From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-02-05T06:00:43+09:00
Subject: Re: [contest] Code challenge

On Wed, Feb 05, 2003 at 05:01:28AM +0900, Yukihiro Matsumoto wrote:
> Hi,
> 
> In message "[contest] Code challenge"
>     on 03/02/05, Mauricio Fern�ndez <batsman.geo@yahoo.com> writes:
> 
> |   You are expected to subclass Unbreakable::A and find a way to override
> |   method #a. Normally all your code should be in the indicated position.
> |   Class B must be directly derived from Unbreakable::A. The following is
> |   not a valid solution:
> |class B
> |  def a; puts "You won!"; end
> |  def kind_of? a
> |    true
> |  end
> |end
> |
> |  Warning
> |
> |   This mission is, to the best of my current knowledge, impossible.
> 
> Is this a valid answer?
> 
>   class B < Unbreakable::A
>     def a; puts "You won!";       end
>     # PUT YOUR CODE HERE!
>     p Unbreakable::A.instance_eval{@no_override.clear}
>     def a; puts "You won!";       end
>   end

I guess yes.
To be honest I thought of that but either overlooked its potential or
forgot to freeze the class iv. (can't remember) :-) Wish I could say I
left it as a back-door, but that is not the case.

But now, what happens if I do:

...
  def no_redef(*args)
    @no_override ||= []
    args.each { |i| @no_override << i }
    @no_override.freeze
  end
...

Is it impossible enough now? ;-) 

My ultimate goal with this contest is seeing if it is at all possible to
prevent redefinition unconditionally, against all attacks. 

And I learn a great deal along the way, too.
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