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    //! Streams
    //!
    //! This module contains a number of functions for working with `Streams`s
    //! that return `Result`s, allowing for short-circuiting computations.

    #[cfg(feature = "compat")]
    use crate::compat::Compat;
    use core::pin::Pin;
    use futures_core::{
        future::{Future, TryFuture},
        stream::TryStream,
        task::{Context, Poll},
    };
    use crate::fns::{
        InspectOkFn, inspect_ok_fn, InspectErrFn, inspect_err_fn, MapErrFn, map_err_fn, IntoFn, into_fn, MapOkFn, map_ok_fn,
    };
    use crate::future::assert_future;
    use crate::stream::{Map, Inspect};
    use crate::stream::assert_stream;

    mod and_then;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::and_then::AndThen;

    delegate_all!(
        /// Stream for the [`err_into`](super::TryStreamExt::err_into) method.
        ErrInto<St, E>(
            MapErr<St, IntoFn<E>>
        ): Debug + Sink + Stream + FusedStream + AccessInner[St, (.)] + New[|x: St| MapErr::new(x, into_fn())]
    );

    delegate_all!(
        /// Stream for the [`inspect_ok`](super::TryStreamExt::inspect_ok) method.
        InspectOk<St, F>(
            Inspect<IntoStream<St>, InspectOkFn<F>>
        ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Inspect::new(IntoStream::new(x), inspect_ok_fn(f))]
    );

    delegate_all!(
        /// Stream for the [`inspect_err`](super::TryStreamExt::inspect_err) method.
        InspectErr<St, F>(
            Inspect<IntoStream<St>, InspectErrFn<F>>
        ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Inspect::new(IntoStream::new(x), inspect_err_fn(f))]
    );

    mod into_stream;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::into_stream::IntoStream;

    delegate_all!(
        /// Stream for the [`map_ok`](super::TryStreamExt::map_ok) method.
        MapOk<St, F>(
            Map<IntoStream<St>, MapOkFn<F>>
        ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Map::new(IntoStream::new(x), map_ok_fn(f))]
    );

    delegate_all!(
        /// Stream for the [`map_err`](super::TryStreamExt::map_err) method.
        MapErr<St, F>(
            Map<IntoStream<St>, MapErrFn<F>>
        ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Map::new(IntoStream::new(x), map_err_fn(f))]
    );

    mod or_else;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::or_else::OrElse;

    mod try_next;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_next::TryNext;

    mod try_for_each;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_for_each::TryForEach;

    mod try_filter;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_filter::TryFilter;

    mod try_filter_map;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_filter_map::TryFilterMap;

    mod try_flatten;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_flatten::TryFlatten;

    mod try_collect;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_collect::TryCollect;

    mod try_concat;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_concat::TryConcat;

    mod try_fold;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_fold::TryFold;

    mod try_unfold;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_unfold::{try_unfold, TryUnfold};

    mod try_skip_while;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_skip_while::TrySkipWhile;

    mod try_take_while;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_take_while::TryTakeWhile;

    cfg_target_has_atomic! {
        #[cfg(feature = "alloc")]
        mod try_buffer_unordered;
        #[cfg(feature = "alloc")]
        #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
        pub use self::try_buffer_unordered::TryBufferUnordered;

        #[cfg(feature = "alloc")]
        mod try_buffered;
        #[cfg(feature = "alloc")]
        #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
        pub use self::try_buffered::TryBuffered;

        #[cfg(feature = "alloc")]
        mod try_for_each_concurrent;
        #[cfg(feature = "alloc")]
        #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
        pub use self::try_for_each_concurrent::TryForEachConcurrent;
    }

    #[cfg(feature = "io")]
    #[cfg(feature = "std")]
    mod into_async_read;
    #[cfg(feature = "io")]
    #[cfg_attr(docsrs, doc(cfg(feature = "io")))]
    #[cfg(feature = "std")]
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::into_async_read::IntoAsyncRead;

    impl<S: ?Sized + TryStream> TryStreamExt for S {}

    /// Adapters specific to `Result`-returning streams
    pub trait TryStreamExt: TryStream {
        /// Wraps the current stream in a new stream which converts the error type
        /// into the one provided.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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 err_into<E>(self) -> ErrInto<Self, E>
        where
            Self: Sized,
            Self::Error: Into<E>,
        {
            assert_stream::<Result<Self::Ok, E>, _>(ErrInto::new(self))
        }

        /// Wraps the current stream in a new stream which maps the success value
        /// using the provided closure.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_ok<T, F>(self, f: F) -> MapOk<Self, F>
        where
            Self: Sized,
            F: FnMut(Self::Ok) -> T,
        {
            assert_stream::<Result<T, Self::Error>, _>(MapOk::new(self, f))
        }

        /// Wraps the current stream in a new stream which maps the error value
        /// using the provided closure.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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 map_err<E, F>(self, f: F) -> MapErr<Self, F>
        where
            Self: Sized,
            F: FnMut(Self::Error) -> E,
        {
            assert_stream::<Result<Self::Ok, E>, _>(MapErr::new(self, 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
        ///     })
        /// });
        /// ```
        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,
        {
            assert_stream::<Result<Fut::Ok, Fut::Error>, _>(AndThen::new(self, 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`](futures_core::future::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 or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
        where
            F: FnMut(Self::Error) -> Fut,
            Fut: TryFuture<Ok = Self::Ok>,
            Self: Sized,
        {
            assert_stream::<Result<Self::Ok, Fut::Error>, _>(OrElse::new(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.
        fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
        where
            F: FnMut(&Self::Ok),
            Self: Sized,
        {
            assert_stream::<Result<Self::Ok, Self::Error>, _>(InspectOk::new(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.
        fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
        where
            F: FnMut(&Self::Error),
            Self: Sized,
        {
            assert_stream::<Result<Self::Ok, Self::Error>, _>(InspectErr::new(self, f))
        }

        /// Wraps a [`TryStream`] into a type that implements
        /// [`Stream`](futures_core::stream::Stream)
        ///
        /// [`TryStream`]s currently do not implement the
        /// [`Stream`](futures_core::stream::Stream) trait because of limitations
        /// of the compiler.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::stream::{Stream, TryStream, TryStreamExt};
        ///
        /// # type T = i32;
        /// # type E = ();
        /// fn make_try_stream() -> impl TryStream<Ok = T, Error = E> { // ... }
        /// # futures::stream::empty()
        /// # }
        /// fn take_stream(stream: impl Stream<Item = Result<T, E>>) { /* ... */ }
        ///
        /// take_stream(make_try_stream().into_stream());
        /// ```
        fn into_stream(self) -> IntoStream<Self>
        where
            Self: Sized,
        {
            assert_stream::<Result<Self::Ok, Self::Error>, _>(IntoStream::new(self))
        }

        /// 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
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_next(&mut self) -> TryNext<'_, Self>
        where
            Self: Unpin,
        {
            assert_future::<Result<Option<Self::Ok>, Self::Error>, _>(TryNext::new(self))
        }

        /// 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`](futures_core::future::Future) where the
        /// [`Output`](futures_core::future::Future::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
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_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,
        {
            assert_future::<Result<(), Self::Error>, _>(TryForEach::new(self, f))
        }

        /// Skip elements on this stream while the provided asynchronous predicate
        /// resolves to `true`.
        ///
        /// This function is similar to
        /// [`StreamExt::skip_while`](crate::stream::StreamExt::skip_while) but exits
        /// early if an error occurs.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_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,
        {
            assert_stream::<Result<Self::Ok, Self::Error>, _>(TrySkipWhile::new(self, f))
        }

        /// Take elements on this stream while the provided asynchronous predicate
        /// resolves to `true`.
        ///
        /// This function is similar to
        /// [`StreamExt::take_while`](crate::stream::StreamExt::take_while) but exits
        /// early if an error occurs.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_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,
        {
            assert_stream::<Result<Self::Ok, Self::Error>, _>(TryTakeWhile::new(self, f))
        }

        /// Attempts to run this stream to completion, executing the provided asynchronous
        /// closure for each element on the stream concurrently as elements become
        /// available, exiting as soon as an error occurs.
        ///
        /// This is similar to
        /// [`StreamExt::for_each_concurrent`](crate::stream::StreamExt::for_each_concurrent),
        /// but will resolve to an error immediately if the underlying stream or the provided
        /// closure return an error.
        ///
        /// This method is only available when the `std` or `alloc` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::channel::oneshot;
        /// use futures::stream::{self, StreamExt, TryStreamExt};
        ///
        /// let (tx1, rx1) = oneshot::channel();
        /// let (tx2, rx2) = oneshot::channel();
        /// let (_tx3, rx3) = oneshot::channel();
        ///
        /// let stream = stream::iter(vec![rx1, rx2, rx3]);
        /// let fut = stream.map(Ok).try_for_each_concurrent(
        ///     /* limit */ 2,
        ///     |rx| async move {
        ///         let res: Result<(), oneshot::Canceled> = rx.await;
        ///         res
        ///     }
        /// );
        ///
        /// tx1.send(()).unwrap();
        /// // Drop the second sender so that `rx2` resolves to `Canceled`.
        /// drop(tx2);
        ///
        /// // The final result is an error because the second future
        /// // resulted in an error.
        /// assert_eq!(Err(oneshot::Canceled), fut.await);
        /// # })
        /// ```
        #[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
        #[cfg(feature = "alloc")]
        fn try_for_each_concurrent<Fut, F>(
            self,
            limit: impl Into<Option<usize>>,
            f: F,
        ) -> TryForEachConcurrent<Self, Fut, F>
        where
            F: FnMut(Self::Ok) -> Fut,
            Fut: Future<Output = Result<(), Self::Error>>,
            Self: Sized,
        {
            assert_future::<Result<(), Self::Error>, _>(TryForEachConcurrent::new(
                self,
                limit.into(),
                f,
            ))
        }

        /// 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
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C>
        where
            Self: Sized,
        {
            assert_future::<Result<C, Self::Error>, _>(TryCollect::new(self))
        }

        /// 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
        /// ```
        /// # futures::executor::block_on(async {
        /// 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<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
        where
            Fut: Future<Output = bool>,
            F: FnMut(&Self::Ok) -> Fut,
            Self: Sized,
        {
            assert_stream::<Result<Self::Ok, Self::Error>, _>(TryFilter::new(self, 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)`](Some) 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
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_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,
        {
            assert_stream::<Result<T, Self::Error>, _>(TryFilterMap::new(self, f))
        }

        /// 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
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_flatten(self) -> TryFlatten<Self>
        where
            Self::Ok: TryStream,
            <Self::Ok as TryStream>::Error: From<Self::Error>,
            Self: Sized,
        {
            assert_stream::<Result<<Self::Ok as TryStream>::Ok, <Self::Ok as TryStream>::Error>, _>(
                TryFlatten::new(self),
            )
        }

        /// 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`](crate::stream::StreamExt::fold), but will
        /// exit early if an error is encountered in either the stream or the
        /// provided closure.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_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,
        {
            assert_future::<Result<T, Self::Error>, _>(TryFold::new(self, f, init))
        }

        /// 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`](std::iter::Extend) trait.
        ///
        /// This method is similar to [`concat`](crate::stream::StreamExt::concat), but will
        /// exit early if an error is encountered in the stream.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// 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_concat(self) -> TryConcat<Self>
        where
            Self: Sized,
            Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default,
        {
            assert_future::<Result<Self::Ok, Self::Error>, _>(TryConcat::new(self))
        }

        /// Attempt to execute several futures from a stream concurrently (unordered).
        ///
        /// This stream's `Ok` type must be a [`TryFuture`](futures_core::future::TryFuture) with an `Error` type
        /// that matches the stream's `Error` type.
        ///
        /// This adaptor will buffer up to `n` futures and then return their
        /// outputs in the order in which they complete. If the underlying stream
        /// returns an error, it will be immediately propagated.
        ///
        /// The returned stream will be a stream of results, each containing either
        /// an error or a future's output. An error can be produced either by the
        /// underlying stream itself or by one of the futures it yielded.
        ///
        /// This method is only available when the `std` or `alloc` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// Results are returned in the order of completion:
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::channel::oneshot;
        /// use futures::stream::{self, StreamExt, TryStreamExt};
        ///
        /// let (send_one, recv_one) = oneshot::channel();
        /// let (send_two, recv_two) = oneshot::channel();
        ///
        /// let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]);
        ///
        /// let mut buffered = stream_of_futures.try_buffer_unordered(10);
        ///
        /// send_two.send(2i32)?;
        /// assert_eq!(buffered.next().await, Some(Ok(2i32)));
        ///
        /// send_one.send(1i32)?;
        /// assert_eq!(buffered.next().await, Some(Ok(1i32)));
        ///
        /// assert_eq!(buffered.next().await, None);
        /// # Ok::<(), i32>(()) }).unwrap();
        /// ```
        ///
        /// Errors from the underlying stream itself are propagated:
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::channel::mpsc;
        /// use futures::stream::{StreamExt, TryStreamExt};
        ///
        /// let (sink, stream_of_futures) = mpsc::unbounded();
        /// let mut buffered = stream_of_futures.try_buffer_unordered(10);
        ///
        /// sink.unbounded_send(Ok(async { Ok(7i32) }))?;
        /// assert_eq!(buffered.next().await, Some(Ok(7i32)));
        ///
        /// sink.unbounded_send(Err("error in the stream"))?;
        /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
        /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
        /// ```
        #[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
        #[cfg(feature = "alloc")]
        fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self>
        where
            Self::Ok: TryFuture<Error = Self::Error>,
            Self: Sized,
        {
            assert_stream::<Result<<Self::Ok as TryFuture>::Ok, Self::Error>, _>(
                TryBufferUnordered::new(self, n),
            )
        }

        /// Attempt to execute several futures from a stream concurrently.
        ///
        /// This stream's `Ok` type must be a [`TryFuture`](futures_core::future::TryFuture) with an `Error` type
        /// that matches the stream's `Error` type.
        ///
        /// This adaptor will buffer up to `n` futures and then return their
        /// outputs in the order. If the underlying stream returns an error, it will
        /// be immediately propagated.
        ///
        /// The returned stream will be a stream of results, each containing either
        /// an error or a future's output. An error can be produced either by the
        /// underlying stream itself or by one of the futures it yielded.
        ///
        /// This method is only available when the `std` or `alloc` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// Results are returned in the order of addition:
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::channel::oneshot;
        /// use futures::future::lazy;
        /// use futures::stream::{self, StreamExt, TryStreamExt};
        ///
        /// let (send_one, recv_one) = oneshot::channel();
        /// let (send_two, recv_two) = oneshot::channel();
        ///
        /// let mut buffered = lazy(move |cx| {
        ///     let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]);
        ///
        ///     let mut buffered = stream_of_futures.try_buffered(10);
        ///
        ///     assert!(buffered.try_poll_next_unpin(cx).is_pending());
        ///
        ///     send_two.send(2i32)?;
        ///     assert!(buffered.try_poll_next_unpin(cx).is_pending());
        ///     Ok::<_, i32>(buffered)
        /// }).await?;
        ///
        /// send_one.send(1i32)?;
        /// assert_eq!(buffered.next().await, Some(Ok(1i32)));
        /// assert_eq!(buffered.next().await, Some(Ok(2i32)));
        ///
        /// assert_eq!(buffered.next().await, None);
        /// # Ok::<(), i32>(()) }).unwrap();
        /// ```
        ///
        /// Errors from the underlying stream itself are propagated:
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::channel::mpsc;
        /// use futures::stream::{StreamExt, TryStreamExt};
        ///
        /// let (sink, stream_of_futures) = mpsc::unbounded();
        /// let mut buffered = stream_of_futures.try_buffered(10);
        ///
        /// sink.unbounded_send(Ok(async { Ok(7i32) }))?;
        /// assert_eq!(buffered.next().await, Some(Ok(7i32)));
        ///
        /// sink.unbounded_send(Err("error in the stream"))?;
        /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
        /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
        /// ```
        #[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
        #[cfg(feature = "alloc")]
        fn try_buffered(self, n: usize) -> TryBuffered<Self>
        where
            Self::Ok: TryFuture<Error = Self::Error>,
            Self: Sized,
        {
            assert_stream::<Result<<Self::Ok as TryFuture>::Ok, Self::Error>, _>(TryBuffered::new(self, n))
        }

        // TODO: false positive warning from rustdoc. Verify once #43466 settles
        //
        /// A convenience method for calling [`TryStream::try_poll_next`] on [`Unpin`]
        /// stream types.
        fn try_poll_next_unpin(
            &mut self,
            cx: &mut Context<'_>,
        ) -> Poll<Option<Result<Self::Ok, Self::Error>>>
        where
            Self: Unpin,
        {
            Pin::new(self).try_poll_next(cx)
        }

        /// Wraps a [`TryStream`] into a stream compatible with libraries using
        /// futures 0.1 `Stream`. Requires the `compat` feature to be enabled.
        /// ```
        /// use futures::future::{FutureExt, TryFutureExt};
        /// # let (tx, rx) = futures::channel::oneshot::channel();
        ///
        /// let future03 = async {
        ///     println!("Running on the pool");
        ///     tx.send(42).unwrap();
        /// };
        ///
        /// let future01 = future03
        ///     .unit_error() // Make it a TryFuture
        ///     .boxed()  // Make it Unpin
        ///     .compat();
        ///
        /// tokio::run(future01);
        /// # assert_eq!(42, futures::executor::block_on(rx).unwrap());
        /// ```
        #[cfg(feature = "compat")]
        #[cfg_attr(docsrs, doc(cfg(feature = "compat")))]
        fn compat(self) -> Compat<Self>
        where
            Self: Sized + Unpin,
        {
            Compat::new(self)
        }

        /// Adapter that converts this stream into an [`AsyncRead`](crate::io::AsyncRead).
        ///
        /// Note that because `into_async_read` moves the stream, the [`Stream`](futures_core::stream::Stream) type must be
        /// [`Unpin`]. If you want to use `into_async_read` with a [`!Unpin`](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.
        ///
        /// This method is only available when the `std` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::stream::{self, TryStreamExt};
        /// use futures::io::AsyncReadExt;
        ///
        /// let stream = stream::iter(vec![Ok(vec![1, 2, 3, 4, 5])]);
        /// let mut reader = stream.into_async_read();
        /// let mut buf = Vec::new();
        ///
        /// assert!(reader.read_to_end(&mut buf).await.is_ok());
        /// assert_eq!(buf, &[1, 2, 3, 4, 5]);
        /// # })
        /// ```
        #[cfg(feature = "io")]
        #[cfg_attr(docsrs, doc(cfg(feature = "io")))]
        #[cfg(feature = "std")]
        fn into_async_read(self) -> IntoAsyncRead<Self>
        where
            Self: Sized + TryStreamExt<Error = std::io::Error> + Unpin,
            Self::Ok: AsRef<[u8]>,
        {
            crate::io::assert_read(IntoAsyncRead::new(self))
        }
    }