Add tapEach

Author: NthPortal

compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala

@@ -233,6 +233,7 @@ class IteratorExtensionMethods[A](private val self: c.Iterator[A]) extends AnyVa
     self.sameElements(that.iterator)
   }
   def concat[B >: A](that: c.TraversableOnce[B]): c.TraversableOnce[B] = self ++ that
+  def tapEach[U](f: A => U): c.Iterator[A] = self.map(a => { f(a); a })
 }
 
 class TraversableOnceExtensionMethods[A](private val self: c.TraversableOnce[A]) extends AnyVal {
@@ -245,6 +246,8 @@ class TraversableExtensionMethods[A](private val self: c.Traversable[A]) extends
 
 class TraversableLikeExtensionMethods[A, Repr](private val self: c.GenTraversableLike[A, Repr])
     extends AnyVal {
+  def tapEach[U](f: A => U)(implicit bf: CanBuildFrom[Repr, A, Repr]): Repr =
+    self.map(a => { f(a); a })
 
   def groupMap[K, B, That](key: A => K)(f: A => B)(
       implicit bf: CanBuildFrom[Repr, B, That]): Map[K, That] = {

compat/src/test/scala/test/scala/collection/CollectionTest.scala

@@ -95,4 +95,19 @@ class CollectionTest {
       .groupMapReduce(_.length)(_ => 1)(_ + _)
     assertEquals(Map(3 -> 3, 4 -> 1), res)
   }
+
+  @Test
+  def tapEach(): Unit = {
+    var count = 0
+    val it = Iterator(1, 2, 3).tapEach(count += _)
+    assertEquals(0, count)
+    it.foreach(_ => ())
+    assertEquals(6, count)
+    List(1, 2, 3).tapEach(count += _)
+    assertEquals(12, count)
+    val stream = Stream(1, 2, 3).tapEach(count += _)
+    assertEquals(13, count)
+    stream.force
+    assertEquals(18, count)
+  }
 }