Burkhard Doliwa <doliwa@temf.tu-darmstadt.de> writes:

Hi all,

I have a problem wrapping a factory function to python. I have two abstract base classes A,B, with some child classes

A<-A1,A2,A3 B<-B1,B2,B3

every child class is either able to clone itself or to return an instance of the corresponding "parallel class", i.e.

A* A1::cloneA() const yields an A1 B* A1::cloneB() const yields an B1

A* B2::cloneA() const yields an A2 B* B2::cloneB() const yields an B2

and so forth. The factory function

object factoryA(const A&, bool isA) { return isA? object(A.cloneA()) : object(A.cloneB()); }

only returns python objects of the base class types, not the derived classes, i.e.

...

...

...

a1=A1() factory(a1,True) result= A object (NOT an A1 object)

How could I create the correct derived class in such a conditional factory function (like the return_value_policy<manage_new_object>() case)?

You might consider: template <class T> T* owned(T* x) { return x; } object factoryA(const A&, bool isA) { return isA? make_function( &owned<A*>, return_value_policy<manage_new_object>() )(ptr(A.cloneA())) : make_function( &owned<B*>, return_value_policy<manage_new_object>() )(ptr(A.cloneB())) ; } However, a more principled approach would have the cloneX functions return an auto_ptr<X> and then do register_ptr_to_python<auto_ptr<X> >() Then you can leave factoryA as it was. -- Dave Abrahams Boost Consulting www.boost-consulting.com