Back when Vassili first started talking about Announcements, I really didn't see the point - I had just switched BottomFeeder over from change/update to Trigger Events, and those seemed sufficient. Now that I've been working with Widgetry (Swallow), I see what the advantage is. Consider a trigger event that notifies you of a keyboard event:

Subscribing:

someObject when: #keyboardEvent send: keyboardEvent: to: self

This depends on the triggering object sending an argument along:

kbdHandler triggerEvent: #keyboardEvent with: keyboardEventObject

Which is fine, except for one thing - the object being sent is sent more or less simply by convention, and the triggering object has to send it along. Now consider the way an Announcement works:

Subscribing:

	(self paneAt: #input) inputField 
		when: KeystrokeAboutToBeProcessed
		send: #possibleCREvent:
		to: self.

What do I expect to see as the argument? An instance of the KeystrokeAboutToBeProcessed class - so instead of pushing symbols around, we push full objects around. This particular one is sent like this:

targetPane 
	announce: (KeystrokeAboutToBeProcessed keyboardEvent: aKeyboardEvent)

The nice thing is, we've moved "up" a level from symbols to objects. None of that was clear to me back when I read about it - it's like an "aha moment" all over again.

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