Scala Concurrency and Futures

Question 1

What is a Scala `Future`?

Accepted Answer

A delayed computation that may complete asynchronously with a value or failure

Answer

A value that will never change

Answer

A scheduled task running on a timer

Answer

A lazy val with error handling

Question 2

What implicit value must be in scope to create a Scala Future?

Accepted Answer

implicit val ec: ExecutionContext

Answer

implicit val context: Context

Answer

implicit val dispatcher: Dispatcher

Answer

implicit val scheduler: Scheduler

Question 3

How do you handle the result of a Future with a callback in Scala?

Accepted Answer

future.onComplete { case Success(v) => ...; case Failure(e) => ... }

Answer

future.thenApply(f)

Answer

future.subscribe(f)

Answer

future.listen(f)

Question 4

What does `Future.sequence` do in Scala?

Accepted Answer

Converts a List[Future[A]] into a Future[List[A]]

Answer

Sequences Futures to run one after another

Answer

Cancels all futures in a list

Answer

Finds the first completed Future

Question 5

What is `Promise` in Scala concurrency?

Accepted Answer

A writable, single-assignment container that you can complete to fulfill a Future

Answer

A Future that always succeeds

Answer

A concurrent queue

Answer

An alternative to Future for blocking code

Question 6

How do you transform the successful result of a Scala Future?

Accepted Answer

future.map(f)

Answer

future.then(f)

Answer

future.transform(f)

Answer

future.apply(f)