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 #include <boost/hana/erase_key.hpp> 18 19 20 BOOST_HANA_NAMESPACE_BEGIN 21 //! @cond 22 template <typename Xs, typename Ys> operator ()(Xs && xs,Ys && ys) const23 constexpr auto difference_t::operator()(Xs&& xs, Ys&& ys) const { 24 using S = typename hana::tag_of<Xs>::type; 25 using Difference = BOOST_HANA_DISPATCH_IF(difference_impl<S>, 26 true 27 ); 28 29 return Difference::apply(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys)); 30 } 31 //! @endcond 32 33 template <typename S, bool condition> 34 struct difference_impl<S, when<condition>> : default_ { 35 template <typename ...Args> 36 static constexpr auto apply(Args&& ...) = delete; 37 }; 38 BOOST_HANA_NAMESPACE_END 39 40 #endif // !BOOST_HANA_DIFFERENCE_HPP 41