rust 基础 —— Option 的 as_ref 与 as_deref

代码：

fn hello(name: &String) {
    println!("Name is {}", name);
}

fn greet(name: &str) {
    println!("Name is {}", name);
}

fn main() {
    let option_name: Option<String> = Some("Alice".to_owned());
    // let r: Option<&String> = option_name.as_ref();
    option_name.as_ref().map(hello);
    // let r2: Option<&str> = option_name.as_deref();
    option_name.as_deref().map(greet);
    println!("{:?}", option_name);
    // as_deref 将 Option<String> 转换成 &str，配合 unwrap_or 的返回值也是 &str，统一了返回值类型
    let r3 = option_name.as_deref().unwrap_or("undefined");
    println!("{:?}", r3);
}