Rust by Example

18.7.1 引数のパース

matchを用いて簡単な引数をパースできます。

use std::env; fn increase(number: i32) { println!("{}", number + 1); } fn decrease(number: i32) { println!("{}", number - 1); } fn help() { println!("usage: match_args <string> Check whether given string is the answer. match_args {{increase|decrease}} <integer> Increase or decrease given integer by one."); } fn main() { let args: Vec<String> = env::args().collect(); match args.len() { // 引数がない場合 1 => { println!("My name is 'match_args'. Try passing some arguments!"); }, // 引数が1つの場合 2 => { match args[1].parse() { Ok(42) => println!("This is the answer!"), _ => println!("This is not the answer."), } }, // コマンドが一つと引数が一つの場合 3 => { let cmd = &args[1]; let num = &args[2]; // 数字をパース let number: i32 = match num.parse() { Ok(n) => { n }, Err(_) => { println!("error: second argument not an integer"); help(); return; }, }; // コマンドをパース match &cmd[..] { "increase" => increase(number), "decrease" => decrease(number), _ => { println!("error: invalid command"); help(); }, } }, // その他の場合 _ => { // ヘルプメッセージを表示 help(); } } }
$ ./match_args Rust
This is not the answer.
$ ./match_args 42
This is the answer!
$ ./match_args do something
error: second argument not an integer
usage:
match_args <string>
    Check whether given string is the answer.
match_args {increase|decrease} <integer>
    Increase or decrease given integer by one.
$ ./match_args do 42
error: invalid command
usage:
match_args <string>
    Check whether given string is the answer.
match_args {increase|decrease} <integer>
    Increase or decrease given integer by one.
$ ./match_args increase 42
43