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46 lines
1.3 KiB
C++
46 lines
1.3 KiB
C++
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/*!
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@file
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Defines `boost::hana::extract`.
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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_EXTRACT_HPP
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#define BOOST_HANA_EXTRACT_HPP
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#include <boost/hana/fwd/extract.hpp>
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#include <boost/hana/concept/comonad.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename W_>
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constexpr decltype(auto) extract_t::operator()(W_&& w) const {
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using W = typename hana::tag_of<W_>::type;
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using Extract = BOOST_HANA_DISPATCH_IF(extract_impl<W>,
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hana::Comonad<W>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Comonad<W>::value,
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"hana::extract(w) requires 'w' to be a Comonad");
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#endif
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return Extract::apply(static_cast<W_&&>(w));
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}
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//! @endcond
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template <typename W, bool condition>
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struct extract_impl<W, when<condition>> : default_ {
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template <typename ...Args>
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static constexpr auto apply(Args&& ...args) = delete;
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_EXTRACT_HPP
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