[857] | 1 | // Copyright David Abrahams 2002.
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| 2 | // Distributed under the Boost Software License, Version 1.0. (See
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| 3 | // accompanying file LICENSE_1_0.txt or copy at
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| 4 | // http://www.boost.org/LICENSE_1_0.txt)
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| 5 | #ifndef AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
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| 6 | # define AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
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| 7 | # include <boost/python/converter/to_python_function_type.hpp>
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| 8 |
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| 9 | namespace boost { namespace python { namespace converter {
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| 10 |
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| 11 | // Given a typesafe to_python conversion function, produces a
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| 12 | // to_python_function_t which can be registered in the usual way.
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| 13 | template <class T, class ToPython>
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| 14 | struct as_to_python_function
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| 15 | {
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| 16 | // Assertion functions used to prevent wrapping of converters
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| 17 | // which take non-const reference parameters. The T* argument in
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| 18 | // the first overload ensures it isn't used in case T is a
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| 19 | // reference.
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| 20 | template <class U>
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| 21 | static void convert_function_must_take_value_or_const_reference(U(*)(T), int, T* = 0) {}
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| 22 | template <class U>
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| 23 | static void convert_function_must_take_value_or_const_reference(U(*)(T const&), long ...) {}
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| 24 |
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| 25 | static PyObject* convert(void const* x)
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| 26 | {
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| 27 | convert_function_must_take_value_or_const_reference(&ToPython::convert, 1L);
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| 28 |
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| 29 | // Yes, the const_cast below opens a hole in const-correctness,
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| 30 | // but it's needed to convert auto_ptr<U> to python.
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| 31 | //
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| 32 | // How big a hole is it? It allows ToPython::convert() to be
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| 33 | // a function which modifies its argument. The upshot is that
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| 34 | // client converters applied to const objects may invoke
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| 35 | // undefined behavior. The damage, however, is limited by the
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| 36 | // use of the assertion function. Thus, the only way this can
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| 37 | // modify its argument is if T is an auto_ptr-like type. There
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| 38 | // is still a const-correctness hole w.r.t. auto_ptr<U> const,
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| 39 | // but c'est la vie.
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| 40 | return ToPython::convert(*const_cast<T*>(static_cast<T const*>(x)));
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| 41 | }
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| 42 | };
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| 43 |
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| 44 | }}} // namespace boost::python::converter
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| 45 |
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| 46 | #endif // AS_TO_PYTHON_FUNCTION_DWA2002121_HPP
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