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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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