| commit | c1c23a035bc395f039d2e252a408fe89616882fe | [log] [tgz] |
|---|---|---|
| author | David Brazdil <dbrazdil@google.com> | Mon Jan 23 13:50:38 2023 +0000 |
| committer | David Brazdil <dbrazdil@google.com> | Tue Jan 24 12:55:34 2023 +0000 |
| tree | 86c18e1e8e917adaf08b798afdb1dc07cd9cab2b | |
| parent | 1a8ffe2eb8c1f9387327ba1008328a21504b7eb4 [diff] |
Update TEST_MAPPING Test: None Change-Id: I59cc41ec81dcccfe742bd181b195f5e42ee9cf4d
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.