简单委托（委托）与多播委托

本文对此进行了很好的解释：

delegate void Del(string s);class TestClass{    static void Hello(string s)    {        System.Console.WriteLine("  Hello, {0}!", s);    }    static void Goodbye(string s)    {        System.Console.WriteLine("  Goodbye, {0}!", s);    }    static void Main()    {        Del a, b, c, d;        // Create the delegate object a that references         // the method Hello:        a = Hello;        // Create the delegate object b that references         // the method Goodbye:        b = Goodbye;        // The two delegates, a and b, are composed to form c:         c = a + b;        // Remove a from the composed delegate, leaving d,         // which calls only the method Goodbye:        d = c - a;        System.Console.WriteLine("Invoking delegate a:");        a("A");        System.Console.WriteLine("Invoking delegate b:");        b("B");        System.Console.WriteLine("Invoking delegate c:");        c("C");        System.Console.WriteLine("Invoking delegate d:");        d("D");    }}