6.8 KiB
[expected.object.general]
22 General utilities library [utilities]
22.8 Expected objects [expected]
22.8.6 Class template expected [expected.expected]
22.8.6.1 General [expected.object.general]
namespace std {template<class T, class E>class expected {public:using value_type = T; using error_type = E; using unexpected_type = unexpected; templateusing rebind = expected<U, error_type>; // [expected.object.cons], constructorsconstexpr expected(); constexpr expected(const expected&); constexpr expected(expected&&) noexcept(see below); template<class U, class G>constexpr explicit(see below) expected(const expected<U, G>&); template<class U, class G>constexpr explicit(see below) expected(expected<U, G>&&); template<class U = remove_cv_t>constexpr explicit(see below) expected(U&& v); templateconstexpr explicit(see below) expected(const unexpected&); templateconstexpr explicit(see below) expected(unexpected&&); template<class... Args>constexpr explicit expected(in_place_t, Args&&...); template<class U, class... Args>constexpr explicit expected(in_place_t, initializer_list, Args&&...); template<class... Args>constexpr explicit expected(unexpect_t, Args&&...); template<class U, class... Args>constexpr explicit expected(unexpect_t, initializer_list, Args&&...); // [expected.object.dtor], destructorconstexpr ~expected(); // [expected.object.assign], assignmentconstexpr expected& operator=(const expected&); constexpr expected& operator=(expected&&) noexcept(see below); template<class U = remove_cv_t> constexpr expected& operator=(U&&); templateconstexpr expected& operator=(const unexpected&); templateconstexpr expected& operator=(unexpected&&); template<class... Args>constexpr T& emplace(Args&&...) noexcept; template<class U, class... Args>constexpr T& emplace(initializer_list, Args&&...) noexcept; // [expected.object.swap], swapconstexpr void swap(expected&) noexcept(see below); friend constexpr void swap(expected& x, expected& y) noexcept(noexcept(x.swap(y))); // [expected.object.obs], observersconstexpr const T* operator->() const noexcept; constexpr T* operator->() noexcept; constexpr const T& operator*() const & noexcept; constexpr T& operator*() & noexcept; constexpr const T&& operator*() const && noexcept; constexpr T&& operator*() && noexcept; constexpr explicit operator bool() const noexcept; constexpr bool has_value() const noexcept; constexpr const T& value() const &; // freestanding-deletedconstexpr T& value() &; // freestanding-deletedconstexpr const T&& value() const &&; // freestanding-deletedconstexpr T&& value() &&; // freestanding-deletedconstexpr const E& error() const & noexcept; constexpr E& error() & noexcept; constexpr const E&& error() const && noexcept; constexpr E&& error() && noexcept; template<class U = remove_cv_t> constexpr T value_or(U&&) const &; template<class U = remove_cv_t> constexpr T value_or(U&&) &&; template constexpr E error_or(G&&) const &; template constexpr E error_or(G&&) &&; // [expected.object.monadic], monadic operationstemplate constexpr auto and_then(F&& f) &; template constexpr auto and_then(F&& f) &&; template constexpr auto and_then(F&& f) const &; template constexpr auto and_then(F&& f) const &&; template constexpr auto or_else(F&& f) &; template constexpr auto or_else(F&& f) &&; template constexpr auto or_else(F&& f) const &; template constexpr auto or_else(F&& f) const &&; template constexpr auto transform(F&& f) &; template constexpr auto transform(F&& f) &&; template constexpr auto transform(F&& f) const &; template constexpr auto transform(F&& f) const &&; template constexpr auto transform_error(F&& f) &; template constexpr auto transform_error(F&& f) &&; template constexpr auto transform_error(F&& f) const &; template constexpr auto transform_error(F&& f) const &&; // [expected.object.eq], equality operatorstemplate<class T2, class E2> requires (!is_void_v)friend constexpr bool operator==(const expected& x, const expected<T2, E2>& y); templatefriend constexpr bool operator==(const expected&, const T2&); templatefriend constexpr bool operator==(const expected&, const unexpected&); private:bool has_val; // exposition onlyunion { T val; // exposition only E unex; // exposition only}; };}
Any object of type expected<T, E> either contains a value of type T or a value of type E nested within ([intro.object]) it.
Member has_val indicates whether the expected<T, E> object contains an object of type T.
A type T is a valid value type for expected, if remove_cv_t is void or a complete non-array object type that is not in_place_t,unexpect_t, or a specialization of unexpected.
A program which instantiates class template expected<T, E> with an argument T that is not a valid value type for expected is ill-formed.
A program that instantiates the definition of the template expected<T, E> with a type for the E parameter that is not a valid template argument for unexpected is ill-formed.
When T is not cv void, it shall meet the Cpp17Destructible requirements (Table 35).
E shall meet the Cpp17Destructible requirements.