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 16:09:43 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 1066753012 22958 80.91.224.253 (21 Oct 2003 16:16:52 GMT) X-Complaints-To: usenet@sea.gmane.org NNTP-Posting-Date: Tue, 21 Oct 2003 16:16:52 +0000 (UTC) Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Tue Oct 21 18:16:46 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 1ABzBe-0007MD-01 for ; Tue, 21 Oct 2003 18:16:46 +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 1ABzBW-0007iR-P0 for geh-help-gnu-emacs@m.gmane.org; Tue, 21 Oct 2003 12:16:38 -0400 Original-Path: shelby.stanford.edu!newsfeed.stanford.edu!logbridge.uoregon.edu!snoopy.risq.qc.ca!charlie.risq.qc.ca!53ab2750!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 19 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 1066752583 132.204.24.42 (Tue, 21 Oct 2003 12:09:43 EDT) Original-NNTP-Posting-Date: Tue, 21 Oct 2003 12:09:43 EDT Original-Xref: shelby.stanford.edu gnu.emacs.help:117487 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:13418 X-Report-Spam: http://spam.gmane.org/gmane.emacs.help:13418 > So let's try augmenting it with additional information, like a timestamp. > This obviously can't be the time that object-identity was called, because > then it will be different every time. It needs to be something associated > with the object itself, like the time it was created or the time that > object-identity was first invoked on it. This implies that every object > needs to have a slot to store its creation time. As a result, the size of > every object will have to grow by at least 4 bytes. Assuming cons cells > are 8 bytes, this means increasing the space they use by 50%. Since most > objects in memory will never have object-identity called on them, this > space is mostly wasted. But since Java has such a function and Java is an attention-grabber, people have been working on clever ways to implement this efficiently. 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. Stefan