From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= Newsgroups: gmane.emacs.bugs Subject: bug#42296: 27.0.91; Correct manual entry for 'concat' w.r.t. allocation [PATCH] Date: Fri, 10 Jul 2020 19:04:48 +0200 Message-ID: <70B05C00-862D-412B-83DA-7129BF49C322@acm.org> References: <83wo3cppc5.fsf@gnu.org> <669987BB-B825-4C2C-B9FD-31F04E0D6013@acm.org> <83r1tkplnc.fsf@gnu.org> <83o8oopk4s.fsf@gnu.org> Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.14\)) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="28573"; mail-complaints-to="usenet@ciao.gmane.io" Cc: 42296@debbugs.gnu.org To: Eli Zaretskii Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Fri Jul 10 19:05:24 2020 Return-path: Envelope-to: geb-bug-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 1jtwSi-0007L7-5v for geb-bug-gnu-emacs@m.gmane-mx.org; Fri, 10 Jul 2020 19:05:24 +0200 Original-Received: from localhost ([::1]:52082 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jtwSh-00072c-6n for geb-bug-gnu-emacs@m.gmane-mx.org; Fri, 10 Jul 2020 13:05:23 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:53750) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jtwSM-00070n-W8 for bug-gnu-emacs@gnu.org; Fri, 10 Jul 2020 13:05:03 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:60010) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jtwSL-0003f8-V9 for bug-gnu-emacs@gnu.org; Fri, 10 Jul 2020 13:05:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1jtwSL-0008CG-OO for bug-gnu-emacs@gnu.org; Fri, 10 Jul 2020 13:05:01 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Fri, 10 Jul 2020 17:05:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 42296 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: patch Original-Received: via spool by 42296-submit@debbugs.gnu.org id=B42296.159440069731495 (code B ref 42296); Fri, 10 Jul 2020 17:05:01 +0000 Original-Received: (at 42296) by debbugs.gnu.org; 10 Jul 2020 17:04:57 +0000 Original-Received: from localhost ([127.0.0.1]:43323 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1jtwSG-0008Bu-QR for submit@debbugs.gnu.org; Fri, 10 Jul 2020 13:04:57 -0400 Original-Received: from mail71c50.megamailservers.eu ([91.136.10.81]:36794 helo=mail92c50.megamailservers.eu) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1jtwSD-0008Bj-8X for 42296@debbugs.gnu.org; Fri, 10 Jul 2020 13:04:55 -0400 X-Authenticated-User: mattiase@bredband.net DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=megamailservers.eu; s=maildub; t=1594400691; bh=E4vZ4vxVjjbYw0lVpm0w+IcieBKUytF8lXzIsnUDHqI=; h=Subject:From:In-Reply-To:Date:Cc:References:To:From; b=T3OnDWO7tXVGpV3E8ZIQo6IgZXwIN1FUV2+artpd++WfH+7ll8Wnx+Oum4WtXQym9 ehhsu2dfEMr5SWDtFcRce/kcxmoSiiBsWfkvyg02nV//2uvi5fK5ITvN2Lh1DRUUKd 4ExA3b7EyEsQYBk0CjBdNFUt+403FRTn9WUi3iw8= Feedback-ID: mattiase@acm.or Original-Received: from [192.168.0.4] (c188-150-171-71.bredband.comhem.se [188.150.171.71]) (authenticated bits=0) by mail92c50.megamailservers.eu (8.14.9/8.13.1) with ESMTP id 06AH4niB021651; Fri, 10 Jul 2020 17:04:50 +0000 In-Reply-To: <83o8oopk4s.fsf@gnu.org> X-Mailer: Apple Mail (2.3445.104.14) X-CTCH-RefID: str=0001.0A782F1A.5F089FB3.0066, ss=1, re=0.000, recu=0.000, reip=0.000, cl=1, cld=1, fgs=0 X-CTCH-VOD: Unknown X-CTCH-Spam: Unknown X-CTCH-Score: 0.000 X-CTCH-Flags: 0 X-CTCH-ScoreCust: 0.000 X-CSC: 0 X-CHA: v=2.3 cv=aY8fYigt c=1 sm=1 tr=0 a=SF+I6pRkHZhrawxbOkkvaA==:117 a=SF+I6pRkHZhrawxbOkkvaA==:17 a=kj9zAlcOel0A:10 a=M51BFTxLslgA:10 a=mDV3o1hIAAAA:8 a=HkhAIVv8MCLDVp_ToZ0A:9 a=CjuIK1q_8ugA:10 a=_FVE-zBwftR9WsbkzFJk:22 X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.io gmane.emacs.bugs:182898 Archived-At: 9 juli 2020 kl. 21.24 skrev Eli Zaretskii : > This function frequently, but not always, constructs a new string > that is not @code{eq} to any existing string. Lisp programs should > not rely on the result being a new string nor on it being @code{eq} > to an existing string. >=20 > When this function returns a string @code{eq] to another, changing > the result will also change that other string; to avoid that, use > @code{copy-sequence} on the result. Thank you! First a minor detail: the word 'frequently' doesn't convey = any useful information since the user isn't supposed to take any chances = -- either the returned value is always new and unaliased, or there is no = such guarantee. The frequency isn't relevant, and we shouldn't encourage = the user to act as if it were by talking about it. > To my mind, immutability (or, rather, the adverse effects of modifying > the result of 'concat') is the result of the identity. So it is > conceptually wrong to talk about mutability _instead_ of the identity. > Identity is the basic reason, immutability is the side effect. Which > is what I tried to say in the text I suggested. I understand what you mean, but do not necessarily agree in every = respect. A string may be unsuitable for modification for several = (overlapping) reasons: * It is a string literal that occurs in the program. * It is a string produced by macro-expansion. * It is a string resulting from other compile-time evaluation (eg, = constant folding). * It is a string residing in read-only storage of some kind (via = dumping). * It aliases another string in the program. * It is an actual read-only string value (which we don't really have = today, but we should not preclude its introduction in the future). Thus mutability and identity are related concepts but neither clearly = dominates the other; stating both is probably useful, for clarity if = nothing else. Saying that mutating the return value merely entails = changing some other string is understating and misleading: the = consequences are not well-defined, and may include mutating programs and = the raising of errors. (It will never reach C levels of undefined = behaviour if we can help it, however.) There is also the question whether the function can return one of its = arguments. If so, the caller not only needs to abstain from mutating the = returned value, but also the argument, even though it may be safely = created by the caller. Currently, (concat x) never returns a string = argument, unless it's a compile-time constant that cannot be mutated = anyway. It's unclear whether we can guarantee this behaviour. But let's be constructive: Taking your proposed text and performing some = light surgery, we might end up with: This function does not always allocate a new string. Callers should not rely on the result being a new string nor on it being @code{eq} to an existing string. In particular, the returned value should not be altered. To obtain a string that can be mutated, use @code{copy-sequence} on the result.