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 `Future[T]` represents an asynchronous computation that will eventually produce a value of type `T` or fail with an exception.

Question 2

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

Accepted Answer

implicit val ec: ExecutionContext

Answer

An `ExecutionContext` determines the thread pool on which the Future runs; it must be available implicitly when creating Futures.

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

`onComplete` registers a callback that receives a `Try[T]` (either `Success` or `Failure`) when the Future completes.

Question 4

What does `Future.sequence` do in Scala?

Accepted Answer

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

Answer

`Future.sequence` takes a collection of Futures and returns a single Future that completes with a collection of all results.

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 `Promise[T]` is a writable container that produces a `Future[T]`; you complete it with `success(value)` or `failure(exception)`.

Scala Practice Test