projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Defines `boost::hana::detail::type_at`. | |
| 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_DETAIL_TYPE_AT_HPP | |
| 11 | #define BOOST_HANA_DETAIL_TYPE_AT_HPP | |
| 12 | ||
| 13 | #include <boost/hana/config.hpp> | |
| 14 | ||
| 15 | #include <cstddef> | |
| 16 | #include <utility> | |
| 17 | ||
| 18 | ||
| 19 | // If possible, use an intrinsic provided by Clang | |
| 20 | #if defined(__has_builtin) | |
| 21 | # if __has_builtin(__type_pack_element) | |
| 22 | # define BOOST_HANA_USE_TYPE_PACK_ELEMENT_INTRINSIC | |
| 23 | # endif | |
| 24 | #endif | |
| 25 | ||
| 26 | BOOST_HANA_NAMESPACE_BEGIN namespace detail { | |
| 27 | namespace td { | |
| 28 | template <std::size_t I, typename T> | |
| 29 | struct elt { using type = T; }; | |
| 30 | ||
| 31 | template <typename Indices, typename ...T> | |
| 32 | struct indexer; | |
| 33 | ||
| 34 | template <std::size_t ...I, typename ...T> | |
| 35 | struct indexer<std::index_sequence<I...>, T...> | |
| 36 | : elt<I, T>... | |
| 37 | { }; | |
| 38 | ||
| 39 | template <std::size_t I, typename T> | |
| 40 | elt<I, T> get_elt(elt<I, T> const&); | |
| 41 | } | |
| 42 | ||
| 43 | //! @ingroup group-details | |
| 44 | //! Classic MPL-style metafunction returning the nth element of a type | |
| 45 | //! parameter pack. | |
| 46 | template <std::size_t n, typename ...T> | |
| 47 | struct type_at { | |
| 48 | #if defined(BOOST_HANA_USE_TYPE_PACK_ELEMENT_INTRINSIC) | |
| 49 | using type = __type_pack_element<n, T...>; | |
| 50 | #else | |
| 51 | using Indexer = td::indexer<std::make_index_sequence<sizeof...(T)>, T...>; | |
| 52 | using type = typename decltype(td::get_elt<n>(Indexer{}))::type; | |
| 53 | #endif | |
| 54 | }; | |
| 55 | } BOOST_HANA_NAMESPACE_END | |
| 56 | ||
| 57 | #endif // !BOOST_HANA_DETAIL_TYPE_AT_HPP |