编辑代码

use std::fmt::Display;  

fn longest_with_an_announcement<'a, T>(x: &'a str, y: &'a str, ann: T) -> &'a str  
    where T: Display  
{  
    println!("Announcement! {}", ann);  
    if x.len() > y.len() {  
        x  
    } else {  
        y  
    }  
}
fn main() {
    let mut astr = "泛型、特性与生命周期";
    let mut bstr = "generic、trait、lifetime";
    println!("{}", longest_with_an_announcement(astr,bstr,"str"));
}