96 lines
2.3 KiB
C++
96 lines
2.3 KiB
C++
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// Copyright David Abrahams 2001.
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef FORWARD_DWA20011215_HPP
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# define FORWARD_DWA20011215_HPP
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# include <boost/mpl/if.hpp>
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# include <boost/type_traits/is_scalar.hpp>
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# include <boost/type_traits/add_const.hpp>
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# include <boost/type_traits/add_reference.hpp>
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# include <boost/ref.hpp>
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# include <boost/python/detail/value_arg.hpp>
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# include <boost/python/detail/copy_ctor_mutates_rhs.hpp>
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# include <boost/mpl/or.hpp>
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namespace boost { namespace python { namespace objects {
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// Very much like boost::reference_wrapper<T>, except that in this
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// case T can be a reference already without causing a
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// reference-to-reference error.
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template <class T>
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struct reference_to_value
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{
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typedef typename add_reference<typename add_const<T>::type>::type reference;
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reference_to_value(reference x) : m_value(x) {}
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reference get() const { return m_value; }
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private:
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reference m_value;
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};
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// A little metaprogram which selects the type to pass through an
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// intermediate forwarding function when the destination argument type
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// is T.
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template <class T>
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struct forward
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: mpl::if_<
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mpl::or_<python::detail::copy_ctor_mutates_rhs<T>, is_scalar<T> >
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, T
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, reference_to_value<T>
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>
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{
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};
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template<typename T>
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struct unforward
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{
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typedef typename unwrap_reference<T>::type& type;
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};
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template<typename T>
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struct unforward<reference_to_value<T> >
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{
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typedef T type;
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};
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template <typename T>
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struct unforward_cref
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: python::detail::value_arg<
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typename unwrap_reference<T>::type
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>
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{
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};
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template<typename T>
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struct unforward_cref<reference_to_value<T> >
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: add_reference<typename add_const<T>::type>
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{
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};
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template <class T>
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typename reference_to_value<T>::reference
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do_unforward(reference_to_value<T> const& x, int)
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{
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return x.get();
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}
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template <class T>
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typename reference_wrapper<T>::type&
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do_unforward(reference_wrapper<T> const& x, int)
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{
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return x.get();
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}
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template <class T>
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T const& do_unforward(T const& x, ...)
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{
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return x;
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}
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}}} // namespace boost::python::objects
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#endif // FORWARD_DWA20011215_HPP
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