Make Show contravariant

typelevel · May 5, 2017 · e96bb75 · e96bb75
1 parent 4e381d2
commit e96bb75
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Showing 6 changed files with 16 additions and 33 deletions.
diff --git a/core/src/main/scala/cats/Show.scala b/core/src/main/scala/cats/Show.scala
@@ -10,7 +10,7 @@ import cats.functor.Contravariant
  * made a toString method, a Show instance will only exist if someone
  * explicitly provided one.
  */
-@typeclass trait Show[T] {
+@typeclass trait Show[-T] {
   def show(f: T): String
 }
 

diff --git a/core/src/main/scala/cats/instances/all.scala b/core/src/main/scala/cats/instances/all.scala
@@ -14,7 +14,6 @@ trait AllInstances
   with    MapInstances
   with    BigIntInstances
   with    BigDecimalInstances
-  with    BitSetInstances
   with    FutureInstances
   with    TryInstances
   with    TupleInstances

diff --git a/core/src/main/scala/cats/instances/bitSet.scala b/core/src/main/scala/cats/instances/bitSet.scala
diff --git a/core/src/main/scala/cats/instances/package.scala b/core/src/main/scala/cats/instances/package.scala
@@ -9,7 +9,6 @@ package object instances {
   object list       extends ListInstances
   object option     extends OptionInstances
   object set        extends SetInstances
-  object bitSet     extends BitSetInstances
   object stream     extends StreamInstances
   object vector     extends VectorInstances
   object map        extends MapInstances

diff --git a/tests/src/test/scala/cats/tests/BitSetTests.scala b/tests/src/test/scala/cats/tests/BitSetTests.scala
diff --git a/tests/src/test/scala/cats/tests/ShowTests.scala b/tests/src/test/scala/cats/tests/ShowTests.scala
@@ -11,7 +11,6 @@ class ShowTests extends CatsSuite {
   checkAll("Contravariant[Show]", SerializableTests.serializable(Contravariant[Show]))
 
   test("show string interpolator") {
-    import cats.syntax.show._
 
     case class Cat(name: String)
     object Cat {
@@ -31,4 +30,19 @@ class ShowTests extends CatsSuite {
 
     assertResult("Good morning, Whiskers!")(show"Good $tod, ${List(cat).head}!")
   }
+
+  test("show string interpolator and contravariance") {
+    trait Animal {
+      val name: String
+    }
+    object Animal {
+      implicit val showAnimal: Show[Animal] =
+        Show.show(_.name)
+    }
+    class Cat(override val name: String, val breed: String) extends Animal
+
+    val cat = new Cat("Whiskers", "Calico")
+
+    assertResult("Good morning, Whiskers!")(show"Good morning, $cat!")
+  }
 }