How do I define the return type of an interface method to be another interface?

Question

I\'m new to interfaces and abstract classes. I want to create a couple of interfaces to define core methods and variables for the objects for a shopping cart system. Then I want

Answer 1

You need to user generics in C# 2 to achieve that:

public interface ICart where T : ICartItem
{
    // ...
    List CartItems { get; set; }
}

public abstract class Cart : ICart
{
    // ...
    public List CartItems { get; set; }
}