How to iterate all the product types in a coproduct using shapeless?

Question

Let\'s say I have a coproduct (a sealed trait) such as

sealed trait Traity
case object Foo extends Traity
case class Bar() extends Traity
case class Baz() extend         


        

Answer 1

For the example use case in your question, this is actually very straightforward:

import shapeless._

class NameHelper[A] {
  def apply[C <: Coproduct, K <: HList]()(implicit
    gen: LabelledGeneric.Aux[A, C],
    keys: ops.union.Keys.Aux[C, K],
    toSet: ops.hlist.ToTraversable.Aux[K, Set, Symbol]
  ): Set[String] = toSet(keys()).map(_.name)
}

def names[A] = new NameHelper[A]

And then:

scala> names[Traity]()
res0: Set[String] = Set(Bar, Baz, Foo)

(I'm using a Set since the order you're getting is just alphabetical—it's not currently possible to enumerate the constructors in declaration order, although I'd personally prefer that.)

If you'd like a more generic answer, an adaptation of the code in the question I linked above shouldn't be too bad—I'd be happy to add it here later.