| 1 | /*============================================================================= |
|---|---|
| 2 | Copyright (c) 2001-2011 Joel de Guzman |
| 3 | |
| 4 | Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 5 | file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| 6 | ==============================================================================*/ |
| 7 | #if !defined(FUSION_VALUE_AT_IMPL_07172005_0952) |
| 8 | #define FUSION_VALUE_AT_IMPL_07172005_0952 |
| 9 | |
| 10 | #include <boost/fusion/support/config.hpp> |
| 11 | #include <boost/fusion/support/detail/access.hpp> |
| 12 | #include <boost/type_traits/is_const.hpp> |
| 13 | #include <boost/mpl/eval_if.hpp> |
| 14 | #include <boost/mpl/bool.hpp> |
| 15 | |
| 16 | namespace boost { namespace fusion |
| 17 | { |
| 18 | struct cons_tag; |
| 19 | |
| 20 | namespace extension |
| 21 | { |
| 22 | template <typename Tag> |
| 23 | struct value_at_impl; |
| 24 | |
| 25 | template <> |
| 26 | struct value_at_impl<cons_tag> |
| 27 | { |
| 28 | template <typename Sequence, typename N> |
| 29 | struct apply |
| 30 | { |
| 31 | typedef typename |
| 32 | mpl::eval_if< |
| 33 | mpl::bool_<N::value == 0> |
| 34 | , mpl::identity<typename Sequence::car_type> |
| 35 | , apply<typename Sequence::cdr_type, mpl::int_<N::value-1> > |
| 36 | >::type |
| 37 | type; |
| 38 | }; |
| 39 | }; |
| 40 | } |
| 41 | }} |
| 42 | |
| 43 | #endif |
| 44 |