Rust中的Option枚举快速入门教程

enum Option<T> {
    Some(T),
    None,
}

impl<T> [T] {
	pub const fn first(&self) -> Option<&T> {
	    if let [first, ..] = self { Some(first) } else { None }
	}
}

fn main() {
	let v = [10, 40, 30];
	assert_eq!(Some(&10), v.first());
	let w: &[i32] = &[];
	assert_eq!(None, w.first());
}

// 想像这是我们业务里的一个函数, 用于对已有的数据再处理
fn process_data(data: &mut Option<String>) {
	// 如果不为None, 则进一步处理
    if let Some(ref mut s) = data {
        s.push_str(" processed");
    }
}
fn main() {
    let mut data = Some(String::from("data"));
    process_data(&mut data);
    println!("{:?}", data); // 输出: Some("data processed")
}

// 某一个配置如果为空, 则给默认值
fn get_config_value(config: &Option<i32>) -> i32 {
    config.unwrap_or(42)
}
fn main() {
    let config_value = Some(99);
    println!("Config value: {}", get_config_value(&config_value)); // 输出: Config value: 99
    let missing_config_value: Option<i32> = None;
    println!("Missing config value: {}", get_config_value(&missing_config_value)); // 输出: Missing config value: 42
}

fn main() {
    let some_number = Some(5);
    // (5*2) + 3
    let result = some_number.map(|n| n * 2).map(|n| n + 3);
    println!("{:?}", result); // 输出: Some(13)
    let no_number: Option<i32> = None;
    let result = no_number.map(|n| n * 2).map(|n| n + 3);
    println!("{:?}", result); // 输出: None
}

fn main() {
    let some_number = Some(5);
    let no_number: Option<i32> = None;
    // 安全使用unwrap
    println!("The number is {}", some_number.unwrap()); // 正常运行
    // 不安全使用unwrap，会导致panic
    // println!("The number is {}", no_number.unwrap()); // panic: called `Option::unwrap()` on a `None` value
}

fn process_option(opt: Option<i32>) {
    match opt {
        Some(value) => println!("Got a value: {}", value),
        None => println!("No value provided"),
    }
}
fn main() {
    let some_number = Some(5);
    let no_number: Option<i32> = None;
    process_option(some_number); // 输出: Got a value: 5
    process_option(no_number);  // 输出: No value provided
}

enum ApiResult<T> {
    Success(T),
    Error(String),
}
fn fetch_data() -> ApiResult<String> {
    // 模拟API调用
    let data = Some("data".to_string());
    match data {
        Some(d) => ApiResult::Success(d),
        None => ApiResult::Error("Failed to fetch data".to_string()),
    }
}
fn main() {
    match fetch_data() {
        ApiResult::Success(data) => println!("Data fetched: {}", data),
        ApiResult::Error(err) => println!("Error: {}", err),
    }
}