From: David Masover <ninja@...>
Date: 2009-02-09T06:42:14+09:00
Subject: Re: best way to protect class instance variables

Robert Dober wrote:
> On Sun, Feb 8, 2009 at 9:48 PM, David Masover <ninja@slaphack.com> wrote:
> What about fine graining the control to the closure?
>   
Doesn't really matter, so long as it can be read and duplicated 
satisfactorily to fool the rest of the module. And your method doesn't 
quite work -- I assume you were wanting blah to return something with [] 
methods that restrict access to the scope'd blah?

class MyBlah
  blah = [0,1]
  @blah = Object.new
  @blah.extend(Module.new do
    define_method :[] { |i| blah[i] }
    define_method :[]= do |idx, value|
      do_checks
      blah[idx] = value
    end
  end)
  class << self
    attr_reader :blah
  end
end

Of course, this prevents the internal array from being modified, so I 
see the point -- if there are other methods sharing the same scope. Even 
then, it's still possible to obliterate the whole thing, it's just not 
as easy to change what a method does by changing the array out from 
under it.

Interesting exercise -- still going to recommend that you don't do this 
without good reason. It's not sufficient to prevent evil things if you 
eval untrusted code, and it's complete overkill versus just having good 
documentation and conventions.