🪄 zio-magic
ANNOUNCEMENT: This library is officially included as a first-class feature of ZIO 2.0 😊
Construct ZLayers automagically, with friendly compile-time hints!
// build.sbt
libraryDependencies += "io.github.kitlangton" %% "zio-magic" % "0.3.12"What's all this then?
// Given a dependency graph (Cake needs Chocolate & Flour, which in turn need Spoon)*
//
// Cake
// / \
// Chocolate Flour
// | |
// Spoon Spoon
//
// *Not an actual recipe.
import zio._
import zio.magic._
def run(args: List[String]): URIO[ZEnv, ExitCode] = {
// An effect requiring Cake and Console. Yum!
val program: URIO[Console with Cake, Unit] =
Cake.isDelicious.flatMap { bool => console.putStrLn(s"Cake is delicious: $bool") }
// The old way
val manually: ULayer[Cake with Console] =
((Spoon.live >>> Flour.live) ++ (Spoon.live >>> Chocolate.live)) >>> Cake.live ++ Console.live
// The magical way (The order doesn't matter)
val magically: UIO[Unit] =
program.inject(
Cake.live,
Flour.live,
Chocolate.live,
Spoon.live,
Console.live
)
magically.exitCode
}And if you leave something off, a compile time clue!
val magically: UIO[Unit] =
program.inject(
Cake.live,
//Flour.live, <-- Oops
Chocolate.live,
Spoon.live,
Console.live
) ZLayer Wiring Error
> provide zio.magic.Example.Flour.Service
> for Cake.liveVersus leaving out a dependency when manually constructing your layer...
val manually: ULayer[Cake with Console] =
(Flour.live ++ (Spoon.live >>> Chocolate.live)) >>> Cake.live ++ Console.live
// ^ A Spoon is missing here! type mismatch;
found : zio.ZLayer[zio.magic.Example.Spoon.Spoon with Any,Nothing,zio.magic.Example.Cake.Cake with zio.console.Console]
(which expands to) zio.ZLayer[zio.Has[zio.magic.Example.Spoon.Service] with Any,Nothing,zio.Has[zio.magic.Example.Cake.Service] with zio.Has[zio.console.Console.Service]]
required: zio.ULayer[zio.magic.Example.Cake.Cake with zio.console.Console]
(which expands to) zio.ZLayer[Any,Nothing,zio.Has[zio.magic.Example.Cake.Service] with zio.Has[zio.console.Console.Service]]
((Flour.live) ++ (Spoon.live >>> Chocolate.live)) >>> Cake.live ++ Console.liveAlso
You can also directly construct a ZLayer (However you must annotate the call to ZLayer.wire[LikeThis], because macros).
val layer = ZLayer.wire[Flour with Console](Console.live, Flour.live, Spoon.live)To construct URLayer[In, Out] use ZLayer.wireSome[In, Out] this way:
val layer = ZLayer.wireSome[CommonEnv, Flour with Console](Console.live, Flour.live, Spoon.live)Alternatively you can provide environment partially with injectSome[Rest](l1, l2, l3) - similarly to .provideSomeLayer.
There's also .injectCustom for which behaves similarly to .provideCustomLayer, only it also provides ZEnv.any to all transitive dependencies.
val program: URIO[Console with Car, Unit] = ???
val carLayer: URLayer[Blocking with Wheels, Car] = ???
val wheelLayer: ULayer[Wheels] = ???
// The ZEnv you use later will provide both Blocking to carLayer and Console to the program
val provided: URIO[ZEnv, Unit] =
program.injectCustom(carLayer, wheelLayer)Specs
inject, injectCustom, injectSome, injectShared, injectCustomShared and injectSomeShared all work for zio-test's Spec.
Debug!
Try ZLayer.wireDebug[Cake] or ZLayer.wireSomeDebug[Blocking with Console, Cake] to print out a pretty tree! Ooh la la!
ZLayer Wiring Graph
===================
â—‰ Cake.live
├─◑ Flour.live
│ ├─◑ Spoon.live
│ │ ╰─◑ Blocking.live
│ ╰─◑ Console.live
╰─◑ Berries.live
╰─◑ Spoon.live
╰─◑ Blocking.liveLet me know if you can think of any helpful variants, and I'll give 'em a whirl!