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.
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§
source§impl<T> Poll<T>
impl<T> Poll<T>
1.36.0 · 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));
1.36.0 (const: 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);
1.36.0 (const: 1.49.0) · sourcepub const fn is_pending(&self) -> bool
pub const fn is_pending(&self) -> bool
source§impl<T, E> Poll<Result<T, E>>
impl<T, E> Poll<Result<T, E>>
1.36.0 · 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)));
1.36.0 · sourcepub 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)));
source§impl<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))));
1.51.0 · 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))));
Trait Implementations§
source§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>,
source§fn from_residual(x: Result<Infallible, E>) -> Poll<Option<Result<T, F>>>
fn from_residual(x: Result<Infallible, E>) -> Poll<Option<Result<T, F>>>
try_trait_v2
#84277)Residual
type. Read moresource§impl<T, E, F> FromResidual<Result<Infallible, E>> for Poll<Result<T, F>>where
F: From<E>,
impl<T, E, F> FromResidual<Result<Infallible, E>> for Poll<Result<T, F>>where
F: From<E>,
source§fn from_residual(x: Result<Infallible, E>) -> Poll<Result<T, F>>
fn from_residual(x: Result<Infallible, E>) -> Poll<Result<T, F>>
try_trait_v2
#84277)Residual
type. Read more1.36.0 · source§impl<T> Ord for Poll<T>where
T: Ord,
impl<T> Ord for Poll<T>where
T: Ord,
1.36.0 · source§impl<T> PartialOrd for Poll<T>where
T: PartialOrd,
impl<T> PartialOrd for Poll<T>where
T: PartialOrd,
source§impl<T, E> Try for Poll<Option<Result<T, E>>>
impl<T, E> Try for Poll<Option<Result<T, E>>>
source§type Output = Poll<Option<T>>
type Output = Poll<Option<T>>
try_trait_v2
#84277)?
when not short-circuiting.source§type Residual = Result<Infallible, E>
type Residual = Result<Infallible, E>
try_trait_v2
#84277)FromResidual::from_residual
as part of ?
when short-circuiting. Read moresource§fn from_output(
c: <Poll<Option<Result<T, E>>> as Try>::Output,
) -> Poll<Option<Result<T, E>>>
fn from_output( c: <Poll<Option<Result<T, E>>> as Try>::Output, ) -> Poll<Option<Result<T, E>>>
try_trait_v2
#84277)Output
type. Read moresource§fn branch(
self,
) -> ControlFlow<<Poll<Option<Result<T, E>>> as Try>::Residual, <Poll<Option<Result<T, E>>> as Try>::Output>
fn branch( self, ) -> ControlFlow<<Poll<Option<Result<T, E>>> as Try>::Residual, <Poll<Option<Result<T, E>>> as Try>::Output>
try_trait_v2
#84277)?
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 moresource§impl<T, E> Try for Poll<Result<T, E>>
impl<T, E> Try for Poll<Result<T, E>>
source§type Output = Poll<T>
type Output = Poll<T>
try_trait_v2
#84277)?
when not short-circuiting.source§type Residual = Result<Infallible, E>
type Residual = Result<Infallible, E>
try_trait_v2
#84277)FromResidual::from_residual
as part of ?
when short-circuiting. Read moresource§fn from_output(c: <Poll<Result<T, E>> as Try>::Output) -> Poll<Result<T, E>>
fn from_output(c: <Poll<Result<T, E>> as Try>::Output) -> Poll<Result<T, E>>
try_trait_v2
#84277)Output
type. Read moresource§fn branch(
self,
) -> ControlFlow<<Poll<Result<T, E>> as Try>::Residual, <Poll<Result<T, E>> as Try>::Output>
fn branch( self, ) -> ControlFlow<<Poll<Result<T, E>> as Try>::Residual, <Poll<Result<T, E>> as Try>::Output>
try_trait_v2
#84277)?
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