Re: using finalizers

[Tomas Hlavaty]

On Sat 01 Jan 2022 at 18:18, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>> > Do you have concrete cases where this difference introduces a
>> > difficulty?

Well, maybe not difficulty but inconvenience and potential future
difficulty.  I found make-finalizer surprising and inconvenient.
But LdBeth pointed out some interesting things I need to read about.

> I miswrote, by "concrete" I meant a real-word use, no a made-up case.

It was a reduced case of:

(defun directory-brook (directory)
  (let (d)
    (letrec ((close (lambda ()
                      (when d
                        (close-directory d)
                        (setq d nil
                              more nil))))
             (more (make-finalizer close)))
      (lambda ()
        (when more
          (unless d
            (setq d (open-directory directory)))
          (let (z (again t))
            (while again
              (setq z (read-directory d))
              (cond
               ((equal z "."))
               ((equal z ".."))
               (z (setq again nil))
               (t (setq again nil) (funcall close))))
            z))))))

There are bits missing but it should give you an idea.

> [ But at least, now I understand what you meant by the fact that the
>   behavior depends on the byte-compiler's analysis.  ]

Great, that was difficult for me to express.

> In any case, I don't think we have much experience with the current
> `make-finalizer` API (nor with other finalizer APIs) in ELisp, so
> I think there's room for tweaks/changes.  But it should be based
> on concrete cases in real world ELisp code.

Understand, thank you.