From dcfb50363a3efd939f1c6eadd97640afbcc120e6 Mon Sep 17 00:00:00 2001
From: Denis Blank <denis.blank@outlook.com>
Date: Fri, 14 Jul 2017 14:32:49 +0200
Subject: [PATCH] Fix tuple_cat when using l-value references * Add basic unit
 tests to ensure the correctness of tuple_cat.

---
 hpx/util/tuple.hpp        | 38 ++++++++++++++------------------------
 tests/unit/util/tuple.cpp | 29 +++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 24 deletions(-)

diff --git a/hpx/util/tuple.hpp b/hpx/util/tuple.hpp
index a1c1e9b68e93..f632dc732c31 100644
--- a/hpx/util/tuple.hpp
+++ b/hpx/util/tuple.hpp
@@ -746,6 +746,7 @@ namespace hpx { namespace util
     //constexpr tuple<Ctypes ...> tuple_cat(Tuples&&...);
     namespace detail
     {
+        /// Deduces to the overall size of all given tuples
         template <std::size_t Size, typename Tuples>
         struct tuple_cat_size_impl;
 
@@ -782,18 +783,12 @@ namespace hpx { namespace util
         {
             typedef tuple_element<I, Head> base_type;
 
+            template <typename THead, typename... TTail>
             static HPX_CONSTEXPR HPX_HOST_DEVICE HPX_FORCEINLINE
-            typename base_type::type&
-            get(Head& head, Tail& ...tail) noexcept
+                auto get(THead&& head, TTail&&... /*tail*/) noexcept
+                -> decltype(base_type::get(std::forward<THead>(head)))
             {
-                return base_type::get(head);
-            }
-
-            static HPX_CONSTEXPR HPX_HOST_DEVICE HPX_FORCEINLINE
-            typename base_type::type const&
-            get(Head const& head, Tail& ...tail) noexcept
-            {
-                return base_type::get(head);
+                return base_type::get(std::forward<THead>(head));
             }
         };
 
@@ -813,18 +808,12 @@ namespace hpx { namespace util
               , detail::pack<Tail...>
             > base_type;
 
+            template <typename THead, typename... TTail>
             static HPX_CONSTEXPR HPX_HOST_DEVICE HPX_FORCEINLINE
-            typename base_type::type&
-            get(Head& head, Tail& ...tail) noexcept
-            {
-                return base_type::get(tail...);
-            }
-
-            static HPX_CONSTEXPR HPX_HOST_DEVICE HPX_FORCEINLINE
-            typename base_type::type const&
-            get(Head const& head, Tail& ...tail) noexcept
+                auto get(THead&& /*head*/, TTail&&... tail) noexcept
+                -> decltype(base_type::get(std::forward<TTail>(tail)...))
             {
-                return base_type::get(tail...);
+                return base_type::get(std::forward<TTail>(tail)...);
             }
         };
 
@@ -861,11 +850,12 @@ namespace hpx { namespace util
 
     template <typename ...Tuples>
     HPX_CONSTEXPR HPX_HOST_DEVICE HPX_FORCEINLINE
-    typename detail::tuple_cat_result<Tuples...>::type
-    tuple_cat(Tuples&&... tuples)
+        typename detail::tuple_cat_result<
+            typename std::decay<Tuples>::type...>::type
+        tuple_cat(Tuples&&... tuples)
     {
-        return detail::tuple_cat_result<Tuples...>::make(
-            std::forward<Tuples>(tuples)...);
+        return detail::tuple_cat_result<typename std::decay<Tuples>::type...>::
+            make(std::forward<Tuples>(tuples)...);
     }
 
     // 20.4.2.7, relational operators
diff --git a/tests/unit/util/tuple.cpp b/tests/unit/util/tuple.cpp
index d83cf799d876..dcf55f92ba1c 100644
--- a/tests/unit/util/tuple.cpp
+++ b/tests/unit/util/tuple.cpp
@@ -328,6 +328,34 @@ void tie_test()
 }
 
 
+// ----------------------------------------------------------------------------
+// - testing cat -----------------------------------------------------------
+// ----------------------------------------------------------------------------
+void tuple_cat_test()
+{
+    hpx::util::tuple<int, float> two = hpx::util::make_tuple(1, 2.f);
+
+    // Cat two tuples
+    {
+        hpx::util::tuple<int, float, int, float> res =
+            hpx::util::tuple_cat(two, two);
+
+        auto expected = hpx::util::make_tuple(1, 2.f, 1, 2.f);
+
+        HPX_TEST((res == expected));
+    }
+
+    // Cat multiple tuples
+    {
+        hpx::util::tuple<int, float, int, float, int, float> res =
+            hpx::util::tuple_cat(two, two, two);
+
+        auto expected = hpx::util::make_tuple(1, 2.f, 1, 2.f, 1, 2.f);
+
+        HPX_TEST((res == expected));
+    }
+}
+
 // ----------------------------------------------------------------------------
 // - testing tuple equality   -------------------------------------------------
 // ----------------------------------------------------------------------------
@@ -429,6 +457,7 @@ int main(int argc, char* argv[])
         mutate_test();
         make_tuple_test();
         tie_test();
+        tuple_cat_test();
         equality_test();
         ordering_test();
         const_tuple_test();