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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::concat`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
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_CONCAT_HPP | |
11 | #define BOOST_HANA_CONCAT_HPP | |
12 | ||
13 | #include <boost/hana/fwd/concat.hpp> | |
14 | ||
15 | #include <boost/hana/at.hpp> | |
16 | #include <boost/hana/concept/monad_plus.hpp> | |
17 | #include <boost/hana/concept/sequence.hpp> | |
18 | #include <boost/hana/config.hpp> | |
19 | #include <boost/hana/core/dispatch.hpp> | |
20 | #include <boost/hana/core/make.hpp> | |
21 | #include <boost/hana/length.hpp> | |
22 | ||
23 | #include <cstddef> | |
24 | #include <type_traits> | |
25 | #include <utility> | |
26 | ||
27 | ||
28 | BOOST_HANA_NAMESPACE_BEGIN | |
29 | //! @cond | |
30 | template <typename Xs, typename Ys> | |
31 | constexpr auto concat_t::operator()(Xs&& xs, Ys&& ys) const { | |
32 | using M = typename hana::tag_of<Xs>::type; | |
33 | using Concat = BOOST_HANA_DISPATCH_IF(concat_impl<M>, | |
34 | hana::MonadPlus<M>::value && | |
35 | std::is_same<typename hana::tag_of<Ys>::type, M>::value | |
36 | ); | |
37 | ||
38 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
39 | static_assert(std::is_same<typename hana::tag_of<Ys>::type, M>::value, | |
40 | "hana::concat(xs, ys) requires 'xs' and 'ys' to have the same tag"); | |
41 | ||
42 | static_assert(hana::MonadPlus<M>::value, | |
43 | "hana::concat(xs, ys) requires 'xs' and 'ys' to be MonadPlus"); | |
44 | #endif | |
45 | ||
46 | return Concat::apply(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys)); | |
47 | } | |
48 | //! @endcond | |
49 | ||
50 | template <typename M, bool condition> | |
51 | struct concat_impl<M, when<condition>> : default_ { | |
52 | template <typename ...Args> | |
53 | static constexpr auto apply(Args&& ...) = delete; | |
54 | }; | |
55 | ||
56 | template <typename S> | |
57 | struct concat_impl<S, when<Sequence<S>::value>> { | |
58 | template <typename Xs, typename Ys, std::size_t ...xi, std::size_t ...yi> | |
59 | static constexpr auto | |
60 | concat_helper(Xs&& xs, Ys&& ys, std::index_sequence<xi...>, | |
61 | std::index_sequence<yi...>) | |
62 | { | |
63 | return hana::make<S>( | |
64 | hana::at_c<xi>(static_cast<Xs&&>(xs))..., | |
65 | hana::at_c<yi>(static_cast<Ys&&>(ys))... | |
66 | ); | |
67 | } | |
68 | ||
69 | template <typename Xs, typename Ys> | |
70 | static constexpr auto apply(Xs&& xs, Ys&& ys) { | |
71 | constexpr std::size_t xi = decltype(hana::length(xs))::value; | |
72 | constexpr std::size_t yi = decltype(hana::length(ys))::value; | |
73 | return concat_helper(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys), | |
74 | std::make_index_sequence<xi>{}, | |
75 | std::make_index_sequence<yi>{}); | |
76 | } | |
77 | }; | |
78 | BOOST_HANA_NAMESPACE_END | |
79 | ||
80 | #endif // !BOOST_HANA_CONCAT_HPP |