Shapeless: map a tuple with some options to options

Question

Having

(Some(1), 2, Some(3))

I expect to get

(Some(1), Some(2), Some(3))

With shapeless is it possible to do so?

Answer 1

Yes it is,

scala> import shapeless._, syntax.std.tuple._
import shapeless._
import syntax.std.tuple._

scala> :paste
// Entering paste mode (ctrl-D to finish)

object opt extends opt0 {
  implicit def optId[T <: Option[_]] = at[T](identity)
}
trait opt0 extends Poly1 {
  implicit def default[T] = at[T](Option(_))
}

// Exiting paste mode, now interpreting.

defined object opt
defined trait opt0

scala> (Some(1), 2, Some(3)) map opt
res0: (Some[Int], Option[Int], Some[Int]) = (Some(1),Some(2),Some(3))

You'll notice that the Some[Int]'s at the first and last position have been preserved whereas the lifted middle element is typed as Option[Int]. I've worked on the assumption that what you actually intended was something like this,

scala> (Option(1), 2, Option(3)) map opt
res1: (Option[Int], Option[Int], Option[Int]) = (Some(1),Some(2),Some(3))