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49 lines
1.3 KiB
C++
49 lines
1.3 KiB
C++
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/*!
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@file
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Defines `boost::hana::keys`.
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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_KEYS_HPP
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#define BOOST_HANA_KEYS_HPP
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#include <boost/hana/fwd/keys.hpp>
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#include <boost/hana/accessors.hpp>
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#include <boost/hana/concept/struct.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/first.hpp>
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#include <boost/hana/transform.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Map>
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constexpr auto keys_t::operator()(Map&& map) const {
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return keys_impl<typename hana::tag_of<Map>::type>::apply(
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static_cast<Map&&>(map)
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);
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}
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//! @endcond
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template <typename T, bool condition>
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struct keys_impl<T, when<condition>> : default_ {
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template <typename ...Args>
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static constexpr auto apply(Args&& ...) = delete;
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};
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template <typename S>
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struct keys_impl<S, when<hana::Struct<S>::value>> {
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template <typename Object>
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static constexpr auto apply(Object const&) {
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return hana::transform(hana::accessors<S>(), hana::first);
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_KEYS_HPP
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