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/*!
@file
Defines `boost::hana::sum`.
@copyright Louis Dionne 2013-2016
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_SUM_HPP
#define BOOST_HANA_SUM_HPP
#include <boost/hana/fwd/sum.hpp>
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/concept/monoid.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/fold_left.hpp>
#include <boost/hana/integral_constant.hpp> // required by fwd decl
#include <boost/hana/plus.hpp>
#include <boost/hana/zero.hpp>
BOOST_HANA_NAMESPACE_BEGIN
template <typename M>
struct sum_t {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Monoid<M>::value,
"hana::sum<M> requires 'M' to be a Monoid");
#endif
template <typename Xs>
constexpr decltype(auto) operator()(Xs&& xs) const {
using S = typename hana::tag_of<Xs>::type;
using Sum = BOOST_HANA_DISPATCH_IF(sum_impl<S>,
hana::Foldable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Foldable<S>::value,
"hana::sum<M>(xs) requires 'xs' to be Foldable");
#endif
return Sum::template apply<M>(static_cast<Xs&&>(xs));
}
};
template <typename T, bool condition>
struct sum_impl<T, when<condition>> : default_ {
template <typename M, typename Xs>
static constexpr decltype(auto) apply(Xs&& xs) {
return hana::fold_left(static_cast<Xs&&>(xs), hana::zero<M>(), hana::plus);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_SUM_HPP
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