ceph/src/boost/boost/spirit/home/x3/support/traits/attribute_of.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2014 Joel de Guzman
   3     Copyright (c) 2013 Agustin Berge
   4     http://spirit.sourceforge.net/
   5
   6     Distributed under the Boost Software License, Version 1.0. (See accompanying
   7     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   8 =============================================================================*/
   9 #if !defined(BOOST_SPIRIT_X3_ATTRIBUTE_OF_JAN_7_2012_0914AM)
  10 #define BOOST_SPIRIT_X3_ATTRIBUTE_OF_JAN_7_2012_0914AM
  11
  12 #include <boost/spirit/home/x3/support/utility/sfinae.hpp>
  13 #include <boost/mpl/identity.hpp>
  14 #include <boost/utility/enable_if.hpp>
  15
  16 namespace boost { namespace spirit { namespace x3 { namespace traits
  17 {
  18     ///////////////////////////////////////////////////////////////////////////
  19     // Get the attribute type of a component. By default, this gets the
  20     // Component's attribute_type typedef or instantiates a nested attribute
  21     // metafunction. Components may specialize this if such an attribute_type
  22     // is not readily available (e.g. expensive to compute at compile time).
  23     ///////////////////////////////////////////////////////////////////////////
  24     template <typename Component, typename Context, typename Enable = void>
  25     struct attribute_of;
  26
  27     namespace detail
  28     {
  29         template <typename Component, typename Context, typename Enable = void>
  30         struct default_attribute_of;
  31
  32         template <typename Component, typename Context>
  33         struct default_attribute_of<Component, Context,
  34             typename disable_if_substitution_failure<
  35                 typename Component::attribute_type>::type>
  36           : mpl::identity<typename Component::attribute_type> {};
  37
  38         template <typename Component, typename Context>
  39         struct default_attribute_of<Component, Context,
  40             typename disable_if_substitution_failure<
  41                 typename Component::template attribute<Context>::type>::type>
  42           : Component::template attribute<Context> {};
  43
  44         template <typename Component, typename Context>
  45         struct default_attribute_of<Component, Context,
  46             typename enable_if_c<Component::is_pass_through_unary>::type>
  47           : attribute_of<typename Component::subject_type, Context>{};
  48     }
  49
  50     template <typename Component, typename Context, typename Enable>
  51     struct attribute_of : detail::default_attribute_of<Component, Context> {};
  52 }}}}
  53
  54 #endif