From: Jeremy Bopp <jeremy@...>
Date: 2010-10-15T00:21:23+09:00
Subject: Re: Freeze method doesn't work

On 10/14/2010 10:00 AM, Sergey U. wrote:
> Freeze should prevent further modifications to 'var'...
> 
> mac-undrgrnd:~ yspro$ irb
> ruby-1.9.2-p0 > var = 4
>  => 4
> ruby-1.9.2-p0 > var.frozen?
>  => false
> ruby-1.9.2-p0 > var.freeze
>  => 4
> ruby-1.9.2-p0 > var.frozen?
>  => true
> ruby-1.9.2-p0 > var = 5
>  => 5
> ruby-1.9.2-p0 > var.frozen?
>  => false
> ruby-1.9.2-p0 >
> 
> What's wrong?

The freeze method doesn't operate on var itself.  It operates on the
object that var references, so the Fixnum object for 4 was frozen in
your test.  However, you are allowed to replace that object with another
any time you please.  The freeze method only prevents you from changing
the object itself:

irb(main):001:0> var = 'abc123'
=> "abc123"
irb(main):002:0> var.frozen?
=> false
irb(main):003:0> var.freeze
=> "abc123"
irb(main):004:0> var.frozen?
=> true
irb(main):005:0> var.sub!(/\d/, 'n')
TypeError: can't modify frozen string
        from (irb):5:in `sub!'
        from (irb):5
        from :0
irb(main):006:0> var
=> "abc123"
irb(main):007:0> var = 'abcn23'
=> "abcn23"
irb(main):008:0> var.frozen?
=> false


-Jeremy