Fix some implicit resolution issues in OptionT.

Add a "test" to check the implicit resolution of OptionT instances.
typelevel · Jun 14, 2016 · 1dffb84 · 1dffb84
1 parent c3cae9e
commit 1dffb84
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Showing 2 changed files with 45 additions and 9 deletions.
diff --git a/core/src/main/scala/cats/data/OptionT.scala b/core/src/main/scala/cats/data/OptionT.scala
@@ -163,15 +163,9 @@ private[data] sealed trait OptionTInstances extends OptionTInstances0 {
 }
 
 private[data] sealed trait OptionTInstances0 extends OptionTInstances1 {
-  implicit def catsDataMonadForOptionT[F[_]](implicit F0: Monad[F]): Monad[OptionT[F, ?]] =
-    new OptionTMonad[F] { implicit val F = F0 }
-
   implicit def catsDataMonadErrorForOptionT[F[_], E](implicit F0: MonadError[F, E]): MonadError[OptionT[F, ?], E] =
     new OptionTMonadError[F, E] { implicit val F = F0 }
 
-  implicit def catsDataTraverseForOptionT[F[_]](implicit F0: Traverse[F]): Traverse[OptionT[F, ?]] =
-    new OptionTTraverse[F] { implicit val F = F0 }
-
   implicit def catsDataSemigroupK[F[_]](implicit F0: Monad[F]): SemigroupK[OptionT[F, ?]] =
     new OptionTSemigroupK[F] { implicit val F = F0 }
 
@@ -182,9 +176,9 @@ private[data] sealed trait OptionTInstances0 extends OptionTInstances1 {
     new OptionTPartialOrder[F, A] { implicit val F = F0 }
 }
 
-private[data] sealed trait OptionTInstances1 {
-  implicit def catsDataFunctorForOptionT[F[_]](implicit F0: Functor[F]): Functor[OptionT[F, ?]] =
-    new OptionTFunctor[F] { implicit val F = F0 }
+private[data] sealed trait OptionTInstances1 extends OptionTInstances2 {
+  implicit def catsDataMonadForOptionT[F[_]](implicit F0: Monad[F]): Monad[OptionT[F, ?]] =
+    new OptionTMonad[F] { implicit val F = F0 }
 
   // do NOT change this to val! I know it looks like it should work, and really I agree, but it doesn't (for... reasons)
   implicit def catsDataTransLiftForOptionT: TransLift.Aux[OptionT, Functor] =
@@ -201,6 +195,16 @@ private[data] sealed trait OptionTInstances1 {
     new OptionTEq[F, A] { implicit val F = F0 }
 }
 
+private[data] sealed trait OptionTInstances2 extends OptionTInstances3 {
+  implicit def catsDataTraverseForOptionT[F[_]](implicit F0: Traverse[F]): Traverse[OptionT[F, ?]] =
+    new OptionTTraverse[F] { implicit val F = F0 }
+}
+
+private[data] sealed trait OptionTInstances3 {
+  implicit def catsDataFunctorForOptionT[F[_]](implicit F0: Functor[F]): Functor[OptionT[F, ?]] =
+    new OptionTFunctor[F] { implicit val F = F0 }
+}
+
 private[data] trait OptionTFunctor[F[_]] extends Functor[OptionT[F, ?]] {
   implicit def F: Functor[F]
 

diff --git a/tests/src/test/scala/cats/tests/OptionTTests.scala b/tests/src/test/scala/cats/tests/OptionTTests.scala
@@ -295,4 +295,36 @@ class OptionTTests extends CatsSuite {
     }
   }
 
+
+  /**
+   * Testing that implicit resolution works. If it compiles, the "test" passes.
+   */
+  object ImplicitResolution{
+    Eq[OptionT[List, Int]]
+    PartialOrder[OptionT[List, Int]]
+    Order[OptionT[List, Int]]
+
+    Semigroup[OptionT[List, Int]]
+    Monoid[OptionT[List, Int]]
+
+    SemigroupK[OptionT[List, ?]]
+    MonoidK[OptionT[List, ?]]
+
+    Functor[OptionT[List, ?]]
+    Monad[OptionT[List, ?]]
+    MonadRec[OptionT[List, ?]]
+
+    import scala.util.Try
+    Functor[OptionT[Try, ?]]
+    Monad[OptionT[Try, ?]]
+    MonadError[OptionT[Try, ?], Throwable]
+
+    Foldable[OptionT[List, ?]]
+    Traverse[OptionT[List, ?]]
+
+    implicit val T = ListWrapper.traverse
+    implicit val M = ListWrapper.monad
+    Functor[OptionT[ListWrapper, ?]]
+  }
+
 }