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.

Implementation of allocated, which is declared in ResourceLike

Combines two Resource instances by lifting the behaviour of a SemigroupK instance into the resource context

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

Implementation of evalMap, which is declared in ResourceLike

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

Implementation of evalTap, which is declared in ResourceLike

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

Implementation of flatMap, which is declared in ResourceLike

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.

Implementation of map, which is declared in ResourceLike

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.

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 parZip, for example via parMapN:

 def mkResource(name: String) = {
   val acquire =
     IO(scala.util.Random.nextInt(1000).millis).flatMap(IO.sleep) *>
     IO(println(s"Acquiring $$name")).as(name)

   val release = 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(msg => IO(println(msg)))

Implementation of parZip, which is declared in ResourceLike

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.

Implementation of use, which is declared in ResourceLike