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59 lines
1.8 KiB
C++
59 lines
1.8 KiB
C++
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/*!
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@file
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Defines `boost::hana::sum`.
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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_SUM_HPP
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#define BOOST_HANA_SUM_HPP
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#include <boost/hana/fwd/sum.hpp>
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#include <boost/hana/concept/foldable.hpp>
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#include <boost/hana/concept/monoid.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/fold_left.hpp>
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#include <boost/hana/integral_constant.hpp> // required by fwd decl
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#include <boost/hana/plus.hpp>
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#include <boost/hana/zero.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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template <typename M>
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struct sum_t {
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Monoid<M>::value,
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"hana::sum<M> requires 'M' to be a Monoid");
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#endif
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template <typename Xs>
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constexpr decltype(auto) operator()(Xs&& xs) const {
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using S = typename hana::tag_of<Xs>::type;
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using Sum = BOOST_HANA_DISPATCH_IF(sum_impl<S>,
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hana::Foldable<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Foldable<S>::value,
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"hana::sum<M>(xs) requires 'xs' to be Foldable");
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#endif
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return Sum::template apply<M>(static_cast<Xs&&>(xs));
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}
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};
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template <typename T, bool condition>
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struct sum_impl<T, when<condition>> : default_ {
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template <typename M, typename Xs>
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static constexpr decltype(auto) apply(Xs&& xs) {
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return hana::fold_left(static_cast<Xs&&>(xs), hana::zero<M>(), hana::plus);
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_SUM_HPP
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