using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

​

        A[] array = ConvertArray<A>();

        Console.WriteLine(array.Length);

    }

    public static T[] ConvertArray<T>() where T : X

    {

        List<A> lst = new List<A>();

        lst.Add(new A());

        lst.Add(new A());

        A[] inputArray = lst.ToArray();

        return inputArray as T[];

    }

}

​

public class A : X

{

}

​

public class X

{

}