commit | 79e85f7a3107c8aa53baa9e63a94e6d6fd7d364e | [log] [tgz] |
---|---|---|
author | Bob Badour <bbadour@google.com> | Fri Feb 12 16:14:12 2021 -0800 |
committer | Bob Badour <bbadour@google.com> | Fri Feb 12 16:14:12 2021 -0800 |
tree | c01a51a93645446f67746de5a39ee1525fa03ed1 | |
parent | 9f03d482f53f1f9e864de25d9071181b5fc16a1f [diff] |
[LSC] Add LOCAL_LICENSE_KINDS to external/rust/crates/once_cell Added SPDX-license-identifier-Apache-2.0 SPDX-license-identifier-MIT to: Android.bp Bug: 68860345 Bug: 151177513 Bug: 151953481 Test: m all Exempt-From-Owner-Approval: janitorial work Change-Id: Ib43876657ff5c06603239292cfa174635bd74e4f
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
.