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From "Adam Murdoch" <>
Subject RE: cvs commit: jakarta-ant/proposal/myrmidon/src/testcases/org/apache/myrmidon/components/configurer
Date Sun, 10 Feb 2002 07:59:02 GMT

> -----Original Message-----
> From: Peter Donald []
> Sent: Saturday, 9 February 2002 7:25 PM
> To: Ant Developers List
> Subject: Re: cvs commit:
> jakarta-ant/proposal/myrmidon/src/testcases/org/apache/myrmidon/componen
> ts/configurer
> On Sat, 9 Feb 2002 20:10, Adam Murdoch wrote:
> > > I still don't understand the motivation for this. Instead of
> > > MyRole lets say
> > >
> > > interface Condition extends DataType {}
> > >
> > > add( Condition c );
> > >
> > > Why would you want to look up an arbitrary DataType? Wouldn't it
> > > be best to
> > > just look up types that implement Condition?
> >
> > Absolutely.  The trick is to come up with a type definition system that
> > lets you figure out which types implement the role interface, while also
> > making those same types available via <property> or TypeInstanceTask.
> Okay 
> > Any thoughts on a better solution?
> Whats wrong with automagically generating this via xdoclet or something 
> similar to what it is doing now? Thus any class that implements DataType 
> directly or indirectly must have a 
> @ant:data name="foo"
> if it wants to be exposed in property or via TypeInstanceTask?

Sure, but you have to have a tag for each of the role interfaces the type happens to implement,
directly or indirectly.  This isn't a bad thing if you want complete control over where a
type can be used.

Personally, I couldn't care less where a type that I write gets used.  I want Ant to figure
it out for me.  Same with the implicit TypeInstanceTask - I want that to just happen.  So,
when I write a type, I don't want to have to do anything more than add a *single* tag that
says 'this is a data-type, and this is its name', and have Ant do the rest for me.

The solution we come up with should deal with both styles.  Unfortunately, I don't think we
can do all this via XDoclet, some of it's going to have to happen when the type is deployed.

How about we use two separate tags to define types:

@ant:data-type name="blah"

Would indicate that the type is to be implicitly registered under all roles that it implements,
and as a TypeInstanceTask.

@ant:type role="some-role" name="blah"

Would indiciate that the type is to be registered only under the specified role.  A type would
have one of these tags for each role that it is to be registered under.

These two tags would probably just translate into an 'implicitRoles' attribute on the type
definition in the antlib descriptor.  The deployer (or more likely some pluggable component)
would take care of implicitly registering the type under all roles that it is castable to,
and adding a TypeInstanceTask definition for the type.


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