整理

include/boost/pfr/detail/config.hpp

@@ -0,0 +1,26 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+// Copyright (c) 2022 Denis Mikhailov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_CONFIG_HPP
+#define BOOST_PFR_DETAIL_CONFIG_HPP
+#pragma once
+
+#include <boost/pfr/config.hpp>
+
+#if !BOOST_PFR_ENABLED
+
+#error Boost.PFR library is not supported in your environment.             \
+       Try one of the possible solutions:                                  \
+       1. try to take away an '-DBOOST_PFR_ENABLED=0', if it exists        \
+       2. enable C++14;                                                    \
+       3. enable C++17;                                                    \
+       4. update your compiler;                                            \
+       or disable this error by '-DBOOST_PFR_ENABLED=1' if you really know what are you doing.
+
+#endif // !BOOST_PFR_ENABLED
+
+#endif // BOOST_PFR_DETAIL_CONFIG_HPP
+

include/boost/pfr/detail/core.hpp

@@ -0,0 +1,26 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_CORE_HPP
+#define BOOST_PFR_DETAIL_CORE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+// Each core provides `boost::pfr::detail::tie_as_tuple` and
+// `boost::pfr::detail::for_each_field_dispatcher` functions.
+//
+// The whole PFR library is build on top of those two functions.
+#if BOOST_PFR_USE_CPP26
+#include <boost/pfr/detail/core26.hpp>
+#elif BOOST_PFR_USE_CPP17
+#   include <boost/pfr/detail/core17.hpp>
+#elif BOOST_PFR_USE_LOOPHOLE
+#   include <boost/pfr/detail/core14_loophole.hpp>
+#else
+#   include <boost/pfr/detail/core14_classic.hpp>
+#endif
+
+#endif // BOOST_PFR_DETAIL_CORE_HPP

include/boost/pfr/detail/core14_classic.hpp

@@ -0,0 +1,708 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_CORE14_CLASSIC_HPP
+#define BOOST_PFR_DETAIL_CORE14_CLASSIC_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+#include <boost/pfr/detail/offset_based_getter.hpp>
+#include <boost/pfr/detail/fields_count.hpp>
+#include <boost/pfr/detail/make_flat_tuple_of_references.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+#include <boost/pfr/detail/size_array.hpp>
+#include <boost/pfr/detail/size_t_.hpp>
+#include <boost/pfr/detail/rvalue_t.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <utility>      // metaprogramming stuff
+#endif
+
+#ifdef __clang__
+#   pragma clang diagnostic push
+#   pragma clang diagnostic ignored "-Wmissing-braces"
+#   pragma clang diagnostic ignored "-Wundefined-inline"
+#   pragma clang diagnostic ignored "-Wundefined-internal"
+#   pragma clang diagnostic ignored "-Wmissing-field-initializers"
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+///////////////////// General utility stuff
+
+template <class T> struct identity {
+    typedef T type;
+};
+
+template <class T>
+constexpr T construct_helper() noexcept { // adding const here allows to deal with copyable only types
+    return {};
+}
+
+template <class T> constexpr size_array<sizeof(T) * 3> fields_count_and_type_ids_with_zeros() noexcept;
+template <class T> constexpr auto flat_array_of_type_ids() noexcept;
+
+///////////////////// All the stuff for representing Type as integer and converting integer back to type
+namespace typeid_conversions {
+
+///////////////////// Helper constants and typedefs
+
+#ifdef _MSC_VER
+#   pragma warning( push )
+    // '<<': check operator precedence for possible error; use parentheses to clarify precedence
+#   pragma warning( disable : 4554 )
+#endif
+
+constexpr std::size_t native_types_mask = 31;
+constexpr std::size_t bits_per_extension = 3;
+constexpr std::size_t extension_mask = (
+    static_cast<std::size_t>((1 << bits_per_extension) - 1)
+        << static_cast<std::size_t>(sizeof(std::size_t) * 8 - bits_per_extension)
+);
+constexpr std::size_t native_ptr_type = (
+    static_cast<std::size_t>(1)
+        << static_cast<std::size_t>(sizeof(std::size_t) * 8 - bits_per_extension)
+);
+constexpr std::size_t native_const_ptr_type = (
+    static_cast<std::size_t>(2)
+        << static_cast<std::size_t>(sizeof(std::size_t) * 8 - bits_per_extension)
+);
+
+constexpr std::size_t native_const_volatile_ptr_type = (
+    static_cast<std::size_t>(3)
+        << static_cast<std::size_t>(sizeof(std::size_t) * 8 - bits_per_extension)
+);
+
+constexpr std::size_t native_volatile_ptr_type = (
+    static_cast<std::size_t>(4)
+        << static_cast<std::size_t>(sizeof(std::size_t) * 8 - bits_per_extension)
+);
+
+constexpr std::size_t native_ref_type = (
+    static_cast<std::size_t>(5)
+        << static_cast<std::size_t>(sizeof(std::size_t) * 8 - bits_per_extension)
+);
+
+template <std::size_t Index, std::size_t Extension>
+using if_extension = std::enable_if_t< (Index & extension_mask) == Extension >*;
+
+///////////////////// Helper functions
+template <std::size_t Unptr>
+constexpr std::size_t type_to_id_extension_apply(std::size_t ext) noexcept {
+    constexpr std::size_t native_id = (Unptr & native_types_mask);
+    constexpr std::size_t extensions = (Unptr & ~native_types_mask);
+    static_assert(
+        !((extensions >> bits_per_extension) & native_types_mask),
+        "====================> Boost.PFR: Too many extensions for a single field (something close to `int************************** p;` is in the POD type)."
+    );
+
+    return (extensions >> bits_per_extension) | native_id | ext;
+}
+
+template <std::size_t Index>
+using remove_1_ext = size_t_<
+    ((Index & ~native_types_mask) << bits_per_extension) | (Index & native_types_mask)
+>;
+
+#ifdef _MSC_VER
+#   pragma warning( pop )
+#endif
+
+///////////////////// Forward declarations
+
+template <class Type> constexpr std::size_t type_to_id(identity<Type*>) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<const Type*>) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<const volatile Type*>) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<volatile Type*>) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<Type&>) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<Type>, std::enable_if_t<std::is_enum<Type>::value>* = nullptr) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<Type>, std::enable_if_t<std::is_empty<Type>::value>* = nullptr) noexcept;
+template <class Type> constexpr std::size_t type_to_id(identity<Type>, std::enable_if_t<std::is_union<Type>::value>* = nullptr) noexcept;
+template <class Type> constexpr size_array<sizeof(Type) * 3> type_to_id(identity<Type>, std::enable_if_t<!std::is_enum<Type>::value && !std::is_empty<Type>::value && !std::is_union<Type>::value>* = 0) noexcept;
+
+template <std::size_t Index> constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_const_ptr_type> = nullptr) noexcept;
+template <std::size_t Index> constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_ptr_type> = nullptr) noexcept;
+template <std::size_t Index> constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_const_volatile_ptr_type> = nullptr) noexcept;
+template <std::size_t Index> constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_volatile_ptr_type> = nullptr) noexcept;
+template <std::size_t Index> constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_ref_type> = nullptr) noexcept;
+
+
+///////////////////// Definitions of type_to_id and id_to_type for fundamental types
+/// @cond
+#define BOOST_MAGIC_GET_REGISTER_TYPE(Type, Index)              \
+    constexpr std::size_t type_to_id(identity<Type>) noexcept { \
+        return Index;                                           \
+    }                                                           \
+    constexpr Type id_to_type( size_t_<Index > ) noexcept {     \
+        return detail::construct_helper<Type>();                \
+    }                                                           \
+    /**/
+/// @endcond
+
+
+// Register all base types here
+BOOST_MAGIC_GET_REGISTER_TYPE(unsigned char         , 1)
+BOOST_MAGIC_GET_REGISTER_TYPE(unsigned short        , 2)
+BOOST_MAGIC_GET_REGISTER_TYPE(unsigned int          , 3)
+BOOST_MAGIC_GET_REGISTER_TYPE(unsigned long         , 4)
+BOOST_MAGIC_GET_REGISTER_TYPE(unsigned long long    , 5)
+BOOST_MAGIC_GET_REGISTER_TYPE(signed char           , 6)
+BOOST_MAGIC_GET_REGISTER_TYPE(short                 , 7)
+BOOST_MAGIC_GET_REGISTER_TYPE(int                   , 8)
+BOOST_MAGIC_GET_REGISTER_TYPE(long                  , 9)
+BOOST_MAGIC_GET_REGISTER_TYPE(long long             , 10)
+BOOST_MAGIC_GET_REGISTER_TYPE(char                  , 11)
+BOOST_MAGIC_GET_REGISTER_TYPE(wchar_t               , 12)
+BOOST_MAGIC_GET_REGISTER_TYPE(char16_t              , 13)
+BOOST_MAGIC_GET_REGISTER_TYPE(char32_t              , 14)
+BOOST_MAGIC_GET_REGISTER_TYPE(float                 , 15)
+BOOST_MAGIC_GET_REGISTER_TYPE(double                , 16)
+BOOST_MAGIC_GET_REGISTER_TYPE(long double           , 17)
+BOOST_MAGIC_GET_REGISTER_TYPE(bool                  , 18)
+BOOST_MAGIC_GET_REGISTER_TYPE(void*                 , 19)
+BOOST_MAGIC_GET_REGISTER_TYPE(const void*           , 20)
+BOOST_MAGIC_GET_REGISTER_TYPE(volatile void*        , 21)
+BOOST_MAGIC_GET_REGISTER_TYPE(const volatile void*  , 22)
+BOOST_MAGIC_GET_REGISTER_TYPE(std::nullptr_t        , 23)
+constexpr std::size_t tuple_begin_tag               = 24;
+constexpr std::size_t tuple_end_tag                 = 25;
+
+#undef BOOST_MAGIC_GET_REGISTER_TYPE
+
+///////////////////// Definitions of type_to_id and id_to_type for types with extensions and nested types
+template <class Type>
+constexpr std::size_t type_to_id(identity<Type*>) noexcept {
+    constexpr auto unptr = typeid_conversions::type_to_id(identity<Type>{});
+    static_assert(
+        std::is_same<const std::size_t, decltype(unptr)>::value,
+        "====================> Boost.PFR: Pointers to user defined types are not supported."
+    );
+    return typeid_conversions::type_to_id_extension_apply<unptr>(native_ptr_type);
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<const Type*>) noexcept {
+    constexpr auto unptr = typeid_conversions::type_to_id(identity<Type>{});
+    static_assert(
+        std::is_same<const std::size_t, decltype(unptr)>::value,
+        "====================> Boost.PFR: Const pointers to user defined types are not supported."
+    );
+    return typeid_conversions::type_to_id_extension_apply<unptr>(native_const_ptr_type);
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<const volatile Type*>) noexcept {
+    constexpr auto unptr = typeid_conversions::type_to_id(identity<Type>{});
+    static_assert(
+        std::is_same<const std::size_t, decltype(unptr)>::value,
+        "====================> Boost.PFR: Const volatile pointers to user defined types are not supported."
+    );
+    return typeid_conversions::type_to_id_extension_apply<unptr>(native_const_volatile_ptr_type);
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<volatile Type*>) noexcept {
+    constexpr auto unptr = typeid_conversions::type_to_id(identity<Type>{});
+    static_assert(
+        std::is_same<const std::size_t, decltype(unptr)>::value,
+        "====================> Boost.PFR: Volatile pointers to user defined types are not supported."
+    );
+    return typeid_conversions::type_to_id_extension_apply<unptr>(native_volatile_ptr_type);
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<Type&>) noexcept {
+    constexpr auto unptr = typeid_conversions::type_to_id(identity<Type>{});
+    static_assert(
+        std::is_same<const std::size_t, decltype(unptr)>::value,
+        "====================> Boost.PFR: References to user defined types are not supported."
+    );
+    return typeid_conversions::type_to_id_extension_apply<unptr>(native_ref_type);
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<Type>, std::enable_if_t<std::is_enum<Type>::value>*) noexcept {
+    return typeid_conversions::type_to_id(identity<typename std::underlying_type<Type>::type >{});
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<Type>, std::enable_if_t<std::is_empty<Type>::value>*) noexcept {
+    static_assert(!std::is_empty<Type>::value, "====================> Boost.PFR: Empty classes/structures as members are not supported.");
+    return 0;
+}
+
+template <class Type>
+constexpr std::size_t type_to_id(identity<Type>, std::enable_if_t<std::is_union<Type>::value>*) noexcept {
+    static_assert(
+        !std::is_union<Type>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    return 0;
+}
+
+template <class Type>
+constexpr size_array<sizeof(Type) * 3> type_to_id(identity<Type>, std::enable_if_t<!std::is_enum<Type>::value && !std::is_empty<Type>::value && !std::is_union<Type>::value>*) noexcept {
+    constexpr auto t = detail::flat_array_of_type_ids<Type>();
+    size_array<sizeof(Type) * 3> result {{tuple_begin_tag}};
+    constexpr bool requires_tuplening = (
+        (t.count_nonzeros() != 1)  || (t.count_nonzeros() == t.count_from_opening_till_matching_parenthis_seq(0, tuple_begin_tag, tuple_end_tag))
+    );
+
+    if (requires_tuplening) {
+        for (std::size_t i = 0; i < t.size(); ++i)
+            result.data[i + 1] = t.data[i];
+        result.data[result.size() - 1] = tuple_end_tag;
+    } else {
+        for (std::size_t i = 0; i < t.size(); ++i)
+            result.data[i] = t.data[i];
+    }
+    return result;
+}
+
+
+
+template <std::size_t Index>
+constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_ptr_type>) noexcept {
+    typedef decltype( typeid_conversions::id_to_type(remove_1_ext<Index>()) )* res_t;
+    return detail::construct_helper<res_t>();
+}
+
+template <std::size_t Index>
+constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_const_ptr_type>) noexcept {
+    typedef const decltype( typeid_conversions::id_to_type(remove_1_ext<Index>()) )* res_t;
+    return detail::construct_helper<res_t>();
+}
+
+template <std::size_t Index>
+constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_const_volatile_ptr_type>) noexcept {
+    typedef const volatile decltype( typeid_conversions::id_to_type(remove_1_ext<Index>()) )* res_t;
+    return detail::construct_helper<res_t>();
+}
+
+
+template <std::size_t Index>
+constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_volatile_ptr_type>) noexcept {
+    typedef volatile decltype( typeid_conversions::id_to_type(remove_1_ext<Index>()) )* res_t;
+    return detail::construct_helper<res_t>();
+}
+
+
+template <std::size_t Index>
+constexpr auto id_to_type(size_t_<Index >, if_extension<Index, native_ref_type>) noexcept {
+    static_assert(!Index, "====================> Boost.PFR: References are not supported");
+    return nullptr;
+}
+
+} // namespace typeid_conversions
+
+///////////////////// Structure that remembers types as integers on a `constexpr operator Type()` call
+struct ubiq_val {
+    std::size_t* ref_;
+
+    template <class T>
+    constexpr void assign(const T& typeids) const noexcept {
+        for (std::size_t i = 0; i < T::size(); ++i)
+            ref_[i] = typeids.data[i];
+    }
+
+    constexpr void assign(std::size_t val) const noexcept {
+        ref_[0] = val;
+    }
+
+    template <class Type>
+    constexpr operator Type() const noexcept {
+        constexpr auto typeids = typeid_conversions::type_to_id(identity<Type>{});
+        assign(typeids);
+        return detail::construct_helper<Type>();
+    }
+};
+
+///////////////////// Structure that remembers size of the type on a `constexpr operator Type()` call
+struct ubiq_sizes {
+    std::size_t& ref_;
+
+    template <class Type>
+    constexpr operator Type() const noexcept {
+        ref_ = sizeof(Type);
+        return detail::construct_helper<Type>();
+    }
+};
+
+///////////////////// Returns array of (offsets without accounting alignments). Required for keeping places for nested type ids
+template <class T, std::size_t N, std::size_t... I>
+constexpr size_array<N> get_type_offsets() noexcept {
+    typedef size_array<N> array_t;
+    array_t sizes{};
+    T tmp{ ubiq_sizes{sizes.data[I]}... };
+    (void)tmp;
+
+    array_t offsets{{0}};
+    for (std::size_t i = 1; i < N; ++i)
+        offsets.data[i] = offsets.data[i - 1] + sizes.data[i - 1];
+
+    return offsets;
+}
+
+///////////////////// Returns array of typeids and zeros if constructor of a type accepts sizeof...(I) parameters
+template <class T, std::size_t N, std::size_t... I>
+constexpr void* flat_type_to_array_of_type_ids(std::size_t* types, std::index_sequence<I...>) noexcept
+{
+    static_assert(
+        N <= sizeof(T),
+        "====================> Boost.PFR: Bit fields are not supported."
+    );
+
+    constexpr auto offsets = detail::get_type_offsets<T, N, I...>();
+    T tmp{ ubiq_val{types + get<I>(offsets) * 3}... };
+    (void)types;
+    (void)tmp;
+    (void)offsets; // If type is empty offsets are not used
+    return nullptr;
+}
+
+///////////////////// Returns array of typeids and zeros
+template <class T>
+constexpr size_array<sizeof(T) * 3> fields_count_and_type_ids_with_zeros() noexcept {
+    size_array<sizeof(T) * 3> types{};
+    constexpr std::size_t N = detail::fields_count<T>();
+    detail::flat_type_to_array_of_type_ids<T, N>(types.data, detail::make_index_sequence<N>());
+    return types;
+}
+
+///////////////////// Returns array of typeids without zeros
+template <class T>
+constexpr auto flat_array_of_type_ids() noexcept {
+    constexpr auto types = detail::fields_count_and_type_ids_with_zeros<T>();
+    constexpr std::size_t count = types.count_nonzeros();
+    size_array<count> res{};
+    std::size_t j = 0;
+    for (std::size_t i = 0; i < decltype(types)::size(); ++i) {
+        if (types.data[i]) {
+            res.data[j] = types.data[i];
+            ++ j;
+        }
+    }
+
+    return res;
+}
+
+///////////////////// Convert array of typeids into sequence_tuple::tuple
+
+template <class T, std::size_t First, std::size_t... I>
+constexpr auto as_flat_tuple_impl(std::index_sequence<First, I...>) noexcept;
+
+template <class T>
+constexpr sequence_tuple::tuple<> as_flat_tuple_impl(std::index_sequence<>) noexcept {
+    return sequence_tuple::tuple<>{};
+}
+
+template <std::size_t Increment, std::size_t... I>
+constexpr auto increment_index_sequence(std::index_sequence<I...>) noexcept {
+    return std::index_sequence<I + Increment...>{};
+}
+
+template <class T, std::size_t V, std::size_t I, std::size_t SubtupleLength>
+constexpr auto prepare_subtuples(size_t_<V>, size_t_<I>, size_t_<SubtupleLength>) noexcept {
+    static_assert(SubtupleLength == 0, "====================> Boost.PFR: Internal error while representing nested field as tuple");
+    return typeid_conversions::id_to_type(size_t_<V>{});
+}
+
+template <class T, std::size_t I, std::size_t SubtupleLength>
+constexpr auto prepare_subtuples(size_t_<typeid_conversions::tuple_end_tag>, size_t_<I>, size_t_<SubtupleLength>) noexcept {
+    static_assert(sizeof(T) == 0, "====================> Boost.PFR: Internal error while representing nested field as tuple");
+    return int{};
+}
+
+template <class T, std::size_t I, std::size_t SubtupleLength>
+constexpr auto prepare_subtuples(size_t_<typeid_conversions::tuple_begin_tag>, size_t_<I>, size_t_<SubtupleLength>) noexcept {
+    static_assert(SubtupleLength > 2, "====================> Boost.PFR: Internal error while representing nested field as tuple");
+    constexpr auto seq = detail::make_index_sequence<SubtupleLength - 2>{};
+    return detail::as_flat_tuple_impl<T>( detail::increment_index_sequence<I + 1>(seq) );
+}
+
+
+template <class Array>
+constexpr Array remove_subtuples(Array indexes_plus_1, const Array& subtuple_lengths) noexcept {
+    for (std::size_t i = 0; i < subtuple_lengths.size(); ++i) {
+        if (subtuple_lengths.data[i]) {
+            const std::size_t skips_count = subtuple_lengths.data[i];
+            for (std::size_t j = i + 1; j < skips_count + i; ++j) {
+                indexes_plus_1.data[j] = 0;
+            }
+            i += skips_count - 1;
+        }
+    }
+    return indexes_plus_1;
+}
+
+template <std::size_t N, class Array>
+constexpr size_array<N> resize_dropping_zeros_and_decrementing(size_t_<N>, const Array& a) noexcept {
+    size_array<N> result{};
+    std::size_t result_indx = 0;
+    for (std::size_t i = 0; i < a.size(); ++i) {
+        if (a.data[i]) {
+            result.data[result_indx] = static_cast<std::size_t>(a.data[i] - 1);
+            ++ result_indx;
+        }
+    }
+
+    return result;
+}
+
+template <class T, std::size_t First, std::size_t... I, std::size_t... INew>
+constexpr auto as_flat_tuple_impl_drop_helpers(std::index_sequence<First, I...>, std::index_sequence<INew...>) noexcept {
+    constexpr auto a = detail::flat_array_of_type_ids<T>();
+
+    constexpr size_array<sizeof...(I) + 1> subtuples_length {{
+        a.count_from_opening_till_matching_parenthis_seq(First, typeid_conversions::tuple_begin_tag, typeid_conversions::tuple_end_tag),
+        a.count_from_opening_till_matching_parenthis_seq(I, typeid_conversions::tuple_begin_tag, typeid_conversions::tuple_end_tag)...
+    }};
+
+    constexpr size_array<sizeof...(I) + 1> type_indexes_with_subtuple_internals {{ 1, 1 + I - First...}};
+    constexpr auto type_indexes_plus_1_and_zeros_as_skips = detail::remove_subtuples(type_indexes_with_subtuple_internals, subtuples_length);
+    constexpr auto new_size = size_t_<type_indexes_plus_1_and_zeros_as_skips.count_nonzeros()>{};
+    constexpr auto type_indexes = detail::resize_dropping_zeros_and_decrementing(new_size, type_indexes_plus_1_and_zeros_as_skips);
+
+    typedef sequence_tuple::tuple<
+        decltype(detail::prepare_subtuples<T>(
+            size_t_< a.data[ First + type_indexes.data[INew] ]          >{},    // id of type
+            size_t_< First + type_indexes.data[INew]                    >{},    // index of current id in `a`
+            size_t_< subtuples_length.data[ type_indexes.data[INew] ]   >{}     // if id of type is tuple, then length of that tuple
+        ))...
+    > subtuples_uncleanuped_t;
+
+    return subtuples_uncleanuped_t{};
+}
+
+template <class Array>
+constexpr std::size_t count_skips_in_array(std::size_t begin_index, std::size_t end_index, const Array& a) noexcept {
+    std::size_t skips = 0;
+    for (std::size_t i = begin_index; i < end_index; ++i) {
+        if (a.data[i] == typeid_conversions::tuple_begin_tag) {
+            const std::size_t this_tuple_size = a.count_from_opening_till_matching_parenthis_seq(i, typeid_conversions::tuple_begin_tag, typeid_conversions::tuple_end_tag) - 1;
+            skips += this_tuple_size;
+            i += this_tuple_size - 1;
+        }
+    }
+
+    return skips;
+}
+
+template <class T, std::size_t First, std::size_t... I>
+constexpr auto as_flat_tuple_impl(std::index_sequence<First, I...>) noexcept {
+    constexpr auto a = detail::flat_array_of_type_ids<T>();
+    constexpr std::size_t count_of_I = sizeof...(I);
+
+    return detail::as_flat_tuple_impl_drop_helpers<T>(
+        std::index_sequence<First, I...>{},
+        detail::make_index_sequence< 1 + count_of_I - count_skips_in_array(First, First + count_of_I, a) >{}
+    );
+}
+
+template <class T>
+constexpr auto internal_tuple_with_same_alignment() noexcept {
+    typedef typename std::remove_cv<T>::type type;
+
+    static_assert(
+        std::is_trivial<type>::value && std::is_standard_layout<type>::value,
+        "====================> Boost.PFR: Type can not be reflected without Loophole or C++17, because it's not POD"
+    );
+    static_assert(!std::is_reference<type>::value, "====================> Boost.PFR: Not applyable");
+    constexpr auto res = detail::as_flat_tuple_impl<type>(
+        detail::make_index_sequence< decltype(detail::flat_array_of_type_ids<type>())::size() >()
+    );
+
+    return res;
+}
+
+template <class T>
+using internal_tuple_with_same_alignment_t = decltype( detail::internal_tuple_with_same_alignment<T>() );
+
+
+///////////////////// Flattening
+struct ubiq_is_flat_refelectable {
+    bool& is_flat_refelectable;
+
+    template <class Type>
+    constexpr operator Type() const noexcept {
+        is_flat_refelectable = std::is_fundamental<std::remove_pointer_t<Type>>::value;
+        return {};
+    }
+};
+
+template <class T, std::size_t... I>
+constexpr bool is_flat_refelectable(std::index_sequence<I...>) noexcept {
+    constexpr std::size_t fields = sizeof...(I);
+    bool result[fields] = {static_cast<bool>(I)...};
+    const T v{ ubiq_is_flat_refelectable{result[I]}... };
+    (void)v;
+
+    for (std::size_t i = 0; i < fields; ++i) {
+        if (!result[i]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+template<class T>
+constexpr bool is_flat_refelectable(std::index_sequence<>) noexcept {
+    return true; ///< all empty structs always flat refelectable
+}
+
+template <class T>
+auto tie_as_flat_tuple(T& lvalue) noexcept {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    using type = std::remove_cv_t<T>;
+    using tuple_type = internal_tuple_with_same_alignment_t<type>;
+
+    offset_based_getter<type, tuple_type> getter;
+    return boost::pfr::detail::make_flat_tuple_of_references(lvalue, getter, size_t_<0>{}, size_t_<tuple_type::size_v>{});
+}
+
+template <class T>
+auto tie_as_tuple(T& val) noexcept {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    static_assert(
+        boost::pfr::detail::is_flat_refelectable<T>( detail::make_index_sequence<boost::pfr::detail::fields_count<T>()>{} ),
+        "====================> Boost.PFR: Not possible in C++14 to represent that type without loosing information. Change type definition or enable C++17"
+    );
+    return boost::pfr::detail::tie_as_flat_tuple(val);
+}
+
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+///////////////////// Structure that can be converted to copy of anything
+struct ubiq_constructor_constexpr_copy {
+    std::size_t ignore;
+
+    template <class Type>
+    constexpr operator Type() const noexcept {
+        static_assert(
+            std::is_trivially_destructible<Type>::value,
+            "====================> Boost.PFR: One of the fields in the type passed to `for_each_field` has non trivial destructor."
+        );
+        return {};
+    }
+};
+
+/////////////////////
+
+template <class T, std::size_t... I>
+struct is_constexpr_aggregate_initializable {
+    template<class T2, std::size_t... I2>
+    static constexpr void* constexpr_aggregate_initializer() noexcept {
+        T2 tmp{ ubiq_constructor_constexpr_copy{I2}... };
+        (void)tmp;
+        return nullptr;
+    }
+
+    template <void* = constexpr_aggregate_initializer<T, I...>() >
+    static std::true_type test(long) noexcept;
+
+    static std::false_type test(...) noexcept;
+
+    static constexpr bool value = decltype(test(0)){};
+};
+
+
+template <class T, class F, std::size_t I0, std::size_t... I, class... Fields>
+void for_each_field_in_depth(T& t, F&& f, std::index_sequence<I0, I...>, identity<Fields>...);
+
+template <class T, class F, class... Fields>
+void for_each_field_in_depth(T& t, F&& f, std::index_sequence<>, identity<Fields>...);
+
+template <class T, class F, class IndexSeq, class... Fields>
+struct next_step {
+    T& t;
+    F& f;
+
+    template <class Field>
+    operator Field() const {
+         boost::pfr::detail::for_each_field_in_depth(
+             t,
+             std::forward<F>(f),
+             IndexSeq{},
+             identity<Fields>{}...,
+             identity<Field>{}
+         );
+
+         return {};
+    }
+};
+
+template <class T, class F, std::size_t I0, std::size_t... I, class... Fields>
+void for_each_field_in_depth(T& t, F&& f, std::index_sequence<I0, I...>, identity<Fields>...) {
+    (void)std::add_const_t<std::remove_reference_t<T>>{
+        Fields{}...,
+        next_step<T, F, std::index_sequence<I...>, Fields...>{t, f},
+        ubiq_constructor_constexpr_copy{I}...
+    };
+}
+
+template <class T, class F, class... Fields>
+void for_each_field_in_depth(T& lvalue, F&& f, std::index_sequence<>, identity<Fields>...) {
+    using tuple_type = sequence_tuple::tuple<Fields...>;
+
+    offset_based_getter<std::remove_cv_t<std::remove_reference_t<T>>, tuple_type> getter;
+    std::forward<F>(f)(
+        boost::pfr::detail::make_flat_tuple_of_references(lvalue, getter, size_t_<0>{}, size_t_<sizeof...(Fields)>{})
+    );
+}
+
+template <class T, class F, std::size_t... I>
+void for_each_field_dispatcher_1(T& t, F&& f, std::index_sequence<I...>, std::true_type /*is_flat_refelectable*/) {
+    std::forward<F>(f)(
+        boost::pfr::detail::tie_as_flat_tuple(t)
+    );
+}
+
+
+template <class T, class F, std::size_t... I>
+void for_each_field_dispatcher_1(T& t, F&& f, std::index_sequence<I...>, std::false_type /*is_flat_refelectable*/) {
+    boost::pfr::detail::for_each_field_in_depth(
+        t,
+        std::forward<F>(f),
+        std::index_sequence<I...>{}
+    );
+}
+
+template <class T, class F, std::size_t... I>
+void for_each_field_dispatcher(T& t, F&& f, std::index_sequence<I...>) {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    static_assert(is_constexpr_aggregate_initializable<T, I...>::value, "====================> Boost.PFR: T must be a constexpr initializable type");
+
+    constexpr bool is_flat_refelectable_val = detail::is_flat_refelectable<T>( std::index_sequence<I...>{} );
+    detail::for_each_field_dispatcher_1(
+        t,
+        std::forward<F>(f),
+        std::index_sequence<I...>{},
+        std::integral_constant<bool, is_flat_refelectable_val>{}
+    );
+}
+
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+
+#ifdef __clang__
+#   pragma clang diagnostic pop
+#endif
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_CORE14_CLASSIC_HPP

include/boost/pfr/detail/core14_loophole.hpp

@@ -0,0 +1,200 @@
+// Copyright (c) 2017-2018 Alexandr Poltavsky, Antony Polukhin.
+// Copyright (c) 2019-2025 Antony Polukhin.
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+// The Great Type Loophole (C++14)
+// Initial implementation by Alexandr Poltavsky, http://alexpolt.github.io
+//
+// Description:
+//  The Great Type Loophole is a technique that allows to exchange type information with template
+//  instantiations. Basically you can assign and read type information during compile time.
+//  Here it is used to detect data members of a data type. I described it for the first time in
+//  this blog post http://alexpolt.github.io/type-loophole.html .
+//
+// This technique exploits the http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#2118
+// CWG 2118. Stateful metaprogramming via friend injection
+// Note: CWG agreed that such techniques should be ill-formed, although the mechanism for prohibiting them is as yet undetermined.
+
+#ifndef BOOST_PFR_DETAIL_CORE14_LOOPHOLE_HPP
+#define BOOST_PFR_DETAIL_CORE14_LOOPHOLE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/offset_based_getter.hpp>
+#include <boost/pfr/detail/fields_count.hpp>
+#include <boost/pfr/detail/make_flat_tuple_of_references.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+#include <boost/pfr/detail/sequence_tuple.hpp>
+#include <boost/pfr/detail/rvalue_t.hpp>
+#include <boost/pfr/detail/unsafe_declval.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <utility>
+#endif
+
+#ifdef __clang__
+#   pragma clang diagnostic push
+#   pragma clang diagnostic ignored "-Wmissing-braces"
+#   pragma clang diagnostic ignored "-Wundefined-inline"
+#   pragma clang diagnostic ignored "-Wundefined-internal"
+#   pragma clang diagnostic ignored "-Wmissing-field-initializers"
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wnon-template-friend"
+#endif
+
+
+namespace boost { namespace pfr { namespace detail {
+
+// tag<T,N> generates friend declarations and helps with overload resolution.
+// There are two types: one with the auto return type, which is the way we read types later.
+// The second one is used in the detection of instantiations without which we'd get multiple
+// definitions.
+
+template <class T, std::size_t N>
+struct tag {
+    friend auto loophole(tag<T,N>);
+};
+
+// The definitions of friend functions.
+template <class T, class U, std::size_t N, bool B>
+struct fn_def_lref {
+    friend auto loophole(tag<T,N>) {
+        // Standard Library containers do not SFINAE on invalid copy constructor. Because of that std::vector<std::unique_ptr<int>> reports that it is copyable,
+        // which leads to an instantiation error at this place.
+        //
+        // To workaround the issue, we check that the type U is movable, and move it in that case.
+        using no_extents_t = std::remove_all_extents_t<U>;
+        return static_cast< std::conditional_t<std::is_move_constructible<no_extents_t>::value, no_extents_t&&, no_extents_t&> >(
+            boost::pfr::detail::unsafe_declval<no_extents_t&>()
+        );
+    }
+};
+template <class T, class U, std::size_t N, bool B>
+struct fn_def_rref {
+    friend auto loophole(tag<T,N>) { return std::move(boost::pfr::detail::unsafe_declval< std::remove_all_extents_t<U>& >()); }
+};
+
+
+// Those specializations are to avoid multiple definition errors.
+template <class T, class U, std::size_t N>
+struct fn_def_lref<T, U, N, true> {};
+
+template <class T, class U, std::size_t N>
+struct fn_def_rref<T, U, N, true> {};
+
+
+// This has a templated conversion operator which in turn triggers instantiations.
+// Important point, using sizeof seems to be more reliable. Also default template
+// arguments are "cached" (I think). To fix that I provide a U template parameter to
+// the ins functions which do the detection using constexpr friend functions and SFINAE.
+template <class T, std::size_t N>
+struct loophole_ubiq_lref {
+    template<class U, std::size_t M> static std::size_t ins(...);
+    template<class U, std::size_t M, std::size_t = sizeof(loophole(tag<T,M>{})) > static char ins(int);
+
+    template<class U, std::size_t = sizeof(fn_def_lref<T, U, N, sizeof(ins<U, N>(0)) == sizeof(char)>)>
+    constexpr operator U&() const&& noexcept; // `const&&` here helps to avoid ambiguity in loophole instantiations. optional_like test validate that behavior.
+};
+
+template <class T, std::size_t N>
+struct loophole_ubiq_rref {
+    template<class U, std::size_t M> static std::size_t ins(...);
+    template<class U, std::size_t M, std::size_t = sizeof(loophole(tag<T,M>{})) > static char ins(int);
+
+    template<class U, std::size_t = sizeof(fn_def_rref<T, U, N, sizeof(ins<U, N>(0)) == sizeof(char)>)>
+    constexpr operator U&&() const&& noexcept; // `const&&` here helps to avoid ambiguity in loophole instantiations. optional_like test validate that behavior.
+};
+
+
+// This is a helper to turn a data structure into a tuple.
+template <class T, class U>
+struct loophole_type_list_lref;
+
+template <typename T, std::size_t... I>
+struct loophole_type_list_lref< T, std::index_sequence<I...> >
+     // Instantiating loopholes:
+    : sequence_tuple::tuple< decltype(T{ loophole_ubiq_lref<T, I>{}... }, 0) >
+{
+    using type = sequence_tuple::tuple< decltype(loophole(tag<T, I>{}))... >;
+};
+
+
+template <class T, class U>
+struct loophole_type_list_rref;
+
+template <typename T, std::size_t... I>
+struct loophole_type_list_rref< T, std::index_sequence<I...> >
+     // Instantiating loopholes:
+    : sequence_tuple::tuple< decltype(T{ loophole_ubiq_rref<T, I>{}... }, 0) >
+{
+    using type = sequence_tuple::tuple< decltype(loophole(tag<T, I>{}))... >;
+};
+
+
+// Lazily returns loophole_type_list_{lr}ref.
+template <bool IsCopyConstructible /*= true*/, class T, class U>
+struct loophole_type_list_selector {
+    using type = loophole_type_list_lref<T, U>;
+};
+
+template <class T, class U>
+struct loophole_type_list_selector<false /*IsCopyConstructible*/, T, U> {
+    using type = loophole_type_list_rref<T, U>;
+};
+
+template <class T>
+auto tie_as_tuple_loophole_impl(T& lvalue) noexcept {
+    using type = std::remove_cv_t<std::remove_reference_t<T>>;
+    using indexes = detail::make_index_sequence<fields_count<type>()>;
+    using loophole_type_list = typename detail::loophole_type_list_selector<
+        std::is_copy_constructible<std::remove_all_extents_t<type>>::value, type, indexes
+    >::type;
+    using tuple_type = typename loophole_type_list::type;
+
+    return boost::pfr::detail::make_flat_tuple_of_references(
+        lvalue,
+        offset_based_getter<type, tuple_type>{},
+        size_t_<0>{},
+        size_t_<tuple_type::size_v>{}
+    );
+}
+
+template <class T>
+auto tie_as_tuple(T& val) noexcept {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    return boost::pfr::detail::tie_as_tuple_loophole_impl(
+        val
+    );
+}
+
+template <class T, class F, std::size_t... I>
+void for_each_field_dispatcher(T& t, F&& f, std::index_sequence<I...>) {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    std::forward<F>(f)(
+        boost::pfr::detail::tie_as_tuple_loophole_impl(t)
+    );
+}
+
+}}} // namespace boost::pfr::detail
+
+
+#ifdef __clang__
+#   pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic pop
+#endif
+
+
+#endif // BOOST_PFR_DETAIL_CORE14_LOOPHOLE_HPP
+

include/boost/pfr/detail/core17.hpp

@@ -0,0 +1,72 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+#ifndef BOOST_PFR_DETAIL_CORE17_HPP
+#define BOOST_PFR_DETAIL_CORE17_HPP
+#pragma once
+
+#include <boost/pfr/detail/core17_generated.hpp>
+#include <boost/pfr/detail/fields_count.hpp>
+#include <boost/pfr/detail/for_each_field_impl.hpp>
+#include <boost/pfr/detail/rvalue_t.hpp>
+
+namespace boost { namespace pfr { namespace detail {
+
+#ifndef _MSC_VER // MSVC fails to compile the following code, but compiles the structured bindings in core17_generated.hpp
+struct do_not_define_std_tuple_size_for_me {
+    bool test1 = true;
+};
+
+template <class T>
+constexpr bool do_structured_bindings_work() noexcept { // ******************************************* IN CASE OF ERROR READ THE FOLLOWING LINES IN boost/pfr/detail/core17.hpp FILE:
+    T val{};
+    auto& [a] = val; // ******************************************* IN CASE OF ERROR READ THE FOLLOWING LINES IN boost/pfr/detail/core17.hpp FILE:
+
+    /****************************************************************************
+    *
+    * It looks like your compiler or Standard Library can not handle C++17
+    * structured bindings.
+    *
+    * Workaround: Define BOOST_PFR_USE_CPP17 to 0
+    * It will disable the C++17 features for Boost.PFR library.
+    *
+    * Sorry for the inconvenience caused.
+    *
+    ****************************************************************************/
+
+    return a;
+}
+
+static_assert(
+    do_structured_bindings_work<do_not_define_std_tuple_size_for_me>(),
+    "====================> Boost.PFR: Your compiler can not handle C++17 structured bindings. Read the above comments for workarounds."
+);
+#endif // #ifndef _MSC_VER
+
+template <class T>
+constexpr auto tie_as_tuple(T& val) noexcept {
+  static_assert(
+    !std::is_union<T>::value,
+    "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+  );
+  typedef size_t_<boost::pfr::detail::fields_count<T>()> fields_count_tag;
+  return boost::pfr::detail::tie_as_tuple(val, fields_count_tag{});
+}
+
+template <class T, class F, std::size_t... I>
+constexpr void for_each_field_dispatcher(T& t, F&& f, std::index_sequence<I...>) {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    std::forward<F>(f)(
+        detail::tie_as_tuple(t)
+    );
+}
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_CORE17_HPP

include/boost/pfr/detail/core26.hpp

@@ -0,0 +1,39 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+// Copyright (c) 2025 Jean-Michaël Celerier
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// boost-no-inspect
+
+#ifndef BOOST_PFR_DETAIL_CORE26_HPP
+#define BOOST_PFR_DETAIL_CORE26_HPP
+#pragma once
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+
+namespace boost::pfr::detail {
+
+template<class T>
+constexpr auto tie_as_tuple(T &val) noexcept {
+    static_assert(!std::is_union<T>::value,
+                  "====================> Boost.PFR: For safety reasons it is forbidden to reflect "
+                  "unions. See `Reflection of unions` section in the docs for more info.");
+    auto &&[... members] = std::forward<T>(val);
+    return sequence_tuple::tuple<std::add_lvalue_reference_t<decltype(members)>...>{members...};
+}
+
+template <class T, class F, std::size_t... I>
+constexpr void for_each_field_dispatcher(T& t, F&& f, std::index_sequence<I...>) {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    std::forward<F>(f)(
+        detail::tie_as_tuple(t)
+    );
+}
+
+} // namespace boost::pfr::detail
+
+#endif

include/boost/pfr/detail/core_name.hpp

@@ -0,0 +1,29 @@
+// Copyright (c) 2023 Bela Schaum, X-Ryl669, Denis Mikhailov.
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+// Initial implementation by Bela Schaum, https://github.com/schaumb
+// The way to make it union and UB free by X-Ryl669, https://github.com/X-Ryl669
+//
+
+#ifndef BOOST_PFR_DETAIL_CORE_NAME_HPP
+#define BOOST_PFR_DETAIL_CORE_NAME_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+// Each core_name provides `boost::pfr::detail::get_name` and
+// `boost::pfr::detail::tie_as_names_tuple` functions.
+//
+// The whole functional of extracting field's names is build on top of those
+// two functions.
+#if BOOST_PFR_CORE_NAME_ENABLED
+#include <boost/pfr/detail/core_name20_static.hpp>
+#else
+#include <boost/pfr/detail/core_name14_disabled.hpp>
+#endif
+
+#endif // BOOST_PFR_DETAIL_CORE_NAME_HPP
+

include/boost/pfr/detail/core_name14_disabled.hpp

@@ -0,0 +1,52 @@
+// Copyright (c) 2023 Bela Schaum, X-Ryl669, Denis Mikhailov.
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+// Initial implementation by Bela Schaum, https://github.com/schaumb
+// The way to make it union and UB free by X-Ryl669, https://github.com/X-Ryl669
+//
+
+#ifndef BOOST_PFR_DETAIL_CORE_NAME14_DISABLED_HPP
+#define BOOST_PFR_DETAIL_CORE_NAME14_DISABLED_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+#include <boost/pfr/detail/sequence_tuple.hpp>
+
+namespace boost { namespace pfr { namespace detail {
+
+template <class T, std::size_t I>
+constexpr auto get_name() noexcept {
+    static_assert(
+        sizeof(T) && false,
+        "====================> Boost.PFR: Field's names extracting functionality requires C++20."
+    );
+
+    return nullptr;
+}
+
+template <class T>
+constexpr auto tie_as_names_tuple() noexcept {
+    static_assert(
+        sizeof(T) && false,
+        "====================> Boost.PFR: Field's names extracting functionality requires C++20."
+    );
+
+    return detail::sequence_tuple::make_sequence_tuple();
+}
+
+
+template <class T, class F>
+constexpr void for_each_field_with_name(T&& /* value */, F&& /* func */) {
+    static_assert(
+        sizeof(T) && false,
+        "====================> Boost.PFR: Field's names extracting functionality requires C++20."
+    );
+}
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_CORE_NAME14_DISABLED_HPP
+

include/boost/pfr/detail/core_name20_static.hpp

@@ -0,0 +1,263 @@
+// Copyright (c) 2023 Bela Schaum, X-Ryl669, Denis Mikhailov.
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+// Initial implementation by Bela Schaum, https://github.com/schaumb
+// The way to make it union and UB free by X-Ryl669, https://github.com/X-Ryl669
+//
+
+#ifndef BOOST_PFR_DETAIL_CORE_NAME20_STATIC_HPP
+#define BOOST_PFR_DETAIL_CORE_NAME20_STATIC_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/core.hpp>
+#include <boost/pfr/detail/fake_object.hpp>
+#include <boost/pfr/detail/fields_count.hpp>
+#include <boost/pfr/detail/for_each_field.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+#include <boost/pfr/detail/sequence_tuple.hpp>
+#include <boost/pfr/detail/stdarray.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <string_view>
+#include <array>
+#include <memory> // for std::addressof
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+struct core_name_skip {
+    std::size_t size_at_begin;
+    std::size_t size_at_end;
+    bool is_backward;
+    std::string_view until_runtime;
+
+    consteval std::string_view apply(std::string_view sv) const noexcept {
+        // We use std::min here to make the compiler diagnostic shorter and
+        // cleaner in case of misconfigured BOOST_PFR_CORE_NAME_PARSING
+        sv.remove_prefix((std::min)(size_at_begin, sv.size()));
+        sv.remove_suffix((std::min)(size_at_end, sv.size()));
+        if (until_runtime.empty()) {
+            return sv;
+        }
+
+        const auto found = is_backward ? sv.rfind(until_runtime)
+                                       : sv.find(until_runtime);
+
+        const auto cut_until = found + until_runtime.size();
+        const auto safe_cut_until = (std::min)(cut_until, sv.size());
+        return sv.substr(safe_cut_until);
+    }
+};
+
+struct backward {
+    explicit consteval backward(std::string_view value) noexcept
+        : value(value)
+    {}
+
+    std::string_view value;
+};
+
+consteval core_name_skip make_core_name_skip(std::size_t size_at_begin,
+                                             std::size_t size_at_end,
+                                             std::string_view until_runtime) noexcept
+{
+    return core_name_skip{size_at_begin, size_at_end, false, until_runtime};
+}
+
+consteval core_name_skip make_core_name_skip(std::size_t size_at_begin,
+                                             std::size_t size_at_end,
+                                             backward until_runtime) noexcept
+{
+    return core_name_skip{size_at_begin, size_at_end, true, until_runtime.value};
+}
+
+// it might be compilation failed without this workaround sometimes
+// See https://github.com/llvm/llvm-project/issues/41751 for details
+template <class>
+consteval std::string_view clang_workaround(std::string_view value) noexcept
+{
+    return value;
+}
+
+template <class MsvcWorkaround, auto ptr>
+consteval auto name_of_field_impl() noexcept {
+    // Some of the following compiler specific macro may be defined only
+    // inside the function body:
+
+#ifndef BOOST_PFR_FUNCTION_SIGNATURE
+#   if defined(__FUNCSIG__)
+#       define BOOST_PFR_FUNCTION_SIGNATURE __FUNCSIG__
+#   elif defined(__PRETTY_FUNCTION__) || defined(__GNUC__) || defined(__clang__)
+#       define BOOST_PFR_FUNCTION_SIGNATURE __PRETTY_FUNCTION__
+#   else
+#       define BOOST_PFR_FUNCTION_SIGNATURE ""
+#   endif
+#endif
+
+    constexpr std::string_view sv = detail::clang_workaround<MsvcWorkaround>(BOOST_PFR_FUNCTION_SIGNATURE);
+    static_assert(!sv.empty(),
+        "====================> Boost.PFR: Field reflection parser configured in a wrong way. "
+        "Please define the BOOST_PFR_FUNCTION_SIGNATURE to a compiler specific macro, "
+        "that outputs the whole function signature including non-type template parameters."
+    );
+
+    constexpr auto skip = detail::make_core_name_skip BOOST_PFR_CORE_NAME_PARSING;
+    static_assert(skip.size_at_begin + skip.size_at_end + skip.until_runtime.size() < sv.size(),
+        "====================> Boost.PFR: Field reflection parser configured in a wrong way. "
+        "It attempts to skip more chars than available. "
+        "Please define BOOST_PFR_CORE_NAME_PARSING to correct values. See documentation section "
+        "'Limitations and Configuration' for more information."
+    );
+    constexpr auto fn = skip.apply(sv);
+    static_assert(
+        !fn.empty(),
+        "====================> Boost.PFR: Extraction of field name is misconfigured for your compiler. "
+        "It skipped all the input, leaving the field name empty. "
+        "Please define BOOST_PFR_CORE_NAME_PARSING to correct values. See documentation section "
+        "'Limitations and Configuration' for more information."
+    );
+    auto res = std::array<char, fn.size()+1>{};
+
+    auto* out = res.data();
+    for (auto x: fn) {
+        *out = x;
+        ++out;
+    }
+
+    return res;
+}
+
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wundefined-var-template"
+
+// clang 16 and earlier don't support address of non-static member as template parameter
+// but fortunately it's possible to use C++20 non-type template parameters in another way
+// even in clang 16 and more older clangs
+// all we need is to wrap pointer into 'clang_wrapper_t' and then pass it into template
+template <class T>
+struct clang_wrapper_t {
+    T v;
+};
+template <class T>
+clang_wrapper_t(T) -> clang_wrapper_t<T>;
+
+template <class T>
+constexpr auto make_clang_wrapper(const T& arg) noexcept {
+    return clang_wrapper_t{arg};
+}
+
+#else
+
+template <class T>
+constexpr const T& make_clang_wrapper(const T& arg) noexcept {
+    // It's everything OK with address of non-static member as template parameter support on this compiler
+    // so we don't need a wrapper here, just pass the pointer into template
+    return arg;
+}
+
+#endif
+
+template <class MsvcWorkaround, auto ptr>
+consteval auto name_of_field() noexcept {
+    // Sanity check: known field name must match the deduced one
+    static_assert(
+        sizeof(MsvcWorkaround)  // do not trigger if `name_of_field()` is not used
+        && std::string_view{
+            detail::name_of_field_impl<
+                core_name_skip, detail::make_clang_wrapper(std::addressof(
+                    detail::fake_object<core_name_skip>().size_at_begin
+                ))
+            >().data()
+        } == "size_at_begin",
+        "====================> Boost.PFR: Extraction of field name is misconfigured for your compiler. "
+        "It does not return the proper field name. "
+        "Please define BOOST_PFR_CORE_NAME_PARSING to correct values. See documentation section "
+        "'Limitations and Configuration' for more information."
+    );
+
+    return detail::name_of_field_impl<MsvcWorkaround, ptr>();
+}
+
+// Storing part of a string literal into an array minimizes the binary size.
+//
+// Without passing 'T' into 'name_of_field' different fields from different structures might have the same name!
+// See https://developercommunity.visualstudio.com/t/__FUNCSIG__-outputs-wrong-value-with-C/10458554 for details
+template <class T, std::size_t I>
+inline constexpr auto stored_name_of_field = detail::name_of_field<T,
+    detail::make_clang_wrapper(std::addressof(detail::sequence_tuple::get<I>(
+        detail::tie_as_tuple(detail::fake_object<T>())
+    )))
+>();
+
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
+template <class T, std::size_t... I>
+constexpr auto tie_as_names_tuple_impl(std::index_sequence<I...>) noexcept {
+    return detail::sequence_tuple::make_sequence_tuple(std::string_view{stored_name_of_field<T, I>.data()}...);
+}
+
+template <class T, std::size_t I>
+constexpr std::string_view get_name() noexcept {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    static_assert(
+        !std::is_array<T>::value,
+        "====================> Boost.PFR: It is impossible to extract name from old C array since it doesn't have named members"
+    );
+    static_assert(
+        sizeof(T) && (BOOST_PFR_USE_CPP17 || BOOST_PFR_USE_CPP26),
+        "====================> Boost.PFR: Extraction of field's names is allowed only when the BOOST_PFR_USE_CPP17 or the BOOST_PFR_USE_CPP26 macro enabled."
+   );
+
+   return stored_name_of_field<T, I>.data();
+}
+
+template <class T>
+constexpr auto tie_as_names_tuple() noexcept {
+    static_assert(
+        !std::is_union<T>::value,
+        "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
+    );
+    static_assert(
+        !std::is_array<T>::value,
+        "====================> Boost.PFR: It is impossible to extract name from old C array since it doesn't have named members"
+    );
+    static_assert(
+        sizeof(T) && BOOST_PFR_USE_CPP17,
+        "====================> Boost.PFR: Extraction of field's names is allowed only when the BOOST_PFR_USE_CPP17 macro enabled."
+    );
+
+    return detail::tie_as_names_tuple_impl<T>(detail::make_index_sequence<detail::fields_count<T>()>{});
+}
+
+template <class T, class F>
+constexpr void for_each_field_with_name(T&& value, F&& func) {
+    return boost::pfr::detail::for_each_field(
+        std::forward<T>(value),
+        [f = std::forward<F>(func)](auto&& field, auto index) mutable {
+            using IndexType = decltype(index);
+            using FieldType = decltype(field);
+            constexpr auto name = boost::pfr::detail::get_name<std::remove_reference_t<T>, IndexType::value>();
+            if constexpr (std::is_invocable_v<F, std::string_view, FieldType, IndexType>) {
+                f(name, std::forward<FieldType>(field), index);
+            } else {
+                f(name, std::forward<FieldType>(field));
+            }
+        });
+}
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_CORE_NAME20_STATIC_HPP
+

include/boost/pfr/detail/detectors.hpp

@@ -0,0 +1,72 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_DETECTORS_HPP
+#define BOOST_PFR_DETAIL_DETECTORS_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <functional>
+#include <type_traits>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+///////////////////// `value` is true if Detector<Tleft, Tright> does not compile (SFINAE)
+    struct can_not_apply{};
+
+    template <template <class, class> class Detector, class Tleft, class Tright>
+    struct not_applicable {
+        static constexpr bool value = std::is_same<
+            Detector<Tleft, Tright>,
+            can_not_apply
+        >::value;
+    };
+
+///////////////////// Detectors for different operators
+    template <class S, class T> auto comp_eq_detector_msvc_helper(long) -> decltype(std::declval<S>() == std::declval<T>());
+    template <class S, class T> can_not_apply comp_eq_detector_msvc_helper(int);
+    template <class T1, class T2> using comp_eq_detector = decltype(comp_eq_detector_msvc_helper<T1,T2>(1L));
+
+    template <class S, class T> auto comp_ne_detector_msvc_helper(long) -> decltype(std::declval<S>() != std::declval<T>());
+    template <class S, class T> can_not_apply comp_ne_detector_msvc_helper(int);
+    template <class T1, class T2> using comp_ne_detector = decltype(comp_ne_detector_msvc_helper<T1,T2>(1L));
+
+    template <class S, class T> auto comp_lt_detector_msvc_helper(long) -> decltype(std::declval<S>() < std::declval<T>());
+    template <class S, class T> can_not_apply comp_lt_detector_msvc_helper(int);
+    template <class T1, class T2> using comp_lt_detector = decltype(comp_lt_detector_msvc_helper<T1,T2>(1L));
+
+    template <class S, class T> auto comp_le_detector_msvc_helper(long) -> decltype(std::declval<S>() <= std::declval<T>());
+    template <class S, class T> can_not_apply comp_le_detector_msvc_helper(int);
+    template <class T1, class T2> using comp_le_detector = decltype(comp_le_detector_msvc_helper<T1,T2>(1L));
+
+    template <class S, class T> auto comp_gt_detector_msvc_helper(long) -> decltype(std::declval<S>() > std::declval<T>());
+    template <class S, class T> can_not_apply comp_gt_detector_msvc_helper(int);
+    template <class T1, class T2> using comp_gt_detector = decltype(comp_gt_detector_msvc_helper<T1,T2>(1L));
+
+    template <class S, class T> auto comp_ge_detector_msvc_helper(long) -> decltype(std::declval<S>() >= std::declval<T>());
+    template <class S, class T> can_not_apply comp_ge_detector_msvc_helper(int);
+    template <class T1, class T2> using comp_ge_detector = decltype(comp_ge_detector_msvc_helper<T1,T2>(1L));
+
+
+    template <class S> auto hash_detector_msvc_helper(long) -> decltype(std::hash<S>{}(std::declval<S>()));
+    template <class S> can_not_apply hash_detector_msvc_helper(int);
+    template <class T1, class T2> using hash_detector = decltype(hash_detector_msvc_helper<T1,T2>(1L));
+
+
+    template <class S, class T> auto ostreamable_detector_msvc_helper(long) -> decltype(std::declval<S>() << std::declval<T>());
+    template <class S, class T> can_not_apply ostreamable_detector_msvc_helper(int);
+    template <class S, class T> using ostreamable_detector = decltype(ostreamable_detector_msvc_helper<S,T>(1L));
+
+    template <class S, class T> auto istreamable_detector_msvc_helper(long) -> decltype(std::declval<S>() >> std::declval<T>());
+    template <class S, class T> can_not_apply istreamable_detector_msvc_helper(int);
+    template <class S, class T> using istreamable_detector = decltype(istreamable_detector_msvc_helper<S,T>(1L));
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_DETECTORS_HPP
+
+

include/boost/pfr/detail/fake_object.hpp

@@ -0,0 +1,54 @@
+// Copyright (c) 2023 Bela Schaum, X-Ryl669, Denis Mikhailov.
+// Copyright (c) 2024-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+// Initial implementation by Bela Schaum, https://github.com/schaumb
+// The way to make it union and UB free by X-Ryl669, https://github.com/X-Ryl669
+//
+
+#ifndef BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
+#define BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#ifdef __clang__
+#   pragma clang diagnostic push
+#   pragma clang diagnostic ignored "-Wundefined-internal"
+#   pragma clang diagnostic ignored "-Wundefined-var-template"
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+// This class has external linkage while T has not sure.
+template <class T>
+struct wrapper {
+    const T value;
+};
+
+// This variable servers as a link-time assert.
+// If linker requires it, then `fake_object()` is used at runtime.
+template <class T>
+extern const wrapper<T> do_not_use_PFR_with_local_types;
+
+// For returning non default constructible types, it's exclusively used in member name retrieval.
+//
+// Neither std::declval nor boost::pfr::detail::unsafe_declval are usable there.
+// This takes advantage of C++20 features, while boost::pfr::detail::unsafe_declval works
+// with the former standards.
+template <class T>
+constexpr const T& fake_object() noexcept {
+    return do_not_use_PFR_with_local_types<T>.value;
+}
+
+}}} // namespace boost::pfr::detail
+
+#ifdef __clang__
+#   pragma clang diagnostic pop
+#endif
+
+#endif // BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
+

include/boost/pfr/detail/fields_count.hpp

@@ -0,0 +1,482 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_FIELDS_COUNT_HPP
+#define BOOST_PFR_DETAIL_FIELDS_COUNT_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+#include <boost/pfr/detail/size_t_.hpp>
+#include <boost/pfr/detail/unsafe_declval.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <limits>
+#include <type_traits>
+#include <utility>      // metaprogramming stuff
+#endif
+
+#ifdef __clang__
+#   pragma clang diagnostic push
+#   pragma clang diagnostic ignored "-Wmissing-braces"
+#   pragma clang diagnostic ignored "-Wundefined-inline"
+#   pragma clang diagnostic ignored "-Wundefined-internal"
+#   pragma clang diagnostic ignored "-Wmissing-field-initializers"
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+///////////////////// min without including <algorithm>
+constexpr std::size_t min_of_size_t(std::size_t a, std::size_t b) noexcept {
+    return b < a ? b : a;
+}
+
+///////////////////// Structure that can be converted to reference to anything
+struct ubiq_lref_constructor {
+    std::size_t ignore;
+    template <class Type> constexpr operator Type&() const && noexcept {  // tweak for template_unconstrained.cpp like cases
+        return detail::unsafe_declval<Type&>();
+    }
+
+    template <class Type> constexpr operator Type&() const & noexcept {  // tweak for optional_chrono.cpp like cases
+        return detail::unsafe_declval<Type&>();
+    }
+};
+
+///////////////////// Structure that can be converted to rvalue reference to anything
+struct ubiq_rref_constructor {
+    std::size_t ignore;
+    template <class Type> /*constexpr*/ operator Type() const && noexcept {  // Allows initialization of rvalue reference fields and move-only types
+        return detail::unsafe_declval<Type>();
+    }
+};
+
+///////////////////// Hand-made is_complete<T> trait
+template <typename T, typename = void>
+struct is_complete : std::false_type
+{};
+
+template <typename T>
+struct is_complete<T, decltype(void(sizeof(T)))> : std::integral_constant<bool, true>
+{};
+
+#ifndef __cpp_lib_is_aggregate
+///////////////////// Hand-made is_aggregate_initializable_n<T> trait
+
+// Structure that can be converted to reference to anything except reference to T
+template <class T, bool IsCopyConstructible>
+struct ubiq_constructor_except {
+    std::size_t ignore;
+    template <class Type> constexpr operator std::enable_if_t<!std::is_same<T, Type>::value, Type&> () const noexcept; // Undefined
+};
+
+template <class T>
+struct ubiq_constructor_except<T, false> {
+    std::size_t ignore;
+    template <class Type> constexpr operator std::enable_if_t<!std::is_same<T, Type>::value, Type&&> () const noexcept; // Undefined
+};
+
+
+// `std::is_constructible<T, ubiq_constructor_except<T>>` consumes a lot of time, so we made a separate lazy trait for it.
+template <std::size_t N, class T> struct is_single_field_and_aggregate_initializable: std::false_type {};
+template <class T> struct is_single_field_and_aggregate_initializable<1, T>: std::integral_constant<
+    bool, !std::is_constructible<T, ubiq_constructor_except<T, std::is_copy_constructible<T>::value>>::value
+> {};
+
+// Hand-made is_aggregate<T> trait:
+// Before C++20 aggregates could be constructed from `decltype(ubiq_?ref_constructor{I})...` but type traits report that
+// there's no constructor from `decltype(ubiq_?ref_constructor{I})...`
+// Special case for N == 1: `std::is_constructible<T, ubiq_?ref_constructor>` returns true if N == 1 and T is copy/move constructible.
+template <class T, std::size_t N, class /*Enable*/ = void>
+struct is_aggregate_initializable_n {
+    static constexpr bool value =
+           std::is_empty<T>::value
+        || std::is_array<T>::value
+    ;
+};
+
+template <class T, std::size_t N>
+struct is_aggregate_initializable_n<T, N, std::enable_if_t<std::is_class<T>::value && !std::is_empty<T>::value>> {
+    template <std::size_t ...I>
+    static constexpr bool is_not_constructible_n(std::index_sequence<I...>) noexcept {
+        return (!std::is_constructible<T, decltype(ubiq_lref_constructor{I})...>::value && !std::is_constructible<T, decltype(ubiq_rref_constructor{I})...>::value)
+            || is_single_field_and_aggregate_initializable<N, T>::value
+        ;
+    }
+
+    static constexpr bool value = is_not_constructible_n(detail::make_index_sequence<N>{});
+};
+
+#endif // #ifndef __cpp_lib_is_aggregate
+
+///////////////////// Detect aggregates with inheritance
+template <class Derived, class U>
+constexpr bool static_assert_non_inherited() noexcept {
+    static_assert(
+            !std::is_base_of<U, Derived>::value,
+            "====================> Boost.PFR: Boost.PFR: Inherited types are not supported."
+    );
+    return true;
+}
+
+template <class Derived>
+struct ubiq_lref_base_asserting {
+    template <class Type> constexpr operator Type&() const &&  // tweak for template_unconstrained.cpp like cases
+        noexcept(detail::static_assert_non_inherited<Derived, Type>())  // force the computation of assert function
+    {
+        return detail::unsafe_declval<Type&>();
+    }
+
+    template <class Type> constexpr operator Type&() const &  // tweak for optional_chrono.cpp like cases
+        noexcept(detail::static_assert_non_inherited<Derived, Type>())  // force the computation of assert function
+    {
+        return detail::unsafe_declval<Type&>();
+    }
+};
+
+template <class Derived>
+struct ubiq_rref_base_asserting {
+    template <class Type> /*constexpr*/ operator Type() const &&  // Allows initialization of rvalue reference fields and move-only types
+        noexcept(detail::static_assert_non_inherited<Derived, Type>())  // force the computation of assert function
+    {
+        return detail::unsafe_declval<Type>();
+    }
+};
+
+template <class T, std::size_t I0, std::size_t... I, class /*Enable*/ = std::enable_if_t<std::is_copy_constructible<T>::value>>
+constexpr auto assert_first_not_base(std::index_sequence<I0, I...>) noexcept
+    -> std::add_pointer_t<decltype(T{ ubiq_lref_base_asserting<T>{}, ubiq_lref_constructor{I}... })>
+{
+    return nullptr;
+}
+
+template <class T, std::size_t I0, std::size_t... I, class /*Enable*/ = std::enable_if_t<!std::is_copy_constructible<T>::value>>
+constexpr auto assert_first_not_base(std::index_sequence<I0, I...>) noexcept
+    -> std::add_pointer_t<decltype(T{ ubiq_rref_base_asserting<T>{}, ubiq_rref_constructor{I}... })>
+{
+    return nullptr;
+}
+
+template <class T>
+constexpr void* assert_first_not_base(std::index_sequence<>) noexcept
+{
+    return nullptr;
+}
+
+template <class T, std::size_t N>
+constexpr void assert_first_not_base(int) noexcept {}
+
+template <class T, std::size_t N>
+constexpr auto assert_first_not_base(long) noexcept
+    -> std::enable_if_t<std::is_class<T>::value>
+{
+    detail::assert_first_not_base<T>(detail::make_index_sequence<N>{});
+}
+
+///////////////////// Helpers for initializable detection
+// Note that these take O(N) compile time and memory!
+template <class T, std::size_t... I, class /*Enable*/ = std::enable_if_t<std::is_copy_constructible<T>::value>>
+constexpr auto enable_if_initializable_helper(std::index_sequence<I...>) noexcept
+    -> std::add_pointer_t<decltype(T{ubiq_lref_constructor{I}...})>;
+
+template <class T, std::size_t... I, class /*Enable*/ = std::enable_if_t<!std::is_copy_constructible<T>::value>>
+constexpr auto enable_if_initializable_helper(std::index_sequence<I...>) noexcept
+    -> std::add_pointer_t<decltype(T{ubiq_rref_constructor{I}...})>;
+
+template <class T, std::size_t N, class U = std::size_t, class /*Enable*/ = decltype(detail::enable_if_initializable_helper<T>(detail::make_index_sequence<N>()))>
+using enable_if_initializable_helper_t = U;
+
+template <class T, std::size_t N>
+constexpr auto is_initializable(long) noexcept
+    -> detail::enable_if_initializable_helper_t<T, N, bool>
+{
+    return true;
+}
+
+template <class T, std::size_t N>
+constexpr bool is_initializable(int) noexcept {
+    return false;
+}
+
+///////////////////// Helpers for range size detection
+template <std::size_t Begin, std::size_t Last>
+using is_one_element_range = std::integral_constant<bool, Begin == Last>;
+
+using multi_element_range = std::false_type;
+using one_element_range = std::true_type;
+
+#if !BOOST_PFR_USE_CPP26
+///////////////////// Fields count next expected compiler limitation
+constexpr std::size_t fields_count_compiler_limitation_next(std::size_t n) noexcept {
+#if defined(_MSC_VER) && (_MSC_VER <= 1920)
+    if (n < 1024)
+        return 1024;
+#else
+    static_cast<void>(n);
+#endif
+    return (std::numeric_limits<std::size_t>::max)();
+}
+
+///////////////////// Fields count upper bound based on sizeof(T)
+template <class T>
+constexpr std::size_t fields_count_upper_bound_loose() noexcept {
+    return sizeof(T) * std::numeric_limits<unsigned char>::digits + 1 /* +1 for "Arrays of Length Zero" extension */;
+}
+
+///////////////////// Fields count binary search.
+// Template instantiation: depth is O(log(result)), count is O(log(result)), cost is O(result * log(result)).
+template <class T, std::size_t Begin, std::size_t Last>
+constexpr std::size_t fields_count_binary_search(detail::one_element_range, long) noexcept {
+    static_assert(
+        Begin == Last,
+        "====================> Boost.PFR: Internal logic error."
+    );
+    return Begin;
+}
+
+template <class T, std::size_t Begin, std::size_t Last>
+constexpr std::size_t fields_count_binary_search(detail::multi_element_range, int) noexcept;
+
+template <class T, std::size_t Begin, std::size_t Last>
+constexpr auto fields_count_binary_search(detail::multi_element_range, long) noexcept
+    -> detail::enable_if_initializable_helper_t<T, (Begin + Last + 1) / 2>
+{
+    constexpr std::size_t next_v = (Begin + Last + 1) / 2;
+    return detail::fields_count_binary_search<T, next_v, Last>(detail::is_one_element_range<next_v, Last>{}, 1L);
+}
+
+template <class T, std::size_t Begin, std::size_t Last>
+constexpr std::size_t fields_count_binary_search(detail::multi_element_range, int) noexcept {
+    constexpr std::size_t next_v = (Begin + Last + 1) / 2 - 1;
+    return detail::fields_count_binary_search<T, Begin, next_v>(detail::is_one_element_range<Begin, next_v>{}, 1L);
+}
+
+template <class T, std::size_t Begin, std::size_t N>
+constexpr std::size_t fields_count_upper_bound(int, int) noexcept {
+    return N - 1;
+}
+
+template <class T, std::size_t Begin, std::size_t N>
+constexpr auto fields_count_upper_bound(long, long) noexcept
+    -> std::enable_if_t<(N > detail::fields_count_upper_bound_loose<T>()), std::size_t>
+{
+    static_assert(
+        !detail::is_initializable<T, detail::fields_count_upper_bound_loose<T>() + 1>(1L),
+        "====================> Boost.PFR: Types with user specified constructors (non-aggregate initializable types) are not supported.");
+    return detail::fields_count_upper_bound_loose<T>();
+}
+
+template <class T, std::size_t Begin, std::size_t N>
+constexpr auto fields_count_upper_bound(long, int) noexcept
+    -> detail::enable_if_initializable_helper_t<T, N>
+{
+    constexpr std::size_t next_optimal = Begin + (N - Begin) * 2;
+    constexpr std::size_t next = detail::min_of_size_t(next_optimal, detail::fields_count_compiler_limitation_next(N));
+    return detail::fields_count_upper_bound<T, Begin, next>(1L, 1L);
+}
+
+///////////////////// Fields count lower bound linear search.
+// Template instantiation: depth is O(log(result)), count is O(result), cost is O(result^2).
+template <class T, std::size_t Begin, std::size_t Last, class RangeSize, std::size_t Result>
+constexpr std::size_t fields_count_lower_bound(RangeSize, size_t_<Result>) noexcept {
+    return Result;
+}
+
+template <class T, std::size_t Begin, std::size_t Last>
+constexpr std::size_t fields_count_lower_bound(detail::one_element_range, size_t_<0> = {}) noexcept {
+    static_assert(
+        Begin == Last,
+        "====================> Boost.PFR: Internal logic error."
+    );
+    return detail::is_initializable<T, Begin>(1L) ? Begin : 0;
+}
+
+template <class T, std::size_t Begin, std::size_t Last>
+constexpr std::size_t fields_count_lower_bound(detail::multi_element_range, size_t_<0> = {}) noexcept {
+    // Binary partition to limit template depth.
+    constexpr std::size_t middle = Begin + (Last - Begin) / 2;
+    constexpr std::size_t result_maybe = detail::fields_count_lower_bound<T, Begin, middle>(
+        detail::is_one_element_range<Begin, middle>{}
+    );
+    return detail::fields_count_lower_bound<T, middle + 1, Last>(
+        detail::is_one_element_range<middle + 1, Last>{},
+        size_t_<result_maybe>{}
+    );
+}
+
+template <class T, std::size_t Begin, std::size_t Result>
+constexpr std::size_t fields_count_lower_bound_unbounded(int, size_t_<Result>) noexcept {
+    return Result;
+}
+
+template <class T, std::size_t Begin>
+constexpr auto fields_count_lower_bound_unbounded(long, size_t_<0>) noexcept
+    -> std::enable_if_t<(Begin >= detail::fields_count_upper_bound_loose<T>()), std::size_t>
+{
+    static_assert(
+        detail::is_initializable<T, detail::fields_count_upper_bound_loose<T>()>(1L),
+        "====================> Boost.PFR: Type must be aggregate initializable.");
+    return detail::fields_count_upper_bound_loose<T>();
+}
+
+template <class T, std::size_t Begin>
+constexpr std::size_t fields_count_lower_bound_unbounded(int, size_t_<0>) noexcept {
+    constexpr std::size_t last = detail::min_of_size_t(Begin * 2, detail::fields_count_upper_bound_loose<T>()) - 1;
+    constexpr std::size_t result_maybe = detail::fields_count_lower_bound<T, Begin, last>(
+        detail::is_one_element_range<Begin, last>{}
+    );
+    return detail::fields_count_lower_bound_unbounded<T, last + 1>(1L, size_t_<result_maybe>{});
+}
+#endif
+
+///////////////////// Choosing between array size, unbounded binary search, and linear search followed by unbounded binary search.
+template <class T>
+constexpr auto fields_count_dispatch(long, long, std::false_type /*are_preconditions_met*/) noexcept {
+    return 0;
+}
+
+template <class T>
+constexpr auto fields_count_dispatch(long, long, std::true_type /*are_preconditions_met*/) noexcept
+    -> std::enable_if_t<std::is_array<T>::value, std::size_t>
+{
+    return sizeof(T) / sizeof(std::remove_all_extents_t<T>);
+}
+
+#if BOOST_PFR_USE_CPP26
+template<class T>
+constexpr auto fields_count_dispatch_impl(const T &t) noexcept
+{
+    const auto &[... elts] = t;
+    return std::integral_constant<std::size_t, sizeof...(elts)>{};
+}
+
+template<class T>
+constexpr auto fields_count_dispatch(long, int, std::true_type /*are_preconditions_met*/) noexcept
+    -> std::enable_if_t<std::is_scalar<T>::value, std::size_t>
+{
+    return 1;
+}
+
+template<class T>
+constexpr auto fields_count_dispatch(int, int, std::true_type /*are_preconditions_met*/) noexcept
+{
+    return decltype(detail::fields_count_dispatch_impl(std::declval<const T &>()))::value;
+}
+#else
+template <class T>
+constexpr auto fields_count_dispatch(long, int, std::true_type /*are_preconditions_met*/) noexcept
+    -> decltype(sizeof(T{}))
+{
+    constexpr std::size_t typical_fields_count = 4;
+    constexpr std::size_t last = detail::fields_count_upper_bound<T, typical_fields_count / 2, typical_fields_count>(1L, 1L);
+    return detail::fields_count_binary_search<T, 0, last>(detail::is_one_element_range<0, last>{}, 1L);
+}
+
+template <class T>
+constexpr std::size_t fields_count_dispatch(int, int, std::true_type /*are_preconditions_met*/) noexcept {
+    // T is not default aggregate initializable. This means that at least one of the members is not default-constructible.
+    // Use linear search to find the smallest valid initializer, after which we unbounded binary search for the largest.
+    constexpr std::size_t begin = detail::fields_count_lower_bound_unbounded<T, 1>(1L, size_t_<0>{});
+
+    constexpr std::size_t last = detail::fields_count_upper_bound<T, begin, begin + 1>(1L, 1L);
+    return detail::fields_count_binary_search<T, begin, last>(detail::is_one_element_range<begin, last>{}, 1L);
+}
+#endif
+
+///////////////////// Returns fields count
+template <class T>
+constexpr std::size_t fields_count() noexcept {
+    using type = std::remove_cv_t<T>;
+
+    constexpr bool type_is_complete = detail::is_complete<type>::value;
+    static_assert(
+        type_is_complete,
+        "====================> Boost.PFR: Type must be complete."
+    );
+
+    constexpr bool type_is_not_a_reference = !std::is_reference<type>::value
+         || !type_is_complete // do not show assert if previous check failed
+    ;
+    static_assert(
+        type_is_not_a_reference,
+        "====================> 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."
+    );
+
+#if BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
+    constexpr bool type_fields_are_move_constructible = true;
+#else
+    constexpr bool type_fields_are_move_constructible =
+        std::is_copy_constructible<std::remove_all_extents_t<type>>::value || (
+            std::is_move_constructible<std::remove_all_extents_t<type>>::value
+            && std::is_move_assignable<std::remove_all_extents_t<type>>::value
+        )
+        || !type_is_not_a_reference // do not show assert if previous check failed
+    ;
+    static_assert(
+        type_fields_are_move_constructible,
+        "====================> Boost.PFR: Type and each field in the type must be copy constructible (or move constructible and move assignable)."
+    );
+#endif  // #if !BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
+
+    constexpr bool type_is_not_polymorphic = !std::is_polymorphic<type>::value;
+    static_assert(
+        type_is_not_polymorphic,
+        "====================> Boost.PFR: Type must have no virtual function, because otherwise it is not aggregate initializable."
+    );
+
+#ifdef __cpp_lib_is_aggregate
+    constexpr bool type_is_aggregate =
+        std::is_aggregate<type>::value             // Does not return `true` for built-in types.
+        || std::is_scalar<type>::value;
+    static_assert(
+        type_is_aggregate,
+        "====================> Boost.PFR: Type must be aggregate initializable."
+    );
+#else
+    constexpr bool type_is_aggregate = true;
+#endif
+
+// Can't use the following. See the non_std_layout.cpp test.
+//#if !BOOST_PFR_USE_CPP17
+//    static_assert(
+//        std::is_standard_layout<type>::value,   // Does not return `true` for structs that have non standard layout members.
+//        "Type must be aggregate initializable."
+//    );
+//#endif
+
+    constexpr bool no_errors =
+        type_is_complete && type_is_not_a_reference && type_fields_are_move_constructible
+        && type_is_not_polymorphic && type_is_aggregate;
+    constexpr std::size_t result
+        = detail::fields_count_dispatch<type>(1L, 1L, std::integral_constant<bool, no_errors>{});
+    detail::assert_first_not_base<type, result>(1L);
+
+#ifndef __cpp_lib_is_aggregate
+    constexpr bool type_is_aggregate_initializable_n =
+        detail::is_aggregate_initializable_n<type, result>::value  // Does not return `true` for built-in types.
+        || std::is_scalar<type>::value;
+    static_assert(
+        type_is_aggregate_initializable_n,
+        "====================> Boost.PFR: Types with user specified constructors (non-aggregate initializable types) are not supported."
+    );
+#else
+    constexpr bool type_is_aggregate_initializable_n = true;
+#endif
+
+    static_assert(
+        result != 0 || std::is_empty<type>::value || std::is_fundamental<type>::value || std::is_reference<type>::value || !no_errors || !type_is_aggregate_initializable_n,
+        "====================> 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."
+    );
+
+    return result;
+}
+
+}}} // namespace boost::pfr::detail
+
+#ifdef __clang__
+#   pragma clang diagnostic pop
+#endif
+
+#endif // BOOST_PFR_DETAIL_FIELDS_COUNT_HPP

include/boost/pfr/detail/for_each_field.hpp

@@ -0,0 +1,65 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_FOR_EACH_FIELD_HPP
+#define BOOST_PFR_DETAIL_FOR_EACH_FIELD_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/core.hpp>
+#include <boost/pfr/detail/fields_count.hpp>
+#include <boost/pfr/detail/for_each_field_impl.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>      // metaprogramming stuff
+#include <utility>          // forward_like
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+template <class T, class F>
+constexpr void for_each_field(T&& value, F&& func) {
+#if BOOST_PFR_USE_CPP26
+    using no_ref = std::remove_reference_t<T>;
+    if constexpr (std::is_aggregate_v<no_ref> || std::is_bounded_array_v<no_ref>) {
+        auto &&[... members] = value;
+        ::boost::pfr::detail::for_each_field_impl(value,
+                                                  std::forward<F>(func),
+                                                  std::make_index_sequence<sizeof...(members)>{},
+                                                  std::is_rvalue_reference<T &&>{});
+    } else {
+        ::boost::pfr::detail::for_each_field_impl(value,
+                                                  std::forward<F>(func),
+                                                  std::make_index_sequence<1>{},
+                                                  std::is_rvalue_reference<T &&>{});
+    }
+#else
+    constexpr std::size_t fields_count_val = boost::pfr::detail::fields_count<std::remove_reference_t<T>>();
+
+    ::boost::pfr::detail::for_each_field_dispatcher(
+        value,
+        [f = std::forward<F>(func)](auto&& t) mutable {
+            // MSVC related workaround. Its lambdas do not capture constexprs.
+            constexpr std::size_t fields_count_val_in_lambda
+                = boost::pfr::detail::fields_count<std::remove_reference_t<T>>();
+
+            ::boost::pfr::detail::for_each_field_impl(
+                t,
+                std::forward<F>(f),
+                detail::make_index_sequence<fields_count_val_in_lambda>{},
+                std::is_rvalue_reference<T&&>{}
+            );
+        },
+        detail::make_index_sequence<fields_count_val>{}
+    );
+#endif
+}
+
+}}} // namespace boost::pfr::detail
+
+
+#endif // BOOST_PFR_DETAIL_FOR_EACH_FIELD_HPP

include/boost/pfr/detail/for_each_field_impl.hpp

@@ -0,0 +1,89 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_FOR_EACH_FIELD_IMPL_HPP
+#define BOOST_PFR_DETAIL_FOR_EACH_FIELD_IMPL_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+#include <boost/pfr/detail/rvalue_t.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <utility>      // metaprogramming stuff
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+template <std::size_t Index>
+using size_t_ = std::integral_constant<std::size_t, Index >;
+
+template <class T, class F, class I, class = decltype(std::declval<F>()(std::declval<T>(), I{}))>
+constexpr void for_each_field_impl_apply(T&& v, F&& f, I i, long) {
+    std::forward<F>(f)(std::forward<T>(v), i);
+}
+
+template <class T, class F, class I>
+constexpr void for_each_field_impl_apply(T&& v, F&& f, I /*i*/, int) {
+    std::forward<F>(f)(std::forward<T>(v));
+}
+
+#if BOOST_PFR_USE_CPP26
+template<class T, class F, std::size_t... I>
+constexpr void for_each_field_impl(T& t, F&& f, std::index_sequence<I...>, auto move_values) {
+    if constexpr (std::is_aggregate_v<T> || std::is_bounded_array_v<T>) {
+        auto &&[... members] = t;
+        if constexpr (move_values)
+            (detail::for_each_field_impl_apply(std::move(members...[I]),
+                                               std::forward<F>(f),
+                                               size_t_<I>{},
+                                               1L),
+             ...);
+        else
+            (detail::for_each_field_impl_apply(
+                 members... [I], std::forward<F>(f), size_t_<I> {}, 1L),
+             ...);
+    } else {
+        if constexpr (move_values)
+            (detail::for_each_field_impl_apply(std::move(t), std::forward<F>(f), size_t_<I>{}, 1L),
+             ...);
+        else
+            (detail::for_each_field_impl_apply(t, std::forward<F>(f), size_t_<I>{}, 1L), ...);
+    }
+}
+#elif !defined(__cpp_fold_expressions) || __cpp_fold_expressions < 201603
+template <class T, class F, std::size_t... I>
+constexpr void for_each_field_impl(T& t, F&& f, std::index_sequence<I...>, std::false_type /*move_values*/) {
+     const int v[] = {0, (
+         detail::for_each_field_impl_apply(sequence_tuple::get<I>(t), std::forward<F>(f), size_t_<I>{}, 1L),
+         0
+     )...};
+     (void)v;
+}
+
+
+template <class T, class F, std::size_t... I>
+constexpr void for_each_field_impl(T& t, F&& f, std::index_sequence<I...>, std::true_type /*move_values*/) {
+     const int v[] = {0, (
+         detail::for_each_field_impl_apply(sequence_tuple::get<I>(std::move(t)), std::forward<F>(f), size_t_<I>{}, 1L),
+         0
+     )...};
+     (void)v;
+}
+#else
+template <class T, class F, std::size_t... I>
+constexpr void for_each_field_impl(T& t, F&& f, std::index_sequence<I...>, std::false_type /*move_values*/) {
+     (detail::for_each_field_impl_apply(sequence_tuple::get<I>(t), std::forward<F>(f), size_t_<I>{}, 1L), ...);
+}
+
+template <class T, class F, std::size_t... I>
+constexpr void for_each_field_impl(T& t, F&& f, std::index_sequence<I...>, std::true_type /*move_values*/) {
+     (detail::for_each_field_impl_apply(sequence_tuple::get<I>(std::move(t)), std::forward<F>(f), size_t_<I>{}, 1L), ...);
+}
+#endif
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_FOR_EACH_FIELD_IMPL_HPP

include/boost/pfr/detail/functional.hpp

@@ -0,0 +1,241 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_FUNCTIONAL_HPP
+#define BOOST_PFR_DETAIL_FUNCTIONAL_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <cstdint>
+#include <functional>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+    template <std::size_t I, std::size_t N>
+    struct equal_impl {
+        template <class T, class U>
+        constexpr static bool cmp(const T& v1, const U& v2) noexcept {
+            return ::boost::pfr::detail::sequence_tuple::get<I>(v1) == ::boost::pfr::detail::sequence_tuple::get<I>(v2)
+                && equal_impl<I + 1, N>::cmp(v1, v2);
+        }
+    };
+
+    template <std::size_t N>
+    struct equal_impl<N, N> {
+        template <class T, class U>
+        constexpr static bool cmp(const T&, const U&) noexcept {
+            return T::size_v == U::size_v;
+        }
+    };
+
+    template <std::size_t I, std::size_t N>
+    struct not_equal_impl {
+        template <class T, class U>
+        constexpr static bool cmp(const T& v1, const U& v2) noexcept {
+            return ::boost::pfr::detail::sequence_tuple::get<I>(v1) != ::boost::pfr::detail::sequence_tuple::get<I>(v2)
+                || not_equal_impl<I + 1, N>::cmp(v1, v2);
+        }
+    };
+
+    template <std::size_t N>
+    struct not_equal_impl<N, N> {
+        template <class T, class U>
+        constexpr static bool cmp(const T&, const U&) noexcept {
+            return T::size_v != U::size_v;
+        }
+    };
+
+    template <std::size_t I, std::size_t N>
+    struct less_impl {
+        template <class T, class U>
+        constexpr static bool cmp(const T& v1, const U& v2) noexcept {
+            return sequence_tuple::get<I>(v1) < sequence_tuple::get<I>(v2)
+                || (sequence_tuple::get<I>(v1) == sequence_tuple::get<I>(v2) && less_impl<I + 1, N>::cmp(v1, v2));
+        }
+    };
+
+    template <std::size_t N>
+    struct less_impl<N, N> {
+        template <class T, class U>
+        constexpr static bool cmp(const T&, const U&) noexcept {
+            return T::size_v < U::size_v;
+        }
+    };
+
+    template <std::size_t I, std::size_t N>
+    struct less_equal_impl {
+        template <class T, class U>
+        constexpr static bool cmp(const T& v1, const U& v2) noexcept {
+            return sequence_tuple::get<I>(v1) < sequence_tuple::get<I>(v2)
+                || (sequence_tuple::get<I>(v1) == sequence_tuple::get<I>(v2) && less_equal_impl<I + 1, N>::cmp(v1, v2));
+        }
+    };
+
+    template <std::size_t N>
+    struct less_equal_impl<N, N> {
+        template <class T, class U>
+        constexpr static bool cmp(const T&, const U&) noexcept {
+            return T::size_v <= U::size_v;
+        }
+    };
+
+    template <std::size_t I, std::size_t N>
+    struct greater_impl {
+        template <class T, class U>
+        constexpr static bool cmp(const T& v1, const U& v2) noexcept {
+            return sequence_tuple::get<I>(v1) > sequence_tuple::get<I>(v2)
+                || (sequence_tuple::get<I>(v1) == sequence_tuple::get<I>(v2) && greater_impl<I + 1, N>::cmp(v1, v2));
+        }
+    };
+
+    template <std::size_t N>
+    struct greater_impl<N, N> {
+        template <class T, class U>
+        constexpr static bool cmp(const T&, const U&) noexcept {
+            return T::size_v > U::size_v;
+        }
+    };
+
+    template <std::size_t I, std::size_t N>
+    struct greater_equal_impl {
+        template <class T, class U>
+        constexpr static bool cmp(const T& v1, const U& v2) noexcept {
+            return sequence_tuple::get<I>(v1) > sequence_tuple::get<I>(v2)
+                || (sequence_tuple::get<I>(v1) == sequence_tuple::get<I>(v2) && greater_equal_impl<I + 1, N>::cmp(v1, v2));
+        }
+    };
+
+    template <std::size_t N>
+    struct greater_equal_impl<N, N> {
+        template <class T, class U>
+        constexpr static bool cmp(const T&, const U&) noexcept {
+            return T::size_v >= U::size_v;
+        }
+    };
+
+    // Hash combine functions copied from Boost.ContainerHash
+    // https://github.com/boostorg/container_hash/blob/171c012d4723c5e93cc7cffe42919afdf8b27dfa/include/boost/container_hash/hash.hpp#L311
+    // that is based on Peter Dimov's proposal
+    // http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
+    // issue 6.18.
+    //
+    // This also contains public domain code from MurmurHash. From the
+    // MurmurHash header:
+    //
+    // MurmurHash3 was written by Austin Appleby, and is placed in the public
+    // domain. The author hereby disclaims copyright to this source code.
+    template <typename SizeT>
+    constexpr void hash_combine(SizeT& seed, SizeT value) noexcept {
+        seed ^= value + 0x9e3779b9 + (seed<<6) + (seed>>2);
+    }
+
+    constexpr auto rotl(std::uint32_t x, std::uint32_t r) noexcept {
+        return (x << r) | (x >> (32 - r));
+    }
+
+    constexpr void hash_combine(std::uint32_t& h1, std::uint32_t k1) noexcept {
+          const std::uint32_t c1 = 0xcc9e2d51;
+          const std::uint32_t c2 = 0x1b873593;
+
+          k1 *= c1;
+          k1 = detail::rotl(k1,15);
+          k1 *= c2;
+
+          h1 ^= k1;
+          h1 = detail::rotl(h1,13);
+          h1 = h1*5+0xe6546b64;
+    }
+
+#if defined(INT64_MIN) && defined(UINT64_MAX)
+    constexpr void hash_combine(std::uint64_t& h, std::uint64_t k) noexcept {
+        const std::uint64_t m = 0xc6a4a7935bd1e995ULL;
+        const int r = 47;
+
+        k *= m;
+        k ^= k >> r;
+        k *= m;
+
+        h ^= k;
+        h *= m;
+
+        // Completely arbitrary number, to prevent 0's
+        // from hashing to 0.
+        h += 0xe6546b64;
+    }
+#endif
+
+    template <typename T>
+    auto compute_hash(const T& value, long /*priority*/)
+        -> decltype(std::hash<T>()(value))
+    {
+        return std::hash<T>()(value);
+    }
+
+    template <typename T>
+    std::size_t compute_hash(const T& /*value*/, int /*priority*/) {
+        static_assert(sizeof(T) && false, "====================> Boost.PFR: std::hash not specialized for type T");
+        return 0;
+    }
+
+    template <std::size_t I, std::size_t N>
+    struct hash_impl {
+        template <class T>
+        constexpr static std::size_t compute(const T& val) noexcept {
+            std::size_t h = detail::compute_hash( ::boost::pfr::detail::sequence_tuple::get<I>(val), 1L );
+            detail::hash_combine(h, hash_impl<I + 1, N>::compute(val) );
+            return h;
+        }
+    };
+
+    template <std::size_t N>
+    struct hash_impl<N, N> {
+        template <class T>
+        constexpr static std::size_t compute(const T&) noexcept {
+            return 0;
+        }
+    };
+
+///////////////////// Define min_element and to avoid inclusion of <algorithm>
+    constexpr std::size_t min_size(std::size_t x, std::size_t y) noexcept {
+        return x < y ? x : y;
+    }
+
+    template <template <std::size_t, std::size_t> class Visitor, class T, class U>
+    constexpr bool binary_visit(const T& x, const U& y) {
+        constexpr std::size_t fields_count_lhs = detail::fields_count<std::remove_reference_t<T>>();
+        constexpr std::size_t fields_count_rhs = detail::fields_count<std::remove_reference_t<U>>();
+        constexpr std::size_t fields_count_min = detail::min_size(fields_count_lhs, fields_count_rhs);
+        typedef Visitor<0, fields_count_min> visitor_t;
+
+#if BOOST_PFR_USE_CPP17 || BOOST_PFR_USE_LOOPHOLE
+        return visitor_t::cmp(detail::tie_as_tuple(x), detail::tie_as_tuple(y));
+#else
+        bool result = true;
+        ::boost::pfr::detail::for_each_field_dispatcher(
+            x,
+            [&result, &y](const auto& lhs) {
+                constexpr std::size_t fields_count_rhs_ = detail::fields_count<std::remove_reference_t<U>>();
+                ::boost::pfr::detail::for_each_field_dispatcher(
+                    y,
+                    [&result, &lhs](const auto& rhs) {
+                        result = visitor_t::cmp(lhs, rhs);
+                    },
+                    detail::make_index_sequence<fields_count_rhs_>{}
+                );
+            },
+            detail::make_index_sequence<fields_count_lhs>{}
+        );
+
+        return result;
+#endif
+    }
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_FUNCTIONAL_HPP

include/boost/pfr/detail/io.hpp

@@ -0,0 +1,89 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_IO_HPP
+#define BOOST_PFR_DETAIL_IO_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <iosfwd>       // stream operators
+#include <iomanip>
+
+#if defined(__has_include)
+#   if __has_include(<string_view>) && BOOST_PFR_USE_CPP17
+#       include <string_view>
+#   endif
+#endif
+
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+inline auto quoted_helper(const std::string& s) noexcept {
+    return std::quoted(s);
+}
+
+#if defined(__has_include)
+#   if __has_include(<string_view>) && BOOST_PFR_USE_CPP17
+template <class CharT, class Traits>
+inline auto quoted_helper(std::basic_string_view<CharT, Traits> s) noexcept {
+    return std::quoted(s);
+}
+#   endif
+#endif
+
+inline auto quoted_helper(std::string& s) noexcept {
+    return std::quoted(s);
+}
+
+template <class T>
+inline decltype(auto) quoted_helper(T&& v) noexcept {
+    return std::forward<T>(v);
+}
+
+template <std::size_t I, std::size_t N>
+struct print_impl {
+    template <class Stream, class T>
+    static void print (Stream& out, const T& value) {
+        if (!!I) out << ", ";
+        out << detail::quoted_helper(boost::pfr::detail::sequence_tuple::get<I>(value));
+        print_impl<I + 1, N>::print(out, value);
+    }
+};
+
+template <std::size_t I>
+struct print_impl<I, I> {
+    template <class Stream, class T> static void print (Stream&, const T&) noexcept {}
+};
+
+
+template <std::size_t I, std::size_t N>
+struct read_impl {
+    template <class Stream, class T>
+    static void read (Stream& in, const T& value) {
+        char ignore = {};
+        if (!!I) {
+            in >> ignore;
+            if (ignore != ',') in.setstate(Stream::failbit);
+            in >> ignore;
+            if (ignore != ' ')  in.setstate(Stream::failbit);
+        }
+        in >> detail::quoted_helper( boost::pfr::detail::sequence_tuple::get<I>(value) );
+        read_impl<I + 1, N>::read(in, value);
+    }
+};
+
+template <std::size_t I>
+struct read_impl<I, I> {
+    template <class Stream, class T> static void read (Stream&, const T&) {}
+};
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_IO_HPP

include/boost/pfr/detail/make_flat_tuple_of_references.hpp

@@ -0,0 +1,98 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_MAKE_FLAT_TUPLE_OF_REFERENCES_HPP
+#define BOOST_PFR_DETAIL_MAKE_FLAT_TUPLE_OF_REFERENCES_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+#include <boost/pfr/detail/rvalue_t.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <utility>      // metaprogramming stuff
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+template <std::size_t Index>
+using size_t_ = std::integral_constant<std::size_t, Index >;
+
+// Helper: Make a "getter" object corresponding to built-in tuple::get
+// For user-defined structures, the getter should be "offset_based_getter"
+struct sequence_tuple_getter {
+  template <std::size_t idx, typename TupleOfReferences>
+  decltype(auto) get(TupleOfReferences&& t, size_t_<idx>) const noexcept {
+    return sequence_tuple::get<idx>(std::forward<TupleOfReferences>(t));
+  }
+};
+
+
+template <class TupleOrUserType, class Getter, std::size_t Begin, std::size_t Size>
+constexpr auto make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<Size>) noexcept;
+
+template <class TupleOrUserType, class Getter, std::size_t Begin>
+constexpr sequence_tuple::tuple<> make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<0>) noexcept;
+
+template <class TupleOrUserType, class Getter, std::size_t Begin>
+constexpr auto make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<1>) noexcept;
+
+template <class... T>
+constexpr auto tie_as_tuple_with_references(T&... args) noexcept {
+    return sequence_tuple::tuple<T&...>{ args... };
+}
+
+template <class... T>
+constexpr decltype(auto) tie_as_tuple_with_references(detail::sequence_tuple::tuple<T...>& t) noexcept {
+    return detail::make_flat_tuple_of_references(t, sequence_tuple_getter{}, size_t_<0>{}, size_t_<sequence_tuple::tuple<T...>::size_v>{});
+}
+
+template <class... T>
+constexpr decltype(auto) tie_as_tuple_with_references(const detail::sequence_tuple::tuple<T...>& t) noexcept {
+    return detail::make_flat_tuple_of_references(t, sequence_tuple_getter{}, size_t_<0>{}, size_t_<sequence_tuple::tuple<T...>::size_v>{});
+}
+
+template <class Tuple1, std::size_t... I1, class Tuple2, std::size_t... I2>
+constexpr auto my_tuple_cat_impl(const Tuple1& t1, std::index_sequence<I1...>, const Tuple2& t2, std::index_sequence<I2...>) noexcept {
+    return detail::tie_as_tuple_with_references(
+        sequence_tuple::get<I1>(t1)...,
+        sequence_tuple::get<I2>(t2)...
+    );
+}
+
+template <class Tuple1, class Tuple2>
+constexpr auto my_tuple_cat(const Tuple1& t1, const Tuple2& t2) noexcept {
+    return detail::my_tuple_cat_impl(
+        t1, detail::make_index_sequence< Tuple1::size_v >{},
+        t2, detail::make_index_sequence< Tuple2::size_v >{}
+    );
+}
+
+template <class TupleOrUserType, class Getter, std::size_t Begin, std::size_t Size>
+constexpr auto make_flat_tuple_of_references(TupleOrUserType& t, const Getter& g, size_t_<Begin>, size_t_<Size>) noexcept {
+    constexpr std::size_t next_size = Size / 2;
+    return detail::my_tuple_cat(
+        detail::make_flat_tuple_of_references(t, g, size_t_<Begin>{}, size_t_<next_size>{}),
+        detail::make_flat_tuple_of_references(t, g, size_t_<Begin + Size / 2>{}, size_t_<Size - next_size>{})
+    );
+}
+
+template <class TupleOrUserType, class Getter, std::size_t Begin>
+constexpr sequence_tuple::tuple<> make_flat_tuple_of_references(TupleOrUserType&, const Getter&, size_t_<Begin>, size_t_<0>) noexcept {
+    return {};
+}
+
+template <class TupleOrUserType, class Getter, std::size_t Begin>
+constexpr auto make_flat_tuple_of_references(TupleOrUserType& t, const Getter& g, size_t_<Begin>, size_t_<1>) noexcept {
+    return detail::tie_as_tuple_with_references(
+        g.get(t, size_t_<Begin>{})
+    );
+}
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_MAKE_FLAT_TUPLE_OF_REFERENCES_HPP

include/boost/pfr/detail/make_integer_sequence.hpp

@@ -0,0 +1,92 @@
+// Copyright (c) 2018 Sergei Fedorov
+// Copyright (c) 2019-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_MAKE_INTEGER_SEQUENCE_HPP
+#define BOOST_PFR_DETAIL_MAKE_INTEGER_SEQUENCE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <utility>
+#include <cstddef>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+#if BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == 0
+
+#ifdef __has_builtin
+#   if __has_builtin(__make_integer_seq)
+#       define BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
+#   endif
+#endif
+
+#ifdef BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
+
+using std::integer_sequence;
+
+// Clang unable to use namespace qualified std::integer_sequence in __make_integer_seq.
+template <typename T, T N>
+using make_integer_sequence = __make_integer_seq<integer_sequence, T, N>;
+
+#undef BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
+
+#else
+
+template <typename T, typename U>
+struct join_sequences;
+
+template <typename T, T... A, T... B>
+struct join_sequences<std::integer_sequence<T, A...>, std::integer_sequence<T, B...>> {
+    using type = std::integer_sequence<T, A..., B...>;
+};
+
+template <typename T, T Min, T Max>
+struct build_sequence_impl {
+    static_assert(Min < Max, "Start of range must be less than its end");
+    static constexpr T size = Max - Min;
+    using type = typename join_sequences<
+            typename build_sequence_impl<T, Min, Min + size / 2>::type,
+            typename build_sequence_impl<T, Min + size / 2 + 1, Max>::type
+        >::type;
+};
+
+template <typename T, T V>
+struct build_sequence_impl<T, V, V> {
+    using type = std::integer_sequence<T, V>;
+};
+
+template <typename T, std::size_t N>
+struct make_integer_sequence_impl : build_sequence_impl<T, 0, N - 1> {};
+
+template <typename T>
+struct make_integer_sequence_impl<T, 0> {
+    using type = std::integer_sequence<T>;
+};
+
+template <typename T, T N>
+using make_integer_sequence = typename make_integer_sequence_impl<T, N>::type;
+
+#endif // !defined BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
+#else // BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == 1
+
+template <typename T, T N>
+using make_integer_sequence = std::make_integer_sequence<T, N>;
+
+#endif // BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == 1
+
+template <std::size_t N>
+using make_index_sequence = make_integer_sequence<std::size_t, N>;
+
+template <typename... T>
+using index_sequence_for = make_index_sequence<sizeof...(T)>;
+
+}}} // namespace boost::pfr::detail
+
+#endif
+

include/boost/pfr/detail/offset_based_getter.hpp

@@ -0,0 +1,143 @@
+// Copyright (c) 2017-2018 Chris Beck
+// Copyright (c) 2019-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_OFFSET_BASED_GETTER_HPP
+#define BOOST_PFR_DETAIL_OFFSET_BASED_GETTER_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+#include <boost/pfr/detail/rvalue_t.hpp>
+#include <boost/pfr/detail/size_t_.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <utility>
+#include <memory>  // std::addressof
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+// Our own implementation of std::aligned_storage. On godbolt with MSVC, I have compilation errors
+// using the standard version, it seems the compiler cannot generate default ctor.
+
+template<std::size_t s, std::size_t a>
+struct internal_aligned_storage {
+   alignas(a) char storage_[s];
+};
+
+// Metafunction that replaces tuple<T1, T2, T3, ...> with
+// tuple<std::aligned_storage_t<sizeof(T1), alignof(T1)>, std::aligned_storage<sizeof(T2), alignof(T2)>, ...>
+//
+// The point is, the new tuple is "layout compatible" in the sense that members have the same offsets,
+// but this tuple is constexpr constructible.
+
+template <typename T>
+struct tuple_of_aligned_storage;
+
+template <typename... Ts>
+struct tuple_of_aligned_storage<sequence_tuple::tuple<Ts...>> {
+  using type = sequence_tuple::tuple<internal_aligned_storage<sizeof(Ts),
+#if defined(__GNUC__) && __GNUC__ < 8 && !defined(__x86_64__) && !defined(__CYGWIN__)
+      // Before GCC-8 the `alignof` was returning the optimal alignment rather than the minimal one.
+      // We have to adjust the alignment because otherwise we get the wrong offset.
+      (alignof(Ts) > 4 ? 4 : alignof(Ts))
+#else
+      alignof(Ts)
+#endif
+  >...>;
+};
+
+// Note: If pfr has a typelist also, could also have an overload for that here
+
+template <typename T>
+using tuple_of_aligned_storage_t = typename tuple_of_aligned_storage<T>::type;
+
+/***
+ * Given a structure type and its sequence of members, we want to build a function
+ * object "getter" that implements a version of `std::get` using offset arithmetic
+ * and reinterpret_cast.
+ *
+ * typename U should be a user-defined struct
+ * typename S should be a sequence_tuple which is layout compatible with U
+ */
+
+template <typename U, typename S>
+class offset_based_getter {
+  using this_t = offset_based_getter<U, S>;
+
+  static_assert(sizeof(U) == sizeof(S), "====================> Boost.PFR: Member sequence does not indicate correct size for struct type! Maybe the user-provided type is not a SimpleAggregate?");
+  static_assert(alignof(U) == alignof(S), "====================> Boost.PFR: Member sequence does not indicate correct alignment for struct type!");
+
+  static_assert(!std::is_const<U>::value, "====================> Boost.PFR: const should be stripped from user-defined type when using offset_based_getter or overload resolution will be ambiguous later, this indicates an error within pfr");
+  static_assert(!std::is_reference<U>::value, "====================> Boost.PFR: reference should be stripped from user-defined type when using offset_based_getter or overload resolution will be ambiguous later, this indicates an error within pfr");
+  static_assert(!std::is_volatile<U>::value, "====================> Boost.PFR: volatile should be stripped from user-defined type when using offset_based_getter or overload resolution will be ambiguous later. this indicates an error within pfr");
+
+  // Get type of idx'th member
+  template <std::size_t idx>
+  using index_t = typename sequence_tuple::tuple_element<idx, S>::type;
+
+  // Get offset of idx'th member
+  // Idea: Layout object has the same offsets as instance of S, so if S and U are layout compatible, then these offset
+  // calculations are correct.
+  template <std::size_t idx>
+  static constexpr std::ptrdiff_t offset() noexcept {
+    constexpr tuple_of_aligned_storage_t<S> layout{};
+    return &sequence_tuple::get<idx>(layout).storage_[0] - &sequence_tuple::get<0>(layout).storage_[0];
+  }
+
+  // Encapsulates offset arithmetic and reinterpret_cast
+  template <std::size_t idx>
+  static index_t<idx> * get_pointer(U * u) noexcept {
+    return reinterpret_cast<index_t<idx> *>(reinterpret_cast<char *>(u) + this_t::offset<idx>());
+  }
+
+  template <std::size_t idx>
+  static const index_t<idx> * get_pointer(const U * u) noexcept {
+    return reinterpret_cast<const index_t<idx> *>(reinterpret_cast<const char *>(u) + this_t::offset<idx>());
+  }
+
+  template <std::size_t idx>
+  static volatile index_t<idx> * get_pointer(volatile U * u) noexcept {
+    return reinterpret_cast<volatile index_t<idx> *>(reinterpret_cast<volatile char *>(u) + this_t::offset<idx>());
+  }
+
+  template <std::size_t idx>
+  static const volatile index_t<idx> * get_pointer(const volatile U * u) noexcept {
+    return reinterpret_cast<const volatile index_t<idx> *>(reinterpret_cast<const volatile char *>(u) + this_t::offset<idx>());
+  }
+
+public:
+  template <std::size_t idx>
+  index_t<idx> & get(U & u, size_t_<idx>) const noexcept {
+    return *this_t::get_pointer<idx>(std::addressof(u));
+  }
+
+  template <std::size_t idx>
+  index_t<idx> const & get(U const & u, size_t_<idx>) const noexcept {
+    return *this_t::get_pointer<idx>(std::addressof(u));
+  }
+
+  template <std::size_t idx>
+  index_t<idx> volatile & get(U volatile & u, size_t_<idx>) const noexcept {
+    return *this_t::get_pointer<idx>(std::addressof(u));
+  }
+
+  template <std::size_t idx>
+  index_t<idx> const volatile & get(U const volatile & u, size_t_<idx>) const noexcept {
+    return *this_t::get_pointer<idx>(std::addressof(u));
+  }
+
+  // rvalues must not be used here, to avoid template instantiation bloats.
+  template <std::size_t idx>
+  index_t<idx> && get(rvalue_t<U> u, size_t_<idx>) const = delete;
+};
+
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_OFFSET_LIST_HPP

include/boost/pfr/detail/possible_reflectable.hpp

@@ -0,0 +1,51 @@
+// Copyright (c) 2022 Denis Mikhailov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_POSSIBLE_REFLECTABLE_HPP
+#define BOOST_PFR_DETAIL_POSSIBLE_REFLECTABLE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+#include <boost/pfr/traits_fwd.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits> // for std::is_aggregate
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+///////////////////// Returns false when the type exactly wasn't be reflectable
+template <class T, class WhatFor>
+constexpr decltype(is_reflectable<T, WhatFor>::value) possible_reflectable(long) noexcept {
+    return is_reflectable<T, WhatFor>::value;
+}
+
+#if BOOST_PFR_ENABLE_IMPLICIT_REFLECTION
+
+template <class T, class WhatFor>
+constexpr bool possible_reflectable(int) noexcept {
+#   if  defined(__cpp_lib_is_aggregate)
+    using type = std::remove_cv_t<T>;
+    return std::is_aggregate<type>();
+#   else
+    return true;
+#   endif
+}
+
+#else
+
+template <class T, class WhatFor>
+constexpr bool possible_reflectable(int) noexcept {
+    // negative answer here won't change behaviour in PFR-dependent libraries(like Fusion)
+    return false;
+}
+
+#endif
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_POSSIBLE_REFLECTABLE_HPP
+
+

include/boost/pfr/detail/rvalue_t.hpp

@@ -0,0 +1,37 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_RVALUE_T_HPP
+#define BOOST_PFR_DETAIL_RVALUE_T_HPP
+#pragma once
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <utility>      // std::enable_if_t
+#endif
+
+// This header provides aliases rvalue_t and lvalue_t.
+//
+// Usage: template <class T> void foo(rvalue<T> rvalue);
+//
+// Those are useful for
+//  * better type safety - you can validate at compile time that only rvalue reference is passed into the function
+//  * documentation and readability - rvalue_t<T> is much better than T&&+SFINAE
+
+namespace boost { namespace pfr { namespace detail {
+
+/// Binds to rvalues only, no copying allowed.
+template <class T
+#ifdef BOOST_PFR_DETAIL_STRICT_RVALUE_TESTING
+    , class = std::enable_if_t<std::is_rvalue_reference<T&&>::value>
+#endif
+>
+using rvalue_t = T&&;
+
+/// Binds to mutable lvalues only
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_RVALUE_T_HPP

include/boost/pfr/detail/sequence_tuple.hpp

@@ -0,0 +1,180 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_SEQUENCE_TUPLE_HPP
+#define BOOST_PFR_DETAIL_SEQUENCE_TUPLE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <utility>      // metaprogramming stuff
+#include <cstddef>      // std::size_t
+#endif
+
+///////////////////// Tuple that holds its values in the supplied order
+namespace boost { namespace pfr { namespace detail { namespace sequence_tuple {
+
+template <std::size_t N, class T>
+struct base_from_member {
+    T value;
+};
+
+template <class I, class ...Tail>
+struct tuple_base;
+
+
+
+template <std::size_t... I, class ...Tail>
+struct tuple_base< std::index_sequence<I...>, Tail... >
+    : base_from_member<I , Tail>...
+{
+    static constexpr std::size_t size_v = sizeof...(I);
+
+    // We do not use `noexcept` in the following functions, because if user forget to put one then clang will issue an error:
+    // "error: exception specification of explicitly defaulted default constructor does not match the calculated one".
+    constexpr tuple_base() = default;
+    constexpr tuple_base(tuple_base&&) = default;
+    constexpr tuple_base(const tuple_base&) = default;
+
+    constexpr tuple_base(Tail... v) noexcept
+        : base_from_member<I, Tail>{ v }...
+    {}
+};
+
+template <>
+struct tuple_base<std::index_sequence<> > {
+    static constexpr std::size_t size_v = 0;
+};
+
+template <std::size_t N, class T>
+constexpr T& get_impl(base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <std::size_t N, class T>
+constexpr const T& get_impl(const base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <std::size_t N, class T>
+constexpr volatile T& get_impl(volatile base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <std::size_t N, class T>
+constexpr const volatile T& get_impl(const volatile base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <std::size_t N, class T>
+constexpr T&& get_impl(base_from_member<N, T>&& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return std::forward<T>(t.value);
+}
+
+
+template <class T, std::size_t N>
+constexpr T& get_by_type_impl(base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr const T& get_by_type_impl(const base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr volatile T& get_by_type_impl(volatile base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr const volatile T& get_by_type_impl(const volatile base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr T&& get_by_type_impl(base_from_member<N, T>&& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return std::forward<T>(t.value);
+}
+
+template <class T, std::size_t N>
+constexpr const T&& get_by_type_impl(const base_from_member<N, T>&& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn,clang-analyzer-core.CallAndMessage)
+    return std::forward<T>(t.value);
+}
+
+
+
+
+template <class ...Values>
+struct tuple: tuple_base<
+    detail::index_sequence_for<Values...>,
+    Values...>
+{
+    using tuple_base<
+        detail::index_sequence_for<Values...>,
+        Values...
+    >::tuple_base;
+
+    constexpr static std::size_t size() noexcept { return sizeof...(Values); }
+    constexpr static bool empty() noexcept { return size() == 0; }
+};
+
+
+template <std::size_t N, class ...T>
+constexpr decltype(auto) get(tuple<T...>& t) noexcept {
+    static_assert(N < tuple<T...>::size_v, "====================> Boost.PFR: Tuple index out of bounds");
+    return sequence_tuple::get_impl<N>(t);
+}
+
+template <std::size_t N, class ...T>
+constexpr decltype(auto) get(const tuple<T...>& t) noexcept {
+    static_assert(N < tuple<T...>::size_v, "====================> Boost.PFR: Tuple index out of bounds");
+    return sequence_tuple::get_impl<N>(t);
+}
+
+template <std::size_t N, class ...T>
+constexpr decltype(auto) get(const volatile tuple<T...>& t) noexcept {
+    static_assert(N < tuple<T...>::size_v, "====================> Boost.PFR: Tuple index out of bounds");
+    return sequence_tuple::get_impl<N>(t);
+}
+
+template <std::size_t N, class ...T>
+constexpr decltype(auto) get(volatile tuple<T...>& t) noexcept {
+    static_assert(N < tuple<T...>::size_v, "====================> Boost.PFR: Tuple index out of bounds");
+    return sequence_tuple::get_impl<N>(t);
+}
+
+template <std::size_t N, class ...T>
+constexpr decltype(auto) get(tuple<T...>&& t) noexcept {
+    static_assert(N < tuple<T...>::size_v, "====================> Boost.PFR: Tuple index out of bounds");
+    return sequence_tuple::get_impl<N>(std::move(t));
+}
+
+template <std::size_t I, class T>
+using tuple_element = std::remove_reference< decltype(
+        ::boost::pfr::detail::sequence_tuple::get<I>( std::declval<T>() )
+    ) >;
+
+template <class... Args>
+constexpr auto make_sequence_tuple(Args... args) noexcept {
+    return ::boost::pfr::detail::sequence_tuple::tuple<Args...>{ args... };
+}
+
+}}}} // namespace boost::pfr::detail::sequence_tuple
+
+#endif // BOOST_PFR_CORE_HPP

include/boost/pfr/detail/size_array.hpp

@@ -0,0 +1,81 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_SIZE_ARRAY_HPP
+#define BOOST_PFR_DETAIL_SIZE_ARRAY_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <cstddef>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+///////////////////// Array that has the constexpr
+template <std::size_t N>
+struct size_array {                         // libc++ misses constexpr on operator[]
+    typedef std::size_t type;
+    std::size_t data[N];
+
+    static constexpr std::size_t size() noexcept { return N; }
+
+    constexpr std::size_t count_nonzeros() const noexcept {
+        std::size_t count = 0;
+        for (std::size_t i = 0; i < size(); ++i) {
+            if (data[i]) {
+                ++ count;
+            }
+        }
+        return count;
+    }
+
+    constexpr std::size_t count_from_opening_till_matching_parenthis_seq(std::size_t from, std::size_t opening_parenthis, std::size_t closing_parenthis) const noexcept {
+        if (data[from] != opening_parenthis) {
+            return 0;
+        }
+        std::size_t unclosed_parnthesis = 0;
+        std::size_t count = 0;
+        for (; ; ++from) {
+            if (data[from] == opening_parenthis) {
+                ++ unclosed_parnthesis;
+            } else if (data[from] == closing_parenthis) {
+                -- unclosed_parnthesis;
+            }
+            ++ count;
+
+            if (unclosed_parnthesis == 0) {
+                return count;
+            }
+        }
+
+        return count;
+    }
+};
+
+template <>
+struct size_array<0> {                         // libc++ misses constexpr on operator[]
+    typedef std::size_t type;
+    std::size_t data[1];
+
+    static constexpr std::size_t size() noexcept { return 0; }
+
+    constexpr std::size_t count_nonzeros() const noexcept {
+        return 0;
+    }
+};
+
+template <std::size_t I, std::size_t N>
+constexpr std::size_t get(const size_array<N>& a) noexcept {
+    static_assert(I < N, "====================> Boost.PFR: Array index out of bounds");
+    return a.data[I];
+}
+
+
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_SIZE_ARRAY_HPP

include/boost/pfr/detail/size_t_.hpp

@@ -0,0 +1,23 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_SIZE_T_HPP
+#define BOOST_PFR_DETAIL_SIZE_T_HPP
+#pragma once
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <cstddef>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+///////////////////// General utility stuff
+template <std::size_t Index>
+using size_t_ = std::integral_constant<std::size_t, Index >;
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_SIZE_T_HPP

include/boost/pfr/detail/stdarray.hpp

@@ -0,0 +1,41 @@
+// Copyright (c) 2023 Denis Mikhailov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_STDARRAY_HPP
+#define BOOST_PFR_DETAIL_STDARRAY_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <array>
+#if BOOST_PFR_CORE_NAME_ENABLED
+#   include <string_view>
+#endif
+#include <utility> // metaprogramming stuff
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+#if BOOST_PFR_CORE_NAME_ENABLED
+template <class T, std::size_t... I>
+constexpr auto make_stdarray_from_tietuple(const T& t, std::index_sequence<I...>) noexcept {
+    return std::array<std::string_view, sizeof...(I)>{
+        boost::pfr::detail::sequence_tuple::get<I>(t)...
+    };
+}
+#else
+template <class T, std::size_t... I>
+constexpr auto make_stdarray_from_tietuple(const T&, std::index_sequence<I...>) noexcept {
+    return nullptr;
+}
+#endif
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_STDARRAY_HPP
+

include/boost/pfr/detail/stdtuple.hpp

@@ -0,0 +1,51 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_STDTUPLE_HPP
+#define BOOST_PFR_DETAIL_STDTUPLE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/sequence_tuple.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <utility>      // metaprogramming stuff
+#include <tuple>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+template <class T, std::size_t... I>
+constexpr auto make_stdtuple_from_tietuple(const T& t, std::index_sequence<I...>) {
+    (void)t;  // workaround for MSVC 14.1 `warning C4100: 't': unreferenced formal parameter`
+    return std::make_tuple(
+        boost::pfr::detail::sequence_tuple::get<I>(t)...
+    );
+}
+
+template <class T, std::size_t... I>
+constexpr auto make_stdtiedtuple_from_tietuple(const T& t, std::index_sequence<I...>) noexcept {
+    (void)t;  // workaround for MSVC 14.1 `warning C4100: 't': unreferenced formal parameter`
+    return std::tie(
+        boost::pfr::detail::sequence_tuple::get<I>(t)...
+    );
+}
+
+template <class T, std::size_t... I>
+constexpr auto make_conststdtiedtuple_from_tietuple(const T& t, std::index_sequence<I...>) noexcept {
+    (void)t;  // workaround for MSVC 14.1 `warning C4100: 't': unreferenced formal parameter`
+    return std::tuple<
+        std::add_lvalue_reference_t<std::add_const_t<
+            std::remove_reference_t<decltype(boost::pfr::detail::sequence_tuple::get<I>(t))>
+        >>...
+    >(
+        boost::pfr::detail::sequence_tuple::get<I>(t)...
+    );
+}
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_STDTUPLE_HPP

include/boost/pfr/detail/tie_from_structure_tuple.hpp

@@ -0,0 +1,46 @@
+// Copyright (c) 2018 Adam Butcher, Antony Polukhin
+// Copyright (c) 2019-2025 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_TIE_FROM_STRUCTURE_TUPLE_HPP
+#define BOOST_PFR_DETAIL_TIE_FROM_STRUCTURE_TUPLE_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#include <boost/pfr/detail/core.hpp>
+
+#include <boost/pfr/detail/stdtuple.hpp>
+#include <boost/pfr/tuple_size.hpp>
+#include <boost/pfr/detail/make_integer_sequence.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <tuple>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+/// \brief A `std::tuple` capable of de-structuring assignment used to support
+/// a tie of multiple lvalue references to fields of an aggregate T.
+///
+/// \sa boost::pfr::tie_from_structure
+template <typename... Elements>
+struct tie_from_structure_tuple : std::tuple<Elements&...> {
+    using base = std::tuple<Elements&...>;
+    using base::base;
+
+    template <typename T>
+    constexpr tie_from_structure_tuple& operator= (T const& t) {
+        base::operator=(
+            detail::make_stdtiedtuple_from_tietuple(
+                detail::tie_as_tuple(t),
+                detail::make_index_sequence<tuple_size_v<T>>()));
+        return *this;
+    }
+};
+
+}}} // namespace boost::pfr::detail
+
+#endif // BOOST_PFR_DETAIL_TIE_FROM_STRUCTURE_TUPLE_HPP

include/boost/pfr/detail/unsafe_declval.hpp

@@ -0,0 +1,49 @@
+// Copyright (c) 2019-2025 Antony Polukhin.
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_PFR_DETAIL_UNSAFE_DECLVAL_HPP
+#define BOOST_PFR_DETAIL_UNSAFE_DECLVAL_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#endif
+
+namespace boost { namespace pfr { namespace detail {
+
+// This function serves as a link-time assert. If linker requires it, then
+// `unsafe_declval()` is used at runtime.
+void report_if_you_see_link_error_with_this_function() noexcept;
+
+// For returning non default constructible types. Do NOT use at runtime!
+//
+// GCCs std::declval may not be used in potentionally evaluated contexts,
+// so we reinvent it.
+template <class T>
+constexpr T unsafe_declval() noexcept {
+    report_if_you_see_link_error_with_this_function();
+
+#ifdef BOOST_PFR_USE_LEGACY_UNSAFE_DECLVAL_IMPLEMENTATION
+    typename std::remove_reference<T>::type* ptr = nullptr;
+    ptr += 42; // suppresses 'null pointer dereference' warnings
+    return static_cast<T>(*ptr);
+#else
+    // Looks like `static_cast<T>(*ptr)` to prvalue fails on clang in C++26.
+    // If this new implementation does not work for some cases, please, fill a
+    // bug report and feel free to
+    // define BOOST_PFR_USE_LEGACY_UNSAFE_DECLVAL_IMPLEMENTATION.
+    using func_ptr_t = T(*)();
+    func_ptr_t ptr = nullptr;
+    return ptr();
+#endif
+}
+
+}}} // namespace boost::pfr::detail
+
+
+#endif // BOOST_PFR_DETAIL_UNSAFE_DECLVAL_HPP
+