From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Eric Abrahamsen Newsgroups: gmane.emacs.help Subject: Re: Two questions about generalized variables Date: Sun, 21 Feb 2016 23:01:48 +0800 Message-ID: <877fhyayzn.fsf@ericabrahamsen.net> References: <87ziuu4p8k.fsf@ericabrahamsen.net> <877fhydw6q.fsf@web.de> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1456066949 21828 80.91.229.3 (21 Feb 2016 15:02:29 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 21 Feb 2016 15:02:29 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sun Feb 21 16:02:21 2016 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aXVWc-0006nK-TJ for geh-help-gnu-emacs@m.gmane.org; Sun, 21 Feb 2016 16:02:19 +0100 Original-Received: from localhost ([::1]:41634 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aXVWc-0002cn-9f for geh-help-gnu-emacs@m.gmane.org; Sun, 21 Feb 2016 10:02:18 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:52221) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aXVWQ-0002ch-Fq for help-gnu-emacs@gnu.org; Sun, 21 Feb 2016 10:02:07 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aXVWM-00067U-On for help-gnu-emacs@gnu.org; Sun, 21 Feb 2016 10:02:06 -0500 Original-Received: from plane.gmane.org ([80.91.229.3]:44324) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aXVWM-000678-Hq for help-gnu-emacs@gnu.org; Sun, 21 Feb 2016 10:02:02 -0500 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1aXVWJ-0006Tq-4X for help-gnu-emacs@gnu.org; Sun, 21 Feb 2016 16:01:59 +0100 Original-Received: from 116.1.108.205 ([116.1.108.205]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 21 Feb 2016 16:01:59 +0100 Original-Received: from eric by 116.1.108.205 with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 21 Feb 2016 16:01:59 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 60 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 116.1.108.205 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux) Cancel-Lock: sha1:zX6dcEpxvdvV6UrGZdtVdJg06HU= X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 80.91.229.3 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 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 Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:109246 Archived-At: Michael Heerdegen writes: > Eric Abrahamsen writes: > >> It looks like plist-get doesn't return a setf-able place. > > But `symbol-plist' has a gv-expander and refers to an alist. > `alist-get' has a gv-expander, too. So i think you would end up with > something like > > (setf (alist-get key (symbol-plist 'symbol)) value) > > I think. I didn't mean symbol property lists! Just the plain old '(:key1 "value1" :key2 "value2") kind. They're useful for a few different things -- in this case, initializing class instances. >> The second question is setting hashtable entries. Right now I have code >> like this: >> >> (setf (gethash uuid my-hashtable) >> (append (list (list 'thingone 'thingtwo)) >> (gethash uuid my-hashtable))) > > Isn't that more or less `push'? I started off with `push', but the code in question doesn't know if the key exists or not, and you can't push to nil. Once you've checked whether the key has a value or not, you might as well be doing gethash/puthash. >> I assume this is no more or less efficient than let-ting the gethash, >> manipulating the value, then using puthash to put it back in. Now I've >> written this: > >> [corrected version from the second message] >> (cl-symbol-macrolet ((entry (gethash uuid my-hashtable))) >> (setf entry (append (list (list 'thingone 'thingtwo)) >> entry))) >> >> This is a simplistic example, but -- is this actually going to be any >> faster or more efficient than the first version? Does it only access >> the hashtable once? > > `push' with `gethash' and the above code expand more or less to the > same. And I think this must access the hash-table twice: once > `gethash', and once `puthash'. Right, I would assume that "(push (list ...) (gethash uuid my-hashtable))" is as efficient as you can get. But I don't think I can use it. But your response nudged me in the right direction -- of course I should have simply expanded the macro to see what it does. And indeed the `cl-symbol-macrolet' phrase expands to a `puthash' plus a `gethash'. So that's my answer -- I guess it's just a syntactic convenience. Thanks! Eric