#2947 Added bifold to Bifoldable typeclass (#3088)

* #2947 Added bifold to Bifoldable typeclass * #2947 Formatted * address Luka's feedback * reformat
typelevel · Nov 5, 2019 · 5ad3c40 · 5ad3c40
1 parent 6d191a5
commit 5ad3c40
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diff --git a/core/src/main/scala/cats/Bifoldable.scala b/core/src/main/scala/cats/Bifoldable.scala
@@ -25,6 +25,11 @@ import simulacrum.typeclass
       val F = self
       val G = ev
     }
+
+  def bifold[A, B](fab: F[A, B])(implicit A: Monoid[A], B: Monoid[B]): (A, B) = {
+    import cats.instances.tuple._
+    bifoldMap(fab)((_, B.empty), (A.empty, _))
+  }
 }
 
 private[cats] trait ComposedBifoldable[F[_, _], G[_, _]] extends Bifoldable[λ[(α, β) => F[G[α, β], G[α, β]]]] {

diff --git a/tests/src/test/scala/cats/tests/BifoldableSuite.scala b/tests/src/test/scala/cats/tests/BifoldableSuite.scala
@@ -10,4 +10,9 @@ class BifoldableSuite extends CatsSuite {
 
   checkAll("Either compose Either", BifoldableTests(eitherComposeEither).bifoldable[Int, Int, Int])
   checkAll("Bifoldable[Either compose Either]", SerializableTests.serializable(eitherComposeEither))
+
+  test("bifold works for 2 monoids") {
+    Bifoldable[Either].bifold(Either.right[Int, String]("something")) should ===((0, "something"))
+    Bifoldable[Either].bifold(Either.left[Int, String](5)) should ===((5, ""))
+  }
 }