Struct async_std::task::LocalKey

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pub struct LocalKey<T: Send + 'static> { /* private fields */ }
Expand description

The key for accessing a task-local value.

Every task-local value is lazily initialized on first access and destroyed when the task completes.

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impl<T: Send + 'static> LocalKey<T>

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pub fn with<F, R>(&'static self, f: F) -> R
where F: FnOnce(&T) -> R,

Gets a reference to the task-local value with this key.

The passed closure receives a reference to the task-local value.

The task-local value will be lazily initialized if this task has not accessed it before.

Panics

This function will panic if not called within the context of a task created by block_on, spawn, or Builder::spawn.

Examples
use std::cell::Cell;

use async_std::task;
use async_std::prelude::*;

task_local! {
    static NUMBER: Cell<u32> = Cell::new(5);
}

task::block_on(async {
    let v = NUMBER.with(|c| c.get());
    assert_eq!(v, 5);
});
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pub fn try_with<F, R>(&'static self, f: F) -> Result<R, AccessError>
where F: FnOnce(&T) -> R,

Attempts to get a reference to the task-local value with this key.

The passed closure receives a reference to the task-local value.

The task-local value will be lazily initialized if this task has not accessed it before.

This function returns an error if not called within the context of a task created by block_on, spawn, or Builder::spawn.

Examples
use std::cell::Cell;

use async_std::task;
use async_std::prelude::*;

task_local! {
    static VAL: Cell<u32> = Cell::new(5);
}

task::block_on(async {
    let v = VAL.try_with(|c| c.get());
    assert_eq!(v, Ok(5));
});

// Returns an error because not called within the context of a task.
assert!(VAL.try_with(|c| c.get()).is_err());

Trait Implementations§

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impl<T: Debug + Send + 'static> Debug for LocalKey<T>

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

Formats the value using the given formatter. Read more

Auto Trait Implementations§

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impl<T> RefUnwindSafe for LocalKey<T>

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impl<T> Send for LocalKey<T>

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impl<T> Sync for LocalKey<T>

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impl<T> Unpin for LocalKey<T>

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impl<T> UnwindSafe for LocalKey<T>

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<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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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.
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more