projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | // Copyright Louis Dionne 2013-2016 |
| 2 | // Distributed under the Boost Software License, Version 1.0. | |
| 3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
| 4 | ||
| 5 | #include <boost/hana/assert.hpp> | |
| 6 | #include <boost/hana/at.hpp> | |
| 7 | #include <boost/hana/core/make.hpp> | |
| 8 | #include <boost/hana/core/tag_of.hpp> | |
| 9 | #include <boost/hana/drop_front.hpp> | |
| 10 | #include <boost/hana/is_empty.hpp> | |
| 11 | #include <boost/hana/not.hpp> | |
| 12 | #include <boost/hana/tuple.hpp> | |
| 13 | ||
| 14 | #include <cstddef> | |
| 15 | namespace hana = boost::hana; | |
| 16 | ||
| 17 | ||
| 18 | struct RefTuple { }; | |
| 19 | ||
| 20 | template <typename ...T> | |
| 21 | struct ref_tuple { | |
| 22 | hana::tuple<T&...> storage_; | |
| 23 | }; | |
| 24 | ||
| 25 | ||
| 26 | namespace boost { namespace hana { | |
| 27 | template <typename ...T> | |
| 28 | struct tag_of<ref_tuple<T...>> { | |
| 29 | using type = RefTuple; | |
| 30 | }; | |
| 31 | ||
| 32 | template <> | |
| 33 | struct make_impl<RefTuple> { | |
| 34 | template <typename ...T> | |
| 35 | static constexpr auto apply(T&& ...t) { | |
| 36 | return ref_tuple<T...>{{t...}}; | |
| 37 | } | |
| 38 | }; | |
| 39 | ||
| 40 | template <> | |
| 41 | struct at_impl<RefTuple> { | |
| 42 | template <typename Xs, typename N> | |
| 43 | static constexpr decltype(auto) apply(Xs&& xs, N const& n) { | |
| 44 | return hana::at(static_cast<Xs&&>(xs).storage_, n); | |
| 45 | } | |
| 46 | }; | |
| 47 | ||
| 48 | template <> | |
| 49 | struct is_empty_impl<RefTuple> { | |
| 50 | template <typename Xs> | |
| 51 | static constexpr auto apply(Xs const& xs) { | |
| 52 | return hana::is_empty(xs.storage_); | |
| 53 | } | |
| 54 | }; | |
| 55 | ||
| 56 | template <> | |
| 57 | struct drop_front_impl<RefTuple> { | |
| 58 | template <std::size_t n, typename T, typename ...U, std::size_t ...i> | |
| 59 | static constexpr auto helper(ref_tuple<T, U...> xs, std::index_sequence<i...>) { | |
| 60 | return hana::make<RefTuple>(hana::at_c<n + i>(xs.storage_)...); | |
| 61 | } | |
| 62 | ||
| 63 | template <typename ...T, typename N> | |
| 64 | static constexpr auto apply(ref_tuple<T...> xs, N const&) { | |
| 65 | return helper<N::value>(xs, std::make_index_sequence<( | |
| 66 | N::value < sizeof...(T) ? sizeof...(T) - N::value : 0 | |
| 67 | )>{}); | |
| 68 | } | |
| 69 | }; | |
| 70 | }} | |
| 71 | ||
| 72 | ||
| 73 | int main() { | |
| 74 | int i = 0, j = 1, k = 2; | |
| 75 | ||
| 76 | auto refs = hana::make<RefTuple>(i, j, k); | |
| 77 | hana::at_c<0>(refs) = 3; | |
| 78 | BOOST_HANA_RUNTIME_CHECK(i == 3); | |
| 79 | ||
| 80 | BOOST_HANA_CONSTANT_CHECK(hana::not_(hana::is_empty(refs))); | |
| 81 | ||
| 82 | ref_tuple<int&, int&> tail = hana::drop_front(refs); | |
| 83 | hana::at_c<0>(tail) = 4; | |
| 84 | BOOST_HANA_RUNTIME_CHECK(j == 4); | |
| 85 | } |