环境

• Rust 1.56.1
• VSCode 1.61.2

概念

参考：https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/option_result.html

示例

返回 Option

use std::num::ParseIntError;

fn double_first(vec: Vec<&str>) -> Option<Result<i32, ParseIntError>> {
    vec.first().map(|first| first.parse::<i32>().map(|n| 2 * n))
}

fn main() {
    let numbers = vec!["42", "93", "18"];
    let empty = vec![];
    let strings = vec!["tofu", "93", "18"];

    println!("The first doubled is {:?}", double_first(numbers));
    println!("The first doubled is {:?}", double_first(empty));
    println!("The first doubled is {:?}", double_first(strings));
}

返回 Result

use std::num::ParseIntError;

fn double_first(vec: Vec<&str>) -> Result<Option<i32>, ParseIntError> {
    let opt = vec.first().map(|first| first.parse::<i32>().map(|n| 2 * n));
    opt.map_or(Ok(None), |r| r.map(Some))
}

fn main() {
    let numbers = vec!["42", "93", "18"];
    let empty = vec![];
    let strings = vec!["tofu", "93", "18"];
    println!("The first doubled is {:?}", double_first(numbers));
    println!("The first doubled is {:?}", double_first(empty));
    println!("The first doubled is {:?}", double_first(strings));
}

总结

了解了 Rust 中处理 Option 和 Result 同时存在的情况。

附录