commit | a848019c9c0b615d8ac5a7de64f88f11bbeb378d | [log] [tgz] |
---|---|---|
author | Treehugger Robot <treehugger-gerrit@google.com> | Tue Feb 16 22:21:41 2021 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Tue Feb 16 22:21:41 2021 +0000 |
tree | 7bebcd0300b1d7658ad5455c5697149ed347ea6a | |
parent | 0eaf98a0d1207cdc80ef7b062866a5859c86aedc [diff] | |
parent | a6a76f5126d7976ab81efca7471cfe00f2aa513e [diff] |
Merge "Clean up rust_test_host TEST_MAPPING after default update" am: 9ac0a4c9be am: 30878de99d am: bb7231b469 am: a6a76f5126 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/once_cell/+/1590471 MUST ONLY BE SUBMITTED BY AUTOMERGER Change-Id: I6d559d561160323ff1aad0899b06aa1efa5bd2d7
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
.