src/Bag.php
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;
        };
    }
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 > $b ? -1 : 1;
        };
    }
Returns a comparison function that calls the `$iteratee` function
for both values being compared before comparing them.

@param callable $iteratee
@param bool     $ascending

@return \Closure