Doobie Shapeless Based Value Class Encoder

Deriver.scala

case class Foo(a: Int)

implicit val fooMeta: Meta[Foo] = valueClassMeta[Foo].apply

private def valueClassMeta[A]: PartiallyAppliedValueClassMeta[A] = new PartiallyAppliedValueClassMeta[A]

private class PartiallyAppliedValueClassMeta[A] {
  def apply[L <: HList, S](
    implicit ev: Generic.Aux[A, L],
    toL: (S :: HNil) =:= L,
    toS: L =:= (S :: HNil),
    tt: TypeTag[A],
    meta: Meta[S]
  ): Meta[A] =
    Meta[S].xmap[A](s => ev.from(toL(s :: HNil)), a => toS(ev.to(a)).head)
}