value_at_impl.hpp 1.1 KB

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  1. /*=============================================================================
  2. Copyright (c) 2001-2013 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_MAP_DETAIL_VALUE_AT_IMPL_02042013_0821)
  7. #define BOOST_FUSION_MAP_DETAIL_VALUE_AT_IMPL_02042013_0821
  8. #include <boost/fusion/support/config.hpp>
  9. #include <boost/mpl/at.hpp>
  10. #include <boost/utility/declval.hpp>
  11. namespace boost { namespace fusion
  12. {
  13. struct map_tag;
  14. namespace extension
  15. {
  16. template <typename Tag>
  17. struct value_at_impl;
  18. template <>
  19. struct value_at_impl<map_tag>
  20. {
  21. template <typename Sequence, typename N>
  22. struct apply
  23. {
  24. typedef mpl::int_<N::value> index;
  25. typedef
  26. decltype(boost::declval<Sequence>().get_val(index()))
  27. type;
  28. };
  29. };
  30. }
  31. }}
  32. #endif