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Re: Question about copy-region-as-kill

From: Colin Walters
Subject: Re: Question about copy-region-as-kill
Date: 09 Apr 2002 18:12:06 -0400

On Tue, 2002-04-09 at 08:07, Richard Stallman wrote:
>     If we had extents like mechanism as the underlying implementation of
>     both text properties and overlays, then I could fall back to just using
>     the raw extents interface to solve my problem.
> That would be indistinguishable in practice form using overlays for
> everything.  It would not be terribly hard to do this, but if indeed
> overlays are slower, then this will make everything that now uses text
> properties slower.

This seems to me to be an implementation issue.  Redisplay is far
outside my area of knowledge, but since XEmacs seems to be "fast enough"
at font-locking, I think this suggests that it doesn't have to be slow.

> Are overlays actually slower, for something like font-lock?
> I don't know.

My subjective feeling is that Emacs overlays are currently substantially
slower than Emacs text properties, yes.  But it would be hard to make an
objective comparison without rewriting font-lock entirely...

> I don't think overlays (whether you call them "extents" or not)
> are lying behind text properties.

The XEmacs manual claims that their text properties are implemented in
terms of extents:

"Text properties are an alternative interface to extents (*note
Extents::), and are built on top of them."

I don't want to actually look at the source, because I would like to
help in the implementation of extents (or the extension of overlays,
however you want to look at it) for Emacs.

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