projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Defines `boost::hana::while_`. | |
| 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_WHILE_HPP | |
| 11 | #define BOOST_HANA_WHILE_HPP | |
| 12 | ||
| 13 | #include <boost/hana/fwd/while.hpp> | |
| 14 | ||
| 15 | #include <boost/hana/bool.hpp> | |
| 16 | #include <boost/hana/concept/constant.hpp> | |
| 17 | #include <boost/hana/concept/constant.hpp> | |
| 18 | #include <boost/hana/concept/logical.hpp> | |
| 19 | #include <boost/hana/config.hpp> | |
| 20 | #include <boost/hana/core/to.hpp> | |
| 21 | #include <boost/hana/core/dispatch.hpp> | |
| 22 | #include <boost/hana/detail/canonical_constant.hpp> | |
| 23 | ||
| 24 | #include <type_traits> | |
| 25 | ||
| 26 | ||
| 27 | BOOST_HANA_NAMESPACE_BEGIN | |
| 28 | //! @cond | |
| 29 | template <typename Pred, typename State, typename F> | |
| 30 | constexpr decltype(auto) while_t::operator()(Pred&& pred, State&& state, F&& f) const { | |
| 31 | using Cond = decltype(pred(state)); | |
| 32 | using Bool = typename hana::tag_of<Cond>::type; | |
| 33 | using While = BOOST_HANA_DISPATCH_IF(while_impl<Bool>, | |
| 34 | hana::Logical<Bool>::value | |
| 35 | ); | |
| 36 | ||
| 37 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
| 38 | static_assert(hana::Logical<Bool>::value, | |
| 39 | "hana::while_(pred, state, f) requires 'pred(state)' to be a Logical"); | |
| 40 | #endif | |
| 41 | ||
| 42 | return While::apply(static_cast<Pred&&>(pred), | |
| 43 | static_cast<State&&>(state), | |
| 44 | static_cast<F&&>(f)); | |
| 45 | } | |
| 46 | //! @endcond | |
| 47 | ||
| 48 | template <typename L, bool condition> | |
| 49 | struct while_impl<L, hana::when<condition>> : hana::default_ { | |
| 50 | template <typename ...Args> | |
| 51 | static constexpr auto apply(Args&& ...) = delete; | |
| 52 | }; | |
| 53 | ||
| 54 | template <typename L> | |
| 55 | struct while_impl<L, hana::when<std::is_arithmetic<L>::value>> { | |
| 56 | template <typename Pred, typename State, typename F> | |
| 57 | static auto apply(Pred&& pred, State&& state, F&& f) | |
| 58 | -> decltype( | |
| 59 | true ? f(static_cast<State&&>(state)) | |
| 60 | : static_cast<State&&>(state) | |
| 61 | ) | |
| 62 | { | |
| 63 | if (pred(state)) { | |
| 64 | decltype(auto) r = f(static_cast<State&&>(state)); | |
| 65 | return hana::while_(static_cast<Pred&&>(pred), | |
| 66 | static_cast<decltype(r)&&>(r), | |
| 67 | static_cast<F&&>(f)); | |
| 68 | } | |
| 69 | else { | |
| 70 | return static_cast<State&&>(state); | |
| 71 | } | |
| 72 | } | |
| 73 | }; | |
| 74 | ||
| 75 | template <typename C> | |
| 76 | struct while_impl<C, hana::when< | |
| 77 | hana::Constant<C>::value && | |
| 78 | hana::Logical<typename C::value_type>::value | |
| 79 | >> { | |
| 80 | template <typename Pred, typename State, typename F> | |
| 81 | static constexpr State | |
| 82 | while_helper(hana::false_, Pred&&, State&& state, F&&) { | |
| 83 | return static_cast<State&&>(state); | |
| 84 | } | |
| 85 | ||
| 86 | template <typename Pred, typename State, typename F> | |
| 87 | static constexpr decltype(auto) | |
| 88 | while_helper(hana::true_, Pred&& pred, State&& state, F&& f) { | |
| 89 | decltype(auto) r = f(static_cast<State&&>(state)); | |
| 90 | return hana::while_(static_cast<Pred&&>(pred), | |
| 91 | static_cast<decltype(r)&&>(r), | |
| 92 | static_cast<F&&>(f)); | |
| 93 | } | |
| 94 | ||
| 95 | template <typename Pred, typename State, typename F> | |
| 96 | static constexpr decltype(auto) | |
| 97 | apply(Pred&& pred, State&& state, F&& f) { | |
| 98 | // Since `pred(state)` returns a `Constant`, we do not actually | |
| 99 | // need to call it; we only need its decltype. However, we still | |
| 100 | // call it to run potential side effects. I'm not sure whether | |
| 101 | // that is desirable, since we pretty much take for granted that | |
| 102 | // functions are pure, but we'll do it like this for now. Also, I | |
| 103 | // think there is something rather deep hidden behind this, and | |
| 104 | // understanding what must be done here should give us a better | |
| 105 | // understanding of something non-trivial. | |
| 106 | auto cond_ = pred(state); | |
| 107 | constexpr auto cond = hana::value(cond_); | |
| 108 | constexpr bool truth_value = hana::if_(cond, true, false); | |
| 109 | return while_helper(hana::bool_c<truth_value>, | |
| 110 | static_cast<Pred&&>(pred), | |
| 111 | static_cast<State&&>(state), | |
| 112 | static_cast<F&&>(f)); | |
| 113 | } | |
| 114 | }; | |
| 115 | BOOST_HANA_NAMESPACE_END | |
| 116 | ||
| 117 | #endif // !BOOST_HANA_WHILE_HPP |