Return the output from free function auto failure(T &&, ...) containing a copy of any errored and/or excepted state. The error and/or exception state is accessed using const error_type &assume_error() const & noexcept and const exception_type &assume_exception() const & noexcept .

Requires: Always available.

Complexity: Whatever that of error_type’s and/or exception_type’s copy constructor is.

Guarantees: None.