title: custom annotation / Metadata in dart lang
body: <p>Can any one explain me the use of annotations in Dart?</p>
  
  <p>In the documentations, I found this example:</p>
  
  
  
  <pre class="lang-dart prettyprint-override"><code>library todo;
  
  class todo {
    final String who;
    final String what;
  
    const todo(this.who, this.what);
  }
  </code></pre>
  
  <p>followed by </p>
  
  <pre class="lang-dart prettyprint-override"><code>import 'todo.dart';
  
  @todo('seth', 'make this do something')
  void doSomething() {
   print('do something');
  }
  </code></pre>
  
  <p>so, what shall I write in the main() to get the doSomething() function executed?</p>
  
  <p>thanks</p>