commit | ffcf21ac95783d536e0c67f2d991500652dd3efc | [log] [tgz] |
---|---|---|
author | android-build-team Robot <android-build-team-robot@google.com> | Sat May 15 03:06:29 2021 +0000 |
committer | android-build-team Robot <android-build-team-robot@google.com> | Sat May 15 03:06:29 2021 +0000 |
tree | 71c77aba563c644c5294b9326b518692929b3d44 | |
parent | f83e505386bdb03e4f05d573793c37a772c01665 [diff] | |
parent | 303088e12fb146ecaae533c1321b5f0b5d0d880c [diff] |
Snap for 7362794 from 303088e12fb146ecaae533c1321b5f0b5d0d880c to sc-v2-release Change-Id: I96ea3b121c160aca54d1732c1bc108326e9cb802
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
.