From: Jacob Fugal <lukfugl@...>
Date: 2006-06-22T07:18:05+09:00
Subject: Re: Achieve pure object oriented design in Ruby

On 6/21/06, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> You can hide it a bit better using a closure, and then attr_accessor
> won't expose it. (Sorry if someone suggested this already...I haven't
> been following closely.)
>
> class A
>   class << self
>     bclass = Class.new do
>       def foo; puts "foo in bclass"; end
>     end
>
>     define_method :new do |*args|
>       bclass.new(*args)
>     end
>   end
> end
>
> A.new.foo # ==> foo in bclass

I think you rather meant:

  class A
    def initialize
      @b_objs = []
    end

    bclass = Class.new do
      def initialize
        puts "creating an instance of bclass"
      end
    end

    define_method :gimme_another_b do |*args|
      @b_objs << bclass.new(*args)
    end
  end

  a = A.new
  a.gimme_another_b # ==> creating an instance of bclass

It looks to me that as long as there is no access to @b_objs, this
successfully hides bclass. But as soon as @b_objs is accessible:

  class A
    attr_reader :b_objs
  end
  bclass = a.b_objs.first.class
  bclass.new # ==> creating an instance of bclass

Not meant to be nitpicking you specifically Joel, just continuing to
demonstrate that one *really* can't prevent things like this in a
language with open and first-class Classes. :)

Jacob Fugal