静态生命周期

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//1.静态生命周期
//定义方法：'static
//生命周期存活于整个程序期间，所有的字符字面值都有static生命周期
//和C语言不同，C语言中static则是更换文件链接属性或者全局变量，Rust使用const
//let s: &'static str = "hello";

use std::fmt::Display;

fn function<'a,T:Display>(x: &'a str,y: &'a str,ann: T) -> &'a str { 
  println!("ann is {}",ann);
  if x.len() < y.len() 
  {
      x
    }else {
        y
      }

  }
fn main() {
    let s1 = String::from("i am s1");
    let s2 = String::from("i am s2");
    let ann = 129;
    let r = function(s1.as_str(),s2.as_str(),ann);
    println!("r = {}",r);
  }