Re: Why does DEF do instancing? (fwd)

jjc ([email protected])
Mon, 16 Oct 1995 11:28:06 -0800

At 10:03 AM 10/16/95, Paul S. Strauss wrote:
>On Oct 13, 5:30pm, Bernie Roehl wrote:
>
>> Chris Laurel writes:
>> > Finn Aarup Nielsen writes:
>> > > I seems stranges to me why the DEF command is instancing.
>> >...
>> Yes, it's legal. Yes, it's portable. And yes, it's an ugly kludge that
>> could be avoided by having a non-instancing DEF.
>
>Several people have suggested replacing this "ugly kludge" with
>difserent ugly kludges, including a non-instancing DEF. (Don't
>even try to claim that's not a kludge.)
>
If end users _are_ going to be using VRML directly, then one can make an
argument that a Prototype/Instantiate semantic is more intuitive than the
current DEF. Gavin wanted an example -- try "Shapes" in Strata Pro. I
disagreed with Gavin's comparison of (bad) C programming as an example of
the need to DEF and USE things in place
(declare-in-place-scalar-C-variables are NOT even analogous to object
definition, IMHO). A better (and obvious) comparison would be C++ objects
-- and they require a hsader file with a non-instantiating DEF.

If end users are NOT going to be using VRML directly, and it becomes the
domain of language generators, authoring tools, compilers, etc., as some
people have suggested, then the intuitive ease is less an issue than
efsiciency and language semantics, and the current DEF is a big lose here
also.

>Instead, why doesn't someone just write a couple of filters that
>translate some sort of programming language into VRML and back?
>That way, you could add whatever features you like and not have
>to clutter VRML with things that end users don't care about?
>
>Any volunteers?

The issue is how to define one of the fundamental constructs of the language!
That's hardly something people don't care about. If end users don't care
about it, then it's because they won't be using it at all, along with any
of the rest of the language (see P. 2 above). Otherwise to anyone who is
actually involved in using the language itself, it's critical.

jeff

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