Scala function return type

Question

I'm trying to change a method into a function, but I'm having troubles with the return type:

sealed trait CronJobStatus
case object CronJobSuccess extends CronJobStatus
case class CronJobFailure(error: Option[String] = None) extends CronJobStatus

My method (which works) is:

def jobNotFoundFailure(name: String): CronJobStatus = CronJobFailure(Some(s"Job with name $name not found"))

When trying to have jobNotFoundFailure as a function, I'm unable to find the right syntax to specify that it returns a CronJobStatus, I've got this function (but it returns CronJobFailure)

val jobNotFoundFailure = (name: String) => CronJobFailure(Some(s"Job with name $name not found"))

Which means I can't use this function where a CronJobStatus is expected. eg when getting an Opt from a map and folding:

cronJobsMap.get(name).fold(jobNotFoundFailure(name))(doDelete)

Answer 1

Another possible option is:

val jobNotFoundFailure = (name: String) =>
  CronJobFailure(Some(s"Job with name $name not found")): CronJobStatus

By the way your code (ignoring the fact that I don't know how doDelete looks like) seems to work even if jobNotFoundFailure is String => CronJobFailure .

cronJobsMap.get(name).fold(jobNotFoundFailure(name))(doDelete)

Whenever CronJobStatus is needed you can put CronJobFailure . Wherever function A => CronJobStatus is needed A => CronJobFailure is also valid because Function1[-T, +R] is covariant in the type of returned value.

Answer 2

You can write

val jobNotFoundFailure: String => CronJobStatus =
  name => CronJobFailure(Some(s"Job with name $name not found"))