From: Robert Klemme <bob.news@...>
Date: 2005-04-22T23:05:10+09:00
Subject: Re: accessor for Class Variable


"Lyndon Samson" <lyndon.samson@gmail.com> schrieb im Newsbeitrag
news:a39f6ad0050421082652ed737e@mail.gmail.com...
> On 4/22/05, Robert Klemme <bob.news@gmx.net> wrote:
> >
> >
> > Class variables are really only useful if you want to access them from
> > instances and from the class in a similar way (via "@@var_name").
> > Otherwise they have more drawbacks than pros so I avoid to use them
> > whenever I can.  (Can't really remember a case where I actually needed
> > them.)
> >
> What about situations like the following ( taken from an attempt at an
> old rubyquiz )
>
> class Op
>     @@lookup = {}
>     def Op.register(newOp, newOpClass)
>        @@lookup[newOp] = newOpClass
>     end
> end
>
> class AddOp < Op
> ..
> end
> class SubOp < Op
> ..
> end
> class MulOp < Op
> ..
> end
> class DivOp < Op
> ..
> end
>
> Op.register("+", AddOp)
> Op.register("-", SubOp)
> Op.register("*", MulOp)
> Op.register("/", DivOp)
>
> They are not really OO 'clean' but better than globals surely?


Yes, but you still don't need a class var - a standard instance var of the
class is sufficient, as you can see:

class Op
    @lookup = {}
    def self.register(newOp, newOpClass)
       @lookup[newOp] = newOpClass
    end
end

.... and even saves two chars typing that I could use to replace "Op" by
"self" in the method definition :-)))

Kind regards

    robert