This is very similar to the IE 4.0 object model in which "expando" objects
can assume new properties (and methods) on the fly (an extendable object
model.)
> -----Original Message-----
> From: Ernest Friedman-Hill [SMTP:[EMAIL PROTECTED]]
> Sent: Thursday, September 03, 1998 2:54 PM
> To: [EMAIL PROTECTED]
> Subject: Re: JESS: COOL-like inheritance
>
> Hi Dave,
>
> Hmm. Hadn't thought of this until you mentioned it. Turns out my
> implementation needed only a bit of polishing for this to pop out for
> free.
>
> It's immediately obvious to me why inheriting a defclass from a
> deftemplate is useful: you can make Beans appear to be subclasses of
> make-believe common ancestor classes without writing any Java code -
> i.e., the example I gave with the 'machine' class can be done with a
> deftemplate instead of a defclass; then Pump and Tank no longer need
> to have a common subclass, but you can group them together for the
> sake of pattern matching. It's very neat, actually - if the Beans have
> property names in common, then a common deftemplate 'superclass' can
> let you match on that shared property, even if the Beans are otherwise
> unrelated. I've modified things so that it behaves this way if the
> superclass is a defclass, as well.
>
> In the other direction, I'm not sure it'd be as useful - the subclass
> deftemplates would lose the magical Java-connectedness of their parent
> defclass, which could be confusing.
>
> Hmm. Maybe, though, I can think of a shceme for creating hybrid
> objects which effectively let you add Jess-only properties to a
> defclassed Bean instance. Would that be useful or interesting?
>
>
> I think Dave Carlson wrote:
> >
> > Outstanding! How about another twist, where a deftemplate inherits from
> a
> > defclass, e.g.
> >
> > (defclass machine jess.examples.pumps.Machine)
> > (defclass pump extends machine jess.examples.pumps.Pump)
> > (deftemplate bigpump extends pump (slot foo))
> >
> > I'm thinking about a non-Java programmer who is writing rules. They are
> > provided with a set of Java objects, but need to create a local subclass
> for
> > use within their rulebase.
> >
> > -- Dave
> >
> > At 02:28 PM 9/1/98 -0700, you wrote:
> > >Hi Folks,
> > >
> > >Just sharing a little bit of info about another Jess 4.2 feature:
> > >you'll be able to define inheritance relationships between
> > >deftemplates and between defclasses. Alan Davis was asking about this a
> > >little while ago, and I just had an insight yesterday about how
> > >to do this efficiently.
> > >
> > >Anyway, so what this looks like is this:
> > >
> > >(deftemplate t1 (slot A) (slot B) (slot C))
> > >(deftemplate t2 extends t1 (slot D) (slot E))
> > >(deftemplate t3 extends t1 (slot F) (slot G))
> > >
> > >Now you can write rules which match on patterns of type t1, t2, or
> > >t3. t2 has slots A,B,C,D,E, and t3 has A,B,C,F,G. Furthermore, rules
> > >written to match patterns of type t1 will also match t2 and t3; rules
> > >that match t2 or t3 patterns won't match the other, or t1.
> > >
> > >Similarly, with defclasses. I modified my 'pumps' example Beans such
> > >that both Tank and Pump inherit from a new class Machine, with one
> > >property (name). Then you can write
> > >
> > >(defclass machine jess.examples.pumps.Machine)
> > >(defclass pump extends machine jess.examples.pumps.Pump)
> > >(defclass tank extends machine jess.examples.pumps.Tank)
> > >
> > >and 'machine' rules will match either 'tank' or 'pump' patterns.
> > >
> > >Any comments on syntax, ideas for extensions, or subtleties, let me
> > >know. I considered using 'is-a' as COOL does instead of 'extends' -
> > >any opinions one way or the other?
> > >
>
>
>
> ---------------------------------------------------------
> Ernest Friedman-Hill
> Distributed Systems Research Phone: (510) 294-2154
> Sandia National Labs FAX: (510) 294-2234
> Org. 8920, MS 9214 [EMAIL PROTECTED]
> PO Box 969 http://herzberg.ca.sandia.gov
> Livermore, CA 94550
>
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