Coursera / Reactive Programming in Scala / Week 3 / Combinators on Futures Sample code for answers C and D of the quiz.

FutureToTry.scala

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Try, Success, Failure}

val f: Future[Int] = Future(1 / 0)

// answer C
def applyC[T](f: Future[T]): Future[Try[T]] = f.map(x => Try(x))

// answer D
def applyD[T](f: Future[T]): Future[Try[T]] = f.map(s => Success(s)) recover { case t => Failure(t) }

applyC(f) onComplete { t => println(s"onComplete input: $t") }
// onComplete input: Failure(java.lang.ArithmeticException: / by zero)

applyD(f) onComplete { t => println(s"onComplete input: $t") }
// onComplete input: Success(Failure(java.lang.ArithmeticException: / by zero))

// Reminder: Future[X].onComplete has the signature: onComplete[U](func: (Try[X]) ⇒ U)
// In our case, X = Try[Int], so:
// applyC's input is a Failure[X], meaning: the future failed
// applyD's input is a Success[X], meaning: the future has succeeded, and the result is a Failure[Int]