Re: [Vala] I found a major bug

[Evan Nemerson <evan coeus-group com>]

On Sat, 2014-12-20 at 00:51 -0200, Flavio Danesse wrote:
> Another thing that does not work as expected is:
>
> this.get_toplevel ()
>
> This should return the main application window, or one Gtk.Window, but
> returns a Gtk.Widget

Because that's what the C function does.  The documentation describes
when the return value will *not* be a Gtk.Window.  See
https://developer.gnome.org/gtk3/stable/GtkWidget.html#gtk-widget-get-toplevel

> 2014-12-20 0:32 GMT-02:00 Flavio Danesse <fdanesse gmail com>:
>
> > I understand, but it is logical that a get back what is asked, things like
> > that are not logical fol:
> >
> > error: invocation of void method not allowed as expression
> > this.get_property("type");

Not sure where you're getting that error from—trying to call
GLib.Object.get_property like that here results in:

        error: 1 missing arguments for `void GLib.Object.get_property
        (string property_name, ref GLib.Value value)'

As for why it returns void instead of GLib.Value, look at the C
function:
https://developer.gnome.org/gobject/stable/gobject-The-Base-Object-Type.html#g-object-get-property

> > In the initial example:
> > this.get_allocation()
> > does not work, though:
> > this.get_allocated_width()
> > if it works.

This is a more interesting example, but again it's a reflection of the C
API:

https://developer.gnome.org/gtk3/stable/GtkWidget.html#gtk-widget-get-allocation
https://developer.gnome.org/gtk3/stable/GtkWidget.html#gtk-widget-get-allocated-width

For this function it would actually be possible to alter the bindings to

        public Gtk.Allocation get_allocation ();

Actually, these days it is generated like that by default, but we have a
line in our metadata file to change it back to avoid breaking backwards
compatibility.

Also, we have to be careful changing out params to return values like
that since in the future the C API may change to include a return value
(which isn't an API break for the C API).  That happened recently in
GtkSourceview and it broke several Vala programs.  See
https://bugzilla.gnome.org/show_bug.cgi?id=738896