Chris@16: /*=============================================================================
Chris@16:     Copyright (c) 2001-2011 Joel de Guzman
Chris@16:     Copyright (c) 2006 Dan Marsden
Chris@16: 
Chris@16:     Distributed under the Boost Software License, Version 1.0. (See accompanying
Chris@16:     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: ==============================================================================*/
Chris@16: #if !defined(FUSION_STRICTEST_TRAVERSAL_20060123_2101)
Chris@16: #define FUSION_STRICTEST_TRAVERSAL_20060123_2101
Chris@16: 
Chris@101: #include <boost/fusion/support/config.hpp>
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/mpl/or.hpp>
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: #include <boost/fusion/support/category_of.hpp>
Chris@16: #include <boost/fusion/mpl.hpp>
Chris@16: #include <boost/fusion/algorithm/iteration/fold.hpp>
Chris@16: #include <boost/type_traits/remove_reference.hpp>
Chris@16: #include <boost/type_traits/is_convertible.hpp>
Chris@16: 
Chris@16: namespace boost { namespace fusion
Chris@16: {
Chris@16:     struct forward_traversal_tag;
Chris@16:     struct bidirectional_traversal_tag;
Chris@16:     struct random_access_traversal_tag;
Chris@16: 
Chris@16:     namespace detail
Chris@16:     {
Chris@16:         template<typename Tag1, typename Tag2,
Chris@16:             bool Tag1Stricter = boost::is_convertible<Tag2,Tag1>::value>
Chris@16:         struct stricter_traversal
Chris@16:         {
Chris@16:             typedef Tag1 type;
Chris@16:         };
Chris@16: 
Chris@16:         template<typename Tag1, typename Tag2>
Chris@16:         struct stricter_traversal<Tag1,Tag2,false>
Chris@16:         {
Chris@16:             typedef Tag2 type;
Chris@16:         };
Chris@16: 
Chris@16:         struct strictest_traversal_impl
Chris@16:         {
Chris@16:             template<typename Sig>
Chris@16:             struct result;
Chris@16: 
Chris@16:             template<typename StrictestSoFar, typename Next>
Chris@16:             struct result<strictest_traversal_impl(StrictestSoFar, Next)>
Chris@16:             {
Chris@16:                 typedef typename remove_reference<Next>::type next_value;
Chris@16:                 typedef typename remove_reference<StrictestSoFar>::type strictest_so_far;
Chris@16: 
Chris@16:                 typedef strictest_so_far tag1;
Chris@16:                 typedef typename traits::category_of<next_value>::type tag2;
Chris@16: 
Chris@16:                 typedef typename stricter_traversal<tag1,tag2>::type type;
Chris@16:             };
Chris@16: 
Chris@16:             // never called, but needed for decltype-based result_of (C++0x)
Chris@16: #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
Chris@16:             template<typename StrictestSoFar, typename Next>
Chris@101:             BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
Chris@16:             typename result<strictest_traversal_impl(StrictestSoFar, Next)>::type
Chris@16:             operator()(StrictestSoFar&&, Next&&) const;
Chris@16: #endif
Chris@16:         };
Chris@16: 
Chris@16:         template<typename Sequence>
Chris@16:         struct strictest_traversal
Chris@16:             : result_of::fold<
Chris@16:             Sequence, fusion::random_access_traversal_tag,
Chris@16:             strictest_traversal_impl>
Chris@16:         {};
Chris@16: 
Chris@16:     }
Chris@16: }}
Chris@16: 
Chris@16: #endif