public ICartState Remove(Product item)
{
var newItems = new List<Product>(Items);
newItems.Remove(item);
return newItems.Count > 0
? (ICartState)new CartStateActive(newItems)
: new CartStateEmpty();
}
public ICartState Add(Product item)
{
var newItems = new List<Product>(Items) { item };
return new CartStateActive(newItems);
}