commit | 12ddc75c597b99aa881626066b812acd2d6147ed | [log] [tgz] |
---|---|---|
author | Xin Li <delphij@google.com> | Sat Feb 20 14:49:01 2021 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Sat Feb 20 14:49:01 2021 +0000 |
tree | 6e7343b6e19bf6a035fc087285e5cbbc291b9bdb | |
parent | f9ff62aa2efd696137a1e26b7eb9405416777f4c [diff] | |
parent | 08fa36f70e174e5866d455a970ddb1b7e38a8b24 [diff] |
[automerger skipped] Mark ab/7061308 as merged in stage. am: 4985b53f0d -s ours am: 7bc9df8740 -s ours am: 08fa36f70e -s ours am skip reason: Change-Id I06e5da9e0a95f5af7206e26a7589ae548ea99c4e with SHA-1 f9218a9a1b is in history Original change: undetermined MUST ONLY BE SUBMITTED BY AUTOMERGER Change-Id: I113bfa87f1c713e1a944bf5de13af912fc4c82cc
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
.