Initial move from Spirit CVS

[SVN r34896]

include/boost/fusion/sequence/intrinsic/has_key.hpp

@@ -0,0 +1,52 @@
+/*=============================================================================
+    Copyright (c) 2001-2006 Joel de Guzman
+
+    Use, modification and distribution is subject to 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_HAS_KEY_09232005_1454)
+#define FUSION_HAS_KEY_09232005_1454
+
+#include <boost/mpl/not.hpp>
+#include <boost/fusion/support/tag_of.hpp>
+#include <boost/type_traits/is_same.hpp>
+
+namespace boost { namespace fusion
+{
+    struct void_;
+    struct fusion_sequence_tag;
+
+    namespace extension
+    {
+        template <typename Tag>
+        struct has_key_impl
+        {
+            template <typename Sequence, typename Key>
+            struct apply
+                : mpl::not_<is_same<typename Sequence::
+                    template meta_at_impl<Key>::type, void_> >
+            {};
+        };
+    }
+    
+    namespace result_of
+    {
+        template <typename Sequence, typename Key>
+        struct has_key 
+            : extension::has_key_impl<typename detail::tag_of<Sequence>::type>::
+                template apply<Sequence, Key>
+        {};
+    }
+
+    template <typename Key, typename Sequence>
+    inline typename result_of::has_key<Sequence, Key>::type
+    has_key(Sequence const& seq)
+    {
+        static typename result_of::has_key<Sequence, Key>::type result;
+        return result;
+    }
+}}
+
+#endif
+