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From: Eli Zaretskii <eliz@gnu.org>
Newsgroups: gmane.emacs.devel
Subject: Re: How to add pseudo vector types
Date: Tue, 03 Aug 2021 16:34:32 +0300
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> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Fu Yuan <casouri@gmail.com>,  stephen_leake@stephe-leake.org,
>  cpitclaudel@gmail.com,  emacs-devel@gnu.org
> Date: Tue, 03 Aug 2021 09:28:57 -0400
> 
> > But that's sub-optimal, no?  Imagine a very large buffer which was
> > narrowed to a small portion near EOB, then a modification made very
> > close to EOB but partially before BEGV, then the buffer widened.  With
> > your method, TS will now have to re-parse almost the entire buffer,
> > whereas we know it needs to re-parse a very small portion of it.
> 
> As a general rule, we will most likely want to work hard to avoid
> exposing the narrowed buffer to TS (i.e. most calls to TS will first
> `widen`).

Sure.  I was thinking about those corner cases where we won't.