zio/interop-cats

ZIO instances for cats-effect type classes

ZIO Interop Cats

Installation

libraryDependencies += "dev.zio" %% "zio-interop-cats" % "<latest-version>"

ZIO Cats Effect 3 instances

ZIO integrates with Typelevel libraries by providing an instance of Concurrent, Temporal and Async for Task as required, for instance, by fs2, doobie and http4s.

For convenience, the ZIO library defines an alias as follows:

type Task[A] = ZIO[Any, Throwable, A]

Therefore, we provide Cats Effect instances based on this specific datatype.

Concurrent

In order to get a Concurrent[Task] or Concurrent[RIO[R, *]] (note * is kind-projector notation) we need to import zio.interop.catz._:

import cats.effect._
import zio._
import zio.interop.catz._

def ceConcurrentForTaskExample = {
  val F: cats.effect.Concurrent[Task] = implicitly
  F.racePair(F.unit, F.unit)
}

Temporal

import cats.effect._
import zio._
import zio.interop.catz._

def ceTemporal = {
  val F: cats.effect.Temporal[Task] = implicitly
  F.sleep(1.second) *> F.unit
}

Async

import cats.effect._
import zio._
import zio.interop.catz._

def ceAsync = {
  val F: cats.effect.Async[Task] = implicitly
  F.racePair(F.unit, F.sleep(1.second) *> F.unit)
}

Other typeclasses

There are many other typeclasses and useful conversions that this library provides implementations for:

• See zio/interop/cats.scala file to see all available typeclass implementations for the Cats Effect 3 typeclasses
• See zio/stream/interop/cats.scala for ZStream typeclass implementations
• See zio/stream/interop/FS2StreamSyntax.scala for FS2 <-> ZStream conversions

cats-core

If you only need instances for cats-core typeclasses, not cats-effect import zio.interop.catz.core._:

import zio.interop.catz.core._

Note that this library only has an Optional dependency on cats-effect – if you or your libraries don't depend on it, this library will not add it to the classpath.

Example

The following example shows how to use ZIO with Doobie (a library for JDBC access) and FS2 (a streaming library), which both rely on Cats Effect instances (cats.effect.Async and cats.effect.Temporal):

import zio.{durationInt as _, *}
import zio.interop.catz.*
import doobie.*
import doobie.implicits.*
import scala.concurrent.duration.*

object Example extends ZIOAppDefault:
  val run = {
    val xa: Transactor[Task] =
      Transactor.fromDriverManager[Task]("org.h2.Driver", "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1", "user", "", None)

    sql"SELECT 42"
      .query[Int]
      .stream
      .transact(xa)
      .delayBy(1.second)
      .evalTap(i => Console.printLine(i))
      .compile
      .drain
      .exitCode
  }

Documentation

Learn more on the ZIO Interop Cats homepage!

Contributing

For the general guidelines, see ZIO contributor's guide.

Code of Conduct

See the Code of Conduct

Support

Come chat with us on .

License

License