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 
55 #endif
56