GNU bug report logs - #17181
24.4.50; previous-single-property-change: odd behavior

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Message #12 received at 17181-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: raman <at> google.com (T.V Raman)
Cc: 17181-done <at> debbugs.gnu.org
Subject: Re: bug#17181: 24.4.50; previous-single-property-change: odd behavior
Date: Thu, 03 Apr 2014 22:27:56 -0400

tags 17181 notabug
thanks

> (put-text-property (point) (point-max) 'test t)
> Move point to the front of "bar" ie  point is at the beginning of the
> line.
> (get-text-property (point) 'test) returns T as expected.
> (point) evaluates to 6
> Consequently, I'd  expect 
> (previous-single-property-change (point) 'test) to return 5 
> instead you get: nil

Buffer positions are *between* characters.  `get-text-property' gets you
the value of the property on "the character after point".
`previous-single-property-change' gets you the nearest change on
*previous* characters.  The property above is nil between point-min and
point, so previous-single-property-change finds no change at all.

The off-by-one error is in your expectations :-(


        Stefan

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