From: Gavin Sinclair <gsinclair@...>
Date: 2002-10-12T23:44:17+09:00
Subject: Re: Things That Newcomers to Ruby Should Know


From: "Brian Candler" <B.Candler@pobox.com> [snipped]


>
> However in practise this is efficient, since there appears to be a very
> compact internal representation of references to Fixnums:
>
> irb(main):001:0> 0.id
> 1
> irb(main):002:0> 1.id
> 3
> irb(main):003:0> 2.id
> 5

When I discovered this some time ago, I wondered deeply what might be occupying
id #s 2, 4, 6, ...

Interesting that "id" is documented in 'ri' to return a Fixnum, but:
  1000000001.id              => 2000000003
  1000000001.id.class        => Bignum

I'm surprised that numbers that high have a predictable ID, as if they're
predefined.  But then maybe the numbers are brought into being only as needed
(except for the first 100, like Python), with a special case formulaic approach
to assigning them an ID, and then all non-Integers are given an even ID so they
don't clash.  When I ran

   a = []
   ObjectSpace.each_object { |obj| a << obj }
   a.find { |obj| obj.id % 2 == 1 }

it returned nil, so that must be the case.

What I also found interesting was that successive runs of this testlet seemed
to produce many more objects.

Any comments?

Gavin