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From "Conor MacNeill" <co...@cortexebusiness.com.au>
Subject RE: [IDEA] Polymorphic types
Date Tue, 29 Jan 2002 22:52:01 GMT


> -----Original Message-----
> From: Tim Dawson [mailto:tim.dawson@notiva.com]
> Sent: Wednesday, 30 January 2002 7:12 AM
> To: ant-dev@jakarta.apache.org
> Subject: Re: [IDEA] Polymorphic types
>
>
> I like the idea of polymorphic types, but I'm not sure about this
> type of implementation -

Agreed. I was not happy with the implemntation. That is why I have not
proceeded with this in Ant 1.x. The idea is, however, pretty good, IMHO. It
would solve the problem of extensibility in ejbjar, for example.

I have experimented further in mutant, which supports polymorphism,
including allowing add methods to be defined in terms of an interface.

> it requires that the type be a subclass
> of another type, and would prohibit interface implementation from
> working. When I first ran into a similar issue a while back I got
> to thinking that what would be a better approach would be to pair
> this issue with the whole deployment descriptor issue, and have
> each type optionally declare a "property" that would be used to
> set it. (the DD issue comes into play because the third
> declaration by necessity breaks the ability to use the simple
> properties file to map the element name to the class)
>
> By default, the property could be the type itself, e.g. <path>'s
> property would be "path", <and> and <or>'s property would be "condition".
>

I guess I don't really follow what you are proposing here. What I did in
mutant is have the name of the nested element identify the add method which
will be called. An ant:refid attribute can be used to identify an existing
instance to be passed to the method. Alternatively, an ant:type attribute
can be used to identify an Ant typdef'd type, an instance of which is to be
created. Introspection/reflection proceeds using this type instance.
Finally, if no ant:refid or ant:type is used, mutant will try to create an
instance of the argument type of the add method.

> I should (in between day-job and family commitments) be able to
> post this some time this week.
>
> Does the general idea though, of actually registering the
> property name work for people? I think it seems fairly obvious,
> especially when the default is to use the element name.
>

Ummm, not sure. :-)

Conor


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