From: Joel VanderWerf <vjoel@...>
Date: 2005-01-25T05:35:35+09:00
Subject: Re: Complex Library Object/Class and its Interface

Trans wrote:
> Aredridel,
> 
> Would that solve the access problem (i.e. being getting that info from
> the class). I just tried:
> 
> | class Parser::Token
> |
> |  class << self
> |
> |    def inherited(klass)
> |      klass.unit self.unit?
> |      klass.exclusive self.exclusive?
> |      klass.start &self.start
> |      klass.stop &self.stop
> |    end
> |
> |     #...
> 
> That solve the inheritence problem, it look like. But I'm jave
> troubles. I'm starting to think that the problem is simply that I'm
> trying to combine two different objects into one.

This inheritance will not be updated when you change the value in the 
parent class.

This seems to come up often enough that maybe ruby needs a built in way 
to inherit mutable and overridable variables in the class hierarchy. 
Class vars, class instance vars, and constants don't quite do this.

You can do it with superhash:

require 'superhash'

class Token
   class_superhash :stuff
   class << self
     def start(*args)
       if args.size > 0
         self.stuff[:start] = args[0]
       else
         self.stuff[:start]
       end
     end
   end
end

class Marker < Token
   start /marker start/
end

class FooMarker < Marker
end

p Marker.start
p FooMarker.start

__END__

Output:

/marker start/
/marker start/