Rust 1.63-compatible RwLock static init example

fib.rs

pub fn init() {
    static INIT_ONCE: std::sync::Once = std::sync::Once::new();
    INIT_ONCE.call_once(|| {
        let mut zero__2 = 0;
        {
            *ZERO__2.write().unwrap() = Some(zero__2);
        }
        zero__2 = zero__2;
        {
            *ZERO__2.write().unwrap() = Some(zero__2);
        }
        println!(
            "{}",
            format!("{}{}", "fib(1)=", fib__1(self::zero__2() + 1).to_string())
        );
        println!(
            "{}",
            format!("{}{}", "fib(10)=", fib__1(self::zero__2() + 10).to_string())
        );
        println!(
            "{}",
            format!("{}{}", "fib(20)=", fib__1(self::zero__2() + 20).to_string())
        );
    });
}

static ZERO__2: std::sync::RwLock<Option<i32>> = std::sync::RwLock::new(None);

// The idea is that pub things ensure init.
pub fn zero() -> i32 {
    init();
    zero__2()
}

// And internal things should only call internal, never the pub version.
fn zero__2() -> i32 {
    ZERO__2.read().unwrap().unwrap()
}

fn fib__1(mut i__3: i32) -> i32 {
    let mut a__5: i32 = 0;
    let mut b__6: i32 = 1;
    while i__3 > 0 {
        let c__7: i32 = a__5 + b__6;
        a__5 = b__6;
        b__6 = c__7;
        i__3 = i__3 - 1;
    }
    return a__5;
}