| commit | 80c59ac8477ecb18e8bfc90c48ce0dc48d276cd3 | [log] [tgz] |
|---|---|---|
| author | James Farrell <[email protected]> | Wed Oct 02 20:16:13 2024 +0000 |
| committer | James Farrell <[email protected]> | Thu Oct 03 13:55:53 2024 +0000 |
| tree | f8b11118509ae3d41f4488a338c46e239c2fe4a6 | |
| parent | 9c15afceb798848f21a8cf95d1caeab108d060a4 [diff] |
Migrate once_cell to monorepo. Bug: http://b/339424309 Test: treehugger Change-Id: I8280cb66852542ba85eccddb9f3f94d83e7499f5
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.