From e360f0700d73f697da3a22c5bab22534d9d9c8b5 Mon Sep 17 00:00:00 2001
From: Antony Polukhin <antoshkka@gmail.com>
Date: Mon, 12 Jan 2026 20:32:43 +0300
Subject: [PATCH] cleanup

---
 include/boost/pfr.hpp             |  1 +
 include/boost/pfr/core.hpp        | 28 ------------
 include/boost/pfr/index_of.hpp    | 72 +++++++++++++++++++++++++++++++
 test/core/run/member_to_index.cpp | 13 +++---
 4 files changed, 81 insertions(+), 33 deletions(-)
 create mode 100644 include/boost/pfr/index_of.hpp

diff --git a/include/boost/pfr.hpp b/include/boost/pfr.hpp
index ce44725..555bdf9 100644
--- a/include/boost/pfr.hpp
+++ b/include/boost/pfr.hpp
@@ -14,6 +14,7 @@
 #include <boost/pfr/core_name.hpp>
 #include <boost/pfr/functions_for.hpp>
 #include <boost/pfr/functors.hpp>
+#include <boost/pfr/index_of.hpp>
 #include <boost/pfr/io.hpp>
 #include <boost/pfr/io_fields.hpp>
 #include <boost/pfr/ops.hpp>
diff --git a/include/boost/pfr/core.hpp b/include/boost/pfr/core.hpp
index 1ba3f78..d621f27 100644
--- a/include/boost/pfr/core.hpp
+++ b/include/boost/pfr/core.hpp
@@ -18,11 +18,9 @@
 #include <boost/pfr/detail/for_each_field.hpp>
 #include <boost/pfr/detail/make_integer_sequence.hpp>
 #include <boost/pfr/detail/tie_from_structure_tuple.hpp>
-#include <boost/pfr/detail/fake_object.hpp>
 
 #include <boost/pfr/tuple_size.hpp>
 
-
 #if !defined(BOOST_PFR_INTERFACE_UNIT)
 #include <type_traits>
 #include <utility>      // metaprogramming stuff
@@ -279,32 +277,6 @@ constexpr detail::tie_from_structure_tuple<Elements...> tie_from_structure(Eleme
     return detail::tie_from_structure_tuple<Elements...>(args...);
 }
 
-    template <typename M>
-    struct visitor {
-        template <class T>
-        constexpr void operator()(const T&, std::size_t) {}
-
-        constexpr void operator()(const M& field, std::size_t idx) {
-            const void* field_address = std::addressof(field);
-            if (target_address == field_address) {
-                result = idx;
-            }
-        }
-
-        const void* target_address;
-        std::size_t result;
-    };
-
-template <typename T, typename M>
-constexpr std::size_t index_of(M T::*mem_ptr) {
-    constexpr const T& value = boost::pfr::detail::fake_object<T>();
-
-    visitor<M> visit{std::addressof(value.*mem_ptr), boost::pfr::tuple_size_v<T>};
-    
-    boost::pfr::for_each_field(value, visit);
-    return visit.result;
-}
-
 BOOST_PFR_END_MODULE_EXPORT
 
 }} // namespace boost::pfr
diff --git a/include/boost/pfr/index_of.hpp b/include/boost/pfr/index_of.hpp
new file mode 100644
index 0000000..2b2a486
--- /dev/null
+++ b/include/boost/pfr/index_of.hpp
@@ -0,0 +1,72 @@
+// Copyright (c) 2025-2026 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_INDEX_OF_HPP
+#define BOOST_PFR_INDEX_OF_HPP
+#pragma once
+
+#include <boost/pfr/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_PFR_INTERFACE_UNIT)
+
+#include <boost/pfr/detail/fake_object.hpp>
+#include <boost/pfr/detail/for_each_field.hpp>
+
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <utility>      // metaprogramming stuff
+#endif
+
+/// \file boost/pfr/index_of.hpp
+/// \copybrief boost::pfr::index_of
+
+namespace boost { namespace pfr {
+
+namespace detail {
+
+template <typename M>
+struct address_comparing_visitor {
+    template <class T>
+    constexpr void operator()(const T&, std::size_t) noexcept {}
+
+    constexpr void operator()(const M& field, std::size_t idx) noexcept {
+        const void* field_address = std::addressof(field);
+        if (target_address == field_address) {
+            result = idx;
+        }
+    }
+
+    const void* const target_address;
+    std::size_t result;
+};
+
+}
+
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
+template <typename T, typename M>
+constexpr std::size_t index_of(M T::*mem_ptr) noexcept {
+    if (mem_ptr == nullptr) {
+        return ~static_cast<std::size_t>(0);
+    }
+
+    constexpr const T& value = boost::pfr::detail::fake_object<T>();
+    detail::address_comparing_visitor<M> visitor{
+        std::addressof(value.*mem_ptr),
+        ~static_cast<std::size_t>(0)
+    };
+    ::boost::pfr::detail::for_each_field(value, visitor);
+
+    return visitor.result;
+}
+
+BOOST_PFR_END_MODULE_EXPORT
+
+}} // namespace boost::pfr
+
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_PFR_INTERFACE_UNIT)
+
+#endif // BOOST_PFR_INDEX_OF_HPP
diff --git a/test/core/run/member_to_index.cpp b/test/core/run/member_to_index.cpp
index f734ad9..2248821 100644
--- a/test/core/run/member_to_index.cpp
+++ b/test/core/run/member_to_index.cpp
@@ -3,9 +3,9 @@
 // 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)
 
-#include <boost/pfr/core.hpp>
+#include <boost/pfr/index_of.hpp>
 
-#include <cassert>
+#include <limits>
 #include <string>
 #include <vector>
 
@@ -21,8 +21,11 @@ int main() {
     static_assert(boost::pfr::index_of(&Sample::y) == 1);
     static_assert(boost::pfr::index_of(&Sample::z) == 2);
 #else
-    assert(boost::pfr::index_of(&Sample::x) == 0);
-    assert(boost::pfr::index_of(&Sample::y) == 1);
-    assert(boost::pfr::index_of(&Sample::z) == 2);
+    if (boost::pfr::index_of(&Sample::x) != 0) return 1;
+    if (boost::pfr::index_of(&Sample::y) != 1) return 2;
+    if (boost::pfr::index_of(&Sample::z) != 2) return 3;
 #endif
+
+    decltype(&Sample::x) mem_ptr = nullptr;
+    if (boost::pfr::index_of(mem_ptr) != (std::numeric_limits<std::size_t>::max)()) return 4;
 }