From -5727339850048645341 X-Google-Thread: f78e5,d622c2d05233cea8 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news4.google.com!news3.google.com!border1.nntp.dca.giganews.com!border2.nntp.dca.giganews.com!nntp.giganews.com!local01.nntp.dca.giganews.com!nntp.speakeasy.net!news.speakeasy.net.POSTED!not-for-mail NNTP-Posting-Date: Wed, 12 Jul 2006 10:20:11 -0500 Return-Path: X-Authentication-Warning: mulga.csse.unimelb.edu.au: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Original-To: std-c++@mailman.ucar.edu Delivered-To: std-c++@mailman.ucar.edu From: "Greg Herlihy" Newsgroups: comp.std.c++ Subject: Re: Template members of template class Organization: http://groups.google.com Message-ID: <1152687147.444426.240120@s13g2000cwa.googlegroups.com> References: <1152613761.862951.8940@35g2000cwc.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Complaints-To: groups-abuse@google.com User-Agent: G2/0.2 X-HTTP-UserAgent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/418.8 (KHTML, like Gecko) Safari/419.3,gzip(gfe),gzip(gfe) Complaints-To: groups-abuse@google.com Injection-Info: s13g2000cwa.googlegroups.com; posting-host=70.231.172.113; posting-account=JdllFQ0AAAC-QghphnHMZz5q0GHnzGUJ X-Greylisting: NO DELAY (Relay+Sender autoqualified); processed by UCSD_GL-v2.1 on mailbox7.ucsd.edu; Tue, 11 July 2006 23:52:43 -0700 (PDT) X-Spamscanner: mailbox7.ucsd.edu (v1.6 Jul 6 2006 14:57:05, 0.0/5.0 3.1.3) X-MailScanner: PASSED (v1.2.8 13552 k6C6qhcZ014102 mailbox7.ucsd.edu) X-Virus-Scanned: amavisd-new at ucar.edu X-Virus-Scanned: amavisd-new at csse.unimelb.edu.au Approved: Fergus Henderson , moderator of comp.std.c++ X-Virus-Scanned: amavisd-new at csse.unimelb.edu.au Date: Wed, 12 Jul 2006 10:18:25 CST Lines: 73 NNTP-Posting-Host: 65.182.171.162 X-Trace: sv3-FifOpNWbvCNGs0ZO+p0YRb5i5wym/XTQO98z9yoYrH7yJelyMOZVxhvNOSaDUztsmq+khJy1s+AQ9IG!jHragB6TIJwW6by/CDQwL38xzmKmMZ6VOaEe1yNjIFFxuKFre/T07BfGnMc1xHbk9GvE03i/SX0Y!V2iBKAK9/erwPQwkNfoyZL1560g47/F8EyHfpYYwpvc= X-Complaints-To: abuse@speakeasy.net X-DMCA-Complaints-To: abuse@speakeasy.net X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.32 Xref: g2news2.google.com comp.std.c++:2687 Geo wrote: > Having spent several hours trying to get the following code to compile > in GCC and failing > > namespace test > { > > template class Formatter__ > { > private: > U ss; > public: > > Formatter__(V out) : ss(out) > { > } > > template Formatter__& operator<<(const T &item) > { > ss << item; > return *this; > } > > template<> Formatter__& operator<<(const char* s) > { > ss << do_stuff(s); > return *this; > } > }; > }; > > I eventually discovered that it was illegal in standard C++. > > My question is, Why ? A (full) specialization of a template defines a single, unique instantation of a general template for a specific set of parameterized types. So in order to specialize a template member function of a class template in full, the parameterized types for both the class template and the member function must be supplied in order to arrive at a single, unambiguous instantiation of the member function template. > I'm not to bothered with the fact that the template specialization > should be at namespace scope, but why can't I specialize operator<< > without specializing Formatter__. What problem does preventing this > solve ? A better question would be what problem would fully specialized member functions for unspecialized class templates solve? It is easy to mistake specializing a function template with overloading a function - but because specializations of a template function are considered only after a function has been already selected when resolving a function call, they are not the same. In fact the existence of a specialization for a template function does not improve its chances of being called for a specific set of parameter types - an outcome that is often as surprising as it is unexpected. Therefore the change to make to the example code above (to have it work as expected) - would be to overload the operator<< member function instead of trying to specialize it: Formatter__& operator<<(const char* s) { ss << do_stuff(s); return *this; } Greg --- [ 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.comeaucomputing.com/csc/faq.html ]