## Sunday, July 31, 2011

### Delegates or interfaces? Functional and OO Dualism

I have a mixed background: doing C#/.NET for ~4 years then switching to Java (switched jobs). I have been in the Java enterprise ecosystem for the last 4 years. I do mostly Java, but enjoy doing a little C# every now and again. C# is really a nice language. Shame its in such a horrible Microsoft-centric ecosystem.

In any case, I've been writing a little thing in C# and needed a type with a single method to "doWork". So coming from a Java bias I created a:
public interface IWorker {
void DoWork();
}

Later, however, I wanted to offer the users an API option of just using a lambda to "doWork". Unfortunately, there is no type conversion from a delegate to the matching "single method interface" (at least that I could find, if someone knows the answer, please share!). So as a shim, I created:
public delegate void WorkerDelegate();

public WorkerWrapper : IWorker {
public WorkerWrapper(WorkerDelegate workerDelegate) {
this.workerDelegate = workerDelegate;
}

public void DoWork() {
workerDelegate();
}
}

So I wrap the lambda in a little wrapper and don't need to change my entire IWorker-based infrastructure. It works, but I'm not happy with this. I know that in the Java lambda mailing list, they are planning to include a "lambda conversion" so that lambdas can be converted to compatible single abstract method (SAM) types. This would've alleviated my need for the shim above as I could've assigned the lambda directly to an IWorker and all would've been well.

I believe the "C# way" would've been for me to use delegates all the way through to begin with. Had someone come along with an IWorker interface then that would've been assignable to my WorkerDelegate.

But is this the right answer? Conceptually, how should I think of these? What is an IWorker in the above case? Is it really just a chunk of code that should be passed around as such? Or is it a member in the space of collaborating types that make up my system...

This is an example of the conceptual problems reconciling a Functional view of the world with an object oriented view of the world (dualism). I know that many people smarter than me have thought about these problems, and I'm hoping that I can find some good articles discussing them.

It feels like we're describing the same concept: a "chunk of code" that is defined by an interface (call it a delegate or a SAM, same thing). I don't think that I would have any dissonance if both were assignable to each other, and thus can be treated as different expressions of the same concept. If this were the case, then maybe I would view delegates as just SAM types -- so my "world view" is still object oriented, I just have an additional, concise lambda syntax to create SAMs. Actually, if this were the case, then you could probably invoke the Liskov substitution principle and call functional-OO dualism reconciled...

But something still seems amiss. There is more to the identity of an IWorker than the fact that it takes no arguments and returns nothing. I suppose the same questions are true of reconciling structural typing to static typing. Hmm.. I have a lot of reading to do.

I imagine there are a number of philosophical problems between functional and OO. This is just the one I ran across and felt dissonance with C#s implementation. Maybe they truly are different things and should be treated as such. I hope (despite my extremely small readership) to get some links to articles on this topic.

Steve