Trait async_std::stream::Stream

source ·
pub trait Stream {
    type Item;

    // Required method
    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Self::Item>>;

    // Provided method
    fn size_hint(&self) -> (usize, Option<usize>) { ... }
}
Expand description

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.

Required Associated Types§

source

type Item

Values yielded by the stream.

Required Methods§

source

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 has finished (returned Ready(None) from poll_next), calling its poll_next method again may panic, block forever, or cause other kinds of problems; the Stream trait places no requirements on the effects of such a call. However, as the poll_next method is not marked unsafe, Rust’s usual rules apply: calls must never cause undefined behavior (memory corruption, incorrect use of unsafe functions, or the like), regardless of the stream’s state.

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.

Provided Methods§

source

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.

Implementations on Foreign Types§

source§

impl Stream for &Signals

source§

type Item = Result<Signal, Error>

source§

fn poll_next( self: Pin<&mut &Signals>, cx: &mut Context<'_>, ) -> Poll<Option<<&Signals as Stream>::Item>>

source§

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

source§

impl Stream for Timer

source§

type Item = Instant

source§

fn poll_next( self: Pin<&mut Timer>, cx: &mut Context<'_>, ) -> Poll<Option<<Timer as Stream>::Item>>

source§

impl Stream for Signals

source§

type Item = Result<Signal, Error>

source§

fn poll_next( self: Pin<&mut Signals>, cx: &mut Context<'_>, ) -> Poll<Option<<Signals as Stream>::Item>>

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

impl<'a, S, T> Stream for Cloned<S>
where T: 'a + Clone, S: Stream<Item = &'a T>,

source§

type Item = T

source§

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

source§

impl<'a, S, T> Stream for Copied<S>
where T: 'a + Copy, S: Stream<Item = &'a T>,

source§

type Item = T

source§

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

source§

impl<A, B> Stream for Zip<A, B>
where A: Stream, B: Stream,

source§

type Item = (<A as Stream>::Item, <B as Stream>::Item)

source§

fn poll_next( self: Pin<&mut Zip<A, B>>, cx: &mut Context<'_>, ) -> Poll<Option<<Zip<A, B> as Stream>::Item>>

source§

impl<F> Stream for OnceFuture<F>
where F: Future,

source§

type Item = <F as Future>::Output

source§

fn poll_next( self: Pin<&mut OnceFuture<F>>, cx: &mut Context<'_>, ) -> Poll<Option<<OnceFuture<F> as Stream>::Item>>

source§

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

source§

type Item = <I as Iterator>::Item

source§

fn poll_next( self: Pin<&mut Iter<I>>, _cx: &mut Context<'_>, ) -> Poll<Option<<Iter<I> as Stream>::Item>>

source§

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

source§

impl<R> Stream for Bytes<R>
where R: AsyncRead + Unpin,

source§

type Item = Result<u8, Error>

source§

fn poll_next( self: Pin<&mut Bytes<R>>, cx: &mut Context<'_>, ) -> Poll<Option<<Bytes<R> as Stream>::Item>>

source§

impl<R> Stream for Lines<R>
where R: AsyncBufRead,

source§

type Item = Result<String, Error>

source§

fn poll_next( self: Pin<&mut Lines<R>>, cx: &mut Context<'_>, ) -> Poll<Option<<Lines<R> as Stream>::Item>>

source§

impl<R> Stream for Split<R>
where R: AsyncBufRead,

source§

type Item = Result<Vec<u8>, Error>

source§

fn poll_next( self: Pin<&mut Split<R>>, cx: &mut Context<'_>, ) -> Poll<Option<<Split<R> as Stream>::Item>>

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

impl<S> Stream for Cycle<S>
where S: Stream + Clone,

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

type Item = (usize, <S as Stream>::Item)

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

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

source§

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

source§

type Item = <S as Stream>::Item

source§

fn poll_next( self: Pin<&mut Inspect<S, F>>, cx: &mut Context<'_>, ) -> Poll<Option<<Inspect<S, F> as Stream>::Item>>

source§

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

source§

type Item = <Fut as Future>::Output

source§

fn poll_next( self: Pin<&mut Then<S, F, Fut>>, cx: &mut Context<'_>, ) -> Poll<Option<<Then<S, F, Fut> as Stream>::Item>>

source§

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

source§

impl<S, F, T> Stream for FilterMap<S, F>
where S: Stream, F: FnMut(<S as Stream>::Item) -> Option<T>,

source§

type Item = T

source§

fn poll_next( self: Pin<&mut FilterMap<S, F>>, cx: &mut Context<'_>, ) -> Poll<Option<<FilterMap<S, F> as Stream>::Item>>

source§

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

source§

type Item = T

source§

fn poll_next( self: Pin<&mut Map<S, F>>, cx: &mut Context<'_>, ) -> Poll<Option<<Map<S, F> as Stream>::Item>>

source§

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

source§

impl<S, P> Stream for Filter<S, P>
where S: Stream, P: FnMut(&<S as Stream>::Item) -> bool,

source§

type Item = <S as Stream>::Item

source§

fn poll_next( self: Pin<&mut Filter<S, P>>, cx: &mut Context<'_>, ) -> Poll<Option<<Filter<S, P> as Stream>::Item>>

source§

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

source§

impl<S, P> Stream for SkipWhile<S, P>
where S: Stream, P: FnMut(&<S as Stream>::Item) -> bool,

source§

type Item = <S as Stream>::Item

source§

fn poll_next( self: Pin<&mut SkipWhile<S, P>>, cx: &mut Context<'_>, ) -> Poll<Option<<SkipWhile<S, P> as Stream>::Item>>

source§

impl<S, P> Stream for TakeWhile<S, P>
where S: Stream, P: FnMut(&<S as Stream>::Item) -> bool,

source§

type Item = <S as Stream>::Item

source§

fn poll_next( self: Pin<&mut TakeWhile<S, P>>, cx: &mut Context<'_>, ) -> Poll<Option<<TakeWhile<S, P> as Stream>::Item>>

source§

impl<S, St, F, B> Stream for Scan<S, St, F>
where S: Stream, F: FnMut(&mut St, <S as Stream>::Item) -> Option<B>,

source§

type Item = B

source§

fn poll_next( self: Pin<&mut Scan<S, St, F>>, cx: &mut Context<'_>, ) -> Poll<Option<B>>

source§

impl<S, U> Stream for Chain<S, U>
where S: Stream, U: Stream<Item = <S as Stream>::Item>,

source§

type Item = <S as Stream>::Item

source§

fn poll_next( self: Pin<&mut Chain<S, U>>, cx: &mut Context<'_>, ) -> Poll<Option<<Chain<S, U> as Stream>::Item>>

source§

impl<S, U> Stream for Flatten<S>
where S: Stream<Item = U>, U: Stream,

source§

type Item = <U as Stream>::Item

source§

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

source§

impl<S, U, F> Stream for FlatMap<S, U, F>
where S: Stream, U: Stream, F: FnMut(<S as Stream>::Item) -> U,

source§

type Item = <U as Stream>::Item

source§

fn poll_next( self: Pin<&mut FlatMap<S, U, F>>, cx: &mut Context<'_>, ) -> Poll<Option<<FlatMap<S, U, F> as Stream>::Item>>

source§

impl<T> Stream for Receiver<T>

source§

type Item = T

source§

fn poll_next( self: Pin<&mut Receiver<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<Receiver<T> as Stream>::Item>>

source§

impl<T> Stream for Unblock<T>
where T: Iterator + Send + 'static, <T as Iterator>::Item: Send + 'static,

source§

type Item = <T as Iterator>::Item

source§

fn poll_next( self: Pin<&mut Unblock<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<T as Iterator>::Item>>

source§

impl<T> Stream for Empty<T>

source§

type Item = T

source§

fn poll_next( self: Pin<&mut Empty<T>>, _: &mut Context<'_>, ) -> Poll<Option<<Empty<T> as Stream>::Item>>

source§

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

source§

impl<T> Stream for Once<T>

source§

type Item = T

source§

fn poll_next(self: Pin<&mut Once<T>>, _: &mut Context<'_>) -> Poll<Option<T>>

source§

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

source§

impl<T> Stream for Pending<T>

source§

type Item = T

source§

fn poll_next(self: Pin<&mut Pending<T>>, _: &mut Context<'_>) -> Poll<Option<T>>

source§

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

source§

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

source§

type Item = T

source§

fn poll_next( self: Pin<&mut Repeat<T>>, _: &mut Context<'_>, ) -> Poll<Option<<Repeat<T> as Stream>::Item>>

source§

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

source§

impl<T, E, F, Fut, Item> Stream for TryUnfold<T, F, Fut>
where F: FnMut(T) -> Fut, Fut: Future<Output = Result<Option<(Item, T)>, E>>,

source§

type Item = Result<Item, E>

source§

fn poll_next( self: Pin<&mut TryUnfold<T, F, Fut>>, cx: &mut Context<'_>, ) -> Poll<Option<<TryUnfold<T, F, Fut> as Stream>::Item>>

source§

impl<T, F> Stream for PollFn<F>
where F: FnMut(&mut Context<'_>) -> Poll<Option<T>>,

source§

type Item = T

source§

fn poll_next(self: Pin<&mut PollFn<F>>, cx: &mut Context<'_>) -> Poll<Option<T>>

source§

impl<T, F> Stream for RepeatWith<F>
where F: FnMut() -> T,

source§

type Item = T

source§

fn poll_next( self: Pin<&mut RepeatWith<F>>, _: &mut Context<'_>, ) -> Poll<Option<<RepeatWith<F> as Stream>::Item>>

source§

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

source§

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

source§

type Item = Item

source§

fn poll_next( self: Pin<&mut Unfold<T, F, Fut>>, cx: &mut Context<'_>, ) -> Poll<Option<<Unfold<T, F, Fut> as Stream>::Item>>

source§

impl<T, S1, S2> Stream for Or<S1, S2>
where S1: Stream<Item = T>, S2: Stream<Item = T>,

source§

type Item = T

source§

fn poll_next( self: Pin<&mut Or<S1, S2>>, cx: &mut Context<'_>, ) -> Poll<Option<<Or<S1, S2> as Stream>::Item>>

source§

impl<T, S1, S2> Stream for Race<S1, S2>
where S1: Stream<Item = T>, S2: Stream<Item = T>,

source§

type Item = T

source§

fn poll_next( self: Pin<&mut Race<S1, S2>>, cx: &mut Context<'_>, ) -> Poll<Option<<Race<S1, S2> as Stream>::Item>>

Implementors§

source§

impl Stream for ReadDir

source§

impl Stream for async_std::net::Incoming<'_>

source§

impl Stream for async_std::os::unix::net::Incoming<'_>

source§

impl Stream for Interval

Available on unstable only.
source§

impl<'a, S, T> Stream for async_std::stream::Cloned<S>
where S: Stream<Item = &'a T>, T: Clone + 'a,

source§

type Item = T

source§

impl<'a, S, T> Stream for async_std::stream::Copied<S>
where S: Stream<Item = &'a T>, T: Copy + 'a,

source§

type Item = T

source§

impl<A: Stream, B: Stream> Stream for async_std::stream::Zip<A, B>

source§

type Item = (<A as Stream>::Item, <B as Stream>::Item)

source§

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

Available on unstable only.
source§

type Item = T

source§

impl<I: Iterator> Stream for FromIter<I>

source§

type Item = <I as Iterator>::Item

source§

impl<L, R, T> Stream for Merge<L, R>
where L: Stream<Item = T>, R: Stream<Item = T>,

Available on unstable only.
source§

type Item = T

source§

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

source§

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

source§

impl<R: BufRead> Stream for async_std::io::Lines<R>

source§

impl<R: BufRead> Stream for async_std::io::Split<R>

source§

impl<S> Stream for async_std::stream::Skip<S>
where S: Stream,

source§

type Item = <S as Stream>::Item

source§

impl<S> Stream for async_std::stream::StepBy<S>
where S: Stream,

source§

type Item = <S as Stream>::Item

source§

impl<S, F> Stream for async_std::stream::Inspect<S, F>
where S: Stream, F: FnMut(&S::Item),

source§

type Item = <S as Stream>::Item

source§

impl<S, F, B> Stream for async_std::stream::Map<S, F>
where S: Stream, F: FnMut(S::Item) -> B,

source§

type Item = B

source§

impl<S, P> Stream for async_std::stream::Filter<S, P>
where S: Stream, P: FnMut(&S::Item) -> bool,

source§

type Item = <S as Stream>::Item

source§

impl<S, P> Stream for async_std::stream::SkipWhile<S, P>
where S: Stream, P: FnMut(&S::Item) -> bool,

source§

type Item = <S as Stream>::Item

source§

impl<S, P> Stream for async_std::stream::TakeWhile<S, P>
where S: Stream, P: FnMut(&S::Item) -> bool,

source§

type Item = <S as Stream>::Item

source§

impl<S, St, F, B> Stream for async_std::stream::Scan<S, St, F>
where S: Stream, F: FnMut(&mut St, S::Item) -> Option<B>,

source§

type Item = B

source§

impl<S, U> Stream for async_std::stream::Flatten<S>
where S: Stream, S::Item: IntoStream<IntoStream = U, Item = U::Item>, U: Stream,

Available on unstable only.
source§

type Item = <U as Stream>::Item

source§

impl<S, U, F> Stream for async_std::stream::FlatMap<S, U, F>
where S: Stream, U: Stream, F: FnMut(S::Item) -> U,

Available on unstable only.
source§

type Item = <U as Stream>::Item

source§

impl<S: Stream> Stream for async_std::stream::Fuse<S>

source§

type Item = <S as Stream>::Item

source§

impl<S: Stream> Stream for async_std::stream::Take<S>

source§

type Item = <S as Stream>::Item

source§

impl<S: Stream> Stream for Timeout<S>

Available on unstable only.
source§

impl<S: Stream, U: Stream<Item = S::Item>> Stream for async_std::stream::Chain<S, U>

source§

type Item = <S as Stream>::Item

source§

impl<T> Stream for async_std::channel::Receiver<T>

source§

type Item = T

source§

impl<T> Stream for async_std::stream::Empty<T>

source§

type Item = T

source§

impl<T> Stream for async_std::stream::Once<T>

source§

type Item = T

source§

impl<T> Stream for async_std::stream::Pending<T>

Available on unstable only.
source§

type Item = T

source§

impl<T, F> Stream for FromFn<F>
where F: FnMut() -> Option<T>,

source§

type Item = T

source§

impl<T, F> Stream for async_std::stream::RepeatWith<F>
where F: FnMut() -> T,

source§

type Item = T

source§

impl<T: Read + Unpin> Stream for async_std::io::Bytes<T>

source§

impl<T: Clone> Stream for async_std::stream::Repeat<T>

source§

type Item = T