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 Hu Chunming
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/*!
@file
Defines `boost::hana::difference`.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_DIFFERENCE_HPP
#define BOOST_HANA_DIFFERENCE_HPP
#include <boost/hana/fwd/difference.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/erase_key.hpp>
namespace boost { namespace hana {
//! @cond
template <typename Xs, typename Ys>
constexpr auto difference_t::operator()(Xs&& xs, Ys&& ys) const {
using S = typename hana::tag_of<Xs>::type;
using Difference = BOOST_HANA_DISPATCH_IF(difference_impl<S>,
true
);
return Difference::apply(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys));
}
//! @endcond
template <typename S, bool condition>
struct difference_impl<S, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_DIFFERENCE_HPP
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