1/*=============================================================================
2 Copyright (c) 2001-2011 Joel de Guzman
3 Copyright (c) 2006 Dan Marsden
4
5 Distributed under the Boost Software License, Version 1.0. (See accompanying
6 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7==============================================================================*/
8#if !defined(FUSION_STRICTEST_TRAVERSAL_20060123_2101)
9#define FUSION_STRICTEST_TRAVERSAL_20060123_2101
10
11#include <boost/fusion/support/config.hpp>
12#include <boost/config.hpp>
13#include <boost/mpl/or.hpp>
14#include <boost/mpl/if.hpp>
15#include <boost/fusion/support/category_of.hpp>
16#include <boost/fusion/mpl.hpp>
17#include <boost/fusion/algorithm/iteration/fold.hpp>
18#include <boost/type_traits/remove_reference.hpp>
19#include <boost/type_traits/is_convertible.hpp>
20
21namespace boost { namespace fusion
22{
23 struct forward_traversal_tag;
24 struct bidirectional_traversal_tag;
25 struct random_access_traversal_tag;
26
27 namespace detail
28 {
29 template<typename Tag1, typename Tag2,
30 bool Tag1Stricter = boost::is_convertible<Tag2,Tag1>::value>
31 struct stricter_traversal
32 {
33 typedef Tag1 type;
34 };
35
36 template<typename Tag1, typename Tag2>
37 struct stricter_traversal<Tag1,Tag2,false>
38 {
39 typedef Tag2 type;
40 };
41
42 struct strictest_traversal_impl
43 {
44 template<typename Sig>
45 struct result;
46
47 template<typename StrictestSoFar, typename Next>
48 struct result<strictest_traversal_impl(StrictestSoFar, Next)>
49 {
50 typedef typename remove_reference<Next>::type next_value;
51 typedef typename remove_reference<StrictestSoFar>::type strictest_so_far;
52
53 typedef strictest_so_far tag1;
54 typedef typename traits::category_of<next_value>::type tag2;
55
56 typedef typename stricter_traversal<tag1,tag2>::type type;
57 };
58
59 // never called, but needed for decltype-based result_of (C++0x)
60#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
61 template<typename StrictestSoFar, typename Next>
62 BOOST_FUSION_GPU_ENABLED
63 typename result<strictest_traversal_impl(StrictestSoFar, Next)>::type
64 operator()(StrictestSoFar&&, Next&&) const;
65#endif
66 };
67
68 template<typename Sequence>
69 struct strictest_traversal
70 : result_of::fold<
71 Sequence, fusion::random_access_traversal_tag,
72 strictest_traversal_impl>
73 {};
74
75 }
76}}
77
78#endif
79