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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::reverse`. | |
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_REVERSE_HPP | |
11 | #define BOOST_HANA_REVERSE_HPP | |
12 | ||
13 | #include <boost/hana/fwd/reverse.hpp> | |
14 | ||
15 | #include <boost/hana/at.hpp> | |
16 | #include <boost/hana/concept/sequence.hpp> | |
17 | #include <boost/hana/config.hpp> | |
18 | #include <boost/hana/core/dispatch.hpp> | |
19 | #include <boost/hana/core/make.hpp> | |
20 | #include <boost/hana/length.hpp> | |
21 | ||
22 | #include <cstddef> | |
23 | #include <utility> | |
24 | ||
25 | ||
26 | BOOST_HANA_NAMESPACE_BEGIN | |
27 | //! @cond | |
28 | template <typename Xs> | |
29 | constexpr auto reverse_t::operator()(Xs&& xs) const { | |
30 | using S = typename hana::tag_of<Xs>::type; | |
31 | using Reverse = BOOST_HANA_DISPATCH_IF(reverse_impl<S>, | |
32 | hana::Sequence<S>::value | |
33 | ); | |
34 | ||
35 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
36 | static_assert(hana::Sequence<S>::value, | |
37 | "hana::reverse(xs) requires 'xs' to be a Sequence"); | |
38 | #endif | |
39 | ||
40 | return Reverse::apply(static_cast<Xs&&>(xs)); | |
41 | } | |
42 | //! @endcond | |
43 | ||
44 | template <typename S, bool condition> | |
45 | struct reverse_impl<S, when<condition>> : default_ { | |
46 | template <typename Xs, std::size_t ...i> | |
47 | static constexpr auto reverse_helper(Xs&& xs, std::index_sequence<i...>) { | |
48 | return hana::make<S>( | |
49 | hana::at_c<sizeof...(i) - i - 1>(static_cast<Xs&&>(xs))... | |
50 | ); | |
51 | } | |
52 | ||
53 | template <typename Xs> | |
54 | static constexpr auto apply(Xs&& xs) { | |
55 | constexpr std::size_t N = decltype(hana::length(xs))::value; | |
56 | return reverse_helper(static_cast<Xs&&>(xs), std::make_index_sequence<N>{}); | |
57 | } | |
58 | }; | |
59 | BOOST_HANA_NAMESPACE_END | |
60 | ||
61 | #endif // !BOOST_HANA_REVERSE_HPP |