using System;

using System.Threading.Tasks;

public class Program

{

    public class A

    {

​

    }

​

    public class B : A

    {

        public static async Task<B> GetB()

        {

            return new B();

        }

    }

​

    public class C

    {

        public Task<B> FieldB;

        public C()

        {

            FieldB = B.GetB();

        }

    }

​

    public class D

    {

        public Task<A> FieldA;

        public D()

        {

            Func<Task<A>> call = async () =>

            {

                var t = await B.GetB(); 

                return (A) t;

            };

​

            FieldA = call();

        }

    }

    public static void Main()

    {

        var C = new C();

​

        var fieldBValue = C.FieldB.Result;

        if (fieldBValue != null)

        {

            Console.WriteLine("fieldValue contains object");

            Console.WriteLine(fieldBValue);

        }

        var D = new D();

        var fieldAValue = D.FieldA.Result;

        if (fieldAValue != null)

        {

            Console.WriteLine("fieldValue contains object");

            Console.WriteLine(fieldAValue);

        }

    }

}