From 5062398155150984443 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,8c9f1307b83ac2db X-Google-Attributes: gidf78e5,public From: fjh@mundook.cs.mu.OZ.AU (Fergus Henderson) Subject: Re: Q: virtual functions not overridable anymore? Date: 1997/09/11 Message-ID: <5v719t$7g1@mulga.cs.mu.OZ.AU>#1/1 X-Deja-AN: 271680439 References: <01bcb109$1e790180$433574cf@worldnet.worldnet.att.net> <3404A0AE.6F7E@Eng.Sun.COM> <5uimip$l56@bgtnsc03.worldnet.att.net> <340D93AA.643A@Eng.Sun.COM> <01bcb951$ea80a440$909c389d@mtayler> <34166C9E.1882@pratique.fr> X-Original-Date: 10 Sep 1997 20:52:13 GMT Organization: Comp Sci, University of Melbourne X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBVAwUBNBhNa0y4NqrwXLNJAQGxkAIAgR9lO/9cp7pDWF6xY0h3lv/g2cdbeuz1 rzhrva3gGixP/eDyB7FhdqBg8gsZEnuPzhVg3uIs5o5mZWqhm6hjGQ== =DU/h Newsgroups: comp.std.c++ Originator: austern@isolde.mti.sgi.com Valentin Bonnard writes: >Colin Rafferty writes: > >> Michael B Taylor writes: >> >> > Maybe I missing something about this whole thread, but it seems to me that >> > the desire to declare a virtual method "final" in some derived class is the >> > same as the desire to declare a method in a class non-virtual. >> > [[...Example defining a class `foo' by inheriting from a class `bar' >> > which has a virtual member `spam()'...]] >> > I'm forced to have spam virtual. >> >> You are only forced into doing this because you have derived from >> `bar'. This is your choice. Since `foo' "is-a" `bar', then it must >> have all the same properties of `bar'. One of these is that its member >> function `spam' is overridable by subclasses. > >You invented a new substitution principle (the Rafferty >substitution principle ?); I never saw it in OO litterature. As in Rafferty's Rules? ;-) This principle would make sense only in a language in which you could dynamically create subclasses of a dynamically chosen class at runtime. In that case, it would be an instance of the Liskov substitution principle. C++ does not allow that sort of dynamic behaviour. Even in a hypothetical language C+=42 that did allow such dynamic class creation and runtime derivation, the principle would not always apply. If you're using private inheritence, then that the fact that `foo' "is-a" `bar' is private, and so classes derived from `foo' should not be able to take advantage of that. -- Fergus Henderson | "I have always known that the pursuit WWW: | of excellence is a lethal habit" PGP: finger fjh@128.250.37.3 | -- the last words of T. S. Garp. --- [ comp.std.c++ is moderated. To submit articles: Try just posting with your newsreader. If that fails, use mailto:std-c++@ncar.ucar.edu comp.std.c++ FAQ: http://reality.sgi.com/austern/std-c++/faq.html Moderation policy: http://reality.sgi.com/austern/std-c++/policy.html Comments? mailto:std-c++-request@ncar.ucar.edu ]