From: pgregory@... (Paul Gregory)
Date: 2002-11-20T00:09:30+09:00
Subject: Need help dynamically creating classes.

I have a system at the moment where I create 'things' based on a base
class SceneObject, these 'things' have a Proc associated with them
that gets called to produce a different representation of the 'thing'
(in my case data to be passed to a 3D renderer). At the moment it all
works like this...

class SceneObject
  def initialize(&generate)
    @generate = generate
  end
  def render
    self.instance_eval(&@generate)
  end
end

class MyObject < SceneObject
  def initialize
    super() do
      # Render some objects
    end
  end
end

a = MyObject.new
a.render

This all works, but I'd like to 'hide' the class definition stuff, the
reason being that the data files passed through this system will be
defined outside, and don't need to look like Ruby code, they 'use'
Ruby code to do the procedural stuff, but other than that I want them
to appear as simple as possible, so hiding classes, inheritance,
initialisation functions etc. would be a big benefit. Ideally I'd like
to do something like this, but can't...

def defineClass(name,&generate)
  eval <<-"end_eval"
    class #{name} < SceneObject
      def initialize
        super(&#{generate})
      end
    end
  end_eval
end

Then in my data files use this function like so...

defineClass("MyObject") do
  # Render some objects
end

a = MyObject.new
a.render


Can anyone offer any advice on how to achieve something like this?

Cheers

PaulG