Hmm. I originally used a debug session & timethese(), did a little mental arithmetic, that jelled with what Anonymonk said, so I went with it.

Now I've put it into a proper script, used cmpthese() to do the arithmetic, and I can't reproduce my original results. In fact, I seem to consistantly get the index version coming out quicker, sometimes markedly so??

Maybe I did the arithmetic wrong, or there is a flaw in my benchmark? I used random strings with (or without) randomly positioned ':' to try cover the failing conditions as well as a good spread of the passing ones. The spread of variation in timings seem to indicate that some combinations cause the regex engine to take much longer than others. I've not managed to get the difference less than 9% in favour of index, and on one occasion, it went as high as 28%. Further investigation is called for:)

#! perl -slw
use strict;
use Benchmark qw[ cmpthese ];

sub rndStr{ join'', map{ $_[ rand scalar @_ ] } 0 .. shift }

our @strings = map{ rndStr 8, ':', 'a' .. 'z' } 1 .. 1000;

our( @a, @b );

cmpthese( -3, {
     regex => q[
         our @a = sort{
             ( $a =~ /:/ <=> $b =~ /:/ )
             ||
             $a cmp $b
         } @strings
     ],
     index => q[
         our @b = sort{
             ( ( index($a,':') >= 0 ) <=> ( index($b,':') >= 0) )
             ||
             $a cmp $b;
         } @strings
     ],
 });

print 'Okay' if "@a" eq "@b";

__END__
P:\test>test3
        Rate regex index
regex 14.6/s    --   -9%
index 16.1/s   10%    --
Okay

P:\test>test3
        Rate regex index
regex 13.7/s    --  -15%
index 16.2/s   18%    --
Okay

P:\test>test3
        Rate regex index
regex 14.5/s    --  -11%
index 16.3/s   13%    --
Okay

P:\test>test3
        Rate regex index
regex 13.1/s    --  -19%
index 16.2/s   23%    --
Okay
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