var b = new B();

var c = new C<B>();

_ = (C<A<int>>)c;

_ = (IC<A<int>>)c;

​

interface IA<T> {}

​

class A<T> : IA<T> {}

​

class B : A<int> {}

​

interface IC<out T> {

    public T value {get;}

    public T DoSomething();

}

​

class C<T> : IC<T> {

    public T value {get;}

    public C() {}

    public C(T val) {

        value = val;

    }

    public T DoSomething() => default;

}