cats-effect-kernel/cats.effect.kernel/Outcome

Outcome

cats.effect.kernel.Outcome

See theOutcome companion object

sealed trait Outcome[F[_], E, A] extends Product with Serializable

Represents the result of the execution of a fiber. It may terminate in one of 3 states:

Succeeded(fa) The fiber completed with a value.

A commonly asked question is why this wraps a value of type F[A] rather than one of type A. This is to support monad transformers. Consider

val oc: OutcomeIO[Int] =
 for {
   fiber <- Spawn[OptionT[IO, *]].start(OptionT.none[IO, Int])
   oc <- fiber.join
 } yield oc

If the fiber succeeds then there is no value of type Int to be wrapped in Succeeded, hence Succeeded contains a value of type OptionT[IO, Int] instead.

In general you can assume that binding on the value of type F[A] contained in Succeeded does not perform further effects. In the case of IO that means that the outcome has been constructed as Outcome.Succeeded(IO.pure(result)).

Errored(e) The fiber exited with an error.
Canceled() The fiber was canceled, either externally or self-canceled via MonadCancel[F]#canceled.

Attributes

Companion:: object
Source:: Outcome.scala
Graph
Supertypes: trait Serializable
trait Product
trait Equals
class Object
trait Matchable
class Any
Known subtypes: class Canceled[F, E, A]
class Errored[F, E, A]
class Succeeded[F, E, A]

Members list

Concise view

Value members

Concrete methods

Attributes

Source:: Outcome.scala

Allows the restoration to a normal development flow from an Outcome.

This can be useful for storing the state of a running computation and then waiters for that data can act and continue forward on that shared outcome. Cancelation is encoded as a CancellationException.