/*! @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