optional.h

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/*
 * This file is part of KnowRob, please consult
 * https://github.com/knowrob/knowrob for license details.
 */
 
#ifndef KNOWROB_PY_CONVERTER_OPTIONAL_H
#define KNOWROB_PY_CONVERTER_OPTIONAL_H
 
#include <boost/python.hpp>
#include "optional"
 
namespace knowrob::py {
    template<typename T>
    struct python_optional : private boost::noncopyable {
        struct conversion : public boost::python::converter::expected_from_python_type<T> {
            static PyObject *convert(std::optional<T> const &value) {
                using namespace boost::python;
                return incref((value ? object(*value) : object()).ptr());
            }
        };
 
        static void *convertible(PyObject *obj) {
            using namespace boost::python;
            return obj == Py_None || extract<T>(obj).check() ? obj : NULL;
        }
 
        static void constructor(
                PyObject *obj,
                boost::python::converter::rvalue_from_python_stage1_data *data
        ) {
            using namespace boost::python;
            void *const storage =
                    reinterpret_cast<
                            converter::rvalue_from_python_storage<std::optional<T> > *
                            >(data)->storage.bytes;
            if (obj == Py_None) {
                new(storage) std::optional<T>();
            } else {
                new(storage) std::optional<T>(extract<T>(obj));
            }
            data->convertible = storage;
        }
 
        explicit python_optional() {
            using namespace boost::python;
            if (!extract<std::optional<T> >(object()).check()) {
                to_python_converter<std::optional<T>, conversion, true>();
                converter::registry::push_back(
                        &convertible,
                        &constructor,
                        type_id<std::optional<T> >(),
                        &conversion::get_pytype
                );
            }
        }
    };
}
 
#endif //KNOWROB_PY_CONVERTER_OPTIONAL_H