rustp-8.方法中的生命周期

struct StuA<'a> {
    name: &'a str,
  }

impl<'a> StuA<'a> {
    fn do_something(&self) -> i32 { //输出不是引用，所以不用写
        3
      }
    fn do_something2(&self,s: &str) -> &str { //省略规则3
    //fn do_something2<'b>(&'b self,s: &str) -> &'b str ｛
        self.name
      }
    
    //报错
    //需要显示标明
//    fn do_something3(&self,s: &str) -> &str {//没法使用,因为s和输出生命周期不同
//        s
//      }
    //----------------------------------
    //显示标明之后
    fn do_something3<'a>(&self,s: &'a str) -> &'a str {
        s
      }
  }
fn main() {
    let s = String::from("Hello");
    let a = StuA(name: &s);

    let s2 = String::from("hello");

    println!("{}",a.do_something());
    println!("{}",a.do_something2(&s2));
    println!("{}",a.do_something3(&s2));
  }