Format by digits

format_by_digits.dart

void main() {
  print(formatByDigits(10000));
  print(formatByDigits(9999));
  print(formatByDigits(12000));
  print(formatByDigits(12000000));
}

String formatByDigits(int number) {
  final s = number.toString().split('');
  return s.reversed
      .mapIndexed(
        (i, e) sync* {
          if (e % 3 == 0 && e != 0) yield '.';
          yield i;
        },
      )
      .toList()
      .reversed
      .join('');
}

extension Abobus<T> on Iterable<T> {
  Iterable<K> mapIndexed<K>(Iterable<K> Function(T, int) fn) sync* {
    final l = toList();
    for (var i = 0; i < length; i++) {
      yield* fn(l[i], i);
    }
  }
}

returns 10.000, 9.999, 12.000, 12.000.000