oc
once_cell
cargo install once_cell
oc

once_cell

Rust library for single assignment cells and lazy statics without macros

by Aleksey Kladov

1.13.1 (see all)License:MIT OR Apache-2.0
cargo install once_cell
Readme

once_cell

Build Status Crates.io API reference

Overview

once_cell provides two new cell-like types, unsync::OnceCell and sync::OnceCell. OnceCell might store arbitrary non-Copy types, can be assigned to at most once and provide direct access to the stored contents. In a nutshell, API looks roughly like this:

impl OnceCell<T> {
    fn new() -> OnceCell<T> { ... }
    fn set(&self, value: T) -> Result<(), T> { ... }
    fn get(&self) -> Option<&T> { ... }
}

Note that, like with RefCell and Mutex, the set method requires only a shared reference. Because of the single assignment restriction get can return an &T instead of Ref<T> or MutexGuard<T>.

once_cell also has a Lazy<T> type, build on top of OnceCell which provides the same API as the lazy_static! macro, but without using any macros:

use std::{sync::Mutex, collections::HashMap};
use once_cell::sync::Lazy;


static GLOBAL_DATA: Lazy<Mutex<HashMap<i32, String>>> = Lazy::new(|| {
let mut m = HashMap::new();
m.insert(13, "Spica".to_string());
m.insert(74, "Hoyten".to_string());
Mutex::new(m)
});




fn main() {
println!("{:?}", GLOBAL_DATA.lock().unwrap());
}

fn main() { println!("{:?}", GLOBAL_DATA.lock().unwrap()); }

More patterns and use-cases are in the docs!

Related crates

The API of once_cell is being proposed for inclusion in std.

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1.13.1
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1.13.0
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1.12.1
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