isNumber static method

Implementation

static bool isNumber(String input) {
  final int len = input.length;
  if (len == 0) return false;
  int i = 0;
  final int first = input.codeUnitAt(0);
  if (first == 0x2B /* + */ || first == 0x2D /* - */) {
    i++;
    if (i >= len) return false;
  }

  bool sawDigit = false;
  while (i < len) {
    final int cu = input.codeUnitAt(i);
    if (cu >= 0x30 && cu <= 0x39) {
      sawDigit = true;
      i++;
      continue;
    }
    break;
  }

  if (i < len && input.codeUnitAt(i) == 0x2E /* . */) {
    i++;
    bool sawFracDigit = false;
    while (i < len) {
      final int cu = input.codeUnitAt(i);
      if (cu >= 0x30 && cu <= 0x39) {
        sawFracDigit = true;
        i++;
        continue;
      }
      return false;
    }
    return sawFracDigit;
  }

  return sawDigit && i == len;
}