Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!spdcc!esegue!compilers-sender
From: dmw9q@uvacs.cs.Virginia.EDU (David M. Warme)
Newsgroups: comp.compilers
Subject: Re: Defining polymorphism vs. overloading
Keywords: design, polymorphism
Message-ID: <9009051416.AA29612@uvacs.cs.Virginia.EDU>
Date: 5 Sep 90 14:16:53 GMT
References: <9008310419.AA06194@karakorum.berkeley.edu> <4c98dcd0b.001a92c@caen.engin.umich.edu>
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: dmw9q@uvacs.cs.Virginia.EDU (David M. Warme)
Organization: University of Virginia Computer Science Department
Lines: 24
Approved: compilers@esegue.segue.boston.ma.us

In article <4c98dcd0b.001a92c@caen.engin.umich.edu> Mark Montague writes:

>So I imagine that every expression of the form
>		myarray[index]
>is silently transformed into
>		*(myarray+index)
>before the compiler even sees it.  Even though it probably doesn't happen
>this way for most compilers, this fictional device lets me ignore questions
>of polymorphism and operator overloading in a non-object-oriented language
>such as C.

     This does not remove polymorphism and/or overloading, it merely
transfers the burden onto + and *.  The expansion you state is THE
DEFINITION of the operator.  A C compiler I wrote does this during
parsing by building two parse-tree nodes (* and +) rather than a
single node for [].  The only detail to consider is that the node used
for * in this case is a specially-flavored * that differs in only one
respect from the "normal" * node:  error messages say "invalid
subscript", rather than "illegal indirection".

					- Dave Warme
-- 
Send compilers articles to compilers@esegue.segue.boston.ma.us
{ima | spdcc | world}!esegue.  Meta-mail to compilers-request@esegue.