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>
pub fn ready(self) -> Ready<T>
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
Constructs the type from a compatible Residual
type. Read more
sourceimpl<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
Constructs the type from a compatible Residual
type. Read more
sourceimpl<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
Constructs the type from a compatible Residual
type. Read more
sourceimpl<T: Ord> Ord for Poll<T>
impl<T: Ord> Ord for Poll<T>
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>
This method returns an ordering between self
and other
values if one exists. Read more
1.0.0 · sourcefn lt(&self, other: &Rhs) -> bool
fn lt(&self, other: &Rhs) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
1.0.0 · sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
sourceimpl<T, E> Try for Poll<Result<T, E>>
impl<T, E> Try for Poll<Result<T, E>>
type Residual = Result<Infallible, E>
type Residual = Result<Infallible, E>
The type of the value passed to FromResidual::from_residual
as part of ?
when short-circuiting. Read more
sourcefn branch(self) -> ControlFlow<Self::Residual, Self::Output>
fn branch(self) -> ControlFlow<Self::Residual, Self::Output>
Used in ?
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
sourceimpl<T, E> Try for Poll<Option<Result<T, E>>>
impl<T, E> Try for Poll<Option<Result<T, E>>>
type Residual = Result<Infallible, E>
type Residual = Result<Infallible, E>
The type of the value passed to FromResidual::from_residual
as part of ?
when short-circuiting. Read more
sourcefn branch(self) -> ControlFlow<Self::Residual, Self::Output>
fn branch(self) -> ControlFlow<Self::Residual, Self::Output>
Used in ?
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
impl<T: Copy> Copy for Poll<T>
impl<T: Eq> Eq for Poll<T>
impl<T> StructuralEq for Poll<T>
impl<T> StructuralPartialEq for Poll<T>
Auto Trait Implementations
impl<T> RefUnwindSafe for Poll<T> where
T: RefUnwindSafe,
impl<T> Send for Poll<T> where
T: Send,
impl<T> Sync for Poll<T> where
T: Sync,
impl<T> Unpin for Poll<T> where
T: Unpin,
impl<T> UnwindSafe for Poll<T> where
T: UnwindSafe,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more