41 lines
1.1 KiB
C++
41 lines
1.1 KiB
C++
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/*!
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@file
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Defines `boost::hana::detail::variadic::at`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_DETAIL_VARIADIC_AT_HPP
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#define BOOST_HANA_DETAIL_VARIADIC_AT_HPP
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#include <boost/hana/config.hpp>
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#include <cstddef>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN namespace detail { namespace variadic {
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template <std::size_t n, typename = std::make_index_sequence<n>>
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struct at_type;
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template <std::size_t n, std::size_t ...ignore>
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struct at_type<n, std::index_sequence<ignore...>> {
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private:
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template <typename Nth>
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static constexpr auto go(decltype(ignore, (void*)0)..., Nth nth, ...)
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{ return nth; }
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public:
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template <typename ...Xs>
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constexpr auto operator()(Xs ...xs) const
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{ return *go(&xs...); }
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};
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template <std::size_t n>
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constexpr at_type<n> at{};
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}} BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_DETAIL_VARIADIC_AT_HPP
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