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dynamic variables and advice
From: |
Madhu |
Subject: |
dynamic variables and advice |
Date: |
Thu, 03 Mar 2022 12:10:42 +0530 (IST) |
I was trying to use the add-function facility to make dired and friends
prompt only for directories. the naive approach with a lot of printf
debugging -
#+begin_src elisp
(defvar read-file-name--directories-p nil
"dynamic variable which should be let-bound in an :around advice
and should be used in a :filter-args advice.")
(defun read-file-name--maybe-filter-directories (args)
"filter-args advice for read-file-name."
(cl-destructuring-bind (prompt &optional dir default-filename
mustmatch initial predicate)
args
(let ((ret (list prompt dir default-filename mustmatch initial
(or predicate
(and read-file-name--maybe-filter-directories-p
#'file-directory-p)))))
(message "rfn-mfd: rfnmfd=%s this-command=%s ret=%s"
read-file-name--maybe-filter-directories-p this-command ret)
ret)))
(advice-add 'read-file-name
:filter-args 'read-file-name--maybe-filter-directories)
(defun rfnmfd-yes (oldfun &rest args)
"an around advice function which sets rfn-mfd-p to t"
(let ((read-file-name--mabe-filter-directories-p t))
(message "rfnmfd-yes: begin")
(prog1 (apply oldfun args)
(message "rfnmfd-yes: done"))))
(advice-add 'dired-read-dir-and-switches :around 'rfnmfd-yes)
#+end_src
Now when I call M-x dired the around advice for
dired-read-dir-and-switches runs, and it binds
read-file-name--directories-p to t and eventually goes on to call
read-file-name where the filter-args advice kicks in.
but in filter-args advice my dynamic variable is bound to nil and not
to t as I'd expect.
How is my expectation wrong or what is actually happening?
- dynamic variables and advice,
Madhu <=