#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(once_cell_get_mut)]
use std::cell::OnceCell;
fn main() {
    let mut cell: OnceCell<u32> = OnceCell::new();
    assert!(cell.get_mut_or_try_init(|| "not a number!".parse()).is_err());
    assert!(cell.get().is_none());
    let value = cell.get_mut_or_try_init(|| "1234".parse());
    assert_eq!(value, Ok(& mut 1234));
    let Ok(value) = value else {
        return;
    };
    *value += 2;
    assert_eq!(cell.get(), Some(& 1236))
}