code: function getTimestamp()
      {
          $lastModifiedTimes = iterator_to_array(itertools\filter(itertools\map(
              function($file) {
                  if (file_exists($file)) {
                      return @filemtime($file);
                  }
              },
              $this->prerequisites
          )));
  
          if ($lastModifiedTimes) {
              return max($lastModifiedTimes);
          }
  
          return 0;
      }
docs: # Returns the time as Unix Epoche represented by an Integer.