text: // Copyright David Abrahams 2002.
  // Distributed under the Boost Software License, Version 1.0. (See
  // accompanying file LICENSE_1_0.txt or copy at
  // http://www.boost.org/LICENSE_1_0.txt)
  #ifndef AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
  # define AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
  # include <boost/python/converter/to_python_function_type.hpp>
  
  namespace boost { namespace python { namespace converter { 
  
  // Given a typesafe to_python conversion function, produces a
  // to_python_function_t which can be registered in the usual way.
  template <class T, class ToPython>
  struct as_to_python_function
  {
      // Assertion functions used to prevent wrapping of converters
      // which take non-const reference parameters. The T* argument in
      // the first overload ensures it isn't used in case T is a
      // reference.
      template <class U>
      static void convert_function_must_take_value_or_const_reference(U(*)(T), int, T* = 0) {}
      template <class U>
      static void convert_function_must_take_value_or_const_reference(U(*)(T const&), long ...) {}
          
      static PyObject* convert(void const* x)
      {
          convert_function_must_take_value_or_const_reference(&ToPython::convert, 1L);
          
          // Yes, the const_cast below opens a hole in const-correctness,
          // but it's needed to convert auto_ptr<U> to python.
          //
          // How big a hole is it?  It allows ToPython::convert() to be
          // a function which modifies its argument. The upshot is that
          // client converters applied to const objects may invoke
          // undefined behavior. The damage, however, is limited by the
          // use of the assertion function. Thus, the only way this can
          // modify its argument is if T is an auto_ptr-like type. There
          // is still a const-correctness hole w.r.t. auto_ptr<U> const,
          // but c'est la vie.
          return ToPython::convert(*const_cast<T*>(static_cast<T const*>(x)));
      }
  #ifndef BOOST_PYTHON_NO_PY_SIGNATURES
      static PyTypeObject const * get_pytype() { return ToPython::get_pytype(); }
  #endif
  };
  
  }}} // namespace boost::python::converter
  
  #endif // AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
  