From fe64eaf41ab62ef38546e4f0202de2c04175ec43 Mon Sep 17 00:00:00 2001
From: Andrea Fiore <andrea.fiore@composable.io>
Date: Sat, 11 Jun 2016 14:25:47 +0100
Subject: [PATCH] Add size to Foldable

This addresses part of what is proposed in #1091.
---
 core/src/main/scala/cats/Foldable.scala             | 3 +++
 tests/src/test/scala/cats/tests/FoldableTests.scala | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/core/src/main/scala/cats/Foldable.scala b/core/src/main/scala/cats/Foldable.scala
index 54303abdd39..d470a9eca26 100644
--- 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
index 512edaf9e3a..7788e43f6fe 100644
--- 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