Add size to Foldable

This addresses part of what is proposed in #1091.
typelevel · Jun 11, 2016 · fe64eaf · fe64eaf
1 parent 5cf9da3
commit fe64eaf
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diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
@@ -1,6 +1,7 @@
 package cats
 
 import scala.collection.mutable
+import cats.std.long._
 import simulacrum.typeclass
 
 /**
@@ -56,6 +57,8 @@ import simulacrum.typeclass
       }
     }
 
+  def size[A](fa: F[A]): Long = foldMap(fa)(_ => 1)
+
   /**
    * Fold implemented using the given Monoid[A] instance.
    */

diff --git a/tests/src/test/scala/cats/tests/FoldableTests.scala b/tests/src/test/scala/cats/tests/FoldableTests.scala
@@ -10,6 +10,12 @@ abstract class FoldableCheck[F[_]: Foldable](name: String)(implicit ArbFInt: Arb
 
   def iterator[T](fa: F[T]): Iterator[T]
 
+  test("size") {
+    forAll { (fa: F[Int]) =>
+      fa.size should === (iterator(fa).size.toLong)
+    }
+  }
+
   test("summation") {
     forAll { (fa: F[Int]) =>
       val total = iterator(fa).sum