tag | 59695925a3df534e986af8f009cf0305fe2805dc | |
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tagger | The Android Open Source Project <initial-contribution@android.com> | Wed Nov 04 12:14:39 2020 -0800 |
object | b1d2e31a07edaf018ea356b6f52b88ded6db9055 |
Platform Tools Release 30.0.5 (6877874)
commit | b1d2e31a07edaf018ea356b6f52b88ded6db9055 | [log] [tgz] |
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author | android-build-prod (mdb) <android-build-team-robot@google.com> | Thu Oct 01 20:31:51 2020 +0000 |
committer | android-build-prod (mdb) <android-build-team-robot@google.com> | Thu Oct 01 20:31:51 2020 +0000 |
tree | a00ac2c58618eb65bab63f2afe07b988c597f851 | |
parent | 936c278fac220e3c0a1090d12572dfd1247e0a5c [diff] | |
parent | a120c7727cbd37fbae8c169fec15acc52d35bb2a [diff] |
Snap for 6877830 from a120c7727cbd37fbae8c169fec15acc52d35bb2a to sdk-release Change-Id: I2cfb8762ff2f9f55a7844f510a95d6918e895904
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
.