From: Joel VanderWerf <vjoel@...>
Date: 2002-11-14T16:23:04+09:00
Subject: Re: Another Newbie question regarding instance variables?

Aleksei Guzev wrote:
> "montana" <montana@buc99.bsd.st> wrote in message
> news:200211131633.gADGXeFJ000838@buc99.bsd.st...
> 
>>The value of an instance variable is only available to the instance of the
> 
> class, whereas the value of the class variable is available to all instances
> of the class? Is this correct?
> 
>>If so the power of an instance variable is then to discern between
> 
> make-ups of similar instances of the same class.
> 
>>Does this sound correct??
>>
>>Thanks.
>>SA
>>
> 
> 
> The class itself is an object too. It's an instance of some class. As well
> as other objects it can have its own variables. Those are called "class
> variables" by consideration. But generally they are instance variables too.
> You should take a closer look at the notion of metaclasses.

Actually, it's clearer to call them "class instance variables".

class C
   @civ = 0        # class instance variable
   @@cv = 1        # class variable
   def foo
     @iv = 2       # instance variable
     p @civ
     p @@cv
     p @iv
   end
end


c = C.new.foo
     # ==> nil     because c has no @civ defined
     #     1       shared by C and c
     #     2