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From: Eli Zaretskii <eliz@gnu.org>
Newsgroups: gmane.emacs.help
Subject: Re: Which Elisp types are mutable?
Date: Mon, 05 Jul 2021 21:48:51 +0300
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In-Reply-To: <4AA1E624-B979-4B08-8AE0-E33A1C9A0E94@gmail.com> (message from
 Philipp on Mon, 5 Jul 2021 20:41:58 +0200)
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> From: Philipp <p.stephani2@gmail.com>
> Date: Mon, 5 Jul 2021 20:41:58 +0200
> Cc: Help Gnu Emacs mailing list <help-gnu-emacs@gnu.org>
> 
> > Well, in my book, "you can't mutate them" is.  You always /can/ mutate
> > a string, but of you do it in certain circumstances, you're asking for
> > trouble.
> 
> You can mutate all objects, because all of them are stored in mutable memory.

Not if you put it in read-only memory: you'd get a segfault with any
modern OS.

> For a reference manual, "you're asking for trouble" isn't a terribly useful statement.

And "you must not mutate them" is?  At least "you're asking for
trouble" explains why not, especially if it actually describes some of
the trouble.