Design by Contract - types of preconditions and exceptions is very powerfull tooling for dealing with situations not expected to happen during coding. I would

Design by Contract - types of preconditions and exceptions is very powerfull tooling for dealing with situations not expected to happen during coding. I would still to keep error handling and detection as separate issues. E.g merely throwing and exception or letting it to happen is often merely error detection, and handling is still to be done somewhere else. I think that exception systems merits are in keeping the subsystems decoupled by giving clear and systematic signaling channel to be used in error-detection situations.