commit | f1da56da3eae0cc829c4ed03716e7ecbe27072cd | [log] [tgz] |
---|---|---|
author | Xin Li <delphij@google.com> | Thu Aug 27 18:30:02 2020 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Thu Aug 27 18:30:02 2020 +0000 |
tree | f5fea32411497f739bbcf2cea1a575b2d83cced2 | |
parent | b6203f2530246c6f5666ef54b041d964428ff1b5 [diff] | |
parent | 88b284f5679892688294af2e256c19d6f8b3e1b7 [diff] |
[automerger skipped] Mark Android R (rvc-dev-plus-aosp-without-vendor@6692709) as merged am: 88b284f567 -s ours am skip reason: Change-Id Ia9cf54801441ec60f51bfdfb89fa5d0846ff6bbc with SHA-1 a6ee52c3a9 is in history Original change: https://googleplex-android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/12469819 Change-Id: I19ab00f246c311d03f95b75d09890aee91d08e11
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
.