LocalKey in async_std::task - Rust (original) (raw)

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.

Source §

Source

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 byblock_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);
});

Source

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 byblock_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());