Backport typelevel#574: Add Resource.liftK

rossabaker · Jul 30, 2019 · 5255e10 · 5255e10
1 parent d4427b4
commit 5255e10
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diff --git a/core/shared/src/main/scala/cats/effect/Resource.scala b/core/shared/src/main/scala/cats/effect/Resource.scala
@@ -325,6 +325,12 @@ object Resource extends ResourceInstances with ResourcePlatform {
   def liftF[F[_], A](fa: F[A])(implicit F: Applicative[F]): Resource[F, A] =
     Resource.suspend(fa.map(a => Resource.pure(a)))
 
+  /**
+   * Lifts an applicative into a resource as a `FunctionK`.  The resource has a no-op release.
+   */
+  def liftK[F[_]](implicit F: Applicative[F]): F ~> Resource[F, ?] =
+    λ[F ~> Resource[F, ?]](Resource.liftF(_))
+
   /**
     * Creates a [[Resource]] by wrapping a Java
     * [[https://docs.oracle.com/javase/8/docs/api/java/lang/AutoCloseable.html AutoCloseable]].

diff --git a/laws/shared/src/test/scala/cats/effect/ResourceTests.scala b/laws/shared/src/test/scala/cats/effect/ResourceTests.scala
@@ -115,6 +115,12 @@ class ResourceTests extends BaseTestsSuite {
     res.value shouldBe Some(Success(ExitCase.Canceled))
   }
 
+  testAsync("liftF(fa) <-> liftK.apply(fa)") { implicit ec =>
+    check { (fa: IO[String], f: String => IO[Int]) =>
+      Resource.liftF(fa).use(f) <-> Resource.liftK[IO].apply(fa).use(f)
+    }
+  }
+
   testAsync("evalMap") { implicit ec =>
     check { (f: Int => IO[Int]) =>
       Resource.liftF(IO(0)).evalMap(f).use(IO.pure) <-> f(0)