rxdart/lib/src/streams/range.dart

import 'dart:async';

/// Returns a Stream that emits a sequence of Integers within a specified
/// range.
///
/// ### Examples
///
///     new RangeStream(1, 3).listen((i) => print(i)); // Prints 1, 2, 3
///
///     new RangeStream(3, 1).listen((i) => print(i)); // Prints 3, 2, 1
class RangeStream extends Stream<int> {
  final Stream<int> stream;

  RangeStream(int startInclusive, int endInclusive)
      : stream = buildStream(startInclusive, endInclusive);

  @override
  StreamSubscription<int> listen(void onData(int event),
      {Function onError, void onDone(), bool cancelOnError}) {
    return stream.listen(onData,
        onError: onError, onDone: onDone, cancelOnError: cancelOnError);
  }

  static Stream<int> buildStream(int startInclusive, int endInclusive) {
    final length = (endInclusive - startInclusive).abs() + 1;

    return Stream.fromIterable(List.generate(
        length,
        (int i) => startInclusive > endInclusive
            ? startInclusive - i
            : startInclusive + i));
  }
}