[Newbies] class variable vs class instance variable uses

Miguel Enrique Cobá Martinez miguel.coba at gmail.com
Wed Aug 5 19:06:41 UTC 2009

El mié, 05-08-2009 a las 09:15 +0200, Göran Krampe escribió:
> Hi!
> Or to rephrase it once more:
> A class variable is like a global, but only accessible from the class, 
> its instances and from subclasses and their instances. Kinda like a 
> "scoped global". A bit similar to a "static" variable in say Java - 
> "There Can Be Only One" :)
> A class instance variable is a much more "natural" thing really. It is 
> simply an instance variable in the class *itself*. Remember that classes 
> are real objects in Smalltalk and thus can have instance variables as 
> well as behavior.
> Also, this means we naturally have "inheritance on the class side" which 
> means that just like class side methods are inherited by subclasses 
> (unlike static methods in Java which really are just like C functions) 
> these class instance variables are also inherited by subclasses. But 
> remember - inheritance doesn't mean that the subclasses will "see" the 
> variable of the superclass - it means that the subclasses will have 
> their *own* such instance variable, which again is natural since each 
> class is a different object.
> And also, naturally, class instance variables are not accessible from 
> the instances of the class!
> So class instance variables behave just like regular instance variables 
> - but *in the class itself*. Btw, if you type a class name, select it, 
> and press alt-i you get an inspector on the class object and you can see 
> all its instance variables, as you can see there is a whole bunch.
> Yes, this was a much longer explanation but might have cleared up some 
> question marks still lingering. :)
> regards, Göran

Thanks Göran for the alternative explanation. Indeed it fills some gaps
in my understanding and use of those features of squeak.

Miguel Cobá
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