Trait futures::prelude::Stream

pub trait Stream {
    type Item;
    fn poll_next(
        self: PinMut<Self>, 
        cx: &mut Context
    ) -> 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.

Required Methods

fn poll_next(self: PinMut<Self>, cx: &mut Context) -> 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.

Implementations on Foreign Types

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: PinMut<WithFlatMap<S, U, St, F>>,     cx: &mut Context ) -> Poll<Option<<S as Stream>::Item>>

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: PinMut<MapErr<St, F>>,     cx: &mut Context ) -> Poll<Option<<MapErr<St, F> 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: PinMut<MapOk<St, F>>,     cx: &mut Context ) -> Poll<Option<<MapOk<St, F> as Stream>::Item>>

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

type Item = <S as Stream>::Item

fn poll_next(     self: PinMut<PinBox<S>>,     cx: &mut Context ) -> Poll<Option<<PinBox<S> as Stream>::Item>>

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

type Item = <S as Stream>::Item

fn poll_next(     self: PinMut<AssertUnwindSafe<S>>,     cx: &mut Context ) -> Poll<Option<<S 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: PinMut<&'a mut S>,     cx: &mut Context ) -> Poll<Option<<&'a mut 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: PinMut<Either<A, B>>,     cx: &mut Context ) -> Poll<Option<<A as Stream>::Item>>

impl<'a, S> Stream for PinMut<'a, S> where     S: Stream + ?Sized,

type Item = <S as Stream>::Item

fn poll_next(     self: PinMut<PinMut<'a, S>>,     cx: &mut Context ) -> Poll<Option<<PinMut<'a, S> as Stream>::Item>>

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

type Item = T

fn poll_next(     self: PinMut<VecDeque<T>>,     _cx: &mut Context ) -> Poll<Option<<VecDeque<T> as Stream>::Item>>

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

type Item = <S as Stream>::Item

fn poll_next(     self: PinMut<Box<S>>,     cx: &mut Context ) -> Poll<Option<<Box<S> as Stream>::Item>>

Implementors

• impl<St> Stream for Take<St> where     St: Stream,  type Item = <St as Stream>::Item;

• impl<S> Stream for Peekable<S> where     S: Stream,  type Item = <S 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;

• impl<S> Stream for Buffer<S> where     S: Sink + Stream,  type Item = <S as Stream>::Item;

• impl<St> Stream for Skip<St> where     St: Stream,  type Item = <St 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;

• 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;

• impl<Fut> Stream for FlattenStream<Fut> where     Fut: Future,     <Fut as Future>::Output: Stream,  type Item = <<Fut as Future>::Output as Stream>::Item;

• impl<S, F> Stream for SinkMapErr<S, F> where     S: Stream,  type Item = <S as Stream>::Item;

• 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;

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

• impl<St1, St2> Stream for Zip<St1, St2> where     St1: Stream,     St2: Stream,  type Item = (<St1 as Stream>::Item, <St2 as Stream>::Item);

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

• 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;

• impl<T> Stream for Repeat<T> where     T: Clone,  type Item = T;

• impl<S> Stream for SplitStream<S> where     S: Stream,  type Item = <S 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;

• impl<Fut> Stream for IntoStream<Fut> where     Fut: Future,  type Item = <Fut as Future>::Output;

• impl<S, E> Stream for SinkErrInto<S, E> where     S: Sink + Stream,     <S as Sink>::SinkError: Into<E>,  type Item = <S as Stream>::Item;

• impl<I> Stream for Iter<I> where     I: Iterator,  type Item = <I as Iterator>::Item;

• impl<Fut> Stream for FuturesUnordered<Fut> where     Fut: Future,  type Item = <Fut as Future>::Output;

• impl<St> Stream for Buffered<St> where     St: Stream,     <St as Stream>::Item: Future,  type Item = <<St as Stream>::Item as Future>::Output;

• impl<S> Stream for Fuse<S> where     S: Stream,  type Item = <S 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;

• impl<T> Stream for Empty<T> type Item = T;

• impl<T, F> Stream for PollFn<F> where     F: FnMut(&mut Context) -> Poll<Option<T>>,  type Item = T;

• 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;

• impl<St> Stream for CatchUnwind<St> where     St: UnwindSafe + Stream,  type Item = Result<<St as Stream>::Item, Box<Any + 'static + Send>>;

• impl<St> Stream for Chunks<St> where     St: Stream,  type Item = Vec<<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>;

• 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;

• impl<Fut> Stream for FuturesOrdered<Fut> where     Fut: Future,  type Item = <Fut as Future>::Output;

• impl<Fut> Stream for Once<Fut> where     Fut: Future,  type Item = <Fut as Future>::Output;

• impl<St> Stream for BufferUnordered<St> where     St: Stream,     <St as Stream>::Item: Future,  type Item = <<St as Stream>::Item as Future>::Output;

• impl<T> Stream for Receiver<T> type Item = T;

• impl<T> Stream for UnboundedReceiver<T> type Item = T;