From: Rajinder Yadav <devguy.ca@...>
Date: 2009-10-16T12:51:37+09:00
Subject: Re: deep cloning, how?

Robert Klemme wrote:
> On 10/15/2009 08:07 PM, Caleb Clausen wrote:
>> On 10/14/09, Robert Klemme <shortcutter@googlemail.com> wrote:
>>> On 14.10.2009 19:03, Caleb Clausen wrote:
>>>
>>>> The documentation of Object#dup seems to suggest that subclasses
>>>> should not override dup, preferring to override clone instead.
>>> Where do you take that from?  In the docs referenced below I cannot find
>>> anything like that.  The only indication I can see is that #dup uses
>>> #initialize_copy and we should probably override that instead of #dup
>>> itself.
>>
>> I'm looking at these 2 sentences:
>>
>>      In general, +clone+ and +dup+ may have different
>>      semantics in descendent classes. While +clone+ is used to duplicate
>>      an object, including its internal state, +dup+ typically uses the
>>      class of the descendent object to create the new instance.
>>
>> Frankly, I've never been real sure what this is supposed to mean, so
>> my reading may well be wrong. In fact, it probably is.
>>
>> initialize_copy apparently is used by both dup and clone. You're
>> right, that should be defined (overridden?) instead of dup/clone
>> themselves. I rarely remember that.
> 
> Mee, too. :-)  Just for the reference
> 
> irb(main):019:0> class X
> irb(main):020:1> def initialize_copy(*a) p [self,a] end
> irb(main):021:1> end
> => nil
> irb(main):022:0> x=X.new
> => #<X:0x8670108>
> irb(main):023:0> x.dup
> [#<X:0x865d9cc>, [#<X:0x8670108>]]
> => #<X:0x865d9cc>
> irb(main):024:0> x.clone
> [#<X:0x864ddb0>, [#<X:0x8670108>]]
> => #<X:0x864ddb0>
> 
> And it's noteworthy that frozen state is only established _after_ 
> initialize_copy has returned:
>

Celeb, Robert thanks for bringing this point home. I keep having to update my 
Ruby notes =) .... let me try the initialize_copy way!

> irb(main):025:0> class X
> irb(main):026:1> def initialize_copy(old)
> irb(main):027:2> @x=1
> irb(main):028:2> end
> irb(main):029:1> end
> => nil
> irb(main):030:0> X.new.freeze.clone
> => #<X:0x86451b0 @x=1>
> 
>>> There are more differences namely in the area of frozen and tainted 
>>> state.
>>>
>>> http://www.ruby-doc.org/core/classes/Object.html#M000351
>>> http://www.ruby-doc.org/core/classes/Object.html#M000352
>>
>> Ah, yes. But only frozen state, not tainted.
> 
> Right you are.
> 
> Kind regards
> 
>     robert
> 


-- 
Kind Regards,
Rajinder Yadav

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