From: ara.t.howard@...
Date: 2006-05-13T02:48:50+09:00
Subject: Re: Inheriting class-based state

On Sat, 13 May 2006, Joel VanderWerf wrote:

> Well, there are "class variables", written @@my_name. But they can have
> some surprising behaviors in current ruby(*), and in future ruby they
> will not be shared up and down the inheritance hierarchy (they will only
> be shared between a class and its instances).
>
> An alternative:
>
> class A
>  class << self
>    attr_accessor :__my_name
>
>    def my_name; A.__my_name; end
>    def my_name=(n); A.__my_name = n; end
>  end
> end
>
> class B < A
> end
>
> B.my_name = "fred"
>
> p A.my_name  # ==> "fred"

one can just use traits for this:

   harp:~ > gem install traits


   harp:~ > cat a.rb
   require 'traits'
   class A; class_trait 'my_name' => 'fred'; end
   class B < A; end

   p A.my_name
   p B.my_name

   B.my_name = 'joe'

   p A.my_name
   p B.my_name


   harp:~ > ruby a.rb
   "fred"
   "fred"
   "fred"
   "joe"


voila - best of both worlds - shared __and__ overridable values if required.


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