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

   1 /*!
   2 @file
   3 Defines `boost::hana::detail::variadic::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_VARIADIC_AT_HPP
  11 #define BOOST_HANA_DETAIL_VARIADIC_AT_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 = std::make_index_sequence<n>>
  21     struct at_type;
  22
  23     template <std::size_t n, std::size_t ...ignore>
  24     struct at_type<n, std::index_sequence<ignore...>> {
  25     private:
  26         template <typename Nth>
  27         static constexpr auto go(decltype(ignore, (void*)0)..., Nth nth, ...)
  28         { return nth; }
  29
  30     public:
  31         template <typename ...Xs>
  32         constexpr auto operator()(Xs ...xs) const
  33         { return *go(&xs...); }
  34     };
  35
  36     template <std::size_t n>
  37     constexpr at_type<n> at{};
  38 }} BOOST_HANA_NAMESPACE_END
  39
  40 #endif // !BOOST_HANA_DETAIL_VARIADIC_AT_HPP