RE: Exceptions (was: RE: [Avalon4:PROPOSAL] Context Consensus)

> >>I agree that container (and all platform code) should be
> >>robust.  But here's a rub.  There is no guarantee that the
> >>Component won't take the Context, squirrel it away, and cast the
> >>thing later when it needs it.  And when THAT happens, who sees the
> >>ClastCastException?  Quite likely some other component, whom is not
> >>expecting those kinds of internal errors to leak out.
> >>
> >>
>
> Disagree - the container can handle these conditions - if its not in
> contextualize state then it will be in the initialization
> stage or the
> starup stage,  In each case, the container has to take responsibility
> for tracking runtime errors and handling the decommission
> responsibilities.


Not necessarily.  Consider this poorly written example:


public interface DoSomethingService {
    void doSomething();
}

public class MyBadComponent implements Contextualizable, DoSomethingService
    private Context m_context;

    /**
     * The context is not immediately used or cast--making container
     * detection of a bad component during initialization impossible.
     */
    public void contextualize( Context context ) {
        m_context = context;
    }

    /**
     * The cast is done at runtime, when another component or client uses
     * the service.  The client code will be the unhappy recipient of the
     * ClassCastException.
     */
    public void doSomething() {
        ( (BlockContext) m_context ).requestShutdown();
    }
}


The only way to handle this scenario is to have a Proxy surround calls to
the runtime interface and intercept the RuntimeExceptions that should never
be thrown--i.e.. NullPointerException, Class**Exception (NotFound, Cast,
etc.),
and let through RuntimeExceptions that should be thrown--i.e..
IllegalArgumentException.

It also demonstrates that an ambiguous service can do something you don't
really want ;).