// 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/type_traits/is_scalar.hpp> # include <boost/type_traits/add_const.hpp> # include <boost/type_traits/add_reference.hpp> # include <boost/ref.hpp> # include <boost/python/detail/value_arg.hpp> # include <boost/python/detail/copy_ctor_mutates_rhs.hpp> # if BOOST_WORKAROUND(BOOST_MSVC, < 1300) # include <boost/type_traits/is_enum.hpp> # include <boost/mpl/and.hpp> # include <boost/mpl/not.hpp> # else # include <boost/mpl/or.hpp> # endif 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 add_reference<typename 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_< # if BOOST_WORKAROUND(BOOST_MSVC, < 1300) // vc6 chokes on unforwarding enums nested in classes mpl::and_< is_scalar<T> , mpl::not_< is_enum<T> > > # else mpl::or_<python::detail::copy_ctor_mutates_rhs<T>, is_scalar<T> > # endif , T , reference_to_value<T> > { }; # ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION 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> > : add_reference<typename add_const<T>::type> { }; # else // no partial specialization namespace detail { typedef char (&yes_reference_to_value_t)[1]; typedef char (&no_reference_to_value_t)[2]; no_reference_to_value_t is_reference_to_value_test(...); template<typename T> yes_reference_to_value_t is_reference_to_value_test(boost::type< reference_to_value<T> >); template<bool wrapped> struct unforwarder { template <class T> struct apply { typedef typename unwrap_reference<T>::type& type; }; }; template<> struct unforwarder<true> { template <class T> struct apply { typedef typename T::reference type; }; }; template<bool wrapped = false> struct cref_unforwarder { template <class T> struct apply : python::detail::value_arg< typename unwrap_reference<T>::type > { }; }; template<> struct cref_unforwarder<true> { template <class T> struct apply : python::detail::value_arg< typename T::reference > { }; }; template<typename T> struct is_reference_to_value { BOOST_STATIC_CONSTANT( bool, value = ( sizeof(is_reference_to_value_test(boost::type<T>())) == sizeof(yes_reference_to_value_t))); typedef mpl::bool_<value> type; }; } template <typename T> struct unforward : public detail::unforwarder< detail::is_reference_to_value<T>::value >::template apply<T> {}; template <typename T> struct unforward_cref : public detail::cref_unforwarder< detail::is_reference_to_value<T>::value >::template apply<T> {}; # endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION 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