Return the output from free function auto failure(T &&, ...) containing a move from any errored state, thus leaving the result’s error value in a moved-from state. Depending on the choice of error_type, this function may therefore be destructive. The error state is accessed using error_type &&assume_error() && noexcept .

Requires: Always available.

Complexity: Whatever that of error_type’s move constructor is.

Guarantees: None.