any method

Future<bool> any (bool test(T element))

Checks whether test accepts any element provided by this stream.

Calls test on each element of the stream. If the call returns true, the returned future is completed with true and processing stops.

If the stream ends without finding an element that test accepts, the returned future is completed with false.

If this stream contains an error, or if the call to test throws, the returned future is completed with that error, and processing stops.

Implementation 

Future<bool> any(bool test(T element)) {
  _Future<bool> future = new _Future<bool>();
  StreamSubscription subscription;
  subscription = this.listen(
      (T element) {
        _runUserCode(() => test(element), (bool isMatch) {
          if (isMatch) {
            _cancelAndValue(subscription, future, true);
          }
        }, _cancelAndErrorClosure(subscription, future));
      },
      onError: future._completeError,
      onDone: () {
        future._complete(false);
      },
      cancelOnError: true);
  return future;
}