I’m trying to create an err function to be used by bash-scripts. The function is supposed to emulate BSD’s err(3) — printing the specified message and exiting with the code specified as the first argument:

function err {
    # set +u
    # The first argument must be an integer exit-code:
    if ! declare -i code=${1:?err called with no arguments}
    then
        code=70 # Use EX_SOFTWARE by default
    fi
    shift
    if [ -t 2 ]
    then
        # Use color -- red -- printing final errors to a terminal:
        printf "e[1;31m%se[1;0mn" "$*" >&2
    else
        echo "$*" >&2
    fi
    set -x
    exit $code
}

This works as expected, when invoked correctly, such as err 1 Date is empty. But, when invoked with no arguments or when the first argument is not numeric, an error in the declare-line is reported, but not handled: depending on whether -u is set, the script either dies right there on the declare-line, or code is initialized with 0, and the script exits with that — instead of 70.

What am I doing wrong?