Update iterators example

Author: odersky

tests/pos-custom-args/captures/iterators.scala

@@ -1,18 +1,22 @@
 package cctest
 
 abstract class Iterator[T]:
-  thisIterator =>
+  thisIterator: ({*} Iterator[T]) =>
 
   def hasNext: Boolean
   def next: T
-  def map(f: {*} T => T): {f} Iterator[T] = new Iterator:
+  def map(f: {*} T => T): {f, this} Iterator[T] = new Iterator:
     def hasNext = thisIterator.hasNext
     def next = f(thisIterator.next)
 end Iterator
 
 class C
 type Cap = {*} C
 
+def map[T, U](it: {*} Iterator[T], f: {*} T => U): {it, f} Iterator[U] = new Iterator:
+  def hasNext = it.hasNext
+  def next = f(it.next)
+
 def test(c: Cap, d: Cap, e: Cap) =
   val it = new Iterator[Int]:
     private var ctr = 0
@@ -21,3 +25,4 @@ def test(c: Cap, d: Cap, e: Cap) =
 
   def f(x: Int): Int = if c == d then x else 10
   val it2 = it.map(f)
+  val it3 = map(it, f)