Chris@16: // Copyright David Abrahams 2001.
Chris@16: // Distributed under the Boost Software License, Version 1.0. (See
Chris@16: // accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: #ifndef FORWARD_DWA20011215_HPP
Chris@16: # define FORWARD_DWA20011215_HPP
Chris@16: 
Chris@16: # include <boost/mpl/if.hpp>
Chris@16: # include <boost/type_traits/is_scalar.hpp>
Chris@16: # include <boost/type_traits/add_const.hpp>
Chris@16: # include <boost/type_traits/add_reference.hpp>
Chris@16: # include <boost/ref.hpp>
Chris@16: # include <boost/python/detail/value_arg.hpp>
Chris@16: # include <boost/python/detail/copy_ctor_mutates_rhs.hpp>
Chris@16: # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
Chris@16: #  include <boost/type_traits/is_enum.hpp>
Chris@16: #  include <boost/mpl/and.hpp>
Chris@16: #  include <boost/mpl/not.hpp>
Chris@16: # else
Chris@16: #  include <boost/mpl/or.hpp>
Chris@16: # endif 
Chris@16: 
Chris@16: namespace boost { namespace python { namespace objects { 
Chris@16: 
Chris@16: // Very much like boost::reference_wrapper<T>, except that in this
Chris@16: // case T can be a reference already without causing a
Chris@16: // reference-to-reference error.
Chris@16: template <class T>
Chris@16: struct reference_to_value
Chris@16: {
Chris@16:     typedef typename add_reference<typename add_const<T>::type>::type reference;
Chris@16:     
Chris@16:     reference_to_value(reference x) : m_value(x) {}
Chris@16:     reference get() const { return m_value; }
Chris@16:  private:
Chris@16:     reference m_value;
Chris@16: };
Chris@16: 
Chris@16: // A little metaprogram which selects the type to pass through an
Chris@16: // intermediate forwarding function when the destination argument type
Chris@16: // is T.
Chris@16: template <class T>
Chris@16: struct forward
Chris@16:     : mpl::if_<
Chris@16: # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
Chris@16:           // vc6 chokes on unforwarding enums nested in classes
Chris@16:           mpl::and_<
Chris@16:               is_scalar<T>
Chris@16:             , mpl::not_< 
Chris@16:                   is_enum<T>
Chris@16:               >
Chris@16:           >
Chris@16: # else 
Chris@16:           mpl::or_<python::detail::copy_ctor_mutates_rhs<T>, is_scalar<T> >
Chris@16: # endif 
Chris@16:         , T
Chris@16:         , reference_to_value<T>
Chris@16:       >
Chris@16: {
Chris@16: };
Chris@16: 
Chris@16: # ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
Chris@16: template<typename T>
Chris@16: struct unforward
Chris@16: {
Chris@16:     typedef typename unwrap_reference<T>::type& type;
Chris@16: };
Chris@16: 
Chris@16: template<typename T>
Chris@16: struct unforward<reference_to_value<T> >
Chris@16: {
Chris@16:     typedef T type;
Chris@16: };
Chris@16: 
Chris@16: template <typename T>
Chris@16: struct unforward_cref
Chris@16:   : python::detail::value_arg<
Chris@16:         typename unwrap_reference<T>::type
Chris@16:     >
Chris@16: {
Chris@16: };
Chris@16: 
Chris@16: template<typename T>
Chris@16: struct unforward_cref<reference_to_value<T> >
Chris@16:   : add_reference<typename add_const<T>::type>
Chris@16: {
Chris@16: };
Chris@16: 
Chris@16: # else // no partial specialization
Chris@16: 
Chris@16: namespace detail
Chris@16: {
Chris@16:   typedef char (&yes_reference_to_value_t)[1];
Chris@16:   typedef char (&no_reference_to_value_t)[2];
Chris@16:       
Chris@16:   no_reference_to_value_t is_reference_to_value_test(...);
Chris@16: 
Chris@16:   template<typename T>
Chris@16:   yes_reference_to_value_t is_reference_to_value_test(boost::type< reference_to_value<T> >);
Chris@16: 
Chris@16:   template<bool wrapped>
Chris@16:   struct unforwarder
Chris@16:   {
Chris@16:       template <class T>
Chris@16:       struct apply
Chris@16:       {
Chris@16:           typedef typename unwrap_reference<T>::type& type;
Chris@16:       };
Chris@16:   };
Chris@16: 
Chris@16:   template<>
Chris@16:   struct unforwarder<true>
Chris@16:   {
Chris@16:       template <class T>
Chris@16:       struct apply
Chris@16:       {
Chris@16:           typedef typename T::reference type;
Chris@16:       };
Chris@16:   };
Chris@16: 
Chris@16:   template<bool wrapped = false>
Chris@16:   struct cref_unforwarder
Chris@16:   {
Chris@16:       template <class T>
Chris@16:       struct apply
Chris@16:         : python::detail::value_arg<
Chris@16:               typename unwrap_reference<T>::type
Chris@16:           >
Chris@16:       {          
Chris@16:       };
Chris@16:   };
Chris@16:       
Chris@16:   template<>
Chris@16:   struct cref_unforwarder<true>
Chris@16:   {
Chris@16:       template <class T>
Chris@16:       struct apply
Chris@16:         : python::detail::value_arg<
Chris@16:               typename T::reference
Chris@16:           >
Chris@16:       {
Chris@16:       };
Chris@16:   };
Chris@16: 
Chris@16:   template<typename T>
Chris@16:   struct is_reference_to_value
Chris@16:   {
Chris@16:       BOOST_STATIC_CONSTANT(
Chris@16:           bool, value = (
Chris@16:               sizeof(is_reference_to_value_test(boost::type<T>()))
Chris@16:               == sizeof(yes_reference_to_value_t)));
Chris@16:       typedef mpl::bool_<value> type;
Chris@16:   };
Chris@16: }
Chris@16: 
Chris@16: template <typename T>
Chris@16: struct unforward
Chris@16:     : public detail::unforwarder<
Chris@16:         detail::is_reference_to_value<T>::value
Chris@16:       >::template apply<T>
Chris@16: {};
Chris@16: 
Chris@16: template <typename T>
Chris@16: struct unforward_cref
Chris@16:     : public detail::cref_unforwarder<
Chris@16:         detail::is_reference_to_value<T>::value
Chris@16:       >::template apply<T>
Chris@16: {};
Chris@16: 
Chris@16: # endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
Chris@16: 
Chris@16: template <class T>
Chris@16: typename reference_to_value<T>::reference
Chris@16: do_unforward(reference_to_value<T> const& x, int)
Chris@16: {
Chris@16:     return x.get();
Chris@16: }
Chris@16: 
Chris@16: template <class T>
Chris@16: typename reference_wrapper<T>::type&
Chris@16: do_unforward(reference_wrapper<T> const& x, int)
Chris@16: {
Chris@16:     return x.get();
Chris@16: }
Chris@16: 
Chris@16: template <class T>
Chris@16: T const& do_unforward(T const& x, ...)
Chris@16: {
Chris@16:     return x;
Chris@16: }
Chris@16: 
Chris@16: }}} // namespace boost::python::objects
Chris@16: 
Chris@16: #endif // FORWARD_DWA20011215_HPP