C#委托的协变性和逆变性

 1 Button button = new Button();
 2 //public delegate void EventHandler(object sender, EventArgs e);
 3 button.Click += LogPlainEvent;
 4 //public delegate void KeyPressEventHandler(object sender, KeyPressEventArgs e);
 5 button.KeyPress += LogPlainEvent;
 6 //public delegate void MouseEventHandler(object sender, MouseEventArgs e);
 7 button.MouseClick += LogPlainEvent;
 8 
 9 public void LogPlainEvent(object sender, EventArgs e)
10 {
11 }

 1 public delegate Stream StreamFactory();
 2 
 3 public MemoryStream GenerateData()
 4 {
 5     return new MemoryStream();
 6 }
 7 
 8 StreamFactory factory = GenerateData;
 9 using (Stream stream = factory())
10 {
11     int data;
12     while((data = stream.ReadByte()) != -1)
13     {
14         Console.WriteLine(data);
15     }
16 }