tag | 84dcb0f2c87c7ee2e0d32f0fe8851a6832f91d16 | |
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tagger | The Android Open Source Project <initial-contribution@android.com> | Mon Apr 29 09:53:44 2024 -0700 |
object | 72279279d588c47a74d0e18fb8161957b9469c6c |
aml_art_341514450 (11720836,com.google.android.art,com.google.android.go.art)
commit | 72279279d588c47a74d0e18fb8161957b9469c6c | [log] [tgz] |
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author | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Fri Jul 07 04:44:04 2023 +0000 |
committer | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Fri Jul 07 04:44:04 2023 +0000 |
tree | 12c59a21225d1e0948cd3b4c7db5e10c2aec25e6 | |
parent | 5ee504876b61a3ebd7ef3bc8a063fdbb239f8a0c [diff] | |
parent | 57465554fc54b04bc9442fdd73a1e8fd6b50dc74 [diff] |
Snap for 10453563 from 57465554fc54b04bc9442fdd73a1e8fd6b50dc74 to mainline-art-release Change-Id: Ie1a0253f20af8c3f2ee3124605206cb7ecb8f57b
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
.