LabelledGeneric based keys descriptions

LabelledGenericDescription.scala

import shapeless._
import shapeless.record._

case class User(
  id: Long,
  name: String,
  age: Int
)
val user = User(15L, "Test", 25)

val gen = LabelledGeneric[User]

val repr = gen.to(user)

val keys = repr.keys

object mapper extends Poly1 {
  implicit val id = at[Witness.`'id`.T](_ => "This is id")
  implicit val name = at[Witness.`'name`.T](_ => "This is name")
  implicit val age = at[Witness.`'age`.T](_ => "This is age")
}

keys.map(mapper)