Scala 3/scala.concurrent/Future

Future

object Future

Future companion object.

Companion
class
Source
Future.scala
class Object
trait Matchable
class Any

Type members

Classlikes

object never extends Future[Nothing]

A Future which is never completed.

A Future which is never completed.

Source
Future.scala

Value members

Concrete methods

final def apply[T](body: => T)(implicit executor: ExecutionContext): Future[T]

Starts an asynchronous computation and returns a Future instance with the result of that computation.

Starts an asynchronous computation and returns a Future instance with the result of that computation.

The following expressions are equivalent:

val f1 = Future(expr)
val f2 = Future.unit.map(_ => expr)
val f3 = Future.unit.transform(_ => Success(expr))

The result becomes available once the asynchronous computation is completed.

Type Params
T

the type of the result

Value Params
body

the asynchronous computation

executor

the execution context on which the future is run

Returns

the Future holding the result of the computation

Source
Future.scala
final def delegate[T](body: => Future[T])(implicit executor: ExecutionContext): Future[T]

Starts an asynchronous computation and returns a Future instance with the result of that computation once it completes.

Starts an asynchronous computation and returns a Future instance with the result of that computation once it completes.

The following expressions are semantically equivalent:

val f1 = Future(expr).flatten
val f2 = Future.delegate(expr)
val f3 = Future.unit.flatMap(_ => expr)

The result becomes available once the resulting Future of the asynchronous computation is completed.

Type Params
T

the type of the result

Value Params
body

the asynchronous computation, returning a Future

executor

the execution context on which the body is evaluated in

Returns

the Future holding the result of the computation

Source
Future.scala
final def failed[T](exception: Throwable): Future[T]

Creates an already completed Future with the specified exception.

Creates an already completed Future with the specified exception.

Type Params
T

the type of the value in the future

Value Params
exception

the non-null instance of Throwable

Returns

the newly created Future instance

Source
Future.scala
final def find[T](futures: Iterable[Future[T]])(p: T => Boolean)(implicit executor: ExecutionContext): Future[Option[T]]

Asynchronously and non-blockingly returns a Future that will hold the optional result of the first Future with a result that matches the predicate, failed Futures will be ignored.

Asynchronously and non-blockingly returns a Future that will hold the optional result of the first Future with a result that matches the predicate, failed Futures will be ignored.

Type Params
T

the type of the value in the future

Value Params
futures

the scala.collection.immutable.Iterable of Futures to search

p

the predicate which indicates if it's a match

Returns

the Future holding the optional result of the search

Source
Future.scala
final def firstCompletedOf[T](futures: IterableOnce[Future[T]])(implicit executor: ExecutionContext): Future[T]

Asynchronously and non-blockingly returns a new Future to the result of the first future in the list that is completed.

Asynchronously and non-blockingly returns a new Future to the result of the first future in the list that is completed. This means no matter if it is completed as a success or as a failure.

Type Params
T

the type of the value in the future

Value Params
futures

the IterableOnce of Futures in which to find the first completed

Returns

the Future holding the result of the future that is first to be completed

Source
Future.scala
final def foldLeft[T, R](futures: Iterable[Future[T]])(zero: R)(op: (R, T) => R)(implicit executor: ExecutionContext): Future[R]

A non-blocking, asynchronous left fold over the specified futures, with the start value of the given zero.

A non-blocking, asynchronous left fold over the specified futures, with the start value of the given zero. The fold is performed asynchronously in left-to-right order as the futures become completed. The result will be the first failure of any of the futures, or any failure in the actual fold, or the result of the fold.

Example:

val futureSum = Future.foldLeft(futures)(0)(_ + _)
Type Params
R

the type of the value of the returned Future

T

the type of the value of the input Futures

Value Params
futures

the scala.collection.immutable.Iterable of Futures to be folded

op

the fold operation to be applied to the zero and futures

zero

the start value of the fold

Returns

the Future holding the result of the fold

Source
Future.scala
final def fromTry[T](result: Try[T]): Future[T]

Creates an already completed Future with the specified result or exception.

Creates an already completed Future with the specified result or exception.

Type Params
T

the type of the value in the Future

Value Params
result

the result of the returned Future instance

Returns

the newly created Future instance

Source
Future.scala
final def reduceLeft[T, R >: T](futures: Iterable[Future[T]])(op: (R, T) => R)(implicit executor: ExecutionContext): Future[R]

Initiates a non-blocking, asynchronous, left reduction over the supplied futures where the zero is the result value of the first Future.

Initiates a non-blocking, asynchronous, left reduction over the supplied futures where the zero is the result value of the first Future.

Example:

val futureSum = Future.reduceLeft(futures)(_ + _)
Type Params
R

the type of the value of the returned Future

T

the type of the value of the input Futures

Value Params
futures

the scala.collection.immutable.Iterable of Futures to be reduced

op

the reduce operation which is applied to the results of the futures

Returns

the Future holding the result of the reduce

Source
Future.scala
final def sequence[A, CC <: ([X] =>> IterableOnce[X]), To](in: CC[Future[A]])(implicit bf: BuildFrom[CC[Future[A]], A, To], executor: ExecutionContext): Future[To]

Simple version of Future.traverse.

Simple version of Future.traverse. Asynchronously and non-blockingly transforms, in essence, a IterableOnce[Future[A]] into a Future[IterableOnce[A]]. Useful for reducing many Futures into a single Future.

Type Params
A

the type of the value inside the Futures

CC

the type of the IterableOnce of Futures

To

the type of the resulting collection

Value Params
in

the IterableOnce of Futures which will be sequenced

Returns

the Future of the resulting collection

Source
Future.scala
final def successful[T](result: T): Future[T]

Creates an already completed Future with the specified result.

Creates an already completed Future with the specified result.

Type Params
T

the type of the value in the future

Value Params
result

the given successful value

Returns

the newly created Future instance

Source
Future.scala
final def traverse[A, B, M <: ([X] =>> IterableOnce[X])](in: M[A])(fn: A => Future[B])(implicit bf: BuildFrom[M[A], B, M[B]], executor: ExecutionContext): Future[M[B]]

Asynchronously and non-blockingly transforms a IterableOnce[A] into a Future[IterableOnce[B]] using the provided function A => Future[B].

Asynchronously and non-blockingly transforms a IterableOnce[A] into a Future[IterableOnce[B]] using the provided function A => Future[B]. This is useful for performing a parallel map. For example, to apply a function to all items of a list in parallel:

val myFutureList = Future.traverse(myList)(x => Future(myFunc(x)))
Type Params
A

the type of the value inside the Futures in the collection

B

the type of the value of the returned Future

M

the type of the collection of Futures

Value Params
fn

the function to be mapped over the collection to produce a collection of Futures

in

the collection to be mapped over with the provided function to produce a collection of Futures that is then sequenced into a Future collection

Returns

the Future of the collection of results

Source
Future.scala

Deprecated methods

@deprecated("use Future.foldLeft instead", "2.12.0")
def fold[T, R](futures: IterableOnce[Future[T]])(zero: R)(@deprecatedName("foldFun") op: (R, T) => R)(implicit executor: ExecutionContext): Future[R]

A non-blocking, asynchronous fold over the specified futures, with the start value of the given zero.

A non-blocking, asynchronous fold over the specified futures, with the start value of the given zero. The fold is performed on the thread where the last future is completed, the result will be the first failure of any of the futures, or any failure in the actual fold, or the result of the fold.

Example:

val futureSum = Future.fold(futures)(0)(_ + _)
Type Params
R

the type of the value of the returned Future

T

the type of the value of the input Futures

Value Params
futures

the IterableOnce of Futures to be folded

op

the fold operation to be applied to the zero and futures

zero

the start value of the fold

Returns

the Future holding the result of the fold

Deprecated
Source
Future.scala
@deprecated("use Future.reduceLeft instead", "2.12.0")
final def reduce[T, R >: T](futures: IterableOnce[Future[T]])(op: (R, T) => R)(implicit executor: ExecutionContext): Future[R]

Initiates a non-blocking, asynchronous, fold over the supplied futures where the fold-zero is the result value of the first Future in the collection.

Initiates a non-blocking, asynchronous, fold over the supplied futures where the fold-zero is the result value of the first Future in the collection.

Example:

val futureSum = Future.reduce(futures)(_ + _)
Type Params
R

the type of the value of the returned Future

T

the type of the value of the input Futures

Value Params
futures

the IterableOnce of Futures to be reduced

op

the reduce operation which is applied to the results of the futures

Returns

the Future holding the result of the reduce

Deprecated
Source
Future.scala

Concrete fields

final val unit: Future[Unit]

A Future which is completed with the Unit value.

A Future which is completed with the Unit value.

Source
Future.scala