From: Ken Bloom <kbloom@...>
Date: 2008-05-02T09:40:13+09:00
Subject: Re: DSL - class-level methods that affect instances

On Thu, 01 May 2008 18:07:11 -0500, Daniel Waite wrote:

> I'm having a problem of design. I've tried a few configurations of class
> collaboration and responsibility, but they all end up feeling messy.
> 
> I'm looking at these (either or, my original attempt was with a module,
> but attr_accessor *looks* like it does what I want):
> 
> class C < Translator::Base
>   translate 'this', :to => 'that'
> end
> 
> class C
>   include Translator
>   translate 'this', :to => 'that'
> end
> 
> With the expectation that...
> 
> c = C.new
> c.translations
> 
> Would yield a hash of the from and to values.
> 
> I have no idea how to break the barrier between class and instance. :(

Use class variables (the @@ variety).

class Translator::Base
  def self.translate word, params
    @@translations ||= {}
    @@translations[word]=params[:to]
  end
  def translations
    @@translations ||= {}
  end
end

class C < Translator::Base
  translate 'a', :to => 'b'
  translate 'c', :to => 'd'
end

C.new.translations #=> {"a"=>"b", "c"=>"d"}


-- 
Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/