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- /*=============================================================================
- Copyright (c) 2001-2014 Joel de Guzman
- Copyright (c) 2013 Agustin Berge
- http://spirit.sourceforge.net/
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- =============================================================================*/
- #if !defined(BOOST_SPIRIT_X3_HAS_ATTRIBUTE_JUN_6_2012_1714PM)
- #define BOOST_SPIRIT_X3_HAS_ATTRIBUTE_JUN_6_2012_1714PM
- #include <boost/spirit/home/x3/support/traits/attribute_of.hpp>
- #include <boost/spirit/home/x3/support/utility/sfinae.hpp>
- #include <boost/mpl/bool.hpp>
- #include <boost/mpl/not.hpp>
- #include <boost/type_traits/is_same.hpp>
- #include <boost/utility/enable_if.hpp>
- namespace boost { namespace spirit { namespace x3
- {
- struct unused_type;
- }}}
- namespace boost { namespace spirit { namespace x3 { namespace traits
- {
- ///////////////////////////////////////////////////////////////////////////
- // Whether a component has an attribute. By default, this compares the
- // component attribute against unused_type. If the component provides a
- // nested constant expression has_attribute as a hint, that value is used
- // instead. Components may specialize this.
- ///////////////////////////////////////////////////////////////////////////
- template <typename Component, typename Context, typename Enable = void>
- struct has_attribute;
-
- namespace detail
- {
- template <typename Component, typename Context, typename Enable = void>
- struct default_has_attribute
- : mpl::not_<is_same<unused_type,
- typename attribute_of<Component, Context>::type>> {};
- template <typename Component, typename Context>
- struct default_has_attribute<Component, Context,
- typename disable_if_substitution_failure<
- mpl::bool_<Component::has_attribute>>::type>
- : mpl::bool_<Component::has_attribute> {};
-
- template <typename Component, typename Context>
- struct default_has_attribute<Component, Context,
- typename enable_if_c<Component::is_pass_through_unary>::type>
- : has_attribute<typename Component::subject_type, Context> {};
- }
-
- template <typename Component, typename Context, typename Enable>
- struct has_attribute : detail::default_has_attribute<Component, Context> {};
- }}}}
- #endif
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