From 7950366072259419787 X-Google-Thread: f78e5,a5065ede37bcf8d6 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!news.glorb.com!news-feed01.roc.ny.frontiernet.net!nntp.frontiernet.net!newshosting.com.MISMATCH!nx01.iad01.newshosting.com!newshosting.com!newsfeed.icl.net!newsfeed.fjserv.net!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: gcc@integrable-solutions.net (Gabriel Dos Reis) Newsgroups: comp.std.c++ Subject: =?iso-8859-15?q?Re:_Problems_interpreting_requirement_for_std::?= =?iso-8859-15?q?copy_(=A725.2.1)?= Date: Tue, 13 Sep 2005 04:20:31 GMT Organization: Integrable Solutions Lines: 55 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <1126258566.887901.223500@g43g2000cwa.googlegroups.com> <432442c7$0$749$5fc3050@dreader2.news.tiscali.nl> NNTP-Posting-Host: news.news.demon.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: news.demon.co.uk 1126585253 22233 158.152.254.254 (13 Sep 2005 04:20:53 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Tue, 13 Sep 2005 04:20:53 +0000 (UTC) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 X-Greylisting: NO DELAY (Relay+Sender autoqualified); processed by UCSD_GL-v2.1 on mailbox7.ucsd.edu; Mon, 12 September 2005 08:10:07 -0700 (PDT) X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id j8D4KVoY018839; Tue, 13 Sep 2005 14:20:31 +1000 (EST) X-Path: comp-std-cpp-robomod!not-for-mail X-NNTP-Posting-Date: Mon, 12 Sep 2005 15:10:01 +0000 (UTC) X-Delivered-To: std-c++@ucar.edu X-Spamscanner: mailbox7.ucsd.edu (v1.6 Aug 4 2005 15:27:38, 0.0/5.0 3.0.4) X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Newsgroups: comp.std.c++ X-MailScanner: PASSED (v1.2.8 96523 j8CFA4dv014723 mailbox7.ucsd.edu) Xref: g2news1.google.com comp.std.c++:2078 squell@alumina.nl (Marc Schoolderman) writes: | kanze wrote: | | > Finally, what about something like: | > copy( l.begin(), l.end(), back_inserter( l ) ) ; | > I think that, realistically, this will generally result in an | > endless loop. And yet, it requires quite a stretch of the | > imagination to say that back_inserter( l ) is in the range of | > [l.begin(),l.end()). | | I think this example is different from the others, since the input and Indeed, this example -- which I originally posted to news:fr.comp.lang.c++ -- is fundamentally different from the vector::iterator case. In the vector::iterator, it is not hard to offer a definition of "overlap" that meets common sense such that the assumptions made by std::copy is violated. | output ranges don't strictly overlap, yet assigning through the output | iterator has the side effect of increasing the input range. Right, that is the crux of the issue. Furthermore, back_inserter(l) does not even belond to the same category as the input. | This also | means the complexity requirement of copy() gets violated since it will | do more than "exactly last - first assignments" -- unless it measures | "last - first" before it enteres the copy loop, but that would be | inefficient for bidirectional iterators. I think "last - first" is flawed because the inputs are InputIterators for which we do not have such notion. | > Globally, I think that the wording of the requires clause for | > copy needs work. But I can't really think of any reasonable way | > to formulate what common sense tells me should be the | > restrictions. | | Perhaps the requirement should be that the output iterator should not | produce any side effects in the range [first, last)? Completely agreed -- and it is the suggestion I made on news:fr.comp.lang.c++. It would suffice to make the code duplicate the content of the list; but it would not suffice to ensure that general termination, let alone "last - first" assignments. --- [ 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 ]