Enum Poll 

pub enum Poll<T> {
    Ready(T),
    Pending,
}

Indicates whether a value is available or if the current task has been scheduled to receive a wakeup instead.

This is returned by Future::poll.

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

impl<T> Poll<T>

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));

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);

pub const fn is_pending(&self) -> bool

Returns true if the poll is a Pending value.

Examples

let x: Poll<u32> = Poll::Ready(2);
assert_eq!(x.is_pending(), false);

let x: Poll<u32> = Poll::Pending;
assert_eq!(x.is_pending(), true);

impl<T, E> Poll<Result<T, E>>

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)));

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, U>> 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)));

impl<T, E> Poll<Option<Result<T, E>>>

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))));

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))));

Trait Implementations

impl<T> Clone for Poll<T>

where T: Clone,

fn clone(&self) -> Poll<T>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Copy for Poll<T>

where T: Copy,

impl<T> Debug for Poll<T>

where T: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> Eq for Poll<T>

where T: Eq,

impl<T> From<T> for Poll<T>

fn from(t: T) -> Poll<T>

Moves the value into a Poll::Ready to make a Poll<T>.

Example

assert_eq!(Poll::from(true), Poll::Ready(true));

impl<T, E, F> FromResidual<Result<Infallible, E>> for Poll<Result<T, F>>

where F: From<E>,

fn from_residual(x: Result<Infallible, E>) -> Poll<Result<T, F>>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)

Constructs the type from a compatible Residual type.

impl<T, E, F> FromResidual<Result<Infallible, E>> for Poll<Option<Result<T, F>>>

where F: From<E>,

fn from_residual(x: Result<Infallible, E>) -> Poll<Option<Result<T, F>>>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)

Constructs the type from a compatible Residual type.

impl<T> Hash for Poll<T>

where T: Hash,

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T> Ord for Poll<T>

where T: Ord,

fn cmp(&self, other: &Poll<T>) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn