From 1448835449789674784 X-Google-Thread: f78e5,3c7d746be594880e X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!news.glorb.com!news.alt.net!comp-std-cpp-robomod!not-for-mail From: "Alf P. Steinbach" Newsgroups: comp.std.c++ Subject: Re: Concerning n2157 and is_empty specification Date: Thu, 15 Mar 2007 12:56:07 CST Organization: Altopia Corp. - Usenet Access - www.altopia.com Lines: 30 Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <55tff8F26esmvU1@mid.individual.net> References: <1173648852.230192.11800@p10g2000cwp.googlegroups.com> <1173805078.208591.62140@v33g2000cwv.googlegroups.com> <55o7vqF261fmfU1@mid.individual.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 X-Orig-X-Trace: individual.net fLEC/M2ZZj/ydzvuirdGsQ1NgGoo9jtRngF3Cs+Nje+5jb9BXp User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8) Gecko/20051201 Thunderbird/1.5 Mnenhy/0.7.3.0 X-Originating-IP: 130.133.1.2 X-Virus-Scanned: amavisd-new at ucar.edu X-Virus-Scanned: amavisd-new at csse.unimelb.edu.au X-Virus-Scanned: amavisd-new at csse.unimelb.edu.au Xref: g2news1.google.com comp.std.c++:8036 * Greg Herlihy: > > Unfortunately, if std::is_empty<> template type trait is hacked in order to > force is_empty::value to evaluate to false, then the is_empty<> > template would no longer be able to test whether a class's base class was > empty and - by extension - to test whether the complete class type may > benefit from the EBCO. In fact, by returning inaccurate results is_empty<> > would no longer have any discernable, useful purpose (that I can discern) - > and would in fact have the less-than-useful effect of propagating the same > errors, illogic and confusion evident in the C++ Templates book's discussion > of empty class types into the C++ Standard itself. Now, now. Why not is_empty yielding false, and is_empty yielding true, where the number is the size of the derived class sans NonEmpty base? That said, being very much less than a luminary in the forefront of C++ technology I'm not fully grokking the purpose of is_empty: is it for compiler writers? -- A: Because it messes up the order in which people normally read text. Q: Why is it such a bad thing? A: Top-posting. Q: What is the most annoying thing on usenet and in e-mail? --- [ 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 ]