cancelable<S> method
- Future<
S> callback(- StreamQueue<
T>
- StreamQueue<
Passes a copy of this queue to callback
, and updates this queue to match
the copy's position once callback
completes.
If the returned CancelableOperation is canceled, this queue instead
continues as though cancelable hadn't been called. Otherwise, it emits
the same value or error as callback
.
See also startTransaction and withTransaction.
final _stdinQueue = StreamQueue(stdin);
/// Returns an operation that completes when the user sends a line to
/// standard input.
///
/// If the operation is canceled, stops waiting for user input.
CancelableOperation<String> nextStdinLine() =>
_stdinQueue.cancelable((queue) => queue.next);
Implementation
CancelableOperation<S> cancelable<S>(
Future<S> Function(StreamQueue<T>) callback) {
var transaction = startTransaction();
var completer = CancelableCompleter<S>(onCancel: () {
transaction.reject();
});
var queue = transaction.newQueue();
completer.complete(callback(queue).whenComplete(() {
if (!completer.isCanceled) transaction.commit(queue);
}));
return completer.operation;
}