From: EbFFA <eflatffa@...>
Date: 2009-08-25T15:06:39+09:00
Subject: doubling numbers with Object#object_id

I was playing with Ruby and wrote an interesting method:

    def double n
      n.object_id - 1
    end

    irb> double 5
      => 10
    irb> double 1
      => 2
    irb> double 0
      => 0
    irb> double -101
      => -202
    irb> double 100000001
      => 200000002
    irb> double 10000000000    # into Bignum territory now
      => -606548539

Anyone know why this works? Why Ruby was implemented this way?

I tried creating an object_id collision based on this doubling rule,
but it seems that all Fixnum object_id`s are odd, and all other
object_id`s are even (in fact they all seem to end in 8). Clever.