GNU bug report logs - #5971
23.1.95; `delete' modifies default value instead of buffer-local value

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Package: emacs;

Reported by: "Drew Adams" <drew.adams <at> oracle.com>

Date: Mon, 19 Apr 2010 02:43:02 UTC

Severity: minor

Tags: notabug, wontfix

Done: Glenn Morris <rgm <at> gnu.org>

Bug is archived. No further changes may be made.

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Message #11 received at 5971 <at> debbugs.gnu.org (full text, mbox):

From: "Drew Adams" <drew.adams <at> oracle.com>
To: "'Stefan Monnier'" <monnier <at> iro.umontreal.ca>
Cc: 5971 <at> debbugs.gnu.org
Subject: RE: bug#5971: 23.1.95;
	`delete' modifies default value instead of buffer-local value
Date: Sun, 18 Apr 2010 22:24:42 -0700

> > This doesn't seem right to me.
>  
> Why not?  That's the whole reason for the existence of two functions:
> `delete' and `remove'.

I'm aware that `delete' modifies the list structure and `remove' uses a copy.
What I don't understand is the interaction with a default value instead of a
buffer-local value. Why would `delete' cause the behavior described?

The same code BTW uses `nconc' apparently without causing such
modify-the-default-value behavior:

(setq wide-n-restrictions
      (nconc (nthcdr arg wide-n-restrictions) latest))

What is the relation between `delete's modification of the list structure of a
cons that is a buffer-local value of a variable and its (apparent) modification
of the default value of the variable?
This bug report was last modified 13 years and 321 days ago.

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