pub enum Poll<T> {
Ready(T),
Pending,
}
Expand description
Indicates whether a value is available or if the current task has been scheduled to receive a wakeup instead.
Variants
Ready(T)
Represents that a value is immediately ready.
Pending
Represents that a value is not ready yet.
When a function returns Pending
, the function must also
ensure that the current task is scheduled to be awoken when
progress can be made.
Implementations
sourceimpl<T> Poll<T>
impl<T> Poll<T>
sourcepub fn map<U, F>(self, f: F) -> Poll<U>where
F: FnOnce(T) -> U,
pub fn map<U, F>(self, f: F) -> Poll<U>where
F: FnOnce(T) -> U,
Maps a Poll<T>
to Poll<U>
by applying a function to a contained value.
Examples
Converts a Poll<String>
into a Poll<usize>
, consuming
the original:
let poll_some_string = Poll::Ready(String::from("Hello, World!"));
// `Poll::map` takes self *by value*, consuming `poll_some_string`
let poll_some_len = poll_some_string.map(|s| s.len());
assert_eq!(poll_some_len, Poll::Ready(13));
Runconst: 1.49.0 · sourcepub const fn is_ready(&self) -> bool
pub const fn is_ready(&self) -> bool
Returns true
if the poll is a Poll::Ready
value.
Examples
let x: Poll<u32> = Poll::Ready(2);
assert_eq!(x.is_ready(), true);
let x: Poll<u32> = Poll::Pending;
assert_eq!(x.is_ready(), false);
Runconst: 1.49.0 · sourcepub const fn is_pending(&self) -> bool
pub const fn is_pending(&self) -> bool
sourcepub fn ready(self) -> Ready<T>
🔬This is a nightly-only experimental API. (poll_ready
#89780)
pub fn ready(self) -> Ready<T>
poll_ready
#89780)Extracts the successful type of a Poll<T>
.
When combined with the ?
operator, this function will
propagate any Poll::Pending
values to the caller, and
extract the T
from Poll::Ready
.
Examples
#![feature(poll_ready)]
use std::task::{Context, Poll};
use std::future::{self, Future};
use std::pin::Pin;
pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
let mut fut = future::ready(42);
let fut = Pin::new(&mut fut);
let num = fut.poll(cx).ready()?;
// ... use num
Poll::Ready(())
}
Runsourceimpl<T, E> Poll<Result<T, E>>
impl<T, E> Poll<Result<T, E>>
sourcepub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>where
F: FnOnce(T) -> U,
pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>where
F: FnOnce(T) -> U,
Maps a Poll<Result<T, E>>
to Poll<Result<U, E>>
by applying a
function to a contained Poll::Ready(Ok)
value, leaving all other
variants untouched.
This function can be used to compose the results of two functions.
Examples
let res: Poll<Result<u8, _>> = Poll::Ready("12".parse());
let squared = res.map_ok(|n| n * n);
assert_eq!(squared, Poll::Ready(Ok(144)));
Runsourcepub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>where
F: FnOnce(E) -> U,
pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>where
F: FnOnce(E) -> U,
Maps a Poll::Ready<Result<T, E>>
to Poll::Ready<Result<T, F>>
by
applying a function to a contained Poll::Ready(Err)
value, leaving all other
variants untouched.
This function can be used to pass through a successful result while handling an error.
Examples
let res: Poll<Result<u8, _>> = Poll::Ready("oops".parse());
let res = res.map_err(|_| 0_u8);
assert_eq!(res, Poll::Ready(Err(0)));
Runsourceimpl<T, E> Poll<Option<Result<T, E>>>
impl<T, E> Poll<Option<Result<T, E>>>
1.51.0 · sourcepub fn map_ok<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>where
F: FnOnce(T) -> U,
pub fn map_ok<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>where
F: FnOnce(T) -> U,
Maps a Poll<Option<Result<T, E>>>
to Poll<Option<Result<U, E>>>
by
applying a function to a contained Poll::Ready(Some(Ok))
value,
leaving all other variants untouched.
This function can be used to compose the results of two functions.
Examples
let res: Poll<Option<Result<u8, _>>> = Poll::Ready(Some("12".parse()));
let squared = res.map_ok(|n| n * n);
assert_eq!(squared, Poll::Ready(Some(Ok(144))));
Run1.51.0 · sourcepub fn map_err<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>where
F: FnOnce(E) -> U,
pub fn map_err<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>where
F: FnOnce(E) -> U,
Maps a Poll::Ready<Option<Result<T, E>>>
to
Poll::Ready<Option<Result<T, F>>>
by applying a function to a
contained Poll::Ready(Some(Err))
value, leaving all other variants
untouched.
This function can be used to pass through a successful result while handling an error.
Examples
let res: Poll<Option<Result<u8, _>>> = Poll::Ready(Some("oops".parse()));
let res = res.map_err(|_| 0_u8);
assert_eq!(res, Poll::Ready(Some(Err(0))));
RunTrait Implementations
sourceimpl<T> FromResidual<Ready<Infallible>> for Poll<T>
impl<T> FromResidual<Ready<Infallible>> for Poll<T>
sourcefn from_residual(residual: Ready<Infallible>) -> Self
fn from_residual(residual: Ready<Infallible>) -> Self
try_trait_v2
#84277)Residual
type. Read moresourceimpl<T, E, F: From<E>> FromResidual<Result<Infallible, E>> for Poll<Option<Result<T, F>>>
impl<T, E, F: From<E>> FromResidual<Result<Infallible, E>> for Poll<Option<Result<T, F>>>
sourcefn from_residual(x: Result<Infallible, E>) -> Self
fn from_residual(x: Result<Infallible, E>) -> Self
try_trait_v2
#84277)Residual
type. Read moresourceimpl<T, E, F: From<E>> FromResidual<Result<Infallible, E>> for Poll<Result<T, F>>
impl<T, E, F: From<E>> FromResidual<Result<Infallible, E>> for Poll<Result<T, F>>
sourcefn from_residual(x: Result<Infallible, E>) -> Self
fn from_residual(x: Result<Infallible, E>) -> Self
try_trait_v2
#84277)Residual
type. Read moresourceimpl<T: Ord> Ord for Poll<T>
impl<T: Ord> Ord for Poll<T>
1.21.0 · sourcefn max(self, other: Self) -> Selfwhere
Self: Sized,
fn max(self, other: Self) -> Selfwhere
Self: Sized,
1.21.0 · sourcefn min(self, other: Self) -> Selfwhere
Self: Sized,
fn min(self, other: Self) -> Selfwhere
Self: Sized,
1.50.0 · sourcefn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized,
Self: PartialOrd,
fn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized,
Self: PartialOrd,
sourceimpl<T: PartialOrd> PartialOrd<Poll<T>> for Poll<T>
impl<T: PartialOrd> PartialOrd<Poll<T>> for Poll<T>
sourcefn partial_cmp(&self, other: &Poll<T>) -> Option<Ordering>
fn partial_cmp(&self, other: &Poll<T>) -> Option<Ordering>
1.0.0 · sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
self
and other
) and is used by the <=
operator. Read moresourceimpl<T, E> Try for Poll<Option<Result<T, E>>>
impl<T, E> Try for Poll<Option<Result<T, E>>>
type Output = Poll<Option<T>>
type Output = Poll<Option<T>>
try_trait_v2
#84277)?
when not short-circuiting.type Residual = Result<Infallible, E>
type Residual = Result<Infallible, E>
try_trait_v2
#84277)FromResidual::from_residual
as part of ?
when short-circuiting. Read moresourcefn from_output(c: Self::Output) -> Self
fn from_output(c: Self::Output) -> Self
try_trait_v2
#84277)Output
type. Read moresourcefn branch(self) -> ControlFlow<Self::Residual, Self::Output>
fn branch(self) -> ControlFlow<Self::Residual, Self::Output>
try_trait_v2
#84277)?
to decide whether the operator should produce a value
(because this returned ControlFlow::Continue
)
or propagate a value back to the caller
(because this returned ControlFlow::Break
). Read moresourceimpl<T, E> Try for Poll<Result<T, E>>
impl<T, E> Try for Poll<Result<T, E>>
type Output = Poll<T>
type Output = Poll<T>
try_trait_v2
#84277)?
when not short-circuiting.type Residual = Result<Infallible, E>
type Residual = Result<Infallible, E>
try_trait_v2
#84277)FromResidual::from_residual
as part of ?
when short-circuiting. Read moresourcefn from_output(c: Self::Output) -> Self
fn from_output(c: Self::Output) -> Self
try_trait_v2
#84277)Output
type. Read moresourcefn branch(self) -> ControlFlow<Self::Residual, Self::Output>
fn branch(self) -> ControlFlow<Self::Residual, Self::Output>
try_trait_v2
#84277)?
to decide whether the operator should produce a value
(because this returned ControlFlow::Continue
)
or propagate a value back to the caller
(because this returned ControlFlow::Break
). Read more