Use iterator, moveNext(), current.

utils/pub/utils.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Generic utility functions. Stuff that should possibly be in core.
  */
 library utils;
 
 import 'dart:async';
@@ skipping 56 matching lines @@
     }
   }
   helper(nested);
   return result;
 }
 
 /**
  * Asserts that [iter] contains only one element, and returns it.
  */
 only(Iterable iter) {
-  var iterator = iter.iterator();
-  assert(iterator.hasNext);
-  var obj = iterator.next();
-  assert(!iterator.hasNext);
+  var iterator = iter.iterator;
+  var currentIsValid = iterator.moveNext();
+  assert(currentIsValid);
+  var obj = iterator.current;
+  assert(!iterator.moveNext());
   return obj;
 }
 
 /**
  * Returns a set containing all elements in [minuend] that are not in
  * [subtrahend].
  */
 Set setMinus(Collection minuend, Collection subtrahend) {
   var minuendSet = new Set.from(minuend);
   minuendSet.removeAll(subtrahend);
@@ skipping 32 matching lines @@
   CryptoUtils.bytesToHex(new SHA1().update(source.charCodes).digest());
 
 /**
  * Returns a [Future] that completes in [milliSeconds].
  */
 Future sleep(int milliSeconds) {
   var completer = new Completer();
   new Timer(milliSeconds, completer.complete);
   return completer.future;
 }