scala> val shares = Map("Apple" -> 23, "MicroSoft" -> 50, "IBM" -> 17)
shares: scala.collection.immutable.Map[java.lang.String,Int] 
      = Map(Apple -> 23, MicroSoft -> 50, IBM -> 17)

scala> val shareholders = shares map {_._1}                           
shareholders: scala.collection.immutable.Iterable[java.lang.String] 
            = List(Apple, MicroSoft, IBM)

scala> val newShares = shares map {case(k, v) => (k, 1.5 * v)}     
newShares: scala.collection.immutable.Map[java.lang.String,Double] 
         = Map(Apple -> 34.5, MicroSoft -> 75.0, IBM -> 25.5)

From this example it seems like the map method is overloaded on return type. Overloading on return type is not possible right? Would somebody please explain what's going on here?