Merge pull request #538 from etaty/features/tagged-unwrap

unwrap tag (tagged)
milessabin · May 6, 2016 · c332f90 · c332f90
2 parents 19ce7ea + 2f1f5bf
commit c332f90
Show file tree

Hide file tree

Showing 2 changed files with 21 additions and 0 deletions.
diff --git a/core/src/main/scala/shapeless/unwrapped.scala b/core/src/main/scala/shapeless/unwrapped.scala
@@ -17,6 +17,7 @@
 package shapeless
 
 import newtype._
+import shapeless.tag._
 
 trait Unwrapped[W] extends Serializable {
   type U
@@ -60,6 +61,12 @@ trait UnwrappedInstances extends LowPriorityUnwrappedInstances {
     chain: Strict[Unwrapped.Aux[UI, UF]]
   ) = chain.value.asInstanceOf[Unwrapped.Aux[Newtype[UI, Ops], UF]]
 
+  implicit def taggedUnwrapped[UI, T]: Unwrapped.Aux[UI @@ T, UI] =
+    new Unwrapped[UI @@ T] {
+      type U = UI
+      def unwrap(w: UI @@ T) = w.asInstanceOf[UI]
+      def wrap(u: UI) = tag[T](u)
+    }
 }
 
 trait LowPriorityUnwrappedInstances {

diff --git a/core/src/test/scala/shapeless/unwrapped.scala b/core/src/test/scala/shapeless/unwrapped.scala
@@ -109,6 +109,20 @@ class UnwrappedTests {
     test.illTyped("unwrapped: String @@ TestTag")
   }
 
+  @Test
+  def testShapelessTagged: Unit = {
+    import shapeless.tag.@@
+    import syntax.unwrapped._
+
+    type Test = String @@ TestTag
+    val tagged = tag[TestTag]("testing")
+
+    val wrapped = "testing".wrap[Test]
+    val unwrapped = wrapped.unwrap
+    assert((wrapped: String @@ TestTag) == tagged)
+    assert((unwrapped: String) == "testing")
+  }
+
   @Test
   def testAlreadyUnwrapped: Unit = {