See also: https://github.com/puffnfresh/wartremover/issues/29

FlatmapOptions.scala

// Welcome to Scala version 2.9.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_15).
// Type in expressions to have them evaluated.
// Type :help for more information.

def foo(n: Int) = Some(n)
// foo: (n: Int)Some[Int]

List(1,2,3,4).map(foo(_))
// res2: List[Some[Int]] = List(Some(1), Some(2), Some(3), Some(4))

List(1,2,3,4).flatMap(foo(_))
// res3: List[Int] = List(1, 2, 3, 4)

List(1,2,3,4).flatMap(foo(_).toList)
// res4: List[Int] = List(1, 2, 3, 4)

// Extra fun!
List(1,2,3,4).toSet()
// res5: Boolean = false

List(1,2,3,4).toSet
// res6: scala.collection.immutable.Set[Int] = Set(1, 2, 3, 4)
````

Still not clear what the issue is here. flatMap on a List[Opton[Int]] returning List[Int] (due to implicit conversion in Predefs) seems like a feature...?

flatMap works because of Option.option2iterable.
I think List(1,2,3,4).toSet() == false is a bug.

@ericacm Some have told me that the presence of that implicit is the "bug" (I.e. another strike against scala, making it broken as a functional language?). The toSet() thing is some kind of syntax idiosyncrasy, supposedly.