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> convert_function_must_take_value_or_const_referenceboost::python::converter::as_to_python_function21 static void convert_function_must_take_value_or_const_reference(U(*)(T), int, T* = 0) {} 22 template <class U> convert_function_must_take_value_or_const_referenceboost::python::converter::as_to_python_function23 static void convert_function_must_take_value_or_const_reference(U(*)(T const&), long ...) {} 24 convertboost::python::converter::as_to_python_function25 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 }; 43 44 }}} // namespace boost::python::converter 45 46 #endif // AS_TO_PYTHON_FUNCTION_DWA2002121_HPP 47