@yohgaki I already said that on internals ... you can't prevent that by creating new classes and/or interfaces. SessionHandlerInterface is useful because of the following:

> php > session_set_save_handler(new stdClass());
> PHP Warning:  session_set_save_handler() expects parameter 1 to be SessionHandlerInterface, object given

SessionWhateverNewHandlerInterface is useless if it's not enforced anywhere, nobody will use it if they can avoid it.

The only thing you can do is add the new methods to the SessionHandler class and hope that E_STRICT will warn users about possible method signature mismatch. Anything else should be detected and called internally.