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