Standard library header  (C++17) (original) (raw)

This header is part of the general utility library.

[edit] Synopsis

// mostly freestanding #include   namespace std { // class template variant template<class... Types> class variant;   // variant helper classes template struct variant_size; // not defined template struct variant_size; template constexpr size_t variant_size_v = variant_size::value;   template<class... Types> struct variant_size<variant<Types...>>;   template<size_t I, class T> struct variant_alternative; // not defined template<size_t I, class T> struct variant_alternative<I, const T>; template<size_t I, class T> using variant_alternative_t = typename variant_alternative<I, T>::type;   template<size_t I, class... Types> struct variant_alternative<I, variant<Types...>>;   inline constexpr size_t variant_npos = -1;   // 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...>&); // freestanding-deleted template<size_t I, class... Types> constexpr variant_alternative_t<I, variant<Types...>>&& get( variant<Types...>&&); // freestanding-deleted template<size_t I, class... Types> constexpr const variant_alternative_t<I, variant<Types...>>& get( const variant<Types...>&); // freestanding-deleted template<size_t I, class... Types> constexpr const variant_alternative_t<I, variant<Types...>>&& get( const variant<Types...>&&); // freestanding-deleted   template<class T, class... Types> constexpr T& get(variant<Types...>&); // freestanding-deleted template<class T, class... Types> constexpr T&& get(variant<Types...>&&); // freestanding-deleted template<class T, class... Types> constexpr const T& get(const variant<Types...>&); // freestanding-deleted template<class T, class... Types> constexpr const T&& get(const variant<Types...>&&); // freestanding-deleted   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 get_if(variant<Types...>) noexcept; template<class T, class... Types> constexpr add_pointer_t get_if(const variant<Types...>) noexcept;   // relational operators template<class... Types> constexpr bool operator==(const variant<Types...>&, const variant<Types...>&); template<class... Types> constexpr bool operator!=(const variant<Types...>&, const variant<Types...>&); template<class... Types> constexpr bool operator<(const variant<Types...>&, const variant<Types...>&); template<class... Types> constexpr bool operator>(const variant<Types...>&, const variant<Types...>&); template<class... Types> constexpr bool operator<=(const variant<Types...>&, const variant<Types...>&); template<class... Types> constexpr bool operator>=(const variant<Types...>&, const variant<Types...>&); template<class... Types> requires(three_way_comparable && ...) constexpr common_comparison_category_t<compare_three_way_result_t...> operator<=>(const variant<Types...>&, const variant<Types...>&);   // visitation template<class Visitor, class... Variants> constexpr /* see description / visit(Visitor&&, Variants&&...); template<class R, class Visitor, class... Variants> constexpr R visit(Visitor&&, Variants&&...);   // class monostate struct monostate;   // monostate relational operators constexpr bool operator==(monostate, monostate) noexcept; constexpr strong_ordering operator<=>(monostate, monostate) noexcept;   // specialized algorithms template<class... Types> constexpr void swap(variant<Types...>&, variant<Types...>&) noexcept(/ see description */);   // class bad_variant_access class bad_variant_access;   // hash support template struct hash; template<class... Types> struct hash<variant<Types...>>; template<> struct hash; }   // deprecated namespace std { template struct variant_size; template struct variant_size;   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>; }

[edit] Class template std::variant

namespace std { template<class... Types> class variant { public: // constructors constexpr variant() noexcept(/* see description /); constexpr variant(const variant&); constexpr variant(variant&&) noexcept(/ see description /);   template constexpr variant(T&&) noexcept(/ see description /);   template<class T, class... Args> constexpr explicit variant(in_place_type_t, Args&&...); template<class T, class U, class... Args> constexpr explicit variant(in_place_type_t, initializer_list, Args&&...);   template<size_t I, class... Args> constexpr explicit variant(in_place_index_t, Args&&...); template<size_t I, class U, class... Args> constexpr explicit variant(in_place_index_t, initializer_list, Args&&...);   // destructor constexpr ~variant();   // assignment constexpr variant& operator=(const variant&); constexpr variant& operator=(variant&&) noexcept(/ see description /);   template constexpr variant& operator=(T&&) noexcept(/ see description /);   // modifiers template<class T, class... Args> constexpr T& emplace(Args&&...); template<class T, class U, class... Args> constexpr T& emplace(initializer_list, Args&&...); template<size_t I, class... Args> constexpr variant_alternative_t<I, variant<Types...>>& emplace(Args&&...); template<size_t I, class U, class... Args> constexpr variant_alternative_t<I, variant<Types...>>& emplace(initializer_list, Args&&...);   // value status constexpr bool valueless_by_exception() const noexcept; constexpr size_t index() const noexcept;   // swap constexpr void swap(variant&) noexcept(/ see description */);   // visitation template<class Self, class Visitor> constexpr decltype(auto) visit(this Self&&, Visitor&&); template<class R, class Self, class Visitor> constexpr R visit(this Self&&, Visitor&&); }; }

[edit] Class std::monostate

namespace std { struct monostate{};   constexpr bool operator==(monostate, monostate) noexcept { return true; }   constexpr strong_ordering operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; } }

[edit] Class std::bad_variant_access

namespace std { class bad_variant_access : public exception { public: // see description for the specification of the special member functions constexpr const char* what() const noexcept override; }; }