Question

This question is as a result of trying Jon Skeet’s answer to this question.

So I have the following code based in the question and answer from the above question link.

 public abstract class DeliveryStrategy { }
public class ParcelDelivery : DeliveryStrategy { }
public class ShippingContainer : DeliveryStrategy { }

public abstract class Order<TDelivery> where TDelivery : DeliveryStrategy
{
    private TDelivery delivery;

    protected Order(TDelivery delivery)
    {
        this.delivery = delivery;
    }

    public TDelivery Delivery
    {
        get { return delivery; }
        set { delivery = value; }
    }
}

public class CustomerOrder : Order<ParcelDelivery>
{
    public CustomerOrder()
        : base(new ParcelDelivery())
    { }
}

public class OverseasOrder : Order<ShippingContainer>
{
    public OverseasOrder() : base(new ShippingContainer())
    {

    }
}

I’m trying understand generics more to improve my skill set, so I have the question of:
Now how can I use foreach to loop through a collection of “Orders”? I’m using C#2.0.

Code Example of what I’m trying to do (does not compile).

List<Order> orders = new List<Order>();

orders.Add(new CustomerOrder());
orders.Add(new CustomerOrder());
orders.Add(new OverseasOrder());
orders.Add(new OverseasOrder());

foreach (Order order in orders)
{
     order.Delivery.ToString();
}

EDIT: Added OverseasOrder to give a better example.

Answer 1

The problem here is that Order is a generic class, so Order<T> and Order is basically two distinct types.

You can do this:

public abstract class Order
{
    public abstract String GetDeliveryMethod();
}

public abstract class Order<TDelivery> : Order
    where TDelivery : DeliveryStrategy
{
    .... the rest of your class

    public override String GetDeliveryMethod()
    {
        return Delivery.ToString();
    }
}

Or… you can redefine Order to be non-generic, in which case you’ll loose some strong typing.