Re: [C++-sig] Raw member and constructor functions

June 6, 2005

      Thanks a lot for this fast answer ! This looks like the way to go. The 
following code does compile but the result under python is unexpected :

#include <boost/python.hpp>
#include <boost/python/raw_function.hpp>
using namespace boost::python;

namespace {
	class X {
	public:
		object memberraw(const tuple& args, const dict& kw)
		{
			return make_tuple(args, kw);
		}
	};

	object memberrawfwd(tuple raw, dict kw)
	{
		tuple arg = extract<tuple&>(raw.slice(1, _))();
		return extract<X&>(raw[0])().
			memberraw(arg, kw);
	}

};

BOOST_PYTHON_MODULE(PythonTest)
{
	class_<X>("X")
		.def("memberraw", raw_function(memberrawfwd))
		;
}

However the following results when run with Python :
...
...
...
a = X()
a.memberraw()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: No registered converter was able to extract a C++ reference to 
type c
lass boost::python::tuple from this Python object of type tuple
Any further help ? Thanks in advance,

Marc

-----Original Message-----
From: c++-sig-bounces@python.org [mailto:c++-sig-bounces@python.org] On 
Behalf Of David Abrahams
Sent: lundi 6 juin 2005 04:31
To: c++-sig@python.org
Subject: Re: [C++-sig] Raw member and constructor functions

"Studious Apprentice" <apprentice_99@hotmail.com> writes:
...
Hello !
I would like to use raw member functions and a raw constructor. However I 
can only manage to have raw functions to work.
The following code works :
#include <boost/python.hpp>
#include <boost/python/raw_function.hpp>
using namespace boost::python;
tuple raw(tuple args, dict kw)
{
  return make_tuple(args, kw);
}
BOOST_PYTHON_MODULE(PythonTest)
{
  def("raw", raw_function(raw));
}
However this code does not compile with MSVC7.1 and results in "error 
C2064: term does not evaluate to a function taking 2 arguments" :
#include <boost/python.hpp>
#include <boost/python/raw_function.hpp>
using namespace boost::python;
class X {
public:
  object memberraw(tuple args, dict kw)
  {
      return object();
  }
};
BOOST_PYTHON_MODULE(PythonTest)
{
  class_<X>("X")
      .def("memberraw", raw_function(&X::memberraw))
      ;
}
As http://www.boost.org/libs/python/doc/v2/raw_function.html says,

   f(tuple(), dict())

must be well-formed where f is the argument to raw_function.  That's
clearly not the case here.  This might work:

tuple raw(tuple raw, dict kw)
{
    extract<X&>(raw[0])().memberraw(raw.slice(1), kw);
}

BOOST_PYTHON_MODULE(PythonTest)
{
	class_<X>("X")
		.def("memberraw", raw_function(raw))
		;
}

--
Dave Abrahams
Boost Consulting
www.boost-consulting.com

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