[C++-sig] Wrapping a class whose constructor takes a pointer to an abstract class

[Jean-Sébastien Guay]

Hi all,

I've just started trying to use boost.python on a personal project of 
mine, and I decided to start with the hardest part :-)  I'm trying to 
wrap OpenSceneGraph... It's going really well for the most part, and I 
do mean really well. In little time I've got a good number of classes 
working and tested. But I've hit a roadblock.

I've done a lot of searching and have found lots of posts on this list 
dealing with pure virtual methods, but never anything about a method 
taking a pointer to an abstract class as a parameter.

I have to wrap the following structure:

     class osg::Shape : public osg::Object
     {
         // has some pure virtual methods, none of which I need to
         // expose to python at this point
     };

     class osg::Sphere : public osg::Shape
     {
         // fully concrete
     };

     class osg::ShapeDrawable
     {
         ShapeDrawable(osg::Shape*, TessellationHints) { /* ... */ }
     };

So the constructor to ShapeDrawable takes a pointer to the abstract base 
class. My attempt to wrap this (leaving out some details) is:

     // Abstract class, so noncopyable and no_init.
     class_<Shape, bases<Object>, ref_ptr<Shape>,
            boost::noncopyable >("Shape", no_init);

     // Concrete derived class.
     class_<Sphere, bases<Shape>, ref_ptr<Sphere> >("Sphere");

     // Details of this class not important for now.
     class_<TessellationHints, bases<Object>,
            ref_ptr<TessellationHints> >("TessellationHints");

     class_<ShapeDrawable, bases<Drawable>,
            ref_ptr<ShapeDrawable> >("ShapeDrawable")
         .def(init<Shape, TessellationHints>())
     ;

The first three classes wrap correctly, but the fourth fails with a 
compiler error saying it cannot instantiate abstract class Shape. OK, I 
understand that, but what can I do about it?

Thanks in advance for any help,

J-S
-- 
______________________________________________________
Jean-Sebastien Guay    jean-sebastien.guay at cm-labs.com
                                http://www.cm-labs.com/
                         http://whitestar02.webhop.org/