ceph/src/boost/libs/phoenix/include/boost/phoenix/core/is_value.hpp

   1 /*==============================================================================
   2     Copyright (c) 2005-2010 Joel de Guzman
   3     Copyright (c) 2015 John Fletcher
   4
   5     Distributed under the Boost Software License, Version 1.0. (See accompanying
   6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 ==============================================================================*/
   8 #ifndef BOOST_PHOENIX_CORE_IS_VALUE_HPP
   9 #define BOOST_PHOENIX_CORE_IS_VALUE_HPP
  10
  11 #include <boost/mpl/bool.hpp>
  12
  13 // Copied from is_actor.hpp
  14
  15 // Note to Thomas and any future maintainer: please make this as
  16 // lightweight as possible (as it is right now).
  17
  18 namespace boost { namespace phoenix
  19 {
  20 ///////////////////////////////////////////////////////////////////////////////
  21 //
  22 //  is_value<T>
  23 //
  24 //      Tests if T is a value. Evaluates to mpl::true_ or mpl::false_
  25 //
  26 ///////////////////////////////////////////////////////////////////////////////
  27
  28     namespace expression {
  29         template <typename T>
  30         struct value;
  31     }
  32
  33     template <typename T, typename Enable = void>
  34     struct is_value
  35         : mpl::false_
  36     {};
  37
  38     template <typename T>
  39     struct is_value<T const>
  40         : is_value<T>
  41     {};
  42
  43     template <typename T>
  44     struct is_value<T &>
  45         : is_value<T>
  46     {};
  47
  48     // This does not seem to work.
  49     // There is an alternative in value.hpp which does work.
  50     template <typename T>
  51     struct is_value< expression::value<T> >
  52         : mpl::true_
  53     {};
  54
  55     template <typename T>
  56     bool is_val(T const & /* t */)
  57     {
  58       return is_value<T>::value;
  59     }
  60
  61   }}
  62
  63 #endif