Re: New hook before-region-change-functions wanted

[Alan Mackenzie <acm@muc.de>]

Hello, Richard.

On Fri, Sep 08, 2017 at 18:22:15 -0400, Richard Stallman wrote:
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>   > I would like to implement a new abnormal hook,
>   > before-change-region-functions.  It would be called just before a change
>   > in the buffer's restriction (i.e., from widen and from narrow-to-region)
>   > and each function on it would take two parameters, the beginning and end
>   > of the new region being set.

> That kind of hook is pandora's box.  It is too powerful, and would
> interact in complex ways.  There will be many cases that are hard to
> implement correctly, or cause trouble.  To implement this probably
> means future hassles for ourselves and for package developers.

I actually implemented it, and it worked as intended.  It's not often I
get criticised for proposing something too powerful.

>   > The reason I want it is as part of the solution to bug #22983
>   > (syntax-ppss returns wrong result).  I envisage two (or possibly more)
>   > mutually independent caches, and a switch being made to the appropriate
>   > cache when the region is changed.

> For this, all you need to do is record, for each alternative cache,
> what buffer restrictions it corresponds to.  Then use the right cache.

> That is a much safer way to do it.

OK.  I will keep my new implementation under lock and key.  As you
suggest, managing without it is not difficult.

Thanks for the criticism.

> -- 
> Dr Richard Stallman
> President, Free Software Foundation (gnu.org, fsf.org)
> Internet Hall-of-Famer (internethalloffame.org)
> Skype: No way! See stallman.org/skype.html.

-- 
Alan Mackenzie (Nuremberg, Germany).