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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::append`. | |
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_APPEND_HPP | |
11 | #define BOOST_HANA_APPEND_HPP | |
12 | ||
13 | #include <boost/hana/fwd/append.hpp> | |
14 | ||
15 | #include <boost/hana/at.hpp> | |
16 | #include <boost/hana/concat.hpp> | |
17 | #include <boost/hana/concept/monad_plus.hpp> | |
18 | #include <boost/hana/concept/sequence.hpp> | |
19 | #include <boost/hana/config.hpp> | |
20 | #include <boost/hana/core/dispatch.hpp> | |
21 | #include <boost/hana/core/make.hpp> | |
22 | #include <boost/hana/length.hpp> | |
23 | #include <boost/hana/lift.hpp> | |
24 | ||
25 | #include <cstddef> | |
26 | #include <utility> | |
27 | ||
28 | ||
29 | BOOST_HANA_NAMESPACE_BEGIN | |
30 | //! @cond | |
31 | template <typename Xs, typename X> | |
32 | constexpr auto append_t::operator()(Xs&& xs, X&& x) const { | |
33 | using M = typename hana::tag_of<Xs>::type; | |
34 | using Append = BOOST_HANA_DISPATCH_IF(append_impl<M>, | |
35 | hana::MonadPlus<M>::value | |
36 | ); | |
37 | ||
38 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
39 | static_assert(hana::MonadPlus<M>::value, | |
40 | "hana::append(xs, x) requires 'xs' to be a MonadPlus"); | |
41 | #endif | |
42 | ||
43 | return Append::apply(static_cast<Xs&&>(xs), static_cast<X&&>(x)); | |
44 | } | |
45 | //! @endcond | |
46 | ||
47 | template <typename M, bool condition> | |
48 | struct append_impl<M, when<condition>> : default_ { | |
49 | template <typename Xs, typename X> | |
50 | static constexpr auto apply(Xs&& xs, X&& x) { | |
51 | return hana::concat(static_cast<Xs&&>(xs), | |
52 | hana::lift<M>(static_cast<X&&>(x))); | |
53 | } | |
54 | }; | |
55 | ||
56 | template <typename S> | |
57 | struct append_impl<S, when<Sequence<S>::value>> { | |
58 | template <typename Xs, typename X, std::size_t ...i> | |
59 | static constexpr auto append_helper(Xs&& xs, X&& x, std::index_sequence<i...>) { | |
60 | return hana::make<S>( | |
61 | hana::at_c<i>(static_cast<Xs&&>(xs))..., static_cast<X&&>(x) | |
62 | ); | |
63 | } | |
64 | ||
65 | template <typename Xs, typename X> | |
66 | static constexpr auto apply(Xs&& xs, X&& x) { | |
67 | constexpr std::size_t N = decltype(hana::length(xs))::value; | |
68 | return append_helper(static_cast<Xs&&>(xs), static_cast<X&&>(x), | |
69 | std::make_index_sequence<N>{}); | |
70 | } | |
71 | }; | |
72 | BOOST_HANA_NAMESPACE_END | |
73 | ||
74 | #endif // !BOOST_HANA_APPEND_HPP |