From 749904d2e6ecb75a2a9b4ae69fcc7e9897d98dab Mon Sep 17 00:00:00 2001
From: Giulio Eulisse <10544+ktf@users.noreply.github.com>
Date: Thu, 23 Jul 2026 14:58:28 +0200
Subject: [PATCH 1/2] DPL: use C++26 extension to expand packs where available

O(1) in both CPU and time rather than O(N) when compiling the pack expansion.

Removes the limit to 100 elements in a struct.

Requires XCode 26.4
---
 .../include/Framework/StructToTuple.h         | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/Framework/Foundation/include/Framework/StructToTuple.h b/Framework/Foundation/include/Framework/StructToTuple.h
index 1c7aa62260bd3..dd968623b4f7c 100644
--- a/Framework/Foundation/include/Framework/StructToTuple.h
+++ b/Framework/Foundation/include/Framework/StructToTuple.h
@@ -174,6 +174,46 @@ consteval int nested_brace_constructible_size()
   return brace_constructible_size<type>() - nesting;
 }
 
+// Structured binding packs (P1061) are C++26, but clang implements them as an
+// extension in every language mode and advertises them via the feature test
+// macro, so we can use them while still compiling as C++20.
+#if defined(__cpp_structured_bindings) && __cpp_structured_bindings >= 202411L
+#define DPL_STRUCTURED_BINDING_PACKS 1
+#endif
+
+#ifdef DPL_STRUCTURED_BINDING_PACKS
+namespace detail
+{
+template <typename... Ts>
+struct first_type;
+template <typename First, typename... Rest>
+struct first_type<First, Rest...> {
+  using type = First;
+};
+template <typename... Ts>
+using first_t = typename first_type<Ts...>::type;
+} // namespace detail
+
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++26-extensions"
+#endif
+template <bool B = false, class T, int D = 0, typename L>
+constexpr auto homogeneous_apply_refs(L l, T&& object)
+{
+  auto&& [...members] = object;
+  if constexpr (sizeof...(members) == 0) {
+    return std::array<bool, 0>();
+  } else {
+    return std::array<detail::first_t<decltype(l(members))...>, sizeof...(members)>{l(members)...};
+  }
+}
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
+#else // DPL_STRUCTURED_BINDING_PACKS
+
 template <bool B = false, class T, int D = nested_brace_constructible_size<B, T>() / 10, typename L>
   requires(D == 9)
 constexpr auto homogeneous_apply_refs(L l, T&& object)
@@ -373,6 +413,8 @@ constexpr auto homogeneous_apply_refs(L l, T&& object)
   // clang-format on
 }
 
+#endif // DPL_STRUCTURED_BINDING_PACKS
+
 template <int D, typename T, typename L>
 constexpr auto homogeneous_apply_refs_sized(L l, T&& object)
 {

From ab4246f8c71dd4456145a5ee81c24534a3ed5a20 Mon Sep 17 00:00:00 2001
From: ALICE Action Bot <alibuild@cern.ch>
Date: Thu, 23 Jul 2026 12:59:22 +0000
Subject: [PATCH 2/2] Please consider the following formatting changes

---
 Framework/Foundation/include/Framework/StructToTuple.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Framework/Foundation/include/Framework/StructToTuple.h b/Framework/Foundation/include/Framework/StructToTuple.h
index dd968623b4f7c..1541449874c3b 100644
--- a/Framework/Foundation/include/Framework/StructToTuple.h
+++ b/Framework/Foundation/include/Framework/StructToTuple.h
@@ -201,7 +201,7 @@ using first_t = typename first_type<Ts...>::type;
 template <bool B = false, class T, int D = 0, typename L>
 constexpr auto homogeneous_apply_refs(L l, T&& object)
 {
-  auto&& [...members] = object;
+  auto&& [... members] = object;
   if constexpr (sizeof...(members) == 0) {
     return std::array<bool, 0>();
   } else {