FutureUtil.scala

// Doesn't compile. Good.
def futureInt(): Future[Int] = Future.value(Future.value(1))

// Compiles. Not good. Caller cannot wait on completion of nested future.
def futureUnit(): Future[Unit] = Future.value(Future.value(()))

// Also compiles. Nice convenience, but not worth the cost of the issues
// it might cause (as above), right?
def futureUnit(): Future[Unit] = Future.value(1)

// Maybe you could argue Future[Unit] is weird (or Unit in general is bad
// because side effects. But is it really avoidable?
// Example use case of Future[Unit]:
// https://github.com/twitter/util/blob/master/util-core/src/main/scala/com/twitter/util/Closable.scala

// I believe this shouldn't compile. Is scala 2.9.x?
def futureUnit(): Future[Unit] = Future.value[Int](1)

// You're right. So I guess the problem boils down to the fact that this compiles:
Future.value[Unit](1)
Future.value[Unit](Future.value(()))