Why OnceLock get_or_init not working?

help
1 
pub struct User {
    pub name: String,
    pub age: u32,
}

use std::sync::{Arc, OnceLock};
use tokio::sync::Mutex;

pub const PROCESSES: OnceLock<Arc<Mutex<Vec<User>>>> = OnceLock::new();

fn main() {
    PROCESSES.get_or_init(|| Arc::new(Mutex::new(vec![])));

    let v = PROCESSES.get().unwrap();
}

I remember I often use it this way, but today’s result made me question my whole existence.
Or perhaps only today did I realize it was wrong??

The result:

thread 'main' panicked at src/main.rs:16:29:
called Option::unwrap() on a None value
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

2

You must use a static item, not a const item. Only static guarantees a single shared memory location.

3 Likes
3

I'm so foolish, I didn't even notice. Thank you for your help. Neither ChatGPT nor DeepSeek pointed out this mistake...

4

LLMs arent typically good at Rust at all beyond the basics.

3 Likes
5

Note that clippy would have warned you about this:

warning: a `const` item should not be interior mutable
 --> src/main.rs:9:1
  |
9 | pub const PROCESSES: OnceLock<Arc<Mutex<Vec<User>>>> = OnceLock::new();
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: consider making this a static item
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#declare_interior_mutable_const
  = note: `#[warn(clippy::declare_interior_mutable_const)]` on by default

warning: a `const` item with interior mutability should not be borrowed
  --> src/main.rs:12:5
   |
12 |     PROCESSES.get_or_init(|| Arc::new(Mutex::new(vec![])));
   |     ^^^^^^^^^
   |
   = help: assign this const to a local or static variable, and use the variable here
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#borrow_interior_mutable_const
   = note: `#[warn(clippy::borrow_interior_mutable_const)]` on by default

warning: a `const` item with interior mutability should not be borrowed
  --> src/main.rs:14:13
   |
14 |     let v = PROCESSES.get().unwrap();
   |             ^^^^^^^^^
   |
   = help: assign this const to a local or static variable, and use the variable here
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#borrow_interior_mutable_const
6 Likes
6

Very good advice, thank you.