Custom validators with specific datatypes

[andyczerwonka]

Given the following silly rule, but just to illustrate:

  case class Id(id: UUID = UUID.randomUUID())
  object Id {
    implicit val validations: Validator[Id] = Validator[Id]
      .rule[UUID](_.id, !_.toString.isEmpty, "is required")
  }

This won't compile (can't create the typeclass because of java.util.UUID. There are other examples, see #51 (comment), which was handled simply by changing the HashMap to a Map. In this case, it's not feasible.

For many code bases that uses UUID's for identity keys. Should we handle this case by manually registering a typeclass for this type? Something like:

  implicit def uuidValidator(implicit v: Validator[String]): Validator[UUID] =
    (id: UUID) => v.validate(id.toString)