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Diffstat (limited to 'boost/hana/detail/variadic/take.hpp')
-rw-r--r-- | boost/hana/detail/variadic/take.hpp | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/boost/hana/detail/variadic/take.hpp b/boost/hana/detail/variadic/take.hpp new file mode 100644 index 0000000000..01da4b5b29 --- /dev/null +++ b/boost/hana/detail/variadic/take.hpp @@ -0,0 +1,51 @@ +/*! +@file +Defines `boost::hana::detail::variadic::take`. + +@copyright Louis Dionne 2013-2016 +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 |