for my $len (2..6) {
    our ($full, $empty);

    my $a = 'A';
    $full .= $a while length($full) < $len;

    print "\nLength $len with ", scalar($full), " items\n";
    cmpthese -1, {
        full  => sub { die unless $full },
        empty => sub { die if $empty    },
        fake  => sub { die unless $full },
    }
}
__END__
Length 2 with AA items
            Rate empty  full  fake
empty 29399327/s    --   -5%  -35%
full  31036076/s    6%    --  -31%
fake  44964665/s   53%   45%    --
...