From: Robert Klemme <shortcutter@...>
Date: 2012-09-18T16:49:55+09:00
Subject: Re: Bug or feature

On Tue, Sep 18, 2012 at 9:36 AM, Damjan Rems <lists@ruby-forum.com> wrote:
> There has probably been some discussion about this problem so sorry if I
> am repeating but it is so crucial that should be mention every once in a
> while.
>
> This simple example:
>
> a=['0']
> 1.upto(2) do
>   b = a.clone
>   c = a.clone
>   b[0] << '1'
>   c[0] += '2'
> end
> p a
>
> yields ['011'] in ruby 1.8.6 and 1.9.3. I think that it should be ['0']
>
> I understand the difference between << an += operator but shouldn't
> clone method make a duplicate of object a, without any link to original
> object.
>
> Or am I missing something.

Yes. #clone is just shallow copy.

irb(main):002:0> a=['foo', 'bar']
=> ["foo", "bar"]
irb(main):003:0> a.map &:object_id
=> [-1072256208, -1072256218]
irb(main):004:0> b = a.clone
=> ["foo", "bar"]
irb(main):005:0> b.map &:object_id
=> [-1072256208, -1072256218]
irb(main):006:0> a.zip(b).all? {|x,y| x.equal? y}
=> true

For full object tree copy you can do

irb(main):007:0> c = Marshal.load(Marshal.dump(a))
=> ["foo", "bar"]
irb(main):008:0> c.map &:object_id
=> [-1072289088, -1072289108]
irb(main):009:0> a.zip(c).all? {|x,y| x.equal? y}
=> false

Kind regards

robert


-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/