This library provides instances required by Cats Effect.
ZIO integrates with Typelevel libraries by providing an instance of ConcurrentEffect
for IO
as required, for instance, by fs2
, doobie
and http4s
. Actually, I lied a little bit, it is not possible to implement ConcurrentEffect
for any error type since ConcurrentEffect
extends MonadError
of Throwable
.
For convenience we have defined an alias as follow:
type Task[A] = IO[Throwable, A]
Therefore, we provide an instance of ConcurrentEffect[Task]
.
In order to get a ConcurrentEffect[Task]
or ConcurrentEffect[RIO[R, *]]
we need an implicit Runtime[R]
in scope. The easiest way to get it is using ZIO.runtime
:
import cats.effect._
import zio._
import zio.interop.catz._
def getCE = {
ZIO.runtime.map { implicit r: Runtime[Any] =>
val F: ConcurrentEffect[Task] = implicitly
}
}
Task.concurrentEffectWith
method can automate this pattern:
import cats.effect._
import zio._
import zio.interop.catz._
def fork = {
Task.concurrentEffectWith { implicit CE =>
CE.start(Task(println("Started task")))
}
}
In order to get a cats.effect.Timer[Task]
instance we need an extra import:
import zio.interop.catz.implicits._
The reason it is not provided by the default "interop" import is that it makes testing programs that require timing capabilities hard so an extra import wherever needed makes reasoning about it much easier.
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.
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:
import doobie.imports._
import fs2.Stream
import zio.Task
import zio.interop.catz._
val xa: Transactor[Task] = Transactor.fromDriverManager[Task](...)
def loadUsers: Stream[Task, User] =
sql"""SELECT * FROM users""".query[User].stream.transact(xa)
val allUsers: List[User] = unsafeRun(loadUsers.compile.toList)