boost/boost/spirit/home/x3/support/traits/variant_has_substitute.hpp

/*=============================================================================
    Copyright (c) 2001-2014 Joel de Guzman
    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_VARIANT_HAS_SUBSTITUTE_APR_18_2014_925AM)
#define BOOST_SPIRIT_X3_VARIANT_HAS_SUBSTITUTE_APR_18_2014_925AM

#if defined(_MSC_VER)
#pragma once
#endif

#include <boost/spirit/home/x3/support/traits/is_substitute.hpp>

namespace boost { namespace spirit { namespace x3 { namespace traits
{
    template <typename Variant, typename Attribute>
    struct variant_has_substitute_impl
    {
        // Find a type from the variant that can be a substitute for Attribute.
        // return true_ if one is found, else false_

        typedef Variant variant_type;
        typedef typename variant_type::types types;
        typedef typename mpl::end<types>::type end;

        typedef typename
            mpl::find_if<types, is_same<mpl::_1, Attribute>>::type
        iter_1;

        typedef typename
            mpl::eval_if<
                is_same<iter_1, end>,
                mpl::find_if<types, traits::is_substitute<mpl::_1, Attribute>>,
                mpl::identity<iter_1>
            >::type
        iter;

        typedef mpl::not_<is_same<iter, end>> type;
    };

    template <typename Variant, typename Attribute>
    struct variant_has_substitute
        : variant_has_substitute_impl<Variant, Attribute>::type {};

    template <typename Attribute>
    struct variant_has_substitute<unused_type, Attribute> : mpl::true_ {};

    template <typename Attribute>
    struct variant_has_substitute<unused_type const, Attribute> : mpl::true_ {};

}}}}

#endif