Guide for implementing a custom refined type (ITT: Some cool FiniteDuration refining cheats)

I love this library, thanks for your work on it

I wanted a way to say a FiniteDuration must be > 5 seconds earlier today and set about looking into writing my own refined type, but it looks tricky - is this really simple, have I missed something?

A guide on extending the library with your own types might be nice (which is why i made this ticket)

[henricook]

I’ve done some shameless thievery from the size validate instance you linked, and i haven’t yet tested this but:

final case class LengthInSeconds[P](lengthInSeconds: P)

object LengthInSeconds {
  implicit def lengthInSecondsValidate[P, RP](
    implicit v: Validate.Aux[Long, P, RP]
  ): Validate.Aux[FiniteDuration, LengthInSeconds[P], LengthInSeconds[v.Res]] =
    // Convert FiniteDuration to seconds and use v to validate that value
    new Validate[FiniteDuration, LengthInSeconds[P]] {
      override type R = LengthInSeconds[v.Res]

      override def validate(duration: FiniteDuration): Res = {
        val r = v.validate(duration.toSeconds)
        r.as(LengthInSeconds(r))
      }

      override def showExpr(duration: FiniteDuration): String =
        v.showExpr(duration.toSeconds)

      override def showResult(duration: FiniteDuration, r: Res): String = {
        val lengthInSeconds = duration.toSeconds
        val nested          = v.showResult(lengthInSeconds, r.detail.lengthInSeconds)
        Resources.predicateTakingResultDetail(s"lengthInSeconds({$duration.toSeconds}) = $lengthInSeconds", r, nested)
      }
    }
}

[fthomas]

You could define a companion object for MySpecialType:

type MySpecialType = FiniteDuration Refined LengthInSeconds[Greater[W.`5`.T]]

object MySpecialType extends RefinedTypeOps[MySpecialType, FiniteDuration]

MySpecialType.from is then the same function as refineV[LengthInSeconds[Greater[W.`5`.T]]](_: FiniteDuration).