From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: [Emacs-diffs] emacs-25 3eb93c0: Rely on conservative stack scanning to find "emacs_value"s Date: Tue, 29 Mar 2016 18:35:10 -0700 Organization: UCLA Computer Science Department Message-ID: <56FB2D4E.5000609@cs.ucla.edu> References: <20151130193446.22218.14685@vcs.savannah.gnu.org> <56892947.80308@dancol.org> <56894233.8010106@cs.ucla.edu> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1459301736 1701 80.91.229.3 (30 Mar 2016 01:35:36 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 30 Mar 2016 01:35:36 +0000 (UTC) To: Philipp Stephani , Daniel Colascione , emacs-devel@gnu.org, Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Wed Mar 30 03:35:27 2016 Return-path: Envelope-to: ged-emacs-devel@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 1al52b-0006Jh-PL for ged-emacs-devel@m.gmane.org; Wed, 30 Mar 2016 03:35:26 +0200 Original-Received: from localhost ([::1]:51386 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1al52X-0000Tt-C1 for ged-emacs-devel@m.gmane.org; Tue, 29 Mar 2016 21:35:21 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:34769) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1al52T-0000Qs-5e for emacs-devel@gnu.org; Tue, 29 Mar 2016 21:35:17 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1al52P-0003dg-W6 for emacs-devel@gnu.org; Tue, 29 Mar 2016 21:35:17 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:40293) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1al52P-0003dW-Py for emacs-devel@gnu.org; Tue, 29 Mar 2016 21:35:13 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 0CF601605F3; Tue, 29 Mar 2016 18:35:12 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id uBQzMsiqEBRz; Tue, 29 Mar 2016 18:35:11 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 54F27161211; Tue, 29 Mar 2016 18:35:11 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id vkVeVANDQ1MC; Tue, 29 Mar 2016 18:35:11 -0700 (PDT) Original-Received: from penguin.cs.ucla.edu (Penguin.CS.UCLA.EDU [131.179.64.200]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 36B8C1605F3; Tue, 29 Mar 2016 18:35:11 -0700 (PDT) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 In-Reply-To: X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 131.179.128.68 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:202432 Archived-At: On 03/29/2016 03:07 AM, Philipp Stephani wrote: > > > > - From a user's perspective, it removes NULL as a sentinel value to > signal an error. It's not clear that this feature is worth the hassle of supporting it. As Stefan mentioned, one can easily use Qnil etc. as sentinels. > - From a developer perspective, it adds low-level complexity, > bit-twiddling, and possibly undefined behavior to a module that should > only contain glue code between two interfaces. The old approach was also complicated; its data structures were more complex and typically a bit slower, and it had more lines of code and it was typically more of a pain to debug at the C level. The new approach's use of undefined bit-twiddling isn't bad, given that even the old approach bit-twiddled with abandon by calling XCAR, XCDR and the like. If the main objection here is seeing bit operations like "<<" in emacs-module.c, we could move uses of these operations from emacs-module.c to lisp.h so that emacs-module.c could be more abstract. Rearrange the deck chairs, so to speak.