commit | 9a0cb5e3a76267fa3fd991980a4bfa6afe4c45e9 | [log] [tgz] |
---|---|---|
author | android-build-prod (mdb) <android-build-team-robot@google.com> | Wed Jul 08 00:17:50 2020 +0000 |
committer | android-build-prod (mdb) <android-build-team-robot@google.com> | Wed Jul 08 00:17:50 2020 +0000 |
tree | 1263a8799a665dd1ff2d1f4df0103c62f31ef5d5 | |
parent | 0f3d5c25db035bae4863fe5f968f9612ca04b675 [diff] | |
parent | 8c364303ba594cafee33960e00df09f3757ed843 [diff] |
Snap for 6660490 from 8c364303ba594cafee33960e00df09f3757ed843 to sdk-release Change-Id: I10b6004aa8b1fff58484291b76adff342e2dbd78
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
.