比如， parse（） 方法，并不能總是把一個(gè)輸入轉(zhuǎn)成數(shù)字， 比如輸入是 H，就不能轉(zhuǎn)成數(shù)字

所以?parse()?返回一個(gè)?Result?表示可能會(huì)失敗。

fn multiply(x: &str, y: &str) -> i32 {

let x = x.parse::<i32>().unwrap(); // maybe Some, maybe None

let y = y.parse::<i32>().unwrap(); // maybe Some, maybe None

x * y

}

fn main() {

let a = "3";

let b = "x";

? ?// println!(format!("{}",multiply(a, b)));

let res = format!("{}", multiply(a, b));

println!("res is {}", res);

}

Result 包含 Ok 和 Err 兩種可能性。

fn multiply(x: &str, y: &str) -> Result<i32, ParseIntError> {

let x = match x.parse::<i32>() {

Ok(x) => x,

Err(e) => return Err(e),

};

let y = match y.parse::<i32>() {

Ok(y) => y,

Err(e) => return Err(e),

};

? ?// x * y// can mot match Result it should be as below:

Ok(x * y)

}

parse 類比靜態(tài)方法， 實(shí)例上，調(diào)用靜態(tài)方法parse::<i32>()