# Struct futures::stream::FuturesOrdered [−] [src]

    #[must_use = "streams do nothing unless polled"]
    pub struct FuturesOrdered<T> where
        T: Future,  { /* fields omitted */ }

An unbounded queue of futures.

This "combinator" is similar to `FuturesUnordered`, but it imposes an 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` in this state will result in `Ok(Async::Ready(None))` to be returned. Futures are submitted to the queue using `push`; however, the future will not be polled at this point. `FuturesOrdered` will only poll managed futures when `FuturesOrdered::poll` is called. As such, it is important to call `poll` after pushing new futures.

If `FuturesOrdered::poll` returns `Ok(Async::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` will either return the future's resolved value or `Ok(Async::NotReady)` if the future has not yet completed. When multiple futures are submitted to the queue, `FuturesOrdered::poll` will return `Ok(Async::NotReady)` 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 `futures_ordered` function in the `stream` module, or you can start with an empty queue with the `FuturesOrdered::new` constructor.

## Methods

### `impl<T> FuturesOrdered<T> where
T: Future,`
[src]

#### `pub fn new() -> FuturesOrdered<T>`
[src]

Constructs a new, empty `FuturesOrdered`

The returned `FuturesOrdered` does not contain any futures and, in this state, `FuturesOrdered::poll` will return `Ok(Async::Ready(None))`.

#### `pub fn len(&self) -> usize`
[src]

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.

#### `pub fn is_empty(&self) -> bool`
[src]

Returns `true` if the queue contains no futures

#### `pub fn push(&mut self, future: T)`
[src]

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` is called in order to receive task notifications.

## Trait Implementations

### `impl<T> Stream for FuturesOrdered<T> where
T: Future,`
[src]

#### `type Item = T::Item`

The type of item this stream will yield on success.

#### `type Error = T::Error`

The type of error this stream may generate.

#### `fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error>`
[src]

Attempt to pull out the next value of this stream, returning `None` if the stream is finished. Read more

####
ⓘImportant traits for Wait<S>

### Important traits for Wait<S>

`impl<S: Stream> Iterator for Wait<S> type Item = Result<S::Item, S::Error>;`
`fn wait(self) -> Wait<Self> where
Self: Sized,`
[src]

Creates an iterator which blocks the current thread until each item of this stream is resolved. Read more

#### `fn into_future(self) -> StreamFuture<Self> where
Self: Sized,`
[src]

Converts this stream into a `Future`. Read more

#### `fn map<U, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> U,
Self: Sized,`
[src]

Converts a stream of type `T` to a stream of type `U`. Read more

#### `fn map_err<U, F>(self, f: F) -> MapErr<Self, F> where
F: FnMut(Self::Error) -> U,
Self: Sized,`
[src]

Converts a stream of error type `T` to a stream of error type `U`. Read more

#### `fn filter<F>(self, f: F) -> Filter<Self, F> where
F: FnMut(&Self::Item) -> bool,
Self: Sized,`
[src]

Filters the values produced by this stream according to the provided predicate. Read more

#### `fn filter_map<F, B>(self, f: F) -> FilterMap<Self, F> where
F: FnMut(Self::Item) -> Option<B>,
Self: Sized,`
[src]

Filters the values produced by this stream while simultaneously mapping them to a different type. Read more

#### `fn then<F, U>(self, f: F) -> Then<Self, F, U> where
F: FnMut(Result<Self::Item, Self::Error>) -> U,
U: IntoFuture,
Self: Sized,`
[src]

Chain on a computation for when a value is ready, passing the resulting item to the provided closure `f`. Read more

#### `fn and_then<F, U>(self, f: F) -> AndThen<Self, F, U> where
F: FnMut(Self::Item) -> U,
U: IntoFuture<Error = Self::Error>,
Self: Sized,`
[src]

Chain on a computation for when a value is ready, passing the successful results to the provided closure `f`. Read more

#### `fn or_else<F, U>(self, f: F) -> OrElse<Self, F, U> where
F: FnMut(Self::Error) -> U,
U: IntoFuture<Item = Self::Item>,
Self: Sized,`
[src]

Chain on a computation for when an error happens, passing the erroneous result to the provided closure `f`. Read more

#### `fn collect(self) -> Collect<Self> where
Self: Sized,`
[src]

Collect all of the values of this stream into a vector, returning a future representing the result of that computation. Read more

#### `fn concat2(self) -> Concat2<Self> where
Self: Sized,
Self::Item: Extend<<Self::Item as IntoIterator>::Item> + IntoIterator + Default,`
[src]

Concatenate all results of a stream into a single extendable destination, returning a future representing the end result. Read more

#### `fn concat(self) -> Concat<Self> where
Self: Sized,
Self::Item: Extend<<Self::Item as IntoIterator>::Item> + IntoIterator,`
[src]

Deprecated since 0.1.14

: please use `Stream::concat2` instead

Concatenate all results of a stream into a single extendable destination, returning a future representing the end result. Read more

#### `fn fold<F, T, Fut>(self, init: T, f: F) -> Fold<Self, F, Fut, T> where
F: FnMut(T, Self::Item) -> Fut,
Fut: IntoFuture<Item = T>,
Self::Error: From<Fut::Error>,
Self: Sized,`
[src]

Execute an accumulating computation over a stream, collecting all the values into one final result. Read more

#### `fn flatten(self) -> Flatten<Self> where
Self::Item: Stream,
<Self::Item as Stream>::Error: From<Self::Error>,
Self: Sized,`
[src]

Flattens a stream of streams into just one continuous stream. Read more

#### `fn skip_while<P, R>(self, pred: P) -> SkipWhile<Self, P, R> where
P: FnMut(&Self::Item) -> R,
R: IntoFuture<Item = bool, Error = Self::Error>,
Self: Sized,`
[src]

Skip elements on this stream while the predicate provided resolves to `true`. Read more

#### `fn take_while<P, R>(self, pred: P) -> TakeWhile<Self, P, R> where
P: FnMut(&Self::Item) -> R,
R: IntoFuture<Item = bool, Error = Self::Error>,
Self: Sized,`
[src]

Take elements from this stream while the predicate provided resolves to `true`. Read more

#### `fn for_each<F, U>(self, f: F) -> ForEach<Self, F, U> where
F: FnMut(Self::Item) -> U,
U: IntoFuture<Item = (), Error = Self::Error>,
Self: Sized,`
[src]

Runs this stream to completion, executing the provided closure for each element on the stream. Read more

#### `fn from_err<E: From<Self::Error>>(self) -> FromErr<Self, E> where
Self: Sized,`
[src]

Map this stream's error to any error implementing `From` for this stream's `Error`, returning a new stream. Read more

#### `fn take(self, amt: u64) -> Take<Self> where
Self: Sized,`
[src]

Creates a new stream of at most `amt` items of the underlying stream. Read more

#### `fn skip(self, amt: u64) -> Skip<Self> where
Self: Sized,`
[src]

Creates a new stream which skips `amt` items of the underlying stream. Read more

#### `fn fuse(self) -> Fuse<Self> where
Self: Sized,`
[src]

Fuse a stream such that `poll` will never again be called once it has finished. Read more

#### `fn by_ref(&mut self) -> &mut Self where
Self: Sized,`
[src]

Borrows a stream, rather than consuming it. Read more

#### `fn catch_unwind(self) -> CatchUnwind<Self> where
Self: Sized + UnwindSafe,`
[src]

Catches unwinding panics while polling the stream. Read more

#### `fn buffered(self, amt: usize) -> Buffered<Self> where
Self::Item: IntoFuture<Error = Self::Error>,
Self: Sized,`
[src]

An adaptor for creating a buffered list of pending futures. Read more

#### `fn buffer_unordered(self, amt: usize) -> BufferUnordered<Self> where
Self::Item: IntoFuture<Error = Self::Error>,
Self: Sized,`
[src]

An adaptor for creating a buffered list of pending futures (unordered). Read more

#### `fn merge<S>(self, other: S) -> Merge<Self, S> where
S: Stream<Error = Self::Error>,
Self: Sized,`
[src]

Deprecated

: functionality provided by `select` now

An adapter for merging the output of two streams. Read more

#### `fn zip<S>(self, other: S) -> Zip<Self, S> where
S: Stream<Error = Self::Error>,
Self: Sized,`
[src]

An adapter for zipping two streams together. Read more

#### `fn chain<S>(self, other: S) -> Chain<Self, S> where
S: Stream<Item = Self::Item, Error = Self::Error>,
Self: Sized,`
[src]

Adapter for chaining two stream. Read more

#### `fn peekable(self) -> Peekable<Self> where
Self: Sized,`
[src]

Creates a new stream which exposes a `peek` method. Read more

#### `fn chunks(self, capacity: usize) -> Chunks<Self> where
Self: Sized,`
[src]

An adaptor for chunking up items of the stream inside a vector. Read more

#### `fn select<S>(self, other: S) -> Select<Self, S> where
S: Stream<Item = Self::Item, Error = Self::Error>,
Self: Sized,`
[src]

Creates a stream that selects the next element from either this stream or the provided one, whichever is ready first. Read more

#### `fn forward<S>(self, sink: S) -> Forward<Self, S> where
S: Sink<SinkItem = Self::Item>,
Self::Error: From<S::SinkError>,
Self: Sized,`
[src]

A future that completes after the given stream has been fully processed into the sink, including flushing. Read more

#### `fn split(self) -> (SplitSink<Self>, SplitStream<Self>) where
Self: Sink + Sized,`
[src]

Splits this `Stream + Sink` object into separate `Stream` and `Sink` objects. Read more

#### `fn inspect<F>(self, f: F) -> Inspect<Self, F> where
F: FnMut(&Self::Item),
Self: Sized,`
[src]

Do something with each item of this stream, afterwards passing it on. Read more

#### `fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where
F: FnMut(&Self::Error),
Self: Sized,`
[src]

Do something with the error of this stream, afterwards passing it on. Read more

### `impl<T: Debug> Debug for FuturesOrdered<T> where
T: Future,`
[src]

#### `fn fmt(&self, fmt: &mut Formatter) -> Result`
[src]

Formats the value using the given formatter. Read more

### `impl<F: Future> FromIterator<F> for FuturesOrdered<F>`
[src]

#### `fn from_iter<T>(iter: T) -> Self where
T: IntoIterator<Item = F>,`
[src]

Creates a value from an iterator. Read more

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