Example: Separator

public class Application : Gtk.Window {

public Application () {
// Prepare Gtk.Window:
this.title = "My Gtk.Separator";
this.window_position = Gtk.WindowPosition.CENTER;
this.destroy.connect (Gtk.main_quit);
this.set_default_size (350, 70);

// The button:
Gtk.Box box = new Gtk.Box (Gtk.Orientation.HORIZONTAL, 1);
this.add (box);

// Dummy content:
Gtk.Label label1 = new Gtk.Label ("Label 1");
box.pack_start (label1, true, true, 0);

// Separator:
Gtk.Separator separator = new Gtk.Separator (Gtk.Orientation.VERTICAL);
box.pack_start (separator, true, true, 0);

// Dummy content:
Gtk.Label label2 = new Gtk.Label ("Label 2");
box.pack_start (label2, true, true, 0);
}

public static int main (string[] args) {
Gtk.init (ref args);

Application app = new Application ();
app.show_all ();
Gtk.main ();
return 0;
}
}

 valac --pkg gtk+-3.0 Gtk.Separator.vala

See: