Daniel Colascione <dancol@dancol.org> writes:

> The feature I'm proposing is higher-level than that.  For example, for
> my personal use, I have something that sits in pre-redisplay-function
> and scans all the windows for applying highlights based on current
> buffer and window selection.  I should have written this thing using the
> appropriate window configuration change hooks, but didn't, because I'm
> lazy and my approach is fast enough for me.

>     ;; Don't do this.

>     (defun window-highlight--pre-redisplay (_window)
>       (window-highlight--rescan-windows))

>     (add-function :after pre-redisplay-function
>        #'window-highlight--pre-redisplay))

> What I'd have wanted instead is something like this:

>   (run-when-changed
>       (list (selected-window) (selected-frame) (frame-focus-state))
>     #'window-highlight--rescan-windows)

> Here, we'd run window-highlight--rescan-windows only when one of its
> dependent conditions (e.g. selected frame) changed.  After any number of
> window and frame changes, we'd run window-highlight--rescan-windows
> *once*, immediately before its effects would become user-visible
> (e.g. just before redisplay, or after commands), and we wouldn't re-run
> it until one of its preconditions changed.

Can your proposal also handle whether user moves cursor?

Another reason why post-command-hook is used is mostly for run code
when user moves cursor position.

post-command-hook would run code even if user/cursor is idle and even
for every /(unrelated)/ function in background, which can lead to high
resource consumption.

I think having alternatives like this for specific commands (or actions)
could help reduce the use of post-command-hook.