source: NonGTP/Boost/boost/python/converter/as_to_python_function.hpp @ 857

Revision 857, 2.0 KB checked in by igarcia, 19 years ago (diff)
Line 
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
9namespace 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.
13template <class T, class ToPython>
14struct 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};
43
44}}} // namespace boost::python::converter
45
46#endif // AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
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