From -5196078196049085570 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,b83a4267f4ac775 X-Google-Attributes: gidf78e5,public From: phalpern@truffle.ma.ultranet.com (Pablo Halpern) Subject: Re: string/cow/algorithm Date: 1998/08/21 Message-ID: <35dfe616.47271311@news.ma.ultranet.com>#1/1 X-Deja-AN: 383385775 X-NNTP-Posting-Host: truffle.ultranet.com Content-Transfer-Encoding: 7bit Approved: stephen.clamage@sun.com (comp.std.c++) References: <6qfr41$oue$1@pigpen.csrlink.net> <35ccc2b4.832003@news3.ibm.net> <6qn19u$sb0$1@pigpen.csrlink.net> <6qnfc9$a0s$1@nnrp1.dejanews.com> <6qovei$5ou$1@shell7.ba.best.com> <6qqd2q$bs9$1@nnrp1.dejanews.com> X-UID: 0000000001 X-Status: $$$T X-Ultra-Time: 21 Aug 1998 03:53:28 GMT Content-Type: text/plain; charset=us-ascii X-Complaints-To: abuse@ultra.net Organization: UltraNet Communications , an RCN Company http://www.ultranet.com/ Mime-Version: 1.0 Newsgroups: comp.std.c++ Originator: clamage@taumet AllanW@my-dejanews.com wrote: >Maybe what we really should have done is require string to disallow >looking at individual characters with char*-type notation; leaving >only iterators. Then any library vendor could implement ref-counting >simply by having the iterator return a proxy which triggers cow when >appropriate. Programs that need char*-type notation wouldn't be >affected, since they could still use array-of-char! > >But that doesn't help *now*, you point out? Granted. But what can we >do now, short of avoiding ref-counting like the plague? What we can do *now* is to use COW implementations that punt (do a deep-copy and mark unsharable) when the caller uses (non-const) operator[], begin(), or end(). My programs rarely use these features of stings. Most common operations on strings is copying, creating substrings, replacing substrings, concatonating and displaying, all of which can be done without marking a string buffer as non-sharable. Replacing single characters is much rarer and can either be done using replace(), or else suffer the performance penalty for using operator[] or non-const iterators. Thus a COW implementation can be just as efficient as you want, if use use it *as if* the operations mentioned were forbidden. ------------------------------------------------------------- Pablo Halpern phalpern@truffle.ultranet.com I am self-employed. Therefore, my opinions *do* represent those of my employer. [ 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://reality.sgi.com/austern_mti/std-c++/faq.html ]