ResourceT

ResourceT can be used as a monad transformer for scala.Function0

import scala.Function0
import cats.instances.function._
import com.thoughtworks.zerocost.resourcet._
type RAII[A] = ResourceT[Function0, A]

Given a resource that creates temporary files

trait MyResource extends AutoCloseable {
  def inUse(): Unit
}
val myResourceStub0 = stub[MyResource]
val myResourceStub1 = stub[MyResource]
val myResourceFactoryMock = mockFunction[MyResource]
myResourceFactoryMock.expects().returns(myResourceStub0)
myResourceFactoryMock.expects().returns(myResourceStub1)
val resource: RAII[MyResource] = ResourceT.autoCloseable[Function0, MyResource](myResourceFactoryMock)

when using temporary file created by resouce in a for / yield block, those temporary files should be available.

import cats.syntax.all._
val usingResouce = for {
  tmpFile0 <- resource
  tmpFile1 <- resource
} yield {
  tmpFile0 should be(myResourceStub0)
  tmpFile1 should be(myResourceStub1)
  tmpFile1.inUse()
}

and those files should have been deleted after the for / yield block.

usingResouce.run.apply()
((myResourceStub0.inUse _): () => Unit).verify().never()
((myResourceStub0.close _): () => Unit).verify().once()
((myResourceStub1.inUse _): () => Unit).verify().once()
((myResourceStub1.close _): () => Unit).verify().once()