Mapping a Scala function with an optional parameter

Question

I'm having trouble mapping a function that takes an optional parameter. I get the same type error as I would if the parameter were not optional. Here's a simple illustration:

scala> def multiple(m: Int, n: Int = 2) = m * n
multiple: (m: Int,n: Int)Int

scala> multiple(5)
res0: Int = 10

scala> multiple(5, 7)
res1: Int = 35

scala> (1 to 10).map(multiple)
<console>:7: error: type mismatch;
 found   : (Int, Int) => Int
 required: (Int) => ?
       (1 to 10).map(multiple)

Here's one way to make it work, but it requires repeating the default argument, which is a maintenance nightmare:

scala> (1 to 5).map { n => multiple(n, 2) } 
res6: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10)

Is there a better way to do it? More generally, why does a function with an optional parameter seem to have the same type as it would if the parameter was not optional? What is the actual type of multiple?

Answer 1

This seems to work:

(1 to 10).map(multiple(_)) 

//res0: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)