Rust 宏魔法之默认参数

use std::any::Any;


macro_rules! requests{
    (
        $($key:expr=> $value:expr);*
        $(;)?
    ) => {
        let mut url: Box<dyn Any> = Box::new("");
        let mut method: Box<dyn Any> = Box::new("");
        let mut timeout: Box<dyn Any> = Box::new(0);

        $(
        match $key {
            "url" => {
                url = Box::new($value);
            },
            "method" => {
                method = Box::new($value);
            },
            "timeout" => {
                timeout = Box::new($value);
            },
            _ => {
                panic!("Error key: {:?}", $key);
            }
        }
        )*

        let mut url: &str = url.downcast_ref::<&str>().unwrap();
        let mut method: &str = method.downcast_ref::<&str>().unwrap();
        let mut timeout: u64 = *timeout.downcast_ref::<i32>().unwrap() as u64;

        println!("url-> {}", url);
        println!("method-> {}", method);
        println!("timeout-> {}", timeout);
    }
}


fn main() {
    requests! {
        "url"=> "https://www.baidu.com/";
        "method"=> "GET";
        "timeout"=> 10;
    };
}