From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Daniel Colascione <dancol@dancol.org>
Cc: Paul Eggert <eggert@cs.ucla.edu>, emacs-devel@gnu.org
Subject: Re: [Emacs-diffs] master b7f83ad: Prefer memset to repeatedly assigning Qnil
Date: Tue, 20 Jan 2015 14:10:08 -0500 [thread overview]
Message-ID: <jwvoapte0ju.fsf-monnier+emacsdiffs@gnu.org> (raw)
In-Reply-To: <54BDED19.3020205@dancol.org> (Daniel Colascione's message of "Mon, 19 Jan 2015 21:52:25 -0800")
> The problem with this approach is that we'll have sections of code that
> exist only to account for an uncommon configuration.
We don't need to keep the code for the "Qnil!=0" case, but we should
limit the reliance on "Qnil==0" to a few specific places where rewriting
it differently is fairly easy difficult. E.g. a few macros in lisp.h
for example.
> They'll bitrot, and the code will grow implicit dependencies on Qnil
> being zero anyway.
That'll happen any way, indeed, by accident. Just like we had places
which relied on 0==make_number(0), which we've had to find the hard way
(and there might still be some such places we haven't yet noticed).
But if we only consciously rely on Qnil==0 in a few special places, then
we're less likely to introduce such dependencies by accident all over
the place.
> It'll be just like GCPRO. I'd rather just declare that Qnil will always
> be zero and take full advantage of the change.
Regarding GCPRO, I'd be happy to get rid of them, but AFAIK they're
still used on a few platforms. If we can fix those remaining platforms
we can get rid of GCPRO.
Stefan
next prev parent reply other threads:[~2015-01-20 19:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20150119090203.4087.82062@vcs.savannah.gnu.org>
[not found] ` <E1YD8Dj-00014b-6G@vcs.savannah.gnu.org>
2015-01-19 14:33 ` [Emacs-diffs] master b7f83ad: Prefer memset to repeatedly assigning Qnil Stefan Monnier
2015-01-19 15:14 ` Daniel Colascione
2015-01-20 4:37 ` Stefan Monnier
2015-01-20 5:52 ` Daniel Colascione
2015-01-20 19:10 ` Stefan Monnier [this message]
2015-01-20 22:00 ` Paul Eggert
2015-01-21 15:31 ` Stefan Monnier
2015-01-22 4:09 ` Paul Eggert
2015-01-20 1:18 ` Paul Eggert
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