Make isEmpty a getter.

samples/ui_lib/observable/observable.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.
 
 #library('observable');
 
 #import('dart:coreimpl');
 
 #source('ChangeEvent.dart');
 #source('EventBatch.dart');
@@ skipping 249 matching lines @@
 
   // Iterable<T>:
   Iterator<T> iterator() => _internal.iterator();
 
   // Collection<T>:
   Collection<T> filter(bool f(T element)) => _internal.filter(f);
   Collection map(f(T element)) => _internal.map(f);
   bool every(bool f(T element)) => _internal.every(f);
   bool some(bool f(T element)) => _internal.some(f);
   void forEach(void f(T element)) { _internal.forEach(f); }
-  bool isEmpty() => length == 0;
+  bool get isEmpty => length == 0;
 }
 
 // TODO(jmesserly): is this too granular? Other similar systems make whole
 // classes observable instead of individual fields. The memory cost of having
 // every field effectively boxed, plus having a listeners list is likely too
 // much. Also, making a value observable necessitates adding ".value" to lots
 // of places, and constructing all fields with the verbose
 // "new ObservableValue<DataType>(myValue)".
 /** A wrapper around a single value whose change can be observed. */
 class ObservableValue<T> extends AbstractObservable {
   ObservableValue(T value, [Observable parent = null])
     : super(parent), _value = value;
 
   T get value => _value;
 
   void set value(T newValue) {
     // Only fire on an actual change.
     // TODO(terry): An object identity test === is needed.  Each DataSource has
     //              its own operator == which does a value compare.  Which
     //              equality check should be done?
     if (newValue !== _value) {
       final oldValue = _value;
       _value = newValue;
       recordPropertyUpdate("value", newValue, oldValue);
     }
   }
 
   T _value;
 }