Resource

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

Linear Supertypes

AnyRef, Any

Known Subclasses

Allocate, Bind, Suspend

Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
def flatMap[B](f: (A) ⇒ Resource[F, B]): Resource[F, B]

Implementation for the flatMap operation, as described via the cats.Monad type class.
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toString(): String

Definition Classes
AnyRef → Any
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
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Docs: object Resource | package effect

sealed abstract class Resource[F[_], A] extends AnyRef

Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def finalize(): Unit

def flatMap[B](f: (A) ⇒ Resource[F, B]): Resource[F, B]

final def getClass(): Class[_]

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

final def synchronized[T0](arg0: ⇒ T0): T0

def toString(): String

def use[B](f: (A) ⇒ F[B])(implicit F: Bracket[F, Throwable]): F[B]

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from AnyRef

Inherited from Any

Ungrouped