Implement C++17 <variant>. Patch from Michael Park!

This patch was reviewed as https://reviews.llvm.org/D23263.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@288547 91177308-0d34-0410-b5e6-96231b3b80d8

include/variant

@@ -0,0 +1,1553 @@
+// -*- C++ -*-
+//===------------------------------ variant -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_VARIANT
+#define _LIBCPP_VARIANT
+
+/*
+   variant synopsis
+
+namespace std {
+
+  // 20.7.2, class template variant
+  template <class... Types>
+  class variant {
+  public:
+
+    // 20.7.2.1, constructors
+    constexpr variant() noexcept(see below);
+    variant(const variant&);
+    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
+    ~variant();
+
+    // 20.7.2.3, assignment
+    variant& operator=(const variant&);
+    variant& operator=(variant&&) noexcept(see below);
+
+    template <class T> variant& operator=(T&&) noexcept(see below);
+
+    // 20.7.2.4, modifiers
+    template <class T, class... Args>
+    void emplace(Args&&...);
+
+    template <class T, class U, class... Args>
+    void emplace(initializer_list<U>, Args&&...);
+
+    template <size_t I, class... Args>
+    void emplace(Args&&...);
+
+    template <size_t I, class U, class...  Args>
+    void emplace(initializer_list<U>, Args&&...);
+
+    // 20.7.2.5, value status
+    constexpr bool valueless_by_exception() const noexcept;
+    constexpr size_t index() const noexcept;
+
+    // 20.7.2.6, swap
+    void swap(variant&) noexcept(see below);
+  };
+
+  // 20.7.3, variant helper classes
+  template <class T> struct variant_size; // undefined
+
+  template <class T>
+  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...>>;
+
+  constexpr size_t variant_npos = -1;
+
+  // 20.7.4, value access
+  template <class T, class... Types>
+  constexpr bool holds_alternative(const variant<Types...>&) noexcept;
+
+  template <size_t I, class... Types>
+  constexpr variant_alternative_t<I, variant<Types...>>&
+  get(variant<Types...>&);
+
+  template <size_t I, class... Types>
+  constexpr variant_alternative_t<I, variant<Types...>>&&
+  get(variant<Types...>&&);
+
+  template <size_t I, class... Types>
+  constexpr variant_alternative_t<I, variant<Types...>> const&
+  get(const variant<Types...>&);
+
+  template <size_t I, class... Types>
+  constexpr variant_alternative_t<I, variant<Types...>> const&&
+  get(const variant<Types...>&&);
+
+  template <class T, class...  Types>
+  constexpr T& get(variant<Types...>&);
+
+  template <class T, class... Types>
+  constexpr T&& get(variant<Types...>&&);
+
+  template <class T, class... Types>
+  constexpr const T& get(const variant<Types...>&);
+
+  template <class T, class... Types>
+  constexpr const T&& get(const variant<Types...>&&);
+
+  template <size_t I, class... Types>
+  constexpr add_pointer_t<variant_alternative_t<I, variant<Types...>>>
+  get_if(variant<Types...>*) noexcept;
+
+  template <size_t I, class... Types>
+  constexpr add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
+  get_if(const variant<Types...>*) noexcept;
+
+  template <class T, class... Types>
+  constexpr add_pointer_t<T>
+  get_if(variant<Types...>*) noexcept;
+
+  template <class T, class... Types>
+  constexpr add_pointer_t<const T>
+  get_if(const variant<Types...>*) noexcept;
+
+  // 20.7.5, relational operators
+  template <class... Types>
+  constexpr bool operator==(const variant<Types...>&, const variant<Types...>&);
+
+  template <class... Types>
+  constexpr bool operator!=(const variant<Types...>&, const variant<Types...>&);
+
+  template <class... Types>
+  constexpr bool operator<(const variant<Types...>&, const variant<Types...>&);
+
+  template <class... Types>
+  constexpr bool operator>(const variant<Types...>&, const variant<Types...>&);
+
+  template <class... Types>
+  constexpr bool operator<=(const variant<Types...>&, const variant<Types...>&);
+
+  template <class... Types>
+  constexpr bool operator>=(const variant<Types...>&, const variant<Types...>&);
+
+  // 20.7.6, visitation
+  template <class Visitor, class... Variants>
+  constexpr see below visit(Visitor&&, Variants&&...);
+
+  // 20.7.7, class monostate
+  struct monostate;
+
+  // 20.7.8, monostate relational operators
+  constexpr bool operator<(monostate, monostate) noexcept;
+  constexpr bool operator>(monostate, monostate) noexcept;
+  constexpr bool operator<=(monostate, monostate) noexcept;
+  constexpr bool operator>=(monostate, monostate) noexcept;
+  constexpr bool operator==(monostate, monostate) noexcept;
+  constexpr bool operator!=(monostate, monostate) noexcept;
+
+  // 20.7.9, specialized algorithms
+  template <class... Types>
+  void swap(variant<Types...>&, variant<Types...>&) noexcept(see below);
+
+  // 20.7.10, class bad_variant_access
+  class bad_variant_access;
+
+  // 20.7.11, hash support
+  template <class T> struct hash;
+  template <class... Types> struct hash<variant<Types...>>;
+  template <> struct hash<monostate>;
+
+} // namespace std
+
+*/
+
+#include <__config>
+#include <__tuple>
+#include <array>
+#include <exception>
+#include <functional>
+#include <initializer_list>
+#include <new>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+namespace std { // explicitly not using versioning namespace
+
+class _LIBCPP_EXCEPTION_ABI bad_variant_access : public exception {
+public:
+  _LIBCPP_FUNC_VIS virtual const char* what() const noexcept;
+};
+
+} // namespace std
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 14
+
+template <class... _Types>
+class _LIBCPP_TYPE_VIS_ONLY variant;
+
+template <class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_size;
+
+template <class _Tp>
+constexpr size_t variant_size_v = variant_size<_Tp>::value;
+
+template <class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_size<const _Tp> : variant_size<_Tp> {};
+
+template <class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_size<volatile _Tp> : variant_size<_Tp> {};
+
+template <class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_size<const volatile _Tp>
+    : variant_size<_Tp> {};
+
+template <class... _Types>
+struct _LIBCPP_TYPE_VIS_ONLY variant_size<variant<_Types...>>
+    : integral_constant<size_t, sizeof...(_Types)> {};
+
+template <size_t _Ip, class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_alternative;
+
+template <size_t _Ip, class _Tp>
+using variant_alternative_t = typename variant_alternative<_Ip, _Tp>::type;
+
+template <size_t _Ip, class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_alternative<_Ip, const _Tp>
+    : add_const<variant_alternative_t<_Ip, _Tp>> {};
+
+template <size_t _Ip, class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_alternative<_Ip, volatile _Tp>
+    : add_volatile<variant_alternative_t<_Ip, _Tp>> {};
+
+template <size_t _Ip, class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY variant_alternative<_Ip, const volatile _Tp>
+    : add_cv<variant_alternative_t<_Ip, _Tp>> {};
+
+template <size_t _Ip, class... _Types>
+struct _LIBCPP_TYPE_VIS_ONLY variant_alternative<_Ip, variant<_Types...>> {
+  static_assert(_Ip < sizeof...(_Types));
+  using type = __type_pack_element<_Ip, _Types...>;
+};
+
+constexpr size_t variant_npos = static_cast<size_t>(-1);
+constexpr unsigned int __variant_npos = static_cast<unsigned int>(-1);
+
+namespace __find_detail {
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr size_t __find_index() {
+  constexpr bool __matches[] = {is_same_v<_Tp, _Types>...};
+  size_t __result = __not_found;
+  for (size_t __i = 0; __i < sizeof...(_Types); ++__i) {
+    if (__matches[__i]) {
+      if (__result != __not_found) {
+        return __ambiguous;
+      }
+      __result = __i;
+    }
+  }
+  return __result;
+}
+
+template <size_t _Index>
+struct __find_unambiguous_index_sfinae_impl
+    : integral_constant<size_t, _Index> {};
+
+template <>
+struct __find_unambiguous_index_sfinae_impl<__not_found> {};
+
+template <>
+struct __find_unambiguous_index_sfinae_impl<__ambiguous> {};
+
+template <class _Tp, class... _Types>
+struct __find_unambiguous_index_sfinae
+    : __find_unambiguous_index_sfinae_impl<__find_index<_Tp, _Types...>()> {};
+
+} // namespace __find_detail
+
+namespace __variant_detail {
+
+struct __valueless_t {};
+
+enum class _Trait { _TriviallyAvailable, _Available, _Unavailable };
+
+template <typename _Tp,
+          template <typename> class _IsTriviallyAvailable,
+          template <typename> class _IsAvailable>
+constexpr _Trait __trait =
+    _IsTriviallyAvailable<_Tp>::value
+        ? _Trait::_TriviallyAvailable
+        : _IsAvailable<_Tp>::value ? _Trait::_Available : _Trait::_Unavailable;
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr _Trait __common_trait(initializer_list<_Trait> __traits) {
+  _Trait __result = _Trait::_TriviallyAvailable;
+  for (_Trait __t : __traits) {
+    if (static_cast<int>(__t) > static_cast<int>(__result)) {
+      __result = __t;
+    }
+  }
+  return __result;
+}
+
+template <typename... _Types>
+struct __traits {
+  static constexpr _Trait __copy_constructible_trait =
+      __common_trait({__trait<_Types,
+                              is_trivially_copy_constructible,
+                              is_copy_constructible>...});
+
+  static constexpr _Trait __move_constructible_trait =
+      __common_trait({__trait<_Types,
+                              is_trivially_move_constructible,
+                              is_move_constructible>...});
+
+  static constexpr _Trait __copy_assignable_trait = __common_trait(
+      {__copy_constructible_trait,
+       __move_constructible_trait,
+       __trait<_Types, is_trivially_copy_assignable, is_copy_assignable>...});
+
+  static constexpr _Trait __move_assignable_trait = __common_trait(
+      {__move_constructible_trait,
+       __trait<_Types, is_trivially_move_assignable, is_move_assignable>...});
+
+  static constexpr _Trait __destructible_trait = __common_trait(
+      {__trait<_Types, is_trivially_destructible, is_destructible>...});
+};
+
+namespace __access {
+
+struct __union {
+  template <class _Vp>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<0>) {
+    return _VSTD::forward<_Vp>(__v).__head;
+  }
+
+  template <class _Vp, size_t _Ip>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto&& __get_alt(_Vp&& __v, in_place_index_t<_Ip>) {
+    return __get_alt(_VSTD::forward<_Vp>(__v).__tail, in_place_index<_Ip - 1>);
+  }
+};
+
+struct __base {
+  template <size_t _Ip, class _Vp>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto&& __get_alt(_Vp&& __v) {
+    return __union::__get_alt(_VSTD::forward<_Vp>(__v).__data,
+                              in_place_index<_Ip>);
+  }
+};
+
+struct __variant {
+  template <size_t _Ip, class _Vp>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto&& __get_alt(_Vp&& __v) {
+    return __base::__get_alt<_Ip>(_VSTD::forward<_Vp>(__v).__impl);
+  }
+};
+
+} // namespace __access
+
+namespace __visitation {
+
+struct __base {
+  template <class _Visitor, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr decltype(auto)
+  __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
+    constexpr auto __fdiagonal =
+        __make_fdiagonal<_Visitor&&,
+                         decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
+    return __fdiagonal[__index](_VSTD::forward<_Visitor>(__visitor),
+                                _VSTD::forward<_Vs>(__vs).__as_base()...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor,
+                                              _Vs&&... __vs) {
+    constexpr auto __fmatrix =
+        __make_fmatrix<_Visitor&&,
+                       decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
+    const size_t __indices[] = {__vs.index()...};
+    return __at(__fmatrix, __indices)(_VSTD::forward<_Visitor>(__visitor),
+                                      _VSTD::forward<_Vs>(__vs).__as_base()...);
+  }
+
+private:
+  template <class _Tp>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr const _Tp& __at_impl(const _Tp& __elem, const size_t*) {
+    return __elem;
+  }
+
+  template <class _Tp, size_t _Np>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto&& __at_impl(const array<_Tp, _Np>& __elems,
+                                    const size_t* __index) {
+    return __at_impl(__elems[*__index], __index + 1);
+  }
+
+  template <class _Tp, size_t _Np, size_t _Ip>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto&& __at(const array<_Tp, _Np>& __elems,
+                               const size_t (&__indices)[_Ip]) {
+    return __at_impl(__elems, begin(__indices));
+  }
+
+  template <class _Fp, class... _Fs>
+  static constexpr void __std_visit_visitor_return_type_check() {
+    static_assert(
+        __all<is_same_v<_Fp, _Fs>...>::value,
+        "`std::visit` requires the visitor to have a single return type.");
+  }
+
+  template <class... _Fs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_farray(_Fs&&... __fs) {
+    __std_visit_visitor_return_type_check<decay_t<_Fs>...>();
+    using __result = array<common_type_t<decay_t<_Fs>...>, sizeof...(_Fs)>;
+    return __result{_VSTD::forward<_Fs>(__fs)...};
+  }
+
+  template <class _Fp, class... _Vs, size_t... _Is>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_dispatch(index_sequence<_Is...>) {
+    struct __dispatcher {
+      static constexpr decltype(auto) __dispatch(_Fp __f, _Vs... __vs) {
+        return __invoke_constexpr(
+            static_cast<_Fp>(__f),
+            __access::__base::__get_alt<_Is>(static_cast<_Vs>(__vs))...);
+      }
+    };
+    return _VSTD::addressof(__dispatcher::__dispatch);
+  }
+
+  template <size_t _Ip, class _Fp, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_fdiagonal_impl() {
+    return __make_dispatch<_Fp, _Vs...>(
+        index_sequence<(__identity<_Vs>{}, _Ip)...>{});
+  }
+
+  template <class _Fp, class... _Vs, size_t... _Is>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_fdiagonal_impl(index_sequence<_Is...>) {
+    return __base::__make_farray(__make_fdiagonal_impl<_Is, _Fp, _Vs...>()...);
+  }
+
+  template <class _Fp, class _Vp, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_fdiagonal() {
+    constexpr size_t _Np = decay_t<_Vp>::__size();
+    static_assert(__all<(_Np == decay_t<_Vs>::__size())...>::value);
+    return __make_fdiagonal_impl<_Fp, _Vp, _Vs...>(make_index_sequence<_Np>{});
+  }
+
+  template <class _Fp, class... _Vs, size_t... _Is>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_fmatrix_impl(index_sequence<_Is...> __is) {
+    return __make_dispatch<_Fp, _Vs...>(__is);
+  }
+
+  template <class _Fp, class... _Vs, size_t... _Is, size_t... _Js, class... _Ls>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_fmatrix_impl(index_sequence<_Is...>,
+                                            index_sequence<_Js...>,
+                                            _Ls... __ls) {
+    return __base::__make_farray(__make_fmatrix_impl<_Fp, _Vs...>(
+        index_sequence<_Is..., _Js>{}, __ls...)...);
+  }
+
+  template <class _Fp, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_fmatrix() {
+    return __make_fmatrix_impl<_Fp, _Vs...>(
+        index_sequence<>{}, make_index_sequence<decay_t<_Vs>::__size()>{}...);
+  }
+};
+
+struct __variant {
+  template <class _Visitor, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr decltype(auto)
+  __visit_alt_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
+    return __base::__visit_alt_at(__index,
+                                  _VSTD::forward<_Visitor>(__visitor),
+                                  _VSTD::forward<_Vs>(__vs).__impl...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr decltype(auto) __visit_alt(_Visitor&& __visitor,
+                                              _Vs&&... __vs) {
+    return __base::__visit_alt(_VSTD::forward<_Visitor>(__visitor),
+                               _VSTD::forward<_Vs>(__vs).__impl...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr decltype(auto)
+  __visit_value_at(size_t __index, _Visitor&& __visitor, _Vs&&... __vs) {
+    return __visit_alt_at(
+        __index,
+        __make_value_visitor(_VSTD::forward<_Visitor>(__visitor)),
+        _VSTD::forward<_Vs>(__vs)...);
+  }
+
+  template <class _Visitor, class... _Vs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr decltype(auto) __visit_value(_Visitor&& __visitor,
+                                                _Vs&&... __vs) {
+    return __visit_alt(
+        __make_value_visitor(_VSTD::forward<_Visitor>(__visitor)),
+        _VSTD::forward<_Vs>(__vs)...);
+  }
+
+private:
+  template <class _Visitor, class... _Values>
+  static constexpr void __std_visit_exhaustive_visitor_check() {
+    static_assert(is_callable_v<_Visitor(_Values...)>,
+                  "`std::visit` requires the visitor to be exhaustive.");
+  }
+
+  template <class _Visitor>
+  struct __value_visitor {
+    template <class... _Alts>
+    inline _LIBCPP_INLINE_VISIBILITY
+    constexpr decltype(auto) operator()(_Alts&&... __alts) const {
+      __std_visit_exhaustive_visitor_check<
+          _Visitor,
+          decltype(_VSTD::forward<_Alts>(__alts).__value)...>();
+      return __invoke_constexpr(_VSTD::forward<_Visitor>(__visitor),
+                                _VSTD::forward<_Alts>(__alts).__value...);
+    }
+    _Visitor&& __visitor;
+  };
+
+  template <class _Visitor>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr auto __make_value_visitor(_Visitor&& __visitor) {
+    return __value_visitor<_Visitor>{_VSTD::forward<_Visitor>(__visitor)};
+  }
+};
+
+} // namespace __visitation
+
+template <size_t _Index, class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY __alt {
+  using __value_type = _Tp;
+
+  template <class... _Args>
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr __alt(in_place_t, _Args&&... __args)
+      : __value(_VSTD::forward<_Args>(__args)...) {}
+
+  __value_type __value;
+};
+
+template <_Trait _DestructibleTrait, size_t _Index, class... _Types>
+union _LIBCPP_TYPE_VIS_ONLY __union;
+
+template <_Trait _DestructibleTrait, size_t _Index>
+union _LIBCPP_TYPE_VIS_ONLY __union<_DestructibleTrait, _Index> {};
+
+#define _LIBCPP_VARIANT_UNION(destructible_trait, destructor)                  \
+  template <size_t _Index, class _Tp, class... _Types>                         \
+  union _LIBCPP_TYPE_VIS_ONLY __union<destructible_trait,                      \
+                                      _Index,                                  \
+                                      _Tp,                                     \
+                                      _Types...> {                             \
+  public:                                                                      \
+    inline _LIBCPP_INLINE_VISIBILITY                                           \
+    explicit constexpr __union(__valueless_t) noexcept : __dummy{} {}          \
+                                                                               \
+    template <class... _Args>                                                  \
+    inline _LIBCPP_INLINE_VISIBILITY                                           \
+    explicit constexpr __union(in_place_index_t<0>, _Args&&... __args)         \
+        : __head(in_place, _VSTD::forward<_Args>(__args)...) {}                \
+                                                                               \
+    template <size_t _Ip, class... _Args>                                      \
+    inline _LIBCPP_INLINE_VISIBILITY                                           \
+    explicit constexpr __union(in_place_index_t<_Ip>, _Args&&... __args)       \
+        : __tail(in_place_index<_Ip - 1>, _VSTD::forward<_Args>(__args)...) {} \
+                                                                               \
+    __union(const __union&) = default;                                         \
+    __union(__union&&) = default;                                              \
+                                                                               \
+    destructor                                                                 \
+                                                                               \
+    __union& operator=(const __union&) = default;                              \
+    __union& operator=(__union&&) = default;                                   \
+                                                                               \
+  private:                                                                     \
+    char __dummy;                                                              \
+    __alt<_Index, _Tp> __head;                                                 \
+    __union<destructible_trait, _Index + 1, _Types...> __tail;                 \
+                                                                               \
+    friend struct __access::__union;                                           \
+  }
+
+_LIBCPP_VARIANT_UNION(_Trait::_TriviallyAvailable, ~__union() = default;);
+_LIBCPP_VARIANT_UNION(_Trait::_Available, ~__union() {});
+_LIBCPP_VARIANT_UNION(_Trait::_Unavailable, ~__union() = delete;);
+
+#undef _LIBCPP_VARIANT_UNION
+
+template <_Trait _DestructibleTrait, class... _Types>
+class _LIBCPP_TYPE_VIS_ONLY __base {
+public:
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr __base(__valueless_t tag) noexcept
+      : __index(__variant_npos), __data(tag) {}
+
+  template <size_t _Ip, class... _Args>
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr __base(in_place_index_t<_Ip>, _Args&&... __args)
+      : __index(_Ip),
+        __data(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr bool valueless_by_exception() const noexcept {
+    return index() == variant_npos;
+  }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr size_t index() const noexcept {
+    return __index == __variant_npos ? variant_npos : __index;
+  }
+
+protected:
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr auto&& __as_base() & { return *this; }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr auto&& __as_base() && { return _VSTD::move(*this); }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr auto&& __as_base() const & { return *this; }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr auto&& __as_base() const && { return _VSTD::move(*this); }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  static constexpr size_t __size() { return sizeof...(_Types); }
+
+  __union<_DestructibleTrait, 0, _Types...> __data;
+  unsigned int __index;
+
+  friend struct __access::__base;
+  friend struct __visitation::__base;
+};
+
+template <class _Traits, _Trait = _Traits::__destructible_trait>
+class _LIBCPP_TYPE_VIS_ONLY __destructor;
+
+#define _LIBCPP_VARIANT_DESTRUCTOR(destructible_trait, destructor, destroy)    \
+  template <class... _Types>                                                   \
+  class _LIBCPP_TYPE_VIS_ONLY __destructor<__traits<_Types...>,                \
+                                           destructible_trait>                 \
+      : public __base<destructible_trait, _Types...> {                         \
+    using __base_type = __base<destructible_trait, _Types...>;                 \
+                                                                               \
+  public:                                                                      \
+    using __base_type::__base_type;                                            \
+    using __base_type::operator=;                                              \
+                                                                               \
+    __destructor(const __destructor&) = default;                               \
+    __destructor(__destructor&&) = default;                                    \
+    destructor                                                                 \
+    __destructor& operator=(const __destructor&) = default;                    \
+    __destructor& operator=(__destructor&&) = default;                         \
+                                                                               \
+  protected:                                                                   \
+    inline _LIBCPP_INLINE_VISIBILITY                                           \
+    destroy                                                                    \
+  }
+
+_LIBCPP_VARIANT_DESTRUCTOR(
+    _Trait::_TriviallyAvailable,
+    ~__destructor() = default;,
+    void __destroy() noexcept { this->__index = __variant_npos; });
+
+_LIBCPP_VARIANT_DESTRUCTOR(
+    _Trait::_Available,
+    ~__destructor() { __destroy(); },
+    void __destroy() noexcept {
+      if (!this->valueless_by_exception()) {
+        __visitation::__base::__visit_alt(
+            [](auto& __alt) noexcept {
+              using __alt_type = decay_t<decltype(__alt)>;
+              __alt.~__alt_type();
+            },
+            *this);
+      }
+      this->__index = __variant_npos;
+    });
+
+_LIBCPP_VARIANT_DESTRUCTOR(
+    _Trait::_Unavailable,
+    ~__destructor() = delete;,
+    void __destroy() noexcept = delete;);
+
+#undef _LIBCPP_VARIANT_DESTRUCTOR
+
+template <class _Traits>
+class _LIBCPP_TYPE_VIS_ONLY __constructor : public __destructor<_Traits> {
+  using __base_type = __destructor<_Traits>;
+
+public:
+  using __base_type::__base_type;
+  using __base_type::operator=;
+
+protected:
+  template <size_t _Ip, class _Tp, class... _Args>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static void __construct_alt(__alt<_Ip, _Tp>& __a, _Args&&... __args) {
+    ::new (_VSTD::addressof(__a))
+        __alt<_Ip, _Tp>(in_place, _VSTD::forward<_Args>(__args)...);
+  }
+
+  template <class _Rhs>
+  inline _LIBCPP_INLINE_VISIBILITY
+  static void __generic_construct(__constructor& __lhs, _Rhs&& __rhs) {
+    __lhs.__destroy();
+    if (!__rhs.valueless_by_exception()) {
+      __visitation::__base::__visit_alt_at(
+          __rhs.index(),
+          [](auto& __lhs_alt, auto&& __rhs_alt) {
+            __construct_alt(
+                __lhs_alt,
+                _VSTD::forward<decltype(__rhs_alt)>(__rhs_alt).__value);
+          },
+          __lhs, _VSTD::forward<_Rhs>(__rhs));
+      __lhs.__index = __rhs.index();
+    }
+  }
+};
+
+template <class _Traits, _Trait = _Traits::__move_constructible_trait>
+class _LIBCPP_TYPE_VIS_ONLY __move_constructor;
+
+#define _LIBCPP_VARIANT_MOVE_CONSTRUCTOR(move_constructible_trait,             \
+                                         move_constructor)                     \
+  template <class... _Types>                                                   \
+  class _LIBCPP_TYPE_VIS_ONLY __move_constructor<__traits<_Types...>,          \
+                                                 move_constructible_trait>     \
+      : public __constructor<__traits<_Types...>> {                            \
+    using __base_type = __constructor<__traits<_Types...>>;                    \
+                                                                               \
+  public:                                                                      \
+    using __base_type::__base_type;                                            \
+    using __base_type::operator=;                                              \
+                                                                               \
+    __move_constructor(const __move_constructor&) = default;                   \
+    move_constructor                                                           \
+    ~__move_constructor() = default;                                           \
+    __move_constructor& operator=(const __move_constructor&) = default;        \
+    __move_constructor& operator=(__move_constructor&&) = default;             \
+  }
+
+_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
+    _Trait::_TriviallyAvailable,
+    __move_constructor(__move_constructor&& __that) = default;);
+
+_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
+    _Trait::_Available,
+    __move_constructor(__move_constructor&& __that) noexcept(
+        __all<is_nothrow_move_constructible_v<_Types>...>::value)
+        : __move_constructor(__valueless_t{}) {
+      this->__generic_construct(*this, _VSTD::move(__that));
+    });
+
+_LIBCPP_VARIANT_MOVE_CONSTRUCTOR(
+    _Trait::_Unavailable,
+    __move_constructor(__move_constructor&&) = delete;);
+
+#undef _LIBCPP_VARIANT_MOVE_CONSTRUCTOR
+
+template <class _Traits, _Trait = _Traits::__copy_constructible_trait>
+class _LIBCPP_TYPE_VIS_ONLY __copy_constructor;
+
+#define _LIBCPP_VARIANT_COPY_CONSTRUCTOR(copy_constructible_trait,             \
+                                         copy_constructor)                     \
+  template <class... _Types>                                                   \
+  class _LIBCPP_TYPE_VIS_ONLY __copy_constructor<__traits<_Types...>,          \
+                                                 copy_constructible_trait>     \
+      : public __move_constructor<__traits<_Types...>> {                       \
+    using __base_type = __move_constructor<__traits<_Types...>>;               \
+                                                                               \
+  public:                                                                      \
+    using __base_type::__base_type;                                            \
+    using __base_type::operator=;                                              \
+                                                                               \
+    copy_constructor                                                           \
+    __copy_constructor(__copy_constructor&&) = default;                        \
+    ~__copy_constructor() = default;                                           \
+    __copy_constructor& operator=(const __copy_constructor&) = default;        \
+    __copy_constructor& operator=(__copy_constructor&&) = default;             \
+  }
+
+_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
+    _Trait::_TriviallyAvailable,
+    __copy_constructor(const __copy_constructor& __that) = default;);
+
+_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
+    _Trait::_Available,
+    __copy_constructor(const __copy_constructor& __that)
+        : __copy_constructor(__valueless_t{}) {
+      this->__generic_construct(*this, __that);
+    });
+
+_LIBCPP_VARIANT_COPY_CONSTRUCTOR(
+    _Trait::_Unavailable,
+    __copy_constructor(const __copy_constructor&) = delete;);
+
+#undef _LIBCPP_VARIANT_COPY_CONSTRUCTOR
+
+template <class _Traits>
+class _LIBCPP_TYPE_VIS_ONLY __assignment : public __copy_constructor<_Traits> {
+  using __base_type = __copy_constructor<_Traits>;
+
+public:
+  using __base_type::__base_type;
+  using __base_type::operator=;
+
+  template <size_t _Ip, class... _Args>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void __emplace(_Args&&... __args) {
+    this->__destroy();
+    this->__construct_alt(__access::__base::__get_alt<_Ip>(*this),
+                          _VSTD::forward<_Args>(__args)...);
+    this->__index = _Ip;
+  }
+
+protected:
+  template <bool _CopyAssign, size_t _Ip, class _Tp, class _Arg>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void __assign_alt(__alt<_Ip, _Tp>& __a,
+                    _Arg&& __arg,
+                    bool_constant<_CopyAssign> __tag) {
+    if (this->index() == _Ip) {
+      __a.__value = _VSTD::forward<_Arg>(__arg);
+    } else {
+      struct {
+        void operator()(true_type) const {
+          __this->__emplace<_Ip>(_Tp(_VSTD::forward<_Arg>(__arg)));
+        }
+        void operator()(false_type) const {
+          __this->__emplace<_Ip>(_VSTD::forward<_Arg>(__arg));
+        }
+        __assignment* __this;
+        _Arg&& __arg;
+      } __impl{this, _VSTD::forward<_Arg>(__arg)};
+      __impl(__tag);
+    }
+  }
+
+  template <class _That>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void __generic_assign(_That&& __that) {
+    if (this->valueless_by_exception() && __that.valueless_by_exception()) {
+      // do nothing.
+    } else if (__that.valueless_by_exception()) {
+      this->__destroy();
+    } else {
+      __visitation::__base::__visit_alt_at(
+          __that.index(),
+          [this](auto& __this_alt, auto&& __that_alt) {
+            this->__assign_alt(
+                __this_alt,
+                _VSTD::forward<decltype(__that_alt)>(__that_alt).__value,
+                is_lvalue_reference<_That>{});
+          },
+          *this, _VSTD::forward<_That>(__that));
+    }
+  }
+};
+
+template <class _Traits, _Trait = _Traits::__move_assignable_trait>
+class _LIBCPP_TYPE_VIS_ONLY __move_assignment;
+
+#define _LIBCPP_VARIANT_MOVE_ASSIGNMENT(move_assignable_trait,                 \
+                                        move_assignment)                       \
+  template <class... _Types>                                                   \
+  class _LIBCPP_TYPE_VIS_ONLY __move_assignment<__traits<_Types...>,           \
+                                                move_assignable_trait>         \
+      : public __assignment<__traits<_Types...>> {                             \
+    using __base_type = __assignment<__traits<_Types...>>;                     \
+                                                                               \
+  public:                                                                      \
+    using __base_type::__base_type;                                            \
+    using __base_type::operator=;                                              \
+                                                                               \
+    __move_assignment(const __move_assignment&) = default;                     \
+    __move_assignment(__move_assignment&&) = default;                          \
+    ~__move_assignment() = default;                                            \
+    __move_assignment& operator=(const __move_assignment&) = default;          \
+    move_assignment                                                            \
+  }
+
+_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
+    _Trait::_TriviallyAvailable,
+    __move_assignment& operator=(__move_assignment&& __that) = default;);
+
+_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
+    _Trait::_Available,
+    __move_assignment& operator=(__move_assignment&& __that) noexcept(
+        __all<(is_nothrow_move_constructible_v<_Types> &&
+               is_nothrow_move_assignable_v<_Types>)...>::value) {
+      this->__generic_assign(_VSTD::move(__that));
+      return *this;
+    });
+
+_LIBCPP_VARIANT_MOVE_ASSIGNMENT(
+    _Trait::_Unavailable,
+    __move_assignment& operator=(__move_assignment&&) = delete;);
+
+#undef _LIBCPP_VARIANT_MOVE_ASSIGNMENT
+
+template <class _Traits, _Trait = _Traits::__copy_assignable_trait>
+class _LIBCPP_TYPE_VIS_ONLY __copy_assignment;
+
+#define _LIBCPP_VARIANT_COPY_ASSIGNMENT(copy_assignable_trait,                 \
+                                        copy_assignment)                       \
+  template <class... _Types>                                                   \
+  class _LIBCPP_TYPE_VIS_ONLY __copy_assignment<__traits<_Types...>,           \
+                                                copy_assignable_trait>         \
+      : public __move_assignment<__traits<_Types...>> {                        \
+    using __base_type = __move_assignment<__traits<_Types...>>;                \
+                                                                               \
+  public:                                                                      \
+    using __base_type::__base_type;                                            \
+    using __base_type::operator=;                                              \
+                                                                               \
+    __copy_assignment(const __copy_assignment&) = default;                     \
+    __copy_assignment(__copy_assignment&&) = default;                          \
+    ~__copy_assignment() = default;                                            \
+    copy_assignment                                                            \
+    __copy_assignment& operator=(__copy_assignment&&) = default;               \
+  }
+
+_LIBCPP_VARIANT_COPY_ASSIGNMENT(
+    _Trait::_TriviallyAvailable,
+    __copy_assignment& operator=(const __copy_assignment& __that) = default;);
+
+_LIBCPP_VARIANT_COPY_ASSIGNMENT(
+    _Trait::_Available,
+    __copy_assignment& operator=(const __copy_assignment& __that) {
+      this->__generic_assign(__that);
+      return *this;
+    });
+
+_LIBCPP_VARIANT_COPY_ASSIGNMENT(
+    _Trait::_Unavailable,
+    __copy_assignment& operator=(const __copy_assignment&) = delete;);
+
+#undef _LIBCPP_VARIANT_COPY_ASSIGNMENT
+
+template <class... _Types>
+class _LIBCPP_TYPE_VIS_ONLY __impl
+    : public __copy_assignment<__traits<_Types...>> {
+  using __base_type = __copy_assignment<__traits<_Types...>>;
+
+public:
+  using __base_type::__base_type;
+  using __base_type::operator=;
+
+  template <size_t _Ip, class _Arg>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void __assign(_Arg&& __arg) {
+    this->__assign_alt(__access::__base::__get_alt<_Ip>(*this),
+                       _VSTD::forward<_Arg>(__arg),
+                       false_type{});
+  }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  void __swap(__impl& __that)  {
+    if (this->valueless_by_exception() && __that.valueless_by_exception()) {
+      // do nothing.
+    } else if (this->index() == __that.index()) {
+      __visitation::__base::__visit_alt_at(
+          this->index(),
+          [](auto& __this_alt, auto& __that_alt) {
+            using _VSTD::swap;
+            swap(__this_alt.__value, __that_alt.__value);
+          },
+          *this,
+          __that);
+    } else {
+      __impl* __lhs = this;
+      __impl* __rhs = _VSTD::addressof(__that);
+      if (__lhs->__move_nothrow() && !__rhs->__move_nothrow()) {
+        _VSTD::swap(__lhs, __rhs);
+      }
+      __impl __tmp(_VSTD::move(*__rhs));
+#ifndef _LIBCPP_NO_EXCEPTIONS
+      // 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 guarentee.
+      try {
+        this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
+      } catch (...) {
+        if (__tmp.__move_nothrow()) {
+          this->__generic_construct(*__rhs, _VSTD::move(__tmp));
+        }
+        throw;
+      }
+#else
+      this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
+#endif
+      this->__generic_construct(*__lhs, _VSTD::move(__tmp));
+    }
+  }
+
+private:
+  inline _LIBCPP_INLINE_VISIBILITY
+  bool __move_nothrow() const {
+    constexpr bool __results[] = {is_nothrow_move_constructible_v<_Types>...};
+    return this->valueless_by_exception() || __results[this->index()];
+  }
+};
+
+template <class... _Types>
+struct __overload;
+
+template <>
+struct __overload<> { void operator()() const; };
+
+template <class _Tp, class... _Types>
+struct __overload<_Tp, _Types...> : __overload<_Types...> {
+  using __overload<_Types...>::operator();
+  __identity<_Tp> operator()(_Tp) const;
+};
+
+template <class _Tp, class... _Types>
+using __best_match_t = typename result_of_t<__overload<_Types...>(_Tp&&)>::type;
+
+} // __variant_detail
+
+template <class... _Types>
+class _LIBCPP_TYPE_VIS_ONLY 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_move_constructible_v<_Types> &&
+                 is_copy_assignable_v<_Types>)...>::value,
+          __all<(is_move_constructible_v<_Types> &&
+                 is_move_assignable_v<_Types>)...>::value> {
+  static_assert(0 < sizeof...(_Types),
+                "variant must consist of at least one alternative.");
+
+  static_assert(__all<!is_array_v<_Types>...>::value,
+                "variant can not have an array type as an alternative.");
+
+  static_assert(__all<!is_reference_v<_Types>...>::value,
+                "variant can not have a reference type as an alternative.");
+
+  static_assert(__all<!is_void_v<_Types>...>::value,
+                "variant can not have a void type as an alternative.");
+
+  using __first_type = variant_alternative_t<0, variant>;
+
+public:
+  template <bool _Dummy = true,
+            enable_if_t<__dependent_type<is_default_constructible<__first_type>,
+                                         _Dummy>::value,
+                        int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr variant() noexcept(is_nothrow_default_constructible_v<__first_type>)
+      : __impl(in_place_index<0>) {}
+
+  variant(const variant&) = default;
+  variant(variant&&) = default;
+
+  template <
+      class _Arg,
+      enable_if_t<!is_same_v<decay_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_constructible_v<_Tp, _Arg>, int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr variant(_Arg&& __arg) noexcept(
+      is_nothrow_constructible_v<_Tp, _Arg>)
+      : __impl(in_place_index<_Ip>, _VSTD::forward<_Arg>(__arg)) {}
+
+  template <size_t _Ip, class... _Args,
+            enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
+            class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
+            enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr variant(
+      in_place_index_t<_Ip>,
+      _Args&&... __args) noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
+      : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}
+
+  template <
+      size_t _Ip,
+      class _Up,
+      class... _Args,
+      enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
+      class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
+      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
+                  int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr variant(
+      in_place_index_t<_Ip>,
+      initializer_list<_Up> __il,
+      _Args&&... __args) noexcept(
+      is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
+      : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}
+
+  template <
+      class _Tp,
+      class... _Args,
+      size_t _Ip =
+          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
+      enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr variant(in_place_type_t<_Tp>, _Args&&... __args) noexcept(
+      is_nothrow_constructible_v<_Tp, _Args...>)
+      : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}
+
+  template <
+      class _Tp,
+      class _Up,
+      class... _Args,
+      size_t _Ip =
+          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
+      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
+                  int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  explicit constexpr variant(
+      in_place_type_t<_Tp>,
+      initializer_list<_Up> __il,
+      _Args&&... __args) noexcept(
+      is_nothrow_constructible_v<_Tp, initializer_list< _Up>&, _Args...>)
+      : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}
+
+  ~variant() = default;
+
+  variant& operator=(const variant&) = default;
+  variant& operator=(variant&&) = default;
+
+  template <
+      class _Arg,
+      enable_if_t<!is_same_v<decay_t<_Arg>, variant>, int> = 0,
+      class _Tp = __variant_detail::__best_match_t<_Arg, _Types...>,
+      size_t _Ip =
+          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
+      enable_if_t<is_assignable_v<_Tp&, _Arg> && is_constructible_v<_Tp, _Arg>,
+                  int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  variant& operator=(_Arg&& __arg) noexcept(
+      is_nothrow_assignable_v<_Tp&, _Arg> &&
+      is_nothrow_constructible_v<_Tp, _Arg>) {
+    __impl.template __assign<_Ip>(_VSTD::forward<_Arg>(__arg));
+    return *this;
+  }
+
+  template <
+      size_t _Ip,
+      class... _Args,
+      enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
+      class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
+      enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void emplace(_Args&&... __args) {
+    __impl.template __emplace<_Ip>(_VSTD::forward<_Args>(__args)...);
+  }
+
+  template <
+      size_t _Ip,
+      class _Up,
+      class... _Args,
+      enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
+      class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
+      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
+                  int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void emplace(initializer_list<_Up> __il, _Args&&... __args) {
+    __impl.template __emplace<_Ip>(__il, _VSTD::forward<_Args>(__args)...);
+  }
+
+  template <
+      class _Tp,
+      class... _Args,
+      size_t _Ip =
+          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
+      enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void emplace(_Args&&... __args) {
+    __impl.template __emplace<_Ip>(_VSTD::forward<_Args>(__args)...);
+  }
+
+  template <
+      class _Tp,
+      class _Up,
+      class... _Args,
+      size_t _Ip =
+          __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,
+      enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
+                  int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void emplace(initializer_list<_Up> __il, _Args&&... __args) {
+    __impl.template __emplace<_Ip>(__il, _VSTD::forward<_Args>(__args)...);
+  }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr bool valueless_by_exception() const noexcept {
+    return __impl.valueless_by_exception();
+  }
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  constexpr size_t index() const noexcept { return __impl.index(); }
+
+  template <
+      bool _Dummy = true,
+      enable_if_t<
+          __all<(
+              __dependent_type<is_move_constructible<_Types>, _Dummy>::value &&
+              __dependent_type<is_swappable<_Types>, _Dummy>::value)...>::value,
+          int> = 0>
+  inline _LIBCPP_INLINE_VISIBILITY
+  void swap(variant& __that) noexcept(
+      __all<(is_nothrow_move_constructible_v<_Types> &&
+             is_nothrow_swappable_v<_Types>)...>::value) {
+    __impl.__swap(__that.__impl);
+  }
+
+private:
+  __variant_detail::__impl<_Types...> __impl;
+
+  friend struct __variant_detail::__access::__variant;
+  friend struct __variant_detail::__visitation::__variant;
+};
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool __holds_alternative(const variant<_Types...>& __v) noexcept {
+  return __v.index() == _Ip;
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool holds_alternative(const variant<_Types...>& __v) noexcept {
+  return __holds_alternative<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <size_t _Ip, class _Vp>
+inline _LIBCPP_INLINE_VISIBILITY
+static constexpr auto&& __generic_get(_Vp&& __v) {
+  using __variant_detail::__access::__variant;
+  if (!__holds_alternative<_Ip>(__v)) {
+    throw bad_variant_access{};
+  }
+  return __variant::__get_alt<_Ip>(_VSTD::forward<_Vp>(__v)).__value;
+}
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr variant_alternative_t<_Ip, variant<_Types...>>& get(
+    variant<_Types...>& __v) {
+  static_assert(_Ip < sizeof...(_Types));
+  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
+  return __generic_get<_Ip>(__v);
+}
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr variant_alternative_t<_Ip, variant<_Types...>>&& get(
+    variant<_Types...>&& __v) {
+  static_assert(_Ip < sizeof...(_Types));
+  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
+  return __generic_get<_Ip>(_VSTD::move(__v));
+}
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr const variant_alternative_t<_Ip, variant<_Types...>>& get(
+    const variant<_Types...>& __v) {
+  static_assert(_Ip < sizeof...(_Types));
+  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
+  return __generic_get<_Ip>(__v);
+}
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr const variant_alternative_t<_Ip, variant<_Types...>>&& get(
+    const variant<_Types...>&& __v) {
+  static_assert(_Ip < sizeof...(_Types));
+  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
+  return __generic_get<_Ip>(_VSTD::move(__v));
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr _Tp& get(variant<_Types...>& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr _Tp&& get(variant<_Types...>&& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(
+      _VSTD::move(__v));
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr const _Tp& get(const variant<_Types...>& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr const _Tp&& get(const variant<_Types...>&& __v) {
+  static_assert(!is_void_v<_Tp>);
+  return _VSTD::get<__find_exactly_one_t<_Tp, _Types...>::value>(
+      _VSTD::move(__v));
+}
+
+template <size_t _Ip, class _Vp>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr auto* __generic_get_if(_Vp* __v) noexcept {
+  using __variant_detail::__access::__variant;
+  return __v && __holds_alternative<_Ip>(*__v)
+             ? _VSTD::addressof(__variant::__get_alt<_Ip>(*__v).__value)
+             : nullptr;
+}
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr add_pointer_t<variant_alternative_t<_Ip, variant<_Types...>>>
+get_if(variant<_Types...>* __v) noexcept {
+  static_assert(_Ip < sizeof...(_Types));
+  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
+  return __generic_get_if<_Ip>(__v);
+}
+
+template <size_t _Ip, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr add_pointer_t<const variant_alternative_t<_Ip, variant<_Types...>>>
+get_if(const variant<_Types...>* __v) noexcept {
+  static_assert(_Ip < sizeof...(_Types));
+  static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
+  return __generic_get_if<_Ip>(__v);
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr add_pointer_t<_Tp>
+get_if(variant<_Types...>* __v) noexcept {
+  static_assert(!is_void_v<_Tp>);
+  return _VSTD::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class _Tp, class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr add_pointer_t<const _Tp>
+get_if(const variant<_Types...>* __v) noexcept {
+  static_assert(!is_void_v<_Tp>);
+  return _VSTD::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
+}
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator==(const variant<_Types...>& __lhs,
+                          const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  if (__lhs.index() != __rhs.index()) return false;
+  if (__lhs.valueless_by_exception()) return true;
+  return __variant::__visit_value_at(__lhs.index(), equal_to<>{}, __lhs, __rhs);
+}
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator!=(const variant<_Types...>& __lhs,
+                          const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  if (__lhs.index() != __rhs.index()) return true;
+  if (__lhs.valueless_by_exception()) return false;
+  return __variant::__visit_value_at(
+      __lhs.index(), not_equal_to<>{}, __lhs, __rhs);
+}
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator<(const variant<_Types...>& __lhs,
+                         const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  if (__rhs.valueless_by_exception()) return false;
+  if (__lhs.valueless_by_exception()) return true;
+  if (__lhs.index() < __rhs.index()) return true;
+  if (__lhs.index() > __rhs.index()) return false;
+  return __variant::__visit_value_at(__lhs.index(), less<>{}, __lhs, __rhs);
+}
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator>(const variant<_Types...>& __lhs,
+                         const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  if (__lhs.valueless_by_exception()) return false;
+  if (__rhs.valueless_by_exception()) return true;
+  if (__lhs.index() > __rhs.index()) return true;
+  if (__lhs.index() < __rhs.index()) return false;
+  return __variant::__visit_value_at(__lhs.index(), greater<>{}, __lhs, __rhs);
+}
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator<=(const variant<_Types...>& __lhs,
+                          const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  if (__lhs.valueless_by_exception()) return true;
+  if (__rhs.valueless_by_exception()) return false;
+  if (__lhs.index() < __rhs.index()) return true;
+  if (__lhs.index() > __rhs.index()) return false;
+  return __variant::__visit_value_at(
+      __lhs.index(), less_equal<>{}, __lhs, __rhs);
+}
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator>=(const variant<_Types...>& __lhs,
+                          const variant<_Types...>& __rhs) {
+  using __variant_detail::__visitation::__variant;
+  if (__rhs.valueless_by_exception()) return true;
+  if (__lhs.valueless_by_exception()) return false;
+  if (__lhs.index() > __rhs.index()) return true;
+  if (__lhs.index() < __rhs.index()) return false;
+  return __variant::__visit_value_at(
+      __lhs.index(), greater_equal<>{}, __lhs, __rhs);
+}
+
+template <class _Visitor, class... _Vs>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr decltype(auto) visit(_Visitor&& __visitor, _Vs&&... __vs) {
+  using __variant_detail::__visitation::__variant;
+  bool __results[] = {__vs.valueless_by_exception()...};
+  for (bool __result : __results) {
+    if (__result) {
+      throw bad_variant_access{};
+    }
+  }
+  return __variant::__visit_value(_VSTD::forward<_Visitor>(__visitor),
+                                  _VSTD::forward<_Vs>(__vs)...);
+}
+
+struct _LIBCPP_TYPE_VIS_ONLY monostate {};
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator<(monostate, monostate) noexcept { return false; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator>(monostate, monostate) noexcept { return false; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator<=(monostate, monostate) noexcept { return true; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator>=(monostate, monostate) noexcept { return true; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator==(monostate, monostate) noexcept { return true; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator!=(monostate, monostate) noexcept { return false; }
+
+template <class... _Types>
+inline _LIBCPP_INLINE_VISIBILITY
+auto swap(variant<_Types...>& __lhs,
+          variant<_Types...>& __rhs) noexcept(noexcept(__lhs.swap(__rhs)))
+    -> decltype(__lhs.swap(__rhs)) {
+  __lhs.swap(__rhs);
+}
+
+template <class... _Types>
+struct _LIBCPP_TYPE_VIS_ONLY hash<variant<_Types...>> {
+  using argument_type = variant<_Types...>;
+  using result_type = size_t;
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  result_type operator()(const argument_type& __v) const {
+    using __variant_detail::__visitation::__variant;
+    return __v.valueless_by_exception()
+               ? __v.index()
+               : __variant::__visit_alt(
+                     [](const auto& __alt) {
+                       using __alt_type = decay_t<decltype(__alt)>;
+                       using __value_type = typename __alt_type::__value_type;
+                       return hash<__value_type>{}(__alt.__value);
+                     },
+                     __v);
+  }
+};
+
+template <>
+struct _LIBCPP_TYPE_VIS_ONLY hash<monostate> {
+  using argument_type = monostate;
+  using result_type = size_t;
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  result_type operator()(const argument_type&) const { return 0; }
+};
+
+#endif  // _LIBCPP_STD_VER > 14
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif  // _LIBCPP_VARIANT

src/variant.cpp

@@ -0,0 +1,18 @@
+//===------------------------ variant.cpp ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "variant"
+
+namespace std {
+
+const char* bad_variant_access::what() const noexcept {
+  return "bad_variant_access";
+}
+
+}  // namespace std

test/libcxx/utilities/variant/variant.variant/variant.assign/copy.pass.cpp

@@ -0,0 +1,181 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// variant& operator=(variant const&);
+
+#include <type_traits>
+#include <variant>
+
+#include "test_macros.h"
+
+struct NTCopyAssign {
+  constexpr NTCopyAssign(int v) : value(v) {}
+  NTCopyAssign(const NTCopyAssign &) = default;
+  NTCopyAssign(NTCopyAssign &&) = default;
+  NTCopyAssign &operator=(const NTCopyAssign &that) {
+    value = that.value;
+    return *this;
+  };
+  NTCopyAssign &operator=(NTCopyAssign &&) = delete;
+  int value;
+};
+
+static_assert(!std::is_trivially_copy_assignable<NTCopyAssign>::value, "");
+static_assert(std::is_copy_assignable<NTCopyAssign>::value, "");
+
+struct TCopyAssign {
+  constexpr TCopyAssign(int v) : value(v) {}
+  TCopyAssign(const TCopyAssign &) = default;
+  TCopyAssign(TCopyAssign &&) = default;
+  TCopyAssign &operator=(const TCopyAssign &) = default;
+  TCopyAssign &operator=(TCopyAssign &&) = delete;
+  int value;
+};
+
+static_assert(std::is_trivially_copy_assignable<TCopyAssign>::value, "");
+
+struct TCopyAssignNTMoveAssign {
+  constexpr TCopyAssignNTMoveAssign(int v) : value(v) {}
+  TCopyAssignNTMoveAssign(const TCopyAssignNTMoveAssign &) = default;
+  TCopyAssignNTMoveAssign(TCopyAssignNTMoveAssign &&) = default;
+  TCopyAssignNTMoveAssign &operator=(const TCopyAssignNTMoveAssign &) = default;
+  TCopyAssignNTMoveAssign &operator=(TCopyAssignNTMoveAssign &&that) {
+    value = that.value;
+    that.value = -1;
+    return *this;
+  }
+  int value;
+};
+
+static_assert(std::is_trivially_copy_assignable_v<TCopyAssignNTMoveAssign>);
+
+void test_copy_assignment_sfinae() {
+  {
+    using V = std::variant<int, long>;
+    static_assert(std::is_trivially_copy_assignable<V>::value, "");
+  }
+  {
+    using V = std::variant<int, NTCopyAssign>;
+    static_assert(!std::is_trivially_copy_assignable<V>::value, "");
+    static_assert(std::is_copy_assignable<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TCopyAssign>;
+    static_assert(std::is_trivially_copy_assignable<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TCopyAssignNTMoveAssign>;
+    static_assert(std::is_trivially_copy_assignable<V>::value, "");
+  }
+}
+
+template <typename T> struct Result { size_t index; T value; };
+
+void test_copy_assignment_same_index() {
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        using V = std::variant<int>;
+        V v(43);
+        V v2(42);
+        v = v2;
+        return {v.index(), std::get<0>(v)};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 0);
+    static_assert(result.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<long> operator()() const {
+        using V = std::variant<int, long, unsigned>;
+        V v(43l);
+        V v2(42l);
+        v = v2;
+        return {v.index(), std::get<1>(v)};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42l);
+  }
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        using V = std::variant<int, TCopyAssign, unsigned>;
+        V v(std::in_place_type<TCopyAssign>, 43);
+        V v2(std::in_place_type<TCopyAssign>, 42);
+        v = v2;
+        return {v.index(), std::get<1>(v).value};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        using V = std::variant<int, TCopyAssignNTMoveAssign, unsigned>;
+        V v(std::in_place_type<TCopyAssignNTMoveAssign>, 43);
+        V v2(std::in_place_type<TCopyAssignNTMoveAssign>, 42);
+        v = v2;
+        return {v.index(), std::get<1>(v).value};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42);
+  }
+}
+
+void test_copy_assignment_different_index() {
+  {
+    struct {
+      constexpr Result<long> operator()() const {
+        using V = std::variant<int, long, unsigned>;
+        V v(43);
+        V v2(42l);
+        v = v2;
+        return {v.index(), std::get<1>(v)};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42l);
+  }
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        using V = std::variant<int, TCopyAssign, unsigned>;
+        V v(std::in_place_type<unsigned>, 43);
+        V v2(std::in_place_type<TCopyAssign>, 42);
+        v = v2;
+        return {v.index(), std::get<1>(v).value};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42);
+  }
+}
+
+int main() {
+  test_copy_assignment_same_index();
+  test_copy_assignment_different_index();
+  test_copy_assignment_sfinae();
+}

test/libcxx/utilities/variant/variant.variant/variant.assign/move.pass.cpp

@@ -0,0 +1,167 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// variant& operator=(variant&&) noexcept(see below);
+
+#include <type_traits>
+#include <variant>
+
+#include "test_macros.h"
+
+struct NTMoveAssign {
+  constexpr NTMoveAssign(int v) : value(v) {}
+  NTMoveAssign(const NTMoveAssign &) = default;
+  NTMoveAssign(NTMoveAssign &&) = default;
+  NTMoveAssign &operator=(const NTMoveAssign &that) = default;
+  NTMoveAssign &operator=(NTMoveAssign &&that) {
+    value = that.value;
+    that.value = -1;
+    return *this;
+  };
+  int value;
+};
+
+static_assert(!std::is_trivially_move_assignable<NTMoveAssign>::value, "");
+static_assert(std::is_move_assignable<NTMoveAssign>::value, "");
+
+struct TMoveAssign {
+  constexpr TMoveAssign(int v) : value(v) {}
+  TMoveAssign(const TMoveAssign &) = delete;
+  TMoveAssign(TMoveAssign &&) = default;
+  TMoveAssign &operator=(const TMoveAssign &) = delete;
+  TMoveAssign &operator=(TMoveAssign &&) = default;
+  int value;
+};
+
+static_assert(std::is_trivially_move_assignable<TMoveAssign>::value, "");
+
+struct TMoveAssignNTCopyAssign {
+  constexpr TMoveAssignNTCopyAssign(int v) : value(v) {}
+  TMoveAssignNTCopyAssign(const TMoveAssignNTCopyAssign &) = default;
+  TMoveAssignNTCopyAssign(TMoveAssignNTCopyAssign &&) = default;
+  TMoveAssignNTCopyAssign &operator=(const TMoveAssignNTCopyAssign &that) {
+    value = that.value;
+    return *this;
+  }
+  TMoveAssignNTCopyAssign &operator=(TMoveAssignNTCopyAssign &&) = default;
+  int value;
+};
+
+static_assert(std::is_trivially_move_assignable_v<TMoveAssignNTCopyAssign>);
+
+void test_move_assignment_sfinae() {
+  {
+    using V = std::variant<int, long>;
+    static_assert(std::is_trivially_move_assignable<V>::value, "");
+  }
+  {
+    using V = std::variant<int, NTMoveAssign>;
+    static_assert(!std::is_trivially_move_assignable<V>::value, "");
+    static_assert(std::is_move_assignable<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TMoveAssign>;
+    static_assert(std::is_trivially_move_assignable<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TMoveAssignNTCopyAssign>;
+    static_assert(std::is_trivially_move_assignable<V>::value, "");
+  }
+}
+
+template <typename T> struct Result { size_t index; T value; };
+
+void test_move_assignment_same_index() {
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        using V = std::variant<int>;
+        V v(43);
+        V v2(42);
+        v = std::move(v2);
+        return {v.index(), std::get<0>(v)};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 0);
+    static_assert(result.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<long> operator()() const {
+        using V = std::variant<int, long, unsigned>;
+        V v(43l);
+        V v2(42l);
+        v = std::move(v2);
+        return {v.index(), std::get<1>(v)};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42l);
+  }
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        using V = std::variant<int, TMoveAssign, unsigned>;
+        V v(std::in_place_type<TMoveAssign>, 43);
+        V v2(std::in_place_type<TMoveAssign>, 42);
+        v = std::move(v2);
+        return {v.index(), std::get<1>(v).value};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42);
+  }
+}
+
+void test_move_assignment_different_index() {
+  {
+    struct {
+      constexpr Result<long> operator()() const {
+        using V = std::variant<int, long, unsigned>;
+        V v(43);
+        V v2(42l);
+        v = std::move(v2);
+        return {v.index(), std::get<1>(v)};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42l);
+  }
+  {
+    struct {
+      constexpr Result<long> operator()() const {
+        using V = std::variant<int, TMoveAssign, unsigned>;
+        V v(std::in_place_type<unsigned>, 43);
+        V v2(std::in_place_type<TMoveAssign>, 42);
+        v = std::move(v2);
+        return {v.index(), std::get<1>(v).value};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42);
+  }
+}
+
+int main() {
+  test_move_assignment_same_index();
+  test_move_assignment_different_index();
+  test_move_assignment_sfinae();
+}

test/libcxx/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp

@@ -0,0 +1,120 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// variant(variant const&);
+
+#include <type_traits>
+#include <variant>
+
+#include "test_macros.h"
+
+struct NTCopy {
+  constexpr NTCopy(int v) : value(v) {}
+  NTCopy(const NTCopy &that) : value(that.value) {}
+  NTCopy(NTCopy &&) = delete;
+  int value;
+};
+
+static_assert(!std::is_trivially_copy_constructible<NTCopy>::value, "");
+static_assert(std::is_copy_constructible<NTCopy>::value, "");
+
+struct TCopy {
+  constexpr TCopy(int v) : value(v) {}
+  TCopy(TCopy const &) = default;
+  TCopy(TCopy &&) = delete;
+  int value;
+};
+
+static_assert(std::is_trivially_copy_constructible<TCopy>::value, "");
+
+struct TCopyNTMove {
+  constexpr TCopyNTMove(int v) : value(v) {}
+  TCopyNTMove(const TCopyNTMove&) = default;
+  TCopyNTMove(TCopyNTMove&& that) : value(that.value) { that.value = -1; }
+  int value;
+};
+
+static_assert(std::is_trivially_copy_constructible<TCopyNTMove>::value, "");
+
+void test_copy_ctor_sfinae() {
+  {
+    using V = std::variant<int, long>;
+    static_assert(std::is_trivially_copy_constructible<V>::value, "");
+  }
+  {
+    using V = std::variant<int, NTCopy>;
+    static_assert(!std::is_trivially_copy_constructible<V>::value, "");
+    static_assert(std::is_copy_constructible<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TCopy>;
+    static_assert(std::is_trivially_copy_constructible<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TCopyNTMove>;
+    static_assert(std::is_trivially_copy_constructible<V>::value, "");
+  }
+}
+
+void test_copy_ctor_basic() {
+  {
+    constexpr std::variant<int> v(std::in_place_index<0>, 42);
+    static_assert(v.index() == 0);
+    constexpr std::variant<int> v2 = v;
+    static_assert(v2.index() == 0);
+    static_assert(std::get<0>(v2) == 42);
+  }
+  {
+    constexpr std::variant<int, long> v(std::in_place_index<1>, 42);
+    static_assert(v.index() == 1);
+    constexpr std::variant<int, long> v2 = v;
+    static_assert(v2.index() == 1);
+    static_assert(std::get<1>(v2) == 42);
+  }
+  {
+    constexpr std::variant<TCopy> v(std::in_place_index<0>, 42);
+    static_assert(v.index() == 0);
+    constexpr std::variant<TCopy> v2(v);
+    static_assert(v2.index() == 0);
+    static_assert(std::get<0>(v2).value == 42);
+  }
+  {
+    constexpr std::variant<int, TCopy> v(std::in_place_index<1>, 42);
+    static_assert(v.index() == 1);
+    constexpr std::variant<int, TCopy> v2(v);
+    static_assert(v2.index() == 1);
+    static_assert(std::get<1>(v2).value == 42);
+  }
+  {
+    constexpr std::variant<TCopyNTMove> v(std::in_place_index<0>, 42);
+    static_assert(v.index() == 0);
+    constexpr std::variant<TCopyNTMove> v2(v);
+    static_assert(v2.index() == 0);
+    static_assert(std::get<0>(v2).value == 42);
+  }
+  {
+    constexpr std::variant<int, TCopyNTMove> v(std::in_place_index<1>, 42);
+    static_assert(v.index() == 1);
+    constexpr std::variant<int, TCopyNTMove> v2(v);
+    static_assert(v2.index() == 1);
+    static_assert(std::get<1>(v2).value == 42);
+  }
+}
+
+int main() {
+  test_copy_ctor_basic();
+  test_copy_ctor_sfinae();
+}

test/libcxx/utilities/variant/variant.variant/variant.ctor/move.pass.cpp

@@ -0,0 +1,153 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// variant(variant&&) noexcept(see below);
+
+#include <type_traits>
+#include <variant>
+
+#include "test_macros.h"
+
+struct NTMove {
+  constexpr NTMove(int v) : value(v) {}
+  NTMove(const NTMove &) = delete;
+  NTMove(NTMove &&that) : value(that.value) { that.value = -1; }
+  int value;
+};
+
+static_assert(!std::is_trivially_move_constructible<NTMove>::value, "");
+static_assert(std::is_move_constructible<NTMove>::value, "");
+
+struct TMove {
+  constexpr TMove(int v) : value(v) {}
+  TMove(const TMove &) = delete;
+  TMove(TMove &&) = default;
+  int value;
+};
+
+static_assert(std::is_trivially_move_constructible<TMove>::value, "");
+
+struct TMoveNTCopy {
+  constexpr TMoveNTCopy(int v) : value(v) {}
+  TMoveNTCopy(const TMoveNTCopy& that) : value(that.value) {}
+  TMoveNTCopy(TMoveNTCopy&&) = default;
+  int value;
+};
+
+static_assert(std::is_trivially_move_constructible<TMoveNTCopy>::value, "");
+
+void test_move_ctor_sfinae() {
+  {
+    using V = std::variant<int, long>;
+    static_assert(std::is_trivially_move_constructible<V>::value, "");
+  }
+  {
+    using V = std::variant<int, NTMove>;
+    static_assert(!std::is_trivially_move_constructible<V>::value, "");
+    static_assert(std::is_move_constructible<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TMove>;
+    static_assert(std::is_trivially_move_constructible<V>::value, "");
+  }
+  {
+    using V = std::variant<int, TMoveNTCopy>;
+    static_assert(std::is_trivially_move_constructible<V>::value, "");
+  }
+}
+
+template <typename T>
+struct Result { size_t index; T value; };
+
+void test_move_ctor_basic() {
+  {
+    struct {
+      constexpr Result<int> operator()() const {
+        std::variant<int> v(std::in_place_index<0>, 42);
+        std::variant<int> v2 = std::move(v);
+        return {v2.index(), std::get<0>(std::move(v2))};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 0);
+    static_assert(result.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<long> operator()() const {
+        std::variant<int, long> v(std::in_place_index<1>, 42);
+        std::variant<int, long> v2 = std::move(v);
+        return {v2.index(), std::get<1>(std::move(v2))};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<TMove> operator()() const {
+        std::variant<TMove> v(std::in_place_index<0>, 42);
+        std::variant<TMove> v2(std::move(v));
+        return {v2.index(), std::get<0>(std::move(v2))};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 0);
+    static_assert(result.value.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<TMove> operator()() const {
+        std::variant<int, TMove> v(std::in_place_index<1>, 42);
+        std::variant<int, TMove> v2(std::move(v));
+        return {v2.index(), std::get<1>(std::move(v2))};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<TMoveNTCopy> operator()() const {
+        std::variant<TMoveNTCopy> v(std::in_place_index<0>, 42);
+        std::variant<TMoveNTCopy> v2(std::move(v));
+        return {v2.index(), std::get<0>(std::move(v2))};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 0);
+    static_assert(result.value.value == 42);
+  }
+  {
+    struct {
+      constexpr Result<TMoveNTCopy> operator()() const {
+        std::variant<int, TMoveNTCopy> v(std::in_place_index<1>, 42);
+        std::variant<int, TMoveNTCopy> v2(std::move(v));
+        return {v2.index(), std::get<1>(std::move(v2))};
+      }
+    } test;
+    constexpr auto result = test();
+    static_assert(result.index == 1);
+    static_assert(result.value.value == 42);
+  }
+}
+
+int main() {
+  test_move_ctor_basic();
+  test_move_ctor_sfinae();
+}

test/libcxx/utilities/variant/version.pass.cpp

@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <variant>
+
+#include <variant>
+
+#ifndef _LIBCPP_VERSION
+#error _LIBCPP_VERSION not defined
+#endif
+
+int main()
+{
+}

test/std/utilities/variant/lit.local.cfg

@@ -1,5 +0,0 @@
-
-# FIXME: Libc++ does not yet implement variant but other STLs benefit from
-# having our tests in-tree. This must be removed when <variant> is added.
-if 'libc++' in config.available_features:
-  config.unsupported = True

test/std/utilities/variant/variant.get/get_if_index.pass.cpp

@@ -32,17 +32,17 @@ void test_const_get_if() {
     static_assert(std::get_if<0>(v) == nullptr, "");
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     constexpr V v(42);
     ASSERT_NOEXCEPT(std::get_if<0>(&v));
-    ASSERT_SAME_TYPE(decltype(std::get_if<0>(&v)), int const *);
+    ASSERT_SAME_TYPE(decltype(std::get_if<0>(&v)), const int *);
     static_assert(*std::get_if<0>(&v) == 42, "");
     static_assert(std::get_if<1>(&v) == nullptr, "");
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     constexpr V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get_if<1>(&v)), long const *);
+    ASSERT_SAME_TYPE(decltype(std::get_if<1>(&v)), const long *);
     static_assert(*std::get_if<1>(&v) == 42, "");
     static_assert(std::get_if<0>(&v) == nullptr, "");
   }
@@ -87,9 +87,9 @@ void test_get_if() {
     assert(std::get_if<1>(&v) == nullptr);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get_if<1>(&v)), long *);
+    ASSERT_SAME_TYPE(decltype(std::get_if<1>(&v)), const long *);
     assert(*std::get_if<1>(&v) == 42);
     assert(std::get_if<0>(&v) == nullptr);
   }

test/std/utilities/variant/variant.get/get_if_type.pass.cpp

@@ -30,18 +30,18 @@ void test_const_get_if() {
     static_assert(std::get_if<int>(v) == nullptr, "");
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     constexpr V v(42);
     ASSERT_NOEXCEPT(std::get_if<int>(&v));
-    ASSERT_SAME_TYPE(decltype(std::get_if<int>(&v)), int const *);
+    ASSERT_SAME_TYPE(decltype(std::get_if<int>(&v)), const int *);
     static_assert(*std::get_if<int>(&v) == 42, "");
-    static_assert(std::get_if<long>(&v) == nullptr, "");
+    static_assert(std::get_if<const long>(&v) == nullptr, "");
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     constexpr V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get_if<long>(&v)), long const *);
-    static_assert(*std::get_if<long>(&v) == 42, "");
+    ASSERT_SAME_TYPE(decltype(std::get_if<const long>(&v)), const long *);
+    static_assert(*std::get_if<const long>(&v) == 42, "");
     static_assert(std::get_if<int>(&v) == nullptr, "");
   }
 // FIXME: Remove these once reference support is reinstated
@@ -77,18 +77,18 @@ void test_get_if() {
     assert(std::get_if<int>(v) == nullptr);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42);
     ASSERT_NOEXCEPT(std::get_if<int>(&v));
     ASSERT_SAME_TYPE(decltype(std::get_if<int>(&v)), int *);
     assert(*std::get_if<int>(&v) == 42);
-    assert(std::get_if<long>(&v) == nullptr);
+    assert(std::get_if<const long>(&v) == nullptr);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get_if<long>(&v)), long *);
-    assert(*std::get_if<long>(&v) == 42);
+    ASSERT_SAME_TYPE(decltype(std::get_if<const long>(&v)), const long *);
+    assert(*std::get_if<const long>(&v) == 42);
     assert(std::get_if<int>(&v) == nullptr);
   }
 // FIXME: Remove these once reference support is reinstated

test/std/utilities/variant/variant.get/get_index.pass.cpp

@@ -34,16 +34,16 @@
 
 void test_const_lvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     constexpr V v(42);
-    // ASSERT_NOT_NOEXCEPT(std::get<0>(v));
-    ASSERT_SAME_TYPE(decltype(std::get<0>(v)), int const &);
+    ASSERT_NOT_NOEXCEPT(std::get<0>(v));
+    ASSERT_SAME_TYPE(decltype(std::get<0>(v)), const int &);
     static_assert(std::get<0>(v) == 42, "");
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     constexpr V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<1>(v)), long const &);
+    ASSERT_SAME_TYPE(decltype(std::get<1>(v)), const long &);
     static_assert(std::get<1>(v) == 42, "");
   }
 // FIXME: Remove these once reference support is reinstated
@@ -74,16 +74,16 @@ void test_const_lvalue_get() {
 
 void test_lvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     V v(42);
     ASSERT_NOT_NOEXCEPT(std::get<0>(v));
     ASSERT_SAME_TYPE(decltype(std::get<0>(v)), int &);
     assert(std::get<0>(v) == 42);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<1>(v)), long &);
+    ASSERT_SAME_TYPE(decltype(std::get<1>(v)), const long &);
     assert(std::get<1>(v) == 42);
   }
 // FIXME: Remove these once reference support is reinstated
@@ -121,16 +121,16 @@ void test_lvalue_get() {
 
 void test_rvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     V v(42);
     ASSERT_NOT_NOEXCEPT(std::get<0>(std::move(v)));
     ASSERT_SAME_TYPE(decltype(std::get<0>(std::move(v))), int &&);
     assert(std::get<0>(std::move(v)) == 42);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<1>(std::move(v))), long &&);
+    ASSERT_SAME_TYPE(decltype(std::get<1>(std::move(v))), const long &&);
     assert(std::get<1>(std::move(v)) == 42);
   }
 // FIXME: Remove these once reference support is reinstated
@@ -170,14 +170,14 @@ void test_rvalue_get() {
 
 void test_const_rvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     const V v(42);
     ASSERT_NOT_NOEXCEPT(std::get<0>(std::move(v)));
     ASSERT_SAME_TYPE(decltype(std::get<0>(std::move(v))), const int &&);
     assert(std::get<0>(std::move(v)) == 42);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     const V v(42l);
     ASSERT_SAME_TYPE(decltype(std::get<1>(std::move(v))), const long &&);
     assert(std::get<1>(std::move(v)) == 42);
@@ -234,7 +234,7 @@ void test_throws_for_all_value_categories() {
     using Idx = decltype(idx);
     try {
       std::get<Idx::value>(std::forward<decltype(v)>(v));
-    } catch (std::bad_variant_access const &) {
+    } catch (const std::bad_variant_access &) {
       return true;
     } catch (...) { /* ... */
     }

test/std/utilities/variant/variant.get/get_type.pass.cpp

@@ -28,17 +28,17 @@
 
 void test_const_lvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     constexpr V v(42);
-    // ASSERT_NOT_NOEXCEPT(std::get<int>(v));
-    ASSERT_SAME_TYPE(decltype(std::get<0>(v)), int const &);
+    ASSERT_NOT_NOEXCEPT(std::get<int>(v));
+    ASSERT_SAME_TYPE(decltype(std::get<0>(v)), const int &);
     static_assert(std::get<int>(v) == 42, "");
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     constexpr V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<long>(v)), long const &);
-    static_assert(std::get<long>(v) == 42, "");
+    ASSERT_SAME_TYPE(decltype(std::get<const long>(v)), const long &);
+    static_assert(std::get<const long>(v) == 42, "");
   }
 // FIXME: Remove these once reference support is reinstated
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
@@ -68,17 +68,17 @@ void test_const_lvalue_get() {
 
 void test_lvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     V v(42);
     ASSERT_NOT_NOEXCEPT(std::get<int>(v));
     ASSERT_SAME_TYPE(decltype(std::get<int>(v)), int &);
     assert(std::get<int>(v) == 42);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<long>(v)), long &);
-    assert(std::get<long>(v) == 42);
+    ASSERT_SAME_TYPE(decltype(std::get<const long>(v)), const long &);
+    assert(std::get<const long>(v) == 42);
   }
 // FIXME: Remove these once reference support is reinstated
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
@@ -115,17 +115,18 @@ void test_lvalue_get() {
 
 void test_rvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     V v(42);
     ASSERT_NOT_NOEXCEPT(std::get<int>(std::move(v)));
     ASSERT_SAME_TYPE(decltype(std::get<int>(std::move(v))), int &&);
     assert(std::get<int>(std::move(v)) == 42);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<long>(std::move(v))), long &&);
-    assert(std::get<long>(std::move(v)) == 42);
+    ASSERT_SAME_TYPE(decltype(std::get<const long>(std::move(v))),
+                     const long &&);
+    assert(std::get<const long>(std::move(v)) == 42);
   }
 // FIXME: Remove these once reference support is reinstated
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
@@ -166,17 +167,18 @@ void test_rvalue_get() {
 
 void test_const_rvalue_get() {
   {
-    using V = std::variant<int>;
+    using V = std::variant<int, const long>;
     const V v(42);
     ASSERT_NOT_NOEXCEPT(std::get<int>(std::move(v)));
     ASSERT_SAME_TYPE(decltype(std::get<int>(std::move(v))), const int &&);
     assert(std::get<int>(std::move(v)) == 42);
   }
   {
-    using V = std::variant<int, long>;
+    using V = std::variant<int, const long>;
     const V v(42l);
-    ASSERT_SAME_TYPE(decltype(std::get<long>(std::move(v))), const long &&);
-    assert(std::get<long>(std::move(v)) == 42);
+    ASSERT_SAME_TYPE(decltype(std::get<const long>(std::move(v))),
+                     const long &&);
+    assert(std::get<const long>(std::move(v)) == 42);
   }
 // FIXME: Remove these once reference support is reinstated
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
@@ -232,7 +234,7 @@ void test_throws_for_all_value_categories() {
     using Idx = decltype(idx);
     try {
       std::get<typename Idx::type>(std::forward<decltype(v)>(v));
-    } catch (std::bad_variant_access const &) {
+    } catch (const std::bad_variant_access &) {
       return true;
     } catch (...) { /* ... */
     }

test/std/utilities/variant/variant.get/holds_alternative.pass.cpp

@@ -15,6 +15,7 @@
 // template <class T, class... Types>
 // constexpr bool holds_alternative(const variant<Types...>& v) noexcept;
 
+#include "test_macros.h"
 #include <variant>
 
 int main() {
@@ -32,6 +33,6 @@ int main() {
   { // noexcept test
     using V = std::variant<int>;
     const V v;
-    static_assert(noexcept(std::holds_alternative<int>(v)), "must be noexcept");
+    ASSERT_NOEXCEPT(std::holds_alternative<int>(v));
   }
 }

test/std/utilities/variant/variant.hash/hash.pass.cpp

@@ -25,7 +25,7 @@
 #ifndef TEST_HAS_NO_EXCEPTIONS
 namespace std {
 template <> struct hash<::MakeEmptyT> {
-  size_t operator()(::MakeEmptyT const &) const {
+  size_t operator()(const ::MakeEmptyT &) const {
     assert(false);
     return 0;
   }
@@ -40,7 +40,6 @@ void test_hash_variant() {
     const V v(std::in_place_index<0>, 42);
     const V v_copy = v;
     V v2(std::in_place_index<0>, 100);
-    const V v3(std::in_place_index<2>, 42);
     const H h{};
     assert(h(v) == h(v));
     assert(h(v) != h(v2));

test/std/utilities/variant/variant.helpers/variant_alternative.pass.cpp

@@ -66,10 +66,10 @@ int main() {
   }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
-    using V = std::variant<int, int &, int const &, int &&, long double>;
+    using V = std::variant<int, int &, const int &, int &&, long double>;
     test<V, 0, int>();
     test<V, 1, int &>();
-    test<V, 2, int const &>();
+    test<V, 2, const int &>();
     test<V, 3, int &&>();
     test<V, 4, long double>();
   }

test/std/utilities/variant/variant.monostate.relops/relops.pass.cpp

@@ -19,6 +19,7 @@
 // constexpr bool operator==(monostate, monostate) noexcept { return true; }
 // constexpr bool operator!=(monostate, monostate) noexcept { return false; }
 
+#include "test_macros.h"
 #include <cassert>
 #include <type_traits>
 #include <variant>
@@ -29,26 +30,26 @@ int main() {
   constexpr M m2{};
   {
     static_assert((m1 < m2) == false, "");
-    static_assert(noexcept(m1 < m2), "");
+    ASSERT_NOEXCEPT(m1 < m2);
   }
   {
     static_assert((m1 > m2) == false, "");
-    static_assert(noexcept(m1 > m2), "");
+    ASSERT_NOEXCEPT(m1 > m2);
   }
   {
     static_assert((m1 <= m2) == true, "");
-    static_assert(noexcept(m1 <= m2), "");
+    ASSERT_NOEXCEPT(m1 <= m2);
   }
   {
     static_assert((m1 >= m2) == true, "");
-    static_assert(noexcept(m1 >= m2), "");
+    ASSERT_NOEXCEPT(m1 >= m2);
   }
   {
     static_assert((m1 == m2) == true, "");
-    static_assert(noexcept(m1 == m2), "");
+    ASSERT_NOEXCEPT(m1 == m2);
   }
   {
     static_assert((m1 != m2) == false, "");
-    static_assert(noexcept(m1 != m2), "");
+    ASSERT_NOEXCEPT(m1 != m2);
   }
 }

test/std/utilities/variant/variant.relops/relops.pass.cpp

@@ -49,27 +49,27 @@ struct MakeEmptyT {
   MakeEmptyT(MakeEmptyT &&) { throw 42; }
   MakeEmptyT &operator=(MakeEmptyT &&) { throw 42; }
 };
-inline bool operator==(MakeEmptyT const &, MakeEmptyT const &) {
+inline bool operator==(const MakeEmptyT &, const MakeEmptyT &) {
   assert(false);
   return false;
 }
-inline bool operator!=(MakeEmptyT const &, MakeEmptyT const &) {
+inline bool operator!=(const MakeEmptyT &, const MakeEmptyT &) {
   assert(false);
   return false;
 }
-inline bool operator<(MakeEmptyT const &, MakeEmptyT const &) {
+inline bool operator<(const MakeEmptyT &, const MakeEmptyT &) {
   assert(false);
   return false;
 }
-inline bool operator<=(MakeEmptyT const &, MakeEmptyT const &) {
+inline bool operator<=(const MakeEmptyT &, const MakeEmptyT &) {
   assert(false);
   return false;
 }
-inline bool operator>(MakeEmptyT const &, MakeEmptyT const &) {
+inline bool operator>(const MakeEmptyT &, const MakeEmptyT &) {
   assert(false);
   return false;
 }
-inline bool operator>=(MakeEmptyT const &, MakeEmptyT const &) {
+inline bool operator>=(const MakeEmptyT &, const MakeEmptyT &) {
   assert(false);
   return false;
 }
@@ -158,7 +158,7 @@ void test_equality() {
 }
 
 template <class Var>
-constexpr bool test_less(Var const &l, Var const &r, bool expect_less,
+constexpr bool test_less(const Var &l, const Var &r, bool expect_less,
                          bool expect_greater) {
   return ((l < r) == expect_less) && (!(l >= r) == expect_less) &&
          ((l > r) == expect_greater) && (!(l <= r) == expect_greater);

test/std/utilities/variant/variant.variant/variant.assign/T.pass.cpp

@@ -116,7 +116,7 @@ void test_T_assignment_sfinae() {
     static_assert(!std::is_assignable<V, int>::value, "ambiguous");
   }
   {
-    using V = std::variant<int, int const &>;
+    using V = std::variant<int, const int &>;
     static_assert(!std::is_assignable<V, int>::value, "ambiguous");
   }
 #endif
@@ -149,9 +149,9 @@ void test_T_assignment_basic() {
     v = std::move(x);
     assert(v.index() == 1);
     assert(&std::get<1>(v) == &x);
-    // 'long' is selected by FUN(int const&) since 'int const&' cannot bind
+    // 'long' is selected by FUN(const int &) since 'const int &' cannot bind
     // to 'int&'.
-    int const &cx = x;
+    const int &cx = x;
     v = cx;
     assert(v.index() == 2);
     assert(std::get<2>(v) == 42);

test/std/utilities/variant/variant.variant/variant.assign/copy.pass.cpp

@@ -24,32 +24,32 @@
 #include "test_macros.h"
 
 struct NoCopy {
-  NoCopy(NoCopy const &) = delete;
-  NoCopy &operator=(NoCopy const &) = default;
+  NoCopy(const NoCopy &) = delete;
+  NoCopy &operator=(const NoCopy &) = default;
 };
 
 struct NothrowCopy {
-  NothrowCopy(NothrowCopy const &) noexcept = default;
-  NothrowCopy &operator=(NothrowCopy const &) noexcept = default;
+  NothrowCopy(const NothrowCopy &) noexcept = default;
+  NothrowCopy &operator=(const NothrowCopy &) noexcept = default;
 };
 
 struct CopyOnly {
-  CopyOnly(CopyOnly const &) = default;
+  CopyOnly(const CopyOnly &) = default;
   CopyOnly(CopyOnly &&) = delete;
-  CopyOnly &operator=(CopyOnly const &) = default;
+  CopyOnly &operator=(const CopyOnly &) = default;
   CopyOnly &operator=(CopyOnly &&) = delete;
 };
 
 struct MoveOnly {
-  MoveOnly(MoveOnly const &) = delete;
+  MoveOnly(const MoveOnly &) = delete;
   MoveOnly(MoveOnly &&) = default;
-  MoveOnly &operator=(MoveOnly const &) = default;
+  MoveOnly &operator=(const MoveOnly &) = default;
 };
 
 struct MoveOnlyNT {
-  MoveOnlyNT(MoveOnlyNT const &) = delete;
+  MoveOnlyNT(const MoveOnlyNT &) = delete;
   MoveOnlyNT(MoveOnlyNT &&) {}
-  MoveOnlyNT &operator=(MoveOnlyNT const &) = default;
+  MoveOnlyNT &operator=(const MoveOnlyNT &) = default;
 };
 
 struct CopyAssign {
@@ -62,7 +62,7 @@ struct CopyAssign {
     copy_construct = copy_assign = move_construct = move_assign = alive = 0;
   }
   CopyAssign(int v) : value(v) { ++alive; }
-  CopyAssign(CopyAssign const &o) : value(o.value) {
+  CopyAssign(const CopyAssign &o) : value(o.value) {
     ++alive;
     ++copy_construct;
   }
@@ -71,7 +71,7 @@ struct CopyAssign {
     ++alive;
     ++move_construct;
   }
-  CopyAssign &operator=(CopyAssign const &o) {
+  CopyAssign &operator=(const CopyAssign &o) {
     value = o.value;
     ++copy_assign;
     return *this;
@@ -93,27 +93,27 @@ int CopyAssign::move_construct = 0;
 int CopyAssign::move_assign = 0;
 
 struct CopyMaybeThrows {
-  CopyMaybeThrows(CopyMaybeThrows const &);
-  CopyMaybeThrows &operator=(CopyMaybeThrows const &);
+  CopyMaybeThrows(const CopyMaybeThrows &);
+  CopyMaybeThrows &operator=(const CopyMaybeThrows &);
 };
 struct CopyDoesThrow {
-  CopyDoesThrow(CopyDoesThrow const &) noexcept(false);
-  CopyDoesThrow &operator=(CopyDoesThrow const &) noexcept(false);
+  CopyDoesThrow(const CopyDoesThrow &) noexcept(false);
+  CopyDoesThrow &operator=(const CopyDoesThrow &) noexcept(false);
 };
 
 #ifndef TEST_HAS_NO_EXCEPTIONS
 struct CopyThrows {
   CopyThrows() = default;
-  CopyThrows(CopyThrows const &) { throw 42; }
-  CopyThrows &operator=(CopyThrows const &) { throw 42; }
+  CopyThrows(const CopyThrows &) { throw 42; }
+  CopyThrows &operator=(const CopyThrows &) { throw 42; }
 };
 
 struct MoveThrows {
   static int alive;
   MoveThrows() { ++alive; }
-  MoveThrows(MoveThrows const &) { ++alive; }
+  MoveThrows(const MoveThrows &) { ++alive; }
   MoveThrows(MoveThrows &&) { throw 42; }
-  MoveThrows &operator=(MoveThrows const &) { return *this; }
+  MoveThrows &operator=(const MoveThrows &) { return *this; }
   MoveThrows &operator=(MoveThrows &&) { throw 42; }
   ~MoveThrows() { --alive; }
 };
@@ -123,13 +123,13 @@ int MoveThrows::alive = 0;
 struct MakeEmptyT {
   static int alive;
   MakeEmptyT() { ++alive; }
-  MakeEmptyT(MakeEmptyT const &) {
+  MakeEmptyT(const MakeEmptyT &) {
     ++alive;
     // Don't throw from the copy constructor since variant's assignment
     // operator performs a copy before committing to the assignment.
   }
   MakeEmptyT(MakeEmptyT &&) { throw 42; }
-  MakeEmptyT &operator=(MakeEmptyT const &) { throw 42; }
+  MakeEmptyT &operator=(const MakeEmptyT &) { throw 42; }
   MakeEmptyT &operator=(MakeEmptyT &&) { throw 42; }
   ~MakeEmptyT() { --alive; }
 };
@@ -164,7 +164,7 @@ void test_copy_assignment_sfinae() {
     static_assert(std::is_copy_assignable<V>::value, "");
   }
   {
-    // variant only provides copy assignment when beth the copy and move
+    // variant only provides copy assignment when both the copy and move
     // constructors are well formed
     using V = std::variant<int, CopyOnly>;
     static_assert(!std::is_copy_assignable<V>::value, "");

test/std/utilities/variant/variant.variant/variant.assign/move.pass.cpp

@@ -26,36 +26,36 @@
 #include "variant_test_helpers.hpp"
 
 struct NoCopy {
-  NoCopy(NoCopy const &) = delete;
-  NoCopy &operator=(NoCopy const &) = default;
+  NoCopy(const NoCopy &) = delete;
+  NoCopy &operator=(const NoCopy &) = default;
 };
 
 struct CopyOnly {
-  CopyOnly(CopyOnly const &) = default;
+  CopyOnly(const CopyOnly &) = default;
   CopyOnly(CopyOnly &&) = delete;
-  CopyOnly &operator=(CopyOnly const &) = default;
+  CopyOnly &operator=(const CopyOnly &) = default;
   CopyOnly &operator=(CopyOnly &&) = delete;
 };
 
 struct MoveOnly {
-  MoveOnly(MoveOnly const &) = delete;
+  MoveOnly(const MoveOnly &) = delete;
   MoveOnly(MoveOnly &&) = default;
-  MoveOnly &operator=(MoveOnly const &) = delete;
+  MoveOnly &operator=(const MoveOnly &) = delete;
   MoveOnly &operator=(MoveOnly &&) = default;
 };
 
 struct MoveOnlyNT {
-  MoveOnlyNT(MoveOnlyNT const &) = delete;
+  MoveOnlyNT(const MoveOnlyNT &) = delete;
   MoveOnlyNT(MoveOnlyNT &&) {}
-  MoveOnlyNT &operator=(MoveOnlyNT const &) = delete;
+  MoveOnlyNT &operator=(const MoveOnlyNT &) = delete;
   MoveOnlyNT &operator=(MoveOnlyNT &&) = default;
 };
 
 struct MoveOnlyOddNothrow {
   MoveOnlyOddNothrow(MoveOnlyOddNothrow &&) noexcept(false) {}
-  MoveOnlyOddNothrow(MoveOnlyOddNothrow const &) = delete;
+  MoveOnlyOddNothrow(const MoveOnlyOddNothrow &) = delete;
   MoveOnlyOddNothrow &operator=(MoveOnlyOddNothrow &&) noexcept = default;
-  MoveOnlyOddNothrow &operator=(MoveOnlyOddNothrow const &) = delete;
+  MoveOnlyOddNothrow &operator=(const MoveOnlyOddNothrow &) = delete;
 };
 
 struct MoveAssignOnly {

test/std/utilities/variant/variant.variant/variant.ctor/T.pass.cpp

@@ -68,7 +68,7 @@ void test_T_ctor_sfinae() {
     static_assert(!std::is_constructible<V, int>::value, "ambiguous");
   }
   {
-    using V = std::variant<int, int const &>;
+    using V = std::variant<int, const int &>;
     static_assert(!std::is_constructible<V, int>::value, "ambiguous");
   }
 #endif
@@ -87,7 +87,7 @@ void test_T_ctor_basic() {
   }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
-    using V = std::variant<int const &, int &&, long>;
+    using V = std::variant<const int &, int &&, long>;
     static_assert(std::is_convertible<int &, V>::value, "must be implicit");
     int x = 42;
     V v(x);
@@ -95,7 +95,7 @@ void test_T_ctor_basic() {
     assert(&std::get<0>(v) == &x);
   }
   {
-    using V = std::variant<int const &, int &&, long>;
+    using V = std::variant<const int &, int &&, long>;
     static_assert(std::is_convertible<int, V>::value, "must be implicit");
     int x = 42;
     V v(std::move(x));

test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp

@@ -24,22 +24,22 @@
 
 struct NonT {
   NonT(int v) : value(v) {}
-  NonT(NonT const &o) : value(o.value) {}
+  NonT(const NonT &o) : value(o.value) {}
   int value;
 };
 static_assert(!std::is_trivially_copy_constructible<NonT>::value, "");
 
 struct NoCopy {
-  NoCopy(NoCopy const &) = delete;
+  NoCopy(const NoCopy &) = delete;
 };
 
 struct MoveOnly {
-  MoveOnly(MoveOnly const &) = delete;
+  MoveOnly(const MoveOnly &) = delete;
   MoveOnly(MoveOnly &&) = default;
 };
 
 struct MoveOnlyNT {
-  MoveOnlyNT(MoveOnlyNT const &) = delete;
+  MoveOnlyNT(const MoveOnlyNT &) = delete;
   MoveOnlyNT(MoveOnlyNT &&) {}
 };
 
@@ -47,13 +47,13 @@ struct MoveOnlyNT {
 struct MakeEmptyT {
   static int alive;
   MakeEmptyT() { ++alive; }
-  MakeEmptyT(MakeEmptyT const &) {
+  MakeEmptyT(const MakeEmptyT &) {
     ++alive;
     // Don't throw from the copy constructor since variant's assignment
     // operator performs a copy before committing to the assignment.
   }
   MakeEmptyT(MakeEmptyT &&) { throw 42; }
-  MakeEmptyT &operator=(MakeEmptyT const &) { throw 42; }
+  MakeEmptyT &operator=(const MakeEmptyT &) { throw 42; }
   MakeEmptyT &operator=(MakeEmptyT &&) { throw 42; }
   ~MakeEmptyT() { --alive; }
 };
@@ -124,7 +124,7 @@ void test_copy_ctor_valueless_by_exception() {
   using V = std::variant<int, MakeEmptyT>;
   V v1;
   makeEmpty(v1);
-  V const &cv1 = v1;
+  const V &cv1 = v1;
   V v(cv1);
   assert(v.valueless_by_exception());
 #endif

test/std/utilities/variant/variant.variant/variant.ctor/default.pass.cpp

@@ -71,7 +71,7 @@ void test_default_ctor_throws() {
   try {
     V v;
     assert(false);
-  } catch (int const &ex) {
+  } catch (const int &ex) {
     assert(ex == 42);
   } catch (...) {
     assert(false);

test/std/utilities/variant/variant.variant/variant.ctor/move.pass.cpp

@@ -28,20 +28,20 @@ struct ThrowsMove {
 };
 
 struct NoCopy {
-  NoCopy(NoCopy const &) = delete;
+  NoCopy(const NoCopy &) = delete;
 };
 
 struct MoveOnly {
   int value;
   MoveOnly(int v) : value(v) {}
-  MoveOnly(MoveOnly const &) = delete;
+  MoveOnly(const MoveOnly &) = delete;
   MoveOnly(MoveOnly &&) = default;
 };
 
 struct MoveOnlyNT {
   int value;
   MoveOnlyNT(int v) : value(v) {}
-  MoveOnlyNT(MoveOnlyNT const &) = delete;
+  MoveOnlyNT(const MoveOnlyNT &) = delete;
   MoveOnlyNT(MoveOnlyNT &&other) : value(other.value) { other.value = -1; }
 };
 
@@ -49,13 +49,13 @@ struct MoveOnlyNT {
 struct MakeEmptyT {
   static int alive;
   MakeEmptyT() { ++alive; }
-  MakeEmptyT(MakeEmptyT const &) {
+  MakeEmptyT(const MakeEmptyT &) {
     ++alive;
     // Don't throw from the copy constructor since variant's assignment
     // operator performs a copy before committing to the assignment.
   }
   MakeEmptyT(MakeEmptyT &&) { throw 42; }
-  MakeEmptyT &operator=(MakeEmptyT const &) { throw 42; }
+  MakeEmptyT &operator=(const MakeEmptyT &) { throw 42; }
   MakeEmptyT &operator=(MakeEmptyT &&) { throw 42; }
   ~MakeEmptyT() { --alive; }
 };

test/std/utilities/variant/variant.variant/variant.dtor/dtor.pass.cpp

@@ -39,7 +39,7 @@ int NonTDtor1::count = 0;
 static_assert(!std::is_trivially_destructible<NonTDtor1>::value, "");
 
 struct TDtor {
-  TDtor(TDtor const &) {} // non-trivial copy
+  TDtor(const TDtor &) {} // non-trivial copy
   ~TDtor() = default;
 };
 static_assert(!std::is_trivially_copy_constructible<TDtor>::value, "");

test/std/utilities/variant/variant.variant/variant.mod/emplace_index_args.pass.cpp

@@ -58,14 +58,14 @@ void test_emplace_sfinae() {
   }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
-    using V = std::variant<int, int &, int const &, int &&, TestTypes::NoCtors>;
+    using V = std::variant<int, int &, const int &, int &&, TestTypes::NoCtors>;
     static_assert(emplace_exists<V, 0>(), "");
     static_assert(emplace_exists<V, 0, int>(), "");
     static_assert(emplace_exists<V, 0, long long>(), "");
     static_assert(!emplace_exists<V, 0, int, int>(), "too many args");
     static_assert(emplace_exists<V, 1, int &>(), "");
     static_assert(!emplace_exists<V, 1>(), "cannot default construct ref");
-    static_assert(!emplace_exists<V, 1, int const &>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 1, const int &>(), "cannot bind ref");
     static_assert(!emplace_exists<V, 1, int &&>(), "cannot bind ref");
     static_assert(emplace_exists<V, 2, int &>(), "");
     static_assert(emplace_exists<V, 2, const int &>(), "");
@@ -74,8 +74,8 @@ void test_emplace_sfinae() {
                   "not constructible from void*");
     static_assert(emplace_exists<V, 3, int>(), "");
     static_assert(!emplace_exists<V, 3, int &>(), "cannot bind ref");
-    static_assert(!emplace_exists<V, 3, int const &>(), "cannot bind ref");
-    static_assert(!emplace_exists<V, 3, int const &&>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 3, const int &>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 3, const int &&>(), "cannot bind ref");
     static_assert(!emplace_exists<V, 4>(), "no ctors");
   }
 #endif
@@ -106,7 +106,7 @@ void test_basic() {
   }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
-    using V = std::variant<int, long, int const &, int &&, TestTypes::NoCtors,
+    using V = std::variant<int, long, const int &, int &&, TestTypes::NoCtors,
                            std::string>;
     const int x = 100;
     int y = 42;

test/std/utilities/variant/variant.variant/variant.mod/emplace_type_args.pass.cpp

@@ -52,12 +52,12 @@ void test_emplace_sfinae() {
     static_assert(!emplace_exists<V, void *, int>(), "cannot construct");
     static_assert(emplace_exists<V, void *, int *>(), "");
     static_assert(!emplace_exists<V, void *, const int *>(), "");
-    static_assert(emplace_exists<V, void const *, const int *>(), "");
-    static_assert(emplace_exists<V, void const *, int *>(), "");
+    static_assert(emplace_exists<V, const void *, const int *>(), "");
+    static_assert(emplace_exists<V, const void *, int *>(), "");
     static_assert(!emplace_exists<V, TestTypes::NoCtors>(), "cannot construct");
   }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
-  using V = std::variant<int, int &, int const &, int &&, long, long,
+  using V = std::variant<int, int &, const int &, int &&, long, long,
                          TestTypes::NoCtors>;
   static_assert(emplace_exists<V, int>(), "");
   static_assert(emplace_exists<V, int, int>(), "");
@@ -65,17 +65,17 @@ void test_emplace_sfinae() {
   static_assert(!emplace_exists<V, int, int, int>(), "too many args");
   static_assert(emplace_exists<V, int &, int &>(), "");
   static_assert(!emplace_exists<V, int &>(), "cannot default construct ref");
-  static_assert(!emplace_exists<V, int &, int const &>(), "cannot bind ref");
+  static_assert(!emplace_exists<V, int &, const int &>(), "cannot bind ref");
   static_assert(!emplace_exists<V, int &, int &&>(), "cannot bind ref");
-  static_assert(emplace_exists<V, int const &, int &>(), "");
-  static_assert(emplace_exists<V, int const &, const int &>(), "");
-  static_assert(emplace_exists<V, int const &, int &&>(), "");
-  static_assert(!emplace_exists<V, int const &, void *>(),
+  static_assert(emplace_exists<V, const int &, int &>(), "");
+  static_assert(emplace_exists<V, const int &, const int &>(), "");
+  static_assert(emplace_exists<V, const int &, int &&>(), "");
+  static_assert(!emplace_exists<V, const int &, void *>(),
                 "not constructible from void*");
   static_assert(emplace_exists<V, int &&, int>(), "");
   static_assert(!emplace_exists<V, int &&, int &>(), "cannot bind ref");
-  static_assert(!emplace_exists<V, int &&, int const &>(), "cannot bind ref");
-  static_assert(!emplace_exists<V, int &&, int const &&>(), "cannot bind ref");
+  static_assert(!emplace_exists<V, int &&, const int &>(), "cannot bind ref");
+  static_assert(!emplace_exists<V, int &&, const int &&>(), "cannot bind ref");
   static_assert(!emplace_exists<V, long, long>(), "ambiguous");
   static_assert(!emplace_exists<V, TestTypes::NoCtors>(),
                 "cannot construct void");
@@ -107,7 +107,7 @@ void test_basic() {
   }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
-    using V = std::variant<int, long, int const &, int &&, TestTypes::NoCtors,
+    using V = std::variant<int, long, const int &, int &&, TestTypes::NoCtors,
                            std::string>;
     const int x = 100;
     int y = 42;
@@ -117,8 +117,8 @@ void test_basic() {
     v.emplace<long>();
     assert(std::get<long>(v) == 0);
     // emplace a reference
-    v.emplace<int const &>(x);
-    assert(&std::get<int const &>(v) == &x);
+    v.emplace<const int &>(x);
+    assert(&std::get<const int &>(v) == &x);
     // emplace an rvalue reference
     v.emplace<int &&>(std::move(y));
     assert(&std::get<int &&>(v) == &y);

test/std/utilities/variant/variant.variant/variant.swap/swap.pass.cpp

@@ -30,14 +30,14 @@ void swap(NotSwappable &, NotSwappable &) = delete;
 
 struct NotCopyable {
   NotCopyable() = default;
-  NotCopyable(NotCopyable const &) = delete;
-  NotCopyable &operator=(NotCopyable const &) = delete;
+  NotCopyable(const NotCopyable &) = delete;
+  NotCopyable &operator=(const NotCopyable &) = delete;
 };
 
 struct NotCopyableWithSwap {
   NotCopyableWithSwap() = default;
-  NotCopyableWithSwap(NotCopyableWithSwap const &) = delete;
-  NotCopyableWithSwap &operator=(NotCopyableWithSwap const &) = delete;
+  NotCopyableWithSwap(const NotCopyableWithSwap &) = delete;
+  NotCopyableWithSwap &operator=(const NotCopyableWithSwap &) = delete;
 };
 void swap(NotCopyableWithSwap &, NotCopyableWithSwap) {}
 
@@ -73,7 +73,7 @@ struct NothrowTypeImp {
   static void reset() { move_called = move_assign_called = swap_called = 0; }
   NothrowTypeImp() = default;
   explicit NothrowTypeImp(int v) : value(v) {}
-  NothrowTypeImp(NothrowTypeImp const &o) noexcept(NT_Copy) : value(o.value) {
+  NothrowTypeImp(const NothrowTypeImp &o) noexcept(NT_Copy) : value(o.value) {
     assert(false);
   } // never called by test
   NothrowTypeImp(NothrowTypeImp &&o) noexcept(NT_Move) : value(o.value) {
@@ -81,7 +81,7 @@ struct NothrowTypeImp {
     do_throw<!NT_Move>();
     o.value = -1;
   }
-  NothrowTypeImp &operator=(NothrowTypeImp const &) noexcept(NT_CopyAssign) {
+  NothrowTypeImp &operator=(const NothrowTypeImp &) noexcept(NT_CopyAssign) {
     assert(false);
     return *this;
   } // never called by the tests

test/std/utilities/variant/variant.variant/variant_reference.fail.cpp

@@ -23,6 +23,6 @@ int main()
 {
     // expected-error@variant:* 3 {{static_assert failed}}
     std::variant<int, int&> v; // expected-note {{requested here}}
-    std::variant<int, int const&> v2; // expected-note {{requested here}}
+    std::variant<int, const int &> v2; // expected-note {{requested here}}
     std::variant<int, int&&> v3; // expected-note {{requested here}}
 }

test/std/utilities/variant/variant.visit/visit.pass.cpp

@@ -77,16 +77,16 @@ struct ForwardingCallObject {
   }
 
   static CallType last_call_type;
-  static TypeID const *last_call_args;
+  static const TypeID *last_call_args;
 };
 
 CallType ForwardingCallObject::last_call_type = CT_None;
-TypeID const *ForwardingCallObject::last_call_args = nullptr;
+const TypeID *ForwardingCallObject::last_call_args = nullptr;
 
 void test_call_operator_forwarding() {
   using Fn = ForwardingCallObject;
   Fn obj{};
-  Fn const &cobj = obj;
+  const Fn &cobj = obj;
   { // test call operator forwarding - single variant, single arg
     using V = std::variant<int>;
     V v(42);
@@ -134,11 +134,11 @@ void test_argument_forwarding() {
   { // single argument - value type
     using V = std::variant<int>;
     V v(42);
-    V const &cv = v;
+    const V &cv = v;
     std::visit(obj, v);
     assert(Fn::check_call<int &>(Val));
     std::visit(obj, cv);
-    assert(Fn::check_call<int const &>(Val));
+    assert(Fn::check_call<const int &>(Val));
     std::visit(obj, std::move(v));
     assert(Fn::check_call<int &&>(Val));
     std::visit(obj, std::move(cv));
@@ -149,7 +149,7 @@ void test_argument_forwarding() {
     using V = std::variant<int &>;
     int x = 42;
     V v(x);
-    V const &cv = v;
+    const V &cv = v;
     std::visit(obj, v);
     assert(Fn::check_call<int &>(Val));
     std::visit(obj, cv);
@@ -163,7 +163,7 @@ void test_argument_forwarding() {
     using V = std::variant<int &&>;
     int x = 42;
     V v(std::move(x));
-    V const &cv = v;
+    const V &cv = v;
     std::visit(obj, v);
     assert(Fn::check_call<int &>(Val));
     std::visit(obj, cv);
@@ -174,16 +174,16 @@ void test_argument_forwarding() {
     assert(Fn::check_call<int &&>(Val));
   }
   { // multi argument - multi variant
-    using S = std::string const &;
+    using S = const std::string &;
     using V = std::variant<int, S, long &&>;
-    std::string const str = "hello";
+    const std::string str = "hello";
     long l = 43;
     V v1(42);
-    V const &cv1 = v1;
+    const V &cv1 = v1;
     V v2(str);
-    V const &cv2 = v2;
+    const V &cv2 = v2;
     V v3(std::move(l));
-    V const &cv3 = v3;
+    const V &cv3 = v3;
     std::visit(obj, v1, v2, v3);
     assert((Fn::check_call<int &, S, long &>(Val)));
     std::visit(obj, cv1, cv2, std::move(v3));
@@ -243,7 +243,7 @@ void test_exceptions() {
   auto test = [&](auto &&... args) {
     try {
       std::visit(obj, args...);
-    } catch (std::bad_variant_access const &) {
+    } catch (const std::bad_variant_access &) {
       return true;
     } catch (...) {
     }