commit | c6e82f702102e98f3c1c95975a1a54b977187dec | [log] [tgz] |
---|---|---|
author | Bernie Innocenti <codewiz@google.com> | Mon Dec 14 23:12:28 2020 +0900 |
committer | Bernie Innocenti <codewiz@google.com> | Tue Dec 15 15:50:52 2020 +0900 |
tree | c78ceedf7897b7d69ab44dcbd7ed4ca6b8ea9d5e | |
parent | 925b59fb3b53db5b28032bc4c33bbf4a5314e356 [diff] |
Allow using once_cell from DnsResolver Test: m Bug: 155855709 Change-Id: Iabf9f2c67faf6e1d325db6110d12418633ec2aff
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
.