无形：有没有办法从案例类或元组中获取Hlist类型

Question

I'm totally new to shapeless. I create a case class from a list as following:

val list = Seq(Some(1), Some(1.0), ...)
val y =
  list
    .toHList[Option[Int]::Option[Double]::Option[Int]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::Option[Double]::HNil]

val z = y.get.tupled
val aa = YieldVariables.tupled(z)

It works well but I'm wondering if there is a way not to write all these types in the toHList[Here] part.

So I want to know if something like list.toHList[find the type yourself] or list.getTypesForHlist or yet MyCaseClass.getTypesForHlist that results to Option[Int]::Option[Double]... exists.

Answer 1

For case classes (and tuples, these are also case classes!), use Generic :

case class A(i: Int, s: String)
shapeless.Generic[A].to(A(1, "")) // Int :: String :: HNil

This is not possible to do on Seq . Indeed, as soon as you've called the constructor, the information about how many element you passed to that constructor is gone from a type perspective. Shapeless also has SingletonProductArgs : a macro for a varargs like syntax that returns an HList instead of a Seq .