From -8936628356674746023 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,8a4cd038fc33ea5a X-Google-Attributes: gidf78e5,public From: herbs@cntc.com (Herb Sutter) Subject: Re: Ambiguous conversion due to private ba Date: 1998/03/26 Message-ID: <3519c29f.2365671125@nr1.toronto.istar.net>#1/1 X-Deja-AN: 337819413 Approved: Fergus Henderson Content-Transfer-Encoding: 7bit References: <3517FB6C.6DE8@central.beasys.com> <6f9nbr$sg5@engnews1.Eng.Sun.COM> <351994FE.15FB7483@pratique.fr> X-Original-Date: Thu, 26 Mar 1998 02:55:53 GMT Content-Type: text/plain; charset=us-ascii Organization: iSTAR internet Incorporated X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUANRoIfuEDnX0m9pzZAQFo7AF+I7kpi2g6EuupedAHBsztFVWQGTEgdeRo fRqHHVaTwPGP5/hPKcpr/BTjWHtwGz2k =P1Rh Mime-Version: 1.0 Newsgroups: comp.std.c++ Valentin Bonnard wrote: >Steve Clamage wrote: >> Thus, private inheritance fails any test of the IsA relationship. > >I would say that private inheritance is a private IsA relationship. >It means that only some trusted functions (member, friends) are >aware of the relationship, which may change in the future. Even member functions can't use Base and Derived objects polymorphically. Private inheritance is far closer to "has-a" membership than it is to public inheritance. That's because private inheritance means "is-implemented-in-terms-of" (not "is-a"), as does membership. Hence one should always prefer membership unless private inheritance is really necessary, which usually means: to access a protected member, to override a virtual function, or to be constructed before base subobjects. --- Herb Sutter (mailto:herbs@cntc.com) Current Network Technologies Corp 2695 North Sheridan Way, Suite 150 www.cntc.com www.peerdirect.com Mississauga Ontario Canada L5K 2N6 --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]