consistency again ( was: Notation for delegation in OMT or BOOCH )

Brook Conner dbc at
Wed Jul 20 02:31:39 UTC 1994

**> On Tue, 19 Jul 94 16:46:53 -0700, Bruce McKenzie <bruce at> said:
 [ more deleted ]
> I would not complicate the implementation for consistency unless there
> was a real gain. I can imagine some pretty useless stuff ( I suggested
> method parents about two years ago :-)  :

  Bruce> possibility of implementing a conscience for an object. Namely,
  Bruce> "Normally, I implement all setPosition:: messages, but when the system
  Bruce> is in a 'panic' state, I ignore them." (implying that "setPosition::"
  Bruce> is a family of messages, and you don't want to put the same state
  Bruce> checking code in each one)

  Bruce> Objective-C provides capabilities to do this, but it would be a bit of
  Bruce> a hack.

  Bruce> Does this sound useful? Have people experimented with this?

Oh yes, it's useful. It can be used in time-critical computing
scenarios to handle different ways of implementing things -- e.g., the
fast-but-sloppy way versus the slow-but-accurate way. For example,
when showing an animation, you might want to keep the frame rate
consistent. So, if the frame rate falls behind, you simply tell the
thing displaying the frames to use a faster method (by telling it to
use a new parent) of getting the frames onto the screen (e.g., half as
many bits, or don't do it at all). When the time becomes available,
change the parent again, back to the slow way of putting the entire
frame on the screen.

Something like this (using your "panic" idea) (excuse the syntax --
consider this semi-pseudocode):

noPanicWay = (| setPosition <- aPoint |)
panicWay = (| setPosition. 
	setPosition: foo = (|| self) "Ignore the argument and don't
myPanicSafeObject = (| parent* <- noPanicWay.
			panic = (|| parent: panicWay ).
			unpanic = (|| parent: noPanicWay )

Now, when you tell myPanicSafeObject to panic, it starts ignoring
assignments. When you unpanic it, it starts performing assignments.


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