commit | 9bd447a74807cab224ff3d39cb07d45cbcf6d2f6 | [log] [tgz] |
---|---|---|
author | Joel Galenson <jgalenson@google.com> | Wed Apr 28 22:10:41 2021 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Wed Apr 28 22:10:41 2021 +0000 |
tree | 71c77aba563c644c5294b9326b518692929b3d44 | |
parent | 5c4dc3f8a058d627249f5854a6bab5bea53779bc [diff] | |
parent | ab288305778efaf40b4f396dd8a2e6df091bd152 [diff] |
Merge "Generate apex_available from c2a instead of a patch" am: c4379c47f7 am: c46660d000 am: ab28830577 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1689909 Change-Id: I10cd90bace17191e942c9e2cf3a12b602c6c7e52
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
.