Clean up some Dart idioms in fn

This CL adds license blocks and cleans up a number of Dart idioms in fn.
Specifically, I've marked several fields as |final| and used Map#putIfAbsent in
some appropriate places.

R=rafaelw@chromium.org

Review URL: https://codereview.chromium.org/973613004

examples/fn/lib/component.dart

+// Copyright 2015 The Chromium Authors. 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 fn;
 
 List<Component> _dirtyComponents = new List<Component>();
@@ -30,7 +34,7 @@ abstract class Component extends Node {
   bool _dirty = true; // components begin dirty because they haven't rendered.
   Node _rendered = null;
   bool _removed = false;
-  int _order;
+  final int _order;
   static int _currentOrder = 0;
   bool _stateful;
   static Component _currentlyRendering;

examples/fn/lib/fn.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
 library fn;
 
 import 'dart:async';
@@ -11,7 +15,7 @@ part 'style.dart';
 
 bool _checkedMode;
 
-bool debugWarnings() {
+bool _debugWarnings() {
   void testFn(double i) {}
 
   if (_checkedMode == null) {

examples/fn/lib/node.dart

+// Copyright 2015 The Chromium Authors. 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 fn;
 
-void parentInsertBefore(sky.ParentNode parent,
+void _parentInsertBefore(sky.ParentNode parent,
                          sky.Node node,
                          sky.Node ref) {
   if (ref != null) {
@@ -41,7 +45,7 @@ class Text extends Node {
   bool _sync(Node old, sky.ParentNode host, sky.Node insertBefore) {
     if (old == null) {
       _root = new sky.Text(data);
-      parentInsertBefore(host, _root, insertBefore);
+      _parentInsertBefore(host, _root, insertBefore);
       return false;
     }
 
@@ -51,7 +55,7 @@ class Text extends Node {
   }
 }
 
-var _emptyList = new List<Node>();
+final List<Node> _emptyList = new List<Node>();
 
 abstract class Element extends Node {
 
@@ -102,7 +106,7 @@ abstract class Element extends Node {
     _className = style == null ? '': style._className;
     _children = children == null ? _emptyList : children;
 
-    if (debugWarnings()) {
+    if (_debugWarnings()) {
       _debugReportDuplicateIds();
     }
   }
@@ -194,7 +198,7 @@ abstract class Element extends Node {
         assert(child._root is sky.Node);
       }
 
-      parentInsertBefore(host, _root, insertBefore);
+      _parentInsertBefore(host, _root, insertBefore);
       return false;
     }
 
@@ -283,7 +287,7 @@ abstract class Element extends Node {
 
       oldNodeIdMap[currentNode._key] = null; // mark it reordered.
       // print("Reparenting ${currentNode._key}");
-      parentInsertBefore(root, oldNode._root, nextSibling);
+      _parentInsertBefore(root, oldNode._root, nextSibling);
       return true;
     }
 
@@ -344,7 +348,7 @@ class Container extends Element {
 
   String get _tagName => 'div';
 
-  static Container _emptyContainer = new Container();
+  static final Container _emptyContainer = new Container();
 
   Element get _emptyElement => _emptyContainer;
 
@@ -389,7 +393,7 @@ class Image extends Element {
 
   String get _tagName => 'img';
 
-  static Image _emptyImage = new Image();
+  static final Image _emptyImage = new Image();
   Element get _emptyElement => _emptyImage;
 
   String src;
@@ -457,7 +461,7 @@ class Anchor extends Element {
 
   String get _tagName => 'a';
 
-  static Anchor _emptyAnchor = new Anchor();
+  static final Anchor _emptyAnchor = new Anchor();
 
   String href;
 

examples/fn/lib/reflect.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
 library reflect;
 
 import 'dart:mirrors';
 import 'dart:collection';
 
-HashMap<ClassMirror, List> _fieldCache = new HashMap<ClassMirror, List>();
+final HashMap<ClassMirror, List> _fieldCache = new HashMap<ClassMirror, List>();
 
 List<Symbol> _getPublicFields(ClassMirror mirror) {
-  var fields = _fieldCache[mirror];
-  if (fields == null) {
-    fields = new List<Symbol>();
-    _fieldCache[mirror] = fields;
+  return _fieldCache.putIfAbsent(mirror, () {
+    List<Symbol> fields = new List<Symbol>();
 
     while (mirror != null) {
       var decls = mirror.declarations;
@@ -25,9 +27,9 @@ List<Symbol> _getPublicFields(ClassMirror mirror) {
 
       mirror = mirror.superclass;
     }
-  }
 
     return fields;
+  });
 }
 
 void copyPublicFields(Object source, Object target) {

examples/fn/lib/style.dart

+// Copyright 2015 The Chromium Authors. 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 fn;
 
 class Style {
   final String _className;
-  static Map<String, Style> _cache = null;
+  static final Map<String, Style> _cache = new HashMap<String, Style>();
 
   static int nextStyleId = 1;
 
   static String nextClassName(String styles) {
     assert(sky.document != null);
-    var className = "style$nextStyleId";
+    String className = "style$nextStyleId";
     nextStyleId++;
 
-    var styleNode = sky.document.createElement('style');
+    sky.Element styleNode = sky.document.createElement('style');
     styleNode.setChild(new sky.Text(".$className { $styles }"));
     sky.document.appendChild(styleNode);
 
@@ -19,17 +23,9 @@ class Style {
   }
 
   factory Style(String styles) {
-    if (_cache == null) {
-      _cache = new HashMap<String, Style>();
-    }
-
-    var style = _cache[styles];
-    if (style == null) {
-      style = new Style._internal(nextClassName(styles));
-      _cache[styles] = style;
-    }
-
-    return style;
+    return _cache.putIfAbsent(styles, () {
+      return new Style._internal(nextClassName(styles));
+    });
   }
 
   Style._internal(this._className);