Derive a custom Validate from an existing one

First let me apologize for creating an issue for a simple question, but I haven’t found another channel.

So, let’s say I would like to refine scala.concurrent.duration.FiniteDuration, e.g. with Positive. My first idea was to simply use Positive and (contra)map it over a function extracting the length from the FiniteDuration which is a Long. But I haven’t found a way to do that, i.e. no public (contra)map method on Validate.

Any help would be highly appreciated.

[hseeberger]

Thanks for the quick answer!

I have changed the title (removed “question”) to better reflect the new nature of this issue (now a feature requirement).

[Primetalk]

For deriving a custom Validate from existing one we might need an equivalence relation:

  final class Equivalence[A, B]

  private val equivalenceInstance = new Equivalence[Any, Any]

  type `<==>`[A, B] = Equivalence[A, B]

  implicit def inferEquivalence[T,A,B](implicit eab: A ==> B, eba: B ==> A) : A <==> B = 
    equivalenceInstance.asInstanceOf[A <==> B]

And then we want to have the following validation inference rule:

  implicit def equivalenceValidation[T, A, B](implicit v: Validate[T, A], e : A <==> B): Validate[T, B] =
    v.asInstanceOf[Validate[T, B]]