add Tuple2K#swap (typelevel#2367)

catostrophe · Sep 15, 2018 · d49ea71 · d49ea71
1 parent 9a59eb6
commit d49ea71
Show file tree

Hide file tree

Showing 2 changed files with 9 additions and 0 deletions.
diff --git a/core/src/main/scala/cats/data/Tuple2K.scala b/core/src/main/scala/cats/data/Tuple2K.scala
@@ -16,6 +16,7 @@ final case class Tuple2K[F[_], G[_], A](first: F[A], second: G[A]) {
   def mapK[H[_]](f: G ~> H): Tuple2K[F, H, A] =
     Tuple2K(first, f(second))
 
+  def swap: Tuple2K[G, F, A] = Tuple2K(second, first)
 }
 
 object Tuple2K extends Tuple2KInstances

diff --git a/tests/src/test/scala/cats/tests/Tuple2KSuite.scala b/tests/src/test/scala/cats/tests/Tuple2KSuite.scala
@@ -114,4 +114,12 @@ class Tuple2KSuite extends CatsSuite {
     }
   }
 
+  test("double swap is identity") {
+    forAll { (l1: Option[String], l2: List[String]) =>
+      val tuple = Tuple2K(l1, l2)
+
+      tuple.swap.swap should === (tuple)
+    }
+  }
+
 }