From: Eric Hodel <drbrain@...7.net>
Date: 2007-09-27T16:43:48+09:00
Subject: Re: object_id 1, 2, 3


On Sep 26, 2007, at 14:00 , Tim Hunter wrote:

> Also, because of the way operating systems dole out memory to C
> programs, the memory addresses are usually going to be very large
> numbers.

> Of course at this point somebody will pipe up and say that what I just
> wrote is untrue on such-and-such an obscure computer, and they'd be
> right.

You don't need to go quite so far.  OS X starts its heap at a low  
memory address:

$ ruby -ve "p ''.object_id"
ruby 1.8.6 (2007-09-23 patchlevel 5000) [powerpc-darwin8.10.0]
1002180

$ ruby -ve "p ''.object_id"
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-freebsd6]
67351450

Also, the way ruby's heap is constructed, addresses will count down  
then jump up to the next chunk of ruby heap slots (provided that no  
GC is done):

$ ruby -e "p %w[a b].map { |o| o.object_id }"
[1002060, 1002050]

Also, on 64 bit platforms ruby objects are twice as big due to bigger  
pointers and whatnot:

$ ruby -ve "p %w[a b].map { |o| o.object_id }"
ruby 1.8.5 (2006-08-25) [amd64-freebsd6]
[2789280, 2789260]