Wrapping classes with pure virtual functions

[gabriel.becedillas at gmail.com]

Chris Lambacher wrote:
> On Thu, Dec 14, 2006 at 01:57:10PM -0800, gabriel.becedillas at gmail.com wrote:
> > Hi,
> > I'm having problems wrapping a hierarchy of classes, actually having
> > problems wrapping the base class. I don't need to use the WrapClass
> > mechanism since I don't want to override classes in Python. My code
> > boils down to:
> >
> > class Base
> > {
> > public:
> > 	virtual ~Base()
> > 	{}
> >
> > 	virtual void f() = 0;
> > };
> >
> > class Derived :
> > 	public Base
> > {
> > public:
> > 	virtual void f()
> > 	{}
> >
> > 	void g()
> > 	{}
> > };
> >
> > int main()
> > {
> > 	boost::python::class_<Base> class_base("Base");
> Why are you trying to make this type visible to python?  It is pure virtual,
> you can never instantiate it.

Because I want to use subclasses of Base polymorphically from Python.
Python will receive an instance of some Base subclass through a another
exported function.

> > 	boost::python::class_<Derived> class_derived("Derived");
> > 	return 0;
> > }
> >
> > The first line inside main (the one exporting Base) is causing the
> > compile time error:
> > error C2259: 'Base' : cannot instantiate abstract class...
> > The probem seems to be that struct value_holder<Base> holds a Base
> > member instance by value, and this is not possible since Base can't be
> > instantiated.
> > I'm using Visual Studio 2005 and boost 1.33.1.
> > Thanks
> > 
> > -- 
> > http://mail.python.org/mailman/listinfo/python-list