constant.hpp 815 B

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  1. /*!
  2. @file
  3. Defines `boost::hana::Constant`.
  4. @copyright Louis Dionne 2013-2017
  5. Distributed under the Boost Software License, Version 1.0.
  6. (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
  7. */
  8. #ifndef BOOST_HANA_CONCEPT_CONSTANT_HPP
  9. #define BOOST_HANA_CONCEPT_CONSTANT_HPP
  10. #include <boost/hana/fwd/concept/constant.hpp>
  11. #include <boost/hana/config.hpp>
  12. #include <boost/hana/core/default.hpp>
  13. #include <boost/hana/core/tag_of.hpp>
  14. #include <boost/hana/detail/integral_constant.hpp>
  15. #include <boost/hana/value.hpp>
  16. BOOST_HANA_NAMESPACE_BEGIN
  17. template <typename C>
  18. struct Constant
  19. : hana::integral_constant<bool,
  20. !is_default<value_impl<typename tag_of<C>::type>>::value
  21. >
  22. { };
  23. BOOST_HANA_NAMESPACE_END
  24. #endif // !BOOST_HANA_CONCEPT_CONSTANT_HPP