From 0da4d8b7e65710a93f7ea1509d3c183ee0df1453 Mon Sep 17 00:00:00 2001
From: Alexander Sinn <64009254+AlexanderSinn@users.noreply.github.com>
Date: Sat, 8 Jun 2024 23:43:47 +0200
Subject: [PATCH] =?UTF-8?q?Add=20structured=20binding=20support=20to=C2=A0?=
 =?UTF-8?q?GpuTuple=20(#3977)?=
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## Summary

This PR adds C++17 structured binding support to `amrex::GpuTuple`.

## Additional background

See case 2
in https://en.cppreference.com/w/cpp/language/structured_binding.
Note that structured bindings will also use the existing `amrex::get`.
---
 Src/Base/AMReX_Tuple.H | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/Src/Base/AMReX_Tuple.H b/Src/Base/AMReX_Tuple.H
index a628a5e30de..4d74198272f 100644
--- a/Src/Base/AMReX_Tuple.H
+++ b/Src/Base/AMReX_Tuple.H
@@ -416,6 +416,23 @@ auto tupleToArray (GpuTuple<T,Ts...> const& tup)
     return detail::tuple_to_array_helper(tup, std::index_sequence_for<T,Ts...>{});
 }
 
-}
+} // namespace amrex
+
+// Spcialize std::tuple_size for GpuTuple. Used by structured bindings.
+template<typename... Ts>
+struct std::tuple_size<amrex::GpuTuple<Ts...>> {
+    static constexpr std::size_t value = sizeof...(Ts);
+};
+
+// Spcialize std::tuple_element for GpuTuple. Used by structured bindings.
+template<typename T, typename... Ts>
+struct std::tuple_element<std::size_t{0}, amrex::GpuTuple<T, Ts...>> {
+    using type = T;
+};
+
+template<std::size_t s, typename T, typename... Ts>
+struct std::tuple_element<s, amrex::GpuTuple<T, Ts...>> {
+    using type = typename std::tuple_element<s-1, amrex::GpuTuple<Ts...>>::type;
+};
 
 #endif /*AMREX_TUPLE_H_*/