using System;

​

using Length = Quantity<LengthUnit>;

​

public interface IUnit

{

}

​

public class Quantity<T> where T : IUnit

{

}

​

public class LengthUnit : IUnit

{

}

​

public class Program

{

    public static void Main(string[] args)

    {

        var len = new Length();

        Console.WriteLine("Hello, world!");

    }

}