ceph/src/boost/boost/pfr/detail/core17.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
   7 #ifndef BOOST_PFR_DETAIL_CORE17_HPP
   8 #define BOOST_PFR_DETAIL_CORE17_HPP
   9
  10 #include <boost/pfr/detail/core17_generated.hpp>
  11 #include <boost/pfr/detail/fields_count.hpp>
  12 #include <boost/pfr/detail/for_each_field_impl.hpp>
  13 #include <boost/pfr/detail/rvalue_t.hpp>
  14
  15 namespace boost { namespace pfr { namespace detail {
  16
  17 #ifndef _MSC_VER // MSVC fails to compile the following code, but compiles the structured bindings in core17_generated.hpp
  18 struct do_not_define_std_tuple_size_for_me {
  19     bool test1 = true;
  20 };
  21
  22 template <class T>
  23 constexpr bool do_structured_bindings_work() noexcept { // ******************************************* IN CASE OF ERROR READ THE FOLLOWING LINES IN boost/pfr/detail/core17.hpp FILE:
  24     T val{};
  25     const auto& [a] = val; // ******************************************* IN CASE OF ERROR READ THE FOLLOWING LINES IN boost/pfr/detail/core17.hpp FILE:
  26
  27     /****************************************************************************
  28     *
  29     * It looks like your compiler or Standard Library can not handle C++17
  30     * structured bindings.
  31     *
  32     * Workaround: Define BOOST_PFR_USE_CPP17 to 0
  33     * It will disable the C++17 features for Boost.PFR library.
  34     *
  35     * Sorry for the inconvenience caused.
  36     *
  37     ****************************************************************************/
  38
  39     return a;
  40 }
  41
  42 static_assert(
  43     do_structured_bindings_work<do_not_define_std_tuple_size_for_me>(),
  44     "====================> Boost.PFR: Your compiler can not handle C++17 structured bindings. Read the above comments for workarounds."
  45 );
  46 #endif // #ifndef _MSC_VER
  47
  48 template <class T>
  49 constexpr auto tie_as_tuple(T& val) noexcept {
  50   static_assert(
  51     !std::is_union<T>::value,
  52     "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
  53   );
  54   typedef size_t_<boost::pfr::detail::fields_count<T>()> fields_count_tag;
  55   return boost::pfr::detail::tie_as_tuple(val, fields_count_tag{});
  56 }
  57
  58 template <class T, class F, std::size_t... I>
  59 void for_each_field_dispatcher(T& t, F&& f, std::index_sequence<I...>) {
  60     static_assert(
  61         !std::is_union<T>::value,
  62         "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
  63     );
  64     std::forward<F>(f)(
  65         detail::tie_as_tuple(t)
  66     );
  67 }
  68
  69 }}} // namespace boost::pfr::detail
  70
  71 #endif // BOOST_PFR_DETAIL_CORE17_HPP