From: Robert Klemme <shortcutter@...>
Date: 2008-09-02T21:19:36+09:00
Subject: Re: Difficult Inheritance Problem

2008/9/2 tobyclemson@gmail.com <tobyclemson@gmail.com>:
> Thank you all for your responses. I ended up using James Coglan's
> solution as that is what I was trying to achieve even if I didn't make
> that clear in my first post. But even so I've learnt something from
> each of your responses.

I believe there is a better approach that solves the inheritance issue
generally.  (Jame's solution will only reuse mappings as long as no
mapping is defined in the current class.) Usually you want to deal
with all the mappings aggregated so far in the inheritance hierarchy.
Thus my solution would be

class DataObject
  class<<self
    attr_writer :difference_mapping

    def difference_mapping
      ancestors.inject({}) do |m,cl|
        m.merge(cl.instance_variable_get("@difference_mapping")) rescue m
      end
    end
  end
end

class Page < DataObject
  self.difference_mapping = {:blah => :blah}
  p [self, difference_mapping]
end

class YourClass < Page
  p [self, difference_mapping]
end

Kind regards

robert


-- 
use.inject do |as, often| as.you_can - without end