Trait futures_util::stream::TryStreamExt
source · pub trait TryStreamExt: TryStream {
Show 21 methods
// Provided methods
fn err_into<E>(self) -> ErrInto<Self, E>
where Self: Sized,
Self::Error: Into<E> { ... }
fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
where Self: Sized,
F: FnMut(Self::Ok) -> T { ... }
fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
where Self: Sized,
F: FnMut(Self::Error) -> E { ... }
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 { ... }
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 { ... }
fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
where F: FnMut(&Self::Ok),
Self: Sized { ... }
fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
where F: FnMut(&Self::Error),
Self: Sized { ... }
fn into_stream(self) -> IntoStream<Self>
where Self: Sized { ... }
fn try_next(&mut self) -> TryNext<'_, Self> ⓘ
where Self: Unpin { ... }
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 { ... }
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 { ... }
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 { ... }
fn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C> ⓘ
where Self: Sized { ... }
fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
where Fut: Future<Output = bool>,
F: FnMut(&Self::Ok) -> Fut,
Self: Sized { ... }
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 { ... }
fn try_flatten(self) -> TryFlatten<Self>
where Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
Self: Sized { ... }
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 { ... }
fn try_concat(self) -> TryConcat<Self> ⓘ
where Self: Sized,
Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default { ... }
fn try_poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>>
where Self: Unpin { ... }
fn try_all<Fut, F>(self, f: F) -> TryAll<Self, Fut, F> ⓘ
where Self: Sized,
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = bool> { ... }
fn try_any<Fut, F>(self, f: F) -> TryAny<Self, Fut, F> ⓘ
where Self: Sized,
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = bool> { ... }
}
Expand description
Adapters specific to Result
-returning streams
Provided Methods§
sourcefn err_into<E>(self) -> ErrInto<Self, E>
fn err_into<E>(self) -> ErrInto<Self, E>
Wraps the current stream in a new stream which converts the error type into the one provided.
§Examples
use futures::stream::{self, TryStreamExt};
let mut stream =
stream::iter(vec![Ok(()), Err(5i32)])
.err_into::<i64>();
assert_eq!(stream.try_next().await, Ok(Some(())));
assert_eq!(stream.try_next().await, Err(5i64));
sourcefn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
Wraps the current stream in a new stream which maps the success value using the provided closure.
§Examples
use futures::stream::{self, TryStreamExt};
let mut stream =
stream::iter(vec![Ok(5), Err(0)])
.map_ok(|x| x + 2);
assert_eq!(stream.try_next().await, Ok(Some(7)));
assert_eq!(stream.try_next().await, Err(0));
sourcefn map_err<E, F>(self, f: F) -> MapErr<Self, F>
fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
Wraps the current stream in a new stream which maps the error value using the provided closure.
§Examples
use futures::stream::{self, TryStreamExt};
let mut stream =
stream::iter(vec![Ok(5), Err(0)])
.map_err(|x| x + 2);
assert_eq!(stream.try_next().await, Ok(Some(5)));
assert_eq!(stream.try_next().await, Err(2));
sourcefn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
Chain on a computation for when a value is ready, passing the successful
results to the provided closure f
.
This function can be used to run a unit of work when the next successful value on a stream is ready. The closure provided will be yielded a value when ready, and the returned future will then be run to completion to produce the next value on this stream.
Any errors produced by this stream will not be passed to the closure, and will be passed through.
The returned value of the closure must implement the TryFuture
trait
and can represent some more work to be done before the composed stream
is finished.
Note that this function consumes the receiving stream and returns a wrapped version of it.
To process the entire stream and return a single future representing
success or error, use try_for_each
instead.
§Examples
use futures::channel::mpsc;
use futures::future;
use futures::stream::TryStreamExt;
let (_tx, rx) = mpsc::channel::<Result<i32, ()>>(1);
let rx = rx.and_then(|result| {
future::ok(if result % 2 == 0 {
Some(result)
} else {
None
})
});
sourcefn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
Chain on a computation for when an error happens, passing the
erroneous result to the provided closure f
.
This function can be used to run a unit of work and attempt to recover from an error if one happens. The closure provided will be yielded an error when one appears, and the returned future will then be run to completion to produce the next value on this stream.
Any successful values produced by this stream will not be passed to the closure, and will be passed through.
The returned value of the closure must implement the TryFuture
trait
and can represent some more work to be done before the composed stream
is finished.
Note that this function consumes the receiving stream and returns a wrapped version of it.
sourcefn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
Do something with the success value of this stream, afterwards passing it on.
This is similar to the StreamExt::inspect
method where it allows
easily inspecting the success value as it passes through the stream, for
example to debug what’s going on.
sourcefn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
Do something with the error value of this stream, afterwards passing it on.
This is similar to the StreamExt::inspect
method where it allows
easily inspecting the error value as it passes through the stream, for
example to debug what’s going on.
sourcefn into_stream(self) -> IntoStream<Self>where
Self: Sized,
fn into_stream(self) -> IntoStream<Self>where
Self: Sized,
Wraps a TryStream
into a type that implements
Stream
TryStream
s currently do not implement the
Stream
trait because of limitations
of the compiler.
§Examples
use futures::stream::{Stream, TryStream, TryStreamExt};
fn make_try_stream() -> impl TryStream<Ok = T, Error = E> { // ... }
fn take_stream(stream: impl Stream<Item = Result<T, E>>) { /* ... */ }
take_stream(make_try_stream().into_stream());
sourcefn try_next(&mut self) -> TryNext<'_, Self> ⓘwhere
Self: Unpin,
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.
This is similar to the Stream::next
combinator, but returns a
Result<Option<T>, E>
rather than an Option<Result<T, E>>
, making
for easy use with the ?
operator.
§Examples
use futures::stream::{self, TryStreamExt};
let mut stream = stream::iter(vec![Ok(()), Err(())]);
assert_eq!(stream.try_next().await, Ok(Some(())));
assert_eq!(stream.try_next().await, Err(()));
sourcefn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F> ⓘ
fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F> ⓘ
Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream.
The provided closure 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
Result<(), Self::Error>
. If any of the intermediate
futures or the stream returns an error, this future will return
immediately with an error.
§Examples
use futures::future;
use futures::stream::{self, TryStreamExt};
let mut x = 0i32;
{
let fut = stream::repeat(Ok(1)).try_for_each(|item| {
x += item;
future::ready(if x == 3 { Err(()) } else { Ok(()) })
});
assert_eq!(fut.await, Err(()));
}
assert_eq!(x, 3);
sourcefn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F>
fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F>
Skip elements on this stream while the provided asynchronous predicate
resolves to true
.
This function is similar to
StreamExt::skip_while
but exits
early if an error occurs.
§Examples
use futures::future;
use futures::stream::{self, TryStreamExt};
let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(3), Ok(2)]);
let stream = stream.try_skip_while(|x| future::ready(Ok(*x < 3)));
let output: Result<Vec<i32>, i32> = stream.try_collect().await;
assert_eq!(output, Ok(vec![3, 2]));
sourcefn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F>
fn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F>
Take elements on this stream while the provided asynchronous predicate
resolves to true
.
This function is similar to
StreamExt::take_while
but exits
early if an error occurs.
§Examples
use futures::future;
use futures::stream::{self, TryStreamExt};
let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2), Ok(3), Ok(2)]);
let stream = stream.try_take_while(|x| future::ready(Ok(*x < 3)));
let output: Result<Vec<i32>, i32> = stream.try_collect().await;
assert_eq!(output, Ok(vec![1, 2]));
sourcefn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C> ⓘwhere
Self: Sized,
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.
This combinator will collect all successful results of this stream and collect them into the specified collection type. If an error happens then all collected elements will be dropped and the error will be returned.
The returned future will be resolved when the stream terminates.
§Examples
use futures::channel::mpsc;
use futures::stream::TryStreamExt;
use std::thread;
let (tx, rx) = mpsc::unbounded();
thread::spawn(move || {
for i in 1..=5 {
tx.unbounded_send(Ok(i)).unwrap();
}
tx.unbounded_send(Err(6)).unwrap();
});
let output: Result<Vec<i32>, i32> = rx.try_collect().await;
assert_eq!(output, Err(6));
sourcefn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
Attempt to filter the values produced by this stream according to the provided asynchronous closure.
As values of this stream are made available, the provided predicate f
will be run on them. If the predicate returns a Future
which resolves
to true
, then the stream will yield the value, but if the predicate
return a Future
which resolves to false
, then the value will be
discarded and the next value will be produced.
All errors are passed through without filtering in this combinator.
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, TryStreamExt};
let stream = stream::iter(vec![Ok(1i32), Ok(2i32), Ok(3i32), Err("error")]);
let mut evens = stream.try_filter(|x| {
future::ready(x % 2 == 0)
});
assert_eq!(evens.next().await, Some(Ok(2)));
assert_eq!(evens.next().await, Some(Err("error")));
sourcefn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F>
fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F>
Attempt to filter 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.
All errors are passed through without filtering in this combinator.
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, TryStreamExt};
use futures::pin_mut;
let stream = stream::iter(vec![Ok(1i32), Ok(6i32), Err("error")]);
let halves = stream.try_filter_map(|x| async move {
let ret = if x % 2 == 0 { Some(x / 2) } else { None };
Ok(ret)
});
pin_mut!(halves);
assert_eq!(halves.next().await, Some(Ok(3)));
assert_eq!(halves.next().await, Some(Err("error")));
sourcefn try_flatten(self) -> TryFlatten<Self>
fn try_flatten(self) -> TryFlatten<Self>
Flattens a stream of streams into just one continuous stream.
If this stream’s elements are themselves streams then this combinator will flatten out the entire stream to one long chain of elements. Any errors are passed through without looking at them, but otherwise each individual stream will get exhausted before moving on to the next.
§Examples
use futures::channel::mpsc;
use futures::stream::{StreamExt, TryStreamExt};
use std::thread;
let (tx1, rx1) = mpsc::unbounded();
let (tx2, rx2) = mpsc::unbounded();
let (tx3, rx3) = mpsc::unbounded();
thread::spawn(move || {
tx1.unbounded_send(Ok(1)).unwrap();
});
thread::spawn(move || {
tx2.unbounded_send(Ok(2)).unwrap();
tx2.unbounded_send(Err(3)).unwrap();
tx2.unbounded_send(Ok(4)).unwrap();
});
thread::spawn(move || {
tx3.unbounded_send(Ok(rx1)).unwrap();
tx3.unbounded_send(Ok(rx2)).unwrap();
tx3.unbounded_send(Err(5)).unwrap();
});
let mut stream = rx3.try_flatten();
assert_eq!(stream.next().await, Some(Ok(1)));
assert_eq!(stream.next().await, Some(Ok(2)));
assert_eq!(stream.next().await, Some(Err(3)));
assert_eq!(stream.next().await, Some(Ok(4)));
assert_eq!(stream.next().await, Some(Err(5)));
assert_eq!(stream.next().await, None);
sourcefn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F> ⓘ
fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F> ⓘ
Attempt to 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.
This method is similar to fold
, but will
exit early if an error is encountered in either the stream or the
provided closure.
§Examples
use futures::stream::{self, TryStreamExt};
let number_stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2)]);
let sum = number_stream.try_fold(0, |acc, x| async move { Ok(acc + x) });
assert_eq!(sum.await, Ok(3));
let number_stream_with_err = stream::iter(vec![Ok::<i32, i32>(1), Err(2), Ok(1)]);
let sum = number_stream_with_err.try_fold(0, |acc, x| async move { Ok(acc + x) });
assert_eq!(sum.await, Err(2));
sourcefn try_concat(self) -> TryConcat<Self> ⓘwhere
Self: Sized,
Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default,
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.
This combinator will extend the first item with the contents of all the subsequent successful results of the stream. If the stream is empty, the default value will be returned.
Works with all collections that implement the Extend
trait.
This method is similar to concat
, but will
exit early if an error is encountered in the stream.
§Examples
use futures::channel::mpsc;
use futures::stream::TryStreamExt;
use std::thread;
let (tx, rx) = mpsc::unbounded::<Result<Vec<i32>, ()>>();
thread::spawn(move || {
for i in (0..3).rev() {
let n = i * 3;
tx.unbounded_send(Ok(vec![n + 1, n + 2, n + 3])).unwrap();
}
});
let result = rx.try_concat().await;
assert_eq!(result, Ok(vec![7, 8, 9, 4, 5, 6, 1, 2, 3]));
sourcefn try_poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>>where
Self: Unpin,
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.
sourcefn try_all<Fut, F>(self, f: F) -> TryAll<Self, Fut, F> ⓘ
fn try_all<Fut, F>(self, f: F) -> TryAll<Self, Fut, F> ⓘ
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.
§Examples
use futures::stream::{self, StreamExt, TryStreamExt};
use std::convert::Infallible;
let number_stream = stream::iter(1..10).map(Ok::<_, Infallible>);
let positive = number_stream.try_all(|i| async move { i > 0 });
assert_eq!(positive.await, Ok(true));
let stream_with_errors = stream::iter([Ok(1), Err("err"), Ok(3)]);
let positive = stream_with_errors.try_all(|i| async move { i > 0 });
assert_eq!(positive.await, Err("err"));
sourcefn try_any<Fut, F>(self, f: F) -> TryAny<Self, Fut, F> ⓘ
fn try_any<Fut, F>(self, f: F) -> TryAny<Self, Fut, F> ⓘ
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.
§Examples
use futures::stream::{self, StreamExt, TryStreamExt};
use std::convert::Infallible;
let number_stream = stream::iter(0..10).map(Ok::<_, Infallible>);
let contain_three = number_stream.try_any(|i| async move { i == 3 });
assert_eq!(contain_three.await, Ok(true));
let stream_with_errors = stream::iter([Ok(1), Err("err"), Ok(3)]);
let contain_three = stream_with_errors.try_any(|i| async move { i == 3 });
assert_eq!(contain_three.await, Err("err"));