[squeak-dev] An old gripe (or: SystemChangeNotifier + Announcements = Sanity?)

Folks -

While doing some preferences stuff I ran into one of my "most-hated"
issues in Squeak. Anyone who has ever encountered SystemChangeNotifier
must have noticed how terrible it is to use it. I mean, just look at
this code:

prefEvent: anEvent
        "Check if this system event defines or removes a preference."
        (anEvent itemKind = SystemChangeNotifier classKind and: [anEvent
isRemoved]) ifTrue:[...].
        anEvent itemKind = SystemChangeNotifier methodKind ifTrue:[
                (anEvent isRemoved or:[anEvent isModified]) ifTrue:[...]
                (anEvent isAdded or:[anEvent isModified]) ifTrue:[...]
        ].

just needless, pointless lines of case statements. How do people feel
about replacing that mess with Announcements? If you really want to have
all events you register for SystemEvent and if you'd like to be more
specific you go for more specifically for ClassEvent or even more
specifically for ClassAddedEvent. It would also remove the need for all
of these weird tests like

        anEvent itemKind = SystemChangeNotifier methodKind and:[anEvent isRemoved]

and just replace them with something like "anEvent isMethodRemoval". It
would likely be faster too, since most places aren't really interested
in *all* events either.

It would mean that Announcents would have to go core but this cleanup
alone seems worth it. I also suspect that adding Announcements and
fixing SystemChangeNotifier may remove more code than it would add.

How do people feel about that?

Cheers,
   - Andreas

>
> It would mean that Announcents would have to go core but this cleanup
> alone seems worth it. I also suspect that adding Announcements and
> fixing SystemChangeNotifier may remove more code than it would add.
>
> How do people feel about that?
>
> Cheers,
>   - Andreas
Sounds good to me.

Keith

Andreas Raab <andreas.raab <at> gmx.de> writes:

Sure. ++ for Announcements.
But one thing just annoys me: uncontrolled proliferation of #is* messages.
Why general Announcement framework should know about every specific annoucement
for example implementing isMethodRemoval ?
That makes me think of the Newspeak doesNotUnderstand hack which install an
invisible ^false method at root object...

Nicolas

nicolas cellier wrote:
> Sure. ++ for Announcements.
> But one thing just annoys me: uncontrolled proliferation of #is* messages.
> Why general Announcement framework should know about every specific annoucement
> for example implementing isMethodRemoval ?

Ah! But that's one of the points of using Announcements. You don't have
to add it too high in the event hierarchy, since you can scope down to
where you need it. E.g., consider this hierarchy:

Announcement
        SystemEvent
                CompilationEvent
                        ClassCompilationEvent
                                ClassAdditionEvent
                                ClassModificationEvent
                                ClassRemovalEvent
                        MethodCompilationEvent
                                MethodAdditionEvent
                                MethodModificationEvent
                                MethodRemovalEvent


Now, only CompilationEvent does need to know about #isMethodRemoval
since you can do, e.g.,

registerForEvents

        SystemChangeNotifier
                on: CompilationEvent
                send: #prefEvent:
                to: self.

Cheers,
   - Andreas

On Thu, 2009-03-05 at 21:32 -0800, Andreas Raab wrote: It sounds really good. I use Announcements for most of my stuff because
you can have specific dependencies that don't need any monkey patching.
I didn't know SystemChangeNotifier but while you are hunting I want to
point you to EventManager which might be replaced after Announcements
found their way into the image.

Norbert

+1 as well, Announcements should be in the core and it's a tiny framework
that many of us use anyway.

Ramon Leon
http://onsmalltalk.com

+1 SystemChangeNotifier is nasty (especially when unloading stuff that
doesn't deliberately handle de-registration). A more "removal tolerant"
system would be nice.

Regards, Gary


----- Original Message -----
From: "Ramon Leon" <[hidden email]>
To: "'The general-purpose Squeak developers list'"
<[hidden email]>
Sent: Friday, March 06, 2009 5:30 PM
Subject: RE: [squeak-dev] An old gripe (or: SystemChangeNotifier+
Announcements = Sanity?)