From -8900827358854171636 X-Google-Thread: f78e5,480a31feed3c6a1b X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!newshub.sdsu.edu!cyclone.bc.net!news.alt.net!comp-std-cpp-robomod!not-for-mail From: Larry Evans Newsgroups: comp.std.c++ Subject: Re: boost::shared_ptr revisited again Date: 10 Jun 2005 15:40:14 GMT Organization: Cox Communications Lines: 26 Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: References: <4299DE64.40403@poczta.onet.pl> <3g55jqFajuhcU1@news.dfncis.de> <1118144437.192255.257840@g47g2000cwa.googlegroups.com> <878y1j9syu.fsf@news.bourguet.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-Path: X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) Delivered-To: std-c++@ucar.edu X-Authentication-Warning: okepread07.mgt.cox.net: news set sender to newsmaster@cox.net using -f User-Agent: Debian Thunderbird 1.0 (X11/20050116) X-Accept-Language: en-us, en X-Complaints-To: abuse@cox.net X-Trace: okepread07 1118415558 24.250.158.183 (Fri, 10 Jun 2005 10:59:18 EDT) NNTP-Posting-Date: Fri, 10 Jun 2005 10:59:18 EDT X-Virus-Scanned: amavisd-new at ucar.edu X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU Xref: g2news1.google.com comp.std.c++:5064 On 06/10/2005 09:00 AM, Andrei Alexandrescu wrote: [snip] > The programmer can choose to implement dispose() or > idunneedthisdudeanymore() or whatnot to make the state of the object a > violation of its invariant (e.g., a date with all fields -1). I > personally think a nicer practice is to put the object in a "valid, but > uninteresting state". But in a memory-safe language like Java, nobody I'm wondering if this isn't very much like polaris' zombie: http://polaris.cs.uiuc.edu/polaris/polaris_developer/node42.html what happens is that the original referent type has a virtual function, is_valid which indicates it's valid. Each deref of the referent checks this to see if it is a valid referent. After all strong smart pointers to the referent are gone; yet, there are still weak smart pointers to the referent, the referent is transformed, via placement new, into a "zombie" whose is_valid indicates it's no longer valid. Of course this requires each refcounted object to be derived from an abstract base class with pure virtual is_valid, but it does save debug time. --- [ 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 ]