@Inheritable
Point2D = Class {x = Int; y = Int}
Point2D.
    norm self = self::x**2 + self::y**2

Point3D = Inherit Point2D, Additional := {z = Int}
Point3D.
    # Overloading is prohibited by default. Remove this decorator and check for errors.
    @Override
    new x, y, z =
        Point3D::__new__ {x; y; z}
    @Override
    norm self = self::x**2 + self::y**2 + self::z**2

p = Point2D.new {x = 1; y = 2}
print! p, p.norm()
q = Point3D.new 1, 2, 3
print! q, q.norm()