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