title: is there any way to cancel a dart Future?
body: <p>In a Dart UI, I have a button [submit] to launch a long async request. The [submit] handler returns a Future. Next, the button [submit] is replaced by a button [cancel] to allow the cancellation of the whole operation. In the [cancel] handler, I would like to cancel the long operation. How can I cancel the Future returned by the submit handler? I found no method to do that.</p>