From: "Brian Schröder" <ruby@...>
Date: 2004-12-11T08:35:17+09:00
Subject: Re: How to make a deep copy of an object (Searching for Idiom)

On Sat, 11 Dec 2004 08:27:25 +0900
Tim Hunter <cyclists@nc.rr.com> wrote:

> Brian Schr�der wrote:
> 
> > Hello Group,
> > 
> > I sometimes which to make a deep copy of an object. I know I could use
> > Marshal, but thats slow so I want to write a routine #deep_copy. (Or
> > should I overwrite
> > #dup ?)
> 
> Brian, the classes in my new RVG library must have deep_copy methods. I
> asked this question on c.l.r a few weeks ago but didn't get any
> suggestions. I did some searching around and found some an old thread on
> ruby_talk which helped, but with ruby-talk down I can't find it right now.
> 
> The general form looks like this:
> 
>             def deep_copy
>                 copy = self.class.new
>                 ivs = instance_variables
>                 ivs.each do |iv|
>                     itv = instance_variable_get(iv)
>                     otv = case
>                         when itv.nil?
>                             nil
>                         when itv.respond_to?(:deep_copy)
>                             itv.deep_copy
>                         when itv.respond_to?(:dup)
>                             itv.dup
>                         else
>                             itv
>                         end
>                     copy.instance_variable_set(iv, otv)
>                 end
>                 return copy
>             end
> 
> The idea is that the instance variables can refer 1) to other objects that
> have a deep_copy method, 2) to "normal" Ruby objects that can be duped, and
> 3) to immediate objects like Fixnum which don't need to be duped, just
> assigned. I also have a special case for nil since it responds to :dup but
> can't actually be duped.
> 
> If #initialize takes arguments, then you'll need a slightly different
> version.
> 
> For testing purposes I also implemented a deep_equal method with the same
> general form.
> 
> P.S. I'd appreciate any hearing any criticisms.
> 

Interesting. But this won't work for instance variables that point to arrays of
deep_copy-able objects. Right?

Maybe this is connected to the "object-state" thread floating around somewehere
else.

Regards,

Brian


-- 
Brian Schr�der
http://ruby.brian-schroeder.de/