Struct SinkPrepareSendFuture 

pub struct SinkPrepareSendFuture<'w, IF, OS, OM> {
    generator: IF,
    output: Option<Pin<&'w mut OS>>,
    tw: PhantomData<fn(OM)>,
}

Future for SinkPrepareExt::prepare_send_from

Fields

generator: IF

Underlying future that will yield a message.

output: Option<Pin<&'w mut OS>>

This Option exists because otherwise SinkPrepareSendFuture::poll() can’t move output out of this struct to put it into the SinkSendable. (The poll() impl cannot borrow from SinkPrepareSendFuture.)

tw: PhantomData<fn(OM)>

fn(OM) gives contravariance in OM.

Variance is confusing. Loosely, a SinkPrepareSendFuture<..OM> consumes an OM. Actually, we don’t really need to add any variance restricions wrt OM, because the &mut OS already implies the correct variance, so we could have used the PhantomData<fn(*const OM)> trick. Happily there is no unsafe anywhere nearby, so it is not possible for us to write a bug due to getting the variance wrong - only to erroneously prevent some use case.

Implementations

impl<'w, IF, OS, OM> SinkPrepareSendFuture<'w, IF, OS, OM>

pub(crate) fn project<'pin>( self: Pin<&'pin mut Self>, ) -> __SinkPrepareSendFutureProjection<'pin, 'w, IF, OS, OM>

pub(crate) fn project_ref<'pin>( self: Pin<&'pin Self>, ) -> __SinkPrepareSendFutureProjectionRef<'pin, 'w, IF, OS, OM>

Trait Implementations

impl<'w, IF, OS, IM, OM> FusedFuture for SinkPrepareSendFuture<'w, IF, OS, OM>

where IF: Future<Output = IM>, OS: Sink<OM>,

fn is_terminated(&self) -> bool

Returns true if the underlying future should no longer be polled.

impl<'w, IF, OS, IM, OM> Future for SinkPrepareSendFuture<'w, IF, OS, OM>

where IF: Future<Output = IM>, OS: Sink<OM>,

type Output = Result<(IM, SinkSendable<'w, OS, OM>), <OS as Sink<OM>>::Error>

The type of value produced on completion.

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

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

impl<'pin, 'w, IF, OS, OM> Unpin for SinkPrepareSendFuture<'w, IF, OS, OM>

where PinnedFieldsOf<__SinkPrepareSendFuture<'pin, 'w, IF, OS, OM>>: Unpin,