smpi_key_elem elem = keyvals_.at(it.first);
if (elem != nullptr && elem->copy_fn.comm_copy_fn != MPI_NULL_COPY_FN) {
ret = elem->copy_fn.comm_copy_fn(this, it.first, nullptr, it.second, &value_out, &flag);
smpi_key_elem elem = keyvals_.at(it.first);
if (elem != nullptr && elem->copy_fn.comm_copy_fn != MPI_NULL_COPY_FN) {
ret = elem->copy_fn.comm_copy_fn(this, it.first, nullptr, it.second, &value_out, &flag);