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use {Async, Poll};
use stream::{Stream, Fuse};
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Zip<S1: Stream, S2: Stream> {
stream1: Fuse<S1>,
stream2: Fuse<S2>,
queued1: Option<S1::Item>,
queued2: Option<S2::Item>,
}
pub fn new<S1, S2>(stream1: S1, stream2: S2) -> Zip<S1, S2>
where S1: Stream, S2: Stream<Error = S1::Error>
{
Zip {
stream1: stream1.fuse(),
stream2: stream2.fuse(),
queued1: None,
queued2: None,
}
}
impl<S1, S2> Stream for Zip<S1, S2>
where S1: Stream, S2: Stream<Error = S1::Error>
{
type Item = (S1::Item, S2::Item);
type Error = S1::Error;
fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
if self.queued1.is_none() {
match self.stream1.poll()? {
Async::Ready(Some(item1)) => self.queued1 = Some(item1),
Async::Ready(None) | Async::NotReady => {}
}
}
if self.queued2.is_none() {
match self.stream2.poll()? {
Async::Ready(Some(item2)) => self.queued2 = Some(item2),
Async::Ready(None) | Async::NotReady => {}
}
}
if self.queued1.is_some() && self.queued2.is_some() {
let pair = (self.queued1.take().unwrap(),
self.queued2.take().unwrap());
Ok(Async::Ready(Some(pair)))
} else if self.stream1.is_done() || self.stream2.is_done() {
Ok(Async::Ready(None))
} else {
Ok(Async::NotReady)
}
}
}