rust 宏

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use std::collections::HashMap;   macro_rules! map {     ($($key:expr => $val:expr),*) => {{         let mut hm = HashMap::new();         $(hm.insert($key, $val);)*         hm     }};    //要返回,相当于是FN,所以必须多加一对{} }     fn main(){     let a = map!("s" => 123, "xx"=>34, "uu"=>123);     println!("{:?}", a); }