Add example int doc for Iterable.expand

sdk/lib/core/iterable.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.core;
 
 /**
  * A collection of values, or "elements", that can be accessed sequentially.
  *
  * The elements of the iterable are accessed by getting an [Iterator]
@@ skipping 163 matching lines @@
   Iterable<E> where(bool test(E element)) => new WhereIterable<E>(this, test);
 
   /**
    * Expands each element of this [Iterable] into zero or more elements.
    *
    * The resulting Iterable runs through the elements returned
    * by [f] for each element of this, in iteration order.
    *
    * The returned [Iterable] is lazy, and calls [f] for each element
    * of this every time it's iterated.
+   *
+   * Example:
+   *
+   *     var lists = [<int>[1, 2, 3], <int>[3, 4, 5]];
+   *     Set<int> ints = lists.expand((list) => list).toSet();
+   *     print(ints);

[floitsch, 2016/08/05 09:38:40]

I prefer not to write the type arguments and sets:

var pairs = [[1, 2], [3, 4]];
var flattened = pairs.expand((pair) => pair).toList();
print(flattened);  // => [1, 2, 3, 4];

var input = [1, 2, 3];
var duplicated = input.expand((i) => [i, i]).toList();
print(duplicated);  // => [1, 1, 2, 2, 3, 3]

[stanm, 2016/08/05 16:48:31]

Done.

+   *
+   *     > {1, 2, 3, 4, 5}
+   *
    */
   Iterable/*<T>*/ expand/*<T>*/(Iterable/*<T>*/ f(E element)) =>
       new ExpandIterable<E, dynamic/*=T*/>(this, f);
 
   /**
    * Returns true if the collection contains an element equal to [element].
    *
    * This operation will check each element in order for being equal to
    * [element], unless it has a more efficient way to find an element
    * equal to [element].
@@ skipping 444 matching lines @@
  */
 abstract class BidirectionalIterator<E> implements Iterator<E> {
   /**
    * Move back to the previous element.
    *
    * Returns true and updates [current] if successful. Returns false
    * and sets [current] to null if there is no previous element.
    */
   bool movePrevious();
 }