#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use std::cell::OnceCell;
fn main() {
    let cell = OnceCell::new();
    assert!(cell.get().is_none());
    let value: &String = cell.get_or_init(|| { "Hello, World!".to_string() });
    assert_eq!(value, "Hello, World!");
    assert!(cell.get().is_some());
}