Scala Future.sequence()

When we have a sequence of Futures, or a list of Futures, or a collection of Futures, we should use one of the Future combinator APIs, Future.sequence(), to deal with this scenario.

This Future.sequence() function converts a list of Futures into a single Future that means collections of Futures into a single Future.

In simple words, List[Future[T]] ======> Future[List[T]].

It is also known as composing Futures. The following diagram demonstrates how Scala Future's sequence() function converts List[Future[T]] into Future[List[T]]:

Consider the following example:

scala> val pricesList:List[Future[Int]] = List(Future(1001),Future(999),Future(-2000),Future(1000)) 
pricesList: List[scala.concurrent.Future[Int]] = List(scala.concurrent.impl.Promise$DefaultPromise@680a66dd, scala.concurrent.impl.Promise$DefaultPromise@2dd8239, scala.concurrent.impl.Promise$DefaultPromise@472698d, scala.concurrent.impl.Promise$DefaultPromise@7b7683d4) 
 
scala> val maxPrice:Future[Int...