52 lines
1.5 KiB
C++
52 lines
1.5 KiB
C++
/*!
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@file
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Defines `boost::hana::detail::variadic::take`.
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@copyright Louis Dionne 2013-2017
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
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#define BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/detail/variadic/split_at.hpp>
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#include <boost/hana/functional/always.hpp>
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#include <boost/hana/functional/reverse_partial.hpp>
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#include <cstddef>
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namespace boost { namespace hana { namespace detail { namespace variadic {
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struct take_impl2 {
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template <typename F, typename ...Xs>
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constexpr decltype(auto) operator()(F&& f, Xs&& ...xs) const {
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return static_cast<F&&>(f)(static_cast<Xs&&>(xs)...);
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}
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};
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struct take_impl1 {
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template <typename ...Xs>
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constexpr auto operator()(Xs&& ...xs) const {
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return hana::always(
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reverse_partial(take_impl2{},
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static_cast<Xs&&>(xs)...)
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);
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}
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};
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template <std::size_t n>
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struct take_t {
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template <typename ...Xs>
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constexpr decltype(auto) operator()(Xs&& ...xs) const {
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return variadic::split_at<n>(static_cast<Xs&&>(xs)...)(take_impl1{});
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}
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};
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template <std::size_t n>
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BOOST_HANA_INLINE_VARIABLE constexpr take_t<n> take{};
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}} }} // end namespace boost::hana
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#endif // !BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
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