From: dblack@...
Date: 2002-08-13T21:21:00+09:00
Subject: Re: Sibling rivalry and class variables

Hi --

On Tue, 13 Aug 2002, Jim Weirich wrote:

> A class instance variable is just a variable that belongs to the class
> object rather than an instance of the class.  You have to do a little
> work to reference a class instance variable from an object of that
> class (setting up a class method is sufficient, perhaps there is an
> easier way).
>
> Elaborating on this suggestion, you could do the following ...
>
>     class Parent
[...]
>       def self.show_civ
>         puts @civ
>       end
>     end
>
>     class Son < Parent
[...]
>       def self.show_civ
>         puts @civ
>       end
>     end

No need to redefine show_civ in the children, is there?

Just for fun, here's a slight variant on your example, using a
technique to create the class's instance variable which for some
reason I've always found rather neat:

    class Parent
      class << self; attr_reader :civ; end
      @@cv = "Parent Class Variable"
      @civ = "Parent Class Instance Variable"
      def show_civ
        puts type.civ
      end
      def show_cv
        puts @@cv
      end
    end

    class Son < Parent
      @@cv = "Son Class Variable"
      @civ = "Son Class Instance Variable"
    end

    class Daughter < Parent
      @@cv = "Daughter Class Variable"
      @civ = "Daughter Class Instance Variable"
    end


(Uh oh, I might end up back at the self.writer=(x) thread if I go much
further... :-)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav