commit | 31616b183e925c3ef053ec0ee7539933bcf2e83a | [log] [tgz] |
---|---|---|
author | Joel Galenson <jgalenson@google.com> | Wed Dec 15 17:27:32 2021 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Wed Dec 15 17:27:32 2021 +0000 |
tree | 387d576f6e5993d9419eed22dbf201caae8baf19 | |
parent | fc1cd6abed6c4840028565832ff515d1de180dab [diff] | |
parent | 1396f279d0828f9ff501b0c018fe073b51be0426 [diff] |
Merge "Refresh Android.bp, cargo2android.json, TEST_MAPPING." am: f4b2fe4d3b am: ef811155ac am: 1396f279d0 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1912526 Change-Id: If164c0bf4a8c2a121f3846e63e3f693a35e633c3
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
.