From mboxrd@z Thu Jan 1 00:00:00 1970 Path: main.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.help Subject: Re: Object identity Date: Tue, 21 Oct 2003 16:50:20 GMT Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Message-ID: References: NNTP-Posting-Host: deer.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: sea.gmane.org 1066755696 29816 80.91.224.253 (21 Oct 2003 17:01:36 GMT) X-Complaints-To: usenet@sea.gmane.org NNTP-Posting-Date: Tue, 21 Oct 2003 17:01:36 +0000 (UTC) Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Tue Oct 21 19:01:34 2003 Return-path: Original-Received: from monty-python.gnu.org ([199.232.76.173]) by deer.gmane.org with esmtp (Exim 3.35 #1 (Debian)) id 1ABzsz-0002Vo-00 for ; Tue, 21 Oct 2003 19:01:34 +0200 Original-Received: from localhost ([127.0.0.1] helo=monty-python.gnu.org) by monty-python.gnu.org with esmtp (Exim 4.24) id 1ABzsY-0000lu-AP for geh-help-gnu-emacs@m.gmane.org; Tue, 21 Oct 2003 13:01:06 -0400 Original-Path: shelby.stanford.edu!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!news-out1.nntp.be!propagator2-sterling!news-in-sterling.nuthinbutnews.com!snoopy.risq.qc.ca!charlie.risq.qc.ca!53ab2750!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 33 User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50 Original-NNTP-Posting-Host: 132.204.24.42 Original-X-Complaints-To: abuse@umontreal.ca Original-X-Trace: charlie.risq.qc.ca 1066755020 132.204.24.42 (Tue, 21 Oct 2003 12:50:20 EDT) Original-NNTP-Posting-Date: Tue, 21 Oct 2003 12:50:20 EDT Original-Xref: shelby.stanford.edu gnu.emacs.help:117494 Original-To: help-gnu-emacs@gnu.org X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.2 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: main.gmane.org gmane.emacs.help:13426 X-Report-Spam: http://spam.gmane.org/gmane.emacs.help:13426 >> I still have no clue what it's useful for, so I tend to find such research >> rather pointless. But I'm probably just missing the point. > The OP explained what it's useful for: emulating weak hash tables in a > system that doesn't have them built in. That's not how I understood his article. He seemed to say that he currently uses an implementation of object-identity which relies on a weak hash-table but that his Emacs's doesn't implement weakness. I.e. he seemed to say he needed weak hash-tables to implement oject-identity, not the other way around. Furthermore, all the systems I know of that offer something like `object-identity' also offer weak hash-tables. Ah... maybe Java uses object-identity to implement some of its hash-table libraries, thus justifying the work done on object-identity? Still if that's the only use, it seems stupid to work on object-identity rather than just provide the has-table functionality directly. > If implementing an identity function like the one the OP requests results > in every object being larger (due to a design like the one I described), There are various tricks possible to pay only for objects on which object-identity was called. It makes `object-identity' slower, of course. > it's likely that this overhead will be much greater than the memory leak in > his application. If the application is long running a 50% overhead can still be significantly better than a memory leak. Stefan