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Re: A strange issue with buffer-undo-list
From: |
Michael Heerdegen |
Subject: |
Re: A strange issue with buffer-undo-list |
Date: |
Tue, 09 Mar 2021 01:32:21 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
Marcin Borkowski <mbork@mbork.pl> writes:
> > Seems so. Where they are used - e.g. in the implementation of
> > `transpose-subr', they are important however. You wouldn't want that
> > undoing a transposition would happen in multiple steps uncovering
> > implementation details.
>
> Agreed, although I don't think undo would kick in within one command
> (without explicit undo boundaries).
Maybe I had not yet completely understood how this works. It seems one
(primitive) undo undoes until it finds a boundary, and boundaries seem
to be implicitly inserted after any command. Then I think the change
group is used in `transpose-subr' to prevent that the transposition or
its undoing is left in a half-done state in case of an error, and it has
more or less no user visible effect if no errors happen.
Someone should really write a short summary on how the undo system is
implemented, it is not trivial and finding out is also not.
Regards,
Michael.