From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: A function to take the regexp-matched subsring directly Date: Sun, 30 Oct 2022 18:07:46 -0400 Message-ID: References: <87h6zl9q4u.fsf@posteo.net> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="7948"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) Cc: daanturo , emacs-devel@gnu.org To: Philip Kaludercic Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sun Oct 30 23:08:34 2022 Return-path: Envelope-to: ged-emacs-devel@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 1opGTp-0001s5-VS for ged-emacs-devel@m.gmane-mx.org; Sun, 30 Oct 2022 23:08:34 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1opGTD-00009l-UB; Sun, 30 Oct 2022 18:07:55 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1opGTC-00009d-GD for emacs-devel@gnu.org; Sun, 30 Oct 2022 18:07:54 -0400 Original-Received: from mailscanner.iro.umontreal.ca ([132.204.25.50]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1opGTA-0001OI-Fq for emacs-devel@gnu.org; Sun, 30 Oct 2022 18:07:54 -0400 Original-Received: from pmg2.iro.umontreal.ca (localhost.localdomain [127.0.0.1]) by pmg2.iro.umontreal.ca (Proxmox) with ESMTP id A17FB80762; Sun, 30 Oct 2022 18:07:49 -0400 (EDT) Original-Received: from mail01.iro.umontreal.ca (unknown [172.31.2.1]) by pmg2.iro.umontreal.ca (Proxmox) with ESMTP id 2688A80667; Sun, 30 Oct 2022 18:07:48 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=iro.umontreal.ca; s=mail; t=1667167668; bh=jLdgooJiBcjqM2fiG4c1qoA2UT8zpvQfWXujpZtNgKU=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=V74Sh39ZsSmL1M5Nnq834btATAEHJYj5EBH9da3xRiXyUygT/OwomjKlq1ZEiGd2v CVYZGHWut7ZS6YC5s+aODff3lL/Vs44W/IFinDTtuz4jyT1O+ib1swd0GCF8ReSliW FOIU4cUb1C8aPJAzkKKEw0W/HFn/pHan/anDe5ZQX6mdHLSkl3Z0IIM6npPRWbZuRU QAx4B2+F6+ayc6YhGD8DmVG4ij3znTRqaB69boNfo+tQCvOUMKCoHJi4jCwz6m2E+y xpXMlLWuCSjCQZPVZT0dT0u19F76sVeGz1H43juUjXn6XOq+jScIEF8jtaFTly9z09 maGiVVKIfQanw== Original-Received: from pastel (65-110-220-202.cpe.pppoe.ca [65.110.220.202]) by mail01.iro.umontreal.ca (Postfix) with ESMTPSA id EC93F1203D7; Sun, 30 Oct 2022 18:07:47 -0400 (EDT) In-Reply-To: <87h6zl9q4u.fsf@posteo.net> (Philip Kaludercic's message of "Sun, 30 Oct 2022 17:29:21 +0000") Received-SPF: pass client-ip=132.204.25.50; envelope-from=monnier@iro.umontreal.ca; helo=mailscanner.iro.umontreal.ca X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: "Emacs-devel" Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:298832 Archived-At: >> `save-match-data` is costly and extremely rarely needed. > What makes it so expensive? The implementation appears to be trivial. It allocates cons cells (by calling `match-data`) to store the values. If you put it in such a place it will be wasted 99% of the time. >> So I'd much rather not save it here. > If the function is supposed to be side-effect-free, then it ought not to > sometimes replace the match data and not touch it when optimised away. The match-data is defined to be something very ephemeral, so it's OK for pure functions to clobber it. Admittedly, here it doesn't just clobber it but sets it to a reliable value, so there's a high risk that someone will rely on that match-data, so better not mark it as pure, indeed, contrary to what I said earlier. Stefan