Trait async_std::stream::Stream

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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§

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type Item

Values yielded by the stream.

Required Methods§

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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§

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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§

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impl Stream for Timer

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type Item = Instant

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

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

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type Item = T

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

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

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type Item = T

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

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

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

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

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

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type Item = <I as Iterator>::Item

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

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

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

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type Item = Result<u8, Error>

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

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

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type Item = Result<String, Error>

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

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

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

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

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

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type Item = <S as Stream>::Item

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

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

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

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type Item = <S as Stream>::Item

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

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

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

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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

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

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

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type Item = <S as Stream>::Item

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

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <Fut as Future>::Output

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

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

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

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type Item = T

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

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

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type Item = T

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

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = B

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

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

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type Item = <S as Stream>::Item

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

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

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type Item = <U as Stream>::Item

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

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

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type Item = <U as Stream>::Item

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

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

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type Item = <T as Iterator>::Item

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

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impl<T> Stream for Empty<T>

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type Item = T

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

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

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impl<T> Stream for Once<T>

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type Item = T

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

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

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impl<T> Stream for Pending<T>

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type Item = T

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

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

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

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type Item = T

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

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

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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>>,

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type Item = Result<Item, E>

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

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

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type Item = T

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

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

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type Item = T

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

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

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

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type Item = Item

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

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

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type Item = T

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

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

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type Item = T

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

Implementors§

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impl Stream for ReadDir

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

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

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impl Stream for Interval

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type Item = ()

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

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type Item = T

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

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type Item = T

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

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

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

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type Item = T

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

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type Item = <I as Iterator>::Item

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

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type Item = T

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

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

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

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

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

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type Item = <S as Stream>::Item

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

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type Item = <S as Stream>::Item

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

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type Item = <S as Stream>::Item

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

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type Item = B

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

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type Item = <S as Stream>::Item

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

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type Item = <S as Stream>::Item

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

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type Item = <S as Stream>::Item

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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>,

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type Item = B

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

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type Item = <U as Stream>::Item

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

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type Item = <U as Stream>::Item

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

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type Item = <S as Stream>::Item

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

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type Item = <S as Stream>::Item

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

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

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type Item = <S as Stream>::Item

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impl<T> Stream for Receiver<T>

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type Item = T

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

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type Item = T

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

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type Item = T

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

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type Item = T

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

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type Item = T

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

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type Item = T

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

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

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type Item = T