Merge pull request #538 from paulp/one-and-implicits

Adjust implicit priorities in OneAnd.
typelevel · Sep 23, 2015 · 9393a2d · 9393a2d
2 parents ca3fb05 + b11f414
commit 9393a2d
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diff --git a/core/src/main/scala/cats/data/OneAnd.scala b/core/src/main/scala/cats/data/OneAnd.scala
@@ -87,7 +87,7 @@ final case class OneAnd[A, F[_]](head: A, tail: F[A]) {
     s"OneAnd(${A.show(head)}, ${FA.show(tail)})"
 }
 
-trait OneAndInstances {
+trait OneAndInstances extends OneAndLowPriority1 {
 
   implicit def oneAndEq[A, F[_]](implicit A: Eq[A], FA: Eq[F[A]]): Eq[OneAnd[A, F]] =
     new Eq[OneAnd[A, F]]{
@@ -97,12 +97,6 @@ trait OneAndInstances {
   implicit def oneAndShow[A, F[_]](implicit A: Show[A], FA: Show[F[A]]): Show[OneAnd[A, F]] =
     Show.show[OneAnd[A, F]](_.show)
 
-  implicit def oneAndFunctor[F[_]](implicit F: Functor[F]): Functor[OneAnd[?, F]] =
-    new Functor[OneAnd[?, F]] {
-      def map[A, B](fa: OneAnd[A, F])(f: A => B): OneAnd[B, F] =
-        OneAnd(f(fa.head), F.map(fa.tail)(f))
-    }
-
   implicit def oneAndSemigroupK[F[_]: MonadCombine]: SemigroupK[OneAnd[?, F]] =
     new SemigroupK[OneAnd[?, F]] {
       def combine[A](a: OneAnd[A, F], b: OneAnd[A, F]): OneAnd[A, F] =
@@ -137,7 +131,7 @@ trait OneAndInstances {
     }
 }
 
-trait OneAndLowPriority {
+trait OneAndLowPriority0 {
   implicit val nelComonad: Comonad[OneAnd[?, List]] =
     new Comonad[OneAnd[?, List]] {
 
@@ -158,4 +152,12 @@ trait OneAndLowPriority {
     }
 }
 
-object OneAnd extends OneAndInstances with OneAndLowPriority
+trait OneAndLowPriority1 extends OneAndLowPriority0 {
+  implicit def oneAndFunctor[F[_]](implicit F: Functor[F]): Functor[OneAnd[?, F]] =
+    new Functor[OneAnd[?, F]] {
+      def map[A, B](fa: OneAnd[A, F])(f: A => B): OneAnd[B, F] =
+        OneAnd(f(fa.head), F.map(fa.tail)(f))
+    }
+}
+
+object OneAnd extends OneAndInstances
diff --git a/tests/src/test/scala/cats/tests/OneAndTests.scala b/tests/src/test/scala/cats/tests/OneAndTests.scala
@@ -33,6 +33,13 @@ class OneAndTests extends CatsSuite {
     checkAll("Foldable[OneAnd[A, ListWrapper]]", SerializableTests.serializable(Foldable[OneAnd[?, ListWrapper]]))
   }
 
+  {
+    // Test functor and subclasses don't have implicit conflicts
+    implicitly[Functor[NonEmptyList]]
+    implicitly[Monad[NonEmptyList]]
+    implicitly[Comonad[NonEmptyList]]
+  }
+
   checkAll("NonEmptyList[Int]", MonadTests[NonEmptyList].monad[Int, Int, Int])
   checkAll("Monad[NonEmptyList[A]]", SerializableTests.serializable(Monad[NonEmptyList]))