Initial move from Spirit CVS

[SVN r34896]

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

@@ -0,0 +1,81 @@
+/*=============================================================================
+    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_AT_05042005_0722)
+#define FUSION_AT_05042005_0722
+
+#include <boost/mpl/int.hpp>
+#include <boost/type_traits/is_const.hpp>
+#include <boost/fusion/support/tag_of.hpp>
+#include <boost/fusion/support/detail/access.hpp>
+
+namespace boost { namespace fusion
+{
+    namespace extension
+    {
+        template <typename Tag>
+        struct at_impl
+        {
+            template <typename Sequence, typename N>
+            struct apply;
+        };
+    }
+
+    namespace result_of
+    {
+        template <typename Sequence, typename N>
+        struct at 
+            : extension::at_impl<typename detail::tag_of<Sequence>::type>::
+                template apply<Sequence, N>
+        {};
+
+        template <typename Sequence, int N>
+        struct at_c
+            : at<Sequence, mpl::int_<N> >
+        {};
+    }
+
+
+    template <typename N, typename Sequence>
+    inline typename 
+        lazy_disable_if<
+            is_const<Sequence>
+          , result_of::at<Sequence, N>
+        >::type
+    at(Sequence& seq)
+    {
+        return result_of::at<Sequence, N>::call(seq);
+    }
+
+    template <typename N, typename Sequence>
+    inline typename result_of::at<Sequence const, N>::type
+    at(Sequence const& seq)
+    {
+        return result_of::at<Sequence const, N>::call(seq);
+    }
+
+    template <int N, typename Sequence>
+    inline typename 
+        lazy_disable_if<
+            is_const<Sequence>
+          , result_of::at_c<Sequence, N>
+        >::type
+    at_c(Sequence& seq)
+    {
+        return at<mpl::int_<N> >(seq);
+    }
+
+    template <int N, typename Sequence>
+    inline typename result_of::at_c<Sequence const, N>::type
+    at_c(Sequence const& seq)
+    {
+        return at<mpl::int_<N> >(seq);
+    }
+}}
+
+#endif
+