Enum core::task::Poll

1.36.0 · source ·
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.

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Ready(T)

Represents that a value is immediately ready.

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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§

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impl<T> Poll<T>

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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));
Run
const: 1.49.0 · source

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);
Run
const: 1.49.0 · source

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);
Run
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impl<T, E> Poll<Result<T, E>>

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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)));
Run
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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)));
Run
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impl<T, E> Poll<Option<Result<T, E>>>

1.51.0 · source

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))));
Run
1.51.0 · source

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))));
Run

Trait Implementations§

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impl<T: Clone> Clone for Poll<T>

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

Returns a copy of the value. Read more
1.0.0 · source§

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

Performs copy-assignment from source. Read more
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impl<T: Debug> Debug for Poll<T>

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

Formats the value using the given formatter. Read more
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impl<T> From<T> for Poll<T>

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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));
Run
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impl<T, E, F: From<E>> FromResidual<Result<Infallible, E>> for Poll<Option<Result<T, F>>>

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

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from a compatible Residual type. Read more
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impl<T, E, F: From<E>> FromResidual<Result<Infallible, E>> for Poll<Result<T, F>>

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

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from a compatible Residual type. Read more
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impl<T: Hash> Hash for Poll<T>

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

Feeds this value into the given Hasher. Read more
1.3.0 · source§

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

Feeds a slice of this type into the given Hasher. Read more
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impl<T: Ord> Ord for Poll<T>

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

This method returns an Ordering between self and other. Read more
1.21.0 · source§

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

Compares and returns the maximum of two values. Read more
1.21.0 · source§

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

Compares and returns the minimum of two values. Read more
1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl<T: PartialEq> PartialEq for Poll<T>

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

This method tests for self and other values to be equal, and is used by ==.
1.0.0 · source§

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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<T: PartialOrd> PartialOrd for Poll<T>

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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 · source§

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 · source§

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
1.0.0 · source§

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

This method tests greater than (for self and other) and is used by the > operator. Read more
1.0.0 · source§

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

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl<T, E> Try for Poll<Option<Result<T, E>>>

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type Output = Poll<Option<T>>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
The type of the value produced by ? when not short-circuiting.
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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. Read more
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fn from_output(c: Self::Output) -> Self

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from its Output type. Read more
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fn branch(self) -> ControlFlow<Self::Residual, Self::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). Read more
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impl<T, E> Try for Poll<Result<T, E>>

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type Output = Poll<T>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
The type of the value produced by ? when not short-circuiting.
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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. Read more
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fn from_output(c: Self::Output) -> Self

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from its Output type. Read more
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fn branch(self) -> ControlFlow<Self::Residual, Self::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). Read more
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impl<T: Copy> Copy for Poll<T>

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impl<T: Eq> Eq for Poll<T>

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impl<T> StructuralPartialEq for Poll<T>

Auto Trait Implementations§

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impl<T> Freeze for Poll<T>
where T: Freeze,

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impl<T> RefUnwindSafe for Poll<T>
where T: RefUnwindSafe,

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impl<T> Send for Poll<T>
where T: Send,

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impl<T> Sync for Poll<T>
where T: Sync,

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impl<T> Unpin for Poll<T>
where T: Unpin,

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impl<T> UnwindSafe for Poll<T>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<!> for T

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fn from(t: !) -> T

Converts to this type from the input type.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.