继承泛型作为函数参数

Question

How can I accomplish this?

class A { }
class B : A { }

class X<T> where T : A { }
class Y<T> : X<T> where T : A { }

private static void f(X<A> x) { }

public static void Main(string[] args)
{
    Y<B> y = new Y<B>();
    f(y); // Compiler error here
}

Y inherited from X, B from A, but it doesn't get compiled.

Answer 1

Change the function definition to:

private static void f<T>(X<T> x) where T : A { }

As you have defined it, you are saying that f() must be passed an instance of X<A> . By defining as I've shown here, you are saying that f() takes any class that has X<A> as a parent.