dkomanov

implicit class BooleanFutureExtensions(val future: Future[Boolean]) extends AnyVal {
  def orFail(e: => Throwable): Future[Boolean] =
    future.transform(t => if (t.isSuccess && !t.get) Failure(e) else t)
}

dkomanov

for {
  _ <- hasPermissions orFail new PermissionDeniedException("...")
  movie <- getMovie
  if !movie.hidden
  actors <- getActors(movie)
  plot <- getPlot(movie)
} yield MovieDescription(movie, actors, plot)

dkomanov

movie <- getMovie.filter(!_.hidden).recoverWith {
  case _: NoSuchElementException => Future.failed(new HiddenMovieException("..."))
}

dkomanov

implicit class FutureExtensions[T](val future: Future[T]) extends AnyVal {
  def filterOrFail(f: T => Boolean, e: => Throwable): Future[T] =
    future.flatMap(value => if (f(value)) Future.successful(value) else Future.failed(e))
}

dkomanov

for {
  _ <- hasPermissions orFail new PermissionDeniedException("...")
  movie <- getMovie.filterOrFail(!_.hidden, new HiddenMovieException("..."))
  actors <- getActors(movie)
  plot <- getPlot(movie)
} yield MovieDescription(movie, actors, plot)

dkomanov

implicit class FutureOfOptionExtensions[T](val v: Future[Option[T]]) extends AnyVal {
  def orFail(e: => Throwable): Future[T] =
    v.flatMap(_.fold[Future[T]](Future.failed(e), Future.successful)
}

dkomanov

for {
  movie <- findMovie("Dark Waters") orFail new MovieNotFoundException("...")
} yield movie

dkomanov

implicit class FutureExtensions[T](val future: Future[T]) extends AnyVal {
  def recoverFilter(f: => T): Future[T] =
    future.recover {
      case _: NoSuchElementException | ControlException => f
    }

  def recoverFilterWith(f: => Future[T]): Future[T] =
    future.recoverWith {
      case _: NoSuchElementException | ControlException => f
    }

dkomanov

Future(42)
  .map[Int](_ => throw new IllegalArgumentException)
  .flatMap[Int](_ => throw new IllegalStateException)
// Effectively: Future.failed(new IllegalArgumentException)

dkomanov

def innocentFunction(param: AnyRef): Future[Int] = {
  require(param != null)
  Future.successful(42)
}

innocentFunction(null)
  .map(_ => throw new IllegalStateException)
// an IllegalArgumentException will be thrown before map call