Dart: #observable of getters - dart

Question

I am trying to understand how observable getters work when they use other class instance properties:
When I bind the implicit getter/setter pair 'name' it updates in the input and in the div and everything is synced nicely.
However the explicit getter 'fullname' is not updating in the HTML. Is there a way to make that work (basically the 'fullname' in the element binding should update as well)?? Maybe I am missing a setter, but then again setter does not make sense here...
Very simple example to demonstrate:
test-element.html
<link rel="import" href="../../packages/polymer/polymer.html">
<polymer-element name="test-element">
<template>
<input value="{{ds.name}}">
<div>{{ds.name}}</div>
<div>{{ds.fullname}}</div>
</template>
<script type="application/dart" src="test1.dart"></script>
</polymer-element>
test-element.dart
import 'package:polymer/polymer.dart';
import 'package:popoli/sysmaster-settings.dart';
#CustomTag('test-element')
class TestElement extends PolymerElement {
#observable VerySimpleTest ds;
TestElement.created() : super.created() {
ds = new VerySimpleTest()..name = 'Peter';
}
}
ds.dart
class VerySimpleTest extends Observable {
#observable String name = '';
#observable String get fullname => 'Test: $name';
VerySimpleTest() : super();
}

Answer 1

You need to notify Polymer that a value has changed the getter depends on.
String set name(String val) {
name = notifyPropertyChange(#fullname, name, val);
}
or this should work too
#ComputedProperty('Test: $name') String get fullname => 'Test: $name';
See http://japhr.blogspot.co.at/2014/08/the-polymerdart-computedproperty.html for more details.

Answer 2

Some minor adaptations on Günter’s proposal make it work for me:
class VerySimpleTest extends Observable {
String _name = '';
// #observable // apparently, not even required
String get name => _name;
// #observable // apparently, not even required
String get fullname => 'Test: $name';
set name(String val) {
String oldVal = _name;
_name = notifyPropertyChange(#name, oldVal, val);
_name = notifyPropertyChange(#fullname, oldVal, val);
}
}