Make mappedBy lazy.

samples/newissues/newissues.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.
 
 import 'dart:html';
 import 'dart:json' as jsonlib;
 
 /// Issue wraps JSON structure that describes a bug.
 class Issue {
   final json;
   Issue(this.json);
 
   void addTo(Element div) {
     div.elements.add(new Element.tag("h2")..text = json[r"title"][r"$t"]);
     div.elements.add(new Element.tag("pre")..text = json[r"content"][r"$t"]);
   }
 }
 
 /// Decodes JSON into a list of Issues.
 List<Issue> getIssues(json) {
   var issues = json["feed"]["entry"];
   if (issues == null) return null;
-  return issues.mappedBy((data) => new Issue(data));
+  return issues.mappedBy((data) => new Issue(data)).toList();
 }
 
 /// Iterates over the recieved issues and construct HTML for them.
 void processJson(json) {
   Element div = query("#content");
   List<Issue> list = getIssues(json);
   if (list == null) {
     div.elements.add(new Element.tag("h2")..text = "... no issues found.");
   } else {
     getIssues(json).forEach((Issue i) => i.addTo(div));
@@ skipping 11 matching lines @@
   new HttpRequest.get(url, callback);
   return c.future;
 }
 
 void main() {
   // Requests new issues from the Dart issue database as json.
   const String url = "https://code.google.com/feeds/issues/p/dart/issues/full";
   const String options = "alt=json&can=new";
   requestJson("$url?$options").then(processJson);
 }