ceph/src/boost/boost/python/object/forward.hpp

   1 // Copyright David Abrahams 2001.
   2 // Distributed under the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5 #ifndef FORWARD_DWA20011215_HPP
   6 # define FORWARD_DWA20011215_HPP
   7
   8 # include <boost/mpl/if.hpp>
   9 # include <boost/ref.hpp>
  10 # include <boost/python/detail/value_arg.hpp>
  11 # include <boost/python/detail/type_traits.hpp>
  12 # include <boost/python/detail/copy_ctor_mutates_rhs.hpp>
  13 # include <boost/mpl/or.hpp>
  14
  15 namespace boost { namespace python { namespace objects {
  16
  17 // Very much like boost::reference_wrapper<T>, except that in this
  18 // case T can be a reference already without causing a
  19 // reference-to-reference error.
  20 template <class T>
  21 struct reference_to_value
  22 {
  23     typedef typename boost::python::detail::add_lvalue_reference<typename
  24         boost::python::detail::add_const<T>::type>::type reference;
  25
  26     reference_to_value(reference x) : m_value(x) {}
  27     reference get() const { return m_value; }
  28  private:
  29     reference m_value;
  30 };
  31
  32 // A little metaprogram which selects the type to pass through an
  33 // intermediate forwarding function when the destination argument type
  34 // is T.
  35 template <class T>
  36 struct forward
  37     : mpl::if_<
  38           mpl::or_<python::detail::copy_ctor_mutates_rhs<T>, boost::python::detail::is_scalar<T> >
  39         , T
  40         , reference_to_value<T>
  41       >
  42 {
  43 };
  44
  45 template<typename T>
  46 struct unforward
  47 {
  48     typedef typename unwrap_reference<T>::type& type;
  49 };
  50
  51 template<typename T>
  52 struct unforward<reference_to_value<T> >
  53 {
  54     typedef T type;
  55 };
  56
  57 template <typename T>
  58 struct unforward_cref
  59   : python::detail::value_arg<
  60         typename unwrap_reference<T>::type
  61     >
  62 {
  63 };
  64
  65 template<typename T>
  66 struct unforward_cref<reference_to_value<T> >
  67   : boost::python::detail::add_lvalue_reference<typename boost::python::detail::add_const<T>::type>
  68 {
  69 };
  70
  71
  72 template <class T>
  73 typename reference_to_value<T>::reference
  74 do_unforward(reference_to_value<T> const& x, int)
  75 {
  76     return x.get();
  77 }
  78
  79 template <class T>
  80 typename reference_wrapper<T>::type&
  81 do_unforward(reference_wrapper<T> const& x, int)
  82 {
  83     return x.get();
  84 }
  85
  86 template <class T>
  87 T const& do_unforward(T const& x, ...)
  88 {
  89     return x;
  90 }
  91
  92 }}} // namespace boost::python::objects
  93
  94 #endif // FORWARD_DWA20011215_HPP