[−][src]Trait futures::stream::Stream

pub trait Stream {
    type Item;
    fn poll_next(
        self: Pin<&mut Self>, 
        lw: &LocalWaker
    ) -> Poll<Option<Self::Item>>;
}

A stream of values produced asynchronously.

If Future<Output = T> is an asynchronous version of T, then Stream<Item = T> is an asynchronous version of Iterator<Item = T>. A stream represents a sequence of value-producing events that occur asynchronously to the caller.

The trait is modeled after Future, but allows poll_next to be called even after a value has been produced, yielding None once the stream has been fully exhausted.

Associated Types

Values yielded by the stream.

Required Methods

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted.

Return value

There are several possible return values, each indicating a distinct stream state:

  • Poll::Pending means that this stream's next value is not ready yet. Implementations will ensure that the current task will be notified when the next value may be ready.

  • Poll::Ready(Some(val)) means that the stream has successfully produced a value, val, and may produce further values on subsequent poll_next calls.

  • Poll::Ready(None) means that the stream has terminated, and poll_next should not be invoked again.

Panics

Once a stream is finished, i.e. Ready(None) has been returned, further calls to poll_next may result in a panic or other "bad behavior". If this is difficult to guard against then the fuse adapter can be used to ensure that poll_next always returns Ready(None) in subsequent calls.

Implementations on Foreign Types

impl<St, F, T> Stream for MapOk<St, F> where
    F: FnMut(<St as TryStream>::Ok) -> T,
    St: TryStream, 
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impl<St, F, E> Stream for MapErr<St, F> where
    F: FnMut(<St as TryStream>::Error) -> E,
    St: TryStream, 
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impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F> where
    F: FnMut(<St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Ok = Option<T>, Error = <St as TryStream>::Error>,
    St: TryStream, 
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impl<S, U, St, F> Stream for WithFlatMap<S, U, St, F> where
    F: FnMut(U) -> St,
    S: Stream + Sink,
    St: Stream<Item = Result<<S as Sink>::SinkItem, <S as Sink>::SinkError>>, 
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impl<S> Stream for Box<S> where
    S: Stream + Unpin + ?Sized, 
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impl<A, B> Stream for Either<A, B> where
    A: Stream,
    B: Stream<Item = <A as Stream>::Item>, 
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impl<S> Stream for AssertUnwindSafe<S> where
    S: Stream, 
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impl<'a, S> Stream for &'a mut S where
    S: Stream + Unpin + ?Sized, 
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impl<P> Stream for Pin<P> where
    P: DerefMut,
    <P as Deref>::Target: Stream, 
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impl<T> Stream for VecDeque<T> where
    T: Unpin, 
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Implementors

impl<'a, T> Stream for LocalStreamObj<'a, T>
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impl<'a, T> Stream for StreamObj<'a, T>
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impl<Fut> Stream for FlattenStream<Fut> where
    Fut: Future,
    <Fut as Future>::Output: Stream, 
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impl<Fut> Stream for futures::future::IntoStream<Fut> where
    Fut: Future, 
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impl<Fut> Stream for FuturesOrdered<Fut> where
    Fut: Future, 
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impl<Fut> Stream for FuturesUnordered<Fut> where
    Fut: Future, 
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impl<Fut> Stream for Once<Fut> where
    Fut: Future, 
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impl<I> Stream for Iter<I> where
    I: Iterator, 
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impl<S> Stream for Buffer<S> where
    S: Sink + Stream, 
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impl<S> Stream for Fuse<S> where
    S: Stream, 
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impl<S> Stream for Peekable<S> where
    S: Stream, 
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impl<S> Stream for SplitStream<S> where
    S: Stream, 
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impl<S, E> Stream for SinkErrInto<S, E> where
    S: Sink + Stream,
    <S as Sink>::SinkError: Into<E>, 
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impl<S, F> Stream for SinkMapErr<S, F> where
    S: Stream, 
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impl<S, U, Fut, F> Stream for With<S, U, Fut, F> where
    F: FnMut(U) -> Fut,
    Fut: Future,
    S: Stream + Sink, 
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impl<St> Stream for Compat01As03<St> where
    St: Stream, 
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impl<St> Stream for BufferUnordered<St> where
    St: Stream,
    <St as Stream>::Item: Future, 
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impl<St> Stream for Buffered<St> where
    St: Stream,
    <St as Stream>::Item: Future, 
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impl<St> Stream for CatchUnwind<St> where
    St: UnwindSafe + Stream, 
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impl<St> Stream for Chunks<St> where
    St: Stream, 
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impl<St> Stream for Flatten<St> where
    St: Stream,
    <St as Stream>::Item: Stream, 
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impl<St> Stream for futures::stream::IntoStream<St> where
    St: TryStream, 
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impl<St> Stream for Skip<St> where
    St: Stream, 
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impl<St> Stream for Take<St> where
    St: Stream, 
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impl<St> Stream for TryBufferUnordered<St> where
    St: TryStream,
    <St as TryStream>::Ok: TryFuture,
    <<St as TryStream>::Ok as TryFuture>::Error == <St as TryStream>::Error, 
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impl<St, E> Stream for ErrInto<St, E> where
    St: TryStream,
    <St as TryStream>::Error: Into<E>, 
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impl<St, F> Stream for Inspect<St, F> where
    F: FnMut(&<St as Stream>::Item),
    St: Stream, 
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impl<St, F, T> Stream for Map<St, F> where
    F: FnMut(<St as Stream>::Item) -> T,
    St: Stream, 
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impl<St, Fut, F> Stream for Filter<St, Fut, F> where
    F: FnMut(&<St as Stream>::Item) -> Fut,
    Fut: Future<Output = bool>,
    St: Stream, 
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impl<St, Fut, F> Stream for SkipWhile<St, Fut, F> where
    F: FnMut(&<St as Stream>::Item) -> Fut,
    Fut: Future<Output = bool>,
    St: Stream, 
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impl<St, Fut, F> Stream for TakeWhile<St, Fut, F> where
    F: FnMut(&<St as Stream>::Item) -> Fut,
    Fut: Future<Output = bool>,
    St: Stream, 
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impl<St, Fut, F> Stream for Then<St, Fut, F> where
    F: FnMut(<St as Stream>::Item) -> Fut,
    Fut: Future,
    St: Stream, 
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impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F> where
    F: FnMut(&<St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Ok = bool, Error = <St as TryStream>::Error>,
    St: TryStream, 
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impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F> where
    F: FnMut(<St as Stream>::Item) -> Fut,
    Fut: Future<Output = Option<T>>,
    St: Stream, 
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impl<St1, St2> Stream for Chain<St1, St2> where
    St1: Stream,
    St2: Stream<Item = <St1 as Stream>::Item>, 
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impl<St1, St2> Stream for Select<St1, St2> where
    St1: Stream,
    St2: Stream<Item = <St1 as Stream>::Item>, 
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impl<St1, St2> Stream for Zip<St1, St2> where
    St1: Stream,
    St2: Stream, 
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impl<T> Stream for Receiver<T>
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impl<T> Stream for UnboundedReceiver<T>
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impl<T> Stream for Empty<T>
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impl<T> Stream for Repeat<T> where
    T: Clone, 
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impl<T, F> Stream for PollFn<F> where
    F: FnMut(&LocalWaker) -> Poll<Option<T>>, 
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impl<T, F, Fut, It> Stream for Unfold<T, F, Fut> where
    F: FnMut(T) -> Fut,
    Fut: Future<Output = Option<(It, T)>>, 
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