dart set final variable in constructor
// You cannot mutate final variables in a constructor body,
// instead you must use a special syntax.
// Also note if you have a super() call, it must be called last.
class Point {
final num x;
final num y;
final num distanceFromOrigin;
// Special syntax
Point(this.x, this.y) :
distanceFromOrigin = sqrt(pow(x, 2) + pow(y, 2));
}