Re: Seeking Advice about refactoring and advice snippet

[Chunyang Xu]

Hi,

It should be easier to use 'kill-buffer-query-functions'

  (defun dont-kill-scratch ()
    (if ((equal (buffer-name) "*scratch*"))
        (progn (message "DENIED! don't kill my precious *scratch*!!")
               nil)
      t))
  
  (add-hook 'kill-buffer-query-functions #'dont-kill-scratch)

Filipe Silva writes:

> Dear good people of the emacs help list,
>
> I have a working snippet that advices both kill-buffer and kill-this-buffer
> to not kill the *scratch* buffer:
>
>       (defun ninrod/scratch-bodyguard (buffer-assassin &rest arguments)
>         (let ((buffer-to-kill (buffer-name (current-buffer))))
>           (if (equal buffer-to-kill "*scratch*")
>               (message "DENIED! don't kill my precious *scratch*!!")
>             (apply buffer-assassin arguments))))
>       (defun ninrod/scratch-protection (buffer-assassin &rest arguments)
>         (let ((buffer-to-kill (car arguments)))
>           (if (equal buffer-to-kill "*scratch*")
>               (message "DENIED! don't kill my precious *scratch*!!")
>             (apply buffer-assassin arguments))))
>       (advice-add #'kill-this-buffer :around #'ninrod/scratch-bodyguard)
>       (advice-add #'kill-buffer :around #'ninrod/scratch-protection)

Considering 'kill-this-buffer' calls 'kill-buffer', advising
'kill-buffer' alone is enough.

> The problem is that these lines:
>
>       (message "DENIED! don't kill my precious *scratch*!!")
>      (apply buffer-assassin arguments))))
>
> Are repeated in both functions, so I thought that I could apply the DRY
> principle and refactor the snippet to this:
>
>     (defun ninrod--protection (buffer-assassin buffer-to-kill &rest
> arguments)
>       (if (equal buffer-to-kill "*scratch*")
>           (message "DENIED! don't kill my precious *scratch*!!")
>         (apply buffer-assassin arguments)))
>     (defun ninrod/scratch-bodyguard (buffer-assassin &rest arguments)
>       (let ((buffer-to-kill (buffer-name (current-buffer))))
>         (ninrod--protection 'buffer-assassin buffer-to-kill arguments)))
>     (defun ninrod/scratch-protection (buffer-assassin &rest arguments)
>       (let ((buffer-to-kill (car arguments)))
>         (ninrod--protection 'buffer-assassin buffer-to-kill arguments)))
>     (advice-add #'kill-this-buffer :around #'ninrod/scratch-bodyguard)
>     (advice-add #'kill-buffer :around #'ninrod/scratch-protection)

You should not quote 'buffer-assassin'. And when you pass '&rest
arguments' to 'ninrod/scratch-protection', you should use
'apply'. Something like the following works from here.

  (defun ninrod/scratch-bodyguard (buffer-assassin &rest arguments)
    (let ((buffer-to-kill (buffer-name (current-buffer))))
      (apply #'ninrod--protection buffer-assassin buffer-to-kill arguments)))
  
  (advice-add #'kill-this-buffer :around #'ninrod/scratch-bodyguard)

> This causes all hell to break loose. Now I can't even close emacs, because
> apparently emacs tries to kill all buffers
> and as I've just tampered with the kill buffer functions, well, it's bad.
> Very bad.
>
> I know I mean well, but I'm must be doing something very stupid. For
> starters, I don't know if I can really pass around
> functions as parameters? So it could be that?
>
> How would you refactor that snippet to apply the dry principle?
>
> thanks in advance,
>
> Filipe.