Fix ambiguity when the base type has both Semigroup and CommutativeSe…

…migroup
typelevel · Jun 10, 2020 · 27741bd · 27741bd
1 parent 1d93305
commit 27741bd
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Showing 2 changed files with 15 additions and 5 deletions.
diff --git a/kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala b/kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala
@@ -147,6 +147,15 @@ class Tests extends TestsConfig with AnyFunSuiteLike with FunSuiteDiscipline wit
 
   import KernelCheck._
 
+  test("The instances in scope are not ambiguous") {
+    implicitly[Monoid[Option[String]]]
+    implicitly[Semigroup[Option[String]]]
+    implicitly[Monoid[Option[Int]]]
+    implicitly[Semigroup[Option[Int]]]
+    implicitly[CommutativeSemigroup[Option[Int]]]
+    implicitly[CommutativeMonoid[Option[Int]]]
+  }
+
   {
     // needed for Cogen[Map[...]]
     implicit val ohe: Ordering[HasEq[Int]] = Ordering.by[HasEq[Int], Int](_.a)

diff --git a/kernel/src/main/scala/cats/kernel/Semigroup.scala b/kernel/src/main/scala/cats/kernel/Semigroup.scala
@@ -179,8 +179,6 @@ object Semigroup
 
   implicit def catsKernelMonoidForString: Monoid[String] = cats.kernel.instances.string.catsKernelStdMonoidForString
 
-  implicit def catsKernelMonoidForOption[A: Semigroup]: Monoid[Option[A]] =
-    cats.kernel.instances.option.catsKernelStdMonoidForOption[A]
   implicit def catsKernelMonoidForList[A]: Monoid[List[A]] = cats.kernel.instances.list.catsKernelStdMonoidForList[A]
   implicit def catsKernelMonoidForVector[A]: Monoid[Vector[A]] =
     cats.kernel.instances.vector.catsKernelStdMonoidForVector[A]
@@ -230,6 +228,8 @@ private[kernel] trait CommutativeMonoidInstances extends MonoidInstances {
     cats.kernel.instances.function.catsKernelCommutativeMonoidForFunction0[A]
   implicit def catsKernelCommutativeMonoidForFunction1[A, B: CommutativeMonoid]: CommutativeMonoid[A => B] =
     cats.kernel.instances.function.catsKernelCommutativeMonoidForFunction1[A, B]
+  implicit def catsKernelCommutativeMonoidForOption[A: CommutativeSemigroup]: CommutativeMonoid[Option[A]] =
+    cats.kernel.instances.option.catsKernelStdCommutativeMonoidForOption[A]
 }
 
 private[kernel] trait MonoidInstances extends BandInstances {
@@ -243,7 +243,10 @@ private[kernel] trait MonoidInstances extends BandInstances {
     cats.kernel.instances.sortedMap.catsKernelStdMonoidForSortedMap[K, V]
   implicit def catsKernelMonoidForEither[A, B: Monoid]: Monoid[Either[A, B]] =
     cats.kernel.instances.either.catsDataMonoidForEither[A, B]
-  implicit def catsKernelMonoidForTry[A: Monoid]: Monoid[Try[A]] = new TryMonoid[A](Monoid[A])
+  implicit def catsKernelMonoidForTry[A: Monoid]: Monoid[Try[A]] =
+    new TryMonoid[A](Monoid[A])
+  implicit def catsKernelMonoidForOption[A: Semigroup]: Monoid[Option[A]] =
+    cats.kernel.instances.option.catsKernelStdMonoidForOption[A]
 }
 
 private[kernel] trait BandInstances extends CommutativeSemigroupInstances {
@@ -269,8 +272,6 @@ private[kernel] trait SemigroupInstances {
     cats.kernel.instances.either.catsDataSemigroupForEither[A, B]
   implicit def catsKernelSemigroupForTry[A: Semigroup]: Semigroup[Try[A]] =
     new TrySemigroup[A](Semigroup[A])
-  implicit def catsKernelCommutativeMonoidForOption[A: CommutativeSemigroup]: CommutativeMonoid[Option[A]] =
-    cats.kernel.instances.option.catsKernelStdCommutativeMonoidForOption[A]
 }
 
 private class TryMonoid[A](A: Monoid[A]) extends TrySemigroup[A](A) with Monoid[Try[A]] {