commit | 461e9d0ab524b6c013732a0dffc308a8dc3bc97f | [log] [tgz] |
---|---|---|
author | Matthew Maurer <mmaurer@google.com> | Tue Jul 07 01:45:37 2020 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Tue Jul 07 01:45:37 2020 +0000 |
tree | 1263a8799a665dd1ff2d1f4df0103c62f31ef5d5 | |
parent | c124d0c9c1f4286513687ea5728024574850614f [diff] | |
parent | 4c41fac50bf423d22d8c3e5fbf8d050f25690e8d [diff] |
Support building all variants. am: 8c364303ba am: fe1a31f7c1 am: a90f22f7b1 am: 4c41fac50b Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1355990 Change-Id: I8b0e4d11d5cd86f8d7d0edbbc3c356bbe3691f26
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
.