• 参数分析

    参数分析

    匹配可以用来解析简单的参数：

    1. use std::env;
    3. fn increase(number: i32) {
    4.     println!("{}", number + 1);
    5. }
    7. fn decrease(number: i32) {
    8.     println!("{}", number - 1);
    9. }
    11. fn help() {
    12.     println!("usage:
    13. match_args <string>
    14.     Check whether given string is the answer.
    15. match_args {{increase|decrease}} <integer>
    16.     Increase or decrease given integer by one.");
    17. }
    19. fn main() {
    20.     let args: Vec<String> = env::args().collect();
    22.     match args.len() {
    23.         // 没有传入参数
    24.         1 => {
    25.             println!("My name is 'match_args'. Try passing some arguments!");
    26.         },
    27.         // 一个传入参数
    28.         2 => {
    29.             match args[1].parse() {
    30.                 Ok(42) => println!("This is the answer!"),
    31.                 _ => println!("This is not the answer."),
    32.             }
    33.         },
    34.         // 一条命令和一个传入参数
    35.         3 => {
    36.             let cmd = &args[1];
    37.             let num = &args[2];
    38.             // 解析数字
    39.             let number: i32 = match num.parse() {
    40.                 Ok(n) => {
    41.                     n
    42.                 },
    43.                 Err(_) => {
    44.                     println!("error: second argument not an integer");
    45.                     help();
    46.                     return;
    47.                 },
    48.             };
    49.             // 解析命令
    50.             match &cmd[..] {
    51.                 "increase" => increase(number),
    52.                 "decrease" => decrease(number),
    53.                 _ => {
    54.                     println!("error: invalid command");
    55.                     help();
    56.                 },
    57.             }
    58.         },
    59.         // 所有其他情况
    60.         _ => {
    61.             // 显示帮助信息
    62.             help();
    63.         }
    64.     }
    65. }
    1. $ ./match_args Rust
    2. This is not the answer.
    3. $ ./match_args 42
    4. This is the answer!
    5. $ ./match_args do something
    6. error: second argument not an integer
    7. usage:
    8. match_args <string>
    9.     Check whether given string is the answer.
    10. match_args {increase|decrease} <integer>
    11.     Increase or decrease given integer by one.
    12. $ ./match_args do 42
    13. error: invalid command
    14. usage:
    15. match_args <string>
    16.     Check whether given string is the answer.
    17. match_args {increase|decrease} <integer>
    18.     Increase or decrease given integer by one.
    19. $ ./match_args increase 42
    20. 43