Labels

continue 和 break 都可以选择接受一个标签参数，用来 终止嵌套循环：

fn main() {
    let s = [[5, 6, 7], [8, 9, 10], [21, 15, 32]];
    let mut found = false;
    let target_value = 10;
    'outer: for i in 0..=2 {
        for j in 0..=2 {
            if s[i][j] == target_value {
                found = true;
                break 'outer;
            }
        }
    }
    print!("{}", found)
}