Re: Quartus warning in NUMERIC_STD.vhd

I agree.

A bad assignment to a null vector will cause other errors.
A null vector declaration alone is innocuous.

   If one bit is 0 to 0 then
no bits must be 0 to -1

Let's see:
-------------------

entity null_string is
end    null_string;

architecture sim of null_string
is
constant null_vec    : std_logic_vector := "";
constant one_vec     : std_logic_vector := "0";
constant two_vec     : std_logic_vector := "00";

begin

    what : process is
    begin
       report "null_vec is "& integer'image(null_vec'left)
                    & " to "& integer'image(null_vec'right);
       report " one_vec is "& integer'image( one_vec'left)
                    & " to "& integer'image( one_vec'right);
       report " two_vec is "& integer'image( two_vec'left)
                    & " to "& integer'image( two_vec'right);
       wait;
    end process what;

end sim;

--VSIM 1> run
--# ** Note: null_vec is 0 to -1
--# ** Note:  one_vec is 0 to 0
--# ** Note:  two_vec is 0 to 1

------------------------

I suppose that null vectors are rare as signals
but null vector constants and variables are necessary to make
clean vector functions.


      --Mike Treseler