From -2969505258625474083 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,3b5faa9aaea18095 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2003-09-30 22:50:46 PST Path: archiver1.google.com!news2.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!kibo.news.demon.net!mutlu.news.demon.net!demon!mail2news.demon.co.uk!devnull From: jhrwalter@yahoo.com (Joerg Walter) Newsgroups: comp.std.c++ Subject: Re: Problem with function template overload resolution Date: Wed, 1 Oct 2003 05:50:43 +0000 (UTC) Organization: http://groups.google.com Lines: 65 Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: <4e6fccc6.0309301317.7a4d3d00@posting.google.com> References: <4e6fccc6.0309162227.1aa4bda7@posting.google.com> <3F6E975F.8050300@grad.hr> <4e6fccc6.0309231302.4c6a4a9f@posting.google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Trace: mail2news.demon.co.uk 1064987443 11335 10.0.0.1 (1 Oct 2003 05:50:43 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Wed, 1 Oct 2003 05:50:43 +0000 (UTC) X-Received: from mulga.cs.mu.oz.au ([128.250.1.22]) by news.demon.co.uk with esmtp (Exim 4.12) id 1A4Zso-0002wf-00 for mail2news@news.news.demon.net; Wed, 01 Oct 2003 05:50:42 +0000 X-Received: by mulga.cs.mu.OZ.AU id PAA27046; Wed, 1 Oct 2003 15:50:32 +1000 (EST) X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Path: comp-std-cpp-robomod!not-for-mail X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Delivered-To: std-c++@ucar.edu X-Newsgroups: comp.std.c++ X-NNTP-Posting-Date: Tue, 30 Sep 2003 21:17:00 +0000 (UTC) X-Spam-Status: No, hits=-3.1 required=5.0 tests=BAYES_01,FORGED_YAHOO_RCVD,QUOTED_EMAIL_TEXT,REFERENCES version=2.55 X-Spam-Checker-Version: SpamAssassin 2.55 (1.174.2.19-2003-05-19-exp) Xref: archiver1.google.com comp.std.c++:10 gp1@paradise.net.nz (Graeme Prentice) wrote in message news:... > On Wed, 24 Sep 2003 15:23:13 +0000 (UTC), jhrwalter@yahoo.com (Joerg > Walter) wrote: > > > > >We're not talking about partial specializations but about the interference > >of explicit specification with argument deduction as far as I understand > >14.1.8 bullet 2: > > > >---------- > >Trailing template arguments that can be deduced (14.8.2) may be omitted from > >the list of explicit template-arguments. ... > >---------- > > This rule means both functions are callable. The two functions are > overloads of each other. The compiler uses the partial ordering rules > to determine if one function is more specialised than the other > 14.5.5.2 para 1 to 5 OK. > Partial ordering applied to these two functions works like this ... > > template > result foo(A const& a) { > std::cout << "foo" << std::endl; > return result(); > } > > template > R foo(A const& a) { > std::cout << "foo" << std::endl; > return R(); > } > > > For the first foo(), synthesize a unique type U for the template type > parameter A and call the second foo i.e. the call is foo( abc ) where > abc is U const &. For this call, the compiler is unable to deduce the > type of the template parameter R so deduction fails. I see. > Now this is done in reverse - for the second foo(), synthesize unique > types U1, U2 for R and A and call the first foo() - the call is > foo(abc) where abc has type U1 const &. Deduction succeeds because the > template parameter A of the first function is deduced as U1. Hence the > second foo is more specialised than the first (para 4 & 5) so the call > foo >(s2); is not ambiguous. I see, too. [...] Thanks a lot for your explanation, Joerg P.S.: but this resolution is still surprising ;-) --- [ 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://www.jamesd.demon.co.uk/csc/faq.html ]