Change 20156 by [EMAIL PROTECTED] on 2003/07/11 19:37:34
Subject: Re: Sort sub and NaNs
From: "John P. Linderman" <[EMAIL PROTECTED]>
Date: Thu, 10 Jul 2003 10:45:06 -0400
Message-Id: <[EMAIL PROTECTED]>
Warn against a potential edge case with sort, <=> and NaNs.
Affected files ...
... //depot/perl/pod/perlfunc.pod#398 edit
Differences ...
==== //depot/perl/pod/perlfunc.pod#398 (text) ====
Index: perl/pod/perlfunc.pod
--- perl/pod/perlfunc.pod#397~20155~ Fri Jul 11 12:11:17 2003
+++ perl/pod/perlfunc.pod Fri Jul 11 12:37:34 2003
@@ -4758,6 +4758,15 @@
sometimes saying the opposite, for example) the results are not
well-defined.
+Because C<< <=> >> returns C<undef> when either operand is C<NaN>
+(not-a-number), and because C<sort> will trigger a fatal error unless the
+result of a comparison is defined, when sorting with a comparison function
+like C<< $a <=> $b >>, be careful about lists that might contain a C<NaN>.
+The following example takes advantage of the fact that C<NaN != NaN> to
+eliminate any C<NaN>s from the input.
+
+ @result = sort { $a <=> $b } grep { $_ == $_ } @input;
+
=item splice ARRAY,OFFSET,LENGTH,LIST
=item splice ARRAY,OFFSET,LENGTH
End of Patch.
