ceph/src/boost/libs/python/include/boost/python/converter/as_to_python_function.hpp

   1 // Copyright David Abrahams 2002.
   2 // Distributed under the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5 #ifndef AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
   6 # define AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
   7 # include <boost/python/converter/to_python_function_type.hpp>
   8
   9 namespace boost { namespace python { namespace converter {
  10
  11 // Given a typesafe to_python conversion function, produces a
  12 // to_python_function_t which can be registered in the usual way.
  13 template <class T, class ToPython>
  14 struct as_to_python_function
  15 {
  16     // Assertion functions used to prevent wrapping of converters
  17     // which take non-const reference parameters. The T* argument in
  18     // the first overload ensures it isn't used in case T is a
  19     // reference.
  20     template <class U>
  21     static void convert_function_must_take_value_or_const_reference(U(*)(T), int, T* = 0) {}
  22     template <class U>
  23     static void convert_function_must_take_value_or_const_reference(U(*)(T const&), long ...) {}
  24
  25     static PyObject* convert(void const* x)
  26     {
  27         convert_function_must_take_value_or_const_reference(&ToPython::convert, 1L);
  28
  29         // Yes, the const_cast below opens a hole in const-correctness,
  30         // but it's needed to convert auto_ptr<U> to python.
  31         //
  32         // How big a hole is it?  It allows ToPython::convert() to be
  33         // a function which modifies its argument. The upshot is that
  34         // client converters applied to const objects may invoke
  35         // undefined behavior. The damage, however, is limited by the
  36         // use of the assertion function. Thus, the only way this can
  37         // modify its argument is if T is an auto_ptr-like type. There
  38         // is still a const-correctness hole w.r.t. auto_ptr<U> const,
  39         // but c'est la vie.
  40         return ToPython::convert(*const_cast<T*>(static_cast<T const*>(x)));
  41     }
  42 #ifndef BOOST_PYTHON_NO_PY_SIGNATURES
  43     static PyTypeObject const * get_pytype() { return ToPython::get_pytype(); }
  44 #endif
  45 };
  46
  47 }}} // namespace boost::python::converter
  48
  49 #endif // AS_TO_PYTHON_FUNCTION_DWA2002121_HPP