From: Daniel Martin <martin@...>
Date: 2006-08-16T20:44:52+09:00
Subject: Re: [QUIZ] Newbie doubts about the quiz

"Kroeger, Simon (ext)" <simon.kroeger.ext@siemens.com> writes:

> You know I like NArray, but perhaps there is an even 
> cooler way this time :)
>
> -----------------------------------------------
> my_array = [1, 2, 3]
> another_one = [1, 2, 3]
>
> p my_array[-1] #=> 3 grmpf...
> p another_one[-1] #=> 3 yeah, what else?
>
> class << my_array
>   def [] index
>     return nil if index < 0
>     super
>   end
> end
>
> p my_array[-1] #=> nil, hehe, nice!
> p another_one[-1] #=> 3 woot, woot
> -----------------------------------------------
>
> I don't know if this is really the right way, but the 
> OP was asking for a super-cool Ruby-esque way, right?

Well, yeah, but in the context of the problem what you need is a
two-dimensional array:

n = (ARGV.first||'6').to_i
my_array = Array.new(n) {
  inner = Array.new(n) {0}
  class << inner
    def [] index
      return nil if index < 0
      super
    end
  end
  inner
}
class << my_array
  def [] index
    return [] if index < 0
    ret = super
    return [] if ret == nil
    ret
  end
end

I could compress three lines there into "super or []", but I don't
know if the OP wants to maybe use "true" and "false" as values in his
array.

Once you do this, you properly get nil for all of:

my_array[0][-1]
my_array[-1][0]
my_array[n][0]
my_array[0][n]

Now, can someone build this into a generic n-dim array class without
using all these singleton classes?