【Rust】可選和錯誤
阿新 • • 發佈:2021-12-24
環境
- Rust 1.56.1
- VSCode 1.61.2
概念
參考: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)); }
總結
瞭解了 Rust 中處理 Option 和 Result 同時存在的情況。