From 4906812681467355614 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,edd477ec92e5348f X-Google-Attributes: gidf78e5,public X-Google-Thread: fc772,ef0c226459c03bdf X-Google-Attributes: gidfc772,public From: "Scott Meyers" Subject: Re: Protected Inheritance Date: 1999/02/05 Message-ID: <5sGu2.19890$202.9738189@news1.teleport.com>#1/1 X-Deja-AN: 441228500 Approved: harkness@skeptics.org Sender: cppmods@netlab.cs.rpi.edu References: ' <79aesq$qlr$1@uuneo.neosoft.com> X-Submission-Address: c++-submit@netlab.cs.rpi.edu X-Approved-For-Group: Fergus Henderson comp.std.c++ X-Original-Date: 05 Feb 99 19:32:18 GMT Organization: - X-Auth: PGPMoose V1.1 PGP comp.lang.c++.moderated iQBVAwUANruxakHMCo9UcraBAQG7ewH+MDaGJeSBmxx9Wn+nyvD1T7DMA3g8jOeh egsa4ylQDn2JJE36jrqKcdweH8vRmGR1QVAVPdvijQth7wMtNYjgig== =wryZ Newsgroups: comp.lang.c++.moderated,comp.std.c++ Siemel Naran wrote in message news:slrn7bjmm5.q36.sbnaran@localhost.localdomain... >On 04 Feb 99 17:00:40 GMT, Scott Meyers wrote: > >> 2 Names in a mem-initializer-id are looked up in the scope of the >> constructor's class and, if not found in that scope, are looked >> up in the scope containing the constructor's definition. > >>Does 12.6.2 really mean that private virtual base classes may be >>initialized only by their immediate descendant classes (excluding >>friendship issues)? > >I think that MSVC is indeed right in compiling your code: > class Base { public: explicit Base(int); }; > class Sub1 : virtual private Base { public: Sub1(); }; > class Sub2 : virtual private Base { public: Sub2(); }; > class Derived : public Sub1, public Sub2 { public: > Derived() : Base(1), Sub1(), Sub2() { } > }; > int main() { Derived(); } >The compilers como and egcs also compile this. > >This is because the Derived class really owns the Base subobject. Where do you find support for this notion of "owernership" in the standard? >The above class Derived is entirely equivalent to this > class Derived : virtual private Base, public Sub1, public Sub2 { public: > Derived() : Base(1), Sub1(), Sub2() { } > }; Maybe. Compilers that lay out objects in the manner described in the ARM would put an extra ptr-to-vbase in this latter definition of Derived, I believe. At any rate, I'd still like to see support in the standard for your interpretation. FWIW, I *hope* it's true that indirect derived classes can initialize private virtual bases, but I still think 12.6.2 can be read to the contrary. Scott Scott Meyers, Ph.D. Voice: 503/638-6028 Author: Effective C++ CD Fax: 503/638-6614 Effective C++ Email: smeyers@aristeia.com More Effective C++ WWW: http://www.aristeia.com/ --- [ 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 ]