# Trait futures_util::stream::TryStreamExt [−] [src]

###

###

###

###

###

    pub trait TryStreamExt: TryStream {
        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>ⓘNotable traits for TryNext<'_, St>impl<St: ?Sized + TryStream + Unpin> Future for TryNext<'_, St>    type Output = Result<Option<St::Ok>, St::Error>;
        where
            Self: Unpin,
        { ... }
        fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F>ⓘNotable traits for TryForEach<St, Fut, F>impl<St, Fut, F> Future for TryForEach<St, Fut, F> where
        St: TryStream,
        F: FnMut(St::Ok) -> Fut,
        Fut: TryFuture<Ok = (), Error = St::Error>,     type Output = Result<(), St::Error>;
        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>ⓘNotable traits for TryCollect<St, C>impl<St, C> Future for TryCollect<St, C> where
        St: TryStream,
        C: Default + Extend<St::Ok>,     type Output = Result<C, St::Error>;
        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>ⓘNotable traits for TryFold<St, Fut, T, F>impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F> where
        St: TryStream,
        F: FnMut(T, St::Ok) -> Fut,
        Fut: TryFuture<Ok = T, Error = St::Error>,     type Output = Result<T, St::Error>;
        where
            F: FnMut(T, Self::Ok) -> Fut,
            Fut: TryFuture<Ok = T, Error = Self::Error>,
            Self: Sized,
        { ... }
        fn try_concat(self) -> TryConcat<Self>ⓘNotable traits for TryConcat<St>impl<St> Future for TryConcat<St> where
        St: TryStream,
        St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default,     type Output = Result<St::Ok, St::Error>;
        where
            Self: Sized,
            Self::Ok: Extend<<Self::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,
        { ... }
    }

Adapters specific to `Result`-returning streams

## Provided methods

### `fn err_into<E>(self) -> ErrInto<Self, E> where
Self: Sized,
Self::Error: Into<E>,` [src]

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));

### `fn map_ok<T, F>(self, f: F) -> MapOk<Self, F> where
Self: Sized,
F: FnMut(Self::Ok) -> T,` [src]

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));

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

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));

### `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,` [src]

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
        })
    });

### `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,` [src]

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.

### `fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F> where
F: FnMut(&Self::Ok),
Self: Sized,` [src]

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.

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

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.

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

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());

### `fn try_next(&mut self) -> TryNext<'_, Self>ⓘ

### Notable traits for TryNext<'_, St>

`impl<St: ?Sized + TryStream + Unpin> Future for TryNext<'_, St> type Output = Result<Option<St::Ok>, St::Error>;`
where
Self: Unpin,` [src]

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(()));

### `fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F>ⓘ

### Notable traits for TryForEach<St, Fut, F>

`impl<St, Fut, F> Future for TryForEach<St, Fut, F> where
St: TryStream,
F: FnMut(St::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = St::Error>, type Output = Result<(), St::Error>;`
where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
Self: Sized,` [src]

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);

### `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,` [src]

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]));

### `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,` [src]

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]));

### `fn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C>ⓘ

### Notable traits for TryCollect<St, C>

`impl<St, C> Future for TryCollect<St, C> where
St: TryStream,
C: Default + Extend<St::Ok>, type Output = Result<C, St::Error>;`
where
Self: Sized,` [src]

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));

### `fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F> where
Fut: Future<Output = bool>,
F: FnMut(&Self::Ok) -> Fut,
Self: Sized,` [src]

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")));

### `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,` [src]

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")));

### `fn try_flatten(self) -> TryFlatten<Self> where
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
Self: Sized,` [src]

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();
    });
    thread::spawn(move || {
        tx3.unbounded_send(Ok(rx1)).unwrap();
        tx3.unbounded_send(Ok(rx2)).unwrap();
        tx3.unbounded_send(Err(4)).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)));

### `fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F>ⓘ

### Notable traits for TryFold<St, Fut, T, F>

`impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F> where
St: TryStream,
F: FnMut(T, St::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = St::Error>, type Output = Result<T, St::Error>;`
where
F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
Self: Sized,` [src]

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));

### `fn try_concat(self) -> TryConcat<Self>ⓘ

### Notable traits for TryConcat<St>

`impl<St> Future for TryConcat<St> where
St: TryStream,
St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default, type Output = Result<St::Ok, St::Error>;`
where
Self: Sized,
Self::Ok: Extend<<Self::Ok as IntoIterator>::Item> + IntoIterator + Default,` [src]

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]));

### `fn try_poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,` [src]

A convenience method for calling `TryStream::try_poll_next` on `Unpin` stream types.

Loading content...

## Implementors

### `impl<S: ?Sized + TryStream> TryStreamExt for S` [src]

Loading content...