code: private function iterateeToComparator(callable $iteratee, $ascending = true)
      {
          return function ($a, $b) use ($iteratee, $ascending) {
              // PHP 7.0
              // return $iteratee($a) <=> $iteratee($b);
  
              $a = $iteratee($a);
              $b = $iteratee($b);
  
              if ($a === $b) {
                  return 0;
              }
  
              if ($ascending) {
                  return $a > $b ? 1 : -1;
              }
  
              return $a > $b ? -1 : 1;
          };
      }
docs: Returns a comparison function that calls the `$iteratee` function
  for both values being compared before comparing them.
  
  @param callable $iteratee
  @param bool     $ascending
  
  @return \Closure