boost/hana/difference.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::difference`.
   4
   5 @copyright Louis Dionne 2013-2017
   6 Distributed under the Boost Software License, Version 1.0.
   7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   8  */
   9
  10 #ifndef BOOST_HANA_DIFFERENCE_HPP
  11 #define BOOST_HANA_DIFFERENCE_HPP
  12
  13 #include <boost/hana/fwd/difference.hpp>
  14
  15 #include <boost/hana/config.hpp>
  16 #include <boost/hana/core/dispatch.hpp>
  17
  18
  19 BOOST_HANA_NAMESPACE_BEGIN
  20     //! @cond
  21     template <typename Xs, typename Ys>
  22     constexpr auto difference_t::operator()(Xs&& xs, Ys&& ys) const {
  23         using S = typename hana::tag_of<Xs>::type;
  24         using Difference = BOOST_HANA_DISPATCH_IF(difference_impl<S>,
  25             true
  26         );
  27
  28         return Difference::apply(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys));
  29     }
  30     //! @endcond
  31
  32     template <typename S, bool condition>
  33     struct difference_impl<S, when<condition>> : default_ {
  34         template <typename ...Args>
  35         static constexpr auto apply(Args&& ...) = delete;
  36     };
  37 BOOST_HANA_NAMESPACE_END
  38
  39 #endif // !BOOST_HANA_DIFFERENCE_HPP