Gtk::ToolButton constructor

[Timofey Misarenkov <rgo interzet ru>]

Hi.

I'm writing now some program using gtkmm and for now I spent two hours
to find explanation for:

 Gdk-CRITICAL **: _gdk_drawable_ref_cairo_surface: assertion
`GDK_IS_DRAWABLE (drawable)' failed

I'm pretty sure I know now what the trouble. I'm using constructor

ToolButton::ToolButton(Widget& icon_widget, const Glib::ustring&
label=Glib::ustring())

and according to constructor signature I'm passing to it reference to
some subclass of Gtk::Widget. But seems that ToolButton wants to see
not just some subclass of _Gtk::Widget_, but more concrete subclass of
Gtk::Misc.

So there is a question: why this constructor of ToolButton asks for
Gtk::Widget while waiting for Gtk::Misc? Why this constructor doesn't
throw an error when receiving Gtk::DrawingArea, that is not subclass of
Gtk::Misc?

May be i'm wrong with it, but seems it would be better to change this
constructor to something like:

ToolButton::ToolButton(Misc& icon_widget, const Glib::ustring&
label=Glib::ustring())

So, the real question is: am I wrong with it?

Thank you.
-- 
Timofey Misarenkov <rgo interzet ru>