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std::expect...sform_error(3) C++ Standard Libary std::expect...sform_error(3) NAME std::expected::transform_error - std::expected::transform_error Synopsis template< class F > (1) (since C++23) constexpr auto transform_error( F&& f ) &; template< class F > (2) (since C++23) constexpr auto transform_error( F&& f ) const&; template< class F > (3) (since C++23) constexpr auto transform_error( F&& f ) &&; template< class F > (4) (since C++23) constexpr auto transform_error( F&& f ) const&&; If *this contains an error value, invokes f with the argument er- ror() and returns a std::expected object that contains its result; otherwise, returns a std::expected object that contains a copy of the contained expected value (ob- tained from operator*). 1,2) Given type G as std::remove_cv_t<std::invoke_result_t<F, de- cltype(error())>>. If G is not a valid template argument for std::unexpected, or G g(std::invoke(std::forward<F>(f), error())); is ill-formed, the pro- gram is ill-formed. The effect is equivalent to if (has_value()) { if (std::is_void_v<T>) return std::expected<T, G>(); else return std::expected<T, G>(std::in_place, **this); } else // the returned std::expected object contains an unexpected value, // which is direct-non-list-initialized with // std::invoke(std::forward<F>(f), error()) return /* an std::expected<T, G> object */; These overloads participate in overload resolution only if std::is_void_v<T> or std::is_constructible_v<T, decltype(**this)> is true. 3,4) Given type G as std::remove_cv_t<std::invoke_result_t<F, decltype(std::move(error()))>>. If G is not a valid template argument for std::unexpected, or G g(std::invoke(std::forward<F>(f), std::move(error()))); is ill- formed, the program is ill-formed. The effect is equivalent to if (has_value()) { if (std::is_void_v<T>) return std::expected<T, G>(); else return std::expected<T, G>(std::in_place, std::move(**this)); } else // the returned std::expected object contains an unexpected value, // which is direct-non-list-initialized with // std::invoke(std::forward<F>(f), std::move(error())) return /* an std::expected<T, G> object */; These overloads participate in overload resolution only if std::is_void_v<T> or std::is_constructible_v<T, decltype(std::move(**this))> is true. Parameters f - a suitable function or Callable object whose call signature re- turns a non-reference type Return value A std::expected object containing either the result of f or an ex- pected value, as described above. 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 transform_error was ill-formed if T is not LWG 3938 C++23 (possibly cv-qualified) void and E is not made well-formed copyable See also returns the expected itself if it contains an expected value; otherwise, or_else returns the result of the given function on the unexpected value (public member function) 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::expect...sform_error(3)
NAME | Synopsis | Parameters | Return value | Example | See also | Category:
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