I am curious why class B has two methods called f, and why calling f returns a List rather than an Iterable.

scala_wtf

scala> abstract class A { def f : Iterable[String] }
defined class A

scala> class B extends A { def f = List("foo", "bar") }
defined class B

scala> class C extends A { val r = math.random; def f = { val v = List("foo", "bar"); if(r < 0.5) v else v.map{_ + "_"} } }
defined class C

scala> (new B).f
res13: List[java.lang.String] = List(foo, bar)

scala> (new C).f
res14: Iterable[String] = List(foo, bar)

scala> (new C).f
res15: Iterable[String] = List(foo_, bar_)

scala> (new B).getClass.getMethods
res19: Array[java.lang.reflect.Method] = Array(public scala.collection.immutable.List B.f(), public scala.collection.Iterable B.f(), public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException, public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException, public final void java.lang.Object.wait() throws java.lang.InterruptedException, public boolean java.lang.Object.equals(java.lang.Object), public java.lang.String java.lang.Object.toString(), public native int java.lang.Object.hashCode(), public final native java.lang.Class java.lang.Object.getClass(), public final native void java.lang.Object.notify(), public final native void java.lang.Object.notifyAll())