Fix C++20 Tensor initialization

diff --git a/include/deal.II/base/tensor.h b/include/deal.II/base/tensor.h
index 40ba24ba1c48f1e1aedf62d29771f0f58d3383e5..b7f2c0e5306213f078b81ee7d2209a659a437d7a 100644 (file)
--- a/include/deal.II/base/tensor.h
+++ b/include/deal.II/base/tensor.h
@@ -1292,7 +1292,11 @@ Tensor<rank_, dim, Number>::Tensor()
       // returning a zero instead.
       []<std::size_t... I>(
         const std::index_sequence<I...> &) constexpr -> decltype(values) {
-        if constexpr (rank_ == 1)
+        if constexpr (dim == 0)
+          {
+            return {};
+          }
+        else if constexpr (rank_ == 1)
           {
             auto get_zero_and_ignore_argument = [](int) {
               return internal::NumberType<Number>::value(0.0);