Overriding methods in vala - gtk3

Question

As an experiemnt, I'm extending the Gtk.HeaderBar class in vala like this, in order to have a Button instead of the title / subtitle Labels:
using Gtk;
public class WebBrowserHeaderBar : HeaderBar {
private Button title_widget;
public WebBrowserHeaderBar(){
this.show_close_button = true;
title_widget = new Button.with_label("title");
this.set_custom_title(title_widget);
}
public void set_title(string title){
title_widget.label = title;
}
}
and then I'm using it like this:
public class MainWindow: Window {
private WebBrowserHeaderBar header;
public MainWindow() {
//this.title = MyWeb.APP_TITLE;
this.window_position = WindowPosition.CENTER;
this.destroy.connect (Gtk.main_quit);
set_default_size (300, 200);
header = new WebBrowserHeaderBar();
header.set_title (MyWeb.APP_TITLE);
this.set_titlebar(header);
}
}
That works, however I get the following warning while compiling:
WebBrowserHeaderBar.vala:15.2-15.22: warning: WebBrowserHeaderBar.set_title hides inherited method `Gtk.HeaderBar.set_title'. Use the `new' keyword if hiding was intentional
public void set_title(string title){
^^^^^^^^^^^^^^^^^^^^^
Compilation succeeded - 1 warning(s)
If I change my method like this public override void set_title(string title){, it won't compile:
WebBrowserHeaderBar.vala:15.2-15.31: error: WebBrowserHeaderBar.set_title: no suitable method found to override
public override void set_title(string title){
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Compilation failed: 1 error(s), 0 warning(s)
Why am I getting this? How can I get rid of the warning and/or successfully override the set_title method?

Answer 1

You can only override methods that are abstract or virtual. Other methods cannot be overridden, but you can hide them using the new keyword:
public new void set_title (string title) {
title_widget.label = title;
}
If the reference is of type WebBrowserHeaderBar, or one of its children, this method will be called. If the reference is of type HeaderBar or one of its superclasses, then the original set_title will be used.
This is a somewhat there-be-dragons feature.