#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/return_internal_reference.hpp>

class Bar
{
 public:
   Bar(int x) : x(x) {}
   int get_x() const { return x; }
   void set_x(int x) { this->x = x; }
 private:
   int x;
};

class Foo
{
 public:
   Foo(int x) : b(x) {}

   // Returns an internal reference
   Bar const& get_bar() const { return b; }

 private:
   Bar b;
};

using namespace boost::python;
BOOST_PYTHON_MODULE(internal_refs)
{
   class_<Bar>("Bar", init<int>())
      .def("get_x", &Bar::get_x)
      .def("set_x", &Bar::set_x)
      ;

   class_<Foo>("Foo", init<int>())
      .def("get_bar", &Foo::get_bar
          , return_internal_reference<>())
      ;
}

//>>> from internal_refs import *
//>>> f = Foo(3)
//>>> b1 = f.get_bar()
//>>> b2 = f.get_bar()
//>>> b1.get_x()
//3
//>>> b2.get_x()
//3
//>>> b1.set_x(42)
//>>> b2.get_x()
//42