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Re: [PATCH] gv.el: minor change, cleaning up

From: Stefan Monnier
Subject: Re: [PATCH] gv.el: minor change, cleaning up
Date: Wed, 16 Jun 2021 09:03:01 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

> Evaluate `(macroexpand-all `(setf (alist-get key alist) value))` and
> it returns the following:
>   (let* () ;; /* bindings omitted */
>     (progn
>      (if p
>          (setcdr p v)
>        (setq alist
>              (cons (setq p
>                          (cons key v))
>                    alist)))
>      v))
> It seems to me that `(setq p ..)` is unnecessary,

It's unnecessary for `setf` (and `push`, and `cl-pushnew`, and
`cl-rotatef`, and `cl-callf` ;-) but it can be necessary for more
complex settings.  I can't remember what was the setting where I found
that I needed it, sadly.  Clearly it must be one where we use the getter
(or the setter) after having used the setter.


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