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Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!uunet!contex!jeff
From: jeff@contex.UUCP (Jeff Carey)
Newsgroups: comp.sys.sgi,comp.lang.c++
Subject: SGI C++ 2.0 Polymorphic Reference Bug
Keywords: SGI PI C++ 2.0 polymophism reference bug
Message-ID: <1688@contex.UUCP>
Date: 12 Mar 91 16:02:07 GMT
Followup-To: comp.sys.sgi
Organization: Xyvision Design Systems, Wakefield MA
Lines: 58


I am using:

System release:		IRIX Release 4D1-3.3.1
C++ release:		S4-C++-2.0
Software Option:	C++ Translator Version 2.0

on a Silicon Graphics PI.
The other day I was testing the code found in the discussion
of "Virtual Base Classes with Virtual Functions", section 10.10c, pp. 233-4,
of _The_Annotated_C++_Reference_Manual_ and found the following bug.  You'll
notice that the bug is in the call made to f() from the MW object reference
(MW&).

---------------------- beginning of test.c++ code ----------------------------

#include <iostream.h>

class W { public: virtual void f() { cout << "W::f\n"; } };

class MW : public virtual W {};

class BW : public virtual W { public: void f() { cout << "BW::f\n"; } };

class BMW : public BW, public MW {};

main()
{
    BMW bmw;

    MW* pmw = &bmw;
    pmw->f();

    MW& rmw = bmw;
    rmw.f();

    return(0);
}

----------------------------- end of test code -------------------------------

I got this result:

$ test
BW::f
W::f

I would have predicted and hoped that the two lines of diagnostics would
result in the same text.
This is a bug isn't it...polymorphism of this sort should be supported by
references as well as pointers, right?!

Ouch ---
jeff
-- 
------------------------
Jeff Carey
contex!jeff@uunet.uu.net