comparator method

@override int comparator(T value1, T value2)

Returns a negative number if value1 is less than value2, zero if they are equal, and a positive number if value1 is greater than value2. Almost the same: value1 - value2

Implementation

@override
int comparator(T value1, T value2) {
  // If K <: Comparable, then we can just use Comparable.compare
  // with no casts.
  Object compare = Comparable.compare;
  if (compare is Comparator<T>) {
    return compare(value1, value2);
  }
  // Otherwise wrap and cast the arguments on each call.
  return Comparable.compare(
      value1 as Comparable<dynamic>, value2 as Comparable<dynamic>);
}