using System;

​

public class Program

{

    public static void Main()

    {

        var handler = new Handler();

        var test = new Test();

        handler.HandleStuff(test);

    }

}

​

​

public class Handler 

{

    public bool HandleStuff(IItem<IItemType> item)

    { 

        // do stuff

        throw new NotImplementedException();

    }

}

​

public class Test : IItem<Stuff>

{

    public bool Process(Stuff item)

    { 

        // do stuff

        throw new NotImplementedException();

    }

}

​

public class Stuff : IItemType

{

}

​

public interface IItem<in T> where T : IItemType

{

    bool Process(T item);

}

​

public interface IItemType

{

}