commit | 4a9d8e8ee32e8ff0c1fea38c19cc50f33068910e | [log] [tgz] |
---|---|---|
author | Andrew Walbran <qwandor@google.com> | Mon May 15 14:48:31 2023 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Mon May 15 14:48:31 2023 +0000 |
tree | ee8588478eee7fc14e8d8b87c3c28b0df8dce1f0 | |
parent | 5d3c9a7e9c62cb0005fddbe1ba7ddb5446e80147 [diff] | |
parent | 19e116cf1e1adee50e5f8bb09b0699f65b75814e [diff] |
Use new no-std flag to cargo2android. am: 19e116cf1e Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/2587125 Change-Id: Ie8a2156f36ca2676ecf71cfc8da4f0aa9e2b02dc 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
.