外循环可以使用break或continue，当在处理嵌套循环时。在这种情况, 循环必须用一些被注解：'label, 标签必须被传递给 break/continue语句.
#![allow(unreachable_code)]
fn main() {
'outer: loop {
println!("Entered the outer loop");
'inner: loop {
println!("Entered the inner loop");
// This would break only the inner loop
//break;
// This breaks the outer loop
break 'outer;
}
println!("This point will never be reached");
}
println!("Exited the outer loop");
}
