commit | a120c7727cbd37fbae8c169fec15acc52d35bb2a | [log] [tgz] |
---|---|---|
author | Chih-Hung Hsieh <chh@google.com> | Thu Aug 27 21:50:20 2020 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Thu Aug 27 21:50:20 2020 +0000 |
tree | a00ac2c58618eb65bab63f2afe07b988c597f851 | |
parent | 88b284f5679892688294af2e256c19d6f8b3e1b7 [diff] | |
parent | 9ef30f242153815c960919484686d1cb67f7cade [diff] |
Fix once_cell/METADATA am: 9ef30f2421 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1414091 Change-Id: I15cb13f743cad083d3f5c00c10f0300e074544df
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
.