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Re: doubt about mode hooks
From: |
Emanuel Berg |
Subject: |
Re: doubt about mode hooks |
Date: |
Mon, 03 Jun 2013 22:14:28 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) |
Luca Ferrari <fluca1978@infinito.it> writes:
> (add-hook 'c-mode-hook (lambda()
> (my-function-hook) )
>
> but then I come across a snippet that does something different:
>
> (setq my-personal-hook 'my-function-hook)
> (add-hook c-mode-hook (lambda ()
> (run-hooks 'my-personal-hook) ) t )
>
> so I was wondering what are the differences and which advantages
> should I get using the second.
If you have something that you wish to hook to several events (or
the same event, but in several modes), you can put that something
in a function, that will, in turn, add the hook. Where you
originally would have put that something, you can now (perhaps
easier) just add a reference to the function, and the material
will be added as a hook.
If that was difficult to follow, let me give you an example. For
almost all my typing, be it programming or not, I don't care for
tabs. So for a lot of modes, I like an untab-all invocation on
write. But, as there are exceptions to this rule (for example, GNU
makefiles which need tabs), I cannot make it global; it has to be
setup mode for mode. Thus:
(defun add-write-contents-hooks-hook ()
(interactive)
(add-hook
'write-contents-hooks
'untab-all
nil ; APPEND unrelated, explicit default nil as optional
t )) ; LOCAL non-nil => make hook local
(add-hook 'emacs-lisp-mode-hook #'add-write-contents-hooks-hook)
(add-hook 'c-mode-common-hook #'add-write-contents-hooks-hook)
(add-hook 'sh-mode-hook #'add-write-contents-hooks-hook)
; ...
I agree hooks can be confusing. As a rule of thumb, don't rely on
them when it is not needed. Lots of stuff can be placed elsewhere,
so they won't slow down everything. If you can solve a problem by
placing stuff in a hook - do it! - but as your skills grow, always
be on the lookout for when the possibility arises to lighten the
burden on the hooks.
--
Emanuel Berg - programmer (hire me! CV below)
computer projects: http://user.it.uu.se/~embe8573
internet activity: http://home.student.uu.se/embe8573