How to get out value from Scala Future onComplete/onSuccess - scala

Question

I have a high level structure of my code as follows. This is just an example replicating the high level structure.:-
import scala.concurrent.Future
class FutureReturnsAValue extends PersonAgeModifier {
def main(args: Array[String]) {
val jhonObj = Person("Jhon", 25)
val punishmentResult = addAgeCurse(jhonObj)
println("The punishment result for Jhonny is " + punishmentResult)
}
def addAgeCurse(person: Person): String = {
val oldAge = person.age
val futureAge = LongProcessingOpForAge(person)
futureAge.onSuccess {
newAge =>
if (newAge = oldAge + 5) {
"screw the kiddo, he aged by 5 years" // somehow return this string
}
else {
"lucky chap, the spell did not affect him" // somehow return this string
}
}
}
}
class PersonAgeModifier {
def LongProcessingOpForAge(person: Person): Future[Int] = {
Future.successful {
person.age + 5
}
}
}
case class Person
(
val name: String,
var age: Int
)
object Person {
def apply(name: String, age: Int) = new Person(name, age)
}
So my requirement is this:- I need the string from the addAgeCurse() method. Now I know some off you may suggest to pass the future value LongProcessingOpForAge() as such to main() but that is not what I want here.
Questions:
What is the cleanest way to obtain the string and pass it to main(). ( By clean , I mean something which does not involve using wait for x duration as I would like to avoid any manual intervention.)
Thanks

Answer 1

Maybe you're asking for:
scala> import concurrent._, ExecutionContext.Implicits._
import concurrent._
import ExecutionContext.Implicits._
scala> def f = Future(42)
f: scala.concurrent.Future[Int]
scala> def g = f.map(_ + 1)
g: scala.concurrent.Future[Int]
scala> :pa
// Entering paste mode (ctrl-D to finish)
object Main extends App {
for (i <- g) println(i)
}
// Exiting paste mode, now interpreting.
defined object Main
scala> Main main null
43
That's the easy idiom to block for your answer. The main thread won't exit until it has it. Use map to transform a future value.