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/*!
@file
Defines `boost::hana::detail::variadic::take`.
@copyright Louis Dionne 2013-2017
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_DETAIL_VARIADIC_TAKE_HPP
#define BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/detail/variadic/split_at.hpp>
#include <boost/hana/functional/always.hpp>
#include <boost/hana/functional/reverse_partial.hpp>
#include <cstddef>
BOOST_HANA_NAMESPACE_BEGIN namespace detail { namespace variadic {
struct take_impl2 {
template <typename F, typename ...Xs>
constexpr decltype(auto) operator()(F&& f, Xs&& ...xs) const {
return static_cast<F&&>(f)(static_cast<Xs&&>(xs)...);
}
};
struct take_impl1 {
template <typename ...Xs>
constexpr auto operator()(Xs&& ...xs) const {
return hana::always(
reverse_partial(take_impl2{},
static_cast<Xs&&>(xs)...)
);
}
};
template <std::size_t n>
struct take_t {
template <typename ...Xs>
constexpr decltype(auto) operator()(Xs&& ...xs) const {
return variadic::split_at<n>(static_cast<Xs&&>(xs)...)(take_impl1{});
}
};
template <std::size_t n>
constexpr take_t<n> take{};
}} BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
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