From 8755928284226131119 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,4441c5f6d7843223 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2002-09-03 10:49:13 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!mutlu.news.demon.net!demon!mail2news.demon.co.uk!devnull From: steve@steveheller.com (Steve Heller) Newsgroups: comp.std.c++ Subject: Re: C++0x Wish List (explicit class) Date: Tue, 3 Sep 2002 17:49:13 +0000 (UTC) Organization: Giganews.Com - Premium News Outsourcing Lines: 44 Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <3D48C729.40503@spamnot.codeweavers.com> <8c8b368d.0208060921.43e9e9d5@posting.google.com> <3D5086C0.664A29E9@bawi.org> <8c8b368d.0208071131.5306ddd2@posting.google.com> <23b84d65.0208081146.169d3d83@posting.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: mail2news.demon.co.uk 1031075353 1619 10.0.0.1 (3 Sep 2002 17:49:13 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Tue, 3 Sep 2002 17:49:13 +0000 (UTC) X-Received: from mulga.cs.mu.oz.au ([128.250.1.22]) by news.demon.co.uk with esmtp (Exim 4.05) id 17mHnb-0000Py-00 for mail2news@news.news.demon.net; Tue, 03 Sep 2002 17:49:11 +0000 X-Received: by mulga.cs.mu.OZ.AU id DAA11350; Wed, 4 Sep 2002 03:49:08 +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++@ncar.ucar.edu X-Newsgroups: comp.std.c++ X-Reply-To: steve@steveheller.com X-Newsreader: Forte Agent 1.91/32.564 X-NNTP-Posting-Date: Tue, 03 Sep 2002 09:54:29 CDT X-DMCA-Notifications: http://www.giganews.com/info/dmca.html 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: 1.1 Xref: archiver1.google.com comp.std.c++:13575 kanze@gabi-soft.de (James Kanze) wrote: >Allan_W@my-dejanews.com (Allan W) wrote in message >news:<23b84d65.0208081146.169d3d83@posting.google.com>... >> rmaddox@isicns.com (Randy Maddox) wrote >> > The other issue is that with either the newly proposed use of >> > explicit or with the private declaration and no definition idiom you >> > can partially change your mind, i.e., add any one of the prohibited >> > operations without affecting the remaining prohibitions. With >> > boost::noncopyable it's all or nothing. > >> Note that you can implement copy constructor in terms of assignment: >> T::T(const T&t) { (*this)=t; } >> Also, while it's not a good idea to implement assignment in terms of >> copy constructor, it is at least possible. > >> Can you think of an example where you'd want to define one of these >> functions but not the others? I can't. > >Yes. Polymorphism and assignment doesn't work well together, Unless you use "safe polymorphism", which hides the pointer in a "manager" object which can be assigned with normal syntax. >but it is >not unusual to want to be able to clone a polymorphic object. In such >cases, I'll declare both the copy constructor and the assignment >operator private; I'll define the copy constructor, but not the >assignment operator. -- Steve Heller http://www.steveheller.com Author of "C++: A Dialog", "Optimizing C++", and other books Free online versions of "Who's Afraid of C++?" and "Optimizing C++" are now available at http://www.steveheller.com/whos and http://www.steveheller.com/opt --- [ 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 ]