Struct futures_util::stream::FuturesOrdered

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pub struct FuturesOrdered<T: Future> { /* private fields */ }
Expand description

An unbounded queue of futures.

This “combinator” is similar to FuturesUnordered, but it imposes a FIFO order on top of the set of futures. While futures in the set will race to completion in parallel, results will only be returned in the order their originating futures were added to the queue.

Futures are pushed into this queue and their realized values are yielded in order. This structure is optimized to manage a large number of futures. Futures managed by FuturesOrdered will only be polled when they generate notifications. This reduces the required amount of work needed to coordinate large numbers of futures.

When a FuturesOrdered is first created, it does not contain any futures. Calling poll_next in this state will result in Poll::Ready(None) to be returned. Futures are submitted to the queue using push_back (or push_front); however, the future will not be polled at this point. FuturesOrdered will only poll managed futures when FuturesOrdered::poll_next is called. As such, it is important to call poll_next after pushing new futures.

If FuturesOrdered::poll_next returns Poll::Ready(None) this means that the queue is currently not managing any futures. A future may be submitted to the queue at a later time. At that point, a call to FuturesOrdered::poll_next will either return the future’s resolved value or Poll::Pending if the future has not yet completed. When multiple futures are submitted to the queue, FuturesOrdered::poll_next will return Poll::Pending until the first future completes, even if some of the later futures have already completed.

Note that you can create a ready-made FuturesOrdered via the collect method, or you can start with an empty queue with the FuturesOrdered::new constructor.

This type is only available when the std or alloc feature of this library is activated, and it is activated by default.

Implementations§

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impl<Fut: Future> FuturesOrdered<Fut>

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pub fn new() -> Self

Constructs a new, empty FuturesOrdered

The returned FuturesOrdered does not contain any futures and, in this state, FuturesOrdered::poll_next will return Poll::Ready(None).

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pub fn len(&self) -> usize

Returns the number of futures contained in the queue.

This represents the total number of in-flight futures, both those currently processing and those that have completed but which are waiting for earlier futures to complete.

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pub fn is_empty(&self) -> bool

Returns true if the queue contains no futures

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pub fn push(&mut self, future: Fut)

👎Deprecated: use push_back instead

Push a future into the queue.

This function submits the given future to the internal set for managing. This function will not call poll on the submitted future. The caller must ensure that FuturesOrdered::poll_next is called in order to receive task notifications.

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pub fn push_back(&mut self, future: Fut)

Pushes a future to the back of the queue.

This function submits the given future to the internal set for managing. This function will not call poll on the submitted future. The caller must ensure that FuturesOrdered::poll_next is called in order to receive task notifications.

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pub fn push_front(&mut self, future: Fut)

Pushes a future to the front of the queue.

This function submits the given future to the internal set for managing. This function will not call poll on the submitted future. The caller must ensure that FuturesOrdered::poll_next is called in order to receive task notifications. This future will be the next future to be returned complete.

Trait Implementations§

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impl<Fut: Future> Debug for FuturesOrdered<Fut>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl<Fut: Future> Default for FuturesOrdered<Fut>

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fn default() -> Self

Returns the “default value” for a type. Read more
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impl<Fut: Future> Extend<Fut> for FuturesOrdered<Fut>

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fn extend<I>(&mut self, iter: I)
where I: IntoIterator<Item = Fut>,

Extends a collection with the contents of an iterator. Read more
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fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)
Extends a collection with exactly one element.
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fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)
Reserves capacity in a collection for the given number of additional elements. Read more
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impl<Fut: Future> FromIterator<Fut> for FuturesOrdered<Fut>

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fn from_iter<T>(iter: T) -> Self
where T: IntoIterator<Item = Fut>,

Creates a value from an iterator. Read more
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impl<Fut: Future> FusedStream for FuturesOrdered<Fut>

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fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.
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impl<Fut: Future> Stream for FuturesOrdered<Fut>

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type Item = <Fut as Future>::Output

Values yielded by the stream.
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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. Read more
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fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream. Read more
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impl<T: Future> Unpin for FuturesOrdered<T>

Auto Trait Implementations§

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impl<T> !Freeze for FuturesOrdered<T>

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impl<T> !RefUnwindSafe for FuturesOrdered<T>

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impl<T> Send for FuturesOrdered<T>
where T: Send, <T as Future>::Output: Send,

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impl<T> Sync for FuturesOrdered<T>
where T: Send + Sync, <T as Future>::Output: Sync,

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impl<T> !UnwindSafe for FuturesOrdered<T>

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> StreamExt for T
where T: Stream + ?Sized,

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fn next(&mut self) -> Next<'_, Self>
where Self: Unpin,

Creates a future that resolves to the next item in the stream. Read more
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fn into_future(self) -> StreamFuture<Self>
where Self: Sized + Unpin,

Converts this stream into a future of (next_item, tail_of_stream). If the stream terminates, then the next item is None. Read more
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fn map<T, F>(self, f: F) -> Map<Self, F>
where F: FnMut(Self::Item) -> T, Self: Sized,

Maps this stream’s items to a different type, returning a new stream of the resulting type. Read more
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fn enumerate(self) -> Enumerate<Self>
where Self: Sized,

Creates a stream which gives the current iteration count as well as the next value. Read more
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fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Filters the values produced by this stream according to the provided asynchronous predicate. Read more
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fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = Option<T>>, Self: Sized,

Filters the values produced by this stream while simultaneously mapping them to a different type according to the provided asynchronous closure. Read more
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fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future, Self: Sized,

Computes from this stream’s items new items of a different type using an asynchronous closure. Read more
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fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C>
where Self: Sized,

Transforms a stream into a collection, returning a future representing the result of that computation. Read more
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fn unzip<A, B, FromA, FromB>(self) -> Unzip<Self, FromA, FromB>
where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Stream<Item = (A, B)>,

Converts a stream of pairs into a future, which resolves to pair of containers. Read more
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fn concat(self) -> Concat<Self>
where Self: Sized, Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default,

Concatenate all items of a stream into a single extendable destination, returning a future representing the end result. Read more
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fn count(self) -> Count<Self>
where Self: Sized,

Drives the stream to completion, counting the number of items. Read more
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fn cycle(self) -> Cycle<Self>
where Self: Sized + Clone,

Repeats a stream endlessly. Read more
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fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F>
where F: FnMut(T, Self::Item) -> Fut, Fut: Future<Output = T>, Self: Sized,

Execute an accumulating asynchronous computation over a stream, collecting all the values into one final result. Read more
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fn any<Fut, F>(self, f: F) -> Any<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Execute predicate over asynchronous stream, and return true if any element in stream satisfied a predicate. Read more
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fn all<Fut, F>(self, f: F) -> All<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Execute predicate over asynchronous stream, and return true if all element in stream satisfied a predicate. Read more
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fn flatten(self) -> Flatten<Self>
where Self::Item: Stream, Self: Sized,

Flattens a stream of streams into just one continuous stream. Read more
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fn flatten_unordered( self, limit: impl Into<Option<usize>>, ) -> FlattenUnordered<Self>
where Self::Item: Stream + Unpin, Self: Sized,

Flattens a stream of streams into just one continuous stream. Polls inner streams produced by the base stream concurrently. Read more
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fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
where F: FnMut(Self::Item) -> U, U: Stream, Self: Sized,

Maps a stream like StreamExt::map but flattens nested Streams. Read more
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fn flat_map_unordered<U, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> FlatMapUnordered<Self, U, F>
where U: Stream + Unpin, F: FnMut(Self::Item) -> U, Self: Sized,

Maps a stream like StreamExt::map but flattens nested Streams and polls them concurrently, yielding items in any order, as they made available. Read more
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fn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F>
where F: FnMut(&mut S, Self::Item) -> Fut, Fut: Future<Output = Option<B>>, Self: Sized,

Combinator similar to StreamExt::fold that holds internal state and produces a new stream. Read more
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fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Skip elements on this stream while the provided asynchronous predicate resolves to true. Read more
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fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Take elements from this stream while the provided asynchronous predicate resolves to true. Read more
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fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut>
where Fut: Future, Self: Sized,

Take elements from this stream until the provided future resolves. Read more
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fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = ()>, Self: Sized,

Runs this stream to completion, executing the provided asynchronous closure for each element on the stream. Read more
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fn for_each_concurrent<Fut, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> ForEachConcurrent<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = ()>, Self: Sized,

Runs this stream to completion, executing the provided asynchronous closure for each element on the stream concurrently as elements become available. Read more
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fn take(self, n: usize) -> Take<Self>
where Self: Sized,

Creates a new stream of at most n items of the underlying stream. Read more
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fn skip(self, n: usize) -> Skip<Self>
where Self: Sized,

Creates a new stream which skips n items of the underlying stream. Read more
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fn fuse(self) -> Fuse<Self>
where Self: Sized,

Fuse a stream such that poll_next will never again be called once it has finished. This method can be used to turn any Stream into a FusedStream. Read more
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fn by_ref(&mut self) -> &mut Self

Borrows a stream, rather than consuming it. Read more
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fn catch_unwind(self) -> CatchUnwind<Self>
where Self: Sized + UnwindSafe,

Catches unwinding panics while polling the stream. Read more
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fn boxed<'a>(self) -> BoxStream<'a, Self::Item>
where Self: Sized + Send + 'a,

Wrap the stream in a Box, pinning it. Read more
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fn boxed_local<'a>(self) -> LocalBoxStream<'a, Self::Item>
where Self: Sized + 'a,

Wrap the stream in a Box, pinning it. Read more
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fn buffered(self, n: usize) -> Buffered<Self>
where Self::Item: Future, Self: Sized,

An adaptor for creating a buffered list of pending futures. Read more
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fn buffer_unordered(self, n: usize) -> BufferUnordered<Self>
where Self::Item: Future, Self: Sized,

An adaptor for creating a buffered list of pending futures (unordered). Read more
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fn zip<St>(self, other: St) -> Zip<Self, St>
where St: Stream, Self: Sized,

An adapter for zipping two streams together. Read more
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fn chain<St>(self, other: St) -> Chain<Self, St>
where St: Stream<Item = Self::Item>, Self: Sized,

Adapter for chaining two streams. Read more
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fn peekable(self) -> Peekable<Self>
where Self: Sized,

Creates a new stream which exposes a peek method. Read more
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fn chunks(self, capacity: usize) -> Chunks<Self>
where Self: Sized,

An adaptor for chunking up items of the stream inside a vector. Read more
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fn ready_chunks(self, capacity: usize) -> ReadyChunks<Self>
where Self: Sized,

An adaptor for chunking up ready items of the stream inside a vector. Read more
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fn forward<S>(self, sink: S) -> Forward<Self, S>
where S: Sink<Self::Ok, Error = Self::Error>, Self: TryStream + Sized,

A future that completes after the given stream has been fully processed into the sink and the sink has been flushed and closed. Read more
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fn split<Item>(self) -> (SplitSink<Self, Item>, SplitStream<Self>)
where Self: Sink<Item> + Sized,

Splits this Stream + Sink object into separate Sink and Stream objects. Read more
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fn inspect<F>(self, f: F) -> Inspect<Self, F>
where F: FnMut(&Self::Item), Self: Sized,

Do something with each item of this stream, afterwards passing it on. Read more
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fn left_stream<B>(self) -> Either<Self, B>
where B: Stream<Item = Self::Item>, Self: Sized,

Wrap this stream in an Either stream, making it the left-hand variant of that Either. Read more
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fn right_stream<B>(self) -> Either<B, Self>
where B: Stream<Item = Self::Item>, Self: Sized,

Wrap this stream in an Either stream, making it the right-hand variant of that Either. Read more
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fn poll_next_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>
where Self: Unpin,

A convenience method for calling Stream::poll_next on Unpin stream types.
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fn select_next_some(&mut self) -> SelectNextSome<'_, Self>
where Self: Unpin + FusedStream,

Returns a Future that resolves when the next item in this stream is ready. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<S, T, E> TryStream for S
where S: Stream<Item = Result<T, E>> + ?Sized,

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type Ok = T

The type of successful values yielded by this future
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type Error = E

The type of failures yielded by this future
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fn try_poll_next( self: Pin<&mut S>, cx: &mut Context<'_>, ) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>

Poll this TryStream as if it were a Stream. Read more
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impl<S> TryStreamExt for S
where S: TryStream + ?Sized,

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fn err_into<E>(self) -> ErrInto<Self, E>
where Self: Sized, Self::Error: Into<E>,

Wraps the current stream in a new stream which converts the error type into the one provided. Read more
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fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
where Self: Sized, F: FnMut(Self::Ok) -> T,

Wraps the current stream in a new stream which maps the success value using the provided closure. Read more
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fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
where Self: Sized, F: FnMut(Self::Error) -> E,

Wraps the current stream in a new stream which maps the error value using the provided closure. Read more
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fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
where F: FnMut(Self::Ok) -> Fut, Fut: TryFuture<Error = Self::Error>, Self: Sized,

Chain on a computation for when a value is ready, passing the successful results to the provided closure f. Read more
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fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
where F: FnMut(Self::Error) -> Fut, Fut: TryFuture<Ok = Self::Ok>, Self: Sized,

Chain on a computation for when an error happens, passing the erroneous result to the provided closure f. Read more
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fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
where F: FnMut(&Self::Ok), Self: Sized,

Do something with the success value of this stream, afterwards passing it on. Read more
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fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
where F: FnMut(&Self::Error), Self: Sized,

Do something with the error value of this stream, afterwards passing it on. Read more
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fn into_stream(self) -> IntoStream<Self>
where Self: Sized,

Wraps a TryStream into a type that implements Stream Read more
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fn try_next(&mut self) -> TryNext<'_, Self>
where Self: Unpin,

Creates a future that attempts to resolve the next item in the stream. If an error is encountered before the next item, the error is returned instead. Read more
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fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F>
where F: FnMut(Self::Ok) -> Fut, Fut: TryFuture<Ok = (), Error = Self::Error>, Self: Sized,

Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream. Read more
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fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F>
where F: FnMut(&Self::Ok) -> Fut, Fut: TryFuture<Ok = bool, Error = Self::Error>, Self: Sized,

Skip elements on this stream while the provided asynchronous predicate resolves to true. Read more
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fn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F>
where F: FnMut(&Self::Ok) -> Fut, Fut: TryFuture<Ok = bool, Error = Self::Error>, Self: Sized,

Take elements on this stream while the provided asynchronous predicate resolves to true. Read more
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fn try_for_each_concurrent<Fut, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> TryForEachConcurrent<Self, Fut, F>
where F: FnMut(Self::Ok) -> Fut, Fut: Future<Output = Result<(), Self::Error>>, Self: Sized,

Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream concurrently as elements become available, exiting as soon as an error occurs. Read more
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fn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C>
where Self: Sized,

Attempt to transform a stream into a collection, returning a future representing the result of that computation. Read more
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fn try_chunks(self, capacity: usize) -> TryChunks<Self>
where Self: Sized,

An adaptor for chunking up successful items of the stream inside a vector. Read more
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fn try_ready_chunks(self, capacity: usize) -> TryReadyChunks<Self>
where Self: Sized,

An adaptor for chunking up successful, ready items of the stream inside a vector. Read more
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fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
where Fut: Future<Output = bool>, F: FnMut(&Self::Ok) -> Fut, Self: Sized,

Attempt to filter the values produced by this stream according to the provided asynchronous closure. Read more
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fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F>
where Fut: TryFuture<Ok = Option<T>, Error = Self::Error>, F: FnMut(Self::Ok) -> Fut, Self: Sized,

Attempt to filter the values produced by this stream while simultaneously mapping them to a different type according to the provided asynchronous closure. Read more
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fn try_flatten_unordered( self, limit: impl Into<Option<usize>>, ) -> TryFlattenUnordered<Self>
where Self::Ok: TryStream + Unpin, <Self::Ok as TryStream>::Error: From<Self::Error>, Self: Sized,

Flattens a stream of streams into just one continuous stream. Produced streams will be polled concurrently and any errors will be passed through without looking at them. If the underlying base stream returns an error, it will be immediately propagated. Read more
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fn try_flatten(self) -> TryFlatten<Self>
where Self::Ok: TryStream, <Self::Ok as TryStream>::Error: From<Self::Error>, Self: Sized,

Flattens a stream of streams into just one continuous stream. Read more
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fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F>
where F: FnMut(T, Self::Ok) -> Fut, Fut: TryFuture<Ok = T, Error = Self::Error>, Self: Sized,

Attempt to execute an accumulating asynchronous computation over a stream, collecting all the values into one final result. Read more
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fn try_concat(self) -> TryConcat<Self>
where Self: Sized, Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default,

Attempt to concatenate all items of a stream into a single extendable destination, returning a future representing the end result. Read more
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fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self>
where Self::Ok: TryFuture<Error = Self::Error>, Self: Sized,

Attempt to execute several futures from a stream concurrently (unordered). Read more
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fn try_buffered(self, n: usize) -> TryBuffered<Self>
where Self::Ok: TryFuture<Error = Self::Error>, Self: Sized,

Attempt to execute several futures from a stream concurrently. Read more
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fn try_poll_next_unpin( &mut self, cx: &mut Context<'_>, ) -> Poll<Option<Result<Self::Ok, Self::Error>>>
where Self: Unpin,

A convenience method for calling TryStream::try_poll_next on Unpin stream types.
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fn into_async_read(self) -> IntoAsyncRead<Self>
where Self: Sized + TryStreamExt<Error = Error>, Self::Ok: AsRef<[u8]>,

Adapter that converts this stream into an AsyncBufRead. Read more
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fn try_all<Fut, F>(self, f: F) -> TryAll<Self, Fut, F>
where Self: Sized, F: FnMut(Self::Ok) -> Fut, Fut: Future<Output = bool>,

Attempt to execute a predicate over an asynchronous stream and evaluate if all items satisfy the predicate. Exits early if an Err is encountered or if an Ok item is found that does not satisfy the predicate. Read more
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fn try_any<Fut, F>(self, f: F) -> TryAny<Self, Fut, F>
where Self: Sized, F: FnMut(Self::Ok) -> Fut, Fut: Future<Output = bool>,

Attempt to execute a predicate over an asynchronous stream and evaluate if any items satisfy the predicate. Exits early if an Err is encountered or if an Ok item is found that satisfies the predicate. Read more