Struct Optional 

pub struct Optional<T> { /* private fields */ }

A reusable future or stream based on Option.

By default, Optional will be empty, similar to Option::None, which would return Poll::Pending when polled, but if a Future or Stream is supplied either upon construction via Optional::new or is set via Optional::replace, it would then be polled once Optional is polled. Once the future is polled to completion, the results will be returned, with Optional being empty.

Implementations

impl<T> Optional<T>

pub fn new(task: T) -> Self

Construct a new Optional with an existing Future or Stream.

pub fn with_future(future: T) -> Self

where T: Future,

Construct a new Optional with an existing Future.

pub fn with_stream(stream: T) -> Self

where T: Stream,

Construct a new Optional with an existing Stream.

pub fn take(&mut self) -> Option<T>

Takes the future or stream out, leaving the Optional empty.

pub fn is_some(&self) -> bool

Returns true if the future or stream still exist.

pub fn is_none(&self) -> bool

Returns false if the future or stream doesn’t exist or has been completed.

pub fn as_ref(&self) -> Option<&T>

Returns reference of the future or stream.

pub fn as_mut(&mut self) -> Option<&mut T>

Returns mutable reference of the future or stream.

pub fn replace(&mut self, task: T) -> Option<T>

Replaces the current the future or stream with a new one, returning the previous value if present.

pub fn set(self: Pin<&mut Self>, task: T)

Replaces the current future or stream in place without moving the previous value.

pub fn as_pin_mut(&mut self) -> Option<Pin<&mut T>>

where T: Unpin,

Returns a constructed Option<Pin<&mut T>>.

pub fn pinned_as_mut(self: Pin<&mut Self>) -> Option<Pin<&mut T>>

Return a constructed Option<Pin<&mut T>>.

pub fn as_pin_ref(&self) -> Option<Pin<&T>>

where T: Unpin,

Returns a constructed Option<Pin<&T>>.

pub fn pinned_as_ref(self: Pin<&Self>) -> Option<Pin<&T>>

Return a constructed Option<Pin<&T>>.

Trait Implementations

impl<T> Default for Optional<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> From<Option<T>> for Optional<T>

fn from(task: Option<T>) -> Self

Converts to this type from the input type.

impl<T> From<T> for Optional<T>

fn from(fut: T) -> Self

Converts to this type from the input type.

impl<F> FusedFuture for Optional<F>

where F: Future,

fn is_terminated(&self) -> bool

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

impl<S> FusedStream for Optional<S>

where S: Stream,

fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.

impl<F> Future for Optional<F>

where F: Future,

type Output = <F as Future>::Output

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<S> Stream for Optional<S>

where S: Stream,

type Item = <S as Stream>::Item

Values yielded by the stream.

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Option<Self::Item>>

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.

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

Returns the bounds on the remaining length of the stream.

impl<'pin, T> Unpin for Optional<T>

where PinnedFieldsOf<__Optional<'pin, T>>: Unpin,