gistfile1.scala

trait QId; trait QSection; trait QProjectType; trait QName
trait QFriendlyName; trait QDescription; trait QCode; trait QAnswers

case class Answer(text: String)

object QuestionTypes {
  type FormQuestionId = Long @@ QId
  type Section = String @@ QSection
  type ProjectType = String @@ QProjectType
  type Name = String @@ QName
  type FriendlyName = String @@ QFriendlyName
  type Description = String @@ QDescription
  type Code = Option[Int] @@ QCode
  type Answers = Seq[Answer] @@ QAnswers

  def extract[A] = new {
    def from[C, Repr <: HList](c: C)(implicit
      gen: Generic.Aux[C, Repr],
      sel: Selector[Repr, A]
    ) = sel(gen.to(c))
  }

}
import QuestionTypes._

case class Question (
  id: FormQuestionId,
  section: Section,
  projectType: ProjectType,
  name: Name,
  friendlyName: FriendlyName,
  description: Description,
  code: Code,
  answers: Answers
)

// given a question of type Question

import QuestionTypes._
val x = extract[Answers].from(question)

// x is of type sel.type#Out, and I would like to get the answers array instead