C#

using System;

namespace ConsoleApplication1
{
    interface IPointD
    {  
        double X {get; set;}
        double Y {get; set;}
    }

    struct PointD : IPointD
    {
        private double x;
        private double y;
        public PointD(double x, double y)
        { this.x = x; this.y = y;}

        public double X 
        { 
            get { return x; } 
            set { x= value; }
        }

        public double Y 
        {
            get { return y; }
            set { y = value; }
        }
    }

	class Class1
	{
        static void Method(IPointD point)
        {
            if (point != null)
            {
                point.X = 10;
                point.Y = 10;
            }
        }

		[STAThread]
		static void Main(string[] args)
		{
            PointD point = new PointD(1, 1);
            IPointD dPoint = (IPointD)point;
            Method(dPoint);

            Console.WriteLine("X = {0}, Y = {1}", point.X, point.Y);
            Console.WriteLine("X = {0}, Y = {1}", dPoint .X, dPoint.Y);
		}
	}
}

IPointD dPoint = (IPointD)point;