projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Defines `boost::hana::at` and `boost::hana::at_c`. | |
| 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_AT_HPP | |
| 11 | #define BOOST_HANA_AT_HPP | |
| 12 | ||
| 13 | #include <boost/hana/fwd/at.hpp> | |
| 14 | ||
| 15 | #include <boost/hana/concept/integral_constant.hpp> | |
| 16 | #include <boost/hana/concept/iterable.hpp> | |
| 17 | #include <boost/hana/config.hpp> | |
| 18 | #include <boost/hana/core/dispatch.hpp> | |
| 19 | #include <boost/hana/integral_constant.hpp> | |
| 20 | ||
| 21 | #include <cstddef> | |
| 22 | ||
| 23 | ||
| 24 | BOOST_HANA_NAMESPACE_BEGIN | |
| 25 | //! @cond | |
| 26 | template <typename Xs, typename N> | |
| 27 | constexpr decltype(auto) at_t::operator()(Xs&& xs, N const& n) const { | |
| 28 | using It = typename hana::tag_of<Xs>::type; | |
| 29 | using At = BOOST_HANA_DISPATCH_IF(at_impl<It>, | |
| 30 | hana::Iterable<It>::value | |
| 31 | ); | |
| 32 | ||
| 33 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
| 34 | static_assert(hana::Iterable<It>::value, | |
| 35 | "hana::at(xs, n) requires 'xs' to be an Iterable"); | |
| 36 | ||
| 37 | static_assert(hana::IntegralConstant<N>::value, | |
| 38 | "hana::at(xs, n) requires 'n' to be an IntegralConstant"); | |
| 39 | #endif | |
| 40 | ||
| 41 | return At::apply(static_cast<Xs&&>(xs), n); | |
| 42 | } | |
| 43 | //! @endcond | |
| 44 | ||
| 45 | template <typename It, bool condition> | |
| 46 | struct at_impl<It, when<condition>> : default_ { | |
| 47 | template <typename ...Args> | |
| 48 | static constexpr auto apply(Args&& ...) = delete; | |
| 49 | }; | |
| 50 | ||
| 51 | template <std::size_t n, typename Xs> | |
| 52 | constexpr decltype(auto) at_c(Xs&& xs) { | |
| 53 | return hana::at(static_cast<Xs&&>(xs), hana::size_t<n>{}); | |
| 54 | } | |
| 55 | BOOST_HANA_NAMESPACE_END | |
| 56 | ||
| 57 | #endif // !BOOST_HANA_AT_HPP |