Macro stack_sync 

macro_rules! stack_sync {
    ($($e:expr),*) => { ... };
}

Creates a Stack that implements Sync, containing the given arguments:

let mut s = Stack::new_sync()
    .push(1)
    .push(2)
    .push(3);

assert_eq!(stack_sync![1, 2, 3], s);

fn is_sync() -> impl Sync {
    stack_sync![0, 1, 1, 2, 3, 5, 8]
}