cant infer

gistfile1.scala

def newMap[A,B](x:A, f: A => B): B = {
  f(x)
}

scala> newMap(1:Int,(_*2))
<console>:9: error: missing parameter type for expanded function ((x$1) => x$1.$times(2))
              newMap(1:Int,(_*2))
                            ^

scala> newMap(1,((_:Int)*2))
res7: Int = 2