c# – 代表逆转(参数兼容性)

When you call a method,you can supply arguments that have more specific types than the parameters of that method. This is ordinary polymorphic behavior. For exactly the same reason,a delegate can have more specific parameter types than its method target. This is called contravariance.

直到最后一句话,这一段才有意义.为什么它是逆变,即这里的预测是逆变？

随附的例子如下.

delegate void StringAction (string s);

class Test
{
    static void Main()
    {
        StringAction sa = new StringAction (ActOnObject);
        sa ("hello");
    }

    static void ActOnObject (object o)
    {
        Console.WriteLine (o); // hello
    }
}