@Inheritable
Point2D = Class {x = Int; y = Int}
Point2D.
    new x, y = Self::__new__ {x; y}
    norm ref self = self::x**2 + self::y**2

Point3D = Inherit Point2D, Additional: {z = Int}
Point3D.
    @Override
    new x, y, z = Self::__new__ {x; y; z}
    @Override
    norm ref self = self::x**2 + self::y**2 + self::z**2

UnpackPoint2D = Class {x = Int; y = Int}, Impl: Unpack

p = UnpackPoint2D.{x = 1; y = 2}
UnpackPoint2D.{x; y} = p