swap method
Swaps the elements at the given indexes in-place.
['a', 'b', 'c']..swap(0, 2); // ['c', 'b', 'a']
Implementation
@Possible({RangeError})
void swap(int a, int b) {
RangeError.checkValidIndex(a, this, 'a');
RangeError.checkValidIndex(b, this, 'b');
final (a1, b1) = (this[a], this[b]);
this[a] = b1;
this[b] = a1;
}