Get default case class arguments via Shapeless

Question

Does shapeless provide a type class/macro that summons a HList containing the default values for all parameters of a case class?

Let's say we have this case class:

case class User(name: String, age: Int = 18)

Then I would like to get such a HList:

None :: Some(() => 18) :: HNil

Answer 1

Default parameters is implemented over synthetic methods. Try it trait. https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/default.scala

import shapeless.Default

case class User(name: String, age: Int = 18)
val d = Default[User]
println(d())

Out:

None :: Some(18) :: HNil