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From "Magesh Umasankar" <>
Subject Re: [IDEA] Polymorphic types
Date Wed, 16 Jan 2002 21:55:30 GMT
From: Conor MacNeill <>

Sorry for the delayed response...  As you might have guessed,
I am finally around to cleaning up some mails... ;-)

> Attached is a patch to the IntrospectionHelper to give a little 
> ploymorphic behaviour for nested elements. I haven't committed this as I 
> thought I'd get some reaction first.

Idea to provide polymorphic behavior is great!

> Basically what this patch does is the following: When a nested creator 
> cannot be found for a particular nested element, a check is done to see 
> if the element corresponds to a datatype. If it does, a search is done 
> for a superclass of the datatype for which the class does have an addXXX 
> style creator.


> In practice, this allows me to use derived types with core tasks without 
> needing to change the core task. For example, if I wanted to use a 
> classfileset type in a <copy> task, I do not need to change copy to add 
> a addClassfileSet() method. I can just use this
>      <copy todir="deptest">
>        <classfileset dir="build/classes" 
> baseclass="build/classes/org/apache/tools/ant/Main.class"/>
>      </copy>

As Stefan said is his email, an interface/implementation
model would be ideal.

> It isn't perfect since some tasks use rolenames in their nested elements
> <blah>
>      <fromfileset>
>      <tofileset>
> </blah>

Maybe you could introduce an optional attribute named 
ispolymorphic to the <fileset> interface?  This would by
default be true.  Users who do not want to use this
feature would set this to false thereby overriding the
polymorphic behavior.

> Nevertheless, I think the patch is useful and makes it much more 
> meaningful to define derived types.

I agree.

> Conor


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