description

# takeWhile method Null safety

Stream<T> takeWhile (

1. bool test(
   1. T element
   )

)

Forwards data events while `test` is successful.

Returns a stream that provides the same events as this stream until `test` fails for a data event. The returned stream is done when either this stream is done, or when this stream first emits a data event that fails `test`.

The `test` call is considered failing if it returns a non-`true` value or if it throws. If the `test` call throws, the error is emitted as the last event on the returned streams.

Stops listening to this stream after the accepted elements.

Internally the method cancels its subscription after these elements. This means that single-subscription (non-broadcast) streams are closed and cannot be reused after a call to this method.

The returned stream is a broadcast stream if this stream is. For a broadcast stream, the events are only tested from the time the returned stream is listened to.

## Implementation

    Stream<T> takeWhile(bool test(T element)) {
      return new _TakeWhileStream<T>(this, test);
    }