| 1 | /*! |
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| 2 | @file |
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| 3 | Defines `boost::hana::second`. |
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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_SECOND_HPP |
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| 11 | #define BOOST_HANA_SECOND_HPP |
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| 12 | |
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| 13 | #include <boost/hana/fwd/second.hpp> |
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| 14 | |
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| 15 | #include <boost/hana/concept/product.hpp> |
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| 16 | #include <boost/hana/config.hpp> |
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| 17 | #include <boost/hana/core/dispatch.hpp> |
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| 18 | |
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| 19 | |
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| 20 | namespace boost { namespace hana { |
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| 21 | //! @cond |
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| 22 | template <typename Pair> |
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| 23 | constexpr decltype(auto) second_t::operator()(Pair&& pair) const { |
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| 24 | using P = typename hana::tag_of<Pair>::type; |
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| 25 | using Second = BOOST_HANA_DISPATCH_IF(second_impl<P>, |
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| 26 | hana::Product<P>::value |
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| 27 | ); |
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| 28 | |
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| 29 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS |
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| 30 | static_assert(hana::Product<P>::value, |
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| 31 | "hana::second(pair) requires 'pair' to be a Product" ); |
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| 32 | #endif |
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| 33 | |
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| 34 | return Second::apply(static_cast<Pair&&>(pair)); |
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| 35 | } |
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| 36 | //! @endcond |
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| 37 | |
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| 38 | template <typename P, bool condition> |
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| 39 | struct second_impl<P, when<condition>> : default_ { |
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| 40 | template <typename ...Args> |
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| 41 | static constexpr auto apply(Args&& ...) = delete; |
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| 42 | }; |
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| 43 | }} // end namespace boost::hana |
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| 44 | |
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| 45 | #endif // !BOOST_HANA_SECOND_HPP |
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| 46 | |
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