use warnings;
use strict;
use Benchmark qw/cmpthese/;
use Test::More tests => 1;

my @dataset = ();
push @dataset, join('', map { (qw/A C G T/)[rand 4] } 1 .. 30 ) for 1 .. 1000;

my $i = $ARGV[0] // 10;

sub test {
    my $fnref = shift;
    my $count;
    for my $read_seq( @dataset ) {
        my $letter = $fnref->($read_seq, $i);
        $count->{$letter}++;
    }
    return $count;
}

sub rfn {
    test( sub {
        my $skip = $_[1];
        $_[0] =~ /.{$skip}(.)/;
        return $1;
    });
};
sub sfn {
    test( sub {
        substr $_[0], $_[1], 1;
    });
};
sub ufn {
    test( sub {
        ... # I'm no unpack expert
    });
};

cmpthese(0, {
    regex  => \&rfn,
    substr => \&sfn,
    #unpack => \&ufn,
});

is_deeply rfn(), sfn(), 'same results';