/*=============================================================================
    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
