mpl/aux_/at_impl.hpp

0001
0002 #ifndef BOOST_MPL_AUX_AT_IMPL_HPP_INCLUDED
0003 #define BOOST_MPL_AUX_AT_IMPL_HPP_INCLUDED
0004
0005 // Copyright Aleksey Gurtovoy 2000-2004
0006 //
0007 // Distributed under the Boost Software License, Version 1.0.
0008 // (See accompanying file LICENSE_1_0.txt or copy at
0009 // http://www.boost.org/LICENSE_1_0.txt)
0010 //
0011 // See http://www.boost.org/libs/mpl for documentation.
0012
0013 // $Id$
0014 // $Date$
0015 // $Revision$
0016
0017 #include <boost/mpl/begin_end.hpp>
0018 #include <boost/mpl/advance.hpp>
0019 #include <boost/mpl/deref.hpp>
0020 #include <boost/mpl/aux_/traits_lambda_spec.hpp>
0021
0022 namespace boost { namespace mpl {
0023
0024 // default implementation; conrete sequences might override it by
0025 // specializing either the 'at_impl' or the primary 'at' template
0026
0027 template< typename Tag >
0028 struct at_impl
0029 {
0030     template< typename Sequence, typename N > struct apply
0031     {
0032         typedef typename advance<
0033               typename begin<Sequence>::type
0034             , N
0035             >::type iter_;
0036
0037         typedef typename deref<iter_>::type type;
0038     };
0039 };
0040
0041 BOOST_MPL_ALGORITM_TRAITS_LAMBDA_SPEC(2, at_impl)
0042
0043 }}
0044
0045 #endif // BOOST_MPL_AUX_AT_IMPL_HPP_INCLUDED