From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Philip Kaludercic Newsgroups: gmane.emacs.devel Subject: Re: A function to take the regexp-matched subsring directly Date: Sun, 30 Oct 2022 17:29:21 +0000 Message-ID: <87h6zl9q4u.fsf@posteo.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="35504"; mail-complaints-to="usenet@ciao.gmane.io" Cc: daanturo , emacs-devel@gnu.org To: Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sun Oct 30 18:29:44 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 1opC7z-0008y8-Dk for ged-emacs-devel@m.gmane-mx.org; Sun, 30 Oct 2022 18:29:43 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1opC7j-0006pf-7O; Sun, 30 Oct 2022 13:29:27 -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 1opC7h-0006pQ-DX for emacs-devel@gnu.org; Sun, 30 Oct 2022 13:29:25 -0400 Original-Received: from mout02.posteo.de ([185.67.36.66]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1opC7f-000134-Op for emacs-devel@gnu.org; Sun, 30 Oct 2022 13:29:25 -0400 Original-Received: from submission (posteo.de [185.67.36.169]) by mout02.posteo.de (Postfix) with ESMTPS id 51BB7240103 for ; Sun, 30 Oct 2022 18:29:22 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1667150962; bh=2fgMQa+RwB4J+i59+KXytGvfLRpM3fiPEEzyoMLPmbg=; h=From:To:Cc:Subject:Autocrypt:Date:From; b=hkEL56+Qzv1V0OwLXz0FHXyIfNgDNA6+YLWnVSz6M3BvEdjTJAEx11OiNWk9NprIj Egb6NPL1b9eud09OdSXRm75xecoiv7Mn04aY6nDOjDkkmVzUDJqWHj6h9LqAKmfUgO 2GawscJxYKi0WmTHY0W369RgpW3NeYIhSXswNHRNSsHnDMHXI7v6bMlBmg2q7RxVJq UTASUWMFQChGZzyFGYwx5DDHqw4JXHqKESjYRJoNgGVqYQXjVXyaWxm5DTWirHLUpb cfVKQA8Y4xU+jmsNSzv2iUSGW1MlOShx3oghMSyCtz6KZhNsseoiQYcSXie5eUXgCQ MMH6lB3zcYDFw== Original-Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4N0jvP3R35z6tn8; Sun, 30 Oct 2022 18:29:21 +0100 (CET) In-Reply-To: (Stefan Monnier's message of "Sun, 30 Oct 2022 11:52:19 -0400") Autocrypt: addr=philipk@posteo.net; prefer-encrypt=nopreference; keydata= mDMEYHHqUhYJKwYBBAHaRw8BAQdAp3GdmYJ6tm5McweY6dEvIYIiry+Oz9rU4MH6NHWK0Ee0QlBo aWxpcCBLYWx1ZGVyY2ljIChnZW5lcmF0ZWQgYnkgYXV0b2NyeXB0LmVsKSA8cGhpbGlwa0Bwb3N0 ZW8ubmV0PoiQBBMWCAA4FiEEDM2H44ZoPt9Ms0eHtVrAHPRh1FwFAmBx6lICGwMFCwkIBwIGFQoJ CAsCBBYCAwECHgECF4AACgkQtVrAHPRh1FyTkgEAjlbGPxFchvMbxzAES3r8QLuZgCxeAXunM9gh io0ePtUBALVhh9G6wIoZhl0gUCbQpoN/UJHI08Gm1qDob5zDxnIHuDgEYHHqUhIKKwYBBAGXVQEF AQEHQNcRB+MUimTMqoxxMMUERpOR+Q4b1KgncDZkhrO2ql1tAwEIB4h4BBgWCAAgFiEEDM2H44Zo Pt9Ms0eHtVrAHPRh1FwFAmBx6lICGwwACgkQtVrAHPRh1Fw1JwD/Qo7kvtib8jy7puyWrSv0MeTS g8qIxgoRWJE/KKdkCLEA/jb9b9/g8nnX+UcwHf/4VfKsjExlnND3FrBviXUW6NcB Received-SPF: pass client-ip=185.67.36.66; envelope-from=philipk@posteo.net; helo=mout02.posteo.de X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H2=-0.001, 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:298828 Archived-At: Stefan Monnier writes: >> +;;;###autoload >> +(defun regexp-match (regexp string &optional n) >> + "Return the N -th matched substring for REGEXP in STRING. >> +N defaults to 0 (the whole match). >> + >> +This function does not change the match data." >> + (declare (pure t) (side-effect-free t)) >> + (let ((n (or n 0))) >> + (save-match-data >> + (when (string-match regexp string) >> + (match-string n string))))) > > `save-match-data` is costly and extremely rarely needed. What makes it so expensive? The implementation appears to be trivial. > 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. >> + (save-match-data >> + (when (string-match regexp string) >> + (let ((match-index (1- (/ (length (match-data)) 2))) >> + matches) >> + (while (<=3D 0 match-index) >> + (push (match-string match-index string) matches) >> + (setq match-index (1- match-index))) >> + matches)))) > > I suspect it'd be more efficient to iterate directly on the `match-data` = rather > than on an integer (which suffers from an O(N=C2=B2) complexity). > > > Stefan