| 1 | /*! |
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| 2 | @file |
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| 3 | Defines `boost::hana::detail::variadic::at`. |
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| 4 | |
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| 5 | Copyright Louis Dionne 2013-2022 |
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| 6 | Distributed under the Boost Software License, Version 1.0. |
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| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 8 | */ |
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| 9 | |
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| 10 | #ifndef BOOST_HANA_DETAIL_VARIADIC_AT_HPP |
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| 11 | #define BOOST_HANA_DETAIL_VARIADIC_AT_HPP |
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| 12 | |
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| 13 | #include <boost/hana/config.hpp> |
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| 14 | |
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| 15 | #include <cstddef> |
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| 16 | #include <utility> |
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| 17 | |
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| 18 | |
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| 19 | namespace boost { namespace hana { namespace detail { namespace variadic { |
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| 20 | template <std::size_t n, typename = std::make_index_sequence<n>> |
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| 21 | struct at_type; |
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| 22 | |
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| 23 | template <std::size_t n, std::size_t ...ignore> |
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| 24 | struct at_type<n, std::index_sequence<ignore...>> { |
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| 25 | private: |
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| 26 | template <typename Nth> |
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| 27 | static constexpr auto go(decltype(ignore, (void*)0)..., Nth nth, ...) |
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| 28 | { return nth; } |
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| 29 | |
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| 30 | public: |
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| 31 | template <typename ...Xs> |
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| 32 | constexpr auto operator()(Xs ...xs) const |
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| 33 | { return *go(&xs...); } |
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| 34 | }; |
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| 35 | |
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| 36 | template <std::size_t n> |
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| 37 | BOOST_HANA_INLINE_VARIABLE constexpr at_type<n> at{}; |
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| 38 | }} }} // end namespace boost::hana |
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| 39 | |
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| 40 | #endif // !BOOST_HANA_DETAIL_VARIADIC_AT_HPP |
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| 41 | |
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