ceph/src/boost/boost/pfr/detail/make_flat_tuple_of_references.hpp

   1 // Copyright (c) 2016-2020 Antony Polukhin
   2 //
   3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   5
   6 #ifndef BOOST_PFR_DETAIL_MAKE_FLAT_TUPLE_OF_REFERENCES_HPP
   7 #define BOOST_PFR_DETAIL_MAKE_FLAT_TUPLE_OF_REFERENCES_HPP
   8 #pragma once
   9
  10 #include <boost/pfr/detail/config.hpp>
  11
  12 #include <utility>      // metaprogramming stuff
  13 #include <boost/pfr/detail/sequence_tuple.hpp>
  14 #include <boost/pfr/detail/rvalue_t.hpp>
  15 #include <boost/pfr/detail/make_integer_sequence.hpp>
  16
  17
  18 namespace boost { namespace pfr { namespace detail {
  19
  20 template <std::size_t Index>
  21 using size_t_ = std::integral_constant<std::size_t, Index >;
  22
  23 // Helper: Make a "getter" object corresponding to built-in tuple::get
  24 // For user-defined structures, the getter should be "offset_based_getter"
  25 struct sequence_tuple_getter {
  26   template <std::size_t idx, typename TupleOfReferences>
  27   decltype(auto) get(TupleOfReferences&& t, size_t_<idx>) const noexcept {
  28     return sequence_tuple::get<idx>(std::forward<TupleOfReferences>(t));
  29   }
  30 };
  31
  32
  33 template <class TupleOrUserType, class Getter, std::size_t Begin, std::size_t Size>
  34 constexpr auto make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<Size>) noexcept;
  35
  36 template <class TupleOrUserType, class Getter, std::size_t Begin>
  37 constexpr sequence_tuple::tuple<> make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<0>) noexcept;
  38
  39 template <class TupleOrUserType, class Getter, std::size_t Begin>
  40 constexpr auto make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<1>) noexcept;
  41
  42 template <class... T>
  43 constexpr auto tie_as_tuple_with_references(T&... args) noexcept {
  44     return sequence_tuple::tuple<T&...>{ args... };
  45 }
  46
  47 template <class... T>
  48 constexpr decltype(auto) tie_as_tuple_with_references(detail::sequence_tuple::tuple<T...>& t) noexcept {
  49     return detail::make_flat_tuple_of_references(t, sequence_tuple_getter{}, size_t_<0>{}, size_t_<sequence_tuple::tuple<T...>::size_v>{});
  50 }
  51
  52 template <class... T>
  53 constexpr decltype(auto) tie_as_tuple_with_references(const detail::sequence_tuple::tuple<T...>& t) noexcept {
  54     return detail::make_flat_tuple_of_references(t, sequence_tuple_getter{}, size_t_<0>{}, size_t_<sequence_tuple::tuple<T...>::size_v>{});
  55 }
  56
  57 template <class Tuple1, std::size_t... I1, class Tuple2, std::size_t... I2>
  58 constexpr auto my_tuple_cat_impl(const Tuple1& t1, std::index_sequence<I1...>, const Tuple2& t2, std::index_sequence<I2...>) noexcept {
  59     return detail::tie_as_tuple_with_references(
  60         sequence_tuple::get<I1>(t1)...,
  61         sequence_tuple::get<I2>(t2)...
  62     );
  63 }
  64
  65 template <class Tuple1, class Tuple2>
  66 constexpr auto my_tuple_cat(const Tuple1& t1, const Tuple2& t2) noexcept {
  67     return detail::my_tuple_cat_impl(
  68         t1, detail::make_index_sequence< Tuple1::size_v >{},
  69         t2, detail::make_index_sequence< Tuple2::size_v >{}
  70     );
  71 }
  72
  73 template <class TupleOrUserType, class Getter, std::size_t Begin, std::size_t Size>
  74 constexpr auto make_flat_tuple_of_references(TupleOrUserType& t, const Getter& g, size_t_<Begin>, size_t_<Size>) noexcept {
  75     constexpr std::size_t next_size = Size / 2;
  76     return detail::my_tuple_cat(
  77         detail::make_flat_tuple_of_references(t, g, size_t_<Begin>{}, size_t_<next_size>{}),
  78         detail::make_flat_tuple_of_references(t, g, size_t_<Begin + Size / 2>{}, size_t_<Size - next_size>{})
  79     );
  80 }
  81
  82 template <class TupleOrUserType, class Getter, std::size_t Begin>
  83 constexpr sequence_tuple::tuple<> make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<0>) noexcept {
  84     return {};
  85 }
  86
  87 template <class TupleOrUserType, class Getter, std::size_t Begin>
  88 constexpr auto make_flat_tuple_of_references(TupleOrUserType& t, const Getter& g, size_t_<Begin>, size_t_<1>) noexcept {
  89     return detail::tie_as_tuple_with_references(
  90         g.get(t, size_t_<Begin>{})
  91     );
  92 }
  93
  94 }}} // namespace boost::pfr::detail
  95
  96 #endif // BOOST_PFR_DETAIL_MAKE_FLAT_TUPLE_OF_REFERENCES_HPP