| commit | da042a5f4242e7db6b8dcaddaf05990864cdd94c | [log] [tgz] |
|---|---|---|
| author | Andrew Walbran <qwandor@google.com> | Tue Nov 14 21:14:08 2023 +0000 |
| committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Tue Nov 14 21:14:08 2023 +0000 |
| tree | f1e300fd061c117d42ca0da249952f2a1ba267b2 | |
| parent | b0ae71bae69401bec5f7aaec19c710e6d599fe95 [diff] | |
| parent | f247c77237c0eb82732b03df964b325e582412a4 [diff] |
Migrate to cargo_embargo. am: 73154adc13 am: 37994c7b5f am: f247c77237 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/2828068 Change-Id: I91cf63d10287ad17d2f3a81ec3e224cdb2121408 Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
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.