From: "Andreas Röhler" <andreas.roehler@easy-emacs.de>
To: John Mastro <john.b.mastro@gmail.com>,
Help Gnu Emacs mailing list <help-gnu-emacs@gnu.org>
Subject: Re: (copy-marker nil)
Date: Mon, 7 May 2018 16:23:17 +0200 [thread overview]
Message-ID: <181880cf-6962-72a2-2c65-25d4b884d3e9@easy-emacs.de> (raw)
In-Reply-To: <CAOj2CQQ_1EJMBgYTqXW7APqoA-CaACbf1hKLS49ofK1pvxz8Ug@mail.gmail.com>
On 07.05.2018 15:39, John Mastro wrote:
> 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))))
>
Thanks. A way to deal with ;)
next prev parent reply other threads:[~2018-05-07 14:23 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
2018-05-07 14:23 ` Andreas Röhler [this message]
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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