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use {Future, Poll, Async};
/// A future which "fuses" a future once it's been resolved.
///
/// Normally futures can behave unpredictable once they're used after a future
/// has been resolved, but `Fuse` is always defined to return `Async::NotReady`
/// from `poll` after it has resolved successfully or returned an error.
///
/// This is created by the `Future::fuse` method.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct Fuse<A: Future> {
future: Option<A>,
}
pub fn new<A: Future>(f: A) -> Fuse<A> {
Fuse {
future: Some(f),
}
}
impl<A: Future> Fuse<A> {
/// Returns whether the underlying future has finished or not.
///
/// If this method returns `true`, then all future calls to `poll`
/// are guaranteed to return `Ok(Async::NotReady)`. If this returns
/// false, then the underlying future has not been driven to
/// completion.
pub fn is_done(&self) -> bool {
self.future.is_none()
}
}
impl<A: Future> Future for Fuse<A> {
type Item = A::Item;
type Error = A::Error;
fn poll(&mut self) -> Poll<A::Item, A::Error> {
let res = self.future.as_mut().map(|f| f.poll());
match res.unwrap_or(Ok(Async::NotReady)) {
res @ Ok(Async::Ready(_)) |
res @ Err(_) => {
self.future = None;
res
}
Ok(Async::NotReady) => Ok(Async::NotReady)
}
}
}
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