ceph/src/boost/libs/hana/include/boost/hana/detail/variadic/drop_into.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::detail::variadic::drop_into`.
   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_VARIADIC_DROP_INTO_HPP
  11 #define BOOST_HANA_DETAIL_VARIADIC_DROP_INTO_HPP
  12
  13 #include <boost/hana/config.hpp>
  14
  15 #include <cstddef>
  16 #include <utility>
  17
  18
  19 BOOST_HANA_NAMESPACE_BEGIN namespace detail { namespace variadic {
  20     template <std::size_t n, typename F, typename = std::make_index_sequence<n>>
  21     struct dropper;
  22
  23     template <std::size_t n, typename F, std::size_t ...ignore>
  24     struct dropper<n, F, std::index_sequence<ignore...>> {
  25         F f;
  26
  27         template <typename ...Rest>
  28         constexpr auto go(decltype(ignore, (void*)0)..., Rest ...rest) const
  29         { return f(*rest...); }
  30
  31         template <typename ...Xs>
  32         constexpr auto operator()(Xs ...xs) const
  33         { return go(&xs...); }
  34     };
  35
  36     template <std::size_t n>
  37     struct make_dropper {
  38         template <typename F>
  39         constexpr auto operator()(F f) const
  40         { return dropper<n, decltype(f)>{f}; }
  41     };
  42
  43     template <std::size_t n>
  44     constexpr make_dropper<n> drop_into{};
  45 }} BOOST_HANA_NAMESPACE_END
  46
  47 #endif // !BOOST_HANA_DETAIL_VARIADIC_DROP_INTO_HPP