Returns true if this outcome compares equal to the other result. Comparison is done using operator== on value_type or error_type if the currently chosen state is the same for both outcome and result, otherwise false is returned. Note that if the outcome is excepted, it will never compare equal to a result.

Requires: operator== must be a valid expression between value_type and A, and between error_type and B. If value_type is void, then so must be A; similarly for error_type and B.

Complexity: Whatever the underlying operator== have. Constexpr and noexcept of underlying operations is propagated.

Guarantees: None.