[C++-sig] No automatic upcasting with std::shared_ptr in function calls?

[VáclavŠmilauer]

Hello,

I have a sample hierarchy of polymorphic classes (A from which B inherits).
One of them (A1, B1) is managed with boost::shared_ptr, the other one
(A2, B2) via std::shared_ptr (I defined the get_pointer template for 
std::shared_ptr).

When I call f1(boost::shared_ptr<A1>) with an object B1 from python,
it is correctly upcast to the pointer to its base class and the c++
function is called. When I call f2(std::shared_ptr<A2>) with B2 argument
from python, no upcasting takes place and I get Boost.Python.Argument
error.

The code is here:

foo.cpp:

#include<boost/shared_ptr.hpp>
/// make boost::python understand std::shared_ptr
#include<memory>
namespace boost {
   template<class T> T* get_pointer(std::shared_ptr<T> p){ return p.get(); }
}

// define a hierarchy
struct A1{ virtual ~A1(){} };
struct B1: public A1{ virtual ~B1(){} };
void f1(boost::shared_ptr<A1> ptr){ std::cerr<<"f1()"<<std::endl; }

struct A2{ virtual ~A2(){} };
struct B2: public A2{ virtual ~B2(){} };
void f2(std::shared_ptr<A2> ptr){ std::cerr<<"f2()"<<std::endl; }

#include<boost/python.hpp>
using namespace boost::python;
BOOST_PYTHON_MODULE(foo){
   class_<A1,boost::shared_ptr<A1>>("A1");
   class_<B1,boost::shared_ptr<B1>,bases<A1>>("B1");
   def("f1",f1);
   class_<A2,std::shared_ptr<A2>>("A2");
   class_<B2,std::shared_ptr<B2>,bases<A2>>("B2");
   def("f2",f2);
}

compiling with (under Linux):

  g++ -std=c++0x foo.cpp -o foo.so -fPIC -shared -lboost_python
  `pkg-config python --libs --cflags`

Running

  PYTHONPATH=. python -c "import foo; foo.f1(foo.B1()); foo.f2(foo.B2());"

I obtain:

  f1()
  Traceback (most recent call last):
    File "<string>", line 1, in <module>
  Boost.Python.ArgumentError: Python argument types in
      foo.f2(B2)
  did not match C++ signature:
      f2(std::shared_ptr<A2>)

Where is the problem?

Cheers, Vaclav