[Vala] Help: Classes cannot have multiple base classes

[Frank Chiu <techium icloud com>]

Greetings fellows,

I installed Vala and GTK on macOS Sierra (via Homebrew) and tried compiling a sample GTK program.  But I got 
tons of errors similar to the one below.

I’m new to Vala and I'd really appreciate any pointers, thanks!

Best,
Frank C



gtk-3.0.gir:650.7-650.47: error: Gtk.AboutDialog: Classes cannot have multiple base classes (`Gtk.Dialog' and 
`Atk.Implementor')
      <implements name="Atk.ImplementorIface"/>
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^