commit | 4985b53f0d9def947e1aae390d5fdef1d490d394 | [log] [tgz] |
---|---|---|
author | Xin Li <delphij@google.com> | Sat Feb 20 00:24:21 2021 -0800 |
committer | Xin Li <delphij@google.com> | Sat Feb 20 00:24:21 2021 -0800 |
tree | 6e7343b6e19bf6a035fc087285e5cbbc291b9bdb | |
parent | c66e8699df1b4d8490c54398e8843b3906c00823 [diff] | |
parent | f9218a9a1bbd3767a78ded68bb829075b01b8e7c [diff] |
Mark ab/7061308 as merged in stage. Bug: 180401296 Merged-In: I06e5da9e0a95f5af7206e26a7589ae548ea99c4e Change-Id: I40988887bd5039b539e2c68ccdeaeb9e17ce1208
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
.