1/*!
2@file
3Defines `boost::hana::detail::variadic::take`.
4
5Copyright Louis Dionne 2013-2022
6Distributed 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_DETAIL_VARIADIC_TAKE_HPP
11#define BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
12
13#include <boost/hana/config.hpp>
14#include <boost/hana/detail/variadic/split_at.hpp>
15#include <boost/hana/functional/always.hpp>
16#include <boost/hana/functional/reverse_partial.hpp>
17
18#include <cstddef>
19
20
21namespace boost { namespace hana { namespace detail { namespace variadic {
22 struct take_impl2 {
23 template <typename F, typename ...Xs>
24 constexpr decltype(auto) operator()(F&& f, Xs&& ...xs) const {
25 return static_cast<F&&>(f)(static_cast<Xs&&>(xs)...);
26 }
27 };
28
29 struct take_impl1 {
30 template <typename ...Xs>
31 constexpr auto operator()(Xs&& ...xs) const {
32 return hana::always(
33 reverse_partial(take_impl2{},
34 static_cast<Xs&&>(xs)...)
35 );
36 }
37 };
38
39 template <std::size_t n>
40 struct take_t {
41 template <typename ...Xs>
42 constexpr decltype(auto) operator()(Xs&& ...xs) const {
43 return variadic::split_at<n>(static_cast<Xs&&>(xs)...)(take_impl1{});
44 }
45 };
46
47 template <std::size_t n>
48 BOOST_HANA_INLINE_VARIABLE constexpr take_t<n> take{};
49}} }} // end namespace boost::hana
50
51#endif // !BOOST_HANA_DETAIL_VARIADIC_TAKE_HPP
52

source code of boost/libs/hana/include/boost/hana/detail/variadic/take.hpp