using System;

​

public class Program

{

    public static void Main()

    {

        Segment<Key> test = new Segment<Key>();

        var test2 = test as ISegment<SomeStructure>;

        Console.WriteLine("Hello World");

    }

}

​

public interface ISegment<out T>

{

}

​

public class SomeStructure

{

}

​

public class Key : SomeStructure

{

}

​

public class Segment<K> : ISegment<K> where K : SomeStructure

{

}