From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Marcin Borkowski Newsgroups: gmane.emacs.help Subject: Re: Is there a way of setting a variable only when it exists? Date: Tue, 15 Mar 2022 07:17:42 +0100 Message-ID: <87a6drviwp.fsf@mbork.pl> References: <87lexdul8e.fsf@mbork.pl> <878rtcir1h.fsf@zoho.eu> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="9184"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: mu4e 1.1.0; emacs 29.0.50 Cc: help-gnu-emacs@gnu.org To: Emanuel Berg Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Mar 15 07:27:46 2022 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1nU0en-0002CL-Qg for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 15 Mar 2022 07:27:45 +0100 Original-Received: from localhost ([::1]:41898 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nU0em-0006eg-4Y for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 15 Mar 2022 02:27:44 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:41148) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nU0VC-0004H4-0W for help-gnu-emacs@gnu.org; Tue, 15 Mar 2022 02:17:50 -0400 Original-Received: from mail.mojserwer.eu ([195.110.48.8]:58306) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nU0VA-0004ue-9E for help-gnu-emacs@gnu.org; Tue, 15 Mar 2022 02:17:49 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by mail.mojserwer.eu (Postfix) with ESMTP id CE4B3E70F3; Tue, 15 Mar 2022 07:17:46 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at mail.mojserwer.eu Original-Received: from mail.mojserwer.eu ([127.0.0.1]) by localhost (mail.mojserwer.eu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id D5jPsOWvkYR4; Tue, 15 Mar 2022 07:17:43 +0100 (CET) Original-Received: from localhost (178235147016.dynamic-3-poz-k-0-1-0.vectranet.pl [178.235.147.16]) by mail.mojserwer.eu (Postfix) with ESMTPSA id 3851AE70B0; Tue, 15 Mar 2022 07:17:43 +0100 (CET) In-reply-to: <878rtcir1h.fsf@zoho.eu> Received-SPF: pass client-ip=195.110.48.8; envelope-from=mbork@mbork.pl; helo=mail.mojserwer.eu X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 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-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:136562 Archived-At: On 2022-03-14, at 14:48, Emanuel Berg via Users list for the GNU Emacs text editor wrote: > Stefan Monnier via Users list for the GNU Emacs text editor wrote: > >>> I assume it would be fairly easy to code such a macro >>> (using `boundp'), but maybe it exists already? >> >> AFAIK it doesn't exist yet. The reason for it is that it is >> not often useful. Typically there are two cases: >> >> - If the var exist, you want to set it and if not you have >> no fallback. In that case, it is typically harmless to set >> the var even when it doesn't exist, so the code just uses >> `setq` without bothering to test `boundp`. >> >> - If the var exist you want to set it, and if it doesn't you >> want to do something else. In that case, the something >> else tends to depend on the specifics so (if (boundp 'foo) >> (setq foo ..) ...) is about s good as it gets. > > If it exists set it with `setq'. If it doesn't exist, create > and set it ... with `setq'? What if it's an internal Emacs variable which might become a user option one day (I submitted a bug report about it) and then my customization silently disappears? It's the "silently" part I want to guard against... Best, -- Marcin Borkowski http://mbork.pl