FreeBSD Manual Pages
std::expected::and_then(3) C++ Standard Libary std::expected::and_then(3) NAME std::expected::and_then - std::expected::and_then Synopsis template< class F > (1) (since C++23) constexpr auto and_then( F&& f ) &; template< class F > (2) (since C++23) constexpr auto and_then( F&& f ) const&; template< class F > (3) (since C++23) constexpr auto and_then( F&& f ) &&; template< class F > (4) (since C++23) constexpr auto and_then( F&& f ) const&&; If *this contains an expected value, invokes f and returns its re- sult; otherwise, returns a std::expected object that contains a copy of error(). If T is not (possibly cv-qualified) void, the contained expected value (obtained from operator*) is passed as an argument to f; otherwise f takes no argument. 1,2) Given type U as * std::remove_cvref_t<std::invoke_result_t<F>> if T is (possibly cv-qualified) void, or * std::remove_cvref_t<std::invoke_result_t<F, decltype(**this)>> otherwise. If U is not a specialization of std::expected, or std::is_same_v<U::error_type, E> is false, the program is ill-formed. The effect is equivalent to if (has_value()) { if constexpr (std::is_void_v<T>) return std::invoke(std::forward<F>(f)); else return std::invoke(std::forward<F>(f), **this); } else return U(std::unexpect, error()); These overloads participate in overload resolution only if std::is_constructible_v<E, decltype(error())> is true. 3,4) Given type U as * std::remove_cvref_t<std::invoke_result_t<F>> if T is (possibly cv-qualified) void, or * std::remove_cvref_t<std::invoke_result_t<F, de- cltype(std::move(**this))>> otherwise. If U is not a specialization of std::expected, or std::is_same_v<U::error_type, E> is false, the program is ill-formed. The effect is equivalent to if (has_value()) { if constexpr (std::is_void_v<T>) return std::invoke(std::forward<F>(f)); else return std::invoke(std::forward<F>(f), std::move(**this)); } else return U(std::unexpect, std::move(error())); These overloads participate in overload resolution only if std::is_constructible_v<E, decltype(std::move(error()))> is true. Parameters f - a suitable function or Callable object that returns a std::ex- pected Return value The result of f or a std::expected object that contains an error value, as described above. Notes Feature-test macro Value Std Feature __cpp_lib_expected 202211L (C++23) Monadic functions for std::ex- pected Example This section is incomplete Reason: no example Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 3938 C++23 and_then was ill-formed if T is not (possibly made well-formed cv-qualified) void and E is not copyable See also unexpect in-place construction tag for unexpected value in ex- pected unexpect_t (tag) (C++23) returns an expected containing the transformed expected value if it transform exists; otherwise, returns the expected itself (public member function) Category: * Todo no example http://cppreference.com 2024.06.10 std::expected::and_then(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | See also | Category:
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::expected::and_then&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>