跟着谷歌学习Rust：第十一课-标准库类型

Option

Rust的Option是一种封装的枚举类型，枚举值有Some和None。Some会返回一个泛型T的值

pub enum Option<T> {
    /// No value.
    #[lang = "None"]
    #[stable(feature = "rust1", since = "1.0.0")]
    None,
    /// Some value of type `T`.
    #[lang = "Some"]
    #[stable(feature = "rust1", since = "1.0.0")]
    Some(#[stable(feature = "rust1", since = "1.0.0")] T),
}

Option主要用于解决一些异常信息。

fn main() {
    let name = "Löwe 老虎 Léopard Gepardi";
    let mut position: Option<usize> = name.find('é');
    if position == None {
        println!("无法获取到值");
    } else {
        println!("获取的值：{}",position.unwrap())
    }
    println!("find returned {position:?}");
    assert_eq!(position.unwrap(), 14);
    position = name.find('Z');
    println!("find returned {position:?}");
    assert_eq!(position.expect("Character not found"), 0);
}

Result

Result与Option类似，但是成功和异常是有明确定义的，分别为Ok和Err。

//Rest的源码
pub enum Result<T, E> {
    /// Contains the success value
    #[lang = "Ok"]
    #[stable(feature = "rust1", since = "1.0.0")]
    Ok(#[stable(feature = "rust1", since = "1.0.0")] T),

    /// Contains the error value
    #[lang = "Err"]
    #[stable(feature = "rust1", since = "1.0.0")]
    Err(#[stable(feature = "rust1", since = "1.0.0")] E),
}

Result的示例：

use std::fs::File;
use std::io::Read;

fn main() {
    let file: Result<File, std::io::Error> = File::open("diary.txt");
    match file {
        //处理Ok的场景
        Ok(mut file) => {
            let mut contents = String::new();
            if let Ok(bytes) = file.read_to_string(&mut contents) {
                println!("Dear diary: {contents} ({bytes} bytes)");
            } else {
                println!("Could not read file content");
            }
        }
        //处理Err的场景
        Err(err) => {
            println!("The diary could not be opened: {err}");
        }
    }
}

参考

Comprehensive Rust