C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  private virtual inheritance          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Dave Moore Guest Posted: Sat Jan 15, 2005 3:23 am    Post subject: private virtual inheritance Recent discussions here: http://groups-beta.google.com/group/comp.lang.c++.moderated/msg/f837c18868c56616 and in comp.std.c++: http://groups-beta.google.com/group/comp.std.c++/msg/3f6fda6a03cb5c6a have gotten me thinking about virtual private inheritance, I found the following example in an older thread of a canonical class hierarchy using private virtual inheritance: class I { /* something */ }; class A : private virtual I { /* implement half of I */ }; class B : private virtual I { /* implement another half of I */ }; class C : public A, public B { /* something */ }; First of all, how *should* this be handled by a Standard conforming compiler? The Standard says (12.6.2 /6) that only the most derived class is responsible for instantiating class I, however class I is not an accessible base class of C, so its constructors cannot be called from C. I messed around with some examples in g++, and it was clear that its implementation treats ctors of private virtual base classes "exceptionally", exposing them to derived classes further down the class hierarchy A more general question is, doesn't this mean that the Standard should require that base classes inherited privately and virtually have no user-defined ctors? Actually, is virtual private inheritance useful for anything? I searched this NG and comp.std.c++ and I couldn't find any *convincing* examples. Thanks, Dave Moore [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top David Bradley Guest Posted: Mon Jan 24, 2005 11:29 am    Post subject: Re: private virtual inheritance Dave Moore wrote: Quote: Actually, is virtual private inheritance useful for anything? I searched this NG and comp.std.c++ and I couldn't find any *convincing* examples. The example you stated is more complex than what I normally find useful for virtual private functions. Normally the pattern I encounter is where I want the derived classes to implement an interface. That interface is used by the base class implementation in satifying it's requirements. This private interface allows me to specify what my derived classes must implement. This interface is an implementation detail and not part of the public interface to the base class. The benefit of this is that it allows me to provide common logic around the private interface without duplicating that for each and every derived class. I'm probably not doing this justice in my description here, but hopefully you see the point. David Bradley [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ Language (Moderated) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.