守卫
可以加上 match
守卫(guard) 来过滤分支。
fn main() { let pair = (2, -2); // 试一试 ^ 将不同的值赋给 `pair` println!("Tell me about {:?}", pair); match pair { (x, y) if x == y => println!("These are twins"), // ^ `if condition`(if 条件)部分是一个守卫 (x, y) if x + y == 0 => println!("Antimatter, kaboom!"), (x, _) if x % 2 == 1 => println!("The first one is odd"), _ => println!("No correlation..."), } }