Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!jarthur!uci-ics!rfg
From: rfg@ics.uci.edu (Ronald Guilmette)
Newsgroups: comp.lang.c++
Subject: Re: What to do about generics and polymorphism in C++
Message-ID: <26108B02.2589@paris.ics.uci.edu>
Date: 28 Mar 90 09:59:31 GMT
References: <152@dumbcat.UUCP> <574@atcmpe.atcmp.nl> <153@dumbcat.UUCP>
Reply-To: rfg@ics.uci.edu (Ronald Guilmette)
Organization: UC Irvine Department of ICS
Lines: 37

In article <153@dumbcat.UUCP> marc@dumbcat.UUCP (Marco S Hyman) writes:
>In article <574@atcmpe.atcmp.nl> leo@atcmp.nl (Leo  Willems) writes:
> > From article <152@dumbcat.UUCP>, by marc@dumbcat.UUCP (Marco S Hyman):
> > > 	void * generic;
> > > 	D something;
> > > 	B1 * b1 = &something;
> > > 	B2 * b2;
> > >
> > > 	++b1->i1;
> > > 	generic = b1;	// no adjustment
> > > 	b2 = generic;	// no adjustment
> >
> > If you apply a cast in the example does it work correct then?
> > (If it works, is it legal or just luck? Andrew Koenig told me a long time
> > ago it is legal, but that was in the 1.2 darkages, in which I still live :-))
>
>G++ (the version I used to check the above example) does not require the
>cast.  My cfront 2.0 hasn't arived for this machine yet so I can't test it,

g++ started out as a C compiler, and got changed into a C++ compiler later.
You can still find occasional reminders of its lineage in places, like
for instance in the fact that the type-checking & type-conversions
have not been "hardened" to cfront standards yet.  (Some people may
prefer the looser typing that g++ provides.)

g++ still allows you to assign a void* to other types of pointer variables.

Cfront doesn't allow this without explicit casting.

>... The moral is *don't* use void* for generics.

I concur.


// Ron Guilmette (rfg@ics.uci.edu)
// C++ Entomologist
// Motto:  If it sticks, force it.  If it breaks, it needed replacing anyway.