fusion: merge of associative iterators/views and the new fold interface

[SVN r58618]

include/boost/fusion/iterator/key_of.hpp

@@ -0,0 +1,42 @@
+/*=============================================================================
+    Copyright (c) 2009 Christopher Schmidt
+
+    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)
+==============================================================================*/
+
+#ifndef BOOST_FUSION_ITERATOR_KEY_OF_HPP
+#define BOOST_FUSION_ITERATOR_KEY_OF_HPP
+
+#include <boost/fusion/support/tag_of.hpp>
+
+namespace boost { namespace fusion
+{
+    struct iterator_facade_tag;
+
+    namespace extension
+    {
+        template <typename>
+        struct key_of_impl;
+
+        template <>
+        struct key_of_impl<iterator_facade_tag>
+        {
+            template <typename It>
+            struct apply
+              : It::template key_of<It>
+            {};
+        };
+    }
+
+    namespace result_of
+    {
+        template <typename It>
+        struct key_of
+          : extension::key_of_impl<typename traits::tag_of<It>::type>::
+                template apply<It>
+        {};
+    }
+}}
+
+#endif