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

From: Richard Stallman
Subject: Re: New hook before-region-change-functions wanted
Date: Fri, 08 Sep 2017 18:22:15 -0400

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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.

  > 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 cashe,
what buffer restrictions it corresponds to.  Then use the right cache.

That is a much safer way to do it.

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.

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