From: Jacob Fugal <lukfugl@...>
Date: 2006-05-06T01:33:38+09:00
Subject: Re: Constant in Ruby.

On 5/5/06, Charlie <peckcharlie@yahoo.com> wrote:
> Thank you everyone for your input. I got this simple example to share:
>
> A = 10       => 10
> X = A.freeze => 10
> A = 20       => 20
> X            => 10

Check the following irb session to see what's happening:

  >> A = 10
  => 10

  >> A.object_id
  => 21

  >> X = A.freeze
  => 10

  >> A.object_id
  => 21

  >> X.object_id
  => 21

  >> A = 20
  warning: already initialized constant A
  => 20

  >> A.object_id
  => 41

  >> X.object_id
  => 21

  >> X
  => 10

A and X are just references to objects. Setting X equal to A makes X
reference the same object as A referenced at the time, but X does not
reference A directly. So changing what A references (assignment) has
no impact on X -- X just keeps on referencing what it was told to
reference. However, if A and X continue to reference the same object
and you perform an in place modification on either, both will see the
change since they still reference that modified object:

  >> A = "foo"
  => "foo"

  >> A.object_id
  => 1661894

  >> X = A
  => "foo"

  >> A.object_id
  => 1661894

  >> X.object_id
  => 1661894

  >> A << "bar"
  => "foobar"

  >> A.object_id
  => 1661894

  >> X.object_id
  => 1661894

  >> X
  => "foobar"

Jacob Fugal