From: John Mastro <john.b.mastro@gmail.com>
To: Help Gnu Emacs mailing list <help-gnu-emacs@gnu.org>
Subject: Re: (copy-marker nil)
Date: Mon, 7 May 2018 06:39:27 -0700 [thread overview]
Message-ID: <CAOj2CQQ_1EJMBgYTqXW7APqoA-CaACbf1hKLS49ofK1pvxz8Ug@mail.gmail.com> (raw)
In-Reply-To: <364c8f2d-06ab-4f81-852f-eb3bac7a0615@easy-emacs.de>
Andreas Röhler <andreas.roehler@easy-emacs.de> wrote:
> being surprised WRT behavior of copy-marker:
>
> (setq a (copy-marker nil)) -> #<marker in no buffer>
> (markerp a) -> t
> a -> #<marker in no buffer>
>
> Is taking nil by copy-marker reasonable?
>
> Wanted to check for a valid buffer position, which doesn't seem
> possible that way. While without copy-marker, the variable a would be
> set to nil, now the result evaluates to #<marker in no buffer>, which
> is a kind of t.
There are other ways to get a marker to no buffer, such as
(let ((a (point-marker)))
(set-marker a nil))
So if you don't control the creation of the marker, it's probably a
scenario you need to take care for either way.
Explicitly testing the marker's buffer should work:
(let ((a (copy-marker nil)))
(and (markerp a)
(buffer-live-p (marker-buffer a))))
--
John
next prev parent reply other threads:[~2018-05-07 13:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-07 8:19 (copy-marker nil) Andreas Röhler
2018-05-07 13:39 ` John Mastro [this message]
2018-05-07 14:23 ` Andreas Röhler
2018-05-07 13:55 ` Noam Postavsky
2018-05-07 14:20 ` Andreas Röhler
2018-05-07 14:26 ` Drew Adams
2018-05-07 17:16 ` Andreas Röhler
2018-05-08 1:46 ` Stefan Monnier
2018-05-08 8:44 ` Andreas Röhler
2018-05-12 22:06 ` Stefan Monnier
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