blob: 28a77fe705b4dd151ba64821b306e58be9c5edbe [file] [log] [blame]
use {Future, Poll, Async};
use future::Either;
/// Future for the `merge` combinator, waiting for one of two differently-typed
/// futures to complete.
///
/// This is created by the `Future::merge` method.
#[must_use = "futures do nothing unless polled"]
#[derive(Debug)]
pub struct Select2<A, B> {
inner: Option<(A, B)>,
}
pub fn new<A, B>(a: A, b: B) -> Select2<A, B> {
Select2 { inner: Some((a, b)) }
}
impl<A, B> Future for Select2<A, B> where A: Future, B: Future {
type Item = Either<(A::Item, B), (B::Item, A)>;
type Error = Either<(A::Error, B), (B::Error, A)>;
fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
let (mut a, mut b) = self.inner.take().expect("cannot poll Select2 twice");
match a.poll() {
Err(e) => Err(Either::A((e, b))),
Ok(Async::Ready(x)) => Ok(Async::Ready(Either::A((x, b)))),
Ok(Async::NotReady) => match b.poll() {
Err(e) => Err(Either::B((e, a))),
Ok(Async::Ready(x)) => Ok(Async::Ready(Either::B((x, a)))),
Ok(Async::NotReady) => {
self.inner = Some((a, b));
Ok(Async::NotReady)
}
}
}
}
}