Re: proper use of add-function

[Noam Postavsky <npostavs@gmail.com>]

On 22 May 2018 at 20:09, Eric Abrahamsen <eric@ericabrahamsen.net> wrote:
> Michael Heerdegen <michael_heerdegen@web.de> writes:
>
>> Eric Abrahamsen <eric@ericabrahamsen.net> writes:
>>
>>> Okay, I see what you and Noam are saying, and in fact what the docstring
>>> is saying. It's just pretty weird that `add-function' works on
>>> variables, and `advice-add' works on functions.

Yeah, this isn't the first time I've seen confusion over this (e.g.,
Bug#30241). The docstring is clear enough when you already know what
it says, but I've just added an extra note that should help guide
people toward advice-add.

[1: e3f00f5637]: 2018-05-22 20:08:01 -0400
  Clarify when to use advice-add vs add-function
  https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=e3f00f5637a2790923a9c4c1d4b7dbf65027d8ce

>> Actually `add-function' works for "places" (including
>> `symbol-function'), so it's the more general and more low-level tool.
>> `advice-add' is higher-level and specialized on function names.
>
> I guess that's why I kept trying to make this work -- I thought the
> `symbol-function' place would allow me to apply my advice to
> 'canonically-space-region. Why doesn't that work?

(add-function
   :filter-args
   (symbol-function 'canonically-space-region)
   #'my-canonical-space-region)

This seems to work for me (although advice-add is preferable for
reasons listed in the manual).