[−][src]Trait futures::prelude::StreamExt

pub trait StreamExt: Stream {
    fn next(&mut self) -> Next<Self>
    where
        Self: Unpin,
    { ... }

    fn into_future(self) -> StreamFuture<Self>
    where
        Self: Unpin,
    { ... }

    fn map<T, F>(self, f: F) -> Map<Self, F>
    where
        F: FnMut(Self::Item) -> T,
    { ... }

    fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
    where
        F: FnMut(&Self::Item) -> Fut,
        Fut: Future<Output = bool>,
    { ... }

    fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F>
    where
        F: FnMut(Self::Item) -> Fut,
        Fut: Future<Output = Option<T>>,
    { ... }

    fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
    where
        F: FnMut(Self::Item) -> Fut,
        Fut: Future,
    { ... }

    fn collect<C>(self) -> Collect<Self, C>
    where
        C: Default + Extend<Self::Item>,
    { ... }

    fn concat(self) -> Concat<Self>
    where
        Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
        Self::Item: IntoIterator,
        Self::Item: Default,
    { ... }

    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>,
    { ... }

    fn flatten(self) -> Flatten<Self>
    where
        Self::Item: Stream,
    { ... }

    fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
    where
        F: FnMut(&Self::Item) -> Fut,
        Fut: Future<Output = bool>,
    { ... }

    fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
    where
        F: FnMut(&Self::Item) -> Fut,
        Fut: Future<Output = bool>,
    { ... }

    fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F>
    where
        F: FnMut(Self::Item) -> Fut,
        Fut: Future<Output = ()>,
    { ... }

    fn for_each_concurrent<Fut, F, impl Into>>(
        self, 
        limit: impl Into>, 
        f: F
    ) -> ForEachConcurrent<Self, Fut, F>
    where
        F: FnMut(Self::Item) -> Fut,
        Fut: Future<Output = ()>,
        impl Into>: Into<Option<usize>>,
    { ... }

    fn take(self, n: u64) -> Take<Self> { ... }

    fn skip(self, n: u64) -> Skip<Self> { ... }

    fn fuse(self) -> Fuse<Self> { ... }

    fn by_ref(&mut self) -> &mut Self { ... }

    fn catch_unwind(self) -> CatchUnwind<Self>
    where
        Self: UnwindSafe,
    { ... }

    fn boxed(self) -> PinBox<Self> { ... }

    fn buffered(self, n: usize) -> Buffered<Self>
    where
        Self::Item: Future,
    { ... }

    fn buffer_unordered(self, n: usize) -> BufferUnordered<Self>
    where
        Self::Item: Future,
    { ... }

    fn zip<St>(self, other: St) -> Zip<Self, St>
    where
        St: Stream,
    { ... }

    fn chain<St>(self, other: St) -> Chain<Self, St>
    where
        St: Stream<Item = Self::Item>,
    { ... }

    fn peekable(self) -> Peekable<Self> { ... }

    fn chunks(self, capacity: usize) -> Chunks<Self> { ... }

    fn select<St>(self, other: St) -> Select<Self, St>
    where
        St: Stream<Item = Self::Item>,
    { ... }

    fn forward<S>(self, sink: S) -> Forward<Self, S>
    where
        S: Sink + Unpin,
        Self: Stream<Item = Result<<S as Sink>::SinkItem, <S as Sink>::SinkError>>,
    { ... }

    fn split(self) -> (SplitSink<Self>, SplitStream<Self>)
    where
        Self: Sink,
    { ... }

    fn inspect<F>(self, f: F) -> Inspect<Self, F>
    where
        F: FnMut(&Self::Item),
    { ... }

    fn left_stream<B>(self) -> Either<Self, B>
    where
        B: Stream<Item = Self::Item>,
    { ... }

    fn right_stream<B>(self) -> Either<B, Self>
    where
        B: Stream<Item = Self::Item>,
    { ... }

    fn poll_next_unpin(&mut self, cx: &mut Context) -> Poll<Option<Self::Item>>
    where
        Self: Unpin,
    { ... }
}

An extension trait for Streams that provides a variety of convenient combinator functions.

Provided Methods

Creates a future that resolves to the next item in the stream.

Note that because next doesn't take ownership over the stream, the Stream type must be [Unpin]. If you want to use next with a !Unpin stream, you'll first have to pin the stream. This can be done by wrapping the stream in a PinBox or pinning it to the stack using the pin_mut! macro.

Examples

#![feature(pin)]
use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let mut stream = stream::iter(1..=3);

assert_eq!(block_on(stream.next()), Some(1));
assert_eq!(block_on(stream.next()), Some(2));
assert_eq!(block_on(stream.next()), Some(3));
assert_eq!(block_on(stream.next()), None);

Converts this stream into a future of (next_item, tail_of_stream). If the stream terminates, then the next item is None.

The returned future can be used to compose streams and futures together by placing everything into the "world of futures".

Note that because into_future moves the stream, the Stream type must be [Unpin]. If you want to use into_future with a !Unpin stream, you'll first have to pin the stream. This can be done by wrapping the stream in a PinBox or pinning it to the stack using the pin_mut! macro.

Examples

#![feature(pin)]
use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=3);

let (item, stream) = block_on(stream.into_future());
assert_eq!(Some(1), item);

let (item, stream) = block_on(stream.into_future());
assert_eq!(Some(2), item);

Maps this stream's items to a different type, returning a new stream of the resulting type.

The provided closure is executed over all elements of this stream as they are made available. It is executed inline with calls to poll_next.

Note that this function consumes the stream passed into it and returns a wrapped version of it, similar to the existing map methods in the standard library.

Examples

use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=3);
let stream = stream.map(|x| x + 3);

assert_eq!(vec![4, 5, 6], block_on(stream.collect::<Vec<_>>()));

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

As values of this stream are made available, the provided predicate f will be run against them. If the predicate returns a Future which resolves to true, then the stream will yield the value, but if the predicate returns a Future which resolves to false, then the value will be discarded and the next value will be produced.

Note that this function consumes the stream passed into it and returns a wrapped version of it, similar to the existing filter methods in the standard library.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=10);
let evens = stream.filter(|x| future::ready(x % 2 == 0));

assert_eq!(vec![2, 4, 6, 8, 10], block_on(evens.collect::<Vec<_>>()));

Filters the values produced by this stream while simultaneously mapping them to a different type according to the provided asynchronous closure.

As values of this stream are made available, the provided function will be run on them. If the future returned by the predicate f resolves to Some(item) then the stream will yield the value item, but if it resolves to None then the next value will be produced.

Note that this function consumes the stream passed into it and returns a wrapped version of it, similar to the existing filter_map methods in the standard library.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=10);
let evens = stream.filter_map(|x| {
    let ret = if x % 2 == 0 { Some(x + 1) } else { None };
    future::ready(ret)
});

assert_eq!(vec![3, 5, 7, 9, 11], block_on(evens.collect::<Vec<_>>()));

Computes from this stream's items new items of a different type using an asynchronous closure.

The provided closure f will be called with an Item once a value is ready, it returns a future which will then be run to completion to produce the next value on this stream.

Note that this function consumes the stream passed into it and returns a wrapped version of it.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=3);
let stream = stream.then(|x| future::ready(x + 3));

assert_eq!(vec![4, 5, 6], block_on(stream.collect::<Vec<_>>()));

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

The returned future will be resolved when the stream terminates.

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

Examples

use futures::channel::mpsc;
use futures::executor::block_on;
use futures::stream::StreamExt;
use std::thread;

let (mut tx, rx) = mpsc::unbounded();

thread::spawn(move || {
    for i in (1..=5) {
        tx.unbounded_send(i).unwrap();
    }
});

let output = block_on(rx.collect::<Vec<i32>>());
assert_eq!(output, vec![1, 2, 3, 4, 5]);

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

This combinator will extend the first item with the contents of all the subsequent results of the stream. If the stream is empty, the default value will be returned.

Works with all collections that implement the Extend trait.

Examples

use futures::channel::mpsc;
use futures::executor::block_on;
use futures::stream::StreamExt;
use std::thread;

let (mut tx, rx) = mpsc::unbounded();

thread::spawn(move || {
    for i in (0..3).rev() {
        let n = i * 3;
        tx.unbounded_send(vec![n + 1, n + 2, n + 3]).unwrap();
    }
});

let result = block_on(rx.concat());

assert_eq!(result, vec![7, 8, 9, 4, 5, 6, 1, 2, 3]);

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

This combinator will accumulate all values returned by this stream according to the closure provided. The initial state is also provided to this method and then is returned again by each execution of the closure. Once the entire stream has been exhausted the returned future will resolve to this value.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let number_stream = stream::iter(0..6);
let sum = number_stream.fold(0, |acc, x| future::ready(acc + x));
assert_eq!(block_on(sum), 15);

Flattens a stream of streams into just one continuous stream.

Examples

use futures::channel::mpsc;
use futures::executor::block_on;
use futures::stream::StreamExt;
use std::thread;

let (tx1, rx1) = mpsc::unbounded();
let (tx2, rx2) = mpsc::unbounded();
let (tx3, rx3) = mpsc::unbounded();

thread::spawn(move || {
    tx1.unbounded_send(1).unwrap();
    tx1.unbounded_send(2).unwrap();
});
thread::spawn(move || {
    tx2.unbounded_send(3).unwrap();
    tx2.unbounded_send(4).unwrap();
});
thread::spawn(move || {
    tx3.unbounded_send(rx1).unwrap();
    tx3.unbounded_send(rx2).unwrap();
});

let output = block_on(rx3.flatten().collect::<Vec<i32>>());
assert_eq!(output, vec![1, 2, 3, 4]);

Skip elements on this stream while the provided asynchronous predicate resolves to true.

This function, like Iterator::skip_while, will skip elements on the stream until the predicate f resolves to false. Once one element returns false all future elements will be returned from the underlying stream.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=10);

let stream = stream.skip_while(|x| future::ready(*x <= 5));

assert_eq!(vec![6, 7, 8, 9, 10], block_on(stream.collect::<Vec<_>>()));

Take elements from this stream while the provided asynchronous predicate resolves to true.

This function, like Iterator::take_while, will take elements from the stream until the predicate f resolves to false. Once one element returns false it will always return that the stream is done.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=10);

let stream = stream.take_while(|x| future::ready(*x <= 5));

assert_eq!(vec![1, 2, 3, 4, 5], block_on(stream.collect::<Vec<_>>()));

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

The closure provided will be called for each item this stream produces, yielding a future. That future will then be executed to completion before moving on to the next item.

The returned value is a Future where the Output type is (); it is executed entirely for its side effects.

To process each item in the stream and produce another stream instead of a single future, use then instead.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let mut x = 0;

{
    let fut = stream::repeat(1).take(3).for_each(|item| {
        x += item;
        future::ready(())
    });
    block_on(fut);
}

assert_eq!(x, 3);

Runs this stream to completion, executing the provided asynchronous closure for each element on the stream concurrently as elements become available.

This is similar to StreamExt::for_each, but the futures produced by the closure are run concurrently (but not in parallel-- this combinator does not introduce any threads).

The closure provided will be called for each item this stream produces, yielding a future. That future will then be executed to completion concurrently with the other futures produced by the closure.

The first argument is an optional limit on the number of concurrent futures. If this limit is not None, no more than limit futures will be run concurrently. The limit argument is of type Into<Option<usize>>, and so can be provided as either None, Some(10), or just 10. Note: a limit of zero is interpreted as no limit at all, and will have the same result as passing in None.

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

Examples

#![feature(async_await, await_macro)]
use futures::channel::oneshot;
use futures::stream::{self, StreamExt};

let (tx1, rx1) = oneshot::channel();
let (tx2, rx2) = oneshot::channel();
let (tx3, rx3) = oneshot::channel();

let fut = stream::iter(vec![rx1, rx2, rx3]).for_each_concurrent(
    /* limit */ 2,
    async move |rx| {
        await!(rx).unwrap();
    }
);
tx1.send(()).unwrap();
tx2.send(()).unwrap();
tx3.send(()).unwrap();
await!(fut);

Creates a new stream of at most n items of the underlying stream.

Once n items have been yielded from this stream then it will always return that the stream is done.

Examples

use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=10).take(3);

assert_eq!(vec![1, 2, 3], block_on(stream.collect::<Vec<_>>()));

Creates a new stream which skips n items of the underlying stream.

Once n items have been skipped from this stream then it will always return the remaining items on this stream.

Examples

use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let stream = stream::iter(1..=10).skip(5);

assert_eq!(vec![6, 7, 8, 9, 10], block_on(stream.collect::<Vec<_>>()));

Fuse a stream such that poll_next will never again be called once it has finished.

Normally, once a stream has returned None from poll_next any further calls could exhibit bad behavior such as block forever, panic, never return, etc. If it is known that poll_next may be called after stream has already finished, then this method can be used to ensure that it has defined semantics.

The poll_next method of a fused stream is guaranteed to return None after the underlying stream has finished.

Examples

#![feature(futures_api)]
use futures::executor::block_on_stream;
use futures::stream::{self, StreamExt};
use futures::task::Poll;

let mut x = 0;
let stream = stream::poll_fn(|_| {
    x += 1;
    match x {
        0..=2 => Poll::Ready(Some(x)),
        3 => Poll::Ready(None),
        _ => panic!("should not happen")
    }
}).fuse();

let mut iter = block_on_stream(stream);
assert_eq!(Some(1), iter.next());
assert_eq!(Some(2), iter.next());
assert_eq!(None, iter.next());
assert_eq!(None, iter.next());
// ...
ⓘImportant traits for &'a mut I

Borrows a stream, rather than consuming it.

This is useful to allow applying stream adaptors while still retaining ownership of the original stream.

Examples

use futures::executor::block_on;
use futures::future;
use futures::stream::{self, StreamExt};

let mut stream = stream::iter(1..5);

let sum = block_on(stream.by_ref()
                         .take(2)
                         .fold(0, |a, b| future::ready(a + b)));
assert_eq!(sum, 3);

// You can use the stream again
let sum = block_on(stream.take(2).fold(0, |a, b| future::ready(a + b)));
assert_eq!(sum, 7);

Catches unwinding panics while polling the stream.

Caught panic (if any) will be the last element of the resulting stream.

In general, panics within a stream can propagate all the way out to the task level. This combinator makes it possible to halt unwinding within the stream itself. It's most commonly used within task executors. This method should not be used for error handling.

Note that this method requires the UnwindSafe bound from the standard library. This isn't always applied automatically, and the standard library provides an AssertUnwindSafe wrapper type to apply it after-the fact. To assist using this method, the Stream trait is also implemented for AssertUnwindSafe<St> where St implements Stream.

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

Examples

use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let stream = stream::iter(vec![Some(10), None, Some(11)]);
// Panic on second element
let stream_panicking = stream.map(|o| o.unwrap());
// Collect all the results
let stream = stream_panicking.catch_unwind();

let results: Vec<Result<i32, _>> = block_on(stream.collect());
match results[0] {
    Ok(10) => {}
    _ => panic!("unexpected result!"),
}
assert!(results[1].is_err());
assert_eq!(results.len(), 2);

Wrap the stream in a Box, pinning it.

An adaptor for creating a buffered list of pending futures.

If this stream's item can be converted into a future, then this adaptor will buffer up to at most n futures and then return the outputs in the same order as the underlying stream. No more than n futures will be buffered at any point in time, and less than n may also be buffered depending on the state of each future.

The returned stream will be a stream of each future's output.

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

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

If this stream's item can be converted into a future, then this adaptor will buffer up to n futures and then return the outputs in the order in which they complete. No more than n futures will be buffered at any point in time, and less than n may also be buffered depending on the state of each future.

The returned stream will be a stream of each future's output.

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

Examples

#![feature(async_await, await_macro)]
use futures::channel::oneshot;
use futures::stream::{self, StreamExt};

let (send_one, recv_one) = oneshot::channel();
let (send_two, recv_two) = oneshot::channel();

let stream_of_futures = stream::iter(vec![recv_one, recv_two]);
let mut buffered = stream_of_futures.buffer_unordered(10);

send_two.send(2i32);
assert_eq!(await!(buffered.next()), Some(Ok(2i32)));

send_one.send(1i32);
assert_eq!(await!(buffered.next()), Some(Ok(1i32)));

assert_eq!(await!(buffered.next()), None);

An adapter for zipping two streams together.

The zipped stream waits for both streams to produce an item, and then returns that pair. If either stream ends then the zipped stream will also end.

Examples

use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let mut stream1 = stream::iter(1..=3);
let mut stream2 = stream::iter(5..=10);

let vec = block_on(stream1.zip(stream2)
                          .collect::<Vec<_>>());
assert_eq!(vec![(1, 5), (2, 6), (3, 7)], vec);

Adapter for chaining two stream.

The resulting stream emits elements from the first stream, and when first stream reaches the end, emits the elements from the second stream.

use futures::executor::block_on;
use futures::stream::{self, StreamExt};

let stream1 = stream::iter(vec![Ok(10), Err(false)]);
let stream2 = stream::iter(vec![Err(true), Ok(20)]);

let stream = stream1.chain(stream2);

let result: Vec<_> = block_on(stream.collect());
assert_eq!(result, vec![
    Ok(10),
    Err(false),
    Err(true),
    Ok(20),
]);

Creates a new stream which exposes a peek method.

Calling peek returns a reference to the next item in the stream.

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

This combinator will attempt to pull items from this stream and buffer them into a local vector. At most capacity items will get buffered before they're yielded from the returned stream.

Note that the vectors returned from this iterator may not always have capacity elements. If the underlying stream ended and only a partial vector was created, it'll be returned. Additionally if an error happens from the underlying stream then the currently buffered items will be yielded.

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

Panics

This method will panic of capacity is zero.

This combinator will attempt to pull items from both streams. Each stream will be polled in a round-robin fashion, and whenever a stream is ready to yield an item that item is yielded.

After one of the two input stream completes, the remaining one will be polled exclusively. The returned stream completes when both input streams have completed.

Note that this method consumes both streams and returns a wrapped version of them.

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

This future will drive the stream to keep producing items until it is exhausted, sending each item to the sink. It will complete once both the stream is exhausted and the sink has received and flushed all items. Note that the sink is not closed.

On completion, the sink is returned.

Note that this combinator is only usable with Unpin sinks. Sinks that are not Unpin will need to be pinned in order to be used with forward.

Splits this Stream + Sink object into separate Stream and Sink objects.

This can be useful when you want to split ownership between tasks, or allow direct interaction between the two objects (e.g. via Sink::send_all).

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

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

This is similar to the Iterator::inspect method in the standard library where it allows easily inspecting each value as it passes through the stream, for example to debug what's going on.

ⓘImportant traits for Either<L, R>

Wrap this stream in an Either stream, making it the left-hand variant of that Either.

This can be used in combination with the right_stream method to write if statements that evaluate to different streams in different branches.

ⓘImportant traits for Either<L, R>

Wrap this stream in an Either stream, making it the right-hand variant of that Either.

This can be used in combination with the left_stream method to write if statements that evaluate to different streams in different branches.

A convenience method for calling Stream::poll_next on [Unpin] stream types.

Implementors