[][src]Trait futures::stream::Stream

#[must_use = "streams do nothing unless polled"]
pub trait Stream {
    type Item;
    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut Context
    ) -> Poll<Option<Self::Item>>; fn size_hint(&self) -> (usize, Option<usize>) { ... } }

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>, 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.

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Provided methods

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.

Specifically, size_hint() returns a tuple where the first element is the lower bound, and the second element is the upper bound.

The second half of the tuple that is returned is an Option<usize>. A None here means that either there is no known upper bound, or the upper bound is larger than usize.

Implementation notes

It is not enforced that a stream implementation yields the declared number of elements. A buggy stream may yield less than the lower bound or more than the upper bound of elements.

size_hint() is primarily intended to be used for optimizations such as reserving space for the elements of the stream, but must not be trusted to e.g., omit bounds checks in unsafe code. An incorrect implementation of size_hint() should not lead to memory safety violations.

That said, the implementation should provide a correct estimation, because otherwise it would be a violation of the trait's protocol.

The default implementation returns (0, None) which is correct for any stream.

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Implementations on Foreign Types

impl<T> Stream for VecDeque<T> where
    T: Unpin
[src]

type Item = T

impl<'_, S> Stream for &'_ mut S where
    S: Stream + Unpin + ?Sized
[src]

type Item = <S as Stream>::Item

impl<S> Stream for AssertUnwindSafe<S> where
    S: Stream
[src]

type Item = <S as Stream>::Item

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

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

impl<S> Stream for Box<S> where
    S: Stream + Unpin + ?Sized
[src]

type Item = <S as Stream>::Item

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Implementors

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

type Item = <A as Stream>::Item

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

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

impl<Fut> Stream for futures::future::IntoStream<Fut> where
    Fut: Future
[src]

type Item = <Fut as Future>::Output

impl<Fut> Stream for TryFlattenStream<Fut> where
    Fut: TryFuture,
    <Fut as TryFuture>::Ok: TryStream,
    <<Fut as TryFuture>::Ok as TryStream>::Error == <Fut as TryFuture>::Error
[src]

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

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

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

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

impl<Fut, S> Stream for FlattenSink<Fut, S> where
    Fut: TryFuture<Ok = S>,
    S: TryStream<Error = <Fut as TryFuture>::Error>, 
[src]

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

impl<I> Stream for Iter<I> where
    I: Iterator
[src]

type Item = <I as Iterator>::Item

impl<R> Stream for Lines<R> where
    R: AsyncBufRead
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type Item = Result<String, Error>

impl<S> Stream for Fuse<S> where
    S: Stream
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type Item = <S as Stream>::Item

impl<S> Stream for Peekable<S> where
    S: Stream
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type Item = <S as Stream>::Item

impl<S> Stream for SplitStream<S> where
    S: Stream
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type Item = <S as Stream>::Item

impl<S, F> Stream for SinkMapErr<S, F> where
    S: Stream
[src]

type Item = <S as Stream>::Item

impl<S, Item> Stream for Buffer<S, Item> where
    S: Sink<Item> + Stream
[src]

type Item = <S as Stream>::Item

impl<S, Item, E> Stream for SinkErrInto<S, Item, E> where
    S: Sink<Item> + Stream,
    <S as Sink<Item>>::Error: Into<E>, 
[src]

type Item = <S as Stream>::Item

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

type Item = <S as Stream>::Item

impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F> where
    F: FnMut(U) -> St,
    S: Stream + Sink<Item>,
    St: Stream<Item = Result<Item, <S as Sink<Item>>::Error>>, 
[src]

type Item = <S as Stream>::Item

impl<S, SinkItem> Stream for Compat01As03Sink<S, SinkItem> where
    S: Stream
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type Item = Result<<S as Stream>::Item, <S as Stream>::Error>

impl<St> Stream for Compat01As03<St> where
    St: Stream
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type Item = Result<<St as Stream>::Item, <St as Stream>::Error>

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

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

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

impl<St> Stream for Chunks<St> where
    St: Stream
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type Item = Vec<<St as Stream>::Item>

impl<St> Stream for Enumerate<St> where
    St: Stream
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type Item = (usize, <St as Stream>::Item)

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

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

impl<St> Stream for futures::stream::IntoStream<St> where
    St: TryStream
[src]

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

impl<St> Stream for SelectAll<St> where
    St: Unpin + Stream
[src]

type Item = <St as Stream>::Item

impl<St> Stream for Skip<St> where
    St: Stream
[src]

type Item = <St as Stream>::Item

impl<St> Stream for Take<St> where
    St: Stream
[src]

type Item = <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
[src]

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

impl<St> Stream for TryFlatten<St> where
    St: TryStream,
    <St as TryStream>::Ok: TryStream,
    <<St as TryStream>::Ok as TryStream>::Error: From<<St as TryStream>::Error>, 
[src]

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

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

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

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

type Item = <St as Stream>::Item

impl<St, F> Stream for InspectErr<St, F> where
    F: FnMut(&<St as TryStream>::Error),
    St: TryStream
[src]

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

impl<St, F> Stream for InspectOk<St, F> where
    F: FnMut(&<St as TryStream>::Ok),
    St: TryStream
[src]

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

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

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

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

type Item = T

impl<St, F, T> Stream for MapOk<St, F> where
    F: FnMut(<St as TryStream>::Ok) -> T,
    St: TryStream
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type Item = Result<T, <St as TryStream>::Error>

impl<St, Fut, F> Stream for AndThen<St, Fut, F> where
    F: FnMut(<St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Error = <St as TryStream>::Error>,
    St: TryStream
[src]

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

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

type Item = <St as Stream>::Item

impl<St, Fut, F> Stream for OrElse<St, Fut, F> where
    F: FnMut(<St as TryStream>::Error) -> Fut,
    Fut: TryFuture<Ok = <St as TryStream>::Ok>,
    St: TryStream
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type Item = Result<<St as TryStream>::Ok, <Fut as TryFuture>::Error>

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

type Item = <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
[src]

type Item = <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
[src]

type Item = <Fut as Future>::Output

impl<St, Fut, F> Stream for TryFilter<St, Fut, F> where
    F: FnMut(&<St as TryStream>::Ok) -> Fut,
    Fut: Future<Output = bool>,
    St: TryStream
[src]

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

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
[src]

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

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
[src]

type Item = T

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
[src]

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

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

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

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

impl<T> Stream for Receiver<T>[src]

type Item = T

impl<T> Stream for UnboundedReceiver<T>[src]

type Item = T

impl<T> Stream for Empty<T>[src]

type Item = T

impl<T> Stream for Pending<T>[src]

type Item = T

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

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

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

type Item = Item

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