From: Florian Beck <fb@miszellen.de>
To: help-gnu-emacs@gnu.org
Subject: Re: replacing a function with another one
Date: Wed, 12 Mar 2014 20:34:37 +0100 [thread overview]
Message-ID: <5320B6CD.5000306@miszellen.de> (raw)
In-Reply-To: <87iorjmidz.fsf@yun.yagibdah.de>
>> (lambda (&rest r) (apply FUNCTION OLDFUN r))
This line tells you what the ADVICE does (in this case the around
advice). But what does it mean?
1. Once you define an advice, instead of OLDFUN, emacs calls
(lambda (&rest r) (apply FUNCTION OLDFUN r)), which is a function that
has any arguments and only calls (apply FUNCTION OLDFUN r)
2. &rest r means all (arbitrarily many) arguments are collected in the
variable r.
3. apply then calls your FUNCTION with OLDFUN and the rest as arguments
For example, define a function:
(defun my-fun (a b)
(list a b))
and a function we will add as an advice:
(defun my-advice (&rest args)
args)
Add it:
(advice-add 'my-fun :around 'my-advice)
Now call (my-fun 'a 'b)
This returns ((lambda (a b) (list a b)) 1 2)
As you can see, your advice function gets called with three arguments of
which the first is the original definition.
With that knowledge, we can redefine our advice function:
(defun my-advice (fun a b)
(funcall fun a 'X))
using the first argument to call the original function.
And that is really all you have to know when advising a function
- define a new function that takes the old function as an additional
first argument
- add the advice (advice-add 'my-fun :around 'my-advice)
Things are even easier with a :before advice, where you can do anything
you want with the arguments:
(defun my-fun2 (a b)
(list a b))
(defun my-advice2 (x y)
(message "List contains %s and %s." x y))
(advice-add 'my-fun2 :before 'my-advice2)
--
Florian Beck
next prev parent reply other threads:[~2014-03-12 19:34 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-08 19:43 replacing a function with another one lee
2014-03-08 19:54 ` Eli Zaretskii
2014-03-09 1:17 ` lee
2014-03-08 22:30 ` Michael Heerdegen
2014-03-09 17:58 ` lee
2014-03-09 19:10 ` Michael Heerdegen
2014-03-09 20:57 ` lee
2014-03-09 22:02 ` Michael Heerdegen
2014-03-10 0:53 ` lee
2014-03-10 2:18 ` Michael Heerdegen
2014-03-10 15:29 ` lee
2014-03-11 0:03 ` Michael Heerdegen
2014-03-11 13:34 ` lee
2014-03-11 23:40 ` Michael Heerdegen
2014-03-12 6:11 ` Michael Heerdegen
2014-03-12 7:07 ` Michael Heerdegen
2014-03-12 14:48 ` lee
2014-03-13 7:19 ` Michael Heerdegen
2014-03-15 19:51 ` lee
2014-03-17 12:00 ` Michael Heerdegen
2014-03-12 14:04 ` lee
2014-03-12 18:26 ` Stefan Monnier
2014-03-12 4:10 ` Michael Heerdegen
2014-03-10 12:44 ` Stefan Monnier
2014-03-10 23:35 ` lee
2014-03-11 0:41 ` Michael Heerdegen
2014-03-11 1:45 ` Michael Heerdegen
2014-03-11 19:05 ` lee
2014-03-11 22:58 ` Michael Heerdegen
2014-03-12 15:11 ` lee
2014-03-12 18:15 ` Stefan Monnier
2014-03-12 21:43 ` lee
2014-03-13 7:22 ` Michael Heerdegen
2014-03-15 20:02 ` lee
2014-03-11 4:11 ` lee
2014-03-11 5:01 ` Michael Heerdegen
2014-03-11 14:25 ` lee
2014-03-11 23:51 ` Michael Heerdegen
2014-03-12 15:22 ` lee
2014-03-13 7:33 ` Michael Heerdegen
2014-03-13 12:29 ` Stefan Monnier
2014-03-15 20:05 ` lee
2014-03-16 17:20 ` Stefan
2014-03-11 6:51 ` Michael Heerdegen
2014-03-11 15:41 ` lee
2014-03-11 23:21 ` Michael Heerdegen
2014-03-12 17:33 ` lee
2014-03-12 19:34 ` Florian Beck [this message]
2014-03-12 19:51 ` Florian Beck
2014-03-13 7:54 ` Michael Heerdegen
2014-03-15 20:14 ` lee
2014-03-12 12:45 ` Stefan Monnier
2014-03-12 17:42 ` lee
2014-03-13 2:43 ` Jambunathan K
2014-03-15 20:17 ` How to propose an emacs patch (Re: replacing a function with another one) lee
2014-03-16 3:21 ` Jambunathan K
2014-03-17 4:35 ` lee
2014-03-10 13:45 ` replacing a function with another one lee
2014-03-10 23:31 ` Michael Heerdegen
2014-03-12 13:16 ` Jambunathan K
2014-03-12 13:18 ` Jambunathan K
2014-03-15 20:22 ` lee
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