Design Patterns discussion

[Ray Ye <rayye AT Catena.com>]

Hi Yehoram,

I have to agree that difference between multicast and observer is too
subtle. It depends on how you design the event handler's interface, whether
you use generic one (loosely typed, which encourage type checking, but more
stable with the new types of events), or strongly typed handler interface
(avoids if/else, but with every new event type added, you would have to
change the handler's interface).

It really depends on what kind of your application is.  If you are
developing a framework type of thing, then you would want to use generic
event handler interface, since you can not foresee how the users of your
framework adding what kinds of events. 

Another pattern you may take a look is "event channel", which derives from
observer, but totally decouples the sender and receiver, and uses "channel"
as the intermediate. You can also add "filter" to the channel, and allow
only the handler's interested events sent out.

Cheers,

Ray

-----Original Message-----
From: Yehoram Shenhar 
[mailto:yshenhar AT powerloc.com]
Sent: Wednesday, November 12, 2003 12:20 PM
To: 
gang-of-4-patterns AT cs.uiuc.edu
Subject: [gang-of-4-patterns] Multicast pattern


Hello,

Has anybody had any experience with the Multicast Pattern?
(http://www.research.ibm.com/designpatterns/pubs/multicast.html).

Are there any other patterns to keep an event-based system strongly typed?

Thanks,

Yehoram Shenhar

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