From a478681120b9c1d2d8b62dde98fabde0eaee4149 Mon Sep 17 00:00:00 2001
From: "Randolph R. Settgast" <settgast1@llnl.gov>
Date: Mon, 16 Oct 2023 12:50:42 -0700
Subject: [PATCH 1/4] implementation of std::tuple_element that allows const
 auto [a,b] = tuple...added some unit testing as well

---
 include/camp/tuple.hpp |  4 ++--
 test/tuple.cpp         | 44 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/camp/tuple.hpp b/include/camp/tuple.hpp
index f5001ea..acbc023 100644
--- a/include/camp/tuple.hpp
+++ b/include/camp/tuple.hpp
@@ -703,7 +703,7 @@ namespace std {
 
   template <size_t i, typename ... T>
   struct tuple_element<i, camp::tuple<T...>> {
-    using type = decltype(camp::get<i>(camp::tuple<T...>{}));
+    using type = ::camp::tuple_element_t<i, camp::tuple<T...>>;
   };
 
   /// This allows structured bindings to be used with camp::tagged_tuple
@@ -718,7 +718,7 @@ namespace std {
 
   template <size_t i, typename TagList, typename... Elements>
   struct tuple_element<i, camp::tagged_tuple<TagList, Elements...>> {
-    using type = decltype(camp::get<i>(camp::tagged_tuple<TagList, Elements...>{}));
+    using type = ::camp::tuple_element_t<i, camp::tagged_tuple<TagList, Elements...>>;
   };
 } // namespace std
 #endif
diff --git a/test/tuple.cpp b/test/tuple.cpp
index cde4bad..b8d25da 100644
--- a/test/tuple.cpp
+++ b/test/tuple.cpp
@@ -360,9 +360,53 @@ TEST(CampTuple, StructuredBindings)
 {
   auto t = camp::make_tuple(3, 9.9);
   auto [a, b] = t;
+  static_assert(std::is_same_v< decltype(a), int > );
+  static_assert(std::is_same_v< decltype(b), double > );
   ASSERT_EQ(a, 3);
   ASSERT_NEAR(b, 9.9, 1e-15);
 }
+
+TEST(CampTuple, StructuredBindingsConst)
+{
+  auto t = camp::make_tuple(3, 9.9);
+  const auto [a, b] = t;
+  static_assert(std::is_same_v< decltype(a), const int > );
+  static_assert(std::is_same_v< decltype(b), const double > );
+  ASSERT_EQ(a, 3);
+  ASSERT_NEAR(b, 9.9, 1e-15);
+}
+
+TEST(CampTuple, StructuredBindingsRef)
+{
+  auto t = camp::make_tuple(3, 9.9);
+  auto & [a, b] = t;
+  static_assert(std::is_same< decltype(a), int >::value ); // Not an int &
+  static_assert(std::is_same< decltype(b), double >::value ); // Not a double &
+  std::cout<<typeid(a).name()<<std::endl;
+  ASSERT_EQ(a, 3);
+  ASSERT_NEAR(b, 9.9, 1e-15);
+
+  a = 4; // Well...kind of an int &
+  b = 10.1; // also kind of a double &
+  ASSERT_EQ(camp::get<0>(t), 4);
+  ASSERT_NEAR(camp::get<1>(t), 10.1, 1e-15);
+}
+
+TEST(CampTuple, StructuredBindingsRefConst)
+{
+  auto t = camp::make_tuple(3, 9.9);
+  const auto & [a, b] = t;
+  static_assert(std::is_same< decltype(a), const int >::value );  // Not an const int &
+  static_assert(std::is_same< decltype(b), const double >::value ); // Not a const double &
+  std::cout<<typeid(a).name()<<std::endl;
+  ASSERT_EQ(a, 3);
+  ASSERT_NEAR(b, 9.9, 1e-15);
+
+  // these should fail to compile.
+  // a = 4;
+  // b = 10.1;
+}
+
 #endif
 
 struct s1;

From 092fe59988a93441d5b671ce828bd735dece5879 Mon Sep 17 00:00:00 2001
From: "Randolph R. Settgast" <settgast1@llnl.gov>
Date: Mon, 16 Oct 2023 13:16:19 -0700
Subject: [PATCH 2/4] downgrade std::is_same_v to std::is_same<>::value

---
 test/tuple.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test/tuple.cpp b/test/tuple.cpp
index b8d25da..fe9bb6a 100644
--- a/test/tuple.cpp
+++ b/test/tuple.cpp
@@ -370,8 +370,8 @@ TEST(CampTuple, StructuredBindingsConst)
 {
   auto t = camp::make_tuple(3, 9.9);
   const auto [a, b] = t;
-  static_assert(std::is_same_v< decltype(a), const int > );
-  static_assert(std::is_same_v< decltype(b), const double > );
+  static_assert(std::is_same< decltype(a), const int >::value );
+  static_assert(std::is_same< decltype(b), const double >::value );
   ASSERT_EQ(a, 3);
   ASSERT_NEAR(b, 9.9, 1e-15);
 }

From 2128a4de35b7c2b59956009912d70fa0280ac83b Mon Sep 17 00:00:00 2001
From: "Randolph R. Settgast" <settgast1@llnl.gov>
Date: Mon, 16 Oct 2023 13:17:55 -0700
Subject: [PATCH 3/4] downgrade std::is_same_v to std::is_same<>::value

---
 test/tuple.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test/tuple.cpp b/test/tuple.cpp
index fe9bb6a..6f507f0 100644
--- a/test/tuple.cpp
+++ b/test/tuple.cpp
@@ -360,8 +360,8 @@ TEST(CampTuple, StructuredBindings)
 {
   auto t = camp::make_tuple(3, 9.9);
   auto [a, b] = t;
-  static_assert(std::is_same_v< decltype(a), int > );
-  static_assert(std::is_same_v< decltype(b), double > );
+  static_assert(std::is_same< decltype(a), int >::value );
+  static_assert(std::is_same< decltype(b), double >::value );
   ASSERT_EQ(a, 3);
   ASSERT_NEAR(b, 9.9, 1e-15);
 }

From b2593988dbcf382daf7152a9c8563bc5cd513e66 Mon Sep 17 00:00:00 2001
From: "Randolph R. Settgast" <settgast1@llnl.gov>
Date: Mon, 16 Oct 2023 13:48:09 -0700
Subject: [PATCH 4/4] removed some debugging output

---
 test/tuple.cpp | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/test/tuple.cpp b/test/tuple.cpp
index 6f507f0..05dd3bf 100644
--- a/test/tuple.cpp
+++ b/test/tuple.cpp
@@ -382,7 +382,6 @@ TEST(CampTuple, StructuredBindingsRef)
   auto & [a, b] = t;
   static_assert(std::is_same< decltype(a), int >::value ); // Not an int &
   static_assert(std::is_same< decltype(b), double >::value ); // Not a double &
-  std::cout<<typeid(a).name()<<std::endl;
   ASSERT_EQ(a, 3);
   ASSERT_NEAR(b, 9.9, 1e-15);
 
@@ -398,15 +397,9 @@ TEST(CampTuple, StructuredBindingsRefConst)
   const auto & [a, b] = t;
   static_assert(std::is_same< decltype(a), const int >::value );  // Not an const int &
   static_assert(std::is_same< decltype(b), const double >::value ); // Not a const double &
-  std::cout<<typeid(a).name()<<std::endl;
   ASSERT_EQ(a, 3);
   ASSERT_NEAR(b, 9.9, 1e-15);
-
-  // these should fail to compile.
-  // a = 4;
-  // b = 10.1;
 }
-
 #endif
 
 struct s1;