From: Daniel Waite <rabbitblue@...>
Date: 2008-05-02T09:55:45+09:00
Subject: Re: DSL - class-level methods that affect instances

Ken Bloom wrote:
> On Thu, 01 May 2008 18:07:11 -0500, Daniel Waite wrote:
> 
>> class C
>> 
>> 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"}

That works! Except it shares translations across all subclasses.

module Translator
  class Base

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

    def translations
      @@translations ||= {}
    end

  end
end

class C < Translator::Base

  translate 'a', :to => 'b'
  translate 'c', :to => 'd'

end

class D < Translator::Base

  translate 'this', :to => 'that'

end

irb(main):028:0> c = C.new
=> #<C:0x4d4e0>
irb(main):029:0> c.translations
=> {"a"=>"b", "c"=>"d", "this"=>"that"}

While I understand the behavior, its undesirable. I'm going to dust off 
Ruby for Rails...
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