Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!orstcs!mist!budd
From: budd@mist.CS.ORST.EDU (Tim Budd)
Newsgroups: comp.lang.c++
Subject: Re: Arguments to Overloaded Operators
Message-ID: <11069@orstcs.CS.ORST.EDU>
Date: 9 Jun 89 21:59:53 GMT
References: <11032@orstcs.CS.ORST.EDU> <6590145@hplsla.HP.COM>
Sender: usenet@orstcs.CS.ORST.EDU
Reply-To: budd@mist.CS.ORST.EDU (Tim Budd)
Organization: Oregon State Univ. -- Computer Science
Lines: 21

The technique used by Jim Adcock in his response to my original
question about the inconsistent handing of left and right arguments
in overloaded opertors is what is known as multiple (or double)
polymorphism.  It was introduced by Dan Ingalls in a paper in the first
OOPSLA conference, and deserves to be more widely known and used.
(Actually, Adcock's idea is a very slight improvement on Ingalls -
rather than encode the type of the receiver in the selector for the reverse
message, i.e., addToInteger, addToFloat, etc, he encodes it
as the overloaded type, i.e. addTo(Integer& x) addTo(Float& x).  In
practice I don't think this makes any difference).  I was aware of this
technique; the point of my note (well hidden) was to point out that you
needed some trick like this, and that overloaded operators didn't solve the
complete problem.

Anyway, to get to the point; I've written a technical report describing
two different generalized arithmetic packages in C++, comparing the
efficiency of Smalltalk style coercive generality to double polymorphism.
This should be back from the printers in a week or so.  If you would
like a copy send me a paper mail address.  (Actually, if you can read
LaTex I can e-mail the raw document).
--tim budd, budd@cs.orst.edu