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/*!
@file
Defines `boost::hana::keys`.
Copyright Louis Dionne 2013-2022
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_KEYS_HPP
#define BOOST_HANA_KEYS_HPP
#include <boost/hana/fwd/keys.hpp>
#include <boost/hana/accessors.hpp>
#include <boost/hana/concept/struct.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/first.hpp>
#include <boost/hana/transform.hpp>
namespace boost { namespace hana {
//! @cond
template <typename Map>
constexpr auto keys_t::operator()(Map&& map) const {
return keys_impl<typename hana::tag_of<Map>::type>::apply(
static_cast<Map&&>(map)
);
}
//! @endcond
template <typename T, bool condition>
struct keys_impl<T, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
template <typename S>
struct keys_impl<S, when<hana::Struct<S>::value>> {
template <typename Object>
static constexpr auto apply(Object const&) {
return hana::transform(hana::accessors<S>(), hana::first);
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_KEYS_HPP
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