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From: rmyers@ics.uci.edu (Richard E. Myers)
Newsgroups: comp.lang.objective-c
Subject: Re: Requirements for Class Variables for Objective-C
Keywords: class variables
Message-ID: <270A66D0.14263@ics.uci.edu>
Date: 3 Oct 90 22:31:43 GMT
References: <5638@stpstn.UUCP>
Reply-To: rmyers@ics.uci.edu (Richard E. Myers)
Organization: UC Irvine Department of ICS
Lines: 52

Though I'm just a novice in Objective-C I have run across a case where
class variables would simplify things.

In answer to your first two questions, I believe class variables would
be useful and that case one would be the better system.

>** 1 -- each subclass has its own copy of its parent's class variables
> 
>   2 -- all subclasses share a single copy of their parent's class variables

  I think at run time each subclass should be thought of as distinct
from its parent and thus have it's own variables.  A programmer
shouldn't have to worry about changes made to the class variables of a
parent class or sibling class effecting its own class variables.
Unless someone can give examples why this ability would be needed then
to minimize side effects system one seems adequate.

  A hypothetical use that makes me favor class variables is as
follows:

  Suppose the first instantiation of a class "PriorityQ" puts its id
into a class variable call "defaultQ".  Subsequent calls to the class
"PriorityQ" using the method "+newORdefault" would then return the id
contained in "defaultQ" or a new id if the "defaultQ" variable is nil.
If (using another method) the variable "defaultQ" was changed then any
new invocations of the "+newORdefault" method would return the new id
in the class variable "defaultQ".

  What bothers me about this example is that (I think) NeXT has produced
a similar effect in their "Conductor" class (which can be found within
the MusicKit).  If class variables don't exist in Objective C then I'm
not sure how they did this.

  I hope I haven't over looked something due to my limited experience
with Objective C.

Cheers,

  -- Richard

-------------------------------------------------------------------------------
 "Programs were devised whose `thinking' was to human thinking as a
 slinky flipping end over end down a staircase is to human locomotion."
							-- D.R. Hoffstadter
-------------------------------------------------------------------------------
Richard Myers / 6 Exeter / Irvine, CA 92715 / 714-854-4410 / rmyers@ics.uci.edu

-- 
-------------------------------------------------------------------------------
 "Programs were devised whose `thinking' was to human thinking as a
 slinky flipping end over end down a staircase is to human locomotion."
							-- D.R. Hoffstadter