------------------------------------------------------------ User_Return_Marshallers: Return a value, have a user data ------------------------------------------------------------
type Handler_Proxy is access function
(Widget : access Widget_Type'Class;
Params : Glib.Values.GValues;
Cb : General_Handler;
User_Data : User_Type) return Return_Type;
type Marshaller is record
Func : General_Handler;
Proxy : Handler_Proxy;
end record;
type Return_Type is (<>);
type User_Type (<>) is private;
type Widget_Type is new Glib.Object.GObject_Record with private;