Trait futures::prelude::Future

#[must_use = "futures do nothing unless you `.await` or poll them"]
#[lang = "future_trait"]
pub trait Future {
    type Output;
    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output>;
}

A future represents an asynchronous computation.

A future is a value that may not have finished computing yet. This kind of "asynchronous value" makes it possible for a thread to continue doing useful work while it waits for the value to become available.

The poll method

The core method of future, poll, attempts to resolve the future into a final value. This method does not block if the value is not ready. Instead, the current task is scheduled to be woken up when it's possible to make further progress by polling again. The context passed to the poll method can provide a Waker, which is a handle for waking up the current task.

When using a future, you generally won't call poll directly, but instead .await the value.

Associated Types

type Output

The type of value produced on completion.

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Required methods

fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output>

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.

Return value

This function returns:

• Poll::Pending if the future is not ready yet
• Poll::Ready(val) with the result val of this future if it finished successfully.

Once a future has finished, clients should not poll it again.

When a future is not ready yet, poll returns Poll::Pending and stores a clone of the Waker copied from the current Context. This Waker is then woken once the future can make progress. For example, a future waiting for a socket to become readable would call .clone() on the Waker and store it. When a signal arrives elsewhere indicating that the socket is readable, Waker::wake is called and the socket future's task is awoken. Once a task has been woken up, it should attempt to poll the future again, which may or may not produce a final value.

Note that on multiple calls to poll, only the Waker from the Context passed to the most recent call should be scheduled to receive a wakeup.

Runtime characteristics

Futures alone are inert; they must be actively polled to make progress, meaning that each time the current task is woken up, it should actively re-poll pending futures that it still has an interest in.

The poll function is not called repeatedly in a tight loop -- instead, it should only be called when the future indicates that it is ready to make progress (by calling wake()). If you're familiar with the poll(2) or select(2) syscalls on Unix it's worth noting that futures typically do not suffer the same problems of "all wakeups must poll all events"; they are more like epoll(4).

An implementation of poll should strive to return quickly, and should not block. Returning quickly prevents unnecessarily clogging up threads or event loops. If it is known ahead of time that a call to poll may end up taking awhile, the work should be offloaded to a thread pool (or something similar) to ensure that poll can return quickly.

Panics

Once a future has completed (returned Ready from poll), calling its poll method again may panic, block forever, or cause other kinds of problems; the Future trait places no requirements on the effects of such a call. However, as the poll method is not marked unsafe, Rust's usual rules apply: calls must never cause undefined behavior (memory corruption, incorrect use of unsafe functions, or the like), regardless of the future's state.

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Trait Implementations

impl<'a, T> UnsafeFutureObj<'a, T> for &'a mut (dyn Future<Output = T> + 'a + Unpin)

fn into_raw(self) -> *mut dyn Future<Output = T> + 'a

Convert an owned instance into a (conceptually owned) fat pointer.

unsafe fn drop(_ptr: *mut dyn Future<Output = T> + 'a)

Drops the future represented by the given fat pointer.

Implementations on Foreign Types

impl<F> Future for AssertUnwindSafe<F> where
    F: Future, 

type Output = <F as Future>::Output

fn poll(
    self: Pin<&mut AssertUnwindSafe<F>>,
    cx: &mut Context
) -> Poll<<AssertUnwindSafe<F> as Future>::Output>

impl<P> Future for Pin<P> where
    P: Unpin + DerefMut,
    <P as Deref>::Target: Future, 

type Output = <<P as Deref>::Target as Future>::Output

fn poll(
    self: Pin<&mut Pin<P>>,
    cx: &mut Context
) -> Poll<<Pin<P> as Future>::Output>

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized, 

type Output = <F as Future>::Output

fn poll(
    self: Pin<&mut &'_ mut F>,
    cx: &mut Context
) -> Poll<<&'_ mut F as Future>::Output>

impl<F> Future for Box<F> where
    F: Unpin + Future + ?Sized, 

type Output = <F as Future>::Output

fn poll(
    self: Pin<&mut Box<F>>,
    cx: &mut Context
) -> Poll<<Box<F> as Future>::Output>

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Implementors

impl<'_, A> Future for ReadToEnd<'_, A> where
    A: AsyncRead + Unpin + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut ReadToEnd<'_, A>>,
    cx: &mut Context
) -> Poll<<ReadToEnd<'_, A> as Future>::Output>

impl<'_, A> Future for ReadToString<'_, A> where
    A: AsyncRead + Unpin + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut ReadToString<'_, A>>,
    cx: &mut Context
) -> Poll<<ReadToString<'_, A> as Future>::Output>

impl<'_, R> Future for Read<'_, R> where
    R: Unpin + AsyncRead + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut Read<'_, R>>,
    cx: &mut Context
) -> Poll<<Read<'_, R> as Future>::Output>

impl<'_, R> Future for ReadExact<'_, R> where
    R: Unpin + AsyncRead + ?Sized, 

type Output = Result<(), Error>

fn poll(
    self: Pin<&mut ReadExact<'_, R>>,
    cx: &mut Context
) -> Poll<<ReadExact<'_, R> as Future>::Output>

impl<'_, R> Future for ReadLine<'_, R> where
    R: Unpin + AsyncBufRead + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut ReadLine<'_, R>>,
    cx: &mut Context
) -> Poll<<ReadLine<'_, R> as Future>::Output>

impl<'_, R> Future for ReadUntil<'_, R> where
    R: Unpin + AsyncBufRead + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut ReadUntil<'_, R>>,
    cx: &mut Context
) -> Poll<<ReadUntil<'_, R> as Future>::Output>

impl<'_, R> Future for ReadVectored<'_, R> where
    R: Unpin + AsyncRead + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut ReadVectored<'_, R>>,
    cx: &mut Context
) -> Poll<<ReadVectored<'_, R> as Future>::Output>

impl<'_, R, W> Future for CopyBufInto<'_, R, W> where
    R: AsyncBufRead,
    W: AsyncWrite + Unpin + ?Sized, 

type Output = Result<u64, Error>

fn poll(
    self: Pin<&mut CopyBufInto<'_, R, W>>,
    cx: &mut Context
) -> Poll<<CopyBufInto<'_, R, W> as Future>::Output>

impl<'_, R, W> Future for CopyInto<'_, R, W> where
    R: AsyncRead,
    W: Unpin + AsyncWrite + ?Sized, 

type Output = Result<u64, Error>

fn poll(
    self: Pin<&mut CopyInto<'_, R, W>>,
    cx: &mut Context
) -> Poll<<CopyInto<'_, R, W> as Future>::Output>

impl<'_, S> Future for Seek<'_, S> where
    S: Unpin + AsyncSeek + ?Sized, 

type Output = Result<u64, Error>

fn poll(
    self: Pin<&mut Seek<'_, S>>,
    cx: &mut Context
) -> Poll<<Seek<'_, S> as Future>::Output>

impl<'_, Si, Item> Future for futures::sink::Close<'_, Si, Item> where
    Si: Unpin + Sink<Item> + ?Sized, 

type Output = Result<(), <Si as Sink<Item>>::Error>

fn poll(
    self: Pin<&mut Close<'_, Si, Item>>,
    cx: &mut Context
) -> Poll<<Close<'_, Si, Item> as Future>::Output>

impl<'_, Si, Item> Future for futures::sink::Flush<'_, Si, Item> where
    Si: Unpin + Sink<Item> + ?Sized, 

type Output = Result<(), <Si as Sink<Item>>::Error>

fn poll(
    self: Pin<&mut Flush<'_, Si, Item>>,
    cx: &mut Context
) -> Poll<<Flush<'_, Si, Item> as Future>::Output>

impl<'_, Si, Item> Future for Send<'_, Si, Item> where
    Si: Unpin + Sink<Item> + ?Sized, 

type Output = Result<(), <Si as Sink<Item>>::Error>

fn poll(
    self: Pin<&mut Send<'_, Si, Item>>,
    cx: &mut Context
) -> Poll<<Send<'_, Si, Item> as Future>::Output>

impl<'_, Si, St> Future for SendAll<'_, Si, St> where
    Si: Sink<<St as Stream>::Item> + Unpin + ?Sized,
    St: Stream + Unpin + ?Sized, 

type Output = Result<(), <Si as Sink<<St as Stream>::Item>>::Error>

fn poll(
    self: Pin<&mut SendAll<'_, Si, St>>,
    cx: &mut Context
) -> Poll<<SendAll<'_, Si, St> as Future>::Output>

impl<'_, St> Future for Next<'_, St> where
    St: Unpin + Stream + ?Sized, 

type Output = Option<<St as Stream>::Item>

fn poll(
    self: Pin<&mut Next<'_, St>>,
    cx: &mut Context
) -> Poll<<Next<'_, St> as Future>::Output>

impl<'_, St> Future for SelectNextSome<'_, St> where
    St: Unpin + FusedStream + ?Sized, 

type Output = <St as Stream>::Item

fn poll(
    self: Pin<&mut SelectNextSome<'_, St>>,
    cx: &mut Context
) -> Poll<<SelectNextSome<'_, St> as Future>::Output>

impl<'_, St> Future for TryNext<'_, St> where
    St: Unpin + TryStream + ?Sized, 

type Output = Result<Option<<St as TryStream>::Ok>, <St as TryStream>::Error>

fn poll(
    self: Pin<&mut TryNext<'_, St>>,
    cx: &mut Context
) -> Poll<<TryNext<'_, St> as Future>::Output>

impl<'_, T> Future for FutureObj<'_, T>

type Output = T

fn poll(self: Pin<&mut FutureObj<'_, T>>, cx: &mut Context) -> Poll<T>

impl<'_, T> Future for LocalFutureObj<'_, T>

type Output = T

fn poll(self: Pin<&mut LocalFutureObj<'_, T>>, cx: &mut Context) -> Poll<T>

impl<'_, W> Future for futures::io::Close<'_, W> where
    W: Unpin + AsyncWrite + ?Sized, 

type Output = Result<(), Error>

fn poll(
    self: Pin<&mut Close<'_, W>>,
    cx: &mut Context
) -> Poll<<Close<'_, W> as Future>::Output>

impl<'_, W> Future for futures::io::Flush<'_, W> where
    W: AsyncWrite + Unpin + ?Sized, 

type Output = Result<(), Error>

fn poll(
    self: Pin<&mut Flush<'_, W>>,
    cx: &mut Context
) -> Poll<<Flush<'_, W> as Future>::Output>

impl<'_, W> Future for Write<'_, W> where
    W: Unpin + AsyncWrite + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut Write<'_, W>>,
    cx: &mut Context
) -> Poll<<Write<'_, W> as Future>::Output>

impl<'_, W> Future for WriteAll<'_, W> where
    W: Unpin + AsyncWrite + ?Sized, 

type Output = Result<(), Error>

fn poll(
    self: Pin<&mut WriteAll<'_, W>>,
    cx: &mut Context
) -> Poll<Result<(), Error>>

impl<'_, W> Future for WriteVectored<'_, W> where
    W: Unpin + AsyncWrite + ?Sized, 

type Output = Result<usize, Error>

fn poll(
    self: Pin<&mut WriteVectored<'_, W>>,
    cx: &mut Context
) -> Poll<<WriteVectored<'_, W> as Future>::Output>

impl<'a, T> Future for BiLockAcquire<'a, T>

type Output = BiLockGuard<'a, T>

fn poll(
    self: Pin<&mut BiLockAcquire<'a, T>>,
    cx: &mut Context
) -> Poll<<BiLockAcquire<'a, T> as Future>::Output>

impl<'a, T> Future for MutexLockFuture<'a, T> where
    T: ?Sized, 

type Output = MutexGuard<'a, T>

fn poll(
    self: Pin<&mut MutexLockFuture<'a, T>>,
    cx: &mut Context
) -> Poll<<MutexLockFuture<'a, T> as Future>::Output>

impl<A, B> Future for Either<A, B> where
    A: Future,
    B: Future<Output = <A as Future>::Output>, 

type Output = <A as Future>::Output

fn poll(
    self: Pin<&mut Either<A, B>>,
    cx: &mut Context
) -> Poll<<A as Future>::Output>

impl<A, B> Future for Select<A, B> where
    A: Future + Unpin,
    B: Future + Unpin, 

type Output = Either<(<A as Future>::Output, B), (<B as Future>::Output, A)>

fn poll(
    self: Pin<&mut Select<A, B>>,
    cx: &mut Context
) -> Poll<<Select<A, B> as Future>::Output>

impl<A, B> Future for TrySelect<A, B> where
    A: Unpin + TryFuture,
    B: Unpin + TryFuture, 

type Output = Result<Either<(<A as TryFuture>::Ok, B), (<B as TryFuture>::Ok, A)>, Either<(<A as TryFuture>::Error, B), (<B as TryFuture>::Error, A)>>

fn poll(
    self: Pin<&mut TrySelect<A, B>>,
    cx: &mut Context
) -> Poll<<TrySelect<A, B> as Future>::Output>

impl<F> Future for JoinAll<F> where
    F: Future, 

type Output = Vec<<F as Future>::Output>

fn poll(
    self: Pin<&mut JoinAll<F>>,
    cx: &mut Context
) -> Poll<<JoinAll<F> as Future>::Output>

impl<F> Future for OptionFuture<F> where
    F: Future, 

type Output = Option<<F as Future>::Output>

fn poll(
    self: Pin<&mut OptionFuture<F>>,
    cx: &mut Context
) -> Poll<<OptionFuture<F> as Future>::Output>

impl<F> Future for TryJoinAll<F> where
    F: TryFuture, 

type Output = Result<Vec<<F as TryFuture>::Ok>, <F as TryFuture>::Error>

fn poll(
    self: Pin<&mut TryJoinAll<F>>,
    cx: &mut Context
) -> Poll<<TryJoinAll<F> as Future>::Output>

impl<F, R> Future for Lazy<F> where
    F: FnOnce(&mut Context) -> R, 

type Output = R

fn poll(self: Pin<&mut Lazy<F>>, cx: &mut Context) -> Poll<R>

impl<Fut> Future for MaybeDone<Fut> where
    Fut: Future, 

type Output = ()

fn poll(
    self: Pin<&mut MaybeDone<Fut>>,
    cx: &mut Context
) -> Poll<<MaybeDone<Fut> as Future>::Output>

impl<Fut> Future for Compat01As03<Fut> where
    Fut: Future, 

type Output = Result<<Fut as Future>::Item, <Fut as Future>::Error>

fn poll(
    self: Pin<&mut Compat01As03<Fut>>,
    cx: &mut Context
) -> Poll<<Compat01As03<Fut> as Future>::Output>

impl<Fut> Future for Abortable<Fut> where
    Fut: Future, 

type Output = Result<<Fut as Future>::Output, Aborted>

fn poll(
    self: Pin<&mut Abortable<Fut>>,
    cx: &mut Context
) -> Poll<<Abortable<Fut> as Future>::Output>

impl<Fut> Future for CatchUnwind<Fut> where
    Fut: Future + UnwindSafe, 

type Output = Result<<Fut as Future>::Output, Box<dyn Any + 'static + Send>>

fn poll(
    self: Pin<&mut CatchUnwind<Fut>>,
    cx: &mut Context
) -> Poll<<CatchUnwind<Fut> as Future>::Output>

impl<Fut> Future for Flatten<Fut> where
    Fut: Future,
    <Fut as Future>::Output: Future, 

type Output = <<Fut as Future>::Output as Future>::Output

fn poll(
    self: Pin<&mut Flatten<Fut>>,
    cx: &mut Context
) -> Poll<<Flatten<Fut> as Future>::Output>

impl<Fut> Future for Fuse<Fut> where
    Fut: Future, 

type Output = <Fut as Future>::Output

fn poll(
    self: Pin<&mut Fuse<Fut>>,
    cx: &mut Context
) -> Poll<<Fut as Future>::Output>

impl<Fut> Future for IntoFuture<Fut> where
    Fut: TryFuture, 

type Output = Result<<Fut as TryFuture>::Ok, <Fut as TryFuture>::Error>

fn poll(
    self: Pin<&mut IntoFuture<Fut>>,
    cx: &mut Context
) -> Poll<<IntoFuture<Fut> as Future>::Output>

impl<Fut> Future for Remote<Fut> where
    Fut: Future, 

type Output = ()

fn poll(self: Pin<&mut Remote<Fut>>, cx: &mut Context) -> Poll<()>

impl<Fut> Future for SelectAll<Fut> where
    Fut: Unpin + Future, 

type Output = (<Fut as Future>::Output, usize, Vec<Fut>)

fn poll(
    self: Pin<&mut SelectAll<Fut>>,
    cx: &mut Context
) -> Poll<<SelectAll<Fut> as Future>::Output>

impl<Fut> Future for SelectOk<Fut> where
    Fut: Unpin + TryFuture, 

type Output = Result<(<Fut as TryFuture>::Ok, Vec<Fut>), <Fut as TryFuture>::Error>

fn poll(
    self: Pin<&mut SelectOk<Fut>>,
    cx: &mut Context
) -> Poll<<SelectOk<Fut> as Future>::Output>

impl<Fut> Future for Shared<Fut> where
    Fut: Future,
    <Fut as Future>::Output: Clone, 

type Output = <Fut as Future>::Output

fn poll(
    self: Pin<&mut Shared<Fut>>,
    cx: &mut Context
) -> Poll<<Shared<Fut> as Future>::Output>

impl<Fut, E> Future for ErrInto<Fut, E> where
    Fut: TryFuture,
    <Fut as TryFuture>::Error: Into<E>, 

type Output = Result<<Fut as TryFuture>::Ok, E>

fn poll(
    self: Pin<&mut ErrInto<Fut, E>>,
    cx: &mut Context
) -> Poll<<ErrInto<Fut, E> as Future>::Output>

impl<Fut, F> Future for Inspect<Fut, F> where
    F: FnOnce(&<Fut as Future>::Output),
    Fut: Future, 

type Output = <Fut as Future>::Output

fn poll(
    self: Pin<&mut Inspect<Fut, F>>,
    cx: &mut Context
) -> Poll<<Fut as Future>::Output>

impl<Fut, F> Future for InspectErr<Fut, F> where
    F: FnOnce(&<Fut as TryFuture>::Error),
    Fut: TryFuture, 

type Output = Result<<Fut as TryFuture>::Ok, <Fut as TryFuture>::Error>

fn poll(
    self: Pin<&mut InspectErr<Fut, F>>,
    cx: &mut Context
) -> Poll<<InspectErr<Fut, F> as Future>::Output>

impl<Fut, F> Future for InspectOk<Fut, F> where
    F: FnOnce(&<Fut as TryFuture>::Ok),
    Fut: TryFuture, 

type Output = Result<<Fut as TryFuture>::Ok, <Fut as TryFuture>::Error>

fn poll(
    self: Pin<&mut InspectOk<Fut, F>>,
    cx: &mut Context
) -> Poll<<InspectOk<Fut, F> as Future>::Output>

impl<Fut, F> Future for UnwrapOrElse<Fut, F> where
    F: FnOnce(<Fut as TryFuture>::Error) -> <Fut as TryFuture>::Ok,
    Fut: TryFuture, 

type Output = <Fut as TryFuture>::Ok

fn poll(
    self: Pin<&mut UnwrapOrElse<Fut, F>>,
    cx: &mut Context
) -> Poll<<UnwrapOrElse<Fut, F> as Future>::Output>

impl<Fut, F, E> Future for MapErr<Fut, F> where
    F: FnOnce(<Fut as TryFuture>::Error) -> E,
    Fut: TryFuture, 

type Output = Result<<Fut as TryFuture>::Ok, E>

fn poll(
    self: Pin<&mut MapErr<Fut, F>>,
    cx: &mut Context
) -> Poll<<MapErr<Fut, F> as Future>::Output>

impl<Fut, F, T> Future for Map<Fut, F> where
    F: FnOnce(<Fut as Future>::Output) -> T,
    Fut: Future, 

type Output = T

fn poll(self: Pin<&mut Map<Fut, F>>, cx: &mut Context) -> Poll<T>

impl<Fut, F, T> Future for MapOk<Fut, F> where
    F: FnOnce(<Fut as TryFuture>::Ok) -> T,
    Fut: TryFuture, 

type Output = Result<T, <Fut as TryFuture>::Error>

fn poll(
    self: Pin<&mut MapOk<Fut, F>>,
    cx: &mut Context
) -> Poll<<MapOk<Fut, F> as Future>::Output>

impl<Fut, T> Future for NeverError<Fut> where
    Fut: Future<Output = T>, 

type Output = Result<T, Infallible>

fn poll(
    self: Pin<&mut NeverError<Fut>>,
    cx: &mut Context
) -> Poll<<NeverError<Fut> as Future>::Output>

impl<Fut, T> Future for UnitError<Fut> where
    Fut: Future<Output = T>, 

type Output = Result<T, ()>

fn poll(self: Pin<&mut UnitError<Fut>>, cx: &mut Context) -> Poll<Result<T, ()>>

impl<Fut1, Fut2> Future for Join<Fut1, Fut2> where
    Fut1: Future,
    Fut2: Future, 

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output)

fn poll(
    self: Pin<&mut Join<Fut1, Fut2>>,
    cx: &mut Context
) -> Poll<<Join<Fut1, Fut2> as Future>::Output>

impl<Fut1, Fut2> Future for TryJoin<Fut1, Fut2> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>, 

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

fn poll(
    self: Pin<&mut TryJoin<Fut1, Fut2>>,
    cx: &mut Context
) -> Poll<<TryJoin<Fut1, Fut2> as Future>::Output>

impl<Fut1, Fut2, F> Future for AndThen<Fut1, Fut2, F> where
    F: FnOnce(<Fut1 as TryFuture>::Ok) -> Fut2,
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>, 

type Output = Result<<Fut2 as TryFuture>::Ok, <Fut2 as TryFuture>::Error>

fn poll(
    self: Pin<&mut AndThen<Fut1, Fut2, F>>,
    cx: &mut Context
) -> Poll<<AndThen<Fut1, Fut2, F> as Future>::Output>

impl<Fut1, Fut2, F> Future for OrElse<Fut1, Fut2, F> where
    F: FnOnce(<Fut1 as TryFuture>::Error) -> Fut2,
    Fut1: TryFuture,
    Fut2: TryFuture<Ok = <Fut1 as TryFuture>::Ok>, 

type Output = Result<<Fut2 as TryFuture>::Ok, <Fut2 as TryFuture>::Error>

fn poll(
    self: Pin<&mut OrElse<Fut1, Fut2, F>>,
    cx: &mut Context
) -> Poll<<OrElse<Fut1, Fut2, F> as Future>::Output>

impl<Fut1, Fut2, F> Future for Then<Fut1, Fut2, F> where
    F: FnOnce(<Fut1 as Future>::Output) -> Fut2,
    Fut1: Future,
    Fut2: Future, 

type Output = <Fut2 as Future>::Output

fn poll(
    self: Pin<&mut Then<Fut1, Fut2, F>>,
    cx: &mut Context
) -> Poll<<Fut2 as Future>::Output>

impl<Fut1, Fut2, Fut3> Future for Join3<Fut1, Fut2, Fut3> where
    Fut1: Future,
    Fut2: Future,
    Fut3: Future, 

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output, <Fut3 as Future>::Output)

fn poll(
    self: Pin<&mut Join3<Fut1, Fut2, Fut3>>,
    cx: &mut Context
) -> Poll<<Join3<Fut1, Fut2, Fut3> as Future>::Output>

impl<Fut1, Fut2, Fut3> Future for TryJoin3<Fut1, Fut2, Fut3> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut3: TryFuture<Error = <Fut1 as TryFuture>::Error>, 

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok, <Fut3 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

fn poll(
    self: Pin<&mut TryJoin3<Fut1, Fut2, Fut3>>,
    cx: &mut Context
) -> Poll<<TryJoin3<Fut1, Fut2, Fut3> as Future>::Output>

impl<Fut1, Fut2, Fut3, Fut4> Future for Join4<Fut1, Fut2, Fut3, Fut4> where
    Fut1: Future,
    Fut2: Future,
    Fut3: Future,
    Fut4: Future, 

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output, <Fut3 as Future>::Output, <Fut4 as Future>::Output)

fn poll(
    self: Pin<&mut Join4<Fut1, Fut2, Fut3, Fut4>>,
    cx: &mut Context
) -> Poll<<Join4<Fut1, Fut2, Fut3, Fut4> as Future>::Output>

impl<Fut1, Fut2, Fut3, Fut4> Future for TryJoin4<Fut1, Fut2, Fut3, Fut4> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut3: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut4: TryFuture<Error = <Fut1 as TryFuture>::Error>, 

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok, <Fut3 as TryFuture>::Ok, <Fut4 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

fn poll(
    self: Pin<&mut TryJoin4<Fut1, Fut2, Fut3, Fut4>>,
    cx: &mut Context
) -> Poll<<TryJoin4<Fut1, Fut2, Fut3, Fut4> as Future>::Output>

impl<Fut1, Fut2, Fut3, Fut4, Fut5> Future for Join5<Fut1, Fut2, Fut3, Fut4, Fut5> where
    Fut1: Future,
    Fut2: Future,
    Fut3: Future,
    Fut4: Future,
    Fut5: Future, 

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output, <Fut3 as Future>::Output, <Fut4 as Future>::Output, <Fut5 as Future>::Output)

fn poll(
    self: Pin<&mut Join5<Fut1, Fut2, Fut3, Fut4, Fut5>>,
    cx: &mut Context
) -> Poll<<Join5<Fut1, Fut2, Fut3, Fut4, Fut5> as Future>::Output>

impl<Fut1, Fut2, Fut3, Fut4, Fut5> Future for TryJoin5<Fut1, Fut2, Fut3, Fut4, Fut5> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut3: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut4: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut5: TryFuture<Error = <Fut1 as TryFuture>::Error>, 

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok, <Fut3 as TryFuture>::Ok, <Fut4 as TryFuture>::Ok, <Fut5 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

fn poll(
    self: Pin<&mut TryJoin5<Fut1, Fut2, Fut3, Fut4, Fut5>>,
    cx: &mut Context
) -> Poll<<TryJoin5<Fut1, Fut2, Fut3, Fut4, Fut5> as Future>::Output>

impl<St> Future for Concat<St> where
    St: Stream,
    <St as Stream>::Item: Extend<<<St as Stream>::Item as IntoIterator>::Item>,
    <St as Stream>::Item: IntoIterator,
    <St as Stream>::Item: Default, 

type Output = <St as Stream>::Item

fn poll(
    self: Pin<&mut Concat<St>>,
    cx: &mut Context
) -> Poll<<Concat<St> as Future>::Output>

impl<St> Future for StreamFuture<St> where
    St: Unpin + Stream, 

type Output = (Option<<St as Stream>::Item>, St)

fn poll(
    self: Pin<&mut StreamFuture<St>>,
    cx: &mut Context
) -> Poll<<StreamFuture<St> as Future>::Output>

impl<St> Future for TryConcat<St> where
    St: TryStream,
    <St as TryStream>::Ok: Extend<<<St as TryStream>::Ok as IntoIterator>::Item>,
    <St as TryStream>::Ok: IntoIterator,
    <St as TryStream>::Ok: Default, 

type Output = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

fn poll(
    self: Pin<&mut TryConcat<St>>,
    cx: &mut Context
) -> Poll<<TryConcat<St> as Future>::Output>

impl<St, C> Future for Collect<St, C> where
    C: Default + Extend<<St as Stream>::Item>,
    St: Stream, 

type Output = C

fn poll(self: Pin<&mut Collect<St, C>>, cx: &mut Context) -> Poll<C>

impl<St, C> Future for TryCollect<St, C> where
    C: Default + Extend<<St as TryStream>::Ok>,
    St: TryStream, 

type Output = Result<C, <St as TryStream>::Error>

fn poll(
    self: Pin<&mut TryCollect<St, C>>,
    cx: &mut Context
) -> Poll<<TryCollect<St, C> as Future>::Output>

impl<St, Fut, F> Future for ForEach<St, Fut, F> where
    F: FnMut(<St as Stream>::Item) -> Fut,
    Fut: Future<Output = ()>,
    St: Stream, 

type Output = ()

fn poll(self: Pin<&mut ForEach<St, Fut, F>>, cx: &mut Context) -> Poll<()>

impl<St, Fut, F> Future for ForEachConcurrent<St, Fut, F> where
    F: FnMut(<St as Stream>::Item) -> Fut,
    Fut: Future<Output = ()>,
    St: Stream, 

type Output = ()

fn poll(
    self: Pin<&mut ForEachConcurrent<St, Fut, F>>,
    cx: &mut Context
) -> Poll<()>

impl<St, Fut, F> Future for TryForEach<St, Fut, F> where
    F: FnMut(<St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Ok = (), Error = <St as TryStream>::Error>,
    St: TryStream, 

type Output = Result<(), <St as TryStream>::Error>

fn poll(
    self: Pin<&mut TryForEach<St, Fut, F>>,
    cx: &mut Context
) -> Poll<<TryForEach<St, Fut, F> as Future>::Output>

impl<St, Fut, F> Future for TryForEachConcurrent<St, Fut, F> where
    F: FnMut(<St as TryStream>::Ok) -> Fut,
    Fut: Future<Output = Result<(), <St as TryStream>::Error>>,
    St: TryStream, 

type Output = Result<(), <St as TryStream>::Error>

fn poll(
    self: Pin<&mut TryForEachConcurrent<St, Fut, F>>,
    cx: &mut Context
) -> Poll<<TryForEachConcurrent<St, Fut, F> as Future>::Output>

impl<St, Fut, T, F> Future for Fold<St, Fut, T, F> where
    F: FnMut(T, <St as Stream>::Item) -> Fut,
    Fut: Future<Output = T>,
    St: Stream, 

type Output = T

fn poll(self: Pin<&mut Fold<St, Fut, T, F>>, cx: &mut Context) -> Poll<T>

impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F> where
    F: FnMut(T, <St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Ok = T, Error = <St as TryStream>::Error>,
    St: TryStream, 

type Output = Result<T, <St as TryStream>::Error>

fn poll(
    self: Pin<&mut TryFold<St, Fut, T, F>>,
    cx: &mut Context
) -> Poll<<TryFold<St, Fut, T, F> as Future>::Output>

impl<St, Si, Item, E> Future for Forward<St, Si> where
    Si: Sink<Item, Error = E>,
    St: Stream<Item = Result<Item, E>>, 

type Output = Result<(), E>

fn poll(
    self: Pin<&mut Forward<St, Si>>,
    cx: &mut Context
) -> Poll<<Forward<St, Si> as Future>::Output>

impl<T> Future for Receiver<T>

type Output = Result<T, Canceled>

fn poll(
    self: Pin<&mut Receiver<T>>,
    cx: &mut Context
) -> Poll<Result<T, Canceled>>

impl<T> Future for Pending<T>

type Output = T

fn poll(self: Pin<&mut Pending<T>>, &mut Context) -> Poll<T>

impl<T> Future for Ready<T>

type Output = T

fn poll(self: Pin<&mut Ready<T>>, _cx: &mut Context) -> Poll<T>

impl<T> Future for RemoteHandle<T> where
    T: 'static + Send, 

type Output = T

fn poll(self: Pin<&mut RemoteHandle<T>>, cx: &mut Context) -> Poll<T>

impl<T, F> Future for PollFn<F> where
    F: FnMut(&mut Context) -> Poll<T>, 

type Output = T

fn poll(self: Pin<&mut PollFn<F>>, cx: &mut Context) -> Poll<T>

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