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Re: Change a symbol's plist member with (let ...)?
From: |
Nicolas Richard |
Subject: |
Re: Change a symbol's plist member with (let ...)? |
Date: |
Fri, 14 Mar 2014 22:37:29 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) |
Thorsten Jolitz <tjolitz@gmail.com> writes:
> #+begin_src emacs-lisp
> (plist-get (symbol-plist 'outline-mode)
> 'derived-mode-parent)
> #+end_src
>
(get 'outline-mode 'derived-mode-parent) looks better to me.
> For the sake of this example, say I want to "con" the function
> `derived-mode-p' and make it believe outline-mode is actually derived
> from lisp-mode (or so ...).
>
> How to do this with working code (not pseudo-code)?
I'm in message-mode right now, and :
(derived-mode-p 'text-mode)
returns: text-mode
But
(letf (((get major-mode 'derived-mode-parent) 'special-mode))
(derived-mode-p 'text-mode))
returns nil.
You could also let-bind major-mode to whatever the code you're calling
expects.
> Or do I have to do it the pedestrian way: do plist-get first, store the
> original value, do plist-put with the new value, call ad-do-it, and then
> restore the original value again with plist-put?
If you already know what you want the function to return, you could simply make
the advice return that value and not call ad-do-it at all.
--
Nico.