commit | ae8138de16c97cb82f1728af9e1f784d9faae7c2 | [log] [tgz] |
---|---|---|
author | David Brazdil <dbrazdil@google.com> | Tue Jan 24 18:55:31 2023 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Tue Jan 24 18:55:31 2023 +0000 |
tree | 86c18e1e8e917adaf08b798afdb1dc07cd9cab2b | |
parent | f91bddd16dd9c3ee48585cc948d7f03a887a8012 [diff] | |
parent | 34625dcc6b1cb8f0f260958114bafa5fc9be1b20 [diff] |
Update TEST_MAPPING am: c1c23a035b am: 6651059bd7 am: 34625dcc6b Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/2399319 Change-Id: I9bf208d7ac8f92edd9fdaa8cd2321a1a8b507d0a Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
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
.