As I'm not familiar with PHP I wonde how do I reduce code duplication here? Both methods are doing exactly the same thing here... except the part where the string is extracted (`filemtime` and `basename`) and joined.

```
private function modified_hash( $files ) {
    $joined = "";

    foreach ( $files as $file ) {
        $joined .= filemtime( $file );
    }

    return $this->checksum( $joined );
}

private function filename_hash( $files ) {
    $joined = "";

    foreach ( $files as $file ) {
        $joined .= basename( $file );
    }

    return $this->checksum( $joined );
}

```