From: Joel VanderWerf <vjoel@...>
Date: 2007-03-27T12:34:14+09:00
Subject: Re: Class Variables for subclases...

Sonny Chee wrote:
> Hey Guys,
> 
> Check out the following:
> 
> class A
>   @@anobject = 'green'
>   def fun2
>     @@anobject
>   end
> end
> 
> class B < A
>   @@anobject = 'blue'
>   def fun2
>     @@anobject
>   end
> end
> 
> puts B.new.fun2    # blue
> puts A.new.fun2    # blue
> 
> So it looks like the subclass B is not defining its own class variable
> but reusing A's class variable @@anobject. Is there a different way to
> specify class variables to overcome this issue?
> 
> Sonny.
> 

You may find it more suitable to use instance variables in your class 
objects, and write accessors so you can get at them from instances of 
your classes.

For example:

class A
   @anobject = 'green'
   def self.anobject
     @anobject
   end
   def fun2
     self.class.anobject
   end
end

class B < A
   @anobject = 'blue'
end

puts B.new.fun2    # blue
puts A.new.fun2    # green


Google (or search the list) for 'ruby class instance variable'.

I think the 'traits' gem does this in a systematic way, though of course 
it's worth playing around to understand the concept first.

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407