The GtkBin widget is a container with just one child. It is not very useful itself, but it is useful for deriving subclasses, since it provides common code needed for handling a single child widget.
Sets our main struct and passes it to the parent class.
Get the main Gtk struct
Gets the child of the gtk.Bin, or NULL if the bin contains no child widget. The returned widget does not have a reference added, so you do not need to unref it.
the main Gtk struct as a void*
the main Gtk struct