From -4995726660776742560 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,8d7ae4b2a3e77f8b X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2003-08-10 10:35:15 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!kibo.news.demon.net!mutlu.news.demon.net!demon!mail2news.demon.co.uk!devnull From: bop2@telia.com ("Bo Persson") Newsgroups: comp.std.c++ Subject: Re: Why is there no range type in the standard library? Date: Sun, 10 Aug 2003 17:35:14 +0000 (UTC) Organization: Telia Internet Lines: 96 Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <95e0e5ef.0308060330.28aefaae@posting.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Trace: mail2news.demon.co.uk 1060536914 135 10.0.0.1 (10 Aug 2003 17:35:14 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Sun, 10 Aug 2003 17:35:14 +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 19lu64-000022-00 for mail2news@news.news.demon.net; Sun, 10 Aug 2003 17:35:13 +0000 X-Received: from localhost (localhost [[UNIX: localhost]]) by mulga.cs.mu.OZ.AU id DAA20720; Mon, 11 Aug 2003 03:35:10 +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-Original-Recipient: X-Newsgroups: comp.std.c++ X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-NNTP-Posting-Date: Sun, 10 Aug 2003 12:20:56 CEST X-Spam-Status: No, hits=-5.4 required=5.0 tests=BAYES_01,PRIORITY_NO_NAME,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++:20553 "Chris Newton" skrev i meddelandet news:bh4192$fan$1@hercules.btinternet.com... > Stefan Heinzmann wrote [abridged]... > > Given that the notion of an iterator range is rather fundamental in > > the standard library, I wonder why this wasn't turned into a class > > template in the STL. Possibly becase it would rule out some kinds of iterators, making the entire concept less powerful. >> Something like this: > > > > template > > struct iterator_range { > > Iter begin, end; This requires the range to be constant. Usually, nothing reqires container.end() to remain constant in a loop. > > > > size_t size() const { return std::distance(begin,end); } This rules out the use of input and output iterators. How would you compute the distance() for some keyboard input? > > bool empty() const { return begin == end; } This requires end() to be a constant. > > bool operator==(const Iter& rhs) const > > { return (begin == rhs.begin) && (end == rhs.end); } This rules out not only input and output iterators, but also filtering iterators. Just because begin() and end() compares equal, the intermediate values does not have to be the same, or the same number. > > // ... potentially more methods here > > }; > > I've often wondered about this myself. A lot of algorithms inherently > run over a range, and a single range object more naturally and flexibly > represents the required concept than a pair of iterators. Consider, for > example, the typical loop implied by many standard algorithms: > > for (iterator_type it = begin_it; it != end_it; ++it) { ... } I would say that this would be typical for a for_each() call, where the iterator values *are* captured at the point of call. An ordinary for loop is much more powerful. > > How could we provide iterators over a circular data structure that > satisfied the usual equality operations, but also allowed us to run such > an algorithm over an entire circular container? What would > container_list::begin() and circular_list::end() mean in a context like > that anyway? The end() function should return a value that is somehow recognized as the end of the list. Works fine for std::list for example. The container requirements are quite simple: begin() returns an iterator that refers to the first element, if any. Otherwise it returns end(). end() returns an iterator that is different from an iterator to any of the elements in the container, using one-of-the-end is just an implementation detail not a requirement. > > In general, I think that supporting the concept of a range would allow > more natural extension of the standard library to support newer data > structures and algorithms, as well as offering a cleaner presentation of > what is already available. But you would also need to keep at least some of the current library, as it presents a more general interface. Then you will have some algorithms for range types and some for iterators. I don't immediately see how this makes it cleaner. Bo Persson bop2@telia.com --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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