Demonstrating Future.sequence always returns the mapped Sequence in the same order it was passed.

FutureExample.scala

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future

val a = Future { 1 } // completes immediately.
val b = Future { Thread.sleep(1000); 2 } // is the last to complete.
val c = Future { Thread.sleep(100); 3 } // completes after 1 but before 2.

Future.sequence(Seq(a, b, c)) map println

// > List(1, 2, 3)