Trait futures_util::stream::StreamExt
source · pub trait StreamExt: Stream {
Show 35 methods
// Provided methods
fn next(&mut self) -> Next<'_, Self> ⓘ
where Self: Unpin { ... }
fn into_future(self) -> StreamFuture<Self> ⓘ
where Self: Sized + Unpin { ... }
fn map<T, F>(self, f: F) -> Map<Self, F>
where F: FnMut(Self::Item) -> T,
Self: Sized { ... }
fn enumerate(self) -> Enumerate<Self>
where Self: Sized { ... }
fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
Self: Sized { ... }
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 { ... }
fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut,
Fut: Future,
Self: Sized { ... }
fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C> ⓘ
where Self: Sized { ... }
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)> { ... }
fn concat(self) -> Concat<Self> ⓘ
where Self: Sized,
Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default { ... }
fn count(self) -> Count<Self> ⓘ
where Self: Sized { ... }
fn cycle(self) -> Cycle<Self>
where Self: Sized + Clone { ... }
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 { ... }
fn any<Fut, F>(self, f: F) -> Any<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = bool>,
Self: Sized { ... }
fn all<Fut, F>(self, f: F) -> All<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = bool>,
Self: Sized { ... }
fn flatten(self) -> Flatten<Self>
where Self::Item: Stream,
Self: Sized { ... }
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
where F: FnMut(Self::Item) -> U,
U: Stream,
Self: Sized { ... }
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 { ... }
fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
Self: Sized { ... }
fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
Self: Sized { ... }
fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut>
where Fut: Future,
Self: Sized { ... }
fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
Self: Sized { ... }
fn take(self, n: usize) -> Take<Self>
where Self: Sized { ... }
fn skip(self, n: usize) -> Skip<Self>
where Self: Sized { ... }
fn fuse(self) -> Fuse<Self>
where Self: Sized { ... }
fn by_ref(&mut self) -> &mut Self { ... }
fn zip<St>(self, other: St) -> Zip<Self, St>
where St: Stream,
Self: Sized { ... }
fn chain<St>(self, other: St) -> Chain<Self, St>
where St: Stream<Item = Self::Item>,
Self: Sized { ... }
fn peekable(self) -> Peekable<Self>
where Self: Sized { ... }
fn forward<S>(self, sink: S) -> Forward<Self, S> ⓘ
where S: Sink<Self::Ok, Error = Self::Error>,
Self: TryStream + Sized { ... }
fn inspect<F>(self, f: F) -> Inspect<Self, F>
where F: FnMut(&Self::Item),
Self: Sized { ... }
fn left_stream<B>(self) -> Either<Self, B> ⓘ
where B: Stream<Item = Self::Item>,
Self: Sized { ... }
fn right_stream<B>(self) -> Either<B, Self> ⓘ
where B: Stream<Item = Self::Item>,
Self: Sized { ... }
fn poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>>
where Self: Unpin { ... }
fn select_next_some(&mut self) -> SelectNextSome<'_, Self> ⓘ
where Self: Unpin + FusedStream { ... }
}
Expand description
An extension trait for Stream
s that provides a variety of convenient
combinator functions.
Provided Methods§
sourcefn next(&mut self) -> Next<'_, Self> ⓘwhere
Self: Unpin,
fn next(&mut self) -> Next<'_, Self> ⓘwhere
Self: Unpin,
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 boxing the stream using [Box::pin
] or
pinning it to the stack using the pin_mut!
macro from the pin_utils
crate.
§Examples
use futures::stream::{self, StreamExt};
let mut stream = stream::iter(1..=3);
assert_eq!(stream.next().await, Some(1));
assert_eq!(stream.next().await, Some(2));
assert_eq!(stream.next().await, Some(3));
assert_eq!(stream.next().await, None);
sourcefn into_future(self) -> StreamFuture<Self> ⓘ
fn into_future(self) -> StreamFuture<Self> ⓘ
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 boxing the stream using [Box::pin
] or
pinning it to the stack using the pin_mut!
macro from the pin_utils
crate.
§Examples
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=3);
let (item, stream) = stream.into_future().await;
assert_eq!(Some(1), item);
let (item, stream) = stream.into_future().await;
assert_eq!(Some(2), item);
sourcefn map<T, F>(self, f: F) -> Map<Self, F>
fn map<T, F>(self, f: F) -> Map<Self, F>
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.
See StreamExt::then
if you want to use a closure that
returns a future instead of a value.
§Examples
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=3);
let stream = stream.map(|x| x + 3);
assert_eq!(vec![4, 5, 6], stream.collect::<Vec<_>>().await);
sourcefn enumerate(self) -> Enumerate<Self>where
Self: Sized,
fn enumerate(self) -> Enumerate<Self>where
Self: Sized,
Creates a stream which gives the current iteration count as well as the next value.
The stream returned yields pairs (i, val)
, where i
is the
current index of iteration and val
is the value returned by the
stream.
enumerate()
keeps its count as a usize
. If you want to count by a
different sized integer, the zip
function provides similar
functionality.
§Overflow Behavior
The method does no guarding against overflows, so enumerating more than
[prim@usize::max_value()
] elements either produces the wrong result or panics. If
debug assertions are enabled, a panic is guaranteed.
§Panics
The returned stream might panic if the to-be-returned index would
overflow a usize
.
§Examples
use futures::stream::{self, StreamExt};
let stream = stream::iter(vec!['a', 'b', 'c']);
let mut stream = stream.enumerate();
assert_eq!(stream.next().await, Some((0, 'a')));
assert_eq!(stream.next().await, Some((1, 'b')));
assert_eq!(stream.next().await, Some((2, 'c')));
assert_eq!(stream.next().await, None);
sourcefn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
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::future;
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=10);
let events = stream.filter(|x| future::ready(x % 2 == 0));
assert_eq!(vec![2, 4, 6, 8, 10], events.collect::<Vec<_>>().await);
sourcefn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F>
fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F>
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::stream::{self, StreamExt};
let stream = stream::iter(1..=10);
let events = stream.filter_map(|x| async move {
if x % 2 == 0 { Some(x + 1) } else { None }
});
assert_eq!(vec![3, 5, 7, 9, 11], events.collect::<Vec<_>>().await);
sourcefn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
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.
See StreamExt::map
if you want to use a closure that
returns a value instead of a future.
§Examples
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=3);
let stream = stream.then(|x| async move { x + 3 });
assert_eq!(vec![4, 5, 6], stream.collect::<Vec<_>>().await);
sourcefn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C> ⓘwhere
Self: Sized,
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.
The returned future will be resolved when the stream terminates.
§Examples
use futures::channel::mpsc;
use futures::stream::StreamExt;
use std::thread;
let (tx, rx) = mpsc::unbounded();
thread::spawn(move || {
for i in 1..=5 {
tx.unbounded_send(i).unwrap();
}
});
let output = rx.collect::<Vec<i32>>().await;
assert_eq!(output, vec![1, 2, 3, 4, 5]);
sourcefn unzip<A, B, FromA, FromB>(self) -> Unzip<Self, FromA, FromB> ⓘ
fn unzip<A, B, FromA, FromB>(self) -> Unzip<Self, FromA, FromB> ⓘ
Converts a stream of pairs into a future, which resolves to pair of containers.
unzip()
produces a future, which resolves to two
collections: one from the left elements of the pairs,
and one from the right elements.
The returned future will be resolved when the stream terminates.
§Examples
use futures::channel::mpsc;
use futures::stream::StreamExt;
use std::thread;
let (tx, rx) = mpsc::unbounded();
thread::spawn(move || {
tx.unbounded_send((1, 2)).unwrap();
tx.unbounded_send((3, 4)).unwrap();
tx.unbounded_send((5, 6)).unwrap();
});
let (o1, o2): (Vec<_>, Vec<_>) = rx.unzip().await;
assert_eq!(o1, vec![1, 3, 5]);
assert_eq!(o2, vec![2, 4, 6]);
sourcefn concat(self) -> Concat<Self> ⓘwhere
Self: Sized,
Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default,
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.
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::stream::StreamExt;
use std::thread;
let (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 = rx.concat().await;
assert_eq!(result, vec![7, 8, 9, 4, 5, 6, 1, 2, 3]);
sourcefn count(self) -> Count<Self> ⓘwhere
Self: Sized,
fn count(self) -> Count<Self> ⓘwhere
Self: Sized,
Drives the stream to completion, counting the number of items.
§Overflow Behavior
The method does no guarding against overflows, so counting elements of a
stream with more than usize::MAX
elements either produces the wrong
result or panics. If debug assertions are enabled, a panic is guaranteed.
§Panics
This function might panic if the iterator has more than usize::MAX
elements.
§Examples
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=10);
let count = stream.count().await;
assert_eq!(count, 10);
sourcefn cycle(self) -> Cycle<Self>
fn cycle(self) -> Cycle<Self>
Repeats a stream endlessly.
The stream never terminates. Note that you likely want to avoid
usage of collect
or such on the returned stream as it will exhaust
available memory as it tries to just fill up all RAM.
§Examples
use futures::stream::{self, StreamExt};
let a = [1, 2, 3];
let mut s = stream::iter(a.iter()).cycle();
assert_eq!(s.next().await, Some(&1));
assert_eq!(s.next().await, Some(&2));
assert_eq!(s.next().await, Some(&3));
assert_eq!(s.next().await, Some(&1));
assert_eq!(s.next().await, Some(&2));
assert_eq!(s.next().await, Some(&3));
assert_eq!(s.next().await, Some(&1));
sourcefn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F> ⓘ
fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F> ⓘ
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::stream::{self, StreamExt};
let number_stream = stream::iter(0..6);
let sum = number_stream.fold(0, |acc, x| async move { acc + x });
assert_eq!(sum.await, 15);
sourcefn any<Fut, F>(self, f: F) -> Any<Self, Fut, F> ⓘ
fn any<Fut, F>(self, f: F) -> Any<Self, Fut, F> ⓘ
Execute predicate over asynchronous stream, and return true
if any element in stream satisfied a predicate.
§Examples
use futures::stream::{self, StreamExt};
let number_stream = stream::iter(0..10);
let contain_three = number_stream.any(|i| async move { i == 3 });
assert_eq!(contain_three.await, true);
sourcefn all<Fut, F>(self, f: F) -> All<Self, Fut, F> ⓘ
fn all<Fut, F>(self, f: F) -> All<Self, Fut, F> ⓘ
Execute predicate over asynchronous stream, and return true
if all element in stream satisfied a predicate.
§Examples
use futures::stream::{self, StreamExt};
let number_stream = stream::iter(0..10);
let less_then_twenty = number_stream.all(|i| async move { i < 20 });
assert_eq!(less_then_twenty.await, true);
sourcefn flatten(self) -> Flatten<Self>
fn flatten(self) -> Flatten<Self>
Flattens a stream of streams into just one continuous stream.
§Examples
use futures::channel::mpsc;
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 = rx3.flatten().collect::<Vec<i32>>().await;
assert_eq!(output, vec![1, 2, 3, 4]);
sourcefn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
Maps a stream like StreamExt::map
but flattens nested Stream
s.
StreamExt::map
is very useful, but if it produces a Stream
instead,
you would have to chain combinators like .map(f).flatten()
while this
combinator provides ability to write .flat_map(f)
instead of chaining.
The provided closure which produces inner streams is executed over all elements of stream as last inner stream is terminated and next stream item is available.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to the existing flat_map
methods in the
standard library.
§Examples
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=3);
let stream = stream.flat_map(|x| stream::iter(vec![x + 3; x]));
assert_eq!(vec![4, 5, 5, 6, 6, 6], stream.collect::<Vec<_>>().await);
sourcefn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F>
fn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F>
Combinator similar to StreamExt::fold
that holds internal state
and produces a new stream.
Accepts initial state and closure which will be applied to each element
of the stream until provided closure returns None
. Once None
is
returned, stream will be terminated.
§Examples
use futures::future;
use futures::stream::{self, StreamExt};
let stream = stream::iter(1..=10);
let stream = stream.scan(0, |state, x| {
*state += x;
future::ready(if *state < 10 { Some(x) } else { None })
});
assert_eq!(vec![1, 2, 3], stream.collect::<Vec<_>>().await);
sourcefn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
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::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], stream.collect::<Vec<_>>().await);
sourcefn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
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::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], stream.collect::<Vec<_>>().await);
sourcefn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut>
fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut>
Take elements from this stream until the provided future resolves.
This function will take elements from the stream until the provided
stopping future fut
resolves. Once the fut
future becomes ready,
this stream combinator will always return that the stream is done.
The stopping future may return any type. Once the stream is stopped
the result of the stopping future may be accessed with TakeUntil::take_result()
.
The stream may also be resumed with TakeUntil::take_future()
.
See the documentation of TakeUntil
for more information.
§Examples
use futures::future;
use futures::stream::{self, StreamExt};
use futures::task::Poll;
let stream = stream::iter(1..=10);
let mut i = 0;
let stop_fut = future::poll_fn(|_cx| {
i += 1;
if i <= 5 {
Poll::Pending
} else {
Poll::Ready(())
}
});
let stream = stream.take_until(stop_fut);
assert_eq!(vec![1, 2, 3, 4, 5], stream.collect::<Vec<_>>().await);
sourcefn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> ⓘ
fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> ⓘ
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::future;
use futures::stream::{self, StreamExt};
let mut x = 0;
{
let fut = stream::repeat(1).take(3).for_each(|item| {
x += item;
future::ready(())
});
fut.await;
}
assert_eq!(x, 3);
sourcefn take(self, n: usize) -> Take<Self>where
Self: Sized,
fn take(self, n: usize) -> Take<Self>where
Self: Sized,
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::stream::{self, StreamExt};
let stream = stream::iter(1..=10).take(3);
assert_eq!(vec![1, 2, 3], stream.collect::<Vec<_>>().await);
sourcefn skip(self, n: usize) -> Skip<Self>where
Self: Sized,
fn skip(self, n: usize) -> Skip<Self>where
Self: Sized,
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::stream::{self, StreamExt};
let stream = stream::iter(1..=10).skip(5);
assert_eq!(vec![6, 7, 8, 9, 10], stream.collect::<Vec<_>>().await);
sourcefn fuse(self) -> Fuse<Self>where
Self: Sized,
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
.
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 fuse
d stream
is guaranteed to return None
after the underlying stream has
finished.
§Examples
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());
// ...
sourcefn by_ref(&mut self) -> &mut Self
fn by_ref(&mut self) -> &mut Self
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::stream::{self, StreamExt};
let mut stream = stream::iter(1..5);
let sum = stream.by_ref()
.take(2)
.fold(0, |a, b| async move { a + b })
.await;
assert_eq!(sum, 3);
// You can use the stream again
let sum = stream.take(2)
.fold(0, |a, b| async move { a + b })
.await;
assert_eq!(sum, 7);
sourcefn zip<St>(self, other: St) -> Zip<Self, St>
fn zip<St>(self, other: St) -> Zip<Self, St>
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::stream::{self, StreamExt};
let stream1 = stream::iter(1..=3);
let stream2 = stream::iter(5..=10);
let vec = stream1.zip(stream2)
.collect::<Vec<_>>()
.await;
assert_eq!(vec![(1, 5), (2, 6), (3, 7)], vec);
sourcefn chain<St>(self, other: St) -> Chain<Self, St>
fn chain<St>(self, other: St) -> Chain<Self, St>
Adapter for chaining two streams.
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::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<_> = stream.collect().await;
assert_eq!(result, vec![
Ok(10),
Err(false),
Err(true),
Ok(20),
]);
sourcefn peekable(self) -> Peekable<Self>where
Self: Sized,
fn peekable(self) -> Peekable<Self>where
Self: Sized,
Creates a new stream which exposes a peek
method.
Calling peek
returns a reference to the next item in the stream.
sourcefn forward<S>(self, sink: S) -> Forward<Self, S> ⓘ
fn forward<S>(self, sink: S) -> Forward<Self, S> ⓘ
A future that completes after the given stream has been fully processed into the sink and the sink has been flushed and closed.
This future will drive the stream to keep producing items until it is
exhausted, sending each item to the sink. It will complete once the
stream is exhausted, the sink has received and flushed all items, and
the sink is closed. Note that neither the original stream nor provided
sink will be output by this future. Pass the sink by Pin<&mut S>
(for example, via forward(&mut sink)
inside an async
fn/block) in
order to preserve access to the Sink
. If the stream produces an error,
that error will be returned by this future without flushing/closing the sink.
sourcefn inspect<F>(self, f: F) -> Inspect<Self, F>
fn inspect<F>(self, f: F) -> Inspect<Self, F>
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.
sourcefn left_stream<B>(self) -> Either<Self, B> ⓘ
fn left_stream<B>(self) -> Either<Self, B> ⓘ
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.
sourcefn right_stream<B>(self) -> Either<B, Self> ⓘ
fn right_stream<B>(self) -> Either<B, Self> ⓘ
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.
sourcefn poll_next_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>where
Self: Unpin,
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.
sourcefn select_next_some(&mut self) -> SelectNextSome<'_, Self> ⓘwhere
Self: Unpin + FusedStream,
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.
This is similar to the next
method, but it won’t
resolve to None
if used on an empty Stream
. Instead, the
returned future type will return true
from
FusedFuture::is_terminated
when the Stream
is empty, allowing
select_next_some
to be easily used with
the select!
macro.
If the future is polled after this Stream
is empty it will panic.
Using the future with a FusedFuture
-aware primitive like the
select!
macro will prevent this.
§Examples
use futures::{future, select};
use futures::stream::{StreamExt, FuturesUnordered};
let mut fut = future::ready(1);
let mut async_tasks = FuturesUnordered::new();
let mut total = 0;
loop {
select! {
num = fut => {
// First, the `ready` future completes.
total += num;
// Then we spawn a new task onto `async_tasks`,
async_tasks.push(async { 5 });
},
// On the next iteration of the loop, the task we spawned
// completes.
num = async_tasks.select_next_some() => {
total += num;
}
// Finally, both the `ready` future and `async_tasks` have
// finished, so we enter the `complete` branch.
complete => break,
}
}
assert_eq!(total, 6);