Question

I have a mess when I combine interfaces and polymorphism.

Say I have the following interface:

public Interface CanSayHello
{
     String SayHello();
}

The following class:

public Class Person : CanSayHello
{
     public String SayHello() { return "Hey, I'm a person just saying hello to you";}
}

And finally the important Class:

public Class PoshPerson: Person
{
     public String SayHello() { return "Hey, I'm too posh to say hello to you";}
}

My first question is would the following code collect the method of PoshClass or Person Class?

public delegate String Collector();
event Collector CollectorEvent;
void GetMethod(CanSayHello c){CollectorEvent += c.SayHello;}

**GetMethod(new PoshPerson());**

If it will collect the method from Person class, I guess that I should declare the method at Person as virtual and the method at PoshPerson override.
I would really like that the two method signatures were equal. Is it possible in any way?

Answer 1

Your example runs Person‘s method. If you change PoshPerson to PoshPerson : Person, CanSayHello (which you might think would change nothing, since Person : CanSayHello), it runs PoshPerson‘s method.

I agree with @millimoose: “I’d avoid method hiding whenever possible, precisely because compile-time polymorphism is not very intuitive.” I would recommend that you change Person.SayHello to virtual, and PoshPerson.SayHello to override. That way regardless of whether you know of the instance as a CanSayHello, Person, or PoshPerson, the current instance type’s method runs.