commit | f6462a15d75b06729abe9d09d40c971c3548a61b | [log] [tgz] |
---|---|---|
author | Haibo Huang <hhb@google.com> | Tue Nov 17 02:04:22 2020 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Tue Nov 17 02:04:22 2020 +0000 |
tree | 359b3d7dabb54a5a665eae86e9a945267558df78 | |
parent | 91176d923b2b1d79b02e4f05dfe10b5faec4d4e1 [diff] | |
parent | 0f5e59407de1a8bd556ef11102a6c033d188e714 [diff] |
Upgrade rust/crates/once_cell to 1.5.2 am: dc66c865e6 am: 455b11071c am: f8a5feccae am: 0f5e59407d Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1497496 Change-Id: I832982e5a8a50718f167982524222a603a8163d6
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
.