scala.concurrent

# Future

###
Related Docs: object Future | package concurrent

#### trait Future[+T] extends Awaitable[T]

The trait that represents futures.

Asynchronous computations that yield futures are created with the `Future` call:

    val s = "Hello"
    val f: Future[String] = Future {
      s + " future!"
    }
    f onSuccess {
      case msg => println(msg)
    }

Source
  Future.scala
See also

  Futures and Promises

Linear Supertypes
Awaitable[T], AnyRef, Any
Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. Future
2. Awaitable
3. AnyRef
4. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

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2. Show All

Visibility

1. Public
2. All

### Abstract Value Members

1. #### abstract def isCompleted: Boolean

   Returns whether the future has already been completed with a value or an exception.

   Returns whether the future has already been completed with a value or an exception.

   Note: using this method yields nondeterministic dataflow programs.

   returns

     `true` if the future is already completed, `false` otherwise

2. #### abstract def onComplete[U](f: (Try[T]) ⇒ U)(implicit executor: ExecutionContext): Unit

   When this future is completed, either through an exception, or a value, apply the provided function.

   When this future is completed, either through an exception, or a value, apply the provided function.

   If the future has already been completed, this will either be applied immediately or be scheduled asynchronously.

   Multiple callbacks may be registered; there is no guarantee that they will be executed in a particular order.

   The provided callback always runs in the provided implicit `ExecutionContext`, though there is no guarantee that the `execute()` method on the `ExecutionContext` will be called once per callback or that `execute()` will be called in the current thread. That is, the implementation may run multiple callbacks in a batch within a single `execute()` and it may run `execute()` either immediately or asynchronously.

3. #### abstract def ready(atMost: Duration)(implicit permit: CanAwait): Future.this.type

   Await the "completed" state of this `Awaitable`.

   Await the "completed" state of this `Awaitable`.

   This method should not be called directly; use Await.ready instead.

   atMost

     maximum wait time, which may be negative (no waiting is done), Duration.Inf for unbounded waiting, or a finite positive duration

   returns

     this `Awaitable`

   Definition Classes
     Awaitable
   Annotations
     @throws( clazz = classOf[TimeoutException] ) @throws( clazz = classOf[InterruptedException] )
   Exceptions thrown

     `IllegalArgumentException` if `atMost` is Duration.Undefined

     `InterruptedException` if the current thread is interrupted while waiting

     `TimeoutException` if after waiting for the specified time this `Awaitable` is still not ready

4. #### abstract def result(atMost: Duration)(implicit permit: CanAwait): T

   Await and return the result (of type `T`) of this `Awaitable`.

   Await and return the result (of type `T`) of this `Awaitable`.

   This method should not be called directly; use Await.result instead.

   atMost

     maximum wait time, which may be negative (no waiting is done), Duration.Inf for unbounded waiting, or a finite positive duration

   returns

     the result value if the `Awaitable` is completed within the specific maximum wait time

   Definition Classes
     Awaitable
   Annotations
     @throws( clazz = classOf[Exception] )
   Exceptions thrown

     `IllegalArgumentException` if `atMost` is Duration.Undefined

     `InterruptedException` if the current thread is interrupted while waiting

     `TimeoutException` if after waiting for the specified time this `Awaitable` is still not ready

5. #### abstract def value: Option[Try[T]]

   The value of this `Future`.

   The value of this `Future`.

   If the future is not completed the returned value will be `None`. If the future is completed the value will be `Some(Success(t))` if it contains a valid result, or `Some(Failure(error))` if it contains an exception.

### Concrete Value Members

1. #### final def !=(arg0: Any): Boolean

   Test two objects for inequality.

   Test two objects for inequality.

   returns

     `true` if !(this == that), false otherwise.

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Equivalent to `x.hashCode` except for boxed numeric types and `null`.

   Equivalent to `x.hashCode` except for boxed numeric types and `null`. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For `null` returns a hashcode where `null.hashCode` throws a `NullPointerException`.

   returns

     a hash value consistent with ==

   Definition Classes
     AnyRef → Any

3. #### def +(other: String): String

   Implicit information
     This member is added by an implicit conversion from Future[T] to any2stringadd[Future[T]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

4. #### def ->[B](y: B): (Future[T], B)

   Implicit information
     This member is added by an implicit conversion from Future[T] to ArrowAssoc[Future[T]] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()

5. #### final def ==(arg0: Any): Boolean

   The expression `x == that` is equivalent to `if (x eq null) that eq null else x.equals(that)`.

   The expression `x == that` is equivalent to `if (x eq null) that eq null else x.equals(that)`.

   returns

     `true` if the receiver object is equivalent to the argument; `false` otherwise.

   Definition Classes
     AnyRef → Any

6. #### def andThen[U](pf: PartialFunction[Try[T], U])(implicit executor: ExecutionContext): Future[T]

   Applies the side-effecting function to the result of this future, and returns a new future with the result of this future.

   Applies the side-effecting function to the result of this future, and returns a new future with the result of this future.

   This method allows one to enforce that the callbacks are executed in a specified order.

   Note that if one of the chained `andThen` callbacks throws an exception, that exception is not propagated to the subsequent `andThen` callbacks. Instead, the subsequent `andThen` callbacks are given the original value of this future.

   The following example prints out `5`:

       val f = Future { 5 }
       f andThen {
         case r => sys.error("runtime exception")
       } andThen {
         case Failure(t) => println(t)
         case Success(v) => println(v)
       }

7. #### final def asInstanceOf[T0]: T0

   Cast the receiver object to be of type `T0`.

   Cast the receiver object to be of type `T0`.

   Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression `1.asInstanceOf[String]` will throw a `ClassCastException` at runtime, while the expression `List(1).asInstanceOf[List[String]]` will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

   returns

     the receiver object.

   Definition Classes
     Any
   Exceptions thrown

     `ClassCastException` if the receiver object is not an instance of the erasure of type `T0`.

8. #### def clone(): AnyRef

   Create a copy of the receiver object.

   Create a copy of the receiver object.

   The default implementation of the `clone` method is platform dependent.

   returns

     a copy of the receiver object.

   Attributes
     protected[java.lang]
   Definition Classes
     AnyRef
   Annotations
     @HotSpotIntrinsicCandidate() @throws( ... )
   Note

     not specified by SLS as a member of AnyRef

9. #### def collect[S](pf: PartialFunction[T, S])(implicit executor: ExecutionContext): Future[S]

   Creates a new future by mapping the value of the current future, if the given partial function is defined at that value.

   Creates a new future by mapping the value of the current future, if the given partial function is defined at that value.

   If the current future contains a value for which the partial function is defined, the new future will also hold that value. Otherwise, the resulting future will fail with a `NoSuchElementException`.

   If the current future fails, then the resulting future also fails.

   Example:

       val f = Future { -5 }
       val g = f collect {
         case x if x < 0 => -x
       }
       val h = f collect {
         case x if x > 0 => x * 2
       }
       Await.result(g, Duration.Zero) // evaluates to 5
       Await.result(h, Duration.Zero) // throw a NoSuchElementException

10. #### def ensuring(cond: (Future[T]) ⇒ Boolean, msg: ⇒ Any): Future[T]

    Implicit information
      This member is added by an implicit conversion from Future[T] to Ensuring[Future[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

11. #### def ensuring(cond: (Future[T]) ⇒ Boolean): Future[T]

    Implicit information
      This member is added by an implicit conversion from Future[T] to Ensuring[Future[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

12. #### def ensuring(cond: Boolean, msg: ⇒ Any): Future[T]

    Implicit information
      This member is added by an implicit conversion from Future[T] to Ensuring[Future[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

13. #### def ensuring(cond: Boolean): Future[T]

    Implicit information
      This member is added by an implicit conversion from Future[T] to Ensuring[Future[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

14. #### final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (`that`) is a reference to the receiver object (`this`).

    Tests whether the argument (`that`) is a reference to the receiver object (`this`).

    The `eq` method implements an equivalence relation on non-null instances of `AnyRef`, and has three additional properties:

    - It is consistent: for any non-null instances `x` and `y` of type `AnyRef`, multiple invocations of `x.eq(y)` consistently returns `true` or consistently returns `false`.
    - For any non-null instance `x` of type `AnyRef`, `x.eq(null)` and `null.eq(x)` returns `false`.
    - `null.eq(null)` returns `true`.

    When overriding the `equals` or `hashCode` methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (`o1 eq o2`), they should be equal to each other (`o1 == o2`) and they should hash to the same value (`o1.hashCode == o2.hashCode`).

    returns

      `true` if the argument is a reference to the receiver object; `false` otherwise.

    Definition Classes
      AnyRef

15. #### def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. Default implementation delegates to `eq`.

    See also `equals` in scala.Any.

    returns

      `true` if the receiver object is equivalent to the argument; `false` otherwise.

    Definition Classes
      AnyRef → Any

16. #### def failed: Future[Throwable]

    Returns a failed projection of this future.

    Returns a failed projection of this future.

    The failed projection is a future holding a value of type `Throwable`.

    It is completed with a value which is the throwable of the original future in case the original future is failed.

    It is failed with a `NoSuchElementException` if the original future is completed successfully.

    Blocking on this future returns a value if the original future is completed with an exception and throws a corresponding exception if the original future fails.

17. #### def fallbackTo[U >: T](that: Future[U]): Future[U]

    Creates a new future which holds the result of this future if it was completed successfully, or, if not, the result of the `that` future if `that` is completed successfully.

    Creates a new future which holds the result of this future if it was completed successfully, or, if not, the result of the `that` future if `that` is completed successfully. If both futures are failed, the resulting future holds the throwable object of the first future.

    Using this method will not cause concurrent programs to become nondeterministic.

    Example:

        val f = Future { sys.error("failed") }
        val g = Future { 5 }
        val h = f fallbackTo g
        Await.result(h, Duration.Zero) // evaluates to 5

18. #### def filter(p: (T) ⇒ Boolean)(implicit executor: ExecutionContext): Future[T]

    Creates a new future by filtering the value of the current future with a predicate.

    Creates a new future by filtering the value of the current future with a predicate.

    If the current future contains a value which satisfies the predicate, the new future will also hold that value. Otherwise, the resulting future will fail with a `NoSuchElementException`.

    If the current future fails, then the resulting future also fails.

    Example:

        val f = Future { 5 }
        val g = f filter { _ % 2 == 1 }
        val h = f filter { _ % 2 == 0 }
        Await.result(g, Duration.Zero) // evaluates to 5
        Await.result(h, Duration.Zero) // throw a NoSuchElementException

19. #### def flatMap[S](f: (T) ⇒ Future[S])(implicit executor: ExecutionContext): Future[S]

    Creates a new future by applying a function to the successful result of this future, and returns the result of the function as the new future.

    Creates a new future by applying a function to the successful result of this future, and returns the result of the function as the new future. If this future is completed with an exception then the new future will also contain this exception.

    Example:

        val f = Future { 5 }
        val g = Future { 3 }
        val h = for {
          x: Int <- f // returns Future(5)
          y: Int <- g // returns Future(3)
        } yield x + y

    is translated to:

        f flatMap { (x: Int) => g map { (y: Int) => x + y } }

20. #### def foreach[U](f: (T) ⇒ U)(implicit executor: ExecutionContext): Unit

    Asynchronously processes the value in the future once the value becomes available.

    Asynchronously processes the value in the future once the value becomes available.

    Will not be called if the future fails.

21. #### def formatted(fmtstr: String): String

    Returns string formatted according to given `format` string.

    Returns string formatted according to given `format` string. Format strings are as for `String.format` (@see java.lang.String.format).

    Implicit information
      This member is added by an implicit conversion from Future[T] to StringFormat[Future[T]] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()

22. #### final def getClass(): Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

      a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
      AnyRef → Any
    Annotations
      @HotSpotIntrinsicCandidate()
    Note

      not specified by SLS as a member of AnyRef

23. #### def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in scala.Any.

    returns

      the hash code value for this object.

    Definition Classes
      AnyRef → Any
    Annotations
      @HotSpotIntrinsicCandidate()

24. #### final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is `T0`.

    Test whether the dynamic type of the receiver object is `T0`.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression `1.isInstanceOf[String]` will return `false`, while the expression `List(1).isInstanceOf[List[String]]` will return `true`. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

      `true` if the receiver object is an instance of erasure of type `T0`; `false` otherwise.

    Definition Classes
      Any

25. #### def map[S](f: (T) ⇒ S)(implicit executor: ExecutionContext): Future[S]

    Creates a new future by applying a function to the successful result of this future.

    Creates a new future by applying a function to the successful result of this future. If this future is completed with an exception then the new future will also contain this exception.

    Example:

        val f = Future { 5 }
        val g = Future { 3 }
        val h = for {
          x: Int <- f // returns Future(5)
          y: Int <- g // returns Future(3)
        } yield x + y

    is translated to:

        f flatMap { (x: Int) => g map { (y: Int) => x + y } }

26. #### def mapTo[S](implicit tag: ClassTag[S]): Future[S]

    Creates a new `Future[S]` which is completed with this `Future`'s result if that conforms to `S`'s erased type or a `ClassCastException` otherwise.

27. #### final def ne(arg0: AnyRef): Boolean

    Equivalent to `!(this eq that)`.

    Equivalent to `!(this eq that)`.

    returns

      `true` if the argument is not a reference to the receiver object; `false` otherwise.

    Definition Classes
      AnyRef

28. #### final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
      AnyRef
    Annotations
      @HotSpotIntrinsicCandidate()
    Note

      not specified by SLS as a member of AnyRef

29. #### final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
      AnyRef
    Annotations
      @HotSpotIntrinsicCandidate()
    Note

      not specified by SLS as a member of AnyRef

30. #### def onFailure[U](pf: PartialFunction[Throwable, U])(implicit executor: ExecutionContext): Unit

    When this future is completed with a failure (i.e., with a throwable), apply the provided callback to the throwable.

    When this future is completed with a failure (i.e., with a throwable), apply the provided callback to the throwable.

    The future may contain a throwable object and this means that the future failed. Futures obtained through combinators have the same exception as the future they were obtained from. The following throwable objects are not contained in the future:

    - `Error` - errors are not contained within futures
    - `InterruptedException` - not contained within futures
    - all `scala.util.control.ControlThrowable` except `NonLocalReturnControl` - not contained within futures

    Instead, the future is completed with a ExecutionException with one of the exceptions above as the cause. If a future is failed with a `scala.runtime.NonLocalReturnControl`, it is completed with a value from that throwable instead.

    If the future has already been completed with a failure, this will either be applied immediately or be scheduled asynchronously.

    Will not be called in case that the future is completed with a value.

    Multiple callbacks may be registered; there is no guarantee that they will be executed in a particular order.

    The provided callback always runs in the provided implicit `ExecutionContext`, though there is no guarantee that the `execute()` method on the `ExecutionContext` will be called once per callback or that `execute()` will be called in the current thread. That is, the implementation may run multiple callbacks in a batch within a single `execute()` and it may run `execute()` either immediately or asynchronously.

31. #### def onSuccess[U](pf: PartialFunction[T, U])(implicit executor: ExecutionContext): Unit

    When this future is completed successfully (i.e., with a value), apply the provided partial function to the value if the partial function is defined at that value.

    When this future is completed successfully (i.e., with a value), apply the provided partial function to the value if the partial function is defined at that value.

    If the future has already been completed with a value, this will either be applied immediately or be scheduled asynchronously.

    Multiple callbacks may be registered; there is no guarantee that they will be executed in a particular order.

    The provided callback always runs in the provided implicit `ExecutionContext`, though there is no guarantee that the `execute()` method on the `ExecutionContext` will be called once per callback or that `execute()` will be called in the current thread. That is, the implementation may run multiple callbacks in a batch within a single `execute()` and it may run `execute()` either immediately or asynchronously.

32. #### def recover[U >: T](pf: PartialFunction[Throwable, U])(implicit executor: ExecutionContext): Future[U]

    Creates a new future that will handle any matching throwable that this future might contain.

    Creates a new future that will handle any matching throwable that this future might contain. If there is no match, or if this future contains a valid result then the new future will contain the same.

    Example:

        Future (6 / 0) recover { case e: ArithmeticException => 0 } // result: 0
        Future (6 / 0) recover { case e: NotFoundException   => 0 } // result: exception
        Future (6 / 2) recover { case e: ArithmeticException => 0 } // result: 3

33. #### def recoverWith[U >: T](pf: PartialFunction[Throwable, Future[U]])(implicit executor: ExecutionContext): Future[U]

    Creates a new future that will handle any matching throwable that this future might contain by assigning it a value of another future.

    Creates a new future that will handle any matching throwable that this future might contain by assigning it a value of another future.

    If there is no match, or if this future contains a valid result then the new future will contain the same result.

    Example:

        val f = Future { Int.MaxValue }
        Future (6 / 0) recoverWith { case e: ArithmeticException => f } // result: Int.MaxValue

34. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

35. #### def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

      a String representation of the object.

    Definition Classes
      AnyRef → Any

36. #### def transform[S](s: (T) ⇒ S, f: (Throwable) ⇒ Throwable)(implicit executor: ExecutionContext): Future[S]

    Creates a new future by applying the 's' function to the successful result of this future, or the 'f' function to the failed result.

    Creates a new future by applying the 's' function to the successful result of this future, or the 'f' function to the failed result. If there is any non-fatal exception thrown when 's' or 'f' is applied, that exception will be propagated to the resulting future.

    s

      function that transforms a successful result of the receiver into a successful result of the returned future

    f

      function that transforms a failure of the receiver into a failure of the returned future

    returns

      a future that will be completed with the transformed value

37. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

38. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

39. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

40. #### final def withFilter(p: (T) ⇒ Boolean)(implicit executor: ExecutionContext): Future[T]

    Used by for-comprehensions.

41. #### def zip[U](that: Future[U]): Future[(T, U)]

    Zips the values of `this` and `that` future, and creates a new future holding the tuple of their results.

    Zips the values of `this` and `that` future, and creates a new future holding the tuple of their results.

    If `this` future fails, the resulting future is failed with the throwable stored in `this`. Otherwise, if `that` future fails, the resulting future is failed with the throwable stored in `that`.

42. #### def →[B](y: B): (Future[T], B)

    Implicit information
      This member is added by an implicit conversion from Future[T] to ArrowAssoc[Future[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Deprecated Value Members

1. #### def finalize(): Unit

   Called by the garbage collector on the receiver object when there are no more references to the object.

   Called by the garbage collector on the receiver object when there are no more references to the object.

   The details of when and if the `finalize` method is invoked, as well as the interaction between `finalize` and non-local returns and exceptions, are all platform dependent.

   Attributes
     protected[java.lang]
   Definition Classes
     AnyRef
   Annotations
     @Deprecated @deprecated @throws( classOf[java.lang.Throwable] )
   Deprecated

     (Since version ) see corresponding Javadoc for more information.

   Note

     not specified by SLS as a member of AnyRef

### Inherited from Awaitable[T]

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from Future[T] to any2stringadd[Future[T]]

### Inherited by implicit conversion StringFormat from Future[T] to StringFormat[Future[T]]

### Inherited by implicit conversion Ensuring from Future[T] to Ensuring[Future[T]]

### Inherited by implicit conversion ArrowAssoc from Future[T] to ArrowAssoc[Future[T]]

### Ungrouped