| commit | 1b2ea50fdcdeca62f23ac071631fdb6ac16c6953 | [log] [tgz] |
|---|---|---|
| author | Joel Galenson <[email protected]> | Wed Apr 28 22:32:38 2021 +0000 |
| committer | Automerger Merge Worker <[email protected]> | Wed Apr 28 22:32:38 2021 +0000 |
| tree | 71c77aba563c644c5294b9326b518692929b3d44 | |
| parent | a83ad720f60bf2d21b6b53e1caab6157071abb40 [diff] | |
| parent | 9bd447a74807cab224ff3d39cb07d45cbcf6d2f6 [diff] |
Merge "Generate apex_available from c2a instead of a patch" am: c4379c47f7 am: c46660d000 am: ab28830577 am: 9bd447a748 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1689909 Change-Id: I7443f122caf8aa1380fb19c6fe96aa7434c5940e
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.