fn main() {
    let a = Option::Some("foo");
    println!("{}", a.iter().all(|x| *x == "foo"));
    println!("{}", a.iter().any(|x| *x == "foo"));
    println!("{}", a.iter().all(|x| *x == "bar"));
    println!("{}", a.iter().any(|x| *x == "bar"));
    let b: Option<&str> = Option::None;
    println!("{}", b.iter().all(|x| *x == "foo"));
    println!("{}", b.iter().any(|x| *x == "foo"));
    println!("{}", b.iter().all(|x| *x == "bar"));
    println!("{}", b.iter().any(|x| *x == "bar"));
}