lib: establish Zircon libc++ and KTL foundation

1 files changed, 1655 insertions, 0 deletions

diff --git a/third_party/libcxx/include/c++/v1/variant b/third_party/libcxx/include/c++/v1/variant
new file mode 100644
index 0000000..9b2c4ee
--- /dev/null
+++ b/third_party/libcxx/include/c++/v1/variant
@@ -0,0 +1,1655 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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);
+    constexpr variant(const variant&);
+    constexpr variant(variant&&) noexcept(see below);
+
+    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<U>, Args&&...);
+
+    template <size_t I, class... Args>
+    constexpr explicit variant(in_place_index_t<I>, Args&&...);
+
+    template <size_t I, class U, class... Args>
+    constexpr explicit variant(
+        in_place_index_t<I>, initializer_list<U>, Args&&...);
+
+    // 20.7.2.2, destructor
+    constexpr ~variant();                                             // constexpr since c++20
+
+    // 20.7.2.3, assignment
+    constexpr variant& operator=(const variant&);
+    constexpr variant& operator=(variant&&) noexcept(see below);
+
+    template <class T>
+    constexpr variant& operator=(T&&) noexcept(see below);            // constexpr since c++20
+
+    // 20.7.2.4, modifiers
+    template <class T, class... Args>
+    constexpr T& emplace(Args&&...);                                  // constexpr since c++20
+
+    template <class T, class U, class... Args>
+    constexpr T& emplace(initializer_list<U>, Args&&...);             // constexpr since c++20
+
+    template <size_t I, class... Args>
+    constexpr variant_alternative_t<I, variant>& emplace(Args&&...);  // constexpr since c++20
+
+    template <size_t I, class U, class...  Args>
+    constexpr variant_alternative_t<I, variant>&
+        emplace(initializer_list<U>, Args&&...);                      // constexpr since c++20
+
+    // 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);
+
+    // [variant.visit], visitation
+    template<class Self, class Visitor>
+      constexpr decltype(auto) visit(this Self&&, Visitor&&); // Since C++26
+    template<class R, class Self, class Visitor>
+      constexpr R visit(this Self&&, Visitor&&);              // Since C++26
+  };
+
+  // 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...>&);
+
+  template <class... Types> requires (three_way_comparable<Types> && ...)
+  constexpr common_comparison_category_t<compare_three_way_result_t<Types>...>
+    operator<=>(const variant<Types...>&, const variant<Types...>&);           // since C++20
+
+  // 20.7.6, visitation
+  template <class Visitor, class... Variants>
+  constexpr see below visit(Visitor&&, Variants&&...);
+
+  template <class R, class Visitor, class... Variants>
+  constexpr R visit(Visitor&&, Variants&&...); // since C++20
+
+  // 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;             // until C++20
+  constexpr bool operator<(monostate, monostate) noexcept;              // until C++20
+  constexpr bool operator>(monostate, monostate) noexcept;              // until C++20
+  constexpr bool operator<=(monostate, monostate) noexcept;             // until C++20
+  constexpr bool operator>=(monostate, monostate) noexcept;             // until C++20
+  constexpr strong_ordering operator<=>(monostate, monostate) noexcept; // since C++20
+
+  // 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
+
+*/
+
+#if __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
+#  include <__cxx03/__config>
+#else
+#  include <__compare/common_comparison_category.h>
+#  include <__compare/compare_three_way_result.h>
+#  include <__compare/ordering.h>
+#  include <__compare/three_way_comparable.h>
+#  include <__config>
+#  include <__exception/exception.h>
+#  include <__functional/hash.h>
+#  include <__functional/operations.h>
+#  include <__functional/unary_function.h>
+#  include <__fwd/variant.h>
+#  include <__memory/addressof.h>
+#  include <__memory/construct_at.h>
+#  include <__tuple/find_index.h>
+#  include <__tuple/sfinae_helpers.h>
+#  include <__type_traits/add_cv_quals.h>
+#  include <__type_traits/add_pointer.h>
+#  include <__type_traits/common_type.h>
+#  include <__type_traits/conditional.h>
+#  include <__type_traits/conjunction.h>
+#  include <__type_traits/decay.h>
+#  include <__type_traits/dependent_type.h>
+#  include <__type_traits/enable_if.h>
+#  include <__type_traits/invoke.h>
+#  include <__type_traits/is_array.h>
+#  include <__type_traits/is_assignable.h>
+#  include <__type_traits/is_constructible.h>
+#  include <__type_traits/is_convertible.h>
+#  include <__type_traits/is_core_convertible.h>
+#  include <__type_traits/is_destructible.h>
+#  include <__type_traits/is_nothrow_assignable.h>
+#  include <__type_traits/is_nothrow_constructible.h>
+#  include <__type_traits/is_reference.h>
+#  include <__type_traits/is_same.h>
+#  include <__type_traits/is_swappable.h>
+#  include <__type_traits/is_trivially_assignable.h>
+#  include <__type_traits/is_trivially_constructible.h>
+#  include <__type_traits/is_trivially_destructible.h>
+#  include <__type_traits/is_trivially_relocatable.h>
+#  include <__type_traits/is_void.h>
+#  include <__type_traits/remove_const.h>
+#  include <__type_traits/remove_cvref.h>
+#  include <__type_traits/remove_reference.h>
+#  include <__type_traits/type_identity.h>
+#  include <__type_traits/void_t.h>
+#  include <__utility/declval.h>
+#  include <__utility/forward.h>
+#  include <__utility/forward_like.h>
+#  include <__utility/in_place.h>
+#  include <__utility/integer_sequence.h>
+#  include <__utility/move.h>
+#  include <__utility/swap.h>
+#  include <__variant/monostate.h>
+#  include <__verbose_abort>
+#  include <initializer_list>
+#  include <limits>
+#  include <version>
+
+// standard-mandated includes
+
+// [variant.syn]
+#  include <compare>
+
+#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#    pragma GCC system_header
+#  endif
+
+_LIBCPP_PUSH_MACROS
+#  include <__undef_macros>
+
+_LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD
+
+class _LIBCPP_EXPORTED_FROM_ABI bad_variant_access : public exception {
+public:
+  [[__nodiscard__]] const char* what() const _NOEXCEPT override;
+};
+
+_LIBCPP_END_UNVERSIONED_NAMESPACE_STD
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#  if _LIBCPP_STD_VER >= 17
+
+// Light N-dimensional array of function pointers. Used in place of std::array to avoid
+// adding a dependency.
+template <class _Tp, size_t _Size>
+struct __farray {
+  static_assert(_Size > 0, "N-dimensional array should never be empty in std::visit");
+  _Tp __buf_[_Size] = {};
+
+  _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator[](size_t __n) const noexcept { return __buf_[__n]; }
+};
+
+[[noreturn]] inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_variant_access() {
+#    if _LIBCPP_HAS_EXCEPTIONS
+  throw bad_variant_access();
+#    else
+  _LIBCPP_VERBOSE_ABORT("bad_variant_access was thrown in -fno-exceptions mode");
+#    endif
+}
+
+// variant_size
+template <class _Tp>
+struct variant_size<const _Tp> : variant_size<_Tp> {};
+
+template <class _Tp>
+struct variant_size<volatile _Tp> : variant_size<_Tp> {};
+
+template <class _Tp>
+struct variant_size<const volatile _Tp> : variant_size<_Tp> {};
+
+template <class... _Types>
+struct variant_size<variant<_Types...>> : integral_constant<size_t, sizeof...(_Types)> {};
+
+// variant_alternative
+template <size_t _Ip, class _Tp>
+struct variant_alternative<_Ip, const _Tp> : add_const<variant_alternative_t<_Ip, _Tp>> {};
+
+template <size_t _Ip, class _Tp>
+struct variant_alternative<_Ip, volatile _Tp> : add_volatile<variant_alternative_t<_Ip, _Tp>> {};
+
+template <size_t _Ip, class _Tp>
+struct variant_alternative<_Ip, const volatile _Tp> : add_cv<variant_alternative_t<_Ip, _Tp>> {};
+
+template <size_t _Ip, class... _Types>
+struct variant_alternative<_Ip, variant<_Types...>> {
+  static_assert(_Ip < sizeof...(_Types), "Index out of bounds in std::variant_alternative<>");
+  using type _LIBCPP_NODEBUG = __type_pack_element<_Ip, _Types...>;
+};
+
+template <size_t _NumAlternatives>
+_LIBCPP_HIDE_FROM_ABI constexpr auto __choose_index_type() {
+#    ifdef _LIBCPP_ABI_VARIANT_INDEX_TYPE_OPTIMIZATION
+  if constexpr (_NumAlternatives < numeric_limits<unsigned char>::max())
+    return static_cast<unsigned char>(0);
+  else if constexpr (_NumAlternatives < numeric_limits<unsigned short>::max())
+    return static_cast<unsigned short>(0);
+  else
+#    endif // _LIBCPP_ABI_VARIANT_INDEX_TYPE_OPTIMIZATION
+    return static_cast<unsigned int>(0);
+}
+
+template <size_t _NumAlts>
+using __variant_index_t _LIBCPP_NODEBUG = decltype(std::__choose_index_type<_NumAlts>());
+
+template <class _IndexType>
+constexpr _IndexType __variant_npos = static_cast<_IndexType>(-1);
+
+template <class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr variant<_Types...>& __as_variant(variant<_Types...>& __vs) noexcept {
+  return __vs;
+}
+
+template <class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr const variant<_Types...>& __as_variant(const variant<_Types...>& __vs) noexcept {
+  return __vs;
+}
+
+template <class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr variant<_Types...>&& __as_variant(variant<_Types...>&& __vs) noexcept {
+  return std::move(__vs);
+}
+
+template <class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr const variant<_Types...>&& __as_variant(const variant<_Types...>&& __vs) noexcept {
+  return std::move(__vs);
+}
+
+namespace __find_detail {
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI 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_detail::__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;
+
+_LIBCPP_HIDE_FROM_ABI 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 =
+      __variant_detail::__common_trait({__trait<_Types, is_trivially_copy_constructible, is_copy_constructible>...});
+
+  static constexpr _Trait __move_constructible_trait =
+      __variant_detail::__common_trait({__trait<_Types, is_trivially_move_constructible, is_move_constructible>...});
+
+  static constexpr _Trait __copy_assignable_trait = __variant_detail::__common_trait(
+      {__copy_constructible_trait, __trait<_Types, is_trivially_copy_assignable, is_copy_assignable>...});
+
+  static constexpr _Trait __move_assignable_trait = __variant_detail::__common_trait(
+      {__move_constructible_trait, __trait<_Types, is_trivially_move_assignable, is_move_assignable>...});
+
+  static constexpr _Trait __destructible_trait =
+      __variant_detail::__common_trait({__trait<_Types, is_trivially_destructible, is_destructible>...});
+};
+
+namespace __access {
+
+struct __union {
+  template <class _Vp>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<0>) {
+    return std::forward<_Vp>(__v).__head;
+  }
+
+  template <class _Vp, size_t _Ip>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<_Ip>) {
+    return __get_alt(std::forward<_Vp>(__v).__tail, in_place_index<_Ip - 1>);
+  }
+};
+
+struct __base {
+  template <size_t _Ip, class _Vp>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto&& __get_alt(_Vp&& __v) {
+    return __union::__get_alt(std::forward<_Vp>(__v).__data, in_place_index<_Ip>);
+  }
+};
+
+struct __variant {
+  template <size_t _Ip, class _Vp>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto&& __get_alt(_Vp&& __v) {
+    return __base::__get_alt<_Ip>(std::forward<_Vp>(__v).__impl_);
+  }
+};
+
+} // namespace __access
+
+namespace __visitation {
+
+struct __base {
+  template <class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto)
+  __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
+    constexpr auto __fdiagonal = __make_fdiagonal<_Visitor&&, decltype(std::forward<_Vs>(__vs).__as_base())...>();
+    return __fdiagonal[__index](std::forward<_Visitor>(__visitor), std::forward<_Vs>(__vs).__as_base()...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor, _Vs&&... __vs) {
+    constexpr auto __fmatrix = __make_fmatrix<_Visitor&&, decltype(std::forward<_Vs>(__vs).__as_base())...>();
+    return __at(__fmatrix, __vs.index()...)(std::forward<_Visitor>(__visitor), std::forward<_Vs>(__vs).__as_base()...);
+  }
+
+private:
+  template <class _Tp>
+  _LIBCPP_HIDE_FROM_ABI static constexpr const _Tp& __at(const _Tp& __elem) {
+    return __elem;
+  }
+
+  template <class _Tp, size_t _Np, typename... _Indices>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto&&
+  __at(const __farray<_Tp, _Np>& __elems, size_t __index, _Indices... __indices) {
+    return __at(__elems[__index], __indices...);
+  }
+
+  template <class _Fp, class... _Fs>
+  static _LIBCPP_HIDE_FROM_ABI 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>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_farray(_Fs&&... __fs) {
+    __std_visit_visitor_return_type_check<__remove_cvref_t<_Fs>...>();
+    using __result = __farray<common_type_t<__remove_cvref_t<_Fs>...>, sizeof...(_Fs)>;
+    return __result{{std::forward<_Fs>(__fs)...}};
+  }
+
+  template <size_t... _Is>
+  struct __dispatcher {
+    template <class _Fp, class... _Vs>
+    _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto) __dispatch(_Fp __f, _Vs... __vs) {
+      return std::__invoke(static_cast<_Fp>(__f), __access::__base::__get_alt<_Is>(static_cast<_Vs>(__vs))...);
+    }
+  };
+
+  template <class _Fp, class... _Vs, size_t... _Is>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_dispatch(index_sequence<_Is...>) {
+    return __dispatcher<_Is...>::template __dispatch<_Fp, _Vs...>;
+  }
+
+  template <size_t _Ip, class _Fp, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_fdiagonal_impl() {
+    return __make_dispatch<_Fp, _Vs...>(index_sequence<((void)__type_identity<_Vs>{}, _Ip)...>{});
+  }
+
+  template <class _Fp, class... _Vs, size_t... _Is>
+  _LIBCPP_HIDE_FROM_ABI 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>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_fdiagonal() {
+    constexpr size_t __np = __remove_cvref_t<_Vp>::__size();
+    static_assert(__all<(__np == __remove_cvref_t<_Vs>::__size())...>::value);
+    return __make_fdiagonal_impl<_Fp, _Vp, _Vs...>(make_index_sequence<__np>{});
+  }
+
+  template <class _Fp, class... _Vs, size_t... _Is>
+  _LIBCPP_HIDE_FROM_ABI 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>
+  _LIBCPP_HIDE_FROM_ABI 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>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_fmatrix() {
+    return __make_fmatrix_impl<_Fp, _Vs...>(
+        index_sequence<>{}, make_index_sequence<__remove_cvref_t<_Vs>::__size()>{}...);
+  }
+};
+
+struct __variant {
+  template <class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto)
+  __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
+    return __base::__visit_alt_at(__index, std::forward<_Visitor>(__visitor), std::forward<_Vs>(__vs).__impl_...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor, _Vs&&... __vs) {
+    return __base::__visit_alt(
+        std::forward<_Visitor>(__visitor), std::__as_variant(std::forward<_Vs>(__vs)).__impl_...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto)
+  __visit_value_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
+    return __visit_alt_at(__index, __make_value_visitor(std::forward<_Visitor>(__visitor)), std::forward<_Vs>(__vs)...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto) __visit_value(_Visitor&& __visitor, _Vs&&... __vs) {
+    return __visit_alt(__make_value_visitor(std::forward<_Visitor>(__visitor)), std::forward<_Vs>(__vs)...);
+  }
+
+#    if _LIBCPP_STD_VER >= 20
+  template <class _Rp, class _Visitor, class... _Vs>
+  _LIBCPP_HIDE_FROM_ABI static constexpr _Rp __visit_value(_Visitor&& __visitor, _Vs&&... __vs) {
+    return __visit_alt(__make_value_visitor<_Rp>(std::forward<_Visitor>(__visitor)), std::forward<_Vs>(__vs)...);
+  }
+#    endif
+
+private:
+  template <class _Visitor, class... _Values>
+  static _LIBCPP_HIDE_FROM_ABI 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>
+    _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Alts&&... __alts) const
+        -> invoke_result_t<_Visitor&&, decltype((std::forward<_Alts>(__alts).__value))...> {
+      __std_visit_exhaustive_visitor_check< _Visitor, decltype((std::forward<_Alts>(__alts).__value))...>();
+      return std::__invoke(std::forward<_Visitor>(__visitor), std::forward<_Alts>(__alts).__value...);
+    }
+    _Visitor&& __visitor;
+  };
+
+#    if _LIBCPP_STD_VER >= 20
+  template <class _Rp, class _Visitor>
+  struct __value_visitor_return_type {
+    template <class... _Alts>
+    _LIBCPP_HIDE_FROM_ABI constexpr _Rp operator()(_Alts&&... __alts) const {
+      __std_visit_exhaustive_visitor_check< _Visitor, decltype((std::forward<_Alts>(__alts).__value))...>();
+      if constexpr (is_void_v<_Rp>) {
+        std::__invoke(std::forward<_Visitor>(__visitor), std::forward<_Alts>(__alts).__value...);
+      } else {
+        return std::__invoke(std::forward<_Visitor>(__visitor), std::forward<_Alts>(__alts).__value...);
+      }
+    }
+
+    _Visitor&& __visitor;
+  };
+#    endif
+
+  template <class _Visitor>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_value_visitor(_Visitor&& __visitor) {
+    return __value_visitor<_Visitor>{std::forward<_Visitor>(__visitor)};
+  }
+
+#    if _LIBCPP_STD_VER >= 20
+  template <class _Rp, class _Visitor>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __make_value_visitor(_Visitor&& __visitor) {
+    return __value_visitor_return_type<_Rp, _Visitor>{std::forward<_Visitor>(__visitor)};
+  }
+#    endif
+};
+
+} // namespace __visitation
+
+// Adding semi-colons in macro expansions helps clang-format to do a better job.
+// This macro is used to avoid compilation errors due to "stray" semi-colons.
+#    define _LIBCPP_EAT_SEMICOLON static_assert(true, "")
+
+template <size_t _Index, class _Tp>
+struct __alt {
+  using __value_type _LIBCPP_NODEBUG = _Tp;
+  static constexpr size_t __index    = _Index;
+
+  template <class... _Args>
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr __alt(in_place_t, _Args&&... __args)
+      : __value(std::forward<_Args>(__args)...) {}
+
+  __value_type __value;
+};
+
+template <_Trait _DestructibleTrait, size_t _Index, class... _Types>
+union __union;
+
+template <_Trait _DestructibleTrait, size_t _Index>
+union __union<_DestructibleTrait, _Index> {};
+
+#    define _LIBCPP_VARIANT_UNION(destructible_trait, destructor_definition)                                           \
+      template <size_t _Index, class _Tp, class... _Types>                                                             \
+      union __union<destructible_trait, _Index, _Tp, _Types...> {                                                      \
+      public:                                                                                                          \
+        _LIBCPP_HIDE_FROM_ABI explicit constexpr __union(__valueless_t) noexcept : __dummy{} {}                        \
+                                                                                                                       \
+        template <class... _Args>                                                                                      \
+        _LIBCPP_HIDE_FROM_ABI explicit constexpr __union(in_place_index_t<0>, _Args&&... __args)                       \
+            : __head(in_place, std::forward<_Args>(__args)...) {}                                                      \
+                                                                                                                       \
+        template <size_t _Ip, class... _Args>                                                                          \
+        _LIBCPP_HIDE_FROM_ABI explicit constexpr __union(in_place_index_t<_Ip>, _Args&&... __args)                     \
+            : __tail(in_place_index<_Ip - 1>, std::forward<_Args>(__args)...) {}                                       \
+                                                                                                                       \
+        _LIBCPP_HIDE_FROM_ABI __union(const __union&)            = default;                                            \
+        _LIBCPP_HIDE_FROM_ABI __union(__union&&)                 = default;                                            \
+        _LIBCPP_HIDE_FROM_ABI __union& operator=(const __union&) = default;                                            \
+        _LIBCPP_HIDE_FROM_ABI __union& operator=(__union&&)      = default;                                            \
+        destructor_definition;                                                                                         \
+                                                                                                                       \
+      private:                                                                                                         \
+        char __dummy;                                                                                                  \
+        __alt<_Index, _Tp> __head;                                                                                     \
+        __union<destructible_trait, _Index + 1, _Types...> __tail;                                                     \
+                                                                                                                       \
+        friend struct __access::__union;                                                                               \
+      }
+
+_LIBCPP_VARIANT_UNION(_Trait::_TriviallyAvailable,
+                      _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__union() = default);
+_LIBCPP_VARIANT_UNION(
+    _Trait::_Available, _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__union() {} _LIBCPP_EAT_SEMICOLON);
+_LIBCPP_VARIANT_UNION(_Trait::_Unavailable, _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__union() = delete);
+
+#    undef _LIBCPP_VARIANT_UNION
+
+template <_Trait _DestructibleTrait, class... _Types>
+class __base {
+public:
+  using __index_t _LIBCPP_NODEBUG = __variant_index_t<sizeof...(_Types)>;
+
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr __base(__valueless_t __tag) noexcept
+      : __data(__tag), __index(__variant_npos<__index_t>) {}
+
+  template <size_t _Ip, class... _Args>
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr __base(in_place_index_t<_Ip>, _Args&&... __args)
+      : __data(in_place_index<_Ip>, std::forward<_Args>(__args)...), __index(_Ip) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr bool valueless_by_exception() const noexcept { return index() == variant_npos; }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr size_t index() const noexcept {
+    return __index == __variant_npos<__index_t> ? variant_npos : __index;
+  }
+
+protected:
+  _LIBCPP_HIDE_FROM_ABI constexpr auto&& __as_base() & { return *this; }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto&& __as_base() && { return std::move(*this); }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto&& __as_base() const& { return *this; }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto&& __as_base() const&& { return std::move(*this); }
+
+  _LIBCPP_HIDE_FROM_ABI 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 __dtor;
+
+#    define _LIBCPP_VARIANT_DESTRUCTOR(destructible_trait, destructor_definition, destroy)                             \
+      template <class... _Types>                                                                                       \
+      class __dtor<__traits<_Types...>, destructible_trait> : public __base<destructible_trait, _Types...> {           \
+        using __base_type _LIBCPP_NODEBUG = __base<destructible_trait, _Types...>;                                     \
+        using __index_t _LIBCPP_NODEBUG   = typename __base_type::__index_t;                                           \
+                                                                                                                       \
+      public:                                                                                                          \
+        using __base_type::__base_type;                                                                                \
+        using __base_type::operator=;                                                                                  \
+        _LIBCPP_HIDE_FROM_ABI __dtor(const __dtor&)            = default;                                              \
+        _LIBCPP_HIDE_FROM_ABI __dtor(__dtor&&)                 = default;                                              \
+        _LIBCPP_HIDE_FROM_ABI __dtor& operator=(const __dtor&) = default;                                              \
+        _LIBCPP_HIDE_FROM_ABI __dtor& operator=(__dtor&&)      = default;                                              \
+        destructor_definition;                                                                                         \
+                                                                                                                       \
+      protected:                                                                                                       \
+        destroy;                                                                                                       \
+      }
+
+_LIBCPP_VARIANT_DESTRUCTOR(
+    _Trait::_TriviallyAvailable,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__dtor() = default,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __destroy() noexcept {
+      this->__index = __variant_npos<__index_t>;
+    } _LIBCPP_EAT_SEMICOLON);
+
+_LIBCPP_VARIANT_DESTRUCTOR(
+    _Trait::_Available,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__dtor() { __destroy(); } _LIBCPP_EAT_SEMICOLON,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __destroy() noexcept {
+      if (!this->valueless_by_exception()) {
+        __visitation::__base::__visit_alt(
+            [](auto& __alt) noexcept {
+              using __alt_type = __remove_cvref_t<decltype(__alt)>;
+              __alt.~__alt_type();
+            },
+            *this);
+      }
+      this->__index = __variant_npos<__index_t>;
+    } _LIBCPP_EAT_SEMICOLON);
+
+_LIBCPP_VARIANT_DESTRUCTOR(_Trait::_Unavailable,
+                           _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__dtor()                 = delete,
+                           _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __destroy() noexcept = delete);
+
+#    undef _LIBCPP_VARIANT_DESTRUCTOR
+
+template <class _Traits>
+class __ctor : public __dtor<_Traits> {
+  using __base_type _LIBCPP_NODEBUG = __dtor<_Traits>;
+
+public:
+  using __base_type::__base_type;
+  using __base_type::operator=;
+
+protected:
+  template <class _Rhs>
+  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX20 void __generic_construct(__ctor& __lhs, _Rhs&& __rhs) {
+    __lhs.__destroy();
+    if (!__rhs.valueless_by_exception()) {
+      auto __rhs_index = __rhs.index();
+      __visitation::__base::__visit_alt_at(
+          __rhs_index,
+          [&__lhs](auto&& __rhs_alt) {
+            std::__construct_at(std::addressof(__lhs.__data),
+                                in_place_index<__decay_t<decltype(__rhs_alt)>::__index>,
+                                std::forward<decltype(__rhs_alt)>(__rhs_alt).__value);
+          },
+          std::forward<_Rhs>(__rhs));
+      __lhs.__index = __rhs_index;
+    }
+  }
+};
+
+template <class _Traits, _Trait = _Traits::__move_constructible_trait>
+class __move_constructor;
+
+#    define _LIBCPP_VARIANT_MOVE_CONSTRUCTOR(move_constructible_trait, move_constructor_definition)                    \
+      template <class... _Types>                                                                                       \
+      class __move_constructor<__traits<_Types...>, move_constructible_trait> : public __ctor<__traits<_Types...>> {   \
+        using __base_type _LIBCPP_NODEBUG = __ctor<__traits<_Types...>>;                                               \
+                                                                                                                       \
+      public:                                                                                                          \
+        using __base_type::__base_type;                                                                                \
+        using __base_type::operator=;                                                                                  \
+                                                                                                                       \
+        _LIBCPP_HIDE_FROM_ABI __move_constructor(const __move_constructor&)            = default;                      \
+        _LIBCPP_HIDE_FROM_ABI ~__move_constructor()                                    = default;                      \
+        _LIBCPP_HIDE_FROM_ABI __move_constructor& operator=(const __move_constructor&) = default;                      \
+        _LIBCPP_HIDE_FROM_ABI __move_constructor& operator=(__move_constructor&&)      = default;                      \
+        move_constructor_definition;                                                                                   \
+      }
+
+_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
+    _Trait::_TriviallyAvailable,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __move_constructor(__move_constructor&& __that) = default);
+
+_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
+    _Trait::_Available,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __move_constructor(__move_constructor&& __that) noexcept(
+        __all<is_nothrow_move_constructible_v<_Types>...>::value) : __move_constructor(__valueless_t{}) {
+      this->__generic_construct(*this, std::move(__that));
+    } _LIBCPP_EAT_SEMICOLON);
+
+_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
+    _Trait::_Unavailable,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __move_constructor(__move_constructor&&) = delete);
+
+#    undef _LIBCPP_VARIANT_MOVE_CONSTRUCTOR
+
+template <class _Traits, _Trait = _Traits::__copy_constructible_trait>
+class __copy_constructor;
+
+#    define _LIBCPP_VARIANT_COPY_CONSTRUCTOR(copy_constructible_trait, copy_constructor_definition)                    \
+      template <class... _Types>                                                                                       \
+      class __copy_constructor<__traits<_Types...>, copy_constructible_trait>                                          \
+          : public __move_constructor<__traits<_Types...>> {                                                           \
+        using __base_type _LIBCPP_NODEBUG = __move_constructor<__traits<_Types...>>;                                   \
+                                                                                                                       \
+      public:                                                                                                          \
+        using __base_type::__base_type;                                                                                \
+        using __base_type::operator=;                                                                                  \
+                                                                                                                       \
+        _LIBCPP_HIDE_FROM_ABI __copy_constructor(__copy_constructor&&)                 = default;                      \
+        _LIBCPP_HIDE_FROM_ABI ~__copy_constructor()                                    = default;                      \
+        _LIBCPP_HIDE_FROM_ABI __copy_constructor& operator=(const __copy_constructor&) = default;                      \
+        _LIBCPP_HIDE_FROM_ABI __copy_constructor& operator=(__copy_constructor&&)      = default;                      \
+        copy_constructor_definition;                                                                                   \
+      }
+
+_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
+    _Trait::_TriviallyAvailable,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __copy_constructor(const __copy_constructor& __that) = default);
+
+_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
+    _Trait::_Available,
+    _LIBCPP_HIDE_FROM_ABI
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 __copy_constructor(const __copy_constructor& __that) : __copy_constructor(
+        __valueless_t{}) { this->__generic_construct(*this, __that); } _LIBCPP_EAT_SEMICOLON);
+
+_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
+    _Trait::_Unavailable,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __copy_constructor(const __copy_constructor&) = delete);
+
+#    undef _LIBCPP_VARIANT_COPY_CONSTRUCTOR
+
+template <class _Traits>
+class __assignment : public __copy_constructor<_Traits> {
+  using __base_type _LIBCPP_NODEBUG = __copy_constructor<_Traits>;
+
+public:
+  using __base_type::__base_type;
+  using __base_type::operator=;
+
+  template <size_t _Ip, class... _Args>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 auto& __emplace(_Args&&... __args) {
+    this->__destroy();
+    std::__construct_at(std::addressof(this->__data), in_place_index<_Ip>, std::forward<_Args>(__args)...);
+    this->__index = _Ip;
+    return __access::__base::__get_alt<_Ip>(*this).__value;
+  }
+
+protected:
+  template <size_t _Ip, class _Tp, class _Arg>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __assign_alt(__alt<_Ip, _Tp>& __a, _Arg&& __arg) {
+    if (this->index() == _Ip) {
+      __a.__value = std::forward<_Arg>(__arg);
+    } else if constexpr (is_nothrow_constructible_v<_Tp, _Arg> || !is_nothrow_move_constructible_v<_Tp>) {
+      this->__emplace<_Ip>(std::forward<_Arg>(__arg));
+    } else {
+      this->__emplace<_Ip>(_Tp(std::forward<_Arg>(__arg)));
+    }
+  }
+
+  template <class _That>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 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, std::forward<decltype(__that_alt)>(__that_alt).__value);
+          },
+          *this,
+          std::forward<_That>(__that));
+    }
+  }
+};
+
+template <class _Traits, _Trait = _Traits::__move_assignable_trait>
+class __move_assignment;
+
+#    define _LIBCPP_VARIANT_MOVE_ASSIGNMENT(move_assignable_trait, move_assignment_definition)                         \
+      template <class... _Types>                                                                                       \
+      class __move_assignment<__traits<_Types...>, move_assignable_trait> : public __assignment<__traits<_Types...>> { \
+        using __base_type _LIBCPP_NODEBUG = __assignment<__traits<_Types...>>;                                         \
+                                                                                                                       \
+      public:                                                                                                          \
+        using __base_type::__base_type;                                                                                \
+        using __base_type::operator=;                                                                                  \
+                                                                                                                       \
+        _LIBCPP_HIDE_FROM_ABI __move_assignment(const __move_assignment&)            = default;                        \
+        _LIBCPP_HIDE_FROM_ABI __move_assignment(__move_assignment&&)                 = default;                        \
+        _LIBCPP_HIDE_FROM_ABI ~__move_assignment()                                   = default;                        \
+        _LIBCPP_HIDE_FROM_ABI __move_assignment& operator=(const __move_assignment&) = default;                        \
+        move_assignment_definition;                                                                                    \
+      }
+
+_LIBCPP_VARIANT_MOVE_ASSIGNMENT(_Trait::_TriviallyAvailable,
+                                _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __move_assignment& operator=(
+                                    __move_assignment&& __that) = default);
+
+_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
+    _Trait::_Available,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __move_assignment&
+    operator=(__move_assignment&& __that) noexcept(
+        __all<(is_nothrow_move_constructible_v<_Types> && is_nothrow_move_assignable_v<_Types>)...>::value) {
+      this->__generic_assign(std::move(__that));
+      return *this;
+    } _LIBCPP_EAT_SEMICOLON);
+
+_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
+    _Trait::_Unavailable,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __move_assignment& operator=(__move_assignment&&) = delete);
+
+#    undef _LIBCPP_VARIANT_MOVE_ASSIGNMENT
+
+template <class _Traits, _Trait = _Traits::__copy_assignable_trait>
+class __copy_assignment;
+
+#    define _LIBCPP_VARIANT_COPY_ASSIGNMENT(copy_assignable_trait, copy_assignment_definition)                         \
+      template <class... _Types>                                                                                       \
+      class __copy_assignment<__traits<_Types...>, copy_assignable_trait>                                              \
+          : public __move_assignment<__traits<_Types...>> {                                                            \
+        using __base_type _LIBCPP_NODEBUG = __move_assignment<__traits<_Types...>>;                                    \
+                                                                                                                       \
+      public:                                                                                                          \
+        using __base_type::__base_type;                                                                                \
+        using __base_type::operator=;                                                                                  \
+                                                                                                                       \
+        _LIBCPP_HIDE_FROM_ABI __copy_assignment(const __copy_assignment&)       = default;                             \
+        _LIBCPP_HIDE_FROM_ABI __copy_assignment(__copy_assignment&&)            = default;                             \
+        _LIBCPP_HIDE_FROM_ABI ~__copy_assignment()                              = default;                             \
+        _LIBCPP_HIDE_FROM_ABI __copy_assignment& operator=(__copy_assignment&&) = default;                             \
+        copy_assignment_definition;                                                                                    \
+      }
+
+_LIBCPP_VARIANT_COPY_ASSIGNMENT(_Trait::_TriviallyAvailable,
+                                _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __copy_assignment& operator=(
+                                    const __copy_assignment& __that) = default);
+
+_LIBCPP_VARIANT_COPY_ASSIGNMENT(
+    _Trait::_Available,
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __copy_assignment&
+    operator=(const __copy_assignment& __that) {
+      this->__generic_assign(__that);
+      return *this;
+    } _LIBCPP_EAT_SEMICOLON);
+
+_LIBCPP_VARIANT_COPY_ASSIGNMENT(_Trait::_Unavailable,
+                                _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __copy_assignment& operator=(
+                                    const __copy_assignment&) = delete);
+
+#    undef _LIBCPP_VARIANT_COPY_ASSIGNMENT
+
+template <class... _Types>
+class __impl : public __copy_assignment<__traits<_Types...>> {
+  using __base_type _LIBCPP_NODEBUG = __copy_assignment<__traits<_Types...>>;
+
+public:
+  using __base_type::__base_type; // get in_place_index_t constructor & friends
+  _LIBCPP_HIDE_FROM_ABI __impl(__impl const&)            = default;
+  _LIBCPP_HIDE_FROM_ABI __impl(__impl&&)                 = default;
+  _LIBCPP_HIDE_FROM_ABI __impl& operator=(__impl const&) = default;
+  _LIBCPP_HIDE_FROM_ABI __impl& operator=(__impl&&)      = default;
+
+  template <size_t _Ip, class _Arg>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __assign(_Arg&& __arg) {
+    this->__assign_alt(__access::__base::__get_alt<_Ip>(*this), std::forward<_Arg>(__arg));
+  }
+
+  inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 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 std::swap;
+            swap(__this_alt.__value, __that_alt.__value);
+          },
+          *this,
+          __that);
+    } else {
+      __impl* __lhs = this;
+      __impl* __rhs = std::addressof(__that);
+      if (__lhs->__move_nothrow() && !__rhs->__move_nothrow()) {
+        std::swap(__lhs, __rhs);
+      }
+      __impl __tmp(std::move(*__rhs));
+#    if _LIBCPP_HAS_EXCEPTIONS
+      if constexpr (__all<is_nothrow_move_constructible_v<_Types>...>::value) {
+        this->__generic_construct(*__rhs, std::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, std::move(*__lhs));
+        } catch (...) {
+          if (__tmp.__move_nothrow()) {
+            this->__generic_construct(*__rhs, std::move(__tmp));
+          }
+          throw;
+        }
+      }
+#    else
+      // this isn't consolidated with the `if constexpr` branch above due to
+      // `throw` being ill-formed with exceptions disabled even when discarded.
+      this->__generic_construct(*__rhs, std::move(*__lhs));
+#    endif
+      this->__generic_construct(*__lhs, std::move(__tmp));
+    }
+  }
+
+private:
+  constexpr inline _LIBCPP_HIDE_FROM_ABI 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 _LIBCPP_NODEBUG = __type_identity<_Dest>;
+};
+
+struct __narrowing_check {
+  template <class _Dest>
+  static auto __test_impl(_Dest (&&)[1]) -> __type_identity<_Dest>;
+  template <class _Dest, class _Source>
+  using _Apply _LIBCPP_NODEBUG = decltype(__test_impl<_Dest>({std::declval<_Source>()}));
+};
+
+template <class _Dest, class _Source>
+using __check_for_narrowing _LIBCPP_NODEBUG =
+    typename _If< 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... _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<index_sequence<_Idx...> > {
+  template <class... _Types>
+  using _Apply _LIBCPP_NODEBUG = __all_overloads<__overload<_Types, _Idx>...>;
+};
+
+template <class... _Types>
+using _MakeOverloads _LIBCPP_NODEBUG =
+    typename __make_overloads_imp<make_index_sequence<sizeof...(_Types)>>::template _Apply<_Types...>;
+
+template <class _Tp, class... _Types>
+using __best_match_t _LIBCPP_NODEBUG = typename invoke_result_t<_MakeOverloads<_Types...>, _Tp, _Tp>::type;
+
+} // namespace __variant_detail
+
+template <class _Visitor, class... _Vs, typename = void_t<decltype(std::__as_variant(std::declval<_Vs>()))...>>
+_LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) visit(_Visitor&& __visitor, _Vs&&... __vs);
+
+#    if _LIBCPP_STD_VER >= 20
+template <class _Rp,
+          class _Visitor,
+          class... _Vs,
+          typename = void_t<decltype(std::__as_variant(std::declval<_Vs>()))...>>
+_LIBCPP_HIDE_FROM_ABI constexpr _Rp visit(_Visitor&& __visitor, _Vs&&... __vs);
+#    endif
+
+template <class... _Types>
+class _LIBCPP_DECLSPEC_EMPTY_BASES _LIBCPP_NO_SPECIALIZATIONS 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 _LIBCPP_NODEBUG = variant_alternative_t<0, variant>;
+
+public:
+  using __trivially_relocatable _LIBCPP_NODEBUG =
+      conditional_t<_And<__libcpp_is_trivially_relocatable<_Types>...>::value, variant, void>;
+
+  template <bool _Dummy                                                                               = true,
+            enable_if_t<__dependent_type<is_default_constructible<__first_type>, _Dummy>::value, int> = 0>
+  _LIBCPP_HIDE_FROM_ABI constexpr variant() noexcept(is_nothrow_default_constructible_v<__first_type>)
+      : __impl_(in_place_index<0>) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr variant(const variant&) = default;
+  _LIBCPP_HIDE_FROM_ABI constexpr variant(variant&&)      = default;
+
+  template < class _Arg,
+             enable_if_t<!is_same_v<__remove_cvref_t<_Arg>, variant>, int>        = 0,
+             enable_if_t<!__is_inplace_type<__remove_cvref_t<_Arg>>::value, int>  = 0,
+             enable_if_t<!__is_inplace_index<__remove_cvref_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>
+  _LIBCPP_HIDE_FROM_ABI constexpr variant(_Arg&& __arg) noexcept(is_nothrow_constructible_v<_Tp, _Arg>)
+      : __impl_(in_place_index<_Ip>, std::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>
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr variant(in_place_index_t<_Ip>, _Args&&... __args) noexcept(
+      is_nothrow_constructible_v<_Tp, _Args...>)
+      : __impl_(in_place_index<_Ip>, std::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>
+  _LIBCPP_HIDE_FROM_ABI 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, std::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>
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr variant(in_place_type_t<_Tp>, _Args&&... __args) noexcept(
+      is_nothrow_constructible_v<_Tp, _Args...>)
+      : __impl_(in_place_index<_Ip>, std::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>
+  _LIBCPP_HIDE_FROM_ABI 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, std::forward<_Args>(__args)...) {}
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~variant() = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr variant& operator=(const variant&) = default;
+  _LIBCPP_HIDE_FROM_ABI constexpr variant& operator=(variant&&)      = default;
+
+  template < class _Arg,
+             enable_if_t<!is_same_v<__remove_cvref_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>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 variant&
+  operator=(_Arg&& __arg) noexcept(is_nothrow_assignable_v<_Tp&, _Arg> && is_nothrow_constructible_v<_Tp, _Arg>) {
+    __impl_.template __assign<_Ip>(std::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>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(_Args&&... __args) {
+    return __impl_.template __emplace<_Ip>(std::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>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
+    return __impl_.template __emplace<_Ip>(__il, std::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>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(_Args&&... __args) {
+    return __impl_.template __emplace<_Ip>(std::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>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
+    return __impl_.template __emplace<_Ip>(__il, std::forward<_Args>(__args)...);
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool valueless_by_exception() const noexcept {
+    return __impl_.valueless_by_exception();
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void swap(variant& __that) noexcept(
+      __all<(is_nothrow_move_constructible_v<_Types> && is_nothrow_swappable_v<_Types>)...>::value) {
+    __impl_.__swap(__that.__impl_);
+  }
+
+#    if _LIBCPP_STD_VER >= 26
+  // Helper class to implement [variant.visit]/10
+  //   Constraints: The call to visit does not use an explicit template-argument-list
+  //   that begins with a type template-argument.
+  struct __variant_visit_barrier_tag {
+    _LIBCPP_HIDE_FROM_ABI explicit __variant_visit_barrier_tag() = default;
+  };
+
+  template <__variant_visit_barrier_tag = __variant_visit_barrier_tag{}, class _Self, class _Visitor>
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) visit(this _Self&& __self, _Visitor&& __visitor) {
+    return std::visit(std::forward<_Visitor>(__visitor), std::__forward_as<_Self, variant>(__self));
+  }
+
+  template <class _Rp, class _Self, class _Visitor>
+  _LIBCPP_HIDE_FROM_ABI constexpr _Rp visit(this _Self&& __self, _Visitor&& __visitor) {
+    return std::visit<_Rp>(std::forward<_Visitor>(__visitor), std::__forward_as<_Self, variant>(__self));
+  }
+#    endif
+
+private:
+  __variant_detail::__impl<_Types...> __impl_;
+
+  friend struct __variant_detail::__access::__variant;
+  friend struct __variant_detail::__visitation::__variant;
+};
+
+template <size_t _Ip, class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr bool __holds_alternative(const variant<_Types...>& __v) noexcept {
+  return __v.index() == _Ip;
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool holds_alternative(const variant<_Types...>& __v) noexcept {
+  return std::__holds_alternative<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <size_t _Ip, class _Vp>
+_LIBCPP_HIDE_FROM_ABI constexpr auto&& __generic_get(_Vp&& __v) {
+  using __variant_detail::__access::__variant;
+  if (!std::__holds_alternative<_Ip>(__v)) {
+    std::__throw_bad_variant_access();
+  }
+  return __variant::__get_alt<_Ip>(std::forward<_Vp>(__v)).__value;
+}
+
+template <size_t _Ip, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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 std::__generic_get<_Ip>(__v);
+}
+
+template <size_t _Ip, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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 std::__generic_get<_Ip>(std::move(__v));
+}
+
+template <size_t _Ip, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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 std::__generic_get<_Ip>(__v);
+}
+
+template <size_t _Ip, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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 std::__generic_get<_Ip>(std::move(__v));
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp& get(variant<_Types...>& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& get(variant<_Types...>&& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(std::move(__v));
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& get(const variant<_Types...>& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const _Tp&& get(const variant<_Types...>&& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(std::move(__v));
+}
+
+template <size_t _Ip, class _Vp>
+_LIBCPP_HIDE_FROM_ABI constexpr auto* __generic_get_if(_Vp* __v) noexcept {
+  using __variant_detail::__access::__variant;
+  return __v && std::__holds_alternative<_Ip>(*__v) ? std::addressof(__variant::__get_alt<_Ip>(*__v).__value) : nullptr;
+}
+
+template <size_t _Ip, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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 std::__generic_get_if<_Ip>(__v);
+}
+
+template <size_t _Ip, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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 std::__generic_get_if<_Ip>(__v);
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<_Tp> get_if(variant<_Types...>* __v) noexcept {
+  static_assert(!is_void_v<_Tp>);
+  return std::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<const _Tp> get_if(const variant<_Types...>* __v) noexcept {
+  static_assert(!is_void_v<_Tp>);
+  return std::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Operator>
+struct __convert_to_bool {
+  template <class _T1, class _T2>
+  _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(_T1&& __t1, _T2&& __t2) const {
+    static_assert(is_convertible<decltype(_Operator{}(std::forward<_T1>(__t1), std::forward<_T2>(__t2))), bool>::value,
+                  "the relational operator does not return a type which is implicitly convertible to bool");
+    return _Operator{}(std::forward<_T1>(__t1), std::forward<_T2>(__t2));
+  }
+};
+
+template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t == __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
+_LIBCPP_HIDE_FROM_ABI 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);
+}
+
+#    if _LIBCPP_STD_VER >= 20
+
+template <class... _Types>
+  requires(three_way_comparable<_Types> && ...)
+_LIBCPP_HIDE_FROM_ABI constexpr common_comparison_category_t<compare_three_way_result_t<_Types>...>
+operator<=>(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  using __result_t = common_comparison_category_t<compare_three_way_result_t<_Types>...>;
+  if (__lhs.valueless_by_exception() && __rhs.valueless_by_exception())
+    return strong_ordering::equal;
+  if (__lhs.valueless_by_exception())
+    return strong_ordering::less;
+  if (__rhs.valueless_by_exception())
+    return strong_ordering::greater;
+  if (auto __c = __lhs.index() <=> __rhs.index(); __c != 0)
+    return __c;
+  auto __three_way = []<class _Type>(const _Type& __v, const _Type& __w) -> __result_t { return __v <=> __w; };
+  return __variant::__visit_value_at(__lhs.index(), __three_way, __lhs, __rhs);
+}
+
+#    endif // _LIBCPP_STD_VER >= 20
+
+template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t != __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
+_LIBCPP_HIDE_FROM_ABI 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>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t < __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
+_LIBCPP_HIDE_FROM_ABI 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>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t > __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
+_LIBCPP_HIDE_FROM_ABI 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>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t <= __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
+_LIBCPP_HIDE_FROM_ABI 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>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t >= __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
+_LIBCPP_HIDE_FROM_ABI 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... _Vs>
+_LIBCPP_HIDE_FROM_ABI constexpr void __throw_if_valueless(_Vs&&... __vs) {
+  const bool __valueless = (... || std::__as_variant(__vs).valueless_by_exception());
+  if (__valueless) {
+    std::__throw_bad_variant_access();
+  }
+}
+
+template < class _Visitor, class... _Vs, typename>
+_LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) visit(_Visitor&& __visitor, _Vs&&... __vs) {
+  using __variant_detail::__visitation::__variant;
+  std::__throw_if_valueless(std::forward<_Vs>(__vs)...);
+  return __variant::__visit_value(std::forward<_Visitor>(__visitor), std::forward<_Vs>(__vs)...);
+}
+
+#    if _LIBCPP_STD_VER >= 20
+template < class _Rp, class _Visitor, class... _Vs, typename>
+_LIBCPP_HIDE_FROM_ABI constexpr _Rp visit(_Visitor&& __visitor, _Vs&&... __vs) {
+  using __variant_detail::__visitation::__variant;
+  std::__throw_if_valueless(std::forward<_Vs>(__vs)...);
+  return __variant::__visit_value<_Rp>(std::forward<_Visitor>(__visitor), std::forward<_Vs>(__vs)...);
+}
+#    endif
+
+template <class... _Types>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 auto
+swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs) noexcept(noexcept(__lhs.swap(__rhs)))
+    -> decltype(__lhs.swap(__rhs)) {
+  return __lhs.swap(__rhs);
+}
+
+template <class... _Types>
+struct hash< __enable_hash_helper<variant<_Types...>, remove_const_t<_Types>...>> {
+#    if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
+  using argument_type _LIBCPP_DEPRECATED_IN_CXX17 = variant<_Types...>;
+  using result_type _LIBCPP_DEPRECATED_IN_CXX17   = size_t;
+#    endif
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI size_t operator()(const variant<_Types...>& __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   = __remove_cvref_t<decltype(__alt)>;
+                    using __value_type = remove_const_t< typename __alt_type::__value_type>;
+                    return hash<__value_type>{}(__alt.__value);
+                  },
+                  __v);
+    return std::__hash_combine(__res, hash<size_t>{}(__v.index()));
+  }
+};
+
+// __unchecked_get is the same as std::get, except, it is UB to use it with the wrong
+// type whereas std::get will throw or returning nullptr. This makes it faster than
+// std::get.
+template <size_t _Ip, class _Vp>
+_LIBCPP_HIDE_FROM_ABI constexpr auto&& __unchecked_get(_Vp&& __v) noexcept {
+  using __variant_detail::__access::__variant;
+  return __variant::__get_alt<_Ip>(std::forward<_Vp>(__v)).__value;
+}
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr auto&& __unchecked_get(const variant<_Types...>& __v) noexcept {
+  return std::__unchecked_get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+_LIBCPP_HIDE_FROM_ABI constexpr auto&& __unchecked_get(variant<_Types...>& __v) noexcept {
+  return std::__unchecked_get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+#  endif // _LIBCPP_STD_VER >= 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
+#    include <cstddef>
+#    include <exception>
+#    include <tuple>
+#    include <type_traits>
+#    include <typeinfo>
+#    include <utility>
+#  endif
+#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
+
+#endif // _LIBCPP_VARIANT