From: Michael Artz <mlartz@...>
Date: 2007-06-06T00:29:27+09:00
Subject: Re: Deep Copy

Robert Klemme wrote:
> On 05.06.2007 16:45, Michael Artz wrote:
>> I'm needing to implement a deep copy operation on a couple of objects,
>> and was wondering if there was a "best practices" for this sort of
>> thing.  I've seen the Marshal.load(Marshal.dump()) idiom, but I'm using
>> singleton classes which can't be dumped.
> 
> It seems they can be dumped - but you get another instance:

hmm, my classes are structured as:

class A
  class B
    class C
    end
  end
end

... and ...

c = A::B::C.new
Marshal.dump(c)

... seems to work just fine, so I'm not quite sure what is going on with 
my code, as I still get a "TypeError: singleton can't be dumped" from 
Marshal.dump.  I'll have to play around with it a bit more.

> You can use #instance_variable_get and #instance_variable_set to access
>   them.

Sweet, thanks!

> Did you consider overriding #dup and / or #clone for this?  Typically
> you would not want a cloned / duped instance to refer to the original
> instance's instance variables (at least if they are mutable like
> collections, strings and other objects).

Yeah, but I can't seem to wrap my head around the recursive cloning. 
For example, in the above scenarion (A::B::C), how do I allocate space 
for the new object without calling clone/dup?  I.e, I'm sure that you 
realize the problem with the following:

class A
  class B
    class C
      def clone
        other = self.clone
      end
    end
  end
end

So how do I get the "other" object within the clone method?  Do I need 
to allow my initialize method to take in an object of the same type and 
perform all the work of the clone method, or is there a better way?

Thanks
-Mike

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