From: "Gennady F. Bystritsky" <gfb@...>
Date: 2002-11-15T01:19:28+09:00
Subject: Re: Another Newbie question regarding instance variables?

I thought that I knew Ruby pretty well until I came accross this thread
about "class instance variables". It always haunted me why it does not work
when I do

   @var = value

outside any method definition, meaning initialization of an instance
variable. Now I see why. Hence the question: is there any practical use for
"class instance variables"? If so, would anybody post an example?

Thanks,
Gennady Bystritsky.

----- Original Message -----
From: "Joel VanderWerf" <vjoel@PATH.Berkeley.EDU>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Wednesday, November 13, 2002 11:23 PM
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
>
>
>
>
>