fixing missing traversal category on binary transform view, by reusing zip_view algorithm

[SVN r40516]

include/boost/fusion/view/detail/strictest_traversal.hpp

@@ -0,0 +1,68 @@
+/*=============================================================================
+    Copyright (c) 2001-2006 Joel de Guzman
+    Copyright (c) 2006 Dan Marsden
+
+    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(FUSION_STRICTEST_TRAVERSAL_20060123_2101)
+#define FUSION_STRICTEST_TRAVERSAL_20060123_2101
+
+#include <boost/mpl/or.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/fusion/support/category_of.hpp>
+#include <boost/fusion/mpl.hpp>
+#include <boost/fusion/algorithm/iteration/fold.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/is_convertible.hpp>
+
+namespace boost { namespace fusion
+{
+    struct forward_traversal_tag;
+    struct bidirectional_traversal_tag;
+    struct random_access_traversal_tag;
+
+    namespace detail
+    {
+        template<typename Tag1, typename Tag2,
+            bool Tag1Stricter = boost::is_convertible<Tag2,Tag1>::value>
+        struct stricter_traversal
+        {
+            typedef Tag1 type;
+        };
+
+        template<typename Tag1, typename Tag2>
+        struct stricter_traversal<Tag1,Tag2,false>
+        {
+            typedef Tag2 type;
+        };
+
+        struct strictest_traversal_impl
+        {
+            template<typename Sig>
+            struct result;
+
+            template<typename Next, typename StrictestSoFar>
+            struct result<strictest_traversal_impl(Next, StrictestSoFar)>
+            {
+                typedef typename remove_reference<Next>::type next_value;
+                typedef typename remove_reference<StrictestSoFar>::type strictest_so_far;
+
+                typedef strictest_so_far tag1;
+                typedef typename traits::category_of<next_value>::type tag2;
+
+                typedef typename stricter_traversal<tag1,tag2>::type type;
+            };
+        };
+
+        template<typename Sequence>
+        struct strictest_traversal
+            : result_of::fold<
+            Sequence, fusion::random_access_traversal_tag,
+            strictest_traversal_impl>
+        {};
+
+    }
+}}
+
+#endif