title: Is it possible to extend base Gtk widget without using GObject style construction?
body: <p>How I did find out from my <a href="https://stackoverflow.com/questions/59854049/how-does-gobject-style-construction-work">previous question</a>, <code>GObject</code> style construction is not required for vala class defenition. But much gtk apps use this way when extend base widget. For example, <a href="https://github.com/elementary/appcenter/blob/master/src/MainWindow.vala#L56" rel="nofollow noreferrer">elementary os app center</a> does it for <code>Gtk.ApplicationWindow</code> class.</p>
  
  <p>So my question is, can I extend any base <code>Gtk</code> class without using <code>Object()</code> construction?</p>