sealed abstract class Resource[F[_], A] extends AnyRef
The Resource
is a data structure that captures the effectful
allocation of a resource, along with its finalizer.
This can be used to wrap expensive resources. Example:
def open(file: File): Resource[IO, BufferedReader] = Resource(IO { val in = new BufferedReader(new FileReader(file)) (in, IO(in.close())) })
Usage is done via use and note that resource usage nests, because its implementation is specified in terms of Bracket:
open(file1).use { in1 => open(file2).use { in2 => readFiles(in1, in2) } }
Resource
forms a MonadError
on the resource type when the
effect type has a cats.MonadError
instance. Nested resources are
released in reverse order of acquisition. Outer resources are
released even if an inner use or release fails.
def mkResource(s: String) = { val acquire = IO(println(s"Acquiring $$s")) *> IO.pure(s) def release(s: String) = IO(println(s"Releasing $$s")) Resource.make(acquire)(release) } val r = for { outer <- mkResource("outer") inner <- mkResource("inner") } yield (outer, inner) r.use { case (a, b) => IO(println(s"Using $$a and $$b")) }
On evaluation the above prints:
Acquiring outer Acquiring inner Using outer and inner Releasing inner Releasing outer
A Resource
is nothing more than a data structure, an ADT, described by
the following node types and that can be interpretted if needed:
Normally users don't need to care about these node types, unless conversions
from Resource
into something else is needed (e.g. conversion from Resource
into a streaming data type).
- F
the effect type in which the resource is allocated and released
- A
the type of resource
- Source
- Resource.scala
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def
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finalize(): Unit
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def
flatMap[B](f: (A) ⇒ Resource[F, B]): Resource[F, B]
Implementation for the
flatMap
operation, as described via thecats.Monad
type class. -
final
def
getClass(): Class[_]
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def
ne(arg0: AnyRef): Boolean
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notify(): Unit
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def
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def
synchronized[T0](arg0: ⇒ T0): T0
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def
toString(): String
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def
use[B](f: (A) ⇒ F[B])(implicit F: Bracket[F, Throwable]): F[B]
Allocates a resource and supplies it to the given function.
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.- f
the function to apply to the allocated resource
- returns
the result of applying [F] to
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final
def
wait(): Unit
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def
wait(arg0: Long, arg1: Int): Unit
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This is the API documentation for the cats-effect library.
See the cats.effect package for a quick overview.
Links
Canonical documentation links:
Related Cats links (the core):