Enum std::task::Poll  1.36.0[−][src]
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
Represents that a value is immediately ready.
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
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));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);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(())
}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)));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)));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))));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))));Trait Implementations
impl<T, E, F> FromResidual<Result<Infallible, E>> for Poll<Option<Result<T, F>>> where
    F: From<E>, 
impl<T, E, F> FromResidual<Result<Infallible, E>> for Poll<Option<Result<T, F>>> where
    F: From<E>, 
This method returns an ordering between self and other values if one exists. Read more
This method tests less than (for self and other) and is used by the < operator. Read more
This method tests less than or equal to (for self and other) and is used by the <=
operator. Read more
This method tests greater than (for self and other) and is used by the > operator. Read more
The type of the value produced by ? when not short-circuiting.
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
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
The type of the value produced by ? when not short-circuiting.
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
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
Auto Trait Implementations
impl<T> RefUnwindSafe for Poll<T> where
    T: RefUnwindSafe, 
impl<T> UnwindSafe for Poll<T> where
    T: UnwindSafe, 
Blanket Implementations
Mutably borrows from an owned value. Read more