Eval

Given a Resource, possibly built by composing multiple Resources monadically, returns the acquired resource, as well as an action that runs all the finalizers for releasing it.

If the outer F fails or is interrupted, allocated guarantees that the finalizers will be called. However, if the outer F succeeds, it's up to the user to ensure the returned F[Unit] is called once A needs to be released. If the returned F[Unit] is not called, the finalizers will not be run.

For this reason, this is an advanced and potentially unsafe api which can cause a resource leak if not used correctly, please prefer use as the standard way of running a Resource program.

Use cases include interacting with side-effectful apis that expect separate acquire and release actions (like the before and after methods of many test frameworks), or complex library code that needs to modify or move the finalizer for an existing resource.

Allocates two resources concurrently, and combines their results in a tuple.

The finalizers for the two resources are also run concurrently with each other, but within each of the two resources, nested finalizers are run in the usual reverse order of acquisition.

Note that Resource also comes with a cats.Parallel instance that offers more convenient access to the same functionality as both, for example via parMapN:

import scala.concurrent.duration._
import cats.effect.{IO, Resource}
import cats.effect.std.Random
import cats.syntax.all._

def mkResource(name: String) = {
 val acquire = for {
   n <- Random.scalaUtilRandom[IO].flatMap(_.nextIntBounded(1000))
   _ <- IO.sleep(n.millis)
   _ <- IO.println(s"Acquiring $$name")
 } yield name

 def release(name: String) =
   IO.println(s"Releasing $$name")

 Resource.make(acquire)(release)
}

val r = (mkResource("one"), mkResource("two"))
 .parMapN((s1, s2) => s"I have $s1 and $s2")
 .use(IO.println(_))

Applies an effectful transformation to the allocated resource. Like a flatMap on F[A] while maintaining the resource context

Applies an effectful transformation to the allocated resource. Like a flatTap on F[A] while maintaining the resource context

Implementation for the flatMap operation, as described via the cats.Monad type class.

Given a mapping function, transforms the resource provided by this Resource.

This is the standard Functor.map.

Given a natural transformation from F to G, transforms this Resource from effect F to effect G. The F and G constraint can also be satisfied by requiring a MonadCancelThrow[F] and MonadCancelThrow[G].

Runs finalizer when this resource is closed. Unlike the release action passed to Resource.make, this will run even if resource acquisition fails or is canceled.

Like onFinalize, but the action performed depends on the exit case.

Runs precede before this resource is allocated.

Races the evaluation of two resource allocations and returns the result of the winner, except in the case of cancelation.

Acquires the resource, runs gb and closes the resource once gb terminates, fails or gets interrupted

Creates a FunctionK that can run gb within a resource, which is then closed once gb terminates, fails or gets interrupted

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

Allocates a resource with a non-terminating use action. Useful to run programs that are expressed entirely in Resource.

The finalisers run when the resulting program fails or gets interrupted.

Allocates the resource and uses it to run the given Kleisli.

Creates a FunctionK that, when applied, will allocate the resource and use it to run the given Kleisli.

Allocates a resource and closes it immediately.