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/*!
@file
Defines `boost::hana::detail::variadic::at`.
@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_AT_HPP
#define BOOST_HANA_DETAIL_VARIADIC_AT_HPP
#include <boost/hana/config.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN namespace detail { namespace variadic {
template <std::size_t n, typename = std::make_index_sequence<n>>
struct at_type;
template <std::size_t n, std::size_t ...ignore>
struct at_type<n, std::index_sequence<ignore...>> {
private:
template <typename Nth>
static constexpr auto go(decltype(ignore, (void*)0)..., Nth nth, ...)
{ return nth; }
public:
template <typename ...Xs>
constexpr auto operator()(Xs ...xs) const
{ return *go(&xs...); }
};
template <std::size_t n>
constexpr at_type<n> at{};
}} BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_VARIADIC_AT_HPP
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