From: Morton Goldberg <m_goldberg@...>
Date: 2007-09-22T09:38:58+09:00
Subject: Re: question re: modules and class variable scope

On Sep 21, 2007, at 6:53 PM, Got Ascii wrote:

> I spent some time trying to find an answer to this but haven't  
> found an
> explanation I understand.  Could someone tell me what is going on  
> here:
>
> module Mod
>   def self.append_features(base)
>     base.extend ClassMethods
>     super
>   end
>   module ClassMethods
>     def growl
>       puts @@donkey
>     end
>   end
> end
>
> class Animal
>   include Mod
>   @@donkey = "heyhaw"
>
>   def self.working_growl
>     puts @@donkey
>   end
> end
>
> # uninitialized class variable @@donkey in Mod::ClassMethods
> Animal.growl
>
> # works fine
> Animal.working_growl

Class variables are not the same as class instance variables. This is  
one of those cases where you want a class instance variable. If you  
change @@donkey to @donkey, everything will work the way you want it to.

I wonder why you don't use the much simpler

<code>
module Mod
    def growl
       puts @donkey
    end
end

class Animal
    extend Mod
    @donkey = "hee-haw"
    def self.working_growl
       puts @donkey
    end
end
</code>

which gives the same result. Maybe your code is a example reduced  
down from a much more complicated situation?

Regards, Morton