ceph/src/boost/boost/hana/detail/index_if.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::detail::index_if`.
   4
   5 @copyright Louis Dionne 2013-2017
   6 @copyright Jason Rice 2017
   7 Distributed under the Boost Software License, Version 1.0.
   8 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   9  */
  10
  11 #ifndef BOOST_HANA_DETAIL_INDEX_IF_HPP
  12 #define BOOST_HANA_DETAIL_INDEX_IF_HPP
  13
  14 #include <boost/hana/config.hpp>
  15 #include <boost/hana/detail/decay.hpp>
  16 #include <boost/hana/integral_constant.hpp>
  17 #include <boost/hana/optional.hpp>
  18
  19 #include <cstddef>
  20 #include <utility>
  21
  22
  23 BOOST_HANA_NAMESPACE_BEGIN namespace detail {
  24     template <std::size_t i, std::size_t N, bool Done>
  25     struct index_if_helper;
  26
  27     template <std::size_t i, std::size_t N>
  28     struct index_if_helper<i, N, false> {
  29         template <typename Pred, typename X1, typename ...Xs>
  30         using f = typename index_if_helper<i + 1, N,
  31             static_cast<bool>(detail::decay<decltype(
  32                 std::declval<Pred>()(std::declval<X1>()))>::type::value)
  33         >::template f<Pred, Xs...>;
  34     };
  35
  36     template <std::size_t N>
  37     struct index_if_helper<N, N, false> {
  38         template <typename ...>
  39         using f = hana::optional<>;
  40     };
  41
  42     template <std::size_t i, std::size_t N>
  43     struct index_if_helper<i, N, true> {
  44         template <typename ...>
  45         using f = hana::optional<hana::size_t<i - 1>>;
  46     };
  47
  48     template <typename Pred, typename ...Xs>
  49     struct index_if {
  50         using type = typename index_if_helper<0, sizeof...(Xs), false>
  51             ::template f<Pred, Xs...>;
  52     };
  53 } BOOST_HANA_NAMESPACE_END
  54
  55 #endif // !BOOST_HANA_DETAIL_INDEX_IF_HPP