From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: Re: new `obarray` type Date: Tue, 14 Mar 2017 20:14:14 +0000 Message-ID: <20170314201414.GA4562@acm> References: <20170313220335.GA5098@acm> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1489522506 22819 195.159.176.226 (14 Mar 2017 20:15:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 14 Mar 2017 20:15:06 +0000 (UTC) User-Agent: Mutt/1.7.2 (2016-11-26) Cc: emacs-devel@gnu.org To: Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Mar 14 21:15:01 2017 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cnsqN-0004qh-Ln for ged-emacs-devel@m.gmane.org; Tue, 14 Mar 2017 21:14:55 +0100 Original-Received: from localhost ([::1]:33324 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cnsqT-0001xH-Mu for ged-emacs-devel@m.gmane.org; Tue, 14 Mar 2017 16:15:01 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:51659) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cnsqK-0001wA-NJ for emacs-devel@gnu.org; Tue, 14 Mar 2017 16:14:53 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cnsqG-0003CL-LY for emacs-devel@gnu.org; Tue, 14 Mar 2017 16:14:52 -0400 Original-Received: from ocolin.muc.de ([193.149.48.4]:59224 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.71) (envelope-from ) id 1cnsqG-0003Bt-Bw for emacs-devel@gnu.org; Tue, 14 Mar 2017 16:14:48 -0400 Original-Received: (qmail 98064 invoked by uid 3782); 14 Mar 2017 20:14:46 -0000 Original-Received: from acm.muc.de (p548C655D.dip0.t-ipconnect.de [84.140.101.93]) by colin.muc.de (tmda-ofmipd) with ESMTP; Tue, 14 Mar 2017 21:14:46 +0100 Original-Received: (qmail 4724 invoked by uid 1000); 14 Mar 2017 20:14:14 -0000 Content-Disposition: inline In-Reply-To: X-Delivery-Agent: TMDA/1.1.12 (Macallan) X-Primary-Address: acm@muc.de X-detected-operating-system: by eggs.gnu.org: FreeBSD 9.x [fuzzy] X-Received-From: 193.149.48.4 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 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" Xref: news.gmane.org gmane.emacs.devel:213028 Archived-At: Hello, Stefan. On Tue, Mar 14, 2017 at 08:52:59 -0400, Stefan Monnier wrote: > > It's not more palatable to this user. It sounds more like "dumbing > > down". There are few things more frustrating whilst debugging than > > having Emacs obfuscating information "for my own good". > The good thing about having the `obarray` type is that e get to choose > how to print them. > I can easily make it so it prints all the symbols in it, would you > prefer that? Yes, please! > > Indeed, why not just print _all_ vectors by printing only their size? > The reason why the patch I sent only prints the number of entries is > that currently the way obarrays are printed you only get to see some of > the symbols but not all. But I guess you're right: it would be more > useful to list all the symbols in it. > [ Time passes... Done! ] Apologies for that. I wasn't really aware that (currently) printing an obarray only displays some of the symbols. > > Not rarely, particularly in CC Mode, I will be dealing with obarrays > > with relatively small numbers of symbols. > Regardless of what we decide to do with obarrays, I strongly recommend > you change cc-mode to use hash-tables instead. My experience with EIEIO > (where I "recently" moved from obarrays to hash-tables) is that it's > measurably faster and the code tends to be clearer (tho that's clearly > subjective). There are currently four uses of (make-vector LENGTH 0) in CC Mode, at least one of which, possibly two, genuinely deal with Lisp symbols. Converting those to hash-tables would probably be a net loss, though converting the ones which just use obarrays as a string look-up would surely gain. > > Of course I want to see these symbols' names when I ask for that > > obarray to be printed. > With hash-tables, you'll them see all, properly printed and even `read`able! > > I'm also not in favour of introducing another vector-like type without a > > very good reason. > Obarrays are very weird, currently, because they combine "plain vectors" > and "plain symbols" in a tricky way. > - Have you ever tried to do `aref` on an obarray? > - The printout lists some of the symbols, but not all. Which ones appear > is arbitrary, unpredictable. > - Have you ever tried to put something else than 0 in an obarray slot? > - An obarray can lead to unexpected space behavior: > (let* ((o (obarray-make)) > (s1 (intern "s1" o)) > (s2 (intern "s2" o))) > (set s1 (make-list 100000 t)) > s2) > might leave you with a 10000-element list preserved as "reachable" as > long as `s2` is reachable, even tho it's clearly not reachable any more. > BTW, my patch doesn't address this GC problem yet. > > positions. Would a new obarray type prevent any vector operations being > > carried out on it, should any package do such things? If so, that would > > be a Bad Thing. > Currently, I haven't changed `aref` to work on obarrays, no. I've never > ever seen code try to do that (I guess in theory it could be potentially > useful, tho I can't think of any operation you could implement reliably > using `aref` on obarrays would be `obarray-empty-p`). > I was planning on allowing `aset` in case some package uses it to do the > equivalent of `clrhash`, but I haven't yet found any package doing that, > so I haven't bothered either. > > This change would create hassle in general for many packages, all of > > which create obarrays with (make-vector LENGTH 0), and would need > > changing to use `make-obarray'. > Of course, (make-vector LENGTH 0) still works. And there's > obarray-make, introduced in Emacs-25, IIRC. But even if we deprecate > (make-vector LENGTH 0) you won't get any byte-compilation warning for it > since we can't detect whether a (make-vector LENGTH 0) is meant as an > obarray or as a normal array that happens to be filled with zeroes. You could prohibit symbol operations on the "wrong" type of vector. > > It would mean having to write yet more compatibility macros (for the > > inevitable day when old style obarrays get removed from Emacs). > To the extent that we can't detect when make-vector is used for an > obarray, I expect that it'll take *many* years until we can drop support > for "old-style" obarrays, so I wouldn't worry about it. > I suspect that even cc-mode will have switch to hash-tables before > support for old-style obarrays is dropped. Hee! Thanks for this reply. I withdraw my objections to the new obarray type. > Stefan -- Alan Mackenzie (Nuremberg, Germany).