1     public interface IShape
 2     {
 3         double Area { get; }
 4 
 5         System.Windows.Rect BoundingBox { get; }
 6     }
 7     /// <summary>
 8     /// WindowsBase.dll下
 9     /// </summary>
10     public sealed class Circle : IShape
11     {
12         private
 
 readonly System.Windows.Point center;
13         public System.Windows.Point Center { get { return center; } }
14 
15         private readonly double radius;
16         public double Radius { get { return radius; } }
17 
18         public Circle(System.Windows.Point center, int radius)
19         {
 
20             this.center = center;
21             this.radius = radius;
22         }
23 
24         public double Area
25         {
26             get { return Math.PI * radius * radius; }
27         }
28 
29         public System.Windows.Rect BoundingBox
30         {
31             get
32
 
             {
33                 return new System.Windows.Rect(center - new System.Windows.Vector(radius, radius), new System.Windows.Size(radius * 2, radius * 2));
34             }
35         }
36     }
37     public sealed class Square : IShape
38     {
39         private readonly Point topLeft;
40         private readonly double sideLength;
41 
42         public Square(Point topLeft, double sideLength)
43         {
44             this.topLeft = topLeft;
45             this.sideLength = sideLength;
46         }
47 
48         public double Area { get { return sideLength * sideLength; } }
49 
50         public Rect BoundingBox
51         {
52             get { return new Rect(topLeft, new Size(sideLength, sideLength)); }
53         }
54     }

 1     class Program
 2     {
 3         delegate T Func<out T>();
 4         delegate void Action<in T>(T obj);
 5         static void Main(string[] args)
 6         {
 7             Func<Square> squareFactory = () => new Square(new Point(5, 5), 10);
 8             Func<IShape> shapeFactory = squareFactory;
 9 
10             Action<IShape> shapePrinter = shape => Console.WriteLine(shape.Area);
11             Action<Square> squarePrinter = shapePrinter;
12 
13             shapePrinter(shapeFactory());
14             squarePrinter(squareFactory());
15         }
16     }

13.3.4 複雜情況