How to manage resources with Scalaz.ZIO

ResourceManagement.scala

// Add in build.sbt
//
// scalaVersion := "2.12.8"
//
// libraryDependencies ++= Seq(
//  "org.scalaz" %% "scalaz-zio" % "0.18",
//  "org.scalatest" %% "scalatest" % "3.0.0" % "test"
// )

import org.scalatest.{Matchers, WordSpecLike}
import scalaz.zio._

class MyResource(var closed: Boolean) {
  println("1. created")

  def close(): Unit = {
    println("3. closed")
    closed = true
  }

  def doSomething: Boolean = {
    require(!closed)
    true
  }
}

class BadManagementTest extends WordSpecLike with Matchers with DefaultRuntime {

  val myResource: ZManaged[Any, Nothing, MyResource] = ZManaged.make(ZIO.succeed({
    new MyResource(false)
  })){ m => UIO.effectTotal(m.close())}

  "Resource" should {
    "not outlive its scope" in {

      val result = unsafeRun(myResource.use(
        r =>
          for {
            b <- ZIO.succeed(r.doSomething)
          } yield b
      ))
      result shouldBe true
    }
  }

  "Multiple use of a resource" should {
    "fail" in {
      // this test fails because the resource is already closed in the first test above.
      val result = unsafeRun(myResource.use(
        r =>
          for {
            b <- ZIO.succeed(r.doSomething)
          } yield b
      ))
      result shouldBe true
    }
  }
}


class GoodManagementTest extends WordSpecLike with Matchers with DefaultRuntime {

  val myResourceIO: Task[ZManaged[Any, Nothing, MyResource]] = ZIO.effect(ZManaged.make(ZIO.succeed({
    new MyResource(false)
  })){ m => UIO.effectTotal(m.close())})

  "Resource" should {
    "not outlive its scope" in {
      val result = unsafeRun(
        for {
          myResource <- myResourceIO
          r <- myResource.use(
            r =>
              for {
                b <- ZIO.succeed(r.doSomething)
              } yield b
          )
        } yield r)
      result shouldBe true
    }
  }

  "Multiple use of a resource" should {
    "not fail" in {
      //
      val result = unsafeRun(
        for {
          myResource <- myResourceIO
          r <- myResource.use(
            r =>
              for {
                b <- ZIO.succeed(r.doSomething)
              } yield b
          )
        } yield r)
      result shouldBe true
    }
  }
}