Shared via Rust Playground

playground.rs

macro_rules! twixt {
    (($cond:expr; $after:expr) { $($body:tt)* } else { $($els:tt)* }) => {{
        if $cond {
            struct Doop;
            impl Drop for Doop { fn drop(&mut self) { $after; } }
            let _d = Doop;
            $($body)*
        } else {
            $($els)*
        }
    }};
    (($cond:expr; $after:expr) { $($body:tt)* }) => {
        twixt!(($cond; $after) { $($body)* } else {})
    }
}

#[test]
fn test() {
    use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
    
    static LOCK: AtomicBool = ATOMIC_BOOL_INIT;
    
    fn get_lock() -> bool {
        !LOCK.compare_and_swap(false, true, Ordering::SeqCst)
    }
    
    fn release_lock() {
        LOCK.compare_and_swap(true, false, Ordering::SeqCst);
    }
    
    assert!(!LOCK.load(Ordering::SeqCst));
    twixt!((get_lock(); release_lock()) {
        assert!(LOCK.load(Ordering::SeqCst));
        println!("acquired lock!");
        twixt!((get_lock(); release_lock()) {
            println!("uh oh, recursively acquired lock");
            assert!(false);
        });
    } else {
        println!("could not acquire lock!");
    });
    assert!(!LOCK.load(Ordering::SeqCst));
}