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Re: Help needed with defadvice


From: Eric Abrahamsen
Subject: Re: Help needed with defadvice
Date: Fri, 22 Nov 2013 13:27:41 +0700
User-agent: Gnus/5.130008 (Ma Gnus v0.8) Emacs/24.3 (gnu/linux)

Perry Smith <address@hidden> writes:

> I have this defadvice:
>
> (defadvice get-buffer-create (around inherit activate)
>   (let ((set-list (mapcar '(lambda ( v )
>                            (cons v (symbol-value v)))
>                         inherited-alist)))
>     (with-current-buffer ad-do-it 
>       (mapcar '(lambda ( c )
>                (message "Setting %s to %s inside %s"
>                         (car c) (cdr c) (buffer-name (current-buffer)))
>                (set (car c) (cdr c)))
>             set-list))))
>
> inherited-alist is a list of symbols that I add to.  When a buffer is 
> created, I run through the list of variables and get their values as seen 
> from the current buffer.  I then call get-buffer-create (via ad-do-it) and do 
> a set on each of the variables.  The "message" is there just for debugging.  
> I get the messages like I expect .... e.g. "Setting foo to dog inside cat.c" 
> or whatever.  All the symbols in inherited-alist are buffer-local variables.
>
> When I get done and get in cat.c and ask for the value of foo, it is always 
> nil.
>
> I have almost the same function:
>
> (defun inherit-from-buffer ( buf )
>   "Set all inherited variables of current buffer to those values of BUF"
>   (interactive "bBuffer: ")
>   (message "Inheriting from %s to %s" buf (buffer-name (current-buffer)))
>   (let ((curbuf (current-buffer))
>       set-list)
>     (set-buffer buf)
>     (setq set-list
>         (mapcar '(lambda ( v )
>                    (cons v (symbol-value v)))
>                 inherited-alist))
>     (set-buffer curbuf)
>     (mapcar '(lambda ( c )
>              (message "Setting %s to %s inside %s"
>                       (car c) (cdr c) (buffer-name (current-buffer)))
>              (set (car c) (cdr c)))
>           set-list)))
>
> which I call interactively from inside cat.c and give it an argument of 
> another buffer to inherit from and it works as expected.  The messages are 
> the same, everything is the same except the function, after the fact, works 
> but doing roughly the same from inside a advice does not.

I don't really know why this wouldn't work, but maybe try changing the
first let to read:

(let* ((curbuf (current-buffer))
       (set-list (mapcar '(lambda ( v )
                            (cons v (buffer-local-value v curbuf)))
                         inherited-alist))))

Does that change anything? You could also get the full list of buffer
locals with `buffer-local-variables', and then assoc values from
inherited-alist in that list.

Hope that does something,
Eric




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