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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::count_if`. | |
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_COUNT_IF_HPP | |
11 | #define BOOST_HANA_COUNT_IF_HPP | |
12 | ||
13 | #include <boost/hana/fwd/count_if.hpp> | |
14 | ||
15 | #include <boost/hana/concept/foldable.hpp> | |
16 | #include <boost/hana/config.hpp> | |
17 | #include <boost/hana/core/dispatch.hpp> | |
18 | #include <boost/hana/detail/algorithm.hpp> | |
19 | #include <boost/hana/detail/fast_and.hpp> | |
20 | #include <boost/hana/integral_constant.hpp> | |
21 | #include <boost/hana/unpack.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 Pred> | |
31 | constexpr auto count_if_t::operator()(Xs&& xs, Pred&& pred) const { | |
32 | using S = typename hana::tag_of<Xs>::type; | |
33 | using CountIf = BOOST_HANA_DISPATCH_IF(count_if_impl<S>, | |
34 | hana::Foldable<S>::value | |
35 | ); | |
36 | ||
37 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
38 | static_assert(hana::Foldable<S>::value, | |
39 | "hana::count_if(xs, pred) requires 'xs' to be Foldable"); | |
40 | #endif | |
41 | ||
42 | return CountIf::apply(static_cast<Xs&&>(xs), | |
43 | static_cast<Pred&&>(pred)); | |
44 | } | |
45 | //! @endcond | |
46 | ||
47 | namespace detail { | |
48 | template <typename Pred> | |
49 | struct count_pred { | |
50 | Pred pred; | |
51 | template <typename ...Xs, typename = typename std::enable_if< | |
52 | detail::fast_and< | |
53 | Constant<decltype((*pred)(std::declval<Xs&&>()))>::value... | |
54 | >::value | |
55 | >::type> | |
56 | constexpr auto operator()(Xs&& ...xs) const { | |
57 | constexpr bool results[] = {false, // <-- avoid empty array | |
58 | static_cast<bool>(hana::value<decltype((*pred)(static_cast<Xs&&>(xs)))>())... | |
59 | }; | |
60 | constexpr std::size_t total = detail::count( | |
61 | results, results + sizeof(results), true | |
62 | ); | |
63 | return hana::size_c<total>; | |
64 | } | |
65 | ||
66 | template <typename ...Xs, typename = void, typename = typename std::enable_if< | |
67 | !detail::fast_and< | |
68 | Constant<decltype((*pred)(std::declval<Xs&&>()))>::value... | |
69 | >::value | |
70 | >::type> | |
71 | constexpr auto operator()(Xs&& ...xs) const { | |
72 | std::size_t total = 0; | |
73 | using Swallow = std::size_t[]; | |
74 | (void)Swallow{0, ((*pred)(static_cast<Xs&&>(xs)) ? ++total : 0)...}; | |
75 | return total; | |
76 | } | |
77 | }; | |
78 | } | |
79 | ||
80 | template <typename T, bool condition> | |
81 | struct count_if_impl<T, when<condition>> : default_ { | |
82 | template <typename Xs, typename Pred> | |
83 | static constexpr decltype(auto) apply(Xs&& xs, Pred&& pred) { | |
84 | // We use a pointer instead of a reference to avoid a Clang ICE. | |
85 | return hana::unpack(static_cast<Xs&&>(xs), | |
86 | detail::count_pred<decltype(&pred)>{&pred} | |
87 | ); | |
88 | } | |
89 | }; | |
90 | BOOST_HANA_NAMESPACE_END | |
91 | ||
92 | #endif // !BOOST_HANA_COUNT_IF_HPP |