C#委托与协变逆变

协变：子类向父类或基类转化

    public class A { }

    public class B : A { }

    public class C : B { }

    class Program
    {
        public static A T1() { return new A(); }
        
        public static B T2(){ return new B();}
        public static C T3() { return new C(); }
        public delegate object testDeleg();
        //public delegate A testDeleg();
        static void Main(string[] args)
        {
            testDeleg testDeleg = T1;
            testDeleg testDeleg1 = T2;
            testDeleg testDeleg2 = T3;
        }
    }

逆变：父类向子类转化

    public class A { }

    public class B : A { }

    public class C : B { }

    class Program
    {
        public static void T1(A a) { }
        public static void T2(B b) { }
        public static void T3(C c) { }
        public delegate void TestDelegate(C c);
        public static TestDelegate dele;
        static void Main(string[] args)
        {
            dele += T1;
            dele += T2;
            dele += T3;
        }
    }