The best feeling in software development?

I've been spending a lot of time in Javascript-land these days and while it's pretty exciting, I sure do miss some of the luxuries that really emphasise the maturity and elegance of statically-typed Scala.
Here's an example. It's incredibly-simple, but one of the most satisfying things in software development in my opinion. First, a quick definition:

trait Insertable {
  val insertedAt: Long
} 

And now, the source of all the joy:

def findMostRecentlyInserted(xs:Set[Insertable]):Option[Insertable] = {

}

Yep, that's it. An empty function. It won't even compile.

But this moment, right here, with type signatures locked down and the cursor flashing in the right spot, is where your brain can finally shift up from boilerplate mode into full power. How am I going to get from that set of candidates to the right one? What will be the fastest way? Will it read well? How should I test this?

If I've got my "good boy" hat on I'll stop here and write a few tests, which will of course fail. But sometimes, I'll just let the Scala compiler guide me - a function this simple is a great example of where strong typing really helps prevent errors. Anyone else with me on this?