46 lines
1.3 KiB
C++
46 lines
1.3 KiB
C++
/*!
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@file
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Defines `boost::hana::is_empty`.
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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_IS_EMPTY_HPP
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#define BOOST_HANA_IS_EMPTY_HPP
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#include <boost/hana/fwd/is_empty.hpp>
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#include <boost/hana/concept/iterable.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 Xs>
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constexpr auto is_empty_t::operator()(Xs const& xs) const {
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using It = typename hana::tag_of<Xs>::type;
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using IsEmpty = BOOST_HANA_DISPATCH_IF(is_empty_impl<It>,
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hana::Iterable<It>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Iterable<It>::value,
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"hana::is_empty(xs) requires 'xs' to be an Iterable");
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#endif
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return IsEmpty::apply(xs);
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}
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//! @endcond
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template <typename It, bool condition>
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struct is_empty_impl<It, 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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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_IS_EMPTY_HPP
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