<_Is..., _Js>{}, __ls...)...);
 }

template <class _Fp, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_fmatrix() {
 return __make_fmatrix_impl<_Fp, _Vs...>(
 index_sequence<>{}, make_index_sequence<__uncvref_t<_Vs>::__size()>{}...);
 }
};

struct __variant {
 template <class _Visitor, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto)
 __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
 return __base::__visit_alt_at(__index,
 _VSTD::forward<_Visitor>(__visitor),
 _VSTD::forward<_Vs>(__vs).__impl...);
 }

template <class _Visitor, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor,
 _Vs&&... __vs) {
 return __base::__visit_alt(_VSTD::forward<_Visitor>(__visitor),
 _VSTD::forward<_Vs>(__vs).__impl...);
 }

template <class _Visitor, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto)
 __visit_value_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
 return __visit_alt_at(
 __index,
 __make_value_visitor(_VSTD::forward<_Visitor>(__visitor)),
 _VSTD::forward<_Vs>(__vs)...);
 }

template <class _Visitor, class... _Vs>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr decltype(auto) __visit_value(_Visitor&& __visitor,
 _Vs&&... __vs) {
 return __visit_alt(
 __make_value_visitor(_VSTD::forward<_Visitor>(__visitor)),
 _VSTD::forward<_Vs>(__vs)...);
 }

private:
 template <class _Visitor, class... _Values>
 static constexpr void __std_visit_exhaustive_visitor_check() {
 static_assert(is_invocable_v<_Visitor, _Values...>,
 "`std::visit` requires the visitor to be exhaustive.");
 }

template <class _Visitor>
 struct __value_visitor {
 template <class... _Alts>
 inline _LIBCPP_INLINE_VISIBILITY
 constexpr decltype(auto) operator()(_Alts&&... __alts) const {
 __std_visit_exhaustive_visitor_check<
 _Visitor,
 decltype((_VSTD::forward<_Alts>(__alts).__value))...>();
 return __invoke_constexpr(_VSTD::forward<_Visitor>(__visitor),
 _VSTD::forward<_Alts>(__alts).__value...);
 }
 _Visitor&& __visitor;
 };

template <class _Visitor>
 inline _LIBCPP_INLINE_VISIBILITY
 static constexpr auto __make_value_visitor(_Visitor&& __visitor) {
 return __value_visitor<_Visitor>{_VSTD::forward<_Visitor>(__visitor)};
 }
};

} // namespace __visitation

template <size_t _Index, class _Tp>
struct _LIBCPP_TEMPLATE_VIS __alt {
 using __value_type = _Tp;

template <class... _Args>
 inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr __alt(in_place_t, _Args&&... __args)
 : __value(_VSTD::forward<_Args>(__args)...) {}

__value_type __value;
};

template <_Trait _DestructibleTrait, size_t _Index, class... _Types>
union _LIBCPP_TEMPLATE_VIS __union;

template <_Trait _DestructibleTrait, size_t _Index>
union _LIBCPP_TEMPLATE_VIS __union<_DestructibleTrait, _Index> {};

#define _LIBCPP_VARIANT_UNION(destructible_trait, destructor) \
 template <size_t _Index, class _Tp, class... _Types> \
 union _LIBCPP_TEMPLATE_VIS __union<destructible_trait, \
 _Index, \
 _Tp, \
 _Types...> { \
 public: \
 inline _LIBCPP_INLINE_VISIBILITY \
 explicit constexpr __union(__valueless_t) noexcept : __dummy{} {} \
 \
 template <class... _Args> \
 inline _LIBCPP_INLINE_VISIBILITY \
 explicit constexpr __union(in_place_index_t<0>, _Args&&... __args) \
 : __head(in_place, _VSTD::forward<_Args>(__args)...) {} \
 \
 template <size_t _Ip, class... _Args> \
 inline _LIBCPP_INLINE_VISIBILITY \
 explicit constexpr __union(in_place_index_t<_Ip>, _Args&&... __args) \
 : __tail(in_place_index<_Ip - 1>, _VSTD::forward<_Args>(__args)...) {} \
 \
 __union(const __union&) = default; \
 __union(__union&&) = default; \
 \
 destructor \
 \
 __union& operator=(const __union&) = default; \
 __union& operator=(__union&&) = default; \
 \
 private: \
 char __dummy; \
 __alt<_Index, _Tp> __head; \
 __union<destructible_trait, _Index + 1, _Types...> __tail; \
 \
 friend struct __access::__union; \
 }

_LIBCPP_VARIANT_UNION(_Trait::_TriviallyAvailable, ~__union() = default;);
_LIBCPP_VARIANT_UNION(_Trait::_Available, ~__union() {});
_LIBCPP_VARIANT_UNION(_Trait::_Unavailable, ~__union() = delete;);

#undef _LIBCPP_VARIANT_UNION

template <_Trait _DestructibleTrait, class... _Types>
class _LIBCPP_TEMPLATE_VIS __base {
public:
 using __index_t = __variant_index_t<sizeof...(_Types)>;

inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr __base(__valueless_t tag) noexcept
 : __data(tag), __index(__variant_npos<__index_t>) {}

template <size_t _Ip, class... _Args>
 inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr __base(in_place_index_t<_Ip>, _Args&&... __args)
 :
 __data(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...),
 __index(_Ip) {}

inline _LIBCPP_INLINE_VISIBILITY
  constexpr bool valueless_by_exception() const noexcept {
    return index() == variant_npos;
  }

inline _LIBCPP_INLINE_VISIBILITY
 constexpr size_t index() const noexcept {
 return __index == __variant_npos<__index_t> ? variant_npos : __index;
 }

protected:
  inline _LIBCPP_INLINE_VISIBILITY
  constexpr auto&& __as_base() & { return *this; }

inline _LIBCPP_INLINE_VISIBILITY
  constexpr auto&& __as_base() && { return _VSTD::move(*this); }

inline _LIBCPP_INLINE_VISIBILITY
  constexpr auto&& __as_base() const & { return *this; }

inline _LIBCPP_INLINE_VISIBILITY
  constexpr auto&& __as_base() const && { return _VSTD::move(*this); }

inline _LIBCPP_INLINE_VISIBILITY
  static constexpr size_t __size() { return sizeof...(_Types); }

__union<_DestructibleTrait, 0, _Types...> __data;
 __index_t __index;

friend struct __access::__base;
  friend struct __visitation::__base;
};

template <class _Traits, _Trait = _Traits::__destructible_trait>
class _LIBCPP_TEMPLATE_VIS __destructor;

#define _LIBCPP_VARIANT_DESTRUCTOR(destructible_trait, destructor, destroy) \
 template <class... _Types> \
 class _LIBCPP_TEMPLATE_VIS __destructor<__traits<_Types...>, \
 destructible_trait> \
 : public __base<destructible_trait, _Types...> { \
 using __base_type = __base<destructible_trait, _Types...>; \
 using __index_t = typename __base_type::__index_t; \
 \
 public: \
 using __base_type::__base_type; \
 using __base_type::operator=; \
 \
 __destructor(const __destructor&) = default; \
 __destructor(__destructor&&) = default; \
 destructor \
 __destructor& operator=(const __destructor&) = default; \
 __destructor& operator=(__destructor&&) = default; \
 \
 protected: \
 inline _LIBCPP_INLINE_VISIBILITY \
 destroy \
 }

_LIBCPP_VARIANT_DESTRUCTOR(
 _Trait::_TriviallyAvailable,
 ~__destructor() = default;,
 void __destroy() noexcept { this->__index = __variant_npos<__index_t>; });

_LIBCPP_VARIANT_DESTRUCTOR(
 _Trait::_Available,
 ~__destructor() { __destroy(); },
 void __destroy() noexcept {
 if (!this->valueless_by_exception()) {
 __visitation::__base::__visit_alt(
 [](auto& __alt) noexcept {
 using __alt_type = __uncvref_t<decltype(__alt)>;
 __alt.~__alt_type();
 },
 *this);
 }
 this->__index = __variant_npos<__index_t>;
 });

_LIBCPP_VARIANT_DESTRUCTOR(
    _Trait::_Unavailable,
    ~__destructor() = delete;,
    void __destroy() noexcept = delete;);

#undef _LIBCPP_VARIANT_DESTRUCTOR

template <class _Traits>
class _LIBCPP_TEMPLATE_VIS __constructor : public __destructor<_Traits> {
 using __base_type = __destructor<_Traits>;

public:
  using __base_type::__base_type;
  using __base_type::operator=;

protected:
 template <size_t _Ip, class _Tp, class... _Args>
 inline _LIBCPP_INLINE_VISIBILITY
 static _Tp& __construct_alt(__alt<_Ip, _Tp>& __a, _Args&&... __args) {
 ::new ((void*)_VSTD::addressof(__a))
 __alt<_Ip, _Tp>(in_place, _VSTD::forward<_Args>(__args)...);
 return __a.__value;
 }

template <class _Rhs>
 inline _LIBCPP_INLINE_VISIBILITY
 static void __generic_construct(__constructor& __lhs, _Rhs&& __rhs) {
 __lhs.__destroy();
 if (!__rhs.valueless_by_exception()) {
 __visitation::__base::__visit_alt_at(
 __rhs.index(),
 [](auto& __lhs_alt, auto&& __rhs_alt) {
 __construct_alt(
 __lhs_alt,
 _VSTD::forward<decltype(__rhs_alt)>(__rhs_alt).__value);
 },
 __lhs, _VSTD::forward<_Rhs>(__rhs));
 __lhs.__index = __rhs.index();
 }
 }
};

template <class _Traits, _Trait = _Traits::__move_constructible_trait>
class _LIBCPP_TEMPLATE_VIS __move_constructor;

#define _LIBCPP_VARIANT_MOVE_CONSTRUCTOR(move_constructible_trait, \
 move_constructor) \
 template <class... _Types> \
 class _LIBCPP_TEMPLATE_VIS __move_constructor<__traits<_Types...>, \
 move_constructible_trait> \
 : public __constructor<__traits<_Types...>> { \
 using __base_type = __constructor<__traits<_Types...>>; \
 \
 public: \
 using __base_type::__base_type; \
 using __base_type::operator=; \
 \
 __move_constructor(const __move_constructor&) = default; \
 move_constructor \
 ~__move_constructor() = default; \
 __move_constructor& operator=(const __move_constructor&) = default; \
 __move_constructor& operator=(__move_constructor&&) = default; \
 }

_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
    _Trait::_TriviallyAvailable,
    __move_constructor(__move_constructor&& __that) = default;);

_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
 _Trait::_Available,
 __move_constructor(__move_constructor&& __that) noexcept(
 __all<is_nothrow_move_constructible_v<_Types>...>::value)
 : __move_constructor(__valueless_t{}) {
 this->__generic_construct(*this, _VSTD::move(__that));
 });

_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
    _Trait::_Unavailable,
    __move_constructor(__move_constructor&&) = delete;);

#undef _LIBCPP_VARIANT_MOVE_CONSTRUCTOR

template <class _Traits, _Trait = _Traits::__copy_constructible_trait>
class _LIBCPP_TEMPLATE_VIS __copy_constructor;

#define _LIBCPP_VARIANT_COPY_CONSTRUCTOR(copy_constructible_trait, \
 copy_constructor) \
 template <class... _Types> \
 class _LIBCPP_TEMPLATE_VIS __copy_constructor<__traits<_Types...>, \
 copy_constructible_trait> \
 : public __move_constructor<__traits<_Types...>> { \
 using __base_type = __move_constructor<__traits<_Types...>>; \
 \
 public: \
 using __base_type::__base_type; \
 using __base_type::operator=; \
 \
 copy_constructor \
 __copy_constructor(__copy_constructor&&) = default; \
 ~__copy_constructor() = default; \
 __copy_constructor& operator=(const __copy_constructor&) = default; \
 __copy_constructor& operator=(__copy_constructor&&) = default; \
 }

_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
    _Trait::_TriviallyAvailable,
    __copy_constructor(const __copy_constructor& __that) = default;);

_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
    _Trait::_Available,
    __copy_constructor(const __copy_constructor& __that)
        : __copy_constructor(__valueless_t{}) {
      this->__generic_construct(*this, __that);
    });

_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
    _Trait::_Unavailable,
    __copy_constructor(const __copy_constructor&) = delete;);

#undef _LIBCPP_VARIANT_COPY_CONSTRUCTOR

template <class _Traits>
class _LIBCPP_TEMPLATE_VIS __assignment : public __copy_constructor<_Traits> {
 using __base_type = __copy_constructor<_Traits>;

public:
  using __base_type::__base_type;
  using __base_type::operator=;

template <size_t _Ip, class... _Args>
 inline _LIBCPP_INLINE_VISIBILITY
 auto& __emplace(_Args&&... __args) {
 this->__destroy();
 auto& __res = this->__construct_alt(__access::__base::__get_alt<_Ip>(*this),
 _VSTD::forward<_Args>(__args)...);
 this->__index = _Ip;
 return __res;
 }

protected:
 template <size_t _Ip, class _Tp, class _Arg>
 inline _LIBCPP_INLINE_VISIBILITY
 void __assign_alt(__alt<_Ip, _Tp>& __a, _Arg&& __arg) {
 if (this->index() == _Ip) {
 __a.__value = _VSTD::forward<_Arg>(__arg);
 } else {
 struct {
 void operator()(true_type) const {
 __this->__emplace<_Ip>(_VSTD::forward<_Arg>(__arg));
 }
 void operator()(false_type) const {
 __this->__emplace<_Ip>(_Tp(_VSTD::forward<_Arg>(__arg)));
 }
 __assignment* __this;
 _Arg&& __arg;
 } __impl{this, _VSTD::forward<_Arg>(__arg)};
 __impl(bool_constant<is_nothrow_constructible_v<_Tp, _Arg> ||
 !is_nothrow_move_constructible_v<_Tp>>{});
 }
 }

template <class _That>
 inline _LIBCPP_INLINE_VISIBILITY
 void __generic_assign(_That&& __that) {
 if (this->valueless_by_exception() && __that.valueless_by_exception()) {
 // do nothing.
 } else if (__that.valueless_by_exception()) {
 this->__destroy();
 } else {
 __visitation::__base::__visit_alt_at(
 __that.index(),
 [this](auto& __this_alt, auto&& __that_alt) {
 this->__assign_alt(
 __this_alt,
 _VSTD::forward<decltype(__that_alt)>(__that_alt).__value);
 },
 *this, _VSTD::forward<_That>(__that));
 }
 }
};

template <class _Traits, _Trait = _Traits::__move_assignable_trait>
class _LIBCPP_TEMPLATE_VIS __move_assignment;

#define _LIBCPP_VARIANT_MOVE_ASSIGNMENT(move_assignable_trait, \
 move_assignment) \
 template <class... _Types> \
 class _LIBCPP_TEMPLATE_VIS __move_assignment<__traits<_Types...>, \
 move_assignable_trait> \
 : public __assignment<__traits<_Types...>> { \
 using __base_type = __assignment<__traits<_Types...>>; \
 \
 public: \
 using __base_type::__base_type; \
 using __base_type::operator=; \
 \
 __move_assignment(const __move_assignment&) = default; \
 __move_assignment(__move_assignment&&) = default; \
 ~__move_assignment() = default; \
 __move_assignment& operator=(const __move_assignment&) = default; \
 move_assignment \
 }

_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
    _Trait::_TriviallyAvailable,
    __move_assignment& operator=(__move_assignment&& __that) = default;);

_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
 _Trait::_Available,
 __move_assignment& operator=(__move_assignment&& __that) noexcept(
 __all<(is_nothrow_move_constructible_v<_Types> &&
 is_nothrow_move_assignable_v<_Types>)...>::value) {
 this->__generic_assign(_VSTD::move(__that));
 return *this;
 });

_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
    _Trait::_Unavailable,
    __move_assignment& operator=(__move_assignment&&) = delete;);

#undef _LIBCPP_VARIANT_MOVE_ASSIGNMENT

template <class _Traits, _Trait = _Traits::__copy_assignable_trait>
class _LIBCPP_TEMPLATE_VIS __copy_assignment;

#define _LIBCPP_VARIANT_COPY_ASSIGNMENT(copy_assignable_trait, \
 copy_assignment) \
 template <class... _Types> \
 class _LIBCPP_TEMPLATE_VIS __copy_assignment<__traits<_Types...>, \
 copy_assignable_trait> \
 : public __move_assignment<__traits<_Types...>> { \
 using __base_type = __move_assignment<__traits<_Types...>>; \
 \
 public: \
 using __base_type::__base_type; \
 using __base_type::operator=; \
 \
 __copy_assignment(const __copy_assignment&) = default; \
 __copy_assignment(__copy_assignment&&) = default; \
 ~__copy_assignment() = default; \
 copy_assignment \
 __copy_assignment& operator=(__copy_assignment&&) = default; \
 }

_LIBCPP_VARIANT_COPY_ASSIGNMENT(
    _Trait::_TriviallyAvailable,
    __copy_assignment& operator=(const __copy_assignment& __that) = default;);

_LIBCPP_VARIANT_COPY_ASSIGNMENT(
    _Trait::_Available,
    __copy_assignment& operator=(const __copy_assignment& __that) {
      this->__generic_assign(__that);
      return *this;
    });

_LIBCPP_VARIANT_COPY_ASSIGNMENT(
    _Trait::_Unavailable,
    __copy_assignment& operator=(const __copy_assignment&) = delete;);

#undef _LIBCPP_VARIANT_COPY_ASSIGNMENT

template <class... _Types>
class _LIBCPP_TEMPLATE_VIS __impl
 : public __copy_assignment<__traits<_Types...>> {
 using __base_type = __copy_assignment<__traits<_Types...>>;

public:
  using __base_type::__base_type;
  using __base_type::operator=;

template <size_t _Ip, class _Arg>
 inline _LIBCPP_INLINE_VISIBILITY
 void __assign(_Arg&& __arg) {
 this->__assign_alt(__access::__base::__get_alt<_Ip>(*this),
 _VSTD::forward<_Arg>(__arg));
 }

inline _LIBCPP_INLINE_VISIBILITY
 void __swap(__impl& __that) {
 if (this->valueless_by_exception() && __that.valueless_by_exception()) {
 // do nothing.
 } else if (this->index() == __that.index()) {
 __visitation::__base::__visit_alt_at(
 this->index(),
 [](auto& __this_alt, auto& __that_alt) {
 using _VSTD::swap;
 swap(__this_alt.__value, __that_alt.__value);
 },
 *this,
 __that);
 } else {
 __impl* __lhs = this;
 __impl* __rhs = _VSTD::addressof(__that);
 if (__lhs->__move_nothrow() && !__rhs->__move_nothrow()) {
 _VSTD::swap(__lhs, __rhs);
 }
 __impl __tmp(_VSTD::move(*__rhs));
 static constexpr bool __is_noexcept =
#ifdef _LIBCPP_NO_EXCEPTIONS
 true;
#else
 __all<(is_nothrow_move_constructible_v<_Types> &&
 is_nothrow_swappable_v<_Types>)...>::value;
#endif
 if constexpr (__is_noexcept) {
 this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
 } else {
 // EXTENSION: When the move construction of `__lhs` into `__rhs` throws
 // and `__tmp` is nothrow move constructible then we move `__tmp` back
 // into `__rhs` and provide the strong exception safety guarantee.
 try {
 this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
 } catch (...) {
 if (__tmp.__move_nothrow()) {
 this->__generic_construct(*__rhs, _VSTD::move(__tmp));
 }
 throw;
 }
 }
 this->__generic_construct(*__lhs, _VSTD::move(__tmp));
 }
 }

private:
 inline _LIBCPP_INLINE_VISIBILITY
 bool __move_nothrow() const {
 constexpr bool __results[] = {is_nothrow_move_constructible_v<_Types>...};
 return this->valueless_by_exception() || __results[this->index()];
 }
};

struct __no_narrowing_check {
 template <class _Dest, class _Source>
 using _Apply = __identity<_Dest>;
};

struct __narrowing_check {
 template <class _Dest>
 static auto __test_impl(_Dest (&&)[1]) -> __identity<_Dest>;
 template <class _Dest, class _Source>
 using _Apply _LIBCPP_NODEBUG_TYPE = decltype(__test_impl<_Dest>({std::declval<_Source>()}));
};

template <class _Dest, class _Source>
using __check_for_narrowing _LIBCPP_NODEBUG_TYPE =
 typename _If<
#ifdef _LIBCPP_ENABLE_NARROWING_CONVERSIONS_IN_VARIANT
 false &&
#endif
 is_arithmetic<_Dest>::value,
 __narrowing_check,
 __no_narrowing_check
 >::template _Apply<_Dest, _Source>;

template <class _Tp, size_t _Idx>
struct __overload {
 template <class _Up>
 auto operator()(_Tp, _Up&&) const -> __check_for_narrowing<_Tp, _Up>;
};

template <class _Tp, size_t>
struct __overload_bool {
 template <class _Up, class _Ap = __uncvref_t<_Up>>
 auto operator()(bool, _Up&&) const
 -> enable_if_t<is_same_v<_Ap, bool>, __identity<_Tp>>;
};

template <size_t _Idx>
struct __overload<bool, _Idx> : __overload_bool<bool, _Idx> {};
template <size_t _Idx>
struct __overload<bool const, _Idx> : __overload_bool<bool const, _Idx> {};
template <size_t _Idx>
struct __overload<bool volatile, _Idx> : __overload_bool<bool volatile, _Idx> {};
template <size_t _Idx>
struct __overload<bool const volatile, _Idx> : __overload_bool<bool const volatile, _Idx> {};

template <class ..._Bases>
struct __all_overloads : _Bases... {
 void operator()() const;
 using _Bases::operator()...;
};

template <class IdxSeq>
struct __make_overloads_imp;

template <size_t ..._Idx>
struct __make_overloads_imp<__tuple_indices<_Idx...> > {
 template <class ..._Types>
 using _Apply _LIBCPP_NODEBUG_TYPE = __all_overloads<__overload<_Types, _Idx>...>;
};

template <class ..._Types>
using _MakeOverloads _LIBCPP_NODEBUG_TYPE = typename __make_overloads_imp<
 __make_indices_imp<sizeof...(_Types), 0> >::template _Apply<_Types...>;

template <class _Tp, class... _Types>
using __best_match_t =
 typename invoke_result_t<_MakeOverloads<_Types...>, _Tp, _Tp>::type;

} // __variant_detail

template <class... _Types>
class _LIBCPP_TEMPLATE_VIS variant
 : private __sfinae_ctor_base<
 __all<is_copy_constructible_v<_Types>...>::value,
 __all<is_move_constructible_v<_Types>...>::value>,
 private __sfinae_assign_base<
 __all<(is_copy_constructible_v<_Types> &&
 is_copy_assignable_v<_Types>)...>::value,
 __all<(is_move_constructible_v<_Types> &&
 is_move_assignable_v<_Types>)...>::value> {
 static_assert(0 < sizeof...(_Types),
 "variant must consist of at least one alternative.");

static_assert(__all<!is_array_v<_Types>...>::value,
 "variant can not have an array type as an alternative.");

static_assert(__all<!is_reference_v<_Types>...>::value,
 "variant can not have a reference type as an alternative.");

static_assert(__all<!is_void_v<_Types>...>::value,
 "variant can not have a void type as an alternative.");

using __first_type = variant_alternative_t<0, variant>;

public:
 template <bool _Dummy = true,
 enable_if_t<__dependent_type<is_default_constructible<__first_type>,
 _Dummy>::value,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 constexpr variant() noexcept(is_nothrow_default_constructible_v<__first_type>)
 : __impl(in_place_index<0>) {}

variant(const variant&) = default;
  variant(variant&&) = default;

template <
 class _Arg,
 enable_if_t<!is_same_v<__uncvref_t<_Arg>, variant>, int> = 0,
 enable_if_t<!__is_inplace_type<__uncvref_t<_Arg>>::value, int> = 0,
 enable_if_t<!__is_inplace_index<__uncvref_t<_Arg>>::value, int> = 0,
 class _Tp = __variant_detail::__best_match_t<_Arg, _Types...>,
 size_t _Ip =
 __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
 enable_if_t<is_constructible_v<_Tp, _Arg>, int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 constexpr variant(_Arg&& __arg) noexcept(
 is_nothrow_constructible_v<_Tp, _Arg>)
 : __impl(in_place_index<_Ip>, _VSTD::forward<_Arg>(__arg)) {}

template <size_t _Ip, class... _Args,
 class = enable_if_t<(_Ip < sizeof...(_Types)), int>,
 class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
 enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr variant(
 in_place_index_t<_Ip>,
 _Args&&... __args) noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
 : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}

template <
 size_t _Ip,
 class _Up,
 class... _Args,
 enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
 class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr variant(
 in_place_index_t<_Ip>,
 initializer_list<_Up> __il,
 _Args&&... __args) noexcept(
 is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
 : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}

template <
 class _Tp,
 class... _Args,
 size_t _Ip =
 __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
 enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr variant(in_place_type_t<_Tp>, _Args&&... __args) noexcept(
 is_nothrow_constructible_v<_Tp, _Args...>)
 : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}

template <
 class _Tp,
 class _Up,
 class... _Args,
 size_t _Ip =
 __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 explicit constexpr variant(
 in_place_type_t<_Tp>,
 initializer_list<_Up> __il,
 _Args&&... __args) noexcept(
 is_nothrow_constructible_v<_Tp, initializer_list< _Up>&, _Args...>)
 : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}

~variant() = default;

variant& operator=(const variant&) = default;
  variant& operator=(variant&&) = default;

template <
 class _Arg,
 enable_if_t<!is_same_v<__uncvref_t<_Arg>, variant>, int> = 0,
 class _Tp = __variant_detail::__best_match_t<_Arg, _Types...>,
 size_t _Ip =
 __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
 enable_if_t<is_assignable_v<_Tp&, _Arg> && is_constructible_v<_Tp, _Arg>,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 variant& operator=(_Arg&& __arg) noexcept(
 is_nothrow_assignable_v<_Tp&, _Arg> &&
 is_nothrow_constructible_v<_Tp, _Arg>) {
 __impl.template __assign<_Ip>(_VSTD::forward<_Arg>(__arg));
 return *this;
 }

template <
 size_t _Ip,
 class... _Args,
 enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
 class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
 enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 _Tp& emplace(_Args&&... __args) {
 return __impl.template __emplace<_Ip>(_VSTD::forward<_Args>(__args)...);
 }

template <
 size_t _Ip,
 class _Up,
 class... _Args,
 enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
 class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
 return __impl.template __emplace<_Ip>(__il, _VSTD::forward<_Args>(__args)...);
 }

template <
 class _Tp,
 class... _Args,
 size_t _Ip =
 __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
 enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 _Tp& emplace(_Args&&... __args) {
 return __impl.template __emplace<_Ip>(_VSTD::forward<_Args>(__args)...);
 }

template <
 class _Tp,
 class _Up,
 class... _Args,
 size_t _Ip =
 __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
 return __impl.template __emplace<_Ip>(__il, _VSTD::forward<_Args>(__args)...);
 }

inline _LIBCPP_INLINE_VISIBILITY
  constexpr bool valueless_by_exception() const noexcept {
    return __impl.valueless_by_exception();
  }

inline _LIBCPP_INLINE_VISIBILITY
  constexpr size_t index() const noexcept { return __impl.index(); }

template <
 bool _Dummy = true,
 enable_if_t<
 __all<(
 __dependent_type<is_move_constructible<_Types>, _Dummy>::value &&
 __dependent_type<is_swappable<_Types>, _Dummy>::value)...>::value,
 int> = 0>
 inline _LIBCPP_INLINE_VISIBILITY
 void swap(variant& __that) noexcept(
 __all<(is_nothrow_move_constructible_v<_Types> &&
 is_nothrow_swappable_v<_Types>)...>::value) {
 __impl.__swap(__that.__impl);
 }

private:
 __variant_detail::__impl<_Types...> __impl;

friend struct __variant_detail::__access::__variant;
  friend struct __variant_detail::__visitation::__variant;
};

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool __holds_alternative(const variant<_Types...>& __v) noexcept {
 return __v.index() == _Ip;
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool holds_alternative(const variant<_Types...>& __v) noexcept {
 return __holds_alternative<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <size_t _Ip, class _Vp>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr auto&& __generic_get(_Vp&& __v) {
 using __variant_detail::__access::__variant;
 if (!__holds_alternative<_Ip>(__v)) {
 __throw_bad_variant_access();
 }
 return __variant::__get_alt<_Ip>(_VSTD::forward<_Vp>(__v)).__value;
}

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr variant_alternative_t<_Ip, variant<_Types...>>& get(
 variant<_Types...>& __v) {
 static_assert(_Ip < sizeof...(_Types));
 static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
 return __generic_get<_Ip>(__v);
}

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr variant_alternative_t<_Ip, variant<_Types...>>&& get(
 variant<_Types...>&& __v) {
 static_assert(_Ip < sizeof...(_Types));
 static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
 return __generic_get<_Ip>(_VSTD::move(__v));
}

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr const variant_alternative_t<_Ip, variant<_Types...>>& get(
 const variant<_Types...>& __v) {
 static_assert(_Ip < sizeof...(_Types));
 static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
 return __generic_get<_Ip>(__v);
}

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr const variant_alternative_t<_Ip, variant<_Types...>>&& get(
 const variant<_Types...>&& __v) {
 static_assert(_Ip < sizeof...(_Types));
 static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
 return __generic_get<_Ip>(_VSTD::move(__v));
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr _Tp& get(variant<_Types...>& __v) {
 static_assert(!is_void_v<_Tp>);
 return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr _Tp&& get(variant<_Types...>&& __v) {
 static_assert(!is_void_v<_Tp>);
 return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(
 _VSTD::move(__v));
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr const _Tp& get(const variant<_Types...>& __v) {
 static_assert(!is_void_v<_Tp>);
 return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr const _Tp&& get(const variant<_Types...>&& __v) {
 static_assert(!is_void_v<_Tp>);
 return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(
 _VSTD::move(__v));
}

template <size_t _Ip, class _Vp>
inline _LIBCPP_INLINE_VISIBILITY
constexpr auto* __generic_get_if(_Vp* __v) noexcept {
 using __variant_detail::__access::__variant;
 return __v && __holds_alternative<_Ip>(*__v)
 ? _VSTD::addressof(__variant::__get_alt<_Ip>(*__v).__value)
 : nullptr;
}

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr add_pointer_t<variant_alternative_t<_Ip, variant<_Types...>>>
get_if(variant<_Types...>* __v) noexcept {
 static_assert(_Ip < sizeof...(_Types));
 static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
 return __generic_get_if<_Ip>(__v);
}

template <size_t _Ip, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr add_pointer_t<const variant_alternative_t<_Ip, variant<_Types...>>>
get_if(const variant<_Types...>* __v) noexcept {
 static_assert(_Ip < sizeof...(_Types));
 static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
 return __generic_get_if<_Ip>(__v);
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr add_pointer_t<_Tp>
get_if(variant<_Types...>* __v) noexcept {
 static_assert(!is_void_v<_Tp>);
 return _VSTD::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Tp, class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr add_pointer_t<const _Tp>
get_if(const variant<_Types...>* __v) noexcept {
 static_assert(!is_void_v<_Tp>);
 return _VSTD::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Operator>
struct __convert_to_bool {
 template <class _T1, class _T2>
 _LIBCPP_INLINE_VISIBILITY constexpr bool operator()(_T1 && __t1, _T2&& __t2) const {
 static_assert(std::is_convertible<decltype(_Operator{}(_VSTD::forward<_T1>(__t1), _VSTD::forward<_T2>(__t2))), bool>::value,
 "the relational operator does not return a type which is implicitly convertible to bool");
 return _Operator{}(_VSTD::forward<_T1>(__t1), _VSTD::forward<_T2>(__t2));
 }
};

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator==(const variant<_Types...>& __lhs,
 const variant<_Types...>& __rhs) {
 using __variant_detail::__visitation::__variant;
 if (__lhs.index() != __rhs.index()) return false;
 if (__lhs.valueless_by_exception()) return true;
 return __variant::__visit_value_at(__lhs.index(), __convert_to_bool<equal_to<>>{}, __lhs, __rhs);
}

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator!=(const variant<_Types...>& __lhs,
 const variant<_Types...>& __rhs) {
 using __variant_detail::__visitation::__variant;
 if (__lhs.index() != __rhs.index()) return true;
 if (__lhs.valueless_by_exception()) return false;
 return __variant::__visit_value_at(
 __lhs.index(), __convert_to_bool<not_equal_to<>>{}, __lhs, __rhs);
}

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator<(const variant<_Types...>& __lhs,
 const variant<_Types...>& __rhs) {
 using __variant_detail::__visitation::__variant;
 if (__rhs.valueless_by_exception()) return false;
 if (__lhs.valueless_by_exception()) return true;
 if (__lhs.index() < __rhs.index()) return true;
 if (__lhs.index() > __rhs.index()) return false;
 return __variant::__visit_value_at(__lhs.index(), __convert_to_bool<less<>>{}, __lhs, __rhs);
}

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator>(const variant<_Types...>& __lhs,
 const variant<_Types...>& __rhs) {
 using __variant_detail::__visitation::__variant;
 if (__lhs.valueless_by_exception()) return false;
 if (__rhs.valueless_by_exception()) return true;
 if (__lhs.index() > __rhs.index()) return true;
 if (__lhs.index() < __rhs.index()) return false;
 return __variant::__visit_value_at(__lhs.index(), __convert_to_bool<greater<>>{}, __lhs, __rhs);
}

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator<=(const variant<_Types...>& __lhs,
 const variant<_Types...>& __rhs) {
 using __variant_detail::__visitation::__variant;
 if (__lhs.valueless_by_exception()) return true;
 if (__rhs.valueless_by_exception()) return false;
 if (__lhs.index() < __rhs.index()) return true;
 if (__lhs.index() > __rhs.index()) return false;
 return __variant::__visit_value_at(
 __lhs.index(), __convert_to_bool<less_equal<>>{}, __lhs, __rhs);
}

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator>=(const variant<_Types...>& __lhs,
 const variant<_Types...>& __rhs) {
 using __variant_detail::__visitation::__variant;
 if (__rhs.valueless_by_exception()) return true;
 if (__lhs.valueless_by_exception()) return false;
 if (__lhs.index() > __rhs.index()) return true;
 if (__lhs.index() < __rhs.index()) return false;
 return __variant::__visit_value_at(
 __lhs.index(), __convert_to_bool<greater_equal<>>{}, __lhs, __rhs);
}

template <class _Visitor, class... _Vs>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
constexpr decltype(auto) visit(_Visitor&& __visitor, _Vs&&... __vs) {
 using __variant_detail::__visitation::__variant;
 bool __results[] = {__vs.valueless_by_exception()...};
 for (bool __result : __results) {
 if (__result) {
 __throw_bad_variant_access();
 }
 }
 return __variant::__visit_value(_VSTD::forward<_Visitor>(__visitor),
 _VSTD::forward<_Vs>(__vs)...);
}

struct _LIBCPP_TEMPLATE_VIS monostate {};

inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator<(monostate, monostate) noexcept { return false; }

inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator>(monostate, monostate) noexcept { return false; }

inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator<=(monostate, monostate) noexcept { return true; }

inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator>=(monostate, monostate) noexcept { return true; }

inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator==(monostate, monostate) noexcept { return true; }

inline _LIBCPP_INLINE_VISIBILITY
constexpr bool operator!=(monostate, monostate) noexcept { return false; }

template <class... _Types>
inline _LIBCPP_INLINE_VISIBILITY
auto swap(variant<_Types...>& __lhs,
 variant<_Types...>& __rhs) noexcept(noexcept(__lhs.swap(__rhs)))
 -> decltype(__lhs.swap(__rhs)) {
 __lhs.swap(__rhs);
}

template <class... _Types>
struct _LIBCPP_TEMPLATE_VIS hash<
 __enable_hash_helper<variant<_Types...>, remove_const_t<_Types>...>> {
 using argument_type = variant<_Types...>;
 using result_type = size_t;

inline _LIBCPP_INLINE_VISIBILITY
 result_type operator()(const argument_type& __v) const {
 using __variant_detail::__visitation::__variant;
 size_t __res =
 __v.valueless_by_exception()
 ? 299792458 // Random value chosen by the universe upon creation
 : __variant::__visit_alt(
 [](const auto& __alt) {
 using __alt_type = __uncvref_t<decltype(__alt)>;
 using __value_type = remove_const_t<
 typename __alt_type::__value_type>;
 return hash<__value_type>{}(__alt.__value);
 },
 __v);
 return __hash_combine(__res, hash<size_t>{}(__v.index()));
 }
};

template <>
struct _LIBCPP_TEMPLATE_VIS hash<monostate> {
 using argument_type = monostate;
 using result_type = size_t;

inline _LIBCPP_INLINE_VISIBILITY
  result_type operator()(const argument_type&) const _NOEXCEPT {
    return 66740831; // return a fundamentally attractive random value.
  }
};

#endif  // _LIBCPP_STD_VER > 14

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif  // _LIBCPP_VARIANT

int main(){
 using V = std::variant<int, double>;
 V a = 5;
 V b = 5.6;

a.swap(b);
}