# Re: Duplication from a Subclass, Object#become

**URL:** <https://www.ruby-forum.com/t/re-duplication-from-a-subclass-object-become/68438>\
**Category:** Ruby\
**Created:** [September 12, 2006, 6:37pm UTC](https://www.ruby-forum.com/t/re-duplication-from-a-subclass-object-become/68438 "2006-09-12T18:37:28Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![phrogz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/2acd7d/32.png) [@phrogz](https://www.ruby-forum.com/u/phrogz)\
**Post date:** [September 12, 2006, 6:37pm UTC](https://www.ruby-forum.com/t/re-duplication-from-a-subclass-object-become/68438/1 "2006-09-12T18:37:28Z")

</div>

From: ts [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

> G\> class Foo  
> G\> def dup  
> G\> # strange, magical, important things happen here  
> G\> # which know about all of Foo’s instance variables
> 
> You can’t use #initialize\_copy ?

No. In this case, “Foo” is actually REXML::Element. Because these  
objects store all their attributes in an Attributes instance, a standard  
(shallow) dup leaves them referencing the same attribute set:

irb(main):001:0\> require ‘rexml/document’  
=\> true  
irb(main):002:0\> e1 = REXML::Element.new( ‘foo’ )  
=\>   
irb(main):003:0\> e1.attributes[‘bar’] = ‘whee’  
=\> “whee”  
irb(main):004:0\> e2 = e1.dup  
=\>   
irb(main):005:0\> e2.attributes[‘la’] = ‘dee da’  
=\> “dee da”  
irb(main):006:0\> e1  
=\>

So, I really want to use Element#clone, but it returns an REXML::Element  
instance when called from my subclass, and I have no control over its  
source code.

---

<div class="post-metadata">

**Author:** ![phrogz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/2acd7d/32.png) [@phrogz](https://www.ruby-forum.com/u/phrogz)\
**Post date:** [September 13, 2006, 6:26am UTC](https://www.ruby-forum.com/t/re-duplication-from-a-subclass-object-become/68438/2 "2006-09-13T06:26:13Z")

</div>

Gavin K. wrote:

> So, I really want to use Element#clone, but it returns an REXML::Element  
> instance when called from my subclass, and I have no control over its  
> source code.

FWIW, I found that I was able to do (typing from memory):

class Foo \< REXML::Element  
def clone  
klone = self.class.superclass.method( :new ).unbind.bind(  
self.class ).call( self )  
# my stuff here  
klone  
end  
end

…but I think I’ll probably end up re-writing my class to  
wrap/delegate to Element, instead of directly inheriting from it. Pity,  
from an rdoc standpoint.

---

<div class="post-metadata">

**Author:** ![phrogz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/2acd7d/32.png) [@phrogz](https://www.ruby-forum.com/u/phrogz)\
**Post date:** [September 13, 2006, 3:39pm UTC](https://www.ruby-forum.com/t/re-duplication-from-a-subclass-object-become/68438/3 "2006-09-13T15:39:21Z")

</div>

Phrogz wrote:

> self.class ).call( self )  
> # my stuff here  
> klone  
> end  
> end
> 
> …but I think I’ll probably end up re-writing my class to  
> wrap/delegate to Element, instead of directly inheriting from it. Pity,  
> from an rdoc standpoint.

I have to agree with you. Again and again I use subclassing and it  
turns out to be more trouble than it’s worth. Delegating always seems  
to be a better course. It seems to me it’s sort of like duck typing.  
Unfortuately delegating means not being able to easily get under the  
hood of the “super class”, e.g. super and instance variables. I wonder  
it some utility methods could help ease that.

T.