Struct futures_util::stream::FilterMap

source · [−]

pub struct FilterMap<St, Fut, F> { /* private fields */ }

Expand description

Stream for the filter_map method.

Implementations

source

impl<St, Fut, F> FilterMap<St, Fut, F> where
 St: Stream,
 F: FnMut(St::Item) -> Fut,
 Fut: Future,

source

pub fn get_ref(&self) -> &St

Acquires a reference to the underlying sink or stream that this combinator is pulling from.

source

pub fn get_mut(&mut self) -> &mut St

Acquires a mutable reference to the underlying sink or stream that this combinator is pulling from.

Note that care must be taken to avoid tampering with the state of the sink or stream which may otherwise confuse this combinator.

source

pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St>ⓘ
Notable traits for Pin
`impl Future for Pin where P: DerefMut, ::Target: Future, type Output = <::Target as Future>::Output;`

Acquires a pinned mutable reference to the underlying sink or stream that this combinator is pulling from.

Note that care must be taken to avoid tampering with the state of the sink or stream which may otherwise confuse this combinator.

source

pub fn into_inner(self) -> St

Consumes this combinator, returning the underlying sink or stream.

Note that this may discard intermediate state of this combinator, so care should be taken to avoid losing resources when this is called.

Trait Implementations

source

impl<St, Fut, F> Debug for FilterMap<St, Fut, F> where
St: Debug,
Fut: Debug,

source

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

source

impl<St, Fut, F, T> FusedStream for FilterMap<St, Fut, F> where
 St: Stream + FusedStream,
 F: FnMut1<St::Item, Output = Fut>,
 Fut: Future<Output = Option<T>>,

source

fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.

source

impl<S, Fut, F, Item> Sink<Item> for FilterMap<S, Fut, F> where
 S: Stream + Sink<Item>,
 F: FnMut1<S::Item, Output = Fut>,
 Fut: Future,

type Error = S::Error

The type of value produced by the sink when an error occurs.

source

fn poll_ready(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>>

Attempts to prepare the Sink to receive a value. Read more

source

fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error>

Begin the process of sending a value to the sink. Each call to this function must be preceded by a successful call to poll_ready which returned Poll::Ready(Ok(())). Read more

source

fn poll_flush(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>>

Flush any remaining output from this sink. Read more

source

fn poll_close(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>>

Flush any remaining output and close this sink, if necessary. Read more

source

impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F> where
 St: Stream,
 F: FnMut1<St::Item, Output = Fut>,
 Fut: Future<Output = Option<T>>,

type Item = T

Values yielded by the stream.

source

fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted. Read more

source

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream. Read more

source

impl<'pin, St, Fut, F> Unpin for FilterMap<St, Fut, F> where
Origin<'__pin, St, Fut, F>: Unpin,

Auto Trait Implementations

impl<St, Fut, F> RefUnwindSafe for FilterMap<St, Fut, F> where
 F: RefUnwindSafe,
 Fut: RefUnwindSafe,
 St: RefUnwindSafe,

impl<St, Fut, F> Send for FilterMap<St, Fut, F> where
 F: Send,
 Fut: Send,
 St: Send,

impl<St, Fut, F> Sync for FilterMap<St, Fut, F> where
 F: Sync,
 Fut: Sync,
 St: Sync,

impl<St, Fut, F> UnwindSafe for FilterMap<St, Fut, F> where
 F: UnwindSafe,
 Fut: UnwindSafe,
 St: UnwindSafe,

Blanket Implementations

source

impl<T> Any for T where
T: 'static + ?Sized,

source

pub fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more

source

impl<T> Borrow<T> for T where
T: ?Sized,

const: unstable · source

pub fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

source

impl<T> BorrowMut<T> for T where
T: ?Sized,

const: unstable · source

pub fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

source

impl<T> From<T> for T

const: unstable · source

pub fn from(t: T) -> T

Performs the conversion.

source

impl<T, U> Into for T where
U: From<T>,

const: unstable · source

pub fn into(self) -> U

Performs the conversion.

source

impl<T, Item> SinkExt<Item> for T where
T: Sink<Item> + ?Sized,

source

fn with<U, Fut, F, E>(self, f: F) -> With<Self, Item, U, Fut, F> where
 F: FnMut(U) -> Fut,
 Fut: Future<Output = Result<Item, E>>,
 E: From<Self::Error>,
 Self: Sized,

Composes a function in front of the sink. Read more

source

fn with_flat_map<U, St, F>(self, f: F) -> WithFlatMap<Self, Item, U, St, F> where
 F: FnMut(U) -> St,
 St: Stream<Item = Result<Item, Self::Error>>,
 Self: Sized,

Composes a function in front of the sink. Read more

source

fn sink_map_err<E, F>(self, f: F) -> SinkMapErr<Self, F> where
F: FnOnce(Self::Error) -> E,
Self: Sized,

Transforms the error returned by the sink.

source

fn sink_err_into<E>(self) -> SinkErrInto<Self, Item, E> where
Self: Sized,
Self::Error: Into<E>,

Map this sink’s error to a different error type using the Into trait. Read more

source

fn buffer(self, capacity: usize) -> Buffer<Self, Item> where
Self: Sized,

Adds a fixed-size buffer to the current sink. Read more

source

fn close(&mut self) -> Close<'_, Self, Item>ⓘ
Notable traits for Close<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Close<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

Close the sink.

source

fn fanout<Si>(self, other: Si) -> Fanout<Self, Si> where
 Self: Sized,
 Item: Clone,
 Si: Sink<Item, Error = Self::Error>,

Fanout items to multiple sinks. Read more

source

fn flush(&mut self) -> Flush<'_, Self, Item>ⓘ
Notable traits for Flush<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Flush<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

Flush the sink, processing all pending items. Read more

source

fn send(&mut self, item: Item) -> Send<'_, Self, Item>ⓘ
Notable traits for Send<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Send<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

A future that completes after the given item has been fully processed into the sink, including flushing. Read more

source

fn feed(&mut self, item: Item) -> Feed<'_, Self, Item>ⓘ
Notable traits for Feed<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Feed<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

A future that completes after the given item has been received by the sink. Read more

source

fn send_all<'a, St>(&'a mut self, stream: &'a mut St) -> SendAll<'a, Self, St>ⓘ
Notable traits for SendAll<'_, Si, St>
`impl<Si, St, Ok, Error> Future for SendAll<'_, Si, St> where Si: Sink<Ok, Error = Error> + Unpin + ?Sized, St: Stream<Item = Result<Ok, Error>> + Unpin + ?Sized, type Output = Result<(), Error>;`
where
 St: TryStream<Ok = Item, Error = Self::Error> + Stream + Unpin + ?Sized,
 Self: Unpin,

A future that completes after the given stream has been fully processed into the sink, including flushing. Read more

source

fn left_sink<Si2>(self) -> Either<Self, Si2>ⓘ
Notable traits for Either<A, B>
`impl<A, B> Future for Either<A, B> where A: Future, B: Future<Output = A::Output>, type Output = A::Output;`
where
 Si2: Sink<Item, Error = Self::Error>,
 Self: Sized,

Wrap this sink in an Either sink, making it the left-hand variant of that Either. Read more

source

fn right_sink<Si1>(self) -> Either<Si1, Self>ⓘ
Notable traits for Either<A, B>
`impl<A, B> Future for Either<A, B> where A: Future, B: Future<Output = A::Output>, type Output = A::Output;`
where
 Si1: Sink<Item, Error = Self::Error>,
 Self: Sized,

Wrap this stream in an Either stream, making it the right-hand variant of that Either. Read more

source

fn poll_ready_unpin(
 &mut self,
 cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>> where
 Self: Unpin,

A convenience method for calling Sink::poll_ready on Unpin sink types. Read more

source

fn start_send_unpin(&mut self, item: Item) -> Result<(), Self::Error> where
Self: Unpin,

A convenience method for calling Sink::start_send on Unpin sink types. Read more

source

fn poll_flush_unpin(
 &mut self,
 cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>> where
 Self: Unpin,

A convenience method for calling Sink::poll_flush on Unpin sink types. Read more

source

fn poll_close_unpin(
 &mut self,
 cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>> where
 Self: Unpin,

A convenience method for calling Sink::poll_close on Unpin sink types. Read more

source

impl<T, U> TryFrom for T where
U: Into<T>,

type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

pub fn try_from(value: U) -> Result<T, <T as TryFrom>::Error>

Performs the conversion.

source

impl<T, U> TryInto for T where
U: TryFrom<T>,

type Error = >::Error

The type returned in the event of a conversion error.

const: unstable · source

pub fn try_into(self) -> Result<U, >::Error>

Performs the conversion.

source

impl<S, T, E> TryStream for S where
S: Stream<Item = Result<T, E>> + ?Sized,

type Ok = T

The type of successful values yielded by this future

type Error = E

The type of failures yielded by this future

source

pub fn try_poll_next(
self: Pin<&mut S>,
cx: &mut Context<'_>
) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>

Poll this TryStream as if it were a Stream. Read more

Struct futures_util::stream::FilterMap

Implementations

impl<St, Fut, F> FilterMap<St, Fut, F> where St: Stream, F: FnMut(St::Item) -> Fut, Fut: Future,

pub fn get_ref(&self) -> &St

pub fn get_mut(&mut self) -> &mut St

pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St>ⓘNotable traits for Pin<P>impl<P> Future for Pin<P> where P: DerefMut, <P as Deref>::Target: Future, type Output = <<P as Deref>::Target as Future>::Output;

pub fn into_inner(self) -> St

Trait Implementations

impl<St, Fut, F> Debug for FilterMap<St, Fut, F> where St: Debug, Fut: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

impl<St, Fut, F, T> FusedStream for FilterMap<St, Fut, F> where St: Stream + FusedStream, F: FnMut1<St::Item, Output = Fut>, Fut: Future<Output = Option<T>>,

fn is_terminated(&self) -> bool

impl<S, Fut, F, Item> Sink<Item> for FilterMap<S, Fut, F> where S: Stream + Sink<Item>, F: FnMut1<S::Item, Output = Fut>, Fut: Future,

type Error = S::Error

fn poll_ready( self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>

fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error>

fn poll_flush( self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>

fn poll_close( self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>

impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F> where St: Stream, F: FnMut1<St::Item, Output = Fut>, Fut: Future<Output = Option<T>>,

type Item = T

fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<'__pin, St, Fut, F> Unpin for FilterMap<St, Fut, F> where __Origin<'__pin, St, Fut, F>: Unpin,

Auto Trait Implementations

impl<St, Fut, F> RefUnwindSafe for FilterMap<St, Fut, F> where F: RefUnwindSafe, Fut: RefUnwindSafe, St: RefUnwindSafe,

impl<St, Fut, F> Send for FilterMap<St, Fut, F> where F: Send, Fut: Send, St: Send,

impl<St, Fut, F> Sync for FilterMap<St, Fut, F> where F: Sync, Fut: Sync, St: Sync,

impl<St, Fut, F> UnwindSafe for FilterMap<St, Fut, F> where F: UnwindSafe, Fut: UnwindSafe, St: UnwindSafe,

Blanket Implementations

impl<T> Any for T where T: 'static + ?Sized,

pub fn type_id(&self) -> TypeId

impl<T> Borrow<T> for T where T: ?Sized,

pub fn borrow(&self) -> &T

impl<T> BorrowMut<T> for T where T: ?Sized,

pub fn borrow_mut(&mut self) -> &mut T

impl<T> From<T> for T

pub fn from(t: T) -> T

impl<T, U> Into<U> for T where U: From<T>,

pub fn into(self) -> U

impl<T, Item> SinkExt<Item> for T where T: Sink<Item> + ?Sized,

fn with<U, Fut, F, E>(self, f: F) -> With<Self, Item, U, Fut, F> where F: FnMut(U) -> Fut, Fut: Future<Output = Result<Item, E>>, E: From<Self::Error>, Self: Sized,

fn with_flat_map<U, St, F>(self, f: F) -> WithFlatMap<Self, Item, U, St, F> where F: FnMut(U) -> St, St: Stream<Item = Result<Item, Self::Error>>, Self: Sized,

fn sink_map_err<E, F>(self, f: F) -> SinkMapErr<Self, F> where F: FnOnce(Self::Error) -> E, Self: Sized,

fn sink_err_into<E>(self) -> SinkErrInto<Self, Item, E> where Self: Sized, Self::Error: Into<E>,

fn buffer(self, capacity: usize) -> Buffer<Self, Item> where Self: Sized,

fn close(&mut self) -> Close<'_, Self, Item>ⓘNotable traits for Close<'_, Si, Item>impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Close<'_, Si, Item> type Output = Result<(), Si::Error>; where Self: Unpin,

fn fanout<Si>(self, other: Si) -> Fanout<Self, Si> where Self: Sized, Item: Clone, Si: Sink<Item, Error = Self::Error>,

fn flush(&mut self) -> Flush<'_, Self, Item>ⓘNotable traits for Flush<'_, Si, Item>impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Flush<'_, Si, Item> type Output = Result<(), Si::Error>; where Self: Unpin,

fn send(&mut self, item: Item) -> Send<'_, Self, Item>ⓘNotable traits for Send<'_, Si, Item>impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Send<'_, Si, Item> type Output = Result<(), Si::Error>; where Self: Unpin,

fn feed(&mut self, item: Item) -> Feed<'_, Self, Item>ⓘNotable traits for Feed<'_, Si, Item>impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Feed<'_, Si, Item> type Output = Result<(), Si::Error>; where Self: Unpin,

fn left_sink<Si2>(self) -> Either<Self, Si2>ⓘNotable traits for Either<A, B>impl<A, B> Future for Either<A, B> where A: Future, B: Future<Output = A::Output>, type Output = A::Output; where Si2: Sink<Item, Error = Self::Error>, Self: Sized,

fn right_sink<Si1>(self) -> Either<Si1, Self>ⓘNotable traits for Either<A, B>impl<A, B> Future for Either<A, B> where A: Future, B: Future<Output = A::Output>, type Output = A::Output; where Si1: Sink<Item, Error = Self::Error>, Self: Sized,

fn poll_ready_unpin( &mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> where Self: Unpin,

fn start_send_unpin(&mut self, item: Item) -> Result<(), Self::Error> where Self: Unpin,

fn poll_flush_unpin( &mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> where Self: Unpin,

fn poll_close_unpin( &mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> where Self: Unpin,

impl<T, U> TryFrom<U> for T where U: Into<T>,

type Error = Infallible

pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto<U> for T where U: TryFrom<T>,

type Error = <U as TryFrom<T>>::Error

pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

impl<S, T, E> TryStream for S where S: Stream<Item = Result<T, E>> + ?Sized,

type Ok = T

type Error = E

pub fn try_poll_next( self: Pin<&mut S>, cx: &mut Context<'_>) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>

impl<St, Fut, F> FilterMap<St, Fut, F> where
St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future,

pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St>ⓘ
Notable traits for Pin<P>
`impl<P> Future for Pin<P> where P: DerefMut, <P as Deref>::Target: Future, type Output = <<P as Deref>::Target as Future>::Output;`

impl<St, Fut, F> Debug for FilterMap<St, Fut, F> where
St: Debug,
Fut: Debug,

impl<St, Fut, F, T> FusedStream for FilterMap<St, Fut, F> where
St: Stream + FusedStream,
F: FnMut1<St::Item, Output = Fut>,
Fut: Future<Output = Option<T>>,

impl<S, Fut, F, Item> Sink<Item> for FilterMap<S, Fut, F> where
S: Stream + Sink<Item>,
F: FnMut1<S::Item, Output = Fut>,
Fut: Future,

fn poll_ready(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>>

fn poll_flush(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>>

fn poll_close(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>>

impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F> where
St: Stream,
F: FnMut1<St::Item, Output = Fut>,
Fut: Future<Output = Option<T>>,

impl<'pin, St, Fut, F> Unpin for FilterMap<St, Fut, F> where
Origin<'__pin, St, Fut, F>: Unpin,

impl<St, Fut, F> RefUnwindSafe for FilterMap<St, Fut, F> where
F: RefUnwindSafe,
Fut: RefUnwindSafe,
St: RefUnwindSafe,

impl<St, Fut, F> Send for FilterMap<St, Fut, F> where
F: Send,
Fut: Send,
St: Send,

impl<St, Fut, F> Sync for FilterMap<St, Fut, F> where
F: Sync,
Fut: Sync,
St: Sync,

impl<St, Fut, F> UnwindSafe for FilterMap<St, Fut, F> where
F: UnwindSafe,
Fut: UnwindSafe,
St: UnwindSafe,

impl<T> Any for T where
T: 'static + ?Sized,

impl<T> Borrow<T> for T where
T: ?Sized,

impl<T> BorrowMut<T> for T where
T: ?Sized,

impl<T, U> Into<U> for T where
U: From<T>,

impl<T, Item> SinkExt<Item> for T where
T: Sink<Item> + ?Sized,

fn with<U, Fut, F, E>(self, f: F) -> With<Self, Item, U, Fut, F> where
F: FnMut(U) -> Fut,
Fut: Future<Output = Result<Item, E>>,
E: From<Self::Error>,
Self: Sized,

fn with_flat_map<U, St, F>(self, f: F) -> WithFlatMap<Self, Item, U, St, F> where
F: FnMut(U) -> St,
St: Stream<Item = Result<Item, Self::Error>>,
Self: Sized,

fn sink_map_err<E, F>(self, f: F) -> SinkMapErr<Self, F> where
F: FnOnce(Self::Error) -> E,
Self: Sized,

fn sink_err_into<E>(self) -> SinkErrInto<Self, Item, E> where
Self: Sized,
Self::Error: Into<E>,

fn buffer(self, capacity: usize) -> Buffer<Self, Item> where
Self: Sized,

fn close(&mut self) -> Close<'_, Self, Item>ⓘ
Notable traits for Close<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Close<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

fn fanout<Si>(self, other: Si) -> Fanout<Self, Si> where
Self: Sized,
Item: Clone,
Si: Sink<Item, Error = Self::Error>,

fn flush(&mut self) -> Flush<'_, Self, Item>ⓘ
Notable traits for Flush<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Flush<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

fn send(&mut self, item: Item) -> Send<'_, Self, Item>ⓘ
Notable traits for Send<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Send<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

fn feed(&mut self, item: Item) -> Feed<'_, Self, Item>ⓘ
Notable traits for Feed<'_, Si, Item>
`impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Feed<'_, Si, Item> type Output = Result<(), Si::Error>;`
where
Self: Unpin,

fn left_sink<Si2>(self) -> Either<Self, Si2>ⓘ
Notable traits for Either<A, B>
`impl<A, B> Future for Either<A, B> where A: Future, B: Future<Output = A::Output>, type Output = A::Output;`
where
Si2: Sink<Item, Error = Self::Error>,
Self: Sized,

fn right_sink<Si1>(self) -> Either<Si1, Self>ⓘ
Notable traits for Either<A, B>
`impl<A, B> Future for Either<A, B> where A: Future, B: Future<Output = A::Output>, type Output = A::Output;`
where
Si1: Sink<Item, Error = Self::Error>,
Self: Sized,

fn poll_ready_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>> where
Self: Unpin,

fn start_send_unpin(&mut self, item: Item) -> Result<(), Self::Error> where
Self: Unpin,

fn poll_flush_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>> where
Self: Unpin,

fn poll_close_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Result<(), Self::Error>> where
Self: Unpin,

impl<T, U> TryFrom<U> for T where
U: Into<T>,

impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

impl<S, T, E> TryStream for S where
S: Stream<Item = Result<T, E>> + ?Sized,

pub fn try_poll_next(
self: Pin<&mut S>,
cx: &mut Context<'_>
) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>