1 /*! 2 @file 3 Defines `boost::hana::sum`. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_SUM_HPP 11 #define BOOST_HANA_SUM_HPP 12 13 #include <boost/hana/fwd/sum.hpp> 14 15 #include <boost/hana/concept/foldable.hpp> 16 #include <boost/hana/concept/monoid.hpp> 17 #include <boost/hana/config.hpp> 18 #include <boost/hana/core/dispatch.hpp> 19 #include <boost/hana/fold_left.hpp> 20 #include <boost/hana/integral_constant.hpp> // required by fwd decl 21 #include <boost/hana/plus.hpp> 22 #include <boost/hana/zero.hpp> 23 24 25 BOOST_HANA_NAMESPACE_BEGIN 26 //! @cond 27 template <typename M> 28 template <typename Xs> operator ()(Xs && xs) const29 constexpr decltype(auto) sum_t<M>::operator()(Xs&& xs) const { 30 using S = typename hana::tag_of<Xs>::type; 31 using Sum = BOOST_HANA_DISPATCH_IF(sum_impl<S>, 32 hana::Foldable<S>::value 33 ); 34 35 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS 36 static_assert(hana::Monoid<M>::value, 37 "hana::sum<M> requires 'M' to be a Monoid"); 38 39 static_assert(hana::Foldable<S>::value, 40 "hana::sum<M>(xs) requires 'xs' to be Foldable"); 41 #endif 42 43 return Sum::template apply<M>(static_cast<Xs&&>(xs)); 44 } 45 //! @endcond 46 47 template <typename T, bool condition> 48 struct sum_impl<T, when<condition>> : default_ { 49 template <typename M, typename Xs> applysum_impl50 static constexpr decltype(auto) apply(Xs&& xs) { 51 return hana::fold_left(static_cast<Xs&&>(xs), hana::zero<M>(), hana::plus); 52 } 53 }; 54 BOOST_HANA_NAMESPACE_END 55 56 #endif // !BOOST_HANA_SUM_HPP 57