| use {Future, Poll, Async}; |
| use future::Either; |
| |
| /// Future for the `select2` combinator, waiting for one of two differently-typed |
| /// futures to complete. |
| /// |
| /// This is created by the [`Future::select2`] method. |
| /// |
| /// [`Future::select2`]: trait.Future.html#method.select2 |
| #[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) |
| } |
| } |
| } |
| } |
| } |