Given a HList how do you get a HMap

Question

I have a HList of Symbols. I want to convert this into HMap with the HList values as the keys and the value mapping set to a generated object based on the key. The generated object holds state hence though default mapping can be known subsequent state is not.

Answer 1

Well... the thing is that Shapeless HMap is not as straight forward as HList, but the following can get you started

import shapeless._
import poly._

val hList = 'omg1 :: 'omg2 :: 'omg3 :: HNil

// lets assume that you want to map Symbols to kv-pairs String -> Int
// hence your HMap will have kv-pairs "omg1" -> 1, "omg2" -> 2...

class BiMapIS[K, V]
implicit val stringToInt = new BiMapIS[String, Int]

object myFoldPolyFunc extends Poly {
  implicit def caseSymbol = use(
    (hmap: HMap[BiMapIS], elem: Symbol) =>
      hmap + (elem.name -> elem.name.last.toString.toInt)
  )
}

val hMap = hList.foldLeft(HMap.empty[BiMapIS])(myFoldPolyFunc)

val v1 = hMap.get("omg1")
// Some(1)

val v2 = hMap.get("omg2")
// Some(2)