From -2840182760235519465 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,fbd36da46c3cc7a0 X-Google-Attributes: gidf78e5,public From: smeyers@aristeia.com (Scott Meyers) Subject: Re: Discussion: type_info Date: 1999/11/24 Message-ID: #1/1 X-Deja-AN: 552718029 X-NNTP-Posting-Host: 216.26.6.150 Approved: stephen.clamage@sun.com (comp.std.c++) References: <81ecdl$pq$1@nnrp1.deja.com> X-UID: 0000000001 X-Status: $$$T X-Complaints-To: news@teleport.com X-Trace: news1.teleport.com 943483902 216.26.6.150 (Wed, 24 Nov 1999 14:51:42 PST) Organization: Teleport Inc. NNTP-Posting-Date: Wed, 24 Nov 1999 14:51:42 PST Newsgroups: comp.std.c++ Originator: clamage@taumet On 23 Nov 1999 16:35:38 GMT, sirwillard@my-deja.com wrote: .... > different references. A lot of the examples I found on DejaNews that > used type_info within a map used the pointer, and in fact the errata > for Item 31 of More Effective C++ by Scott Meyers recommends a simple > std::map, HitFunctionPtr>. So many > people have gotten this one wrong. .... > So you can't rely on the collating order of the pointer within the > map. Instead, we'll have to use the collation order of the type_info > object itself. A logical idea would be to simply specialize > std::less. In fact, most of the people who realized you > couldn't use the pointer collation suggested doing just this. However, > in one thread it was pointed out that according to the standard this > would produce "undefined behavior", specifically because the standard > library impementors are free to provide their own specialization for > any built in types, and if they did you'd violate the "one definition > rule". So this is out. Just for the record, I don't think it's out for the design I sketch in the MEC++ errata, because it's okay to specialize less for pair, which is the type I propose putting into the map. That is, I agree that you can't specialize std::less for a pointer type, but I believe you can specialize it for a std::pair containing pointer types. Scott -- Scott Meyers, Ph.D. smeyers@aristeia.com Software Development Consultant http://www.aristeia.com/ Visit http://meyerscd.awl.com/ to demo the Effective C++ CD [ 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 ]