About `unload-feature'

About `unload-feature'

[Xue Fuqiao]

(info "(elisp) Unloading") says:

Before restoring the previous definitions, `unload-feature' runs `remove-hook' to remove functions in the library from certain hooks.  These hooks include variables whose names end in `-hook' (or the deprecated suffix `-hooks'), plus those listed in `unload-feature-special-hooks', as well as `auto-mode-alist'. This is to prevent Emacs from ceasing to function because important hooks refer to functions that are no longer defined.

What does `ceasing to function' mean?  Can anybody help?  Thanks.
-- 
Best regards, Xue Fuqiao.
http://www.emacswiki.org/emacs/XueFuqiao

Re: About `unload-feature'

[Dmitry Gutov]

Xue Fuqiao <xfq.free@gmail.com> writes:

> (info "(elisp) Unloading") says:
>
> Before restoring the previous definitions, `unload-feature' runs `remove-hook'
> to remove functions in the library from certain hooks. These hooks include
> variables whose names end in `-hook' (or the deprecated suffix `-hooks'), plus
> those listed in `unload-feature-special-hooks', as well as `auto-mode-alist'.
> This is to prevent Emacs from ceasing to function because important hooks refer
> to functions that are no longer defined.
>
> What does `ceasing to function' mean?  Can anybody help?  Thanks.

Looks like a hyperbole.

It would still function, but signal [lots of] "function is undefined" errors.

Re: About `unload-feature'

[Barry Margolin]

In article <mailman.16498.1357082632.855.help-gnu-emacs@gnu.org>,
 Dmitry Gutov <dgutov@yandex.ru> wrote:

> Xue Fuqiao <xfq.free@gmail.com> writes:
> 
> > (info "(elisp) Unloading") says:
> >
> > Before restoring the previous definitions, `unload-feature' runs 
> > `remove-hook'
> > to remove functions in the library from certain hooks. These hooks include
> > variables whose names end in `-hook' (or the deprecated suffix `-hooks'), 
> > plus
> > those listed in `unload-feature-special-hooks', as well as 
> > `auto-mode-alist'.
> > This is to prevent Emacs from ceasing to function because important hooks 
> > refer
> > to functions that are no longer defined.
> >
> > What does `ceasing to function' mean?  Can anybody help?  Thanks.
> 
> Looks like a hyperbole.
> 
> It would still function, but signal [lots of] "function is undefined" errors.

There are some hooks that are run very frequently -- if these signalled 
an error every time, Emacs would be effectively unusable.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

Re: About `unload-feature'

[Xue Fuqiao]

On Wed, 02 Jan 2013 03:23:41 +0400
Dmitry Gutov <dgutov@yandex.ru> wrote:

> Looks like a hyperbole.
> 
> It would still function, but signal [lots of] "function is undefined" errors.

Thanks.
-- 
Best regards, Xue Fuqiao.
http://www.emacswiki.org/emacs/XueFuqiao

Re: About `unload-feature'

[Stefan Monnier]

> What does `ceasing to function' mean?

To see an example of "ceases to function", try for example:

   M-: (use-global-map (make-keymap)) RET

There are of course many other ways to make Emacs cease to function.
The sky is the limit.


        Stefan