| commit | 363b365d1cd84c9a3003f5651e10fecfacbc9744 | [log] [tgz] |
|---|---|---|
| author | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Fri Nov 10 00:12:30 2023 +0000 |
| committer | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Fri Nov 10 00:12:30 2023 +0000 |
| tree | b621ef37e2474482f8371237f834d10624eb3c92 | |
| parent | 26726305b6523555bdea35c8f61275e783ea635d [diff] | |
| parent | 28bb8772535dba79a7d40d288458b500657f129e [diff] |
Snap for 11078623 from 28bb8772535dba79a7d40d288458b500657f129e to 24Q1-release Change-Id: Ibafedffb7df84a948daa103b37f5d0b06ccf2a56
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.