Import stripped Arm GNU Toolchain 13.2.Rel1HEADumineko

https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads

Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c

1 files changed, 1946 insertions, 0 deletions

diff --git a/aarch64-none-linux-gnu/include/c++/13.2.1/variant b/aarch64-none-linux-gnu/include/c++/13.2.1/variant
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+// <variant> -*- C++ -*-
+
+// Copyright (C) 2016-2023 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file variant
+ *  This is the `<variant>` C++ Library header.
+ */
+
+#ifndef _GLIBCXX_VARIANT
+#define _GLIBCXX_VARIANT 1
+
+#pragma GCC system_header
+
+#if __cplusplus >= 201703L
+
+#include <initializer_list>
+#include <type_traits>
+#include <bits/enable_special_members.h>
+#include <bits/exception_defines.h>
+#include <bits/functional_hash.h>
+#include <bits/invoke.h>
+#include <bits/parse_numbers.h>
+#include <bits/stl_iterator_base_funcs.h>
+#include <bits/stl_construct.h>
+#include <bits/utility.h> // in_place_index_t
+#if __cplusplus >= 202002L
+# include <compare>
+#endif
+
+#if __cpp_concepts >= 202002L && __cpp_constexpr >= 201811L
+// P2231R1 constexpr needs constexpr unions and constrained destructors.
+# define __cpp_lib_variant 202106L
+#else
+# include <ext/aligned_buffer.h> // Use __aligned_membuf instead of union.
+# define __cpp_lib_variant 202102L
+#endif
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  template<typename... _Types> class tuple;
+  template<typename... _Types> class variant;
+  template <typename> struct hash;
+
+  template<typename _Variant>
+    struct variant_size;
+
+  template<typename _Variant>
+    struct variant_size<const _Variant> : variant_size<_Variant> {};
+
+  template<typename _Variant>
+    struct variant_size<volatile _Variant> : variant_size<_Variant> {};
+
+  template<typename _Variant>
+    struct variant_size<const volatile _Variant> : variant_size<_Variant> {};
+
+  template<typename... _Types>
+    struct variant_size<variant<_Types...>>
+    : std::integral_constant<size_t, sizeof...(_Types)> {};
+
+  template<typename _Variant>
+    inline constexpr size_t variant_size_v = variant_size<_Variant>::value;
+
+  template<typename... _Types>
+    inline constexpr size_t
+    variant_size_v<variant<_Types...>> = sizeof...(_Types);
+
+  template<typename... _Types>
+    inline constexpr size_t
+    variant_size_v<const variant<_Types...>> = sizeof...(_Types);
+
+  template<size_t _Np, typename _Variant>
+    struct variant_alternative;
+
+  template<size_t _Np, typename... _Types>
+    struct variant_alternative<_Np, variant<_Types...>>
+    {
+      static_assert(_Np < sizeof...(_Types));
+
+      using type = typename _Nth_type<_Np, _Types...>::type;
+    };
+
+  template<size_t _Np, typename _Variant>
+    using variant_alternative_t =
+      typename variant_alternative<_Np, _Variant>::type;
+
+  template<size_t _Np, typename _Variant>
+    struct variant_alternative<_Np, const _Variant>
+    { using type = const variant_alternative_t<_Np, _Variant>; };
+
+  template<size_t _Np, typename _Variant>
+    struct variant_alternative<_Np, volatile _Variant>
+    { using type = volatile variant_alternative_t<_Np, _Variant>; };
+
+  template<size_t _Np, typename _Variant>
+    struct variant_alternative<_Np, const volatile _Variant>
+    { using type = const volatile variant_alternative_t<_Np, _Variant>; };
+
+  inline constexpr size_t variant_npos = -1;
+
+  template<size_t _Np, typename... _Types>
+    constexpr variant_alternative_t<_Np, variant<_Types...>>&
+    get(variant<_Types...>&);
+
+  template<size_t _Np, typename... _Types>
+    constexpr variant_alternative_t<_Np, variant<_Types...>>&&
+    get(variant<_Types...>&&);
+
+  template<size_t _Np, typename... _Types>
+    constexpr variant_alternative_t<_Np, variant<_Types...>> const&
+    get(const variant<_Types...>&);
+
+  template<size_t _Np, typename... _Types>
+    constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
+    get(const variant<_Types...>&&);
+
+  template<typename _Result_type, typename _Visitor, typename... _Variants>
+    constexpr decltype(auto)
+    __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
+
+  template <typename... _Types, typename _Tp>
+    _GLIBCXX20_CONSTEXPR
+    decltype(auto)
+    __variant_cast(_Tp&& __rhs)
+    {
+      if constexpr (is_lvalue_reference_v<_Tp>)
+	{
+	  if constexpr (is_const_v<remove_reference_t<_Tp>>)
+	    return static_cast<const variant<_Types...>&>(__rhs);
+	  else
+	    return static_cast<variant<_Types...>&>(__rhs);
+	}
+      else
+        return static_cast<variant<_Types...>&&>(__rhs);
+    }
+
+namespace __detail
+{
+namespace __variant
+{
+  // used for raw visitation
+  struct __variant_cookie {};
+  // used for raw visitation with indices passed in
+  struct __variant_idx_cookie { using type = __variant_idx_cookie; };
+  // Used to enable deduction (and same-type checking) for std::visit:
+  template<typename _Tp> struct __deduce_visit_result { using type = _Tp; };
+
+  // Visit variants that might be valueless.
+  template<typename _Visitor, typename... _Variants>
+    constexpr void
+    __raw_visit(_Visitor&& __visitor, _Variants&&... __variants)
+    {
+      std::__do_visit<__variant_cookie>(std::forward<_Visitor>(__visitor),
+				        std::forward<_Variants>(__variants)...);
+    }
+
+  // Visit variants that might be valueless, passing indices to the visitor.
+  template<typename _Visitor, typename... _Variants>
+    constexpr void
+    __raw_idx_visit(_Visitor&& __visitor, _Variants&&... __variants)
+    {
+      std::__do_visit<__variant_idx_cookie>(std::forward<_Visitor>(__visitor),
+	  std::forward<_Variants>(__variants)...);
+    }
+
+  // The __as function templates implement the exposition-only "as-variant"
+
+  template<typename... _Types>
+    constexpr std::variant<_Types...>&
+    __as(std::variant<_Types...>& __v) noexcept
+    { return __v; }
+
+  template<typename... _Types>
+    constexpr const std::variant<_Types...>&
+    __as(const std::variant<_Types...>& __v) noexcept
+    { return __v; }
+
+  template<typename... _Types>
+    constexpr std::variant<_Types...>&&
+    __as(std::variant<_Types...>&& __v) noexcept
+    { return std::move(__v); }
+
+  template<typename... _Types>
+    constexpr const std::variant<_Types...>&&
+    __as(const std::variant<_Types...>&& __v) noexcept
+    { return std::move(__v); }
+
+  // For C++17:
+  // _Uninitialized<T> is guaranteed to be a trivially destructible type,
+  // even if T is not.
+  // For C++20:
+  // _Uninitialized<T> is trivially destructible iff T is, so _Variant_union
+  // needs a constrained non-trivial destructor.
+  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
+    struct _Uninitialized;
+
+  template<typename _Type>
+    struct _Uninitialized<_Type, true>
+    {
+      template<typename... _Args>
+	constexpr
+	_Uninitialized(in_place_index_t<0>, _Args&&... __args)
+	: _M_storage(std::forward<_Args>(__args)...)
+	{ }
+
+      constexpr const _Type& _M_get() const & noexcept
+      { return _M_storage; }
+
+      constexpr _Type& _M_get() & noexcept
+      { return _M_storage; }
+
+      constexpr const _Type&& _M_get() const && noexcept
+      { return std::move(_M_storage); }
+
+      constexpr _Type&& _M_get() && noexcept
+      { return std::move(_M_storage); }
+
+      _Type _M_storage;
+    };
+
+  template<typename _Type>
+    struct _Uninitialized<_Type, false>
+    {
+#if __cpp_lib_variant >= 202106L
+      template<typename... _Args>
+	constexpr
+	_Uninitialized(in_place_index_t<0>, _Args&&... __args)
+	: _M_storage(std::forward<_Args>(__args)...)
+	{ }
+
+      constexpr ~_Uninitialized() { }
+
+      _Uninitialized(const _Uninitialized&) = default;
+      _Uninitialized(_Uninitialized&&) = default;
+      _Uninitialized& operator=(const _Uninitialized&) = default;
+      _Uninitialized& operator=(_Uninitialized&&) = default;
+
+      constexpr const _Type& _M_get() const & noexcept
+      { return _M_storage; }
+
+      constexpr _Type& _M_get() & noexcept
+      { return _M_storage; }
+
+      constexpr const _Type&& _M_get() const && noexcept
+      { return std::move(_M_storage); }
+
+      constexpr _Type&& _M_get() && noexcept
+      { return std::move(_M_storage); }
+
+      struct _Empty_byte { };
+
+      union {
+	_Empty_byte _M_empty;
+	_Type _M_storage;
+      };
+#else
+      template<typename... _Args>
+	constexpr
+	_Uninitialized(in_place_index_t<0>, _Args&&... __args)
+	{
+	  ::new ((void*)std::addressof(_M_storage))
+	    _Type(std::forward<_Args>(__args)...);
+	}
+
+      const _Type& _M_get() const & noexcept
+      { return *_M_storage._M_ptr(); }
+
+      _Type& _M_get() & noexcept
+      { return *_M_storage._M_ptr(); }
+
+      const _Type&& _M_get() const && noexcept
+      { return std::move(*_M_storage._M_ptr()); }
+
+      _Type&& _M_get() && noexcept
+      { return std::move(*_M_storage._M_ptr()); }
+
+      __gnu_cxx::__aligned_membuf<_Type> _M_storage;
+#endif
+    };
+
+  template<size_t _Np, typename _Union>
+    constexpr decltype(auto)
+    __get_n(_Union&& __u) noexcept
+    {
+      if constexpr (_Np == 0)
+	return std::forward<_Union>(__u)._M_first._M_get();
+      else if constexpr (_Np == 1)
+	return std::forward<_Union>(__u)._M_rest._M_first._M_get();
+      else if constexpr (_Np == 2)
+	return std::forward<_Union>(__u)._M_rest._M_rest._M_first._M_get();
+      else
+	return __variant::__get_n<_Np - 3>(
+		 std::forward<_Union>(__u)._M_rest._M_rest._M_rest);
+    }
+
+  // Returns the typed storage for __v.
+  template<size_t _Np, typename _Variant>
+    constexpr decltype(auto)
+    __get(_Variant&& __v) noexcept
+    { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); }
+
+  template<typename... _Types>
+    struct _Traits
+    {
+      static constexpr bool _S_default_ctor =
+	  is_default_constructible_v<typename _Nth_type<0, _Types...>::type>;
+      static constexpr bool _S_copy_ctor =
+	  (is_copy_constructible_v<_Types> && ...);
+      static constexpr bool _S_move_ctor =
+	  (is_move_constructible_v<_Types> && ...);
+      static constexpr bool _S_copy_assign =
+	  _S_copy_ctor
+	  && (is_copy_assignable_v<_Types> && ...);
+      static constexpr bool _S_move_assign =
+	  _S_move_ctor
+	  && (is_move_assignable_v<_Types> && ...);
+
+      static constexpr bool _S_trivial_dtor =
+	  (is_trivially_destructible_v<_Types> && ...);
+      static constexpr bool _S_trivial_copy_ctor =
+	  (is_trivially_copy_constructible_v<_Types> && ...);
+      static constexpr bool _S_trivial_move_ctor =
+	  (is_trivially_move_constructible_v<_Types> && ...);
+      static constexpr bool _S_trivial_copy_assign =
+	  _S_trivial_dtor && _S_trivial_copy_ctor
+	  && (is_trivially_copy_assignable_v<_Types> && ...);
+      static constexpr bool _S_trivial_move_assign =
+	  _S_trivial_dtor && _S_trivial_move_ctor
+	  && (is_trivially_move_assignable_v<_Types> && ...);
+
+      // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
+      // are always nothrow.
+      static constexpr bool _S_nothrow_default_ctor =
+	  is_nothrow_default_constructible_v<
+	      typename _Nth_type<0, _Types...>::type>;
+      static constexpr bool _S_nothrow_copy_ctor = false;
+      static constexpr bool _S_nothrow_move_ctor =
+	  (is_nothrow_move_constructible_v<_Types> && ...);
+      static constexpr bool _S_nothrow_copy_assign = false;
+      static constexpr bool _S_nothrow_move_assign =
+	  _S_nothrow_move_ctor
+	  && (is_nothrow_move_assignable_v<_Types> && ...);
+    };
+
+  // Defines members and ctors.
+  template<typename... _Types>
+    union _Variadic_union
+    {
+      _Variadic_union() = default;
+
+      template<size_t _Np, typename... _Args>
+	_Variadic_union(in_place_index_t<_Np>, _Args&&...) = delete;
+    };
+
+  template<typename _First, typename... _Rest>
+    union _Variadic_union<_First, _Rest...>
+    {
+      constexpr _Variadic_union() : _M_rest() { }
+
+      template<typename... _Args>
+	constexpr
+	_Variadic_union(in_place_index_t<0>, _Args&&... __args)
+	: _M_first(in_place_index<0>, std::forward<_Args>(__args)...)
+	{ }
+
+      template<size_t _Np, typename... _Args>
+	constexpr
+	_Variadic_union(in_place_index_t<_Np>, _Args&&... __args)
+	: _M_rest(in_place_index<_Np-1>, std::forward<_Args>(__args)...)
+	{ }
+
+#if __cpp_lib_variant >= 202106L
+      _Variadic_union(const _Variadic_union&) = default;
+      _Variadic_union(_Variadic_union&&) = default;
+      _Variadic_union& operator=(const _Variadic_union&) = default;
+      _Variadic_union& operator=(_Variadic_union&&) = default;
+
+      ~_Variadic_union() = default;
+
+      constexpr ~_Variadic_union()
+	requires (!__has_trivial_destructor(_First))
+	      || (!__has_trivial_destructor(_Variadic_union<_Rest...>))
+      { }
+#endif
+
+      _Uninitialized<_First> _M_first;
+      _Variadic_union<_Rest...> _M_rest;
+    };
+
+  // _Never_valueless_alt is true for variant alternatives that can
+  // always be placed in a variant without it becoming valueless.
+
+  // For suitably-small, trivially copyable types we can create temporaries
+  // on the stack and then memcpy them into place.
+  template<typename _Tp>
+    struct _Never_valueless_alt
+    : __and_<bool_constant<sizeof(_Tp) <= 256>, is_trivially_copyable<_Tp>>
+    { };
+
+  // Specialize _Never_valueless_alt for other types which have a
+  // non-throwing and cheap move construction and move assignment operator,
+  // so that emplacing the type will provide the strong exception-safety
+  // guarantee, by creating and moving a temporary.
+  // Whether _Never_valueless_alt<T> is true or not affects the ABI of a
+  // variant using that alternative, so we can't change the value later!
+
+  // True if every alternative in _Types... can be emplaced in a variant
+  // without it becoming valueless. If this is true, variant<_Types...>
+  // can never be valueless, which enables some minor optimizations.
+  template <typename... _Types>
+    constexpr bool __never_valueless()
+    {
+      return _Traits<_Types...>::_S_move_assign
+	&& (_Never_valueless_alt<_Types>::value && ...);
+    }
+
+  // Defines index and the dtor, possibly trivial.
+  template<bool __trivially_destructible, typename... _Types>
+    struct _Variant_storage;
+
+  template <typename... _Types>
+    using __select_index =
+      typename __select_int::_Select_int_base<sizeof...(_Types),
+					      unsigned char,
+					      unsigned short>::type::value_type;
+
+  template<typename... _Types>
+    struct _Variant_storage<false, _Types...>
+    {
+      constexpr
+      _Variant_storage()
+      : _M_index(static_cast<__index_type>(variant_npos))
+      { }
+
+      template<size_t _Np, typename... _Args>
+	constexpr
+	_Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
+	: _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
+	_M_index{_Np}
+	{ }
+
+      constexpr void
+      _M_reset()
+      {
+	if (!_M_valid()) [[unlikely]]
+	  return;
+
+	std::__do_visit<void>([](auto&& __this_mem) mutable
+	  {
+	    std::_Destroy(std::__addressof(__this_mem));
+	  }, __variant_cast<_Types...>(*this));
+
+	_M_index = static_cast<__index_type>(variant_npos);
+      }
+
+      _GLIBCXX20_CONSTEXPR
+      ~_Variant_storage()
+      { _M_reset(); }
+
+      constexpr bool
+      _M_valid() const noexcept
+      {
+	if constexpr (__variant::__never_valueless<_Types...>())
+	  return true;
+	return this->_M_index != __index_type(variant_npos);
+      }
+
+      _Variadic_union<_Types...> _M_u;
+      using __index_type = __select_index<_Types...>;
+      __index_type _M_index;
+    };
+
+  template<typename... _Types>
+    struct _Variant_storage<true, _Types...>
+    {
+      constexpr
+      _Variant_storage()
+      : _M_index(static_cast<__index_type>(variant_npos))
+      { }
+
+      template<size_t _Np, typename... _Args>
+	constexpr
+	_Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
+	: _M_u(in_place_index<_Np>, std::forward<_Args>(__args)...),
+	_M_index{_Np}
+	{ }
+
+      constexpr void
+      _M_reset() noexcept
+      { _M_index = static_cast<__index_type>(variant_npos); }
+
+      constexpr bool
+      _M_valid() const noexcept
+      {
+	if constexpr (__variant::__never_valueless<_Types...>())
+	  return true;
+	// It would be nice if we could just return true for -fno-exceptions.
+	// It's possible (but inadvisable) that a std::variant could become
+	// valueless in a translation unit compiled with -fexceptions and then
+	// be passed to functions compiled with -fno-exceptions. We would need
+	// some #ifdef _GLIBCXX_NO_EXCEPTIONS_GLOBALLY property to elide all
+	// checks for valueless_by_exception().
+	return this->_M_index != static_cast<__index_type>(variant_npos);
+      }
+
+      _Variadic_union<_Types...> _M_u;
+      using __index_type = __select_index<_Types...>;
+      __index_type _M_index;
+    };
+
+  // Implementation of v.emplace<N>(args...).
+  template<size_t _Np, bool _Triv, typename... _Types, typename... _Args>
+    _GLIBCXX20_CONSTEXPR
+    inline void
+    __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args)
+    {
+      __v._M_reset();
+      auto* __addr = std::__addressof(__variant::__get_n<_Np>(__v._M_u));
+      std::_Construct(__addr, std::forward<_Args>(__args)...);
+      // Construction didn't throw, so can set the new index now:
+      __v._M_index = _Np;
+    }
+
+  template<typename... _Types>
+    using _Variant_storage_alias =
+	_Variant_storage<_Traits<_Types...>::_S_trivial_dtor, _Types...>;
+
+  // The following are (Copy|Move) (ctor|assign) layers for forwarding
+  // triviality and handling non-trivial SMF behaviors.
+
+  template<bool, typename... _Types>
+    struct _Copy_ctor_base : _Variant_storage_alias<_Types...>
+    {
+      using _Base = _Variant_storage_alias<_Types...>;
+      using _Base::_Base;
+
+      _GLIBCXX20_CONSTEXPR
+      _Copy_ctor_base(const _Copy_ctor_base& __rhs)
+	  noexcept(_Traits<_Types...>::_S_nothrow_copy_ctor)
+      {
+	__variant::__raw_idx_visit(
+	  [this](auto&& __rhs_mem, auto __rhs_index) mutable
+	  {
+	    constexpr size_t __j = __rhs_index;
+	    if constexpr (__j != variant_npos)
+	      std::_Construct(std::__addressof(this->_M_u),
+			      in_place_index<__j>, __rhs_mem);
+	  }, __variant_cast<_Types...>(__rhs));
+	this->_M_index = __rhs._M_index;
+      }
+
+      _Copy_ctor_base(_Copy_ctor_base&&) = default;
+      _Copy_ctor_base& operator=(const _Copy_ctor_base&) = default;
+      _Copy_ctor_base& operator=(_Copy_ctor_base&&) = default;
+    };
+
+  template<typename... _Types>
+    struct _Copy_ctor_base<true, _Types...> : _Variant_storage_alias<_Types...>
+    {
+      using _Base = _Variant_storage_alias<_Types...>;
+      using _Base::_Base;
+    };
+
+  template<typename... _Types>
+    using _Copy_ctor_alias =
+	_Copy_ctor_base<_Traits<_Types...>::_S_trivial_copy_ctor, _Types...>;
+
+  template<bool, typename... _Types>
+    struct _Move_ctor_base : _Copy_ctor_alias<_Types...>
+    {
+      using _Base = _Copy_ctor_alias<_Types...>;
+      using _Base::_Base;
+
+      _GLIBCXX20_CONSTEXPR
+      _Move_ctor_base(_Move_ctor_base&& __rhs)
+	  noexcept(_Traits<_Types...>::_S_nothrow_move_ctor)
+      {
+	__variant::__raw_idx_visit(
+	  [this](auto&& __rhs_mem, auto __rhs_index) mutable
+	  {
+	    constexpr size_t __j = __rhs_index;
+	    if constexpr (__j != variant_npos)
+	      std::_Construct(std::__addressof(this->_M_u),
+			      in_place_index<__j>,
+			      std::forward<decltype(__rhs_mem)>(__rhs_mem));
+	  }, __variant_cast<_Types...>(std::move(__rhs)));
+	this->_M_index = __rhs._M_index;
+      }
+
+      _Move_ctor_base(const _Move_ctor_base&) = default;
+      _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
+      _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
+    };
+
+  template<typename... _Types>
+    struct _Move_ctor_base<true, _Types...> : _Copy_ctor_alias<_Types...>
+    {
+      using _Base = _Copy_ctor_alias<_Types...>;
+      using _Base::_Base;
+    };
+
+  template<typename... _Types>
+    using _Move_ctor_alias =
+	_Move_ctor_base<_Traits<_Types...>::_S_trivial_move_ctor, _Types...>;
+
+  template<bool, typename... _Types>
+    struct _Copy_assign_base : _Move_ctor_alias<_Types...>
+    {
+      using _Base = _Move_ctor_alias<_Types...>;
+      using _Base::_Base;
+
+      _GLIBCXX20_CONSTEXPR
+      _Copy_assign_base&
+      operator=(const _Copy_assign_base& __rhs)
+	  noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
+      {
+	__variant::__raw_idx_visit(
+	  [this](auto&& __rhs_mem, auto __rhs_index) mutable
+	  {
+	    constexpr size_t __j = __rhs_index;
+	    if constexpr (__j == variant_npos)
+	      this->_M_reset(); // Make *this valueless.
+	    else if (this->_M_index == __j)
+	      __variant::__get<__j>(*this) = __rhs_mem;
+	    else
+	      {
+		using _Tj = typename _Nth_type<__j, _Types...>::type;
+		if constexpr (is_nothrow_copy_constructible_v<_Tj>
+			      || !is_nothrow_move_constructible_v<_Tj>)
+		  __variant::__emplace<__j>(*this, __rhs_mem);
+		else
+		  {
+		    using _Variant = variant<_Types...>;
+		    _Variant& __self = __variant_cast<_Types...>(*this);
+		    __self = _Variant(in_place_index<__j>, __rhs_mem);
+		  }
+	      }
+	  }, __variant_cast<_Types...>(__rhs));
+	return *this;
+      }
+
+      _Copy_assign_base(const _Copy_assign_base&) = default;
+      _Copy_assign_base(_Copy_assign_base&&) = default;
+      _Copy_assign_base& operator=(_Copy_assign_base&&) = default;
+    };
+
+  template<typename... _Types>
+    struct _Copy_assign_base<true, _Types...> : _Move_ctor_alias<_Types...>
+    {
+      using _Base = _Move_ctor_alias<_Types...>;
+      using _Base::_Base;
+    };
+
+  template<typename... _Types>
+    using _Copy_assign_alias =
+      _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
+
+  template<bool, typename... _Types>
+    struct _Move_assign_base : _Copy_assign_alias<_Types...>
+    {
+      using _Base = _Copy_assign_alias<_Types...>;
+      using _Base::_Base;
+
+      _GLIBCXX20_CONSTEXPR
+      _Move_assign_base&
+      operator=(_Move_assign_base&& __rhs)
+	  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
+      {
+	__variant::__raw_idx_visit(
+	  [this](auto&& __rhs_mem, auto __rhs_index) mutable
+	  {
+	    constexpr size_t __j = __rhs_index;
+	    if constexpr (__j != variant_npos)
+	      {
+		if (this->_M_index == __j)
+		  __variant::__get<__j>(*this) = std::move(__rhs_mem);
+		else
+		  {
+		    using _Tj = typename _Nth_type<__j, _Types...>::type;
+		    if constexpr (is_nothrow_move_constructible_v<_Tj>)
+		      __variant::__emplace<__j>(*this, std::move(__rhs_mem));
+		    else
+		      {
+			using _Variant = variant<_Types...>;
+			_Variant& __self = __variant_cast<_Types...>(*this);
+			__self.template emplace<__j>(std::move(__rhs_mem));
+		      }
+		  }
+	      }
+	    else
+	      this->_M_reset();
+	  }, __variant_cast<_Types...>(__rhs));
+	return *this;
+      }
+
+      _Move_assign_base(const _Move_assign_base&) = default;
+      _Move_assign_base(_Move_assign_base&&) = default;
+      _Move_assign_base& operator=(const _Move_assign_base&) = default;
+    };
+
+  template<typename... _Types>
+    struct _Move_assign_base<true, _Types...> : _Copy_assign_alias<_Types...>
+    {
+      using _Base = _Copy_assign_alias<_Types...>;
+      using _Base::_Base;
+    };
+
+  template<typename... _Types>
+    using _Move_assign_alias =
+      _Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
+
+  template<typename... _Types>
+    struct _Variant_base : _Move_assign_alias<_Types...>
+    {
+      using _Base = _Move_assign_alias<_Types...>;
+
+      constexpr
+      _Variant_base() noexcept(_Traits<_Types...>::_S_nothrow_default_ctor)
+      : _Variant_base(in_place_index<0>) { }
+
+      template<size_t _Np, typename... _Args>
+	constexpr explicit
+	_Variant_base(in_place_index_t<_Np> __i, _Args&&... __args)
+	: _Base(__i, std::forward<_Args>(__args)...)
+	{ }
+
+      _Variant_base(const _Variant_base&) = default;
+      _Variant_base(_Variant_base&&) = default;
+      _Variant_base& operator=(const _Variant_base&) = default;
+      _Variant_base& operator=(_Variant_base&&) = default;
+    };
+
+  template<typename _Tp, typename... _Types>
+    inline constexpr bool __exactly_once
+      = std::__find_uniq_type_in_pack<_Tp, _Types...>() < sizeof...(_Types);
+
+  // Helper used to check for valid conversions that don't involve narrowing.
+  template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
+
+  // "Build an imaginary function FUN(Ti) for each alternative type Ti"
+  template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
+    struct _Build_FUN
+    {
+      // This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
+      // but only static functions will be considered in the call below.
+      void _S_fun() = delete;
+    };
+
+  // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
+  template<size_t _Ind, typename _Tp, typename _Ti>
+    struct _Build_FUN<_Ind, _Tp, _Ti,
+		      void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
+    {
+      // This is the FUN function for type _Ti, with index _Ind
+      static integral_constant<size_t, _Ind> _S_fun(_Ti);
+    };
+
+  template<typename _Tp, typename _Variant,
+	   typename = make_index_sequence<variant_size_v<_Variant>>>
+    struct _Build_FUNs;
+
+  template<typename _Tp, typename... _Ti, size_t... _Ind>
+    struct _Build_FUNs<_Tp, variant<_Ti...>, index_sequence<_Ind...>>
+    : _Build_FUN<_Ind, _Tp, _Ti>...
+    {
+      using _Build_FUN<_Ind, _Tp, _Ti>::_S_fun...;
+    };
+
+  // The index j of the overload FUN(Tj) selected by overload resolution
+  // for FUN(std::forward<_Tp>(t))
+  template<typename _Tp, typename _Variant>
+    using _FUN_type
+      = decltype(_Build_FUNs<_Tp, _Variant>::_S_fun(std::declval<_Tp>()));
+
+  // The index selected for FUN(std::forward<T>(t)), or variant_npos if none.
+  template<typename _Tp, typename _Variant, typename = void>
+    inline constexpr size_t
+    __accepted_index = variant_npos;
+
+  template<typename _Tp, typename _Variant>
+    inline constexpr size_t
+    __accepted_index<_Tp, _Variant, void_t<_FUN_type<_Tp, _Variant>>>
+      = _FUN_type<_Tp, _Variant>::value;
+
+  template<typename _Maybe_variant_cookie, typename _Variant,
+	   typename = __remove_cvref_t<_Variant>>
+    inline constexpr bool
+    __extra_visit_slot_needed = false;
+
+  template<typename _Var, typename... _Types>
+    inline constexpr bool
+    __extra_visit_slot_needed<__variant_cookie, _Var, variant<_Types...>>
+      = !__variant::__never_valueless<_Types...>();
+
+  template<typename _Var, typename... _Types>
+    inline constexpr bool
+    __extra_visit_slot_needed<__variant_idx_cookie, _Var, variant<_Types...>>
+      = !__variant::__never_valueless<_Types...>();
+
+  // Used for storing a multi-dimensional vtable.
+  template<typename _Tp, size_t... _Dimensions>
+    struct _Multi_array;
+
+  // Partial specialization with rank zero, stores a single _Tp element.
+  template<typename _Tp>
+    struct _Multi_array<_Tp>
+    {
+      template<typename>
+	struct __untag_result
+	: false_type
+	{ using element_type = _Tp; };
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wignored-qualifiers"
+      template <typename... _Args>
+	struct __untag_result<const void(*)(_Args...)>
+	: false_type
+	{ using element_type = void(*)(_Args...); };
+#pragma GCC diagnostic pop
+
+      template <typename... _Args>
+	struct __untag_result<__variant_cookie(*)(_Args...)>
+	: false_type
+	{ using element_type = void(*)(_Args...); };
+
+      template <typename... _Args>
+	struct __untag_result<__variant_idx_cookie(*)(_Args...)>
+	: false_type
+	{ using element_type = void(*)(_Args...); };
+
+      template <typename _Res, typename... _Args>
+	struct __untag_result<__deduce_visit_result<_Res>(*)(_Args...)>
+	: true_type
+	{ using element_type = _Res(*)(_Args...); };
+
+      using __result_is_deduced = __untag_result<_Tp>;
+
+      constexpr const typename __untag_result<_Tp>::element_type&
+      _M_access() const
+      { return _M_data; }
+
+      typename __untag_result<_Tp>::element_type _M_data;
+    };
+
+  // Partial specialization with rank >= 1.
+  template<typename _Ret,
+	   typename _Visitor,
+	   typename... _Variants,
+	   size_t __first, size_t... __rest>
+    struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
+    {
+      static constexpr size_t __index =
+	sizeof...(_Variants) - sizeof...(__rest) - 1;
+
+      using _Variant = typename _Nth_type<__index, _Variants...>::type;
+
+      static constexpr int __do_cookie =
+	__extra_visit_slot_needed<_Ret, _Variant> ? 1 : 0;
+
+      using _Tp = _Ret(*)(_Visitor, _Variants...);
+
+      template<typename... _Args>
+	constexpr decltype(auto)
+	_M_access(size_t __first_index, _Args... __rest_indices) const
+        {
+	  return _M_arr[__first_index + __do_cookie]
+	    ._M_access(__rest_indices...);
+	}
+
+      _Multi_array<_Tp, __rest...> _M_arr[__first + __do_cookie];
+    };
+
+  // Creates a multi-dimensional vtable recursively.
+  //
+  // For example,
+  // visit([](auto, auto){},
+  //       variant<int, char>(),  // typedef'ed as V1
+  //       variant<float, double, long double>())  // typedef'ed as V2
+  // will trigger instantiations of:
+  // __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 2, 3>,
+  //                   tuple<V1&&, V2&&>, std::index_sequence<>>
+  //   __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
+  //                     tuple<V1&&, V2&&>, std::index_sequence<0>>
+  //     __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
+  //                       tuple<V1&&, V2&&>, std::index_sequence<0, 0>>
+  //     __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
+  //                       tuple<V1&&, V2&&>, std::index_sequence<0, 1>>
+  //     __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
+  //                       tuple<V1&&, V2&&>, std::index_sequence<0, 2>>
+  //   __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&), 3>,
+  //                     tuple<V1&&, V2&&>, std::index_sequence<1>>
+  //     __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
+  //                       tuple<V1&&, V2&&>, std::index_sequence<1, 0>>
+  //     __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
+  //                       tuple<V1&&, V2&&>, std::index_sequence<1, 1>>
+  //     __gen_vtable_impl<_Multi_array<void(*)(V1&&, V2&&)>,
+  //                       tuple<V1&&, V2&&>, std::index_sequence<1, 2>>
+  // The returned multi-dimensional vtable can be fast accessed by the visitor
+  // using index calculation.
+  template<typename _Array_type, typename _Index_seq>
+    struct __gen_vtable_impl;
+
+  // Defines the _S_apply() member that returns a _Multi_array populated
+  // with function pointers that perform the visitation expressions e(m)
+  // for each valid pack of indexes into the variant types _Variants.
+  //
+  // This partial specialization builds up the index sequences by recursively
+  // calling _S_apply() on the next specialization of __gen_vtable_impl.
+  // The base case of the recursion defines the actual function pointers.
+  template<typename _Result_type, typename _Visitor, size_t... __dimensions,
+	   typename... _Variants, size_t... __indices>
+    struct __gen_vtable_impl<
+	_Multi_array<_Result_type (*)(_Visitor, _Variants...), __dimensions...>,
+	std::index_sequence<__indices...>>
+    {
+      using _Next =
+	  remove_reference_t<typename _Nth_type<sizeof...(__indices),
+			     _Variants...>::type>;
+      using _Array_type =
+	  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
+		       __dimensions...>;
+
+      static constexpr _Array_type
+      _S_apply()
+      {
+	_Array_type __vtable{};
+	_S_apply_all_alts(
+	  __vtable, make_index_sequence<variant_size_v<_Next>>());
+	return __vtable;
+      }
+
+      template<size_t... __var_indices>
+	static constexpr void
+	_S_apply_all_alts(_Array_type& __vtable,
+			  std::index_sequence<__var_indices...>)
+	{
+	  if constexpr (__extra_visit_slot_needed<_Result_type, _Next>)
+	    (_S_apply_single_alt<true, __var_indices>(
+	      __vtable._M_arr[__var_indices + 1],
+	      &(__vtable._M_arr[0])), ...);
+	  else
+	    (_S_apply_single_alt<false, __var_indices>(
+	      __vtable._M_arr[__var_indices]), ...);
+	}
+
+      template<bool __do_cookie, size_t __index, typename _Tp>
+	static constexpr void
+	_S_apply_single_alt(_Tp& __element, _Tp* __cookie_element = nullptr)
+	{
+	  if constexpr (__do_cookie)
+	    {
+	      __element = __gen_vtable_impl<
+		_Tp,
+		std::index_sequence<__indices..., __index>>::_S_apply();
+	      *__cookie_element = __gen_vtable_impl<
+		_Tp,
+		std::index_sequence<__indices..., variant_npos>>::_S_apply();
+	    }
+	  else
+	    {
+	      auto __tmp_element = __gen_vtable_impl<
+		remove_reference_t<decltype(__element)>,
+		std::index_sequence<__indices..., __index>>::_S_apply();
+	      static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
+			    "std::visit requires the visitor to have the same "
+			    "return type for all alternatives of a variant");
+	      __element = __tmp_element;
+	    }
+	}
+    };
+
+  // This partial specialization is the base case for the recursion.
+  // It populates a _Multi_array element with the address of a function
+  // that invokes the visitor with the alternatives specified by __indices.
+  template<typename _Result_type, typename _Visitor, typename... _Variants,
+	   size_t... __indices>
+    struct __gen_vtable_impl<
+      _Multi_array<_Result_type (*)(_Visitor, _Variants...)>,
+		   std::index_sequence<__indices...>>
+    {
+      using _Array_type =
+	  _Multi_array<_Result_type (*)(_Visitor, _Variants...)>;
+
+      template<size_t __index, typename _Variant>
+	static constexpr decltype(auto)
+	__element_by_index_or_cookie(_Variant&& __var) noexcept
+        {
+	  if constexpr (__index != variant_npos)
+	    return __variant::__get<__index>(std::forward<_Variant>(__var));
+	  else
+	    return __variant_cookie{};
+	}
+
+      static constexpr decltype(auto)
+      __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
+      {
+	if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
+	  // For raw visitation using indices, pass the indices to the visitor
+	  // and discard the return value:
+	  std::__invoke(std::forward<_Visitor>(__visitor),
+	      __element_by_index_or_cookie<__indices>(
+		std::forward<_Variants>(__vars))...,
+	      integral_constant<size_t, __indices>()...);
+	else if constexpr (is_same_v<_Result_type, __variant_cookie>)
+	  // For raw visitation without indices, and discard the return value:
+	  std::__invoke(std::forward<_Visitor>(__visitor),
+	      __element_by_index_or_cookie<__indices>(
+		std::forward<_Variants>(__vars))...);
+	else if constexpr (_Array_type::__result_is_deduced::value)
+	  // For the usual std::visit case deduce the return value:
+	  return std::__invoke(std::forward<_Visitor>(__visitor),
+	      __element_by_index_or_cookie<__indices>(
+		std::forward<_Variants>(__vars))...);
+	else // for std::visit<R> use INVOKE<R>
+	  return std::__invoke_r<_Result_type>(
+	      std::forward<_Visitor>(__visitor),
+	      __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
+      }
+
+      static constexpr auto
+      _S_apply()
+      {
+	if constexpr (_Array_type::__result_is_deduced::value)
+	  {
+	    constexpr bool __visit_ret_type_mismatch =
+	      !is_same_v<typename _Result_type::type,
+			 decltype(__visit_invoke(std::declval<_Visitor>(),
+				    std::declval<_Variants>()...))>;
+	    if constexpr (__visit_ret_type_mismatch)
+	      {
+		struct __cannot_match {};
+		return __cannot_match{};
+	      }
+	    else
+	      return _Array_type{&__visit_invoke};
+	  }
+	else
+	  return _Array_type{&__visit_invoke};
+      }
+    };
+
+  template<typename _Result_type, typename _Visitor, typename... _Variants>
+    struct __gen_vtable
+    {
+      using _Array_type =
+	  _Multi_array<_Result_type (*)(_Visitor, _Variants...),
+		       variant_size_v<remove_reference_t<_Variants>>...>;
+
+      static constexpr _Array_type _S_vtable
+	= __gen_vtable_impl<_Array_type, std::index_sequence<>>::_S_apply();
+    };
+
+  template<size_t _Np, typename _Tp>
+    struct _Base_dedup : public _Tp { };
+
+  template<typename _Variant, typename __indices>
+    struct _Variant_hash_base;
+
+  template<typename... _Types, size_t... __indices>
+    struct _Variant_hash_base<variant<_Types...>,
+			      std::index_sequence<__indices...>>
+    : _Base_dedup<__indices, __poison_hash<remove_const_t<_Types>>>... { };
+
+  // Equivalent to decltype(get<_Np>(as-variant(declval<_Variant>())))
+  template<size_t _Np, typename _Variant,
+      typename _AsV = decltype(__variant::__as(std::declval<_Variant>())),
+      typename _Tp = variant_alternative_t<_Np, remove_reference_t<_AsV>>>
+    using __get_t
+      = __conditional_t<is_lvalue_reference_v<_Variant>, _Tp&, _Tp&&>;
+
+  // Return type of std::visit.
+  template<typename _Visitor, typename... _Variants>
+    using __visit_result_t
+      = invoke_result_t<_Visitor, __get_t<0, _Variants>...>;
+
+  template<typename _Tp, typename... _Types>
+    constexpr inline bool __same_types = (is_same_v<_Tp, _Types> && ...);
+
+  template <typename _Visitor, typename _Variant, size_t... _Idxs>
+    constexpr bool __check_visitor_results(std::index_sequence<_Idxs...>)
+    {
+      return __same_types<
+	invoke_result_t<_Visitor, __get_t<_Idxs, _Variant>>...
+	>;
+    }
+
+} // namespace __variant
+} // namespace __detail
+
+  template<typename _Tp, typename... _Types>
+    constexpr bool
+    holds_alternative(const variant<_Types...>& __v) noexcept
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      return __v.index() == std::__find_uniq_type_in_pack<_Tp, _Types...>();
+    }
+
+  template<typename _Tp, typename... _Types>
+    constexpr _Tp&
+    get(variant<_Types...>& __v)
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      static_assert(!is_void_v<_Tp>, "_Tp must not be void");
+      constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+      return std::get<__n>(__v);
+    }
+
+  template<typename _Tp, typename... _Types>
+    constexpr _Tp&&
+    get(variant<_Types...>&& __v)
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      static_assert(!is_void_v<_Tp>, "_Tp must not be void");
+      constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+      return std::get<__n>(std::move(__v));
+    }
+
+  template<typename _Tp, typename... _Types>
+    constexpr const _Tp&
+    get(const variant<_Types...>& __v)
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      static_assert(!is_void_v<_Tp>, "_Tp must not be void");
+      constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+      return std::get<__n>(__v);
+    }
+
+  template<typename _Tp, typename... _Types>
+    constexpr const _Tp&&
+    get(const variant<_Types...>&& __v)
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      static_assert(!is_void_v<_Tp>, "_Tp must not be void");
+      constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+      return std::get<__n>(std::move(__v));
+    }
+
+  template<size_t _Np, typename... _Types>
+    constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
+    get_if(variant<_Types...>* __ptr) noexcept
+    {
+      using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
+      static_assert(_Np < sizeof...(_Types),
+		    "The index must be in [0, number of alternatives)");
+      static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
+      if (__ptr && __ptr->index() == _Np)
+	return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
+      return nullptr;
+    }
+
+  template<size_t _Np, typename... _Types>
+    constexpr
+    add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
+    get_if(const variant<_Types...>* __ptr) noexcept
+    {
+      using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
+      static_assert(_Np < sizeof...(_Types),
+		    "The index must be in [0, number of alternatives)");
+      static_assert(!is_void_v<_Alternative_type>, "_Tp must not be void");
+      if (__ptr && __ptr->index() == _Np)
+	return std::addressof(__detail::__variant::__get<_Np>(*__ptr));
+      return nullptr;
+    }
+
+  template<typename _Tp, typename... _Types>
+    constexpr add_pointer_t<_Tp>
+    get_if(variant<_Types...>* __ptr) noexcept
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      static_assert(!is_void_v<_Tp>, "_Tp must not be void");
+      constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+      return std::get_if<__n>(__ptr);
+    }
+
+  template<typename _Tp, typename... _Types>
+    constexpr add_pointer_t<const _Tp>
+    get_if(const variant<_Types...>* __ptr) noexcept
+    {
+      static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
+		    "T must occur exactly once in alternatives");
+      static_assert(!is_void_v<_Tp>, "_Tp must not be void");
+      constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+      return std::get_if<__n>(__ptr);
+    }
+
+  struct monostate { };
+
+#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP, __NAME) \
+  template<typename... _Types> \
+    constexpr bool operator __OP(const variant<_Types...>& __lhs, \
+				 const variant<_Types...>& __rhs) \
+    { \
+      bool __ret = true; \
+      __detail::__variant::__raw_idx_visit( \
+        [&__ret, &__lhs] (auto&& __rhs_mem, auto __rhs_index) mutable \
+        { \
+	  if constexpr (__rhs_index != variant_npos) \
+	    { \
+	      if (__lhs.index() == __rhs_index) \
+	        { \
+		  auto& __this_mem = std::get<__rhs_index>(__lhs);	\
+                  __ret = __this_mem __OP __rhs_mem; \
+                } \
+	      else \
+		__ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
+            } \
+          else \
+            __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
+	}, __rhs); \
+      return __ret; \
+    }
+
+  _VARIANT_RELATION_FUNCTION_TEMPLATE(<, less)
+  _VARIANT_RELATION_FUNCTION_TEMPLATE(<=, less_equal)
+  _VARIANT_RELATION_FUNCTION_TEMPLATE(==, equal)
+  _VARIANT_RELATION_FUNCTION_TEMPLATE(!=, not_equal)
+  _VARIANT_RELATION_FUNCTION_TEMPLATE(>=, greater_equal)
+  _VARIANT_RELATION_FUNCTION_TEMPLATE(>, greater)
+
+#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
+
+  constexpr bool operator==(monostate, monostate) noexcept { return true; }
+
+#ifdef __cpp_lib_three_way_comparison
+  template<typename... _Types>
+    requires (three_way_comparable<_Types> && ...)
+    constexpr
+    common_comparison_category_t<compare_three_way_result_t<_Types>...>
+    operator<=>(const variant<_Types...>& __v, const variant<_Types...>& __w)
+    {
+      common_comparison_category_t<compare_three_way_result_t<_Types>...> __ret
+	= strong_ordering::equal;
+
+      __detail::__variant::__raw_idx_visit(
+	[&__ret, &__v] (auto&& __w_mem, auto __w_index) mutable
+	{
+	  if constexpr (__w_index != variant_npos)
+	    {
+	      if (__v.index() == __w_index)
+		{
+		  auto& __this_mem = std::get<__w_index>(__v);
+		  __ret = __this_mem <=> __w_mem;
+		  return;
+		}
+	    }
+	  __ret = (__v.index() + 1) <=> (__w_index + 1);
+	}, __w);
+      return __ret;
+    }
+
+  constexpr strong_ordering
+  operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
+#else
+  constexpr bool operator!=(monostate, monostate) noexcept { return false; }
+  constexpr bool operator<(monostate, monostate) noexcept { return false; }
+  constexpr bool operator>(monostate, monostate) noexcept { return false; }
+  constexpr bool operator<=(monostate, monostate) noexcept { return true; }
+  constexpr bool operator>=(monostate, monostate) noexcept { return true; }
+#endif
+
+  template<typename _Visitor, typename... _Variants>
+    constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
+    visit(_Visitor&&, _Variants&&...);
+
+  template<typename... _Types>
+    _GLIBCXX20_CONSTEXPR
+    inline enable_if_t<(is_move_constructible_v<_Types> && ...)
+			&& (is_swappable_v<_Types> && ...)>
+    swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
+    noexcept(noexcept(__lhs.swap(__rhs)))
+    { __lhs.swap(__rhs); }
+
+  template<typename... _Types>
+    enable_if_t<!((is_move_constructible_v<_Types> && ...)
+		   && (is_swappable_v<_Types> && ...))>
+    swap(variant<_Types...>&, variant<_Types...>&) = delete;
+
+  class bad_variant_access : public exception
+  {
+  public:
+    bad_variant_access() noexcept { }
+
+    const char* what() const noexcept override
+    { return _M_reason; }
+
+  private:
+    bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
+
+    // Must point to a string with static storage duration:
+    const char* _M_reason = "bad variant access";
+
+    friend void __throw_bad_variant_access(const char* __what);
+  };
+
+  // Must only be called with a string literal
+  inline void
+  __throw_bad_variant_access(const char* __what)
+  { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
+
+  inline void
+  __throw_bad_variant_access(bool __valueless)
+  {
+    if (__valueless) [[__unlikely__]]
+      __throw_bad_variant_access("std::get: variant is valueless");
+    else
+      __throw_bad_variant_access("std::get: wrong index for variant");
+  }
+
+  template<typename... _Types>
+    class variant
+    : private __detail::__variant::_Variant_base<_Types...>,
+      private _Enable_default_constructor<
+	__detail::__variant::_Traits<_Types...>::_S_default_ctor,
+	  variant<_Types...>>,
+      private _Enable_copy_move<
+	__detail::__variant::_Traits<_Types...>::_S_copy_ctor,
+	__detail::__variant::_Traits<_Types...>::_S_copy_assign,
+	__detail::__variant::_Traits<_Types...>::_S_move_ctor,
+	__detail::__variant::_Traits<_Types...>::_S_move_assign,
+	variant<_Types...>>
+    {
+    private:
+      template <typename... _UTypes, typename _Tp>
+	friend _GLIBCXX20_CONSTEXPR decltype(auto)
+	__variant_cast(_Tp&&);
+
+      static_assert(sizeof...(_Types) > 0,
+		    "variant must have at least one alternative");
+      static_assert(!(std::is_reference_v<_Types> || ...),
+		    "variant must have no reference alternative");
+      static_assert(!(std::is_void_v<_Types> || ...),
+		    "variant must have no void alternative");
+
+      using _Base = __detail::__variant::_Variant_base<_Types...>;
+      using _Default_ctor_enabler =
+	_Enable_default_constructor<
+	  __detail::__variant::_Traits<_Types...>::_S_default_ctor,
+	    variant<_Types...>>;
+
+      template<typename _Tp>
+	static constexpr bool __not_self
+	  = !is_same_v<__remove_cvref_t<_Tp>, variant>;
+
+      template<typename _Tp>
+	static constexpr bool
+	__exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
+
+      template<typename _Tp>
+	static constexpr size_t __accepted_index
+	  = __detail::__variant::__accepted_index<_Tp, variant>;
+
+      template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
+	using __to_type = typename _Nth_type<_Np, _Types...>::type;
+
+      template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
+	using __accepted_type = __to_type<__accepted_index<_Tp>>;
+
+      template<typename _Tp>
+	static constexpr size_t __index_of
+	  = std::__find_uniq_type_in_pack<_Tp, _Types...>();
+
+      using _Traits = __detail::__variant::_Traits<_Types...>;
+
+      template<typename _Tp>
+	struct __is_in_place_tag : false_type { };
+      template<typename _Tp>
+	struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
+      template<size_t _Np>
+	struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
+
+      template<typename _Tp>
+	static constexpr bool __not_in_place_tag
+	  = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
+
+    public:
+      variant() = default;
+      variant(const variant& __rhs) = default;
+      variant(variant&&) = default;
+      variant& operator=(const variant&) = default;
+      variant& operator=(variant&&) = default;
+      _GLIBCXX20_CONSTEXPR ~variant() = default;
+
+      template<typename _Tp,
+	       typename = enable_if_t<sizeof...(_Types) != 0>,
+	       typename = enable_if_t<__not_in_place_tag<_Tp>>,
+	       typename _Tj = __accepted_type<_Tp&&>,
+	       typename = enable_if_t<__exactly_once<_Tj>
+				      && is_constructible_v<_Tj, _Tp>>>
+	constexpr
+	variant(_Tp&& __t)
+	noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
+	: variant(in_place_index<__accepted_index<_Tp>>,
+		  std::forward<_Tp>(__t))
+	{ }
+
+      template<typename _Tp, typename... _Args,
+	       typename = enable_if_t<__exactly_once<_Tp>
+				      && is_constructible_v<_Tp, _Args...>>>
+	constexpr explicit
+	variant(in_place_type_t<_Tp>, _Args&&... __args)
+	: variant(in_place_index<__index_of<_Tp>>,
+		  std::forward<_Args>(__args)...)
+	{ }
+
+      template<typename _Tp, typename _Up, typename... _Args,
+	       typename = enable_if_t<__exactly_once<_Tp>
+				      && is_constructible_v<_Tp,
+					   initializer_list<_Up>&, _Args...>>>
+	constexpr explicit
+	variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
+		_Args&&... __args)
+	: variant(in_place_index<__index_of<_Tp>>, __il,
+		  std::forward<_Args>(__args)...)
+	{ }
+
+      template<size_t _Np, typename... _Args,
+	       typename _Tp = __to_type<_Np>,
+	       typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
+	constexpr explicit
+	variant(in_place_index_t<_Np>, _Args&&... __args)
+	: _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
+	_Default_ctor_enabler(_Enable_default_constructor_tag{})
+	{ }
+
+      template<size_t _Np, typename _Up, typename... _Args,
+	       typename _Tp = __to_type<_Np>,
+	       typename = enable_if_t<is_constructible_v<_Tp,
+							 initializer_list<_Up>&,
+							 _Args...>>>
+	constexpr explicit
+	variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
+		_Args&&... __args)
+	: _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...),
+	_Default_ctor_enabler(_Enable_default_constructor_tag{})
+	{ }
+
+      template<typename _Tp>
+	_GLIBCXX20_CONSTEXPR
+	enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
+		    && is_constructible_v<__accepted_type<_Tp&&>, _Tp>
+		    && is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
+		    variant&>
+	operator=(_Tp&& __rhs)
+	noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
+		 && is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
+	{
+	  constexpr auto __index = __accepted_index<_Tp>;
+	  if (index() == __index)
+	    std::get<__index>(*this) = std::forward<_Tp>(__rhs);
+	  else
+	    {
+	      using _Tj = __accepted_type<_Tp&&>;
+	      if constexpr (is_nothrow_constructible_v<_Tj, _Tp>
+			    || !is_nothrow_move_constructible_v<_Tj>)
+		this->emplace<__index>(std::forward<_Tp>(__rhs));
+	      else
+		// _GLIBCXX_RESOLVE_LIB_DEFECTS
+		// 3585. converting assignment with immovable alternative
+		this->emplace<__index>(_Tj(std::forward<_Tp>(__rhs)));
+	    }
+	  return *this;
+	}
+
+      template<typename _Tp, typename... _Args>
+	_GLIBCXX20_CONSTEXPR
+	enable_if_t<is_constructible_v<_Tp, _Args...> && __exactly_once<_Tp>,
+		    _Tp&>
+	emplace(_Args&&... __args)
+	{
+	  constexpr size_t __index = __index_of<_Tp>;
+	  return this->emplace<__index>(std::forward<_Args>(__args)...);
+	}
+
+      template<typename _Tp, typename _Up, typename... _Args>
+	_GLIBCXX20_CONSTEXPR
+	enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
+		    && __exactly_once<_Tp>,
+		    _Tp&>
+	emplace(initializer_list<_Up> __il, _Args&&... __args)
+	{
+	  constexpr size_t __index = __index_of<_Tp>;
+	  return this->emplace<__index>(__il, std::forward<_Args>(__args)...);
+	}
+
+      template<size_t _Np, typename... _Args>
+	_GLIBCXX20_CONSTEXPR
+	enable_if_t<is_constructible_v<__to_type<_Np>, _Args...>,
+		    __to_type<_Np>&>
+	emplace(_Args&&... __args)
+	{
+	  namespace __variant = std::__detail::__variant;
+	  using type = typename _Nth_type<_Np, _Types...>::type;
+	  // Provide the strong exception-safety guarantee when possible,
+	  // to avoid becoming valueless.
+	  if constexpr (is_nothrow_constructible_v<type, _Args...>)
+	    {
+	      __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
+	    }
+	  else if constexpr (is_scalar_v<type>)
+	    {
+	      // This might invoke a potentially-throwing conversion operator:
+	      const type __tmp(std::forward<_Args>(__args)...);
+	      // But this won't throw:
+	      __variant::__emplace<_Np>(*this, __tmp);
+	    }
+	  else if constexpr (__variant::_Never_valueless_alt<type>()
+	      && _Traits::_S_move_assign)
+	    {
+	      // This construction might throw:
+	      variant __tmp(in_place_index<_Np>,
+			    std::forward<_Args>(__args)...);
+	      // But _Never_valueless_alt<type> means this won't:
+	      *this = std::move(__tmp);
+	    }
+	  else
+	    {
+	      // This case only provides the basic exception-safety guarantee,
+	      // i.e. the variant can become valueless.
+	      __variant::__emplace<_Np>(*this, std::forward<_Args>(__args)...);
+	    }
+	  return std::get<_Np>(*this);
+	}
+
+      template<size_t _Np, typename _Up, typename... _Args>
+	_GLIBCXX20_CONSTEXPR
+	enable_if_t<is_constructible_v<__to_type<_Np>,
+				       initializer_list<_Up>&, _Args...>,
+		    __to_type<_Np>&>
+	emplace(initializer_list<_Up> __il, _Args&&... __args)
+	{
+	  namespace __variant = std::__detail::__variant;
+	  using type = typename _Nth_type<_Np, _Types...>::type;
+	  // Provide the strong exception-safety guarantee when possible,
+	  // to avoid becoming valueless.
+	  if constexpr (is_nothrow_constructible_v<type,
+						   initializer_list<_Up>&,
+						   _Args...>)
+	    {
+	      __variant::__emplace<_Np>(*this, __il,
+					std::forward<_Args>(__args)...);
+	    }
+	  else if constexpr (__variant::_Never_valueless_alt<type>()
+	      && _Traits::_S_move_assign)
+	    {
+	      // This construction might throw:
+	      variant __tmp(in_place_index<_Np>, __il,
+			    std::forward<_Args>(__args)...);
+	      // But _Never_valueless_alt<type> means this won't:
+	      *this = std::move(__tmp);
+	    }
+	  else
+	    {
+	      // This case only provides the basic exception-safety guarantee,
+	      // i.e. the variant can become valueless.
+	      __variant::__emplace<_Np>(*this, __il,
+					std::forward<_Args>(__args)...);
+	    }
+	  return std::get<_Np>(*this);
+	}
+
+      template<size_t _Np, typename... _Args>
+	enable_if_t<!(_Np < sizeof...(_Types))> emplace(_Args&&...) = delete;
+
+      template<typename _Tp, typename... _Args>
+	enable_if_t<!__exactly_once<_Tp>> emplace(_Args&&...) = delete;
+
+      constexpr bool valueless_by_exception() const noexcept
+      { return !this->_M_valid(); }
+
+      constexpr size_t index() const noexcept
+      {
+	using __index_type = typename _Base::__index_type;
+	if constexpr (__detail::__variant::__never_valueless<_Types...>())
+	  return this->_M_index;
+	else if constexpr (sizeof...(_Types) <= __index_type(-1) / 2)
+	  return make_signed_t<__index_type>(this->_M_index);
+	else
+	  return size_t(__index_type(this->_M_index + 1)) - 1;
+      }
+
+      _GLIBCXX20_CONSTEXPR
+      void
+      swap(variant& __rhs)
+      noexcept((__is_nothrow_swappable<_Types>::value && ...)
+	       && is_nothrow_move_constructible_v<variant>)
+      {
+	static_assert((is_move_constructible_v<_Types> && ...));
+
+	// Handle this here to simplify the visitation.
+	if (__rhs.valueless_by_exception()) [[__unlikely__]]
+	  {
+	    if (!this->valueless_by_exception()) [[__likely__]]
+	      __rhs.swap(*this);
+	    return;
+	  }
+
+	namespace __variant = __detail::__variant;
+
+	__variant::__raw_idx_visit(
+	  [this, &__rhs](auto&& __rhs_mem, auto __rhs_index) mutable
+	  {
+	    constexpr size_t __j = __rhs_index;
+	    if constexpr (__j != variant_npos)
+	      {
+		if (this->index() == __j)
+		  {
+		    using std::swap;
+		    swap(std::get<__j>(*this), __rhs_mem);
+		  }
+		else
+		  {
+		    auto __tmp(std::move(__rhs_mem));
+
+		    if constexpr (_Traits::_S_trivial_move_assign)
+		      __rhs = std::move(*this);
+		    else
+		      __variant::__raw_idx_visit(
+			[&__rhs](auto&& __this_mem, auto __this_index) mutable
+			{
+			  constexpr size_t __k = __this_index;
+			  if constexpr (__k != variant_npos)
+			    __variant::__emplace<__k>(__rhs,
+						      std::move(__this_mem));
+			}, *this);
+
+		    __variant::__emplace<__j>(*this, std::move(__tmp));
+		  }
+	      }
+	  }, __rhs);
+      }
+
+#if defined(__clang__) && __clang_major__ <= 7
+    public:
+      using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
+#endif
+
+    private:
+      template<size_t _Np, typename _Vp>
+	friend constexpr decltype(auto)
+	__detail::__variant::__get(_Vp&& __v) noexcept;
+
+#define _VARIANT_RELATION_FUNCTION_TEMPLATE(__OP) \
+      template<typename... _Tp> \
+	friend constexpr bool \
+	operator __OP(const variant<_Tp...>& __lhs, \
+		      const variant<_Tp...>& __rhs);
+
+      _VARIANT_RELATION_FUNCTION_TEMPLATE(<)
+      _VARIANT_RELATION_FUNCTION_TEMPLATE(<=)
+      _VARIANT_RELATION_FUNCTION_TEMPLATE(==)
+      _VARIANT_RELATION_FUNCTION_TEMPLATE(!=)
+      _VARIANT_RELATION_FUNCTION_TEMPLATE(>=)
+      _VARIANT_RELATION_FUNCTION_TEMPLATE(>)
+
+#undef _VARIANT_RELATION_FUNCTION_TEMPLATE
+    };
+
+  template<size_t _Np, typename... _Types>
+    constexpr variant_alternative_t<_Np, variant<_Types...>>&
+    get(variant<_Types...>& __v)
+    {
+      static_assert(_Np < sizeof...(_Types),
+		    "The index must be in [0, number of alternatives)");
+      if (__v.index() != _Np)
+	__throw_bad_variant_access(__v.valueless_by_exception());
+      return __detail::__variant::__get<_Np>(__v);
+    }
+
+  template<size_t _Np, typename... _Types>
+    constexpr variant_alternative_t<_Np, variant<_Types...>>&&
+    get(variant<_Types...>&& __v)
+    {
+      static_assert(_Np < sizeof...(_Types),
+		    "The index must be in [0, number of alternatives)");
+      if (__v.index() != _Np)
+	__throw_bad_variant_access(__v.valueless_by_exception());
+      return __detail::__variant::__get<_Np>(std::move(__v));
+    }
+
+  template<size_t _Np, typename... _Types>
+    constexpr const variant_alternative_t<_Np, variant<_Types...>>&
+    get(const variant<_Types...>& __v)
+    {
+      static_assert(_Np < sizeof...(_Types),
+		    "The index must be in [0, number of alternatives)");
+      if (__v.index() != _Np)
+	__throw_bad_variant_access(__v.valueless_by_exception());
+      return __detail::__variant::__get<_Np>(__v);
+    }
+
+  template<size_t _Np, typename... _Types>
+    constexpr const variant_alternative_t<_Np, variant<_Types...>>&&
+    get(const variant<_Types...>&& __v)
+    {
+      static_assert(_Np < sizeof...(_Types),
+		    "The index must be in [0, number of alternatives)");
+      if (__v.index() != _Np)
+	__throw_bad_variant_access(__v.valueless_by_exception());
+      return __detail::__variant::__get<_Np>(std::move(__v));
+    }
+
+  /// @cond undocumented
+  template<typename _Result_type, typename _Visitor, typename... _Variants>
+    constexpr decltype(auto)
+    __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
+    {
+      // Get the silly case of visiting no variants out of the way first.
+      if constexpr (sizeof...(_Variants) == 0)
+	{
+	  if constexpr (is_void_v<_Result_type>)
+	    return (void) std::forward<_Visitor>(__visitor)();
+	  else
+	    return std::forward<_Visitor>(__visitor)();
+	}
+      else
+	{
+	  constexpr size_t __max = 11; // "These go to eleven."
+
+	  // The type of the first variant in the pack.
+	  using _V0 = typename _Nth_type<0, _Variants...>::type;
+	  // The number of alternatives in that first variant.
+	  constexpr auto __n = variant_size_v<remove_reference_t<_V0>>;
+
+	  if constexpr (sizeof...(_Variants) > 1 || __n > __max)
+	    {
+	      // Use a jump table for the general case.
+	      constexpr auto& __vtable = __detail::__variant::__gen_vtable<
+		_Result_type, _Visitor&&, _Variants&&...>::_S_vtable;
+
+	      auto __func_ptr = __vtable._M_access(__variants.index()...);
+	      return (*__func_ptr)(std::forward<_Visitor>(__visitor),
+				   std::forward<_Variants>(__variants)...);
+	    }
+	  else // We have a single variant with a small number of alternatives.
+	    {
+	      // A name for the first variant in the pack.
+	      _V0& __v0
+		= [](_V0& __v, ...) -> _V0& { return __v; }(__variants...);
+
+	      using __detail::__variant::_Multi_array;
+	      using __detail::__variant::__gen_vtable_impl;
+	      using _Ma = _Multi_array<_Result_type (*)(_Visitor&&, _V0&&)>;
+
+#ifdef _GLIBCXX_DEBUG
+# define _GLIBCXX_VISIT_UNREACHABLE __builtin_trap
+#else
+# define _GLIBCXX_VISIT_UNREACHABLE __builtin_unreachable
+#endif
+
+#define _GLIBCXX_VISIT_CASE(N)						\
+  case N:								\
+  {									\
+    if constexpr (N < __n)						\
+      {									\
+	return __gen_vtable_impl<_Ma, index_sequence<N>>::		\
+	  __visit_invoke(std::forward<_Visitor>(__visitor),		\
+			 std::forward<_V0>(__v0));		\
+      }									\
+    else _GLIBCXX_VISIT_UNREACHABLE();					\
+  }
+
+	      switch (__v0.index())
+		{
+		  _GLIBCXX_VISIT_CASE(0)
+		  _GLIBCXX_VISIT_CASE(1)
+		  _GLIBCXX_VISIT_CASE(2)
+		  _GLIBCXX_VISIT_CASE(3)
+		  _GLIBCXX_VISIT_CASE(4)
+		  _GLIBCXX_VISIT_CASE(5)
+		  _GLIBCXX_VISIT_CASE(6)
+		  _GLIBCXX_VISIT_CASE(7)
+		  _GLIBCXX_VISIT_CASE(8)
+		  _GLIBCXX_VISIT_CASE(9)
+		  _GLIBCXX_VISIT_CASE(10)
+		case variant_npos:
+		  using __detail::__variant::__variant_idx_cookie;
+		  using __detail::__variant::__variant_cookie;
+		  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
+				|| is_same_v<_Result_type, __variant_cookie>)
+		    {
+		      using _Npos = index_sequence<variant_npos>;
+		      return __gen_vtable_impl<_Ma, _Npos>::
+			__visit_invoke(std::forward<_Visitor>(__visitor),
+				       std::forward<_V0>(__v0));
+		    }
+		  else
+		    _GLIBCXX_VISIT_UNREACHABLE();
+		default:
+		  _GLIBCXX_VISIT_UNREACHABLE();
+		}
+#undef _GLIBCXX_VISIT_CASE
+#undef _GLIBCXX_VISIT_UNREACHABLE
+	    }
+	}
+    }
+  /// @endcond
+
+  template<typename _Visitor, typename... _Variants>
+    constexpr __detail::__variant::__visit_result_t<_Visitor, _Variants...>
+    visit(_Visitor&& __visitor, _Variants&&... __variants)
+    {
+      namespace __variant = std::__detail::__variant;
+
+      if ((__variant::__as(__variants).valueless_by_exception() || ...))
+	__throw_bad_variant_access("std::visit: variant is valueless");
+
+      using _Result_type
+	= __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
+
+      using _Tag = __detail::__variant::__deduce_visit_result<_Result_type>;
+
+      if constexpr (sizeof...(_Variants) == 1)
+	{
+	  using _Vp = decltype(__variant::__as(std::declval<_Variants>()...));
+
+	  constexpr bool __visit_rettypes_match = __detail::__variant::
+	    __check_visitor_results<_Visitor, _Vp>(
+	      make_index_sequence<variant_size_v<remove_reference_t<_Vp>>>());
+	  if constexpr (!__visit_rettypes_match)
+	    {
+	      static_assert(__visit_rettypes_match,
+			  "std::visit requires the visitor to have the same "
+			  "return type for all alternatives of a variant");
+	      return;
+	    }
+	  else
+	    return std::__do_visit<_Tag>(
+	      std::forward<_Visitor>(__visitor),
+	      static_cast<_Vp>(__variants)...);
+	}
+      else
+	return std::__do_visit<_Tag>(
+	  std::forward<_Visitor>(__visitor),
+	  __variant::__as(std::forward<_Variants>(__variants))...);
+    }
+
+#if __cplusplus > 201703L
+  template<typename _Res, typename _Visitor, typename... _Variants>
+    constexpr _Res
+    visit(_Visitor&& __visitor, _Variants&&... __variants)
+    {
+      namespace __variant = std::__detail::__variant;
+
+      if ((__variant::__as(__variants).valueless_by_exception() || ...))
+	__throw_bad_variant_access("std::visit<R>: variant is valueless");
+
+      return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
+	  __variant::__as(std::forward<_Variants>(__variants))...);
+    }
+#endif
+
+  /// @cond undocumented
+  template<bool, typename... _Types>
+    struct __variant_hash_call_base_impl
+    {
+      size_t
+      operator()(const variant<_Types...>& __t) const
+      noexcept((is_nothrow_invocable_v<hash<decay_t<_Types>>, _Types> && ...))
+      {
+	size_t __ret;
+	__detail::__variant::__raw_visit(
+	  [&__t, &__ret](auto&& __t_mem) mutable
+	  {
+	    using _Type = __remove_cvref_t<decltype(__t_mem)>;
+	    if constexpr (!is_same_v<_Type,
+			             __detail::__variant::__variant_cookie>)
+	      __ret = std::hash<size_t>{}(__t.index())
+		      + std::hash<_Type>{}(__t_mem);
+	    else
+	      __ret = std::hash<size_t>{}(__t.index());
+	  }, __t);
+	return __ret;
+      }
+    };
+
+  template<typename... _Types>
+    struct __variant_hash_call_base_impl<false, _Types...> {};
+
+  template<typename... _Types>
+    using __variant_hash_call_base =
+    __variant_hash_call_base_impl<(__poison_hash<remove_const_t<_Types>>::
+				   __enable_hash_call &&...), _Types...>;
+  /// @endcond
+
+  template<typename... _Types>
+    struct hash<variant<_Types...>>
+    : private __detail::__variant::_Variant_hash_base<
+	variant<_Types...>, std::index_sequence_for<_Types...>>,
+      public __variant_hash_call_base<_Types...>
+    {
+      using result_type [[__deprecated__]] = size_t;
+      using argument_type [[__deprecated__]] = variant<_Types...>;
+    };
+
+  template<>
+    struct hash<monostate>
+    {
+      using result_type [[__deprecated__]] = size_t;
+      using argument_type [[__deprecated__]] = monostate;
+
+      size_t
+      operator()(const monostate&) const noexcept
+      {
+	constexpr size_t __magic_monostate_hash = -7777;
+	return __magic_monostate_hash;
+      }
+    };
+
+  template<typename... _Types>
+    struct __is_fast_hash<hash<variant<_Types...>>>
+    : bool_constant<(__is_fast_hash<_Types>::value && ...)>
+    { };
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+
+#endif // C++17
+
+#endif // _GLIBCXX_VARIANT