Enum Poll

pub enum Poll {
    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 Poll

pub fn map(self, f: F) -> Poll

where F: FnOnce(T) -> U,

Maps a Poll to Poll 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 = Poll::Ready(2);
assert_eq!(x.is_ready(), true);

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

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

impl Poll<Result>

pub fn map_ok(self, f: F) -> Poll<Result>

where F: FnOnce(T) -> U,

Maps a Poll> to Poll> 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_>> = Poll::Ready("12".parse());
let squared = res.map_ok(|n| n * n);
assert_eq!(squared, Poll::Ready(Ok(144)));

pub fn map_err(self, f: F) -> Poll<Result>

where F: FnOnce(E) -> U,

Maps a Poll::Ready> to Poll::Ready> 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_>> = Poll::Ready("oops".parse());
let res = res.map_err(|_| 0_u8);
assert_eq!(res, Poll::Ready(Err(0)));

impl Poll<Option<Result>>

pub fn map_ok(self, f: F) -> Poll<Option<Result>>

where F: FnOnce(T) -> U,

Maps a Poll>> to Poll>> 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_>>> = 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(self, f: F) -> Poll<Option<Result>>

where F: FnOnce(E) -> U,

Maps a Poll::Ready>> to Poll::Ready>> 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_>>> = Poll::Ready(Some("oops".parse()));
let res = res.map_err(|_| 0_u8);
assert_eq!(res, Poll::Ready(Some(Err(0))));

Trait Implementations

impl Clone for Poll

where T: Clone,

fn clone(&self) -> Poll

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Poll

where T: Debug,

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

Formats the value using the given formatter.

impl From for Poll

fn from(t: T) -> Poll

Moves the value into a Poll::Ready to make a Poll.

Example

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

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

where F: From,

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

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

Constructs the type from a compatible Residual type.

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

where F: From,

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

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

Constructs the type from a compatible Residual type.

impl Hash for Poll

where T: Hash,

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

where __H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Poll

where T: Ord,

fn cmp(&self, other: &Poll) -> 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 clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Poll

where T: PartialEq,

fn eq(&self, other: &Poll) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for Poll

where T: PartialOrd,

fn partial_cmp(&self, other: &Poll) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Try for Poll<Option<Result>>

type Output = Poll<Option>

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

The type of the value produced by ? when not short-circuiting.

type Residual = Result<Infallible, E>

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

The type of the value passed to FromResidual::from_residual as part of ? when short-circuiting.

fn from_output( c: <Poll<Option<Result>> as Try>::Output, ) -> Poll<Option<Result>>

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

Constructs the type from its Output type.

fn branch( self, ) -> ControlFlow<<Poll<Option<Result>> as Try>::Residual, <Poll<Option<Result>> as Try>::Output>

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

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).

impl Try for Poll<Result>

type Output = Poll

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

The type of the value produced by ? when not short-circuiting.

type Residual = Result<Infallible, E>

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

The type of the value passed to FromResidual::from_residual as part of ? when short-circuiting.

fn from_output(c: <Poll<Result> as Try>::Output) -> Poll<Result>

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

Constructs the type from its Output type.

fn branch( self, ) -> ControlFlow<<Poll<Result> as Try>::Residual, <Poll<Result> as Try>::Output>

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

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).

impl Copy for Poll

where T: Copy,

impl Eq for Poll

where T: Eq,

impl StructuralPartialEq for Poll