From: Joel VanderWerf <vjoel@...>
Date: 2007-02-09T06:51:00+09:00
Subject: Re: Class-tree variables

oinkoink wrote:
> There's been a lot of blog traffic lately about class variables vs.
> class instance variables.
> I'd like to give an example of something in-between: class-tree
> variables.  These are sort
> of like class variables, but they only point downward in the
> inheritance tree rather than
> up.  That is, each class in an inheritance tree can get a variable
> which refers to itself and
> all its descendents.  Class-tree variables are implemented by class
> variables, but the
> implementation occurs only in the top (root) class and is inherited by
> the rest of the tree.
...

This is a solution to a slightly different problem (inheritance of 
hashes of attributes), but it might be interesting anyway:

http://redshift.sourceforge.net/superhash/

A little example:

require 'superhash'

class A
   class_superhash :options

   options[:foo] = "A foo"
   options[:bar] = "A bar"

   def options; self.class.options; end
end

class B < A
   options[:foo] = "B foo"
end

p A.options
p B.options.to_hash
p B.new.options.to_hash

__END__

output:

{:foo=>"A foo", :bar=>"A bar"}
{:foo=>"B foo", :bar=>"A bar"}
{:foo=>"B foo", :bar=>"A bar"}

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407