cmpthese( -1, { 'sum_list' => sub { sum_list(1..1_000_000); }, 'sum_by_ref' => sub { sum_by_ref([1..1_000_000]); }, }); Result: Rate sum_list sum_by_ref sum_list 4.13/s -- -9% sum_by_ref 4.55/s 10% --