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fundamentals-bio/izumi.functional.lifecycle/Lifecycle

Lifecycle

izumi.functional.lifecycle.Lifecycle
See theLifecycle companion object
trait Lifecycle[+F[_], +A]

Lifecycle is a class that describes the effectful allocation of a resource and its finalizer. This can be used to represent expensive resources.

Resources can be created using Lifecycle.make:

 def open(file: File): Lifecycle[IO, BufferedReader] =
   Lifecycle.make(
     acquire = IO { new BufferedReader(new FileReader(file)) }
   )(release = reader => IO { reader.close() })

Using inheritance from Lifecycle.Basic:

 final class BufferedReaderResource(
   file: File
 ) extends Lifecycle.Basic[IO, BufferedReader] {
   def acquire: IO[BufferedReader] = IO { new BufferedReader(new FileReader(file)) }
   def release(reader: BufferedReader): IO[BufferedReader] = IO { reader.close() }
 }

Using constructor-based inheritance from Lifecycle.Make, Lifecycle.LiftF, etc:

 final class BufferedReaderResource(
   file: File
 ) extends Lifecycle.Make[IO, BufferedReader](
   acquire = IO { new BufferedReader(new FileReader(file)) },
   release = reader => IO { reader.close() },
 )

Or by converting from an existing cats.effect.Resource or a zio.managed.ZManaged:

Usage is done via use:

 open(file1).use {
   reader1 =>
     open(file2).use {
       reader2 =>
         readFiles(reader1, reader2)
     }
 }

Lifecycles can be combined into larger Lifecycles via Lifecycle#flatMap (and the associated for-comprehension syntax):

val res: Lifecycle[IO, (BufferedReader, BufferedReader)] = {
  for {
    reader1 <- open(file1)
    reader2 <- open(file2)
  } yield (reader1, reader2)
}

Nested resources are released in reverse order of acquisition. Outer resources are released even if an inner use or release fails.

Lifecycle can be used without an effect-type with Lifecycle.Simple it can also mimic Java's initialization-after-construction with Lifecycle.Mutable

Use Lifecycle's to specify lifecycles of objects injected into the object graph.

 import distage.{Lifecycle, ModuleDef, Injector}
 import cats.effect.IO

 class DBConnection
 class MessageQueueConnection

 val dbResource = Lifecycle.make(IO { println("Connecting to DB!"); new DBConnection })(_ => IO(println("Disconnecting DB")))
 val mqResource = Lifecycle.make(IO { println("Connecting to Message Queue!"); new MessageQueueConnection })(_ => IO(println("Disconnecting Message Queue")))

 class MyApp(db: DBConnection, mq: MessageQueueConnection) {
   val run = IO(println("Hello World!"))
 }

 val module = new ModuleDef {
   make[DBConnection].fromResource(dbResource)
   make[MessageQueueConnection].fromResource(mqResource)
   make[MyApp]
 }

 Injector[IO]()
   .produceGet[MyApp](module)
   .use(_.run())
   .unsafeRunSync()

Will produce the following output:

 Connecting to DB!
 Connecting to Message Queue!
 Hello World!
 Disconnecting Message Queue
 Disconnecting DB

The lifecycle of the entire object graph is itself expressed with Lifecycle, you can control it by controlling the scope of .use or by manually invoking Lifecycle#acquire and Lifecycle#release.

== Inheritance helpers ==

The following helpers allow defining Lifecycle sub-classes using expression-like syntax:

The main reason to employ them is to workaround a limitation in Scala 2's eta-expansion — when converting a method to a function value, Scala always tries to fulfill implicit parameters eagerly instead of making them parameters of the function value, this limitation makes it harder to inject implicits using distage.

However, when using distage's type-based syntax: make[A].fromResource[A.Resource[F]] — this limitation does not apply and implicits inject successfully.

So to workaround the limitation you can convert an expression based resource-constructor such as:

 import distage.Lifecycle, cats.Monad

 class A
 object A {
   def resource[F[_]](implicit F: Monad[F]): Lifecycle[F, A] = Lifecycle.pure(new A)
 }

Into a class-based form:

 import distage.Lifecycle, cats.Monad

 class A
 object A {
   final class Resource[F[_]](implicit F: Monad[F])
     extends Lifecycle.Of(
       Lifecycle.pure(new A)
     )
 }

And inject successfully using make[A].fromResource[A.Resource[F]] syntax of izumi.distage.model.definition.dsl.ModuleDefDSL.

The following helpers ease defining Lifecycle sub-classes using traditional inheritance where acquire/release parts are defined as methods:

Attributes

See also:
Companion:
object
Graph
Supertypes
class Object
trait Matchable
class Any
Known subtypes
trait Basic[F, A]
class Make[F, A]
class Make_[F, A]
class NoClose[F, A]
trait Simple[A]
trait FromCats[F, A]
trait FromPair[F, A]
class MakePair[F, A]
trait FromZIO[R, E, A]
class NoCloseBase[F, A]
class LiftF[F, A]
class SelfNoClose[F, A]
trait OfInner[F, A]
class Of[F, A]
class FromAutoCloseable[F, A]
class OfCats[F, A]
class OfZIO[R, E, A]
trait Self[F, A]
trait Mutable[A]
trait SelfOf[F, A]
trait MutableOf[A]

Members list

Concise view

Type members

Types

Value members

Abstract methods

def acquire: F[InnerResource]

The action in F used to acquire the resource.

The action in F used to acquire the resource.

Attributes

Note:

the acquire action is performed uninterruptibly, when F is an effect type that supports interruption/cancellation.

def extract[B >: A](resource: InnerResource): Either[F[B], B]

Either an action in F or a pure function used to extract the A from the InnerResource

Either an action in F or a pure function used to extract the A from the InnerResource

The effect in the Left branch will be performed interruptibly, it is not afforded the same kind of safety as acquire and release actions when F is an effect type that supports interruption/cancellation.

When F is Identity, it doesn't matter whether the output is a Left or Right branch.

When consuming the output of extract you can use _.fold(identity, F.pure) to convert the Either to F[B]

Attributes

See also:

Lifecycle.Basic extract doesn't have to be defined when inheriting from Lifecycle.Basic

def release(resource: InnerResource): F[Unit]

The action in F used to release, close or deallocate the resource after it has been acquired and used through izumi.distage.model.definition.Lifecycle.SyntaxUse#use.

The action in F used to release, close or deallocate the resource after it has been acquired and used through izumi.distage.model.definition.Lifecycle.SyntaxUse#use.

Attributes

Note:

the release action is performed uninterruptibly, when F is an effect type that supports interruption/cancellation.

Concrete methods

final def beforeAcquire[G[x] : QuasiApplicative](f: => G[Unit]): Lifecycle[G, A]
final def beforeRelease[G[x] : QuasiApplicative](f: InnerResource => G[Unit]): Lifecycle[G, A]

Prepend release action to existing

Prepend release action to existing

Attributes

final def catchAll[G[x] : QuasiIO, B >: A](recover: Throwable => Lifecycle[G, B]): Lifecycle[G, B]
final def catchSome[G[x] : QuasiIO, B >: A](recover: PartialFunction[Throwable, Lifecycle[G, B]]): Lifecycle[G, B]
final def evalMap[G[x] : QuasiPrimitives, B](f: A => G[B]): Lifecycle[G, B]
final def evalTap[G[x] : QuasiPrimitives](f: A => G[Unit]): Lifecycle[G, A]
final def flatMap[G[x] : QuasiPrimitives, B](f: A => Lifecycle[G, B]): Lifecycle[G, B]
final def flatten[G[x] : QuasiPrimitives, B](implicit evidence$3: QuasiPrimitives[G], ev: A <:< Lifecycle[G, B]): Lifecycle[G, B]
final def map[G[x] : QuasiFunctor, B](f: A => B): Lifecycle[G, B]
def mapK[G[x], H[_]](f: Morphism1[G, H]): Lifecycle[H, A]
Implicitly added by SyntaxLifecycleMapK
final def redeem[G[x] : QuasiIO, B](onFailure: Throwable => Lifecycle[G, B], onSuccess: A => Lifecycle[G, B]): Lifecycle[G, B]
def toCats[G[x] : Applicative]: Resource[G, A]
Implicitly added by SyntaxLifecycleCats

Convert Lifecycle to cats.effect.Resource

Convert Lifecycle to cats.effect.Resource

Attributes

def toEffect[F[_]](implicit F: QuasiIO[F]): Lifecycle[F, A]
Implicitly added by SyntaxLifecycleIdentity
def toZIO: ZManaged[R, E, A]
Implicitly added by SyntaxLifecycleZIO

Convert Lifecycle to zio.managed.ZManaged

Convert Lifecycle to zio.managed.ZManaged

Attributes

def unsafeAllocate()(implicit F: QuasiPrimitives[F]): F[(A, () => F[Unit])]
Implicitly added by SyntaxUnsafeGet

Unsafely acquire the resource, return it and the finalizer. The resource will be leaked unless the finalizer is used.

Unsafely acquire the resource, return it and the finalizer. The resource will be leaked unless the finalizer is used.

This function only makes sense in code examples or at top-level, please use SyntaxUse#use otherwise!

Attributes

Note:

will acquire the resource without an uninterruptible section

def unsafeGet()(implicit F: QuasiPrimitives[F]): F[A]
Implicitly added by SyntaxUnsafeGet

Unsafely acquire the resource and throw away the finalizer, this will leak the resource and cause it to never be cleaned up.

Unsafely acquire the resource and throw away the finalizer, this will leak the resource and cause it to never be cleaned up.

This function only makes sense in code examples or at top-level, please use SyntaxUse#use otherwise!

Attributes

Note:

will acquire the resource without an uninterruptible section

def use[B](use: A => F[B])(implicit F: QuasiPrimitives[F]): F[B]
Implicitly added by SyntaxUse
def useEffect(implicit F: QuasiPrimitives[F]): F[A]
Implicitly added by SyntaxUseEffect
final def void[G[x] : QuasiFunctor]: Lifecycle[G, Unit]
final def widen[B >: A]: Lifecycle[F, B]
def widenError[E1 >: E]: Lifecycle[[_] =>> F[E1, _$43], A]
Implicitly added by SyntaxWidenError
final def widenF[G[x]]: Lifecycle[G, A]
final def wrapAcquire[G[x]](f: (=> G[InnerResource]) => G[InnerResource]): Lifecycle[G, A]

Wrap acquire action of this resource in another effect, e.g. for logging purposes

Wrap acquire action of this resource in another effect, e.g. for logging purposes

Attributes

final def wrapRelease[G[x]](f: (InnerResource => G[Unit], InnerResource) => G[Unit]): Lifecycle[G, A]

Wrap release action of this resource in another effect, e.g. for logging purposes

Wrap release action of this resource in another effect, e.g. for logging purposes

Attributes

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