Using PHP 5.5 Generators to simulate an array with duplicate keys

Duplicate Keys in Array

function duplicateKeys($string) {
    $string = strtolower($string);
    $length = strlen($string);
    for ($i = 0; $i < $length; ++$i) {
        yield ord(strpos($string, $string[$i])) => $string[$i];
    }
}

foreach (duplicateKeys('badass') as $i => $value) {
    echo $i , ' -> ' , $value, PHP_EOL;
}