[Boost-users] How can I wrap class functions that return a reference?

From: Patrick Ye (ye.patrick_at_[hidden])
Date: 2007-05-17 05:07:53

Hi guys,

I'm very new to boost.python, so my question might have been already answered.

I'm having a lot of trouble creating interfaces for class member
functions that return a reference to an object.

For example if we have the following class:

class	btQuadWord
{
        protected:
                btScalar	m_x;
                btScalar	m_y;
                btScalar	m_z;
                btScalar	m_unusedW;

        public:
                SIMD_FORCE_INLINE const btScalar& getX() const { return m_x; }
};

and we have the following interface code:

 class_<btQuadWord>("btQuadWord")
        .def("getX", &btQuadWord::getX)
        ;

I would get the following error messages (ignore the line numbers):

/usr/include/boost/python/detail/invoke.hpp: In function 'PyObject*
boost::python::detail::invoke(boost::python::detail::invoke_tag_<false,
true>, const RC&, F&, TC&) [with RC =
boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const
btScalar&>, F = const btScalar& (btQuadWord::*)()const, TC =
boost::python::arg_from_python<btQuadWord&>]':
/usr/include/boost/python/detail/caller.hpp:199:   instantiated from
'PyObject* boost::python::detail::caller_arity<1u>::impl<F, Policies,
Sig>::operator()(PyObject*, PyObject*) [with F = const btScalar&
(btQuadWord::*)()const, Policies =
boost::python::default_call_policies, Sig = boost::mpl::vector2<const
btScalar&, btQuadWord&>]'
/usr/include/boost/python/object/py_function.hpp:38:   instantiated
from 'PyObject*
boost::python::objects::caller_py_function_impl<Caller>::operator()(PyObject*,
PyObject*) [with Caller = boost::python::detail::caller<const
btScalar& (btQuadWord::*)()const,
boost::python::default_call_policies, boost::mpl::vector2<const
btScalar&, btQuadWord&> >]'
interface.cpp:112:   instantiated from here
/usr/include/boost/python/detail/invoke.hpp:88: error: no match for
call to '(const
boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const
btScalar&>) (const float&)'

Now, btScalar here is just a #define for double, I've had similar
problems when the return reference is to a class object.

Is there anyway to get around this problem?

Thanks a lot.

Patrick

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