posted on Friday, January 21, 2005 6:18 PM by roydictus

Fun with Interfaces

Let's have some fun with interfaces. This posting was inspired by a recent call for help from a colleague.

Say you have two basic interfaces, IAlice and IBob, as in the following code:

 

using System;

namespace FunWithInterfaces
{
    public interface IAlice
    {
        string AliceSays();
    }
}

and

using System;

namespace FunWithInterfaces
{
    public interface IBob
    {
        string BobSays();
    }
}

And say you have a third interface, ICouple, which just inherits from these two:

using System;

namespace FunWithInterfaces
{
    public interface ICouple : IAlice, IBob
    {
    }
}

Now, so far, so good. What if you had a class, Carol -- who speaks for both Alice and Bob -- who implements IAlice and IBob, like so:

using System;

namespace FunWithInterfaces
{

    /// <summary>
    /// Carol speaks for both Alice and Bob --
    /// but does she speak for the couple?
    /// </summary>
    public class Carol : IAlice, IBob
    {

        public string AliceSays()
        {
            return "Bob, come home!";
        } // AliceSays

        public string BobSays()
        {
            return "I can't, watching sports!";
        }

    }
}

Does Carol also speak for the couple? That is, is she automatically seen by the .Net Framework as implementing ICouple?

What happens when you do this?

ICouple somebody = (ICouple) new Carol();

Try to find the answer before trying it out :-)

 

 

 

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