Other Supported Monads

As of RC5, zio-direct now supports ZStream and ZPure as well as scala.concurrent.Future and scala.List. The latter two are largely fully functional but largely for demonstration purposes.

Note that all of these are currently only supported in Scala 3.

ZStream

To use zio-direct with ZStream, add the following to your build.sbt file.

libraryDependencies += "dev.zio" %% "zio-direct-streams" % "1.0.0-RC7"

You can then use zio-direct with ZStream:

import zio.direct.stream._

val out =
  defer {
    val a = ZStream(1, 2, 3).each
    val b = ZStream("foo", "bar").each
    (a, b)
  }

out.runCollect
// ZIO.succeed(Chunk((1,"foo"),(1,"bar"),(2,"foo"),(2,"bar"),(3,"foo"),(3,"bar")))

Note that if you are also using zio-direct with ZIO, you should rename the defer function to avoid conflicts:

import zio.direct.stream.{ defer => deferStream, _ }
import zio.direct._

// The `run` function of ZStream is called `each`
val outStream: ZStream[Any, Nothing, (Int, String)] =
  deferStream {
    val a = ZStream(1, 2, 3).each
    val b = ZStream("foo", "bar").each
    (a, b)
  }

val outZio: ZIO[Any, Nothing, Chunk[(Int, String)]] =
  defer {
    val a: Chunk[(Int, String)] = outStream.runCollect.run
    val b = ZIO.succeed((123, "baz")).run
    a :+ b
  }

// Yields:
// ZIO.succeed(Chunk((1,"foo"),(1,"bar"),(2,"foo"),(2,"bar"),(3,"foo"),(3,"bar"),(123, "baz")))

ZPure

Note that Metals auto-complete/type-info popups may be sluggish when using ZPure, especially when try/catch constructs are being used. In some cases, you may need to wait for a "Loading..." popup message for 20-30 seconds although the actual (bloop) compile time will just be a few seconds.

To use zio-direct with ZPure, add the following to your build.sbt file.

libraryDependencies += "dev.zio" %% "zio-direct-pure" % "1.0.0-RC7"

In order to use zio-direct with ZPure, you first need to define a deferWith[W, S] context which will define the Logging (W) and State (S) types for your ZPure computation.

Due to limitations of Scala 3, you may need to create the state object type in a separate file (or you may get cyclical-dependency compile-time errors).

val dc = deferWith[String, MyState]
import dc._

// The `run` function of ZStream is called `eval`
val out =
  defer {
    val s1 = ZPure.get[MyState].eval.value
    ZPure.set(MyState("bar")).eval
    val s2 = ZPure.get[MyState].eval.value
    (s1, s2)
  }

out.provideState(MyState("foo")).run
// ("foo", "bar")

In order to avoid having to specify the state-type over and over again, several helpers are provided (they are imported from dc._).

val dc = deferWith[String, MyState]
import dc._

// The `run` function of ZStream is called `eval`
val out =
  defer {
    val s1 = getState().value
    setState(MyState("bar"))
    val s2 = getState().value
    (s1, s2)
  }

out.provideState(MyState("foo")).run
// ("foo", "bar")

List and Future

Support for Scala's List and Future objects is provided from zio-direct.

To use zio-direct with List do the following:

import zio.direct.list._

val out =
  defer {
    val a = List(1, 2, 3)
    val b = List("foo", "bar")
    (a, b)
  }

// Yields:
// List((1,"foo"),(1,"bar"),(2,"foo"),(2,"bar"),(3,"foo"),(3,"bar"))

To use zio-direct with Future do the following:

import zio.direct.future._
import scala.concurrent.ExecutionContext.Implicits.global

val out =
  defer {
    Future("a").run match {
      case "a" => Future(1).run
      case "b" => Future(2).run
    }
  }

// Yields: Future(1)

Note that it is not necessary to implement ExecutionContext.Implicits.global. You can implicitly pass in any ExecutionContext you want. It just needs to be in-scope when you call the defer function (i.e. zio.direct.future.defer).

import zio.direct.future._

def out(implicit ctx: ExecutionContext) =
  defer {
    Future("a").run match {
      case "a" => Future(1).run
      case "b" => Future(2).run
    }
  }

out(scala.concurrent.ExecutionContext.global)
// Yields: Future(1)