move safe last impl to TraversableViewLike

also align with lastOption impl in terms of empty/hasElements

Author: Martijn Hoekstra

src/library/scala/collection/TraversableLike.scala

@@ -428,13 +428,10 @@ trait TraversableLike[+A, +Repr] extends Any
     * @throws NoSuchElementException If the $coll is empty.
     */
   def last: A = {
-    var lst: A = null.asInstanceOf[A]
-    var hasElements = false
-    for (x <- this){
-      hasElements = true
+    var lst = head
+    for (x <- this)
       lst = x
-    }
-    if (hasElements) lst else throw new NoSuchElementException("last of empty traversable")
+    lst
   }
 
   /** Optionally selects the last element.

src/library/scala/collection/TraversableViewLike.scala

@@ -112,6 +112,18 @@ trait TraversableViewLike[+A,
 
       None
     }
+
+    override def last: B = {
+      // (Should be) better than allocating a Some for every element.
+      var empty = true
+      var result: B = null.asInstanceOf[B]
+      for (x <- this) {
+        empty = false
+        result = x
+      }
+      if (empty) throw new NoSuchElementException("last of empty traversable") else result
+    }
+
     override def lastOption: Option[B] = {
       // (Should be) better than allocating a Some for every element.
       var empty = true