From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: =?ISO-8859-1?Q?Nordl=F6w?= Newsgroups: gmane.emacs.help Subject: Re: Hash-table elements Date: Thu, 1 Oct 2009 07:52:28 -0700 (PDT) Organization: http://groups.google.com Message-ID: <5230b46a-f95e-4497-a6e7-5c7d71d30b87@l2g2000yqd.googlegroups.com> References: <0c37c5b5-6683-4705-a2e4-e0c5ccb34614@e12g2000yqi.googlegroups.com> <7c7hvhki0b.fsf@pbourguignon.lefevre.anevia.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1254411735 28798 80.91.229.12 (1 Oct 2009 15:42:15 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 1 Oct 2009 15:42:15 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Oct 01 17:42:08 2009 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.50) id 1MtNnD-0006ZO-RZ for geh-help-gnu-emacs@m.gmane.org; Thu, 01 Oct 2009 17:42:08 +0200 Original-Received: from localhost ([127.0.0.1]:44498 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MtNnD-0008Bi-DU for geh-help-gnu-emacs@m.gmane.org; Thu, 01 Oct 2009 11:42:07 -0400 Original-Path: news.stanford.edu!usenet.stanford.edu!postnews.google.com!l2g2000yqd.googlegroups.com!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 42 Original-NNTP-Posting-Host: 150.227.15.253 Original-X-Trace: posting.google.com 1254408748 14754 127.0.0.1 (1 Oct 2009 14:52:28 GMT) Original-X-Complaints-To: groups-abuse@google.com Original-NNTP-Posting-Date: Thu, 1 Oct 2009 14:52:28 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: l2g2000yqd.googlegroups.com; posting-host=150.227.15.253; posting-account=ytJKAgoAAAA1tg4ScoRszebXiIldA5vg User-Agent: G2/1.0 X-HTTP-Via: 1.1 ip1-w.foi.se:8080 (IronPort-WSA/6.3.0-523) X-HTTP-UserAgent: Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/532.1 (KHTML, like Gecko) Chrome/4.0.219.0 Safari/532.1,gzip(gfe),gzip(gfe) Original-Xref: news.stanford.edu gnu.emacs.help:173487 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:68603 Archived-At: On Sep 29, 3:17=A0pm, p...@informatimago.com (Pascal J. Bourguignon) wrote: > Nordl=F6w writes: > > Can hash-tables contain references other "global" structures? > > > I have a hash-table that maps filenames to their metadata,file-scan- > > hits/misses. > > I don't want to pull-change-push the whole meta-data value whenever I > > change parts of these metadata/hits. > > > Is this possible somehow? > > Yes. =A0Only do not modify the keys! =A0You wouldn't be able to retrieve > them, since changing the state of a key would probably change its hash > value, and therefore the bucket where the hash-table stored it. > But you can do whatever you want on the value. > > (require 'cl) > (let ((h (make-hash-table))) > > =A0 =A0(let ((value (list 1 2 3)) > =A0 =A0 =A0 =A0 =A0(key =A0 :my-list)) > > =A0 =A0 =A0 (setf (gethash key h) value) > =A0 =A0 =A0 (setf (car value) 0 > =A0 =A0 =A0 =A0 =A0 =A0 (cdr value) 'z) > =A0 =A0 =A0 (gethash key h))) > --> (0 . z) > > -- > __Pascal Bourguignon__ So with the use of setf() we realize the reference pattern in Emacs- Lisp as we use pointers in C? So the value of (gethash key h) is actually a reference to "value" and when "value" goes out of scope the interpreter knows that it is referenced from another structure and does not delete its contents? I have understood it correctly? /Nordl=F6w