From: ara.t.howard@...
Date: 2006-04-12T00:52:01+09:00
Subject: Re: class variables and inheritance (ActiveRecord problem)

On Wed, 12 Apr 2006, Andrew Thompson wrote:

> Stephen Bannasch wrote:
>
>> I'd like to be able to create a class variable that will apply to all
>> objects made from that class and ALSO create a derived class with a
>> different class variable that is used in objects created from the
>> derived class WITHOUT affecting the class variable defined in the
>> original class.
>
> Try a class instance  variable vs a class variable:
>
> class C
>    @somevar = 'x'
>    class << C
>        def somevar
>            @somevar
>        end
>
>        def somevar=(var)
>            @somevar=var
>        end
>    end
> end
>
> Its not as easily accessible as a class variable (only accessible from
> class methods) and you'd have to initialize it to something in derived
> classes (otherwise it's nil) but its non-inherited. Not totally what you
> want, but maybe it'll help.
>
> Andrew

this is one of the things traits.rb solves:

   harp:~ > yes | sudo gem install traits.rb > /dev/null 2>&1


   harp:~ > cat a.rb
   require 'traits'

   class Base
     class_trait 'a' => 42
   end

   class Derived < Base
   end

   class Derived2 < Base
     a 42.0
   end

   p Base.a
   p Derived.a
   p Derived2.a


   harp:~ > ruby a.rb
   42
   42
   42.0

the inheritence is smart and allows overriding.

regards.

-a
-- 
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama