间接访问变量使得不可能分支和使用该变量，而无需重新绑定。匹配提供@印记就是出于这样的目的：
| // A function `age` which returns a `u32`. |
| fn age() -> u32 { |
| 15 |
| } |
| fn main() { |
| println!("Tell me type of person you are"); |
| match age() { |
| 0 => println!("I'm not born yet I guess"), |
| // Could `match` 1 ... 12 directly but then what age |
| // would the child be? Instead, bind to `n` for the |
| // sequence of 1 .. 12. Now the age can be reported. |
| n @ 1 ... 12 => println!("I'm a child of age {:?}", n), |
| n @ 13 ... 19 => println!("I'm a teen of age {:?}", n), |
| // Nothing bound. Return the result. |
| n => println!("I'm an old person of age {:?}", n), |
| } |
| } |
