GNU bug report logs - #62009
29.0.60; Emacs crashes on setf symbol-name

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Message #44 received at 62009 <at> debbugs.gnu.org (full text, mbox):

From: Augusto Stoffel <arstoffel <at> gmail.com>
To: Daniel Mendler <mail <at> daniel-mendler.de>
Cc: Philip Kaludercic <philipk <at> posteo.net>, michael_heerdegen <at> web.de,
 Gregory Heytings <gregory <at> heytings.org>, monnier <at> iro.umontreal.ca,
 62009 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#62009: 29.0.60; Emacs crashes on setf symbol-name
Date: Fri, 10 Mar 2023 12:23:54 +0100

On Fri, 10 Mar 2023 at 12:09, Daniel Mendler wrote:

> On 3/10/23 11:59, Gregory Heytings wrote:
>> That would also come with a performance overhead, as there is currently no 
>> way to distinguist strings that are used for symbol names from other 
>> strings.  Not to mention the added complexity in the code.
>
> One could check if the string is located in read-only memory. Or one
> could add a flag bit to the string data structure (and possibly to other
> data structures too). Freezing data structures such that they become
> read-only is a generally useful feature. There won't be any performance
> overhead of the check since a branch not taken is fast thanks to the
> branch predictor.

Note also that in-place modification of strings is arbitrarily costly,
cf. (aset "ascii" 0 ?😼).  Not to mention that it's rarely a good or
necessary move to make, as far as programming style is concerned.

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