Converting a List to a Case Class - scala

Question

As an exercise, I am trying to see if I can take a List[Any] and "cast" it into a case class using shapeless.
A very basic example of what I am trying to achieve:
case class Foo(i: Int, j: String)
val foo: Option[Foo] = fromListToCaseClass[Foo]( List(1:Any, "hi":Any) )
Here is how I am shaping my solution (this can be quite off):
def fromListToCaseClass[CC <: Product](a: List[Any]): Option[CC] = a.toHList[???].map( x => Generic[CC].from(x) )
Here is my reasoning:
I know that you can go from a case class to an HList[T] (CC -> HList[T]); where T is the type of the HList. I also know that you can create an HList from a list (list -> Option[HList]) as long as you know the type of the HList. Finally I know that you can go from an HList to a case class (HList -> CC).
CC -> HList[T]
list -> Option[HList[T]] -> Option[CC]
I am wondering if this makes sense or if I am way off here. Can we make this work? Any other suggestions? Thanks!

Answer 1

This can be done very straightforwardly using shapeless's Generic and FromTraversable type classes,
import scala.collection.GenTraversable
import shapeless._, ops.traversable.FromTraversable
class FromListToCaseClass[T] {
def apply[R <: HList](l: GenTraversable[_])
(implicit gen: Generic.Aux[T, R], tl: FromTraversable[R]): Option[T] =
tl(l).map(gen.from)
}
def fromListToCaseClass[T] = new FromListToCaseClass[T]
(There's some accidental complexity here due to Scala's awkwardness when it comes to mixing explicit and inferred type parameters: we want to specify T explicitly, but have R inferred for us).
Sample REPL session ...
scala> case class Foo(i: Int, j: String)
defined class Foo
scala> fromListToCaseClass[Foo](List(23, "foo"))
res0: Option[Foo] = Some(Foo(23,foo))
scala> fromListToCaseClass[Foo](List(23, false))
res1: Option[Foo] = None

Answer 2

You can do it with shapeless the following way:
import shapeless._
trait Creator[A] { def apply(list:List[Any]): Option[A] }
object Creator {
def as[A](list: List[Any])(implicit c: Creator[A]): Option[A] = c(list)
def instance[A](parse: List[Any] => Option[A]): Creator[A] = new Creator[A] {
def apply(list:List[Any]): Option[A] = parse(list)
}
def arbitraryCreate[A] = instance(list => list.headOption.map(_.asInstanceOf[A]))
implicit val stringCreate = arbitraryCreate[String]
implicit val intCreate = arbitraryCreate[Int]
implicit val hnilCreate = instance(s => if (s.isEmpty) Some(HNil) else None)
implicit def hconsCreate[H: Creator, T <: HList: Creator]: Creator[H :: T] =
instance {
case Nil => None
case list => for {
h <- as[H](list)
t <- as[T](list.tail)
} yield h :: t
}
implicit def caseClassCreate[C, R <: HList](
implicit gen: Generic.Aux[C, R],
rc: Creator[R]): Creator[C] =
instance(s => rc(s).map(gen.from))
}
And
val foo:Option[Foo] = Creator.as[Foo](List(1, "hi"))