commit | 98d15465566ebb4279151a33bcf22568f8388b94 | [log] [tgz] |
---|---|---|
author | Linux Build Service Account <lnxbuild@localhost> | Sun Jan 16 14:30:26 2022 -0800 |
committer | Linux Build Service Account <lnxbuild@localhost> | Sun Jan 16 14:30:26 2022 -0800 |
tree | 71c77aba563c644c5294b9326b518692929b3d44 | |
parent | 1c715c05305ed9808d6f1cc7b7fc9c0da1ad2167 [diff] | |
parent | 9f155ef74fad315279f3a4221c810786fc21bb4c [diff] |
Merge 9f155ef74fad315279f3a4221c810786fc21bb4c on remote branch Change-Id: Ieaaf7cd1efa081b6f365a325a6d27f4f8f495135
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()); }
More patterns and use-cases are in the docs!
The API of once_cell
is being proposed for inclusion in std
.