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§
Required Methods§
sourcefn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Self::Item>>
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 subsequentpoll_next
calls. -
Poll::Ready(None)
means that the stream has terminated, andpoll_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§
sourcefn size_hint(&self) -> (usize, Option<usize>)
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 IntervalStream
impl Stream for IntervalStream
source§impl Stream for InterfacesAddedStream<'_>
impl Stream for InterfacesAddedStream<'_>
type Item = InterfacesAdded
fn poll_next( self: Pin<&mut InterfacesAddedStream<'_>>, cx: &mut Context<'_>, ) -> Poll<Option<<InterfacesAddedStream<'_> as Stream>::Item>>
source§impl Stream for InterfacesRemovedStream<'_>
impl Stream for InterfacesRemovedStream<'_>
type Item = InterfacesRemoved
fn poll_next( self: Pin<&mut InterfacesRemovedStream<'_>>, cx: &mut Context<'_>, ) -> Poll<Option<<InterfacesRemovedStream<'_> as Stream>::Item>>
source§impl Stream for NameAcquiredStream<'_>
impl Stream for NameAcquiredStream<'_>
type Item = NameAcquired
fn poll_next( self: Pin<&mut NameAcquiredStream<'_>>, cx: &mut Context<'_>, ) -> Poll<Option<<NameAcquiredStream<'_> as Stream>::Item>>
source§impl Stream for NameLostStream<'_>
impl Stream for NameLostStream<'_>
source§impl Stream for NameOwnerChangedStream<'_>
impl Stream for NameOwnerChangedStream<'_>
type Item = NameOwnerChanged
fn poll_next( self: Pin<&mut NameOwnerChangedStream<'_>>, cx: &mut Context<'_>, ) -> Poll<Option<<NameOwnerChangedStream<'_> as Stream>::Item>>
source§impl Stream for PropertiesChangedStream<'_>
impl Stream for PropertiesChangedStream<'_>
type Item = PropertiesChanged
fn poll_next( self: Pin<&mut PropertiesChangedStream<'_>>, cx: &mut Context<'_>, ) -> Poll<Option<<PropertiesChangedStream<'_> as Stream>::Item>>
source§impl Stream for MessageStream
impl Stream for MessageStream
source§impl<'a> Stream for OwnerChangedStream<'a>
impl<'a> Stream for OwnerChangedStream<'a>
source§impl<'a> Stream for SignalStream<'a>
impl<'a> Stream for SignalStream<'a>
source§impl<'a, T> Stream for PropertyStream<'a, T>where
T: Unpin,
impl<'a, T> Stream for PropertyStream<'a, T>where
T: Unpin,
type Item = PropertyChanged<'a, T>
fn poll_next( self: Pin<&mut PropertyStream<'a, T>>, cx: &mut Context<'_>, ) -> Poll<Option<<PropertyStream<'a, T> as Stream>::Item>>
source§impl<F> Stream for OnceFuture<F>where
F: Future,
impl<F> Stream for OnceFuture<F>where
F: Future,
source§impl<R> Stream for Lines<R>where
R: AsyncBufRead,
impl<R> Stream for Lines<R>where
R: AsyncBufRead,
source§impl<R> Stream for Split<R>where
R: AsyncBufRead,
impl<R> Stream for Split<R>where
R: AsyncBufRead,
source§impl<S> Stream for IntoOrdering<S>where
S: OrderedStream,
impl<S> Stream for IntoOrdering<S>where
S: OrderedStream,
source§impl<S> Stream for IntoStream<S>where
S: OrderedStream,
impl<S> Stream for IntoStream<S>where
S: OrderedStream,
source§impl<S> Stream for IntoTupleStream<S>where
S: OrderedStream,
impl<S> Stream for IntoTupleStream<S>where
S: OrderedStream,
source§impl<S> Stream for StreamNotifyClose<S>where
S: Stream,
impl<S> Stream for StreamNotifyClose<S>where
S: Stream,
source§impl<S> Stream for ChunksTimeout<S>where
S: Stream,
impl<S> Stream for ChunksTimeout<S>where
S: Stream,
source§impl<S> Stream for TimeoutRepeating<S>where
S: Stream,
impl<S> Stream for TimeoutRepeating<S>where
S: Stream,
source§impl<S> Stream for AssertUnwindSafe<S>where
S: Stream,
impl<S> Stream for AssertUnwindSafe<S>where
S: Stream,
source§impl<T> Stream for ReceiverStream<T>
impl<T> Stream for ReceiverStream<T>
source§impl<T> Stream for UnboundedReceiverStream<T>
impl<T> Stream for UnboundedReceiverStream<T>
source§impl<T, F> Stream for RepeatWith<F>where
F: FnMut() -> T,
impl<T, F> Stream for RepeatWith<F>where
F: FnMut() -> T,
Implementors§
source§impl<A, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::RepeatWith<F>where
F: FnMut() -> A,
impl<A, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::RepeatWith<F>where
F: FnMut() -> A,
source§impl<B, St, S, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Scan<St, S, Fut, F>
impl<B, St, S, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Scan<St, S, Fut, F>
source§impl<F> Stream for FlattenStream<F>
impl<F> Stream for FlattenStream<F>
source§impl<F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::future::IntoStream<F>
impl<F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::future::IntoStream<F>
source§impl<Fut> Stream for TryFlattenStream<Fut>
impl<Fut> Stream for TryFlattenStream<Fut>
source§impl<Fut> Stream for FuturesOrdered<Fut>where
Fut: Future,
impl<Fut> Stream for FuturesOrdered<Fut>where
Fut: Future,
source§impl<Fut> Stream for FuturesUnordered<Fut>where
Fut: Future,
impl<Fut> Stream for FuturesUnordered<Fut>where
Fut: Future,
source§impl<Fut> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Once<Fut>where
Fut: Future,
impl<Fut> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Once<Fut>where
Fut: Future,
source§impl<Fut, Si> Stream for FlattenSink<Fut, Si>where
TryFlatten<Fut, Si>: Stream,
impl<Fut, Si> Stream for FlattenSink<Fut, Si>where
TryFlatten<Fut, Si>: Stream,
source§impl<I> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Iter<I>where
I: Iterator,
impl<I> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Iter<I>where
I: Iterator,
source§impl<R> Stream for cosmic::iced_winit::graphics::futures::futures::io::Lines<R>where
R: AsyncBufRead,
impl<R> Stream for cosmic::iced_winit::graphics::futures::futures::io::Lines<R>where
R: AsyncBufRead,
source§impl<S> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Fuse<S>where
S: Stream,
impl<S> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Fuse<S>where
S: Stream,
source§impl<S> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Peekable<S>where
S: Stream,
impl<S> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Peekable<S>where
S: Stream,
source§impl<S, Item, E> Stream for SinkErrInto<S, Item, E>
impl<S, Item, E> Stream for SinkErrInto<S, Item, E>
source§impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
source§impl<St1, St2> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Chain<St1, St2>
impl<St1, St2> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Chain<St1, St2>
source§impl<St1, St2> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Zip<St1, St2>
impl<St1, St2> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Zip<St1, St2>
source§impl<St1, St2, Clos, State> Stream for SelectWithStrategy<St1, St2, Clos, State>
impl<St1, St2, Clos, State> Stream for SelectWithStrategy<St1, St2, Clos, State>
source§impl<St> Stream for BufferUnordered<St>
impl<St> Stream for BufferUnordered<St>
source§impl<St> Stream for CatchUnwind<St>where
St: Stream + UnwindSafe,
impl<St> Stream for CatchUnwind<St>where
St: Stream + UnwindSafe,
source§impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Cycle<St>
impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Cycle<St>
source§impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Enumerate<St>where
St: Stream,
impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Enumerate<St>where
St: Stream,
source§impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Flatten<St>
impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Flatten<St>
source§impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::IntoStream<St>where
St: TryStream,
impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::IntoStream<St>where
St: TryStream,
source§impl<St> Stream for ReadyChunks<St>where
St: Stream,
impl<St> Stream for ReadyChunks<St>where
St: Stream,
source§impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Skip<St>where
St: Stream,
impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Skip<St>where
St: Stream,
source§impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Take<St>where
St: Stream,
impl<St> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Take<St>where
St: Stream,
source§impl<St> Stream for TryBufferUnordered<St>
impl<St> Stream for TryBufferUnordered<St>
source§impl<St> Stream for TryBuffered<St>
impl<St> Stream for TryBuffered<St>
source§impl<St> Stream for TryFlatten<St>
impl<St> Stream for TryFlatten<St>
source§impl<St> Stream for TryFlattenUnordered<St>
impl<St> Stream for TryFlattenUnordered<St>
source§impl<St> Stream for TryReadyChunks<St>where
St: TryStream,
impl<St> Stream for TryReadyChunks<St>where
St: TryStream,
source§impl<St, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Inspect<St, F>
impl<St, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Inspect<St, F>
source§impl<St, F> Stream for InspectErr<St, F>
impl<St, F> Stream for InspectErr<St, F>
source§impl<St, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Map<St, F>
impl<St, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Map<St, F>
source§impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Filter<St, Fut, F>
impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Filter<St, Fut, F>
source§impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::SkipWhile<St, Fut, F>
impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::SkipWhile<St, Fut, F>
source§impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::TakeWhile<St, Fut, F>
impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::TakeWhile<St, Fut, F>
source§impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Then<St, Fut, F>
impl<St, Fut, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Then<St, Fut, F>
source§impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F>
impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F>
source§impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>
impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>
source§impl<St, Fut, F, T> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::FilterMap<St, Fut, F>
impl<St, Fut, F, T> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::FilterMap<St, Fut, F>
source§impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F>
impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F>
source§impl<St, U, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::FlatMap<St, U, F>
impl<St, U, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::FlatMap<St, U, F>
source§impl<St, U, F> Stream for FlatMapUnordered<St, U, F>
impl<St, U, F> Stream for FlatMapUnordered<St, U, F>
source§impl<T> Stream for cosmic::iced_winit::graphics::futures::futures::channel::mpsc::Receiver<T>
impl<T> Stream for cosmic::iced_winit::graphics::futures::futures::channel::mpsc::Receiver<T>
source§impl<T> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Pending<T>
impl<T> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Pending<T>
source§impl<T> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Repeat<T>where
T: Clone,
impl<T> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::stream::Repeat<T>where
T: Clone,
source§impl<T, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::future::PollImmediate<F>where
F: Future<Output = T>,
impl<T, F> Stream for cosmic::iced_winit::graphics::futures::futures::prelude::future::PollImmediate<F>where
F: Future<Output = T>,
A Stream implementation that can be polled repeatedly until the future is done. The stream will never return Poll::Pending so polling it in a tight loop is worse than using a blocking synchronous function.
use futures::task::Poll;
use futures::{StreamExt, future, pin_mut};
use future::FusedFuture;
let f = async { 1_u32 };
pin_mut!(f);
let mut r = future::poll_immediate(f);
assert_eq!(r.next().await, Some(Poll::Ready(1)));
let f = async {futures::pending!(); 42_u8};
pin_mut!(f);
let mut p = future::poll_immediate(f);
assert_eq!(p.next().await, Some(Poll::Pending));
assert!(!p.is_terminated());
assert_eq!(p.next().await, Some(Poll::Ready(42)));
assert!(p.is_terminated());
assert_eq!(p.next().await, None);