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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::flatten`. | |
4 | ||
b32b8144 | 5 | @copyright Louis Dionne 2013-2017 |
7c673cae FG |
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_FLATTEN_HPP | |
11 | #define BOOST_HANA_FLATTEN_HPP | |
12 | ||
13 | #include <boost/hana/fwd/flatten.hpp> | |
14 | ||
15 | #include <boost/hana/concept/monad.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/detail/unpack_flatten.hpp> | |
21 | #include <boost/hana/functional/id.hpp> | |
22 | #include <boost/hana/fwd/chain.hpp> | |
23 | ||
24 | #include <cstddef> | |
25 | #include <utility> | |
26 | ||
27 | ||
28 | BOOST_HANA_NAMESPACE_BEGIN | |
29 | //! @cond | |
30 | template <typename Xs> | |
31 | constexpr auto flatten_t::operator()(Xs&& xs) const { | |
32 | using M = typename hana::tag_of<Xs>::type; | |
33 | using Flatten = BOOST_HANA_DISPATCH_IF(flatten_impl<M>, | |
34 | hana::Monad<M>::value | |
35 | ); | |
36 | ||
37 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
38 | static_assert(hana::Monad<M>::value, | |
39 | "hana::flatten(xs) requires 'xs' to be a Monad"); | |
40 | #endif | |
41 | ||
42 | return Flatten::apply(static_cast<Xs&&>(xs)); | |
43 | } | |
44 | //! @endcond | |
45 | ||
46 | template <typename M, bool condition> | |
47 | struct flatten_impl<M, when<condition>> : default_ { | |
48 | template <typename Xs> | |
49 | static constexpr auto apply(Xs&& xs) | |
50 | { return hana::chain(static_cast<Xs&&>(xs), hana::id); } | |
51 | }; | |
52 | ||
53 | template <typename S> | |
54 | struct flatten_impl<S, when<Sequence<S>::value>> { | |
55 | template <typename Xs> | |
56 | static constexpr auto apply(Xs&& xs) { | |
57 | return detail::unpack_flatten(static_cast<Xs&&>(xs), hana::make<S>); | |
58 | } | |
59 | }; | |
60 | BOOST_HANA_NAMESPACE_END | |
61 | ||
62 | #endif // !BOOST_HANA_FLATTEN_HPP |