There doesn't seem to be a significant difference between the  [AaEeIiOoUu]{2} and  [AaEeIiOoUu][AaEeIiOoUu] variations under Strawberry 5.14.4, but I was a bit surprised that there's so little improvement over the  /i version. 

c:\@Work\Perl\monks>perl -wMstrict -le
"use Benchmark qw(cmpthese);
 ;;
 print 'Perl version: ', $];
 ;;
 my $s = 'Aid bears out ';
 $s = $s x 10_000_000;
 print 'length: ', length $s;
 ;;
 cmpthese(-1, {
   '/i'       => sub { $s =~ m{ (?i) [aeiou]{2}          }xmsg },
   '[Aa]{2}'  => sub { $s =~ m{ [AaEeIiOoUu]{2}          }xmsg },
   '[Aa][Aa]' => sub { $s =~ m{ [AaEeIiOoUu][AaEeIiOoUu] }xmsg },
   });
"
Perl version: 5.014004
length: 140000000
              Rate       /i  [Aa]{2} [Aa][Aa]
/i       3276565/s       --      -8%      -9%
[Aa]{2}  3558515/s       9%       --      -1%
[Aa][Aa] 3600879/s      10%       1%       --

[download]

The results are closer to what you suggest under ActiveState 5.8.9, but with  /i still surprisingly high. 

c:\@Work\Perl>perl -wMstrict -le
"(source code as above)
"
Perl version: 5.008009
length: 140000000
              Rate  [Aa]{2}       /i [Aa][Aa]
[Aa]{2}  3276565/s       --      -6%     -16%
/i       3480139/s       6%       --     -11%
[Aa][Aa] 3918166/s      20%      13%       --

[download]

Still, as you say, it's a bit of a micro-optimization.

In reply to Re^4: Vowel search by AnomalousMonk
in thread Vowel search by Noob@Perl

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