add method
The next number is v.
Implementation
void add(double v) {
final at = _number++;
if (at < _numberCount && _numbers[at] == v) return;
if (at == _numbers.length) {
_numbers = Float64List(at * 2)..setRange(0, at, _numbers);
}
_numbers[at] = v;
_changed = true;
}