1-tuple: fix copy assignment of tuple containing refs (#1812)

follow up on #1811

Author: havogt

include/gridtools/common/tuple.hpp

@@ -235,8 +235,6 @@ namespace gridtools {
 
         tuple(tuple const &) = default;
         tuple(tuple &&) = default;
-        tuple &operator=(tuple const &) = default;
-        tuple &operator=(tuple &&) = default;
 
         constexpr GT_FUNCTION tuple(T const &arg) noexcept : m_value(arg) {}
 
@@ -260,6 +258,15 @@ namespace gridtools {
             swap(m_value, other.m_value);
         }
 
+        constexpr GT_FUNCTION tuple &operator=(tuple const &other) noexcept {
+            m_value = other.m_value;
+            return *this;
+        }
+        constexpr GT_FUNCTION tuple &operator=(tuple &&other) noexcept {
+            m_value = std::move(other.m_value);
+            return *this;
+        }
+
         template <class Arg, std::enable_if_t<std::is_assignable_v<T &, Arg const &>, int> = 0>
         constexpr GT_FUNCTION tuple &operator=(tuple<Arg> const &src) noexcept {
             m_value = src.m_value;

tests/unit_tests/common/test_tuple.cpp

@@ -226,6 +226,15 @@ namespace gridtools {
             EXPECT_EQ(1, get<0>(testee));
         }
 
+        TEST(onetuple, copy_assign_nested_ref) {
+            int src_int = 1;
+            int dst_int = 0;
+            tuple<tuple<int &>> src = {{src_int}};
+            tuple<tuple<int &>> testee = {{dst_int}};
+            testee = src;
+            EXPECT_EQ(1, get<0>(get<0>(testee)));
+        }
+
         TEST(tuple, move_assign) {
             tuple<move_only, move_only> testee;
             auto &res = testee = tuple<move_only, move_only>{move_only{47}, move_only{2}};