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