From a37668034078628f4b4155cc23ec1dd2ed06813a Mon Sep 17 00:00:00 2001
From: Alexander Karatarakis <alex@karatarakis.com>
Date: Tue, 10 Dec 2024 15:26:36 -0800
Subject: [PATCH] [reflection] Add customization for_each_field() directly

---
 include/fixed_containers/reflection.hpp | 21 +++++++++++----
 test/reflection_test.cpp                | 35 +++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/include/fixed_containers/reflection.hpp b/include/fixed_containers/reflection.hpp
index c4cc030e..e6c3e2d2 100644
--- a/include/fixed_containers/reflection.hpp
+++ b/include/fixed_containers/reflection.hpp
@@ -219,6 +219,20 @@ template <typename T>
 inline constexpr auto FIELD_NAMES = fixed_containers::reflection_detail::field_names_of_impl<
     fixed_containers::reflection_detail::field_count_of_impl(std::decay_t<T>{})>(std::decay_t<T>{});
 
+template <typename T>
+struct ReflectionHelper
+{
+    template <typename T2, typename Func>
+    static constexpr void for_each_field(T2&& instance, Func&& func)
+    {
+        auto tuple_view = tuples::as_tuple_view<FIELD_NAMES<std::decay_t<T2>>.size()>(instance);
+        tuples::for_each_entry(
+            tuple_view,
+            [&func]<typename Field>(std::size_t index, Field&& field)
+            { func(FIELD_NAMES<std::decay_t<T2>>.at(index), std::forward<Field>(field)); });
+    }
+};
+
 }  // namespace fixed_containers::reflection::customize
 
 namespace fixed_containers::reflection
@@ -244,11 +258,8 @@ template <typename T, typename Func>
     requires(Reflectable<std::decay_t<T>>)
 constexpr void for_each_field(T&& instance, Func&& func)
 {
-    constexpr const auto& FIELD_NAMES = field_names_of<T>();
-    auto tuple_view = tuples::as_tuple_view<FIELD_NAMES.size()>(instance);
-    tuples::for_each_entry(tuple_view,
-                           [&func]<typename Field>(std::size_t index, Field&& field)
-                           { func(FIELD_NAMES.at(index), std::forward<Field>(field)); });
+    fixed_containers::reflection::customize::ReflectionHelper<std::decay_t<T>>::for_each_field(
+        std::forward<T>(instance), std::forward<Func>(func));
 }
 
 }  // namespace fixed_containers::reflection
diff --git a/test/reflection_test.cpp b/test/reflection_test.cpp
index f6e449bc..2d141f47 100644
--- a/test/reflection_test.cpp
+++ b/test/reflection_test.cpp
@@ -628,6 +628,41 @@ inline constexpr auto fixed_containers::reflection::customize::FIELD_NAMES<MyCus
         "c",
     });
 
+template <>
+struct fixed_containers::reflection::customize::ReflectionHelper<MyCustomStruct>
+{
+    template <typename T2, typename Func>
+        requires std::same_as<std::decay_t<T2>, MyCustomStruct>
+    static constexpr void for_each_field(T2&& instance, Func&& func)
+    {
+        // Apply it twice for unit testing purposes
+        func(FIELD_NAMES<MyCustomStruct>.at(0), instance.a);
+        func(FIELD_NAMES<MyCustomStruct>.at(1), instance.b);
+        func(FIELD_NAMES<MyCustomStruct>.at(2), instance.c);
+
+        func(FIELD_NAMES<MyCustomStruct>.at(0), instance.a);
+        func(FIELD_NAMES<MyCustomStruct>.at(1), instance.b);
+        func(FIELD_NAMES<MyCustomStruct>.at(2), instance.c);
+    }
+};
+
 static_assert(fixed_containers::reflection::field_names_of<MyCustomStruct>().size() == 3);
 
+namespace fixed_containers
+{
+
+TEST(Reflection, Customization)
+{
+    constexpr auto RESULT = []()
+    {
+        MyCustomStruct instance{};
+        std::size_t counter = 0;
+        reflection::for_each_field(
+            instance, [&]<typename T>(const std::string_view& /*name*/, const T&) { counter++; });
+        return counter;
+    }();
+
+    static_assert(6 == RESULT);
+}
+}  // namespace fixed_containers
 #endif