[C++-sig] why does this produce a dangling reference?

[FLETCHER, Shayne, FM]

Hi All:

Here's what seems to me to be a fairly simple use case that unfortunately
suffers from the "attempt to return dangling reference" problem (using
current CVS snapshot). Can anyone help me understand what I'm doing wrong
and what I can do to overcome the problem?

class period
{};

class rate_impl{
private:
  period m_period;

public:
  virtual ~rate_impl()
  {}
  virtual period const& get_floating_frequency() const
  {
    return m_period;
  }
  virtual void generate_dates() const
  {
    period p = get_floating_frequency(); // ! causes 'dangling reference'
  }
};

struct rate_impl_wrapper : rate_impl{
  PyObject* m_self;

  rate_impl_wrapper(PyObject* self)
    : m_self(self)
  {}
  period const& get_floating_frequency() const
  {
    return boost::python::call_method(m_self
      ,"get_floating_frequency"
      , (boost::type<period const&>*)0);
  }
  period const& default_get_floating_frequency() const
  {
    return rate_impl::get_floating_frequency();
  }
  void generate_dates() const
  {
    boost::python::call_method(m_self
      , "generate_dates"
      , (boost::type<void>*)0);
  }
  void default_generate_dates() const
  {
    rate_impl::generate_dates();
  }
};

BOOST_PYTHON_MODULE(isle)
{
class_<period>("period", init<>())
  ;
class_<rate_impl
       , rate_impl_wrapper
       , boost::noncopyable>("rate_impl", init<>())
       .def("get_floating_frequency"
            , &rate_impl::get_floating_frequency
            , &rate_impl_wrapper::default_get_floating_frequency
            , return_value_policy<copy_const_reference>())
       .def("generate_dates"
         , &rate_impl::generate_dates
         , &rate_impl_wrapper::default_generate_dates)        
   ;
}

Then in Python,

import isle
rate = isle.rate_impl()
rate.generate_dates()

The end result is:

Traceback (most recent call last):
  File "test_rate.py", line 3, in ?
    rate.generate_dates()
ReferenceError: Attempt to return dangling reference to object of type:
class period

- Shayne.




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