Scala: Convert a Sealed Trait instance to an HList

Question

Consider the following:

sealed trait baseData {
  def weight: Int
  def priority: Int
} 

case class data1(override val weight: Int, override val priority: Int) extends baseData

How would I define a function with the following signature that transforms data1 into an HList?

def toHlist[A <: baseData] (data: A) = {}

I want to pass in a trait instance into the toHlist function instead of the actual case class because there will be more than one case class extending the trait. I also don't want to hardcode any fields; I'm looking for a totally generic solution.

I'm sure this is doable with the Shapeless library, but haven't been able to figure out how.

EDIT

toHList needs to be able to handle a baseData pointer to a case class instance, as so:

val data: baseData = data1(1,2)
toHlist(data)

The reason for this is that we will have more than one case class extending baseData, and we will now know which one to pass to toHlist until run time.

score 0 · Answer 1 · answered Jul 19 '16 at 09:41

0

This probably isn't the final answer, but it will help you refine your question,

scala> def toHlist[A <: baseData](data: A)(implicit gen: Generic[A]): gen.Repr = gen.to(data)
toHlist: [A <: baseData](data: A)(implicit gen: shapeless.Generic[A])gen.Repr

scala> toHlist(data1(23, 13))
res0: shapeless.::[Int,shapeless.::[Int,shapeless.HNil]] = 23 :: 13 :: HNil

answered Jul 19 '16 at 09:41

Miles Sabin

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Thanks! This works with `toHlist(data1(23, 13))`, but won't if we all we have is a pointer to the base trait: `val data: baseData = data1(23,13)`, `toHlist(data)`. In my case, I won't know which case class to pass in until runtime. Any ideas there? – Cigogne Eveillée Jul 19 '16 at 15:10
Could you update your question in the light of the above? – Miles Sabin Jul 20 '16 at 12:38
See above. Thanks! – Cigogne Eveillée Jul 20 '16 at 23:35

Scala: Convert a Sealed Trait instance to an HList

1 Answers1