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Date: Wed, 22 Aug 2007 10:14:57 -0700 (PDT)
From: Matt Benson <gudnabrsam@yahoo.com>
Subject: Re: svn commit: r568511 -
 /ant/core/trunk/src/main/org/apache/tools/ant/PropertyHelper.java
To: Ant Developers List <dev@ant.apache.org>
In-Reply-To: <dffc72020708221003s544b32e9g2f40b90f10dc7e12@mail.gmail.com>
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--- Peter Reilly <peter.kitt.reilly@gmail.com> wrote:

> On 8/22/07, Matt Benson <gudnabrsam@yahoo.com>
> wrote:
> >
> > --- Peter Reilly <peter.kitt.reilly@gmail.com>
> wrote:
> >
> > > On 8/22/07, Matt Benson <gudnabrsam@yahoo.com>
> > > wrote:
> >
> > [SNIP]
> > > > though I'd still like an opinion on the proxy
> > > > mechanism I suggested for delegate
> recursion...
> > > :)
> > >
> > > I did not reply because I did not understand the
> > > proposal :-)
> > >
> > [SNIP]
> >
> > Okay--when a PH calls a delegate it passes itself
> down
> > in case the delegate needs to make calls against
> the
> > PH.  This would imply a sort of property decorator
> > pattern.  Anyway, I think in this case a delegate
> > calling PH.get() might need to be able to discern
> the
> > difference between NullReturn and no-such-property
> > null.  The first thing that occurred to me was
> that
> > the PH could pass the delegate not itself, but a
> sort
> > of proxy to itself that would fail to decode
> > NullResult but instead return it to the delegate
> > unharmed so that the delegate could handle the
> > difference between them.  Since this would need to
> be
> > passed down over and over again I thought it could
> > live as a member of each PropertyHelper instance.
> 
> I think that I sort of follow, however I do not
> think that
> it can be a member of the PH instance since PH needs
> to be ThreadSafe.
> 
> My idea was that the nullreturn was a message to PH
> (i.e.
> end the chain) and not to the PH delegates.
> 
> Perhaps a new method PH.evalulateProperty(project,
> name) (like
> PH.getProperty(project, name),
>    could return a PHResultObject -
>    the tostring of which would be the current
> stringy form - ie
>    ${xx} (a delegate could change this to a "null"
> and the getObject()
>    would return null or the object
>    if present. setX(String, File etc) would be
> called with the
>    toString() method and setX(Object) would be
> called with the
>    getObject() method.
> 
>   If a delegate can resolve a property, it can
> return a PHResultObject
>   if it wants to do something like handing nulls.
> 
> 

My mind is swimming, and I don't really have the time
to try and make complete sense of all this right now. 
:(  I would say we could just leave the issue until it
causes a problem, but I'd rather have as many issues
as possible ironed out before 1.8.0 is released or
we'll have further API ugliness.  But we've got some
time until then.

-Matt

> Peter
> 
> 
> >
> > Does that make sense?
> >
> > -Matt
> >
> >
> >
> >
>
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