[C++-sig] Possible bug for return_internal_reference with shared_ptr

[Dr. Michael Knecht]

Hallo,

i am using internal reference with shared pointers to handle borrowed
references. Here the code:

begin cpp--------------------
#include <boost/shared_ptr.hpp>
#include <boost/python.hpp>

using namespace boost;
using namespace python;

class B {
public:
    B() : _a(0) {}
    void set(const int & a) { _a = a; }
    const int & get() const { return _a; }
private:
    int _a;
};

typedef shared_ptr<B> ptr_type;

class A {
public:
    A() : _a(new B()) {}
    void set(const ptr_type & a) { _a = a; }
    const ptr_type & get1() const { return _a; }
    const ptr_type & get2() const { return _a; }
private:
    ptr_type _a;
};

BOOST_PYTHON_MODULE(ptr_test)
{
    class_<A, shared_ptr<A> >("A")
        .def("set", &A::set)
        .def("get1", &A::get1,
return_value_policy<copy_const_reference>())
        .def("get2", &A::get2,  return_internal_reference<>())
    ;
    class_<B, shared_ptr<B> >("B")
        .def("set", &B::set)
        .def("get", &B::get,
return_value_policy<copy_const_reference>())
    ;   
}
end cpp ---------------------

begin python ---------
from ptr_test import *

a = A()

b1 = a.get1()
print b1.get()

b2 = a.get2()
print b2.get()
end python -------------------- 

If I execute the python script I get the following error message:

TypeError: No Python class registered for C++ class boost::shared_ptr<B>

begin out --------------------
0
Traceback (most recent call last):
  File "test.py", line 8, in ?
    b2 = a.get2()
TypeError: No Python class registered for C++ class boost::shared_ptr<B>
end out -----------------------

So return_value_policy<copy_const_reference> is working and
return_internal_reference<> not!

Any ideas why boost/python can not handle this? I think to handle
internal references is importend for containers and iterators.