From -4882872257024956275 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,206db806b836bf67 X-Google-Attributes: gidf78e5,public From: "Bradd W. Szonye" Subject: Re: Pointers to incomplete type Date: 1998/01/27 Message-ID: <6ajsuq$108@examiner.concentric.net>#1/1 X-Deja-AN: 319803766 References: <69osom$jf3@examiner.concentric.net><6a0a4g$rf1@shell.magma.ca><6a0t54$k83@examiner.concentric.net><6a3be4$6qu$1@uuneo.neosoft.com><6a7fli$gtj@examiner.concentric.net> <6aisf1$n8s$1@uuneo.neosoft.com> X-Original-Date: Tue, 27 Jan 1998 00:54:19 -0500 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2106.4 Organization: Concentric Internet Services X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBVAwUBNM5mOky4NqrwXLNJAQHTrwIAxT0qkc0ASlEqZhD/Y8jxNDs/tcPqpfW5 /O+6DOo7c595aqeBLt27uZgbu6SbkWoDu7nX9hzcZaeCpAa/BdZCkA== =Nwb/ Newsgroups: comp.std.c++ Originator: austern@isolde.mti.sgi.com Bill Wade wrote in message <6aisf1$n8s$1@uuneo.neosoft.com>... > >If you just want smaller impact in the objects, make all pointers contain >the vtable for the fully constructed, most derived object. In the objects, >use a single bit to indicate if it is fully constructed. For partially >constructed object use some other means (an expensive global mapping from >pointers to current dynamic type) for dynamic type resolution. > >You could also have a slightly different language where even for partially >constructed objects, virtual dispatch occurred using the fully constructed >object's methods. [Briefly: you're right about the vidx model not playing well with sl's.] I wouldn't want that! If that were acceptable, I wouldn't worry so much about the model being conforming. However, you did (indirectly) give me an idea! The big clue was "use an expensive mapping" for the tricky case. You might not be able to find a spare bit in the object, but you can do something else. Instead of setting the global pointer to the most derived class, give it a trap representation. Use some sort of snap technique (like float emulation) to adjust the vptrs when used. I guess you'd still have to store the "real" vptr somewhere (thereby losing at least some of the space savings for this class), but then I don't expect that a lot of polymorphic classes are handing out their this pointers during construction. Thanks for the tip! --- Bradd W. Szonye bradds@concentric.net http://www.concentric.net/~Bradds --- [ 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 ]