commit | 533bf1317cfb4320a512a8dd06cc508fb596505c | [log] [tgz] |
---|---|---|
author | David LeGare <legare@google.com> | Wed Mar 02 16:21:26 2022 +0000 |
committer | David LeGare <legare@google.com> | Wed Mar 02 16:21:26 2022 +0000 |
tree | 95353df6eca9bf63f57a86070e6fad69c6061276 | |
parent | f4b2fe4d3be5c56fffeb0bdb4b365470bd865646 [diff] |
Update once_cell to 1.9.0 Test: cd external/rust/crates && atest --host -c Change-Id: Iddd1b8516f9187f948c45695a889ed6b987566ca
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
.