commit | 23b98f30ab6cddb3c78ca7b7ffb04fd015ac8514 | [log] [tgz] |
---|---|---|
author | Xin Li <delphij@google.com> | Fri Oct 09 03:22:57 2020 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Fri Oct 09 03:22:57 2020 +0000 |
tree | a00ac2c58618eb65bab63f2afe07b988c597f851 | |
parent | 9d0c06449db152cc22b885ae41ec782d6f471f57 [diff] | |
parent | efdc47504c607eb71f13740c6b80e484766c6178 [diff] |
[automerger skipped] Skip ab/6749736 in stage. am: 47c6bcb312 -s ours am: efdc47504c -s ours am skip reason: Change-Id If268b2287bc2b590b7537493a00844b839468f6c with SHA-1 b0a2b7f763 is in history Original change: https://googleplex-android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/12797262 Change-Id: I30b76d0fa3803109dd072ea80d418af55587ea4b
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
.