Trait futures::prelude::Stream

#[must_use = "streams do nothing unless polled"]
pub trait Stream {
    type Item;
    fn poll_next(
        self: Pin<&mut Self>, 
        waker: &Waker
    ) -> 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

type Item

Values yielded by the stream.

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Required methods

fn poll_next(self: Pin<&mut Self>, waker: &Waker) -> Poll<Option<Self::Item>>

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.

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Implementations on Foreign Types

impl<St, F, E> Stream for MapErr<St, F> where
    F: FnMut(<St as TryStream>::Error) -> E,
    St: TryStream, 

type Item = Result<<St as TryStream>::Ok, E>

fn poll_next(
    self: Pin<&mut MapErr<St, F>>,
    waker: &Waker
) -> Poll<Option<<MapErr<St, F> as Stream>::Item>>

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>>, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut WithFlatMap<S, U, St, F>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<St, F, T> Stream for MapOk<St, F> where
    F: FnMut(<St as TryStream>::Ok) -> T,
    St: TryStream, 

type Item = Result<T, <St as TryStream>::Error>

fn poll_next(
    self: Pin<&mut MapOk<St, F>>,
    waker: &Waker
) -> Poll<Option<<MapOk<St, F> as Stream>::Item>>

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, 

type Item = Result<T, <St as TryStream>::Error>

fn poll_next(
    self: Pin<&mut TryFilterMap<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<Result<T, <St as TryStream>::Error>>>

impl<T> Stream for VecDeque<T> where
    T: Unpin, 

type Item = T

fn poll_next(
    self: Pin<&mut VecDeque<T>>,
    _lw: &Waker
) -> Poll<Option<<VecDeque<T> as Stream>::Item>>

impl<S> Stream for AssertUnwindSafe<S> where
    S: Stream, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut AssertUnwindSafe<S>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<P> Stream for Pin<P> where
    P: DerefMut + Unpin,
    <P as Deref>::Target: Stream, 

type Item = <<P as Deref>::Target as Stream>::Item

fn poll_next(
    self: Pin<&mut Pin<P>>,
    waker: &Waker
) -> Poll<Option<<Pin<P> as Stream>::Item>>

impl<S> Stream for Box<S> where
    S: Stream + Unpin + ?Sized, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut Box<S>>,
    waker: &Waker
) -> Poll<Option<<Box<S> as Stream>::Item>>

impl<A, B> Stream for Either<A, B> where
    A: Stream,
    B: Stream<Item = <A as Stream>::Item>, 

type Item = <A as Stream>::Item

fn poll_next(
    self: Pin<&mut Either<A, B>>,
    waker: &Waker
) -> Poll<Option<<A as Stream>::Item>>

impl<'a, S> Stream for &'a mut S where
    S: Stream + Unpin + ?Sized, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut &'a mut S>,
    waker: &Waker
) -> Poll<Option<<&'a mut S as Stream>::Item>>

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Implementors

impl<'a, T> Stream for LocalStreamObj<'a, T>

type Item = T

fn poll_next(
    self: Pin<&mut LocalStreamObj<'a, T>>,
    waker: &Waker
) -> Poll<Option<T>>

impl<'a, T> Stream for StreamObj<'a, T>

type Item = T

fn poll_next(self: Pin<&mut StreamObj<'a, T>>, waker: &Waker) -> Poll<Option<T>>

impl<Fut> Stream for FlattenStream<Fut> where
    Fut: Future,
    <Fut as Future>::Output: Stream, 

type Item = <<Fut as Future>::Output as Stream>::Item

fn poll_next(
    self: Pin<&mut FlattenStream<Fut>>,
    waker: &Waker
) -> Poll<Option<<FlattenStream<Fut> as Stream>::Item>>

impl<Fut> Stream for futures::future::IntoStream<Fut> where
    Fut: Future, 

type Item = <Fut as Future>::Output

fn poll_next(
    self: Pin<&mut IntoStream<Fut>>,
    waker: &Waker
) -> Poll<Option<<IntoStream<Fut> as Stream>::Item>>

impl<Fut> Stream for FuturesOrdered<Fut> where
    Fut: Future, 

type Item = <Fut as Future>::Output

fn poll_next(
    self: Pin<&mut FuturesOrdered<Fut>>,
    waker: &Waker
) -> Poll<Option<<FuturesOrdered<Fut> as Stream>::Item>>

impl<Fut> Stream for FuturesUnordered<Fut> where
    Fut: Future, 

type Item = <Fut as Future>::Output

fn poll_next(
    self: Pin<&mut FuturesUnordered<Fut>>,
    waker: &Waker
) -> Poll<Option<<FuturesUnordered<Fut> as Stream>::Item>>

impl<Fut> Stream for Once<Fut> where
    Fut: Future, 

type Item = <Fut as Future>::Output

fn poll_next(
    self: Pin<&mut Once<Fut>>,
    waker: &Waker
) -> Poll<Option<<Fut as Future>::Output>>

impl<I> Stream for Iter<I> where
    I: Iterator, 

type Item = <I as Iterator>::Item

fn poll_next(
    self: Pin<&mut Iter<I>>,
    &Waker
) -> Poll<Option<<I as Iterator>::Item>>

impl<S> Stream for Buffer<S> where
    S: Sink + Stream, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut Buffer<S>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<S> Stream for Fuse<S> where
    S: Stream, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut Fuse<S>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<S> Stream for Peekable<S> where
    S: Stream, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut Peekable<S>>,
    waker: &Waker
) -> Poll<Option<<Peekable<S> as Stream>::Item>>

impl<S> Stream for SplitStream<S> where
    S: Stream, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut SplitStream<S>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<S, E> Stream for SinkErrInto<S, E> where
    S: Sink + Stream,
    <S as Sink>::SinkError: Into<E>, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut SinkErrInto<S, E>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<S, F> Stream for SinkMapErr<S, F> where
    S: Stream, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut SinkMapErr<S, F>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<S, U, Fut, F> Stream for With<S, U, Fut, F> where
    F: FnMut(U) -> Fut,
    Fut: Future,
    S: Stream + Sink, 

type Item = <S as Stream>::Item

fn poll_next(
    self: Pin<&mut With<S, U, Fut, F>>,
    waker: &Waker
) -> Poll<Option<<S as Stream>::Item>>

impl<St> Stream for Compat01As03<St> where
    St: Stream, 

type Item = Result<<St as Stream>::Item, <St as Stream>::Error>

fn poll_next(
    self: Pin<&mut Compat01As03<St>>,
    waker: &Waker
) -> Poll<Option<<Compat01As03<St> as Stream>::Item>>

impl<St> Stream for BufferUnordered<St> where
    St: Stream,
    <St as Stream>::Item: Future, 

type Item = <<St as Stream>::Item as Future>::Output

fn poll_next(
    self: Pin<&mut BufferUnordered<St>>,
    waker: &Waker
) -> Poll<Option<<BufferUnordered<St> as Stream>::Item>>

impl<St> Stream for Buffered<St> where
    St: Stream,
    <St as Stream>::Item: Future, 

type Item = <<St as Stream>::Item as Future>::Output

fn poll_next(
    self: Pin<&mut Buffered<St>>,
    waker: &Waker
) -> Poll<Option<<Buffered<St> as Stream>::Item>>

impl<St> Stream for CatchUnwind<St> where
    St: UnwindSafe + Stream, 

type Item = Result<<St as Stream>::Item, Box<dyn Any + 'static + Send>>

fn poll_next(
    self: Pin<&mut CatchUnwind<St>>,
    waker: &Waker
) -> Poll<Option<<CatchUnwind<St> as Stream>::Item>>

impl<St> Stream for Chunks<St> where
    St: Stream, 

type Item = Vec<<St as Stream>::Item>

fn poll_next(
    self: Pin<&mut Chunks<St>>,
    waker: &Waker
) -> Poll<Option<<Chunks<St> as Stream>::Item>>

impl<St> Stream for Flatten<St> where
    St: Stream,
    <St as Stream>::Item: Stream, 

type Item = <<St as Stream>::Item as Stream>::Item

fn poll_next(
    self: Pin<&mut Flatten<St>>,
    waker: &Waker
) -> Poll<Option<<Flatten<St> as Stream>::Item>>

impl<St> Stream for futures::stream::IntoStream<St> where
    St: TryStream, 

type Item = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

fn poll_next(
    self: Pin<&mut IntoStream<St>>,
    waker: &Waker
) -> Poll<Option<<IntoStream<St> as Stream>::Item>>

impl<St> Stream for SelectAll<St> where
    St: Unpin + Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut SelectAll<St>>,
    waker: &Waker
) -> Poll<Option<<SelectAll<St> as Stream>::Item>>

impl<St> Stream for Skip<St> where
    St: Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut Skip<St>>,
    waker: &Waker
) -> Poll<Option<<St as Stream>::Item>>

impl<St> Stream for Take<St> where
    St: Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut Take<St>>,
    waker: &Waker
) -> Poll<Option<<St as Stream>::Item>>

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, 

type Item = Result<<<St as TryStream>::Ok as TryFuture>::Ok, <St as TryStream>::Error>

fn poll_next(
    self: Pin<&mut TryBufferUnordered<St>>,
    waker: &Waker
) -> Poll<Option<<TryBufferUnordered<St> as Stream>::Item>>

impl<St, E> Stream for ErrInto<St, E> where
    St: TryStream,
    <St as TryStream>::Error: Into<E>, 

type Item = Result<<St as TryStream>::Ok, E>

fn poll_next(
    self: Pin<&mut ErrInto<St, E>>,
    waker: &Waker
) -> Poll<Option<<ErrInto<St, E> as Stream>::Item>>

impl<St, F> Stream for Inspect<St, F> where
    F: FnMut(&<St as Stream>::Item),
    St: Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut Inspect<St, F>>,
    waker: &Waker
) -> Poll<Option<<St as Stream>::Item>>

impl<St, F, T> Stream for Map<St, F> where
    F: FnMut(<St as Stream>::Item) -> T,
    St: Stream, 

type Item = T

fn poll_next(self: Pin<&mut Map<St, F>>, waker: &Waker) -> Poll<Option<T>>

impl<St, Fut, F> Stream for Filter<St, Fut, F> where
    F: FnMut(&<St as Stream>::Item) -> Fut,
    Fut: Future<Output = bool>,
    St: Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut Filter<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<<St as Stream>::Item>>

impl<St, Fut, F> Stream for SkipWhile<St, Fut, F> where
    F: FnMut(&<St as Stream>::Item) -> Fut,
    Fut: Future<Output = bool>,
    St: Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut SkipWhile<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<<St as Stream>::Item>>

impl<St, Fut, F> Stream for TakeWhile<St, Fut, F> where
    F: FnMut(&<St as Stream>::Item) -> Fut,
    Fut: Future<Output = bool>,
    St: Stream, 

type Item = <St as Stream>::Item

fn poll_next(
    self: Pin<&mut TakeWhile<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<<St as Stream>::Item>>

impl<St, Fut, F> Stream for Then<St, Fut, F> where
    F: FnMut(<St as Stream>::Item) -> Fut,
    Fut: Future,
    St: Stream, 

type Item = <Fut as Future>::Output

fn poll_next(
    self: Pin<&mut Then<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<<Fut as Future>::Output>>

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, 

type Item = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

fn poll_next(
    self: Pin<&mut TrySkipWhile<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<<TrySkipWhile<St, Fut, F> as Stream>::Item>>

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, 

type Item = T

fn poll_next(
    self: Pin<&mut FilterMap<St, Fut, F>>,
    waker: &Waker
) -> Poll<Option<T>>

impl<St1, St2> Stream for Chain<St1, St2> where
    St1: Stream,
    St2: Stream<Item = <St1 as Stream>::Item>, 

type Item = <St1 as Stream>::Item

fn poll_next(
    self: Pin<&mut Chain<St1, St2>>,
    waker: &Waker
) -> Poll<Option<<Chain<St1, St2> as Stream>::Item>>

impl<St1, St2> Stream for Select<St1, St2> where
    St1: Stream,
    St2: Stream<Item = <St1 as Stream>::Item>, 

type Item = <St1 as Stream>::Item

fn poll_next(
    self: Pin<&mut Select<St1, St2>>,
    waker: &Waker
) -> Poll<Option<<St1 as Stream>::Item>>

impl<St1, St2> Stream for Zip<St1, St2> where
    St1: Stream,
    St2: Stream, 

type Item = (<St1 as Stream>::Item, <St2 as Stream>::Item)

fn poll_next(
    self: Pin<&mut Zip<St1, St2>>,
    waker: &Waker
) -> Poll<Option<<Zip<St1, St2> as Stream>::Item>>

impl<T> Stream for Receiver<T>

type Item = T

fn poll_next(self: Pin<&mut Receiver<T>>, waker: &Waker) -> Poll<Option<T>>

impl<T> Stream for UnboundedReceiver<T>

type Item = T

fn poll_next(
    self: Pin<&mut UnboundedReceiver<T>>,
    waker: &Waker
) -> Poll<Option<T>>

impl<T> Stream for Empty<T>

type Item = T

fn poll_next(
    self: Pin<&mut Empty<T>>,
    &Waker
) -> Poll<Option<<Empty<T> as Stream>::Item>>

impl<T> Stream for Repeat<T> where
    T: Clone, 

type Item = T

fn poll_next(
    self: Pin<&mut Repeat<T>>,
    &Waker
) -> Poll<Option<<Repeat<T> as Stream>::Item>>

impl<T, F> Stream for PollFn<F> where
    F: FnMut(&Waker) -> Poll<Option<T>>, 

type Item = T

fn poll_next(self: Pin<&mut PollFn<F>>, waker: &Waker) -> Poll<Option<T>>

impl<T, F, Fut, It> Stream for Unfold<T, F, Fut> where
    F: FnMut(T) -> Fut,
    Fut: Future<Output = Option<(It, T)>>, 

type Item = It

fn poll_next(
    self: Pin<&mut Unfold<T, F, Fut>>,
    waker: &Waker
) -> Poll<Option<It>>

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