Imported existing code

libraries/include/boost/mpl/aux_/at_impl.hpp

@@ -0,0 +1,45 @@
+
+#ifndef BOOST_MPL_AUX_AT_IMPL_HPP_INCLUDED
+#define BOOST_MPL_AUX_AT_IMPL_HPP_INCLUDED
+
+// Copyright Aleksey Gurtovoy 2000-2004
+//
+// 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)
+//
+// See http://www.boost.org/libs/mpl for documentation.
+
+// $Id: at_impl.hpp 49267 2008-10-11 06:19:02Z agurtovoy $
+// $Date: 2008-10-11 02:19:02 -0400 (Sat, 11 Oct 2008) $
+// $Revision: 49267 $
+
+#include <boost/mpl/begin_end.hpp>
+#include <boost/mpl/advance.hpp>
+#include <boost/mpl/deref.hpp>
+#include <boost/mpl/aux_/traits_lambda_spec.hpp>
+
+namespace boost { namespace mpl {
+
+// default implementation; conrete sequences might override it by 
+// specializing either the 'at_impl' or the primary 'at' template
+
+template< typename Tag >
+struct at_impl
+{
+    template< typename Sequence, typename N > struct apply
+    {
+        typedef typename advance<
+              typename begin<Sequence>::type
+            , N
+            >::type iter_;
+
+        typedef typename deref<iter_>::type type;
+    };
+};
+
+BOOST_MPL_ALGORITM_TRAITS_LAMBDA_SPEC(2, at_impl)
+
+}}
+
+#endif // BOOST_MPL_AUX_AT_IMPL_HPP_INCLUDED