GNU bug report logs - #13122
transpose-subr defeats save-excursion

Previous Next

Full log

Message #36 received at 13122 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Tino Calancha <tino.calancha <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 13122 <at> debbugs.gnu.org
Subject: Re: bug#13122: save-excursion not saving point
Date: Sat, 27 Apr 2019 11:59:48 +0200

On Apr 27 2019, Tino Calancha <tino.calancha <at> gmail.com> wrote:

> On Sat, 27 Apr 2019, Eli Zaretskii wrote:
>
>>> From: Tino Calancha <tino.calancha <at> gmail.com>
>>> Date: Sat, 27 Apr 2019 04:53:56 +0900
>>>
>>> ;; Following expression should eval as non-nil
>>> (let ((pos 3))
>>>   (with-temp-buffer
>>>     (insert "abcdef")
>>>     (goto-char pos)
>>>     (save-excursion (transpose-chars 2))
>>>     (= pos (point))))
>>> => nil
>
> I read that warning; maybe getting `nil' is above is expected; if that's
> the case then we can close the report again.

Since the form inside save-excursion can modify the text before point,
there is never a guarantee that the numeric value of point stays the
same.  And if point points inside the modified text, it is generally
unspecified how point moves during the modification.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.