at_impl.hpp 1.5 KB

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  1. /*=============================================================================
  2. Copyright (c) 2001-2011 Joel de Guzman
  3. Distributed under the Boost Software License, Version 1.0. (See accompanying
  4. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  5. ==============================================================================*/
  6. #if !defined(BOOST_FUSION_AT_IMPL_09262006_1920)
  7. #define BOOST_FUSION_AT_IMPL_09262006_1920
  8. #include <boost/fusion/support/config.hpp>
  9. #include <boost/tuple/tuple.hpp>
  10. #include <boost/mpl/if.hpp>
  11. namespace boost { namespace fusion
  12. {
  13. struct boost_tuple_tag;
  14. namespace extension
  15. {
  16. template<typename T>
  17. struct at_impl;
  18. template <>
  19. struct at_impl<boost_tuple_tag>
  20. {
  21. template <typename Sequence, typename N>
  22. struct apply
  23. {
  24. typedef typename
  25. tuples::element<N::value, Sequence>::type
  26. element;
  27. typedef typename
  28. mpl::if_<
  29. is_const<Sequence>
  30. , typename tuples::access_traits<element>::const_type
  31. , typename tuples::access_traits<element>::non_const_type
  32. >::type
  33. type;
  34. BOOST_FUSION_GPU_ENABLED
  35. static type
  36. call(Sequence& seq)
  37. {
  38. return tuples::get<N::value>(seq);
  39. }
  40. };
  41. };
  42. }
  43. }}
  44. #endif