Reval

jam.monad.Reval

See theReval companion object

sealed abstract class Reval[F[_], +A]

Reval is a data structure which encodes the idea of allocating an object which has an associated finalizer. Can be thought of as a mix of cats.effect.Resource and cats.Eval. There are two allocation strategies:

later: allocates the object once when it is needed
always: allocates the object every time it is needed

For example:

scala> var c = 0
scala> val a = Reval.thunkLater[IO, Int]{c += 1; c}
scala> a.replicateA(3).map(_.sum).usePure.unsafeRunSync() // List(1, 1, 1).sum
val res0: Int = 3

scala> var c = 0
scala> val a = Reval.thunkAlways[IO, Int]{c += 1; c}
scala> a.replicateA(3).map(_.sum).usePure.unsafeRunSync() // List(1, 2, 3).sum
val res0: Int = 6

Common pitfalls:

later with multiple use calls will allocate later objects for each use

scala> var c = 0
scala> val a = Reval.thunkLater[IO, Int] { c += 1; c }
scala> (a.usePure, a.usePure).mapN(_ + _).unsafeRunSync() // 1 + 2
val res1: Int = 3

Attributes

Companion:: object
Graph
Supertypes: class Object
trait Matchable
class Any
Known subtypes: class Eval[F, A]
class FlatMap[F, A, B]
class Memoize[F, A]

Members list

Concise view

Value members

Concrete methods

Represents a reval as a cats.effect.Resource.

Attributes

Ensures that the object will be allocated once.

Attributes

Evaluates f after the object finalizer is called.

Attributes

Evaluates f before the object is allocated.

Attributes

Allocates an object and supplies it to the given function. The finalizer is called as soon as the resulting F[B] is completed, whether normally or as a raised error.

Attributes

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