value_at_key_impl.hpp 1.1 KB

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  1. /*=============================================================================
  2. Copyright (c) 2001-2013 Joel de Guzman
  3. Copyright (c) 2018 Kohei Takahashi
  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(BOOST_FUSION_MAP_DETAIL_VALUE_AT_KEY_IMPL_02042013_0821)
  8. #define BOOST_FUSION_MAP_DETAIL_VALUE_AT_KEY_IMPL_02042013_0821
  9. #include <boost/fusion/support/config.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_key_impl;
  18. template <>
  19. struct value_at_key_impl<map_tag>
  20. {
  21. template <typename Sequence, typename Key>
  22. struct apply : BOOST_FUSION_DECLTYPE_N3031((
  23. boost::declval<Sequence>().get_val(mpl::identity<Key>())
  24. ))
  25. {};
  26. };
  27. }
  28. }}
  29. #endif