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From: rlw@well.UUCP (Bob Weissman)
Newsgroups: net.lang.st80,net.lang.c++
Subject: Re: Xerox Star "traits"
Message-ID: <754@well.UUCP>
Date: Tue, 11-Mar-86 15:03:30 EST
Article-I.D.: well.754
Posted: Tue Mar 11 15:03:30 1986
Date-Received: Fri, 14-Mar-86 04:29:40 EST
References: <296@bambi.UUCP> <185@umcp-cs.UUCP>
Distribution: net
Organization: Whole Earth Lectronic Link, Sausalito, CA
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Xref: watmath net.lang.st80:328 net.lang.c++:78
Summary: Traits Exist The Traits Article Exists

In article <185@umcp-cs.UUCP>, mark@umcp-cs.UUCP (Mark Weiser) writes:
> In article <296@bambi.UUCP> mike@bambi.UUCP writes:
> >Does someone know how the "traits" multiple-inheritance scheme was implemented
> >on the Xerox Star?  There are a couple of clues in the literature (see
> >for example the paper in the '82 Siggraph proceedings) but the exact
> >implementation details were "beyond the scope of this paper."  Other
> >papers mention something called a "traits manager", but don't say how it
> >works.
> 
> I've used Mesa (have an XDE machine next to me right now), but my reading
> of the traits paper is that it was all done with mirrors, or more exactly,
> managers.  The paper never comes out and says there was any preprocessor
> to Mesa code at all, and if there was, why not say so?  So I think the traits
> business was a discipline, programmer enforced, nothing more.  But I would
> like to know for sure.

I worked on the Xerox Star.  Traits were indeed more than "mirrors" or
"programmer discipline".  The traits mechanism was a true implementation of
multiple-inheritance subclassing.  Yes, there was a pre-processor stage,
called Trait Analysis, which was run once for each version of Star which
introduced new classes, subclasses, or traits.  

I'm hesitant to give out more details, since I don't have a copy of
the trade-secret agreement I signed with Xerox sitting in front of me.

I refer interested readers to the original Traits paper,
"Traits: An Approach to Multiple-Inheritance Subclassing", by
Curry, Baer, Lipkie, and Lee, in the Proceedings of the SIGOA Conference
on Office Information Systems, 1982, ACM order number 611820.  The
article itself is ACM 0-89791-075-3/82/006/0001.

-- Bob Weissman
   G.WEISSMAN@SU-SCORE.ARPA
   ...!well!rlw