difference.hpp 854 B

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  1. /*!
  2. @file
  3. Forward declares `boost::hana::difference`.
  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_FWD_DIFFERENCE_HPP
  9. #define BOOST_HANA_FWD_DIFFERENCE_HPP
  10. #include <boost/hana/config.hpp>
  11. #include <boost/hana/core/when.hpp>
  12. BOOST_HANA_NAMESPACE_BEGIN
  13. // Note: This function is documented per datatype/concept only.
  14. //! @cond
  15. template <typename S, typename = void>
  16. struct difference_impl : difference_impl<S, when<true>> { };
  17. //! @endcond
  18. struct difference_t {
  19. template <typename Xs, typename Ys>
  20. constexpr auto operator()(Xs&&, Ys&&) const;
  21. };
  22. constexpr difference_t difference{};
  23. BOOST_HANA_NAMESPACE_END
  24. #endif // !BOOST_HANA_FWD_DIFFERENCE_HPP