ceph/src/boost/libs/phoenix/include/boost/phoenix/core/nothing.hpp

   1 /*==============================================================================
   2     Copyright (c) 2005-2010 Joel de Guzman
   3
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 ==============================================================================*/
   7 #ifndef BOOST_PHOENIX_CORE_NOTHING_HPP
   8 #define BOOST_PHOENIX_CORE_NOTHING_HPP
   9
  10 #include <boost/phoenix/core/limits.hpp>
  11 #include <boost/mpl/void.hpp>
  12 #include <boost/phoenix/core/actor.hpp>
  13 #include <boost/phoenix/core/call.hpp>
  14 #include <boost/phoenix/core/expression.hpp>
  15 #include <boost/phoenix/core/value.hpp>
  16
  17 namespace boost { namespace phoenix
  18 {
  19     /////////////////////////////////////////////////////////////////////////////
  20     //
  21     //  null_actor
  22     //
  23     //      An actor that does nothing (a "bum", if you will :-).
  24     //
  25     /////////////////////////////////////////////////////////////////////////////
  26
  27     namespace detail
  28     {
  29         struct nothing {};
  30     }
  31
  32     namespace expression
  33     {
  34         struct null
  35             : expression::value<detail::nothing>
  36         {};
  37     }
  38
  39     template<typename Dummy>
  40     struct is_custom_terminal<detail::nothing, Dummy>
  41       : mpl::true_
  42     {};
  43
  44     template<typename Dummy>
  45     struct custom_terminal<detail::nothing, Dummy>
  46     {
  47         typedef void result_type;
  48         template <typename Context>
  49         void operator()(detail::nothing, Context &) const
  50         {
  51         }
  52     };
  53
  54     typedef expression::null::type nothing_type BOOST_ATTRIBUTE_UNUSED;
  55 #ifndef BOOST_PHOENIX_NO_PREDEFINED_TERMINALS
  56     nothing_type const BOOST_ATTRIBUTE_UNUSED nothing = {{{}}};
  57 #endif
  58 }}
  59
  60 #endif