title: How to extend a class in Dart/Flutter
body: <p>I have class A:</p>
  
  <pre><code>class A{
      String title;
      String content;
      IconData iconData;
      Function onTab;
      A({this.title, this.content, this.iconData, this.onTab});
  }
  </code></pre>
  
  <p>How can i create class B that extends class A with additional variable like following:</p>
  
  <pre><code>class B extends A{
      bool read;
      B({this.read});
  }
  </code></pre>
  
  <p>Tried with this but not working</p>
  
  <pre><code>let o = new B(
            title: "New notification",
            iconData: Icons.notifications,
            content: "Lorem ipsum doro si maet 100",
            read: false,
            onTab: (context) =&gt; {
  
            });
  </code></pre>