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From: Eli Zaretskii <eliz@gnu.org>
Newsgroups: gmane.emacs.devel
Subject: Re: newline cache
Date: Tue, 22 Apr 2014 20:46:16 +0300
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To: Stefan Monnier <monnier@IRO.UMontreal.CA>
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> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: Eli Zaretskii <eliz@gnu.org>, emacs-devel@gnu.org
> Date: Tue, 22 Apr 2014 10:28:19 -0400
> 
> Maybe add a monitoring code, which (when enabled at compile-time) always
> checks the return value of that cache against the non-cached result?

As I explained in a previous message, when the value returned by the
cache is wrong, it's too late, because the corruption happened some
time in the past.  It's like debugging memory allocation bugs by
catching exceptions in 'free'.