Question about assertion in stream_xbar.sv

[dawidzim]

Hey!
I have question about assertion in src/stream_xbar.sv:

  for (genvar i = 0; unsigned'(i) < NumInp; i++) begin : gen_sel_assertions
    assert property (@(posedge clk_i) (valid_i[i] |-> sel_i[i] < sel_oup_t'(NumOut))) else
        $fatal(1, "Non-existing output is selected!");
  end

Why do you use : sel_oup_t'(NumOut) if for example NumOut = 4 so sel_oup_t is logic[1:0] so result from this cast will be always 0. So (valid_i[i] |-> sel_i[i] < 0)