// Copyright (c) 2016-2020 Antony Polukhin
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_PFR_DETAIL_FIELDS_COUNT_HPP
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#define BOOST_PFR_DETAIL_FIELDS_COUNT_HPP
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#pragma once
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#include <boost/pfr/detail/config.hpp>
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#include <boost/pfr/detail/make_integer_sequence.hpp>
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#include <boost/pfr/detail/size_t_.hpp>
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#include <boost/pfr/detail/unsafe_declval.hpp>
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#include <climits> // CHAR_BIT
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#include <type_traits>
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#include <utility> // metaprogramming stuff
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#ifdef __clang__
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# pragma clang diagnostic push
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# pragma clang diagnostic ignored "-Wmissing-braces"
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# pragma clang diagnostic ignored "-Wundefined-inline"
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# pragma clang diagnostic ignored "-Wundefined-internal"
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# pragma clang diagnostic ignored "-Wmissing-field-initializers"
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#endif
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namespace boost { namespace pfr { namespace detail {
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///////////////////// Structure that can be converted to reference to anything
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struct ubiq_lref_constructor {
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std::size_t ignore;
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template <class Type> constexpr operator Type&() const && noexcept { // Allows initialization of reference fields (T& and const T&)
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return detail::unsafe_declval<Type&>();
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};
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};
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///////////////////// Structure that can be converted to rvalue reference to anything
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struct ubiq_rref_constructor {
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std::size_t ignore;
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template <class Type> /*constexpr*/ operator Type&&() const && noexcept { // Allows initialization of rvalue reference fields and move-only types
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return detail::unsafe_declval<Type&&>();
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};
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};
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#ifndef __cpp_lib_is_aggregate
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///////////////////// Hand-made is_aggregate_initializable_n<T> trait
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// Structure that can be converted to reference to anything except reference to T
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template <class T, bool IsCopyConstructible>
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struct ubiq_constructor_except {
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std::size_t ignore;
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template <class Type> constexpr operator std::enable_if_t<!std::is_same<T, Type>::value, Type&> () const noexcept; // Undefined
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};
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template <class T>
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struct ubiq_constructor_except<T, false> {
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std::size_t ignore;
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template <class Type> constexpr operator std::enable_if_t<!std::is_same<T, Type>::value, Type&&> () const noexcept; // Undefined
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};
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// `std::is_constructible<T, ubiq_constructor_except<T>>` consumes a lot of time, so we made a separate lazy trait for it.
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template <std::size_t N, class T> struct is_single_field_and_aggregate_initializable: std::false_type {};
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template <class T> struct is_single_field_and_aggregate_initializable<1, T>: std::integral_constant<
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bool, !std::is_constructible<T, ubiq_constructor_except<T, std::is_copy_constructible<T>::value>>::value
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> {};
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// Hand-made is_aggregate<T> trait:
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// Before C++20 aggregates could be constructed from `decltype(ubiq_?ref_constructor{I})...` but type traits report that
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// there's no constructor from `decltype(ubiq_?ref_constructor{I})...`
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// Special case for N == 1: `std::is_constructible<T, ubiq_?ref_constructor>` returns true if N == 1 and T is copy/move constructible.
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template <class T, std::size_t N>
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struct is_aggregate_initializable_n {
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template <std::size_t ...I>
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static constexpr bool is_not_constructible_n(std::index_sequence<I...>) noexcept {
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return (!std::is_constructible<T, decltype(ubiq_lref_constructor{I})...>::value && !std::is_constructible<T, decltype(ubiq_rref_constructor{I})...>::value)
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|| is_single_field_and_aggregate_initializable<N, T>::value
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;
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}
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static constexpr bool value =
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std::is_empty<T>::value
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|| std::is_array<T>::value
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|| std::is_fundamental<T>::value
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|| is_not_constructible_n(detail::make_index_sequence<N>{})
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;
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};
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#endif // #ifndef __cpp_lib_is_aggregate
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///////////////////// Helper for SFINAE on fields count
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template <class T, std::size_t... I, class /*Enable*/ = typename std::enable_if<std::is_copy_constructible<T>::value>::type>
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constexpr auto enable_if_constructible_helper(std::index_sequence<I...>) noexcept
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-> typename std::add_pointer<decltype(T{ ubiq_lref_constructor{I}... })>::type;
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template <class T, std::size_t... I, class /*Enable*/ = typename std::enable_if<!std::is_copy_constructible<T>::value>::type>
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constexpr auto enable_if_constructible_helper(std::index_sequence<I...>) noexcept
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-> typename std::add_pointer<decltype(T{ ubiq_rref_constructor{I}... })>::type;
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template <class T, std::size_t N, class /*Enable*/ = decltype( enable_if_constructible_helper<T>(detail::make_index_sequence<N>()) ) >
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using enable_if_constructible_helper_t = std::size_t;
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///////////////////// Helpers for range size detection
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template <std::size_t Begin, std::size_t Last>
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using is_one_element_range = std::integral_constant<bool, Begin == Last>;
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using multi_element_range = std::false_type;
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using one_element_range = std::true_type;
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///////////////////// Non greedy fields count search. Templates instantiation depth is log(sizeof(T)), templates instantiation count is log(sizeof(T)).
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template <class T, std::size_t Begin, std::size_t Middle>
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constexpr std::size_t detect_fields_count(detail::one_element_range, long) noexcept {
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static_assert(
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Begin == Middle,
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"====================> Boost.PFR: Internal logic error."
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);
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return Begin;
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}
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template <class T, std::size_t Begin, std::size_t Middle>
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constexpr std::size_t detect_fields_count(detail::multi_element_range, int) noexcept;
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template <class T, std::size_t Begin, std::size_t Middle>
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constexpr auto detect_fields_count(detail::multi_element_range, long) noexcept
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-> detail::enable_if_constructible_helper_t<T, Middle>
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{
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constexpr std::size_t next_v = Middle + (Middle - Begin + 1) / 2;
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return detail::detect_fields_count<T, Middle, next_v>(detail::is_one_element_range<Middle, next_v>{}, 1L);
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}
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template <class T, std::size_t Begin, std::size_t Middle>
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constexpr std::size_t detect_fields_count(detail::multi_element_range, int) noexcept {
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constexpr std::size_t next_v = Begin + (Middle - Begin) / 2;
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return detail::detect_fields_count<T, Begin, next_v>(detail::is_one_element_range<Begin, next_v>{}, 1L);
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}
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///////////////////// Greedy search. Templates instantiation depth is log(sizeof(T)), templates instantiation count is log(sizeof(T))*T in worst case.
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template <class T, std::size_t N>
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constexpr auto detect_fields_count_greedy_remember(long) noexcept
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-> detail::enable_if_constructible_helper_t<T, N>
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{
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return N;
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}
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template <class T, std::size_t N>
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constexpr std::size_t detect_fields_count_greedy_remember(int) noexcept {
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return 0;
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}
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template <class T, std::size_t Begin, std::size_t Last>
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constexpr std::size_t detect_fields_count_greedy(detail::one_element_range) noexcept {
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static_assert(
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Begin == Last,
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"====================> Boost.PFR: Internal logic error."
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);
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return detail::detect_fields_count_greedy_remember<T, Begin>(1L);
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}
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template <class T, std::size_t Begin, std::size_t Last>
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constexpr std::size_t detect_fields_count_greedy(detail::multi_element_range) noexcept {
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constexpr std::size_t middle = Begin + (Last - Begin) / 2;
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constexpr std::size_t fields_count_big_range = detail::detect_fields_count_greedy<T, middle + 1, Last>(
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detail::is_one_element_range<middle + 1, Last>{}
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);
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constexpr std::size_t small_range_begin = (fields_count_big_range ? 0 : Begin);
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constexpr std::size_t small_range_last = (fields_count_big_range ? 0 : middle);
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constexpr std::size_t fields_count_small_range = detail::detect_fields_count_greedy<T, small_range_begin, small_range_last>(
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detail::is_one_element_range<small_range_begin, small_range_last>{}
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);
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return fields_count_big_range ? fields_count_big_range : fields_count_small_range;
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}
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///////////////////// Choosing between array size, greedy and non greedy search.
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template <class T, std::size_t N>
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constexpr auto detect_fields_count_dispatch(size_t_<N>, long, long) noexcept
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-> typename std::enable_if<std::is_array<T>::value, std::size_t>::type
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{
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return sizeof(T) / sizeof(typename std::remove_all_extents<T>::type);
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}
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template <class T, std::size_t N>
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constexpr auto detect_fields_count_dispatch(size_t_<N>, long, int) noexcept
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-> decltype(sizeof(T{}))
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{
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constexpr std::size_t middle = N / 2 + 1;
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return detail::detect_fields_count<T, 0, middle>(detail::multi_element_range{}, 1L);
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}
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template <class T, std::size_t N>
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constexpr std::size_t detect_fields_count_dispatch(size_t_<N>, int, int) noexcept {
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// T is not default aggregate initialzable. It means that at least one of the members is not default constructible,
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// so we have to check all the aggregate initializations for T up to N parameters and return the bigest succeeded
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// (we can not use binary search for detecting fields count).
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return detail::detect_fields_count_greedy<T, 0, N>(detail::multi_element_range{});
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}
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///////////////////// Returns fields count
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template <class T>
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constexpr std::size_t fields_count() noexcept {
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using type = std::remove_cv_t<T>;
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static_assert(
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!std::is_reference<type>::value,
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"====================> Boost.PFR: Attempt to get fields count on a reference. This is not allowed because that could hide an issue and different library users expect different behavior in that case."
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);
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static_assert(
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std::is_copy_constructible<std::remove_all_extents_t<type>>::value || (
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std::is_move_constructible<std::remove_all_extents_t<type>>::value
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&& std::is_move_assignable<std::remove_all_extents_t<type>>::value
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),
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"====================> Boost.PFR: Type and each field in the type must be copy constructible (or move constructible and move assignable)."
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);
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static_assert(
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!std::is_polymorphic<type>::value,
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"====================> Boost.PFR: Type must have no virtual function, because otherwise it is not aggregate initializable."
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);
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#ifdef __cpp_lib_is_aggregate
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static_assert(
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std::is_aggregate<type>::value // Does not return `true` for built-in types.
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|| std::is_scalar<type>::value,
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"====================> Boost.PFR: Type must be aggregate initializable."
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);
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#endif
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// Can't use the following. See the non_std_layout.cpp test.
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//#if !BOOST_PFR_USE_CPP17
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// static_assert(
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// std::is_standard_layout<type>::value, // Does not return `true` for structs that have non standard layout members.
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// "Type must be aggregate initializable."
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// );
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//#endif
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constexpr std::size_t max_fields_count = (sizeof(type) * CHAR_BIT); // We multiply by CHAR_BIT because the type may have bitfields in T
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constexpr std::size_t result = detail::detect_fields_count_dispatch<type>(size_t_<max_fields_count>{}, 1L, 1L);
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#ifndef __cpp_lib_is_aggregate
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static_assert(
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is_aggregate_initializable_n<type, result>::value,
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"====================> Boost.PFR: Types with user specified constructors (non-aggregate initializable types) are not supported."
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);
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#endif
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static_assert(
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result != 0 || std::is_empty<type>::value || std::is_fundamental<type>::value || std::is_reference<type>::value,
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"====================> Boost.PFR: If there's no other failed static asserts then something went wrong. Please report this issue to the github along with the structure you're reflecting."
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);
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return result;
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}
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}}} // namespace boost::pfr::detail
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#ifdef __clang__
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# pragma clang diagnostic pop
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#endif
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#endif // BOOST_PFR_DETAIL_FIELDS_COUNT_HPP
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