using System;

using System.Threading.Tasks;

​

ICommand<IOrderCommand> concreateType = null!;

​

var command = (ICommand<CreateOrderCommand>)concreateType; // correct contravariant cast

​

public class OrderResult

{

​

}

​

public interface IOrderCommand

{

​

}

​

public interface ICommand<in T> where T : IOrderCommand

{

    Task<OrderResult> HandleAsync(T orderCommand);

}

​

public class CreateOrderCommand : IOrderCommand

{

​

}

​

public class Concreate : ICommand<CreateOrderCommand>

{

    public Task<OrderResult> HandleAsync(CreateOrderCommand command)

    {

        throw new NotImplementedException();

    }

}