.expect("Failed to read line"); let guess: u32 = guess.trim().parse().expect("Please type a number!"); println!("You guessed: {guess}"); match guess.cmp(&secret_number) { Ordering::Equal => println!("You win!"), } 这行新代码是： let guess: u32 = guess.trim().parse().expect("Please type a number!"); 这里创建了一个叫做 guess 的变量。不过等等，不是已经有了一个叫做 guess 的变量了吗？确 实如此，不过 Rust 允许用一个新值来 遮蔽 （Shadowing） guessed: 59 You win! Please input your guess. quit thread 'main' panicked at src/main.rs:28:47: Please type a number!: ParseIntError { kind: InvalidDigit } note: run with `RUST_BACKTRACE=1` environment variable