commit | 47c6bcb3125b01cf9596418650e3362097b6f969 | [log] [tgz] |
---|---|---|
author | Xin Li <delphij@google.com> | Thu Oct 08 17:21:33 2020 -0700 |
committer | Xin Li <delphij@google.com> | Thu Oct 08 17:21:33 2020 -0700 |
tree | a00ac2c58618eb65bab63f2afe07b988c597f851 | |
parent | a120c7727cbd37fbae8c169fec15acc52d35bb2a [diff] | |
parent | b0a2b7f7633c6640bb3dfcfb913f24c9eba8d506 [diff] |
Skip ab/6749736 in stage. Merged-In: If268b2287bc2b590b7537493a00844b839468f6c Change-Id: Iec308945699b4933794c35c56ec44d2285cdaaaf
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
.