public static void Main()
        {
            SamplePoint p1 = new SamplePoint(11, 21, 32);   // OK

            Console.WriteLine($"p1: x={p1.x}, y={p1.y}, z={p1.z}");
            SamplePoint p2 = new SamplePoint();

            p2.x = 55;   // OK
            Console.WriteLine($"p2: x={p2.x}, y={p2.y}, z={p2.z}");
        }
 public static void Examples()
 {
     SamplePoint.Main();
     ReadonlyRefReturns();
 }