From: James Coglan <jcoglan@...>
Date: 2008-08-27T18:54:20+09:00
Subject: Re: Difficult Inheritance Problem

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> Is there a way to define a class level variable that descends down the
> inheritance tree unless it is overridden in the same way as this is
> possible for methods? I mean I could wrap the data structure in a
> method but that does not seem like a very clean solution.



Try this, perhaps:



class DataObject
  class << self
    attr_writer :mapping

    def mapping
      @mapping || (self == DataObject ? nil : superclass.mapping)
    end
  end
end

class Page < DataObject; end

DataObject.mapping = 'foo'

puts Page.mapping #=> 'foo'



You could write a class helper to generate these methods. I think Rails has
something called 'write_inheritable_attribute' somewhere that does the same
thing.

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