Rust 使用 `let` 绑定来增加值的生命周期

我编写了以下代码来读取stdin中的整数数组:

use std::io::{self, BufRead};

fn main() {
    let stdin = io::stdin();
    for line in stdin.lock().lines() {
        let xs: Vec<i32> = line.unwrap()
            .trim()
            .split(' ')
            .map(|s| s.parse().unwrap())
            .collect();

        println!("{:?}", xs);
    }
}

这很好，但是，我觉得let xs行有点长，所以我把它分成两部分:

use std::io::{self, BufRead};

fn main() {
    let stdin = io::stdin();
    for line in stdin.lock().lines() {
        let ss = line.unwrap().trim().split(' ');
        let xs: Vec<i32> = ss.map(|s| s.parse().unwrap()).collect();

        println!("{:?}", xs);
    }
}

这没用！Rust回复了以下错误:

error[E0597]: borrowed value does not live long enough
  --> src/main.rs:6:18
   |
6  |         let ss = line.unwrap().trim().split(' ');
   |                  ^^^^^^^^^^^^^                  - temporary value dropped here while still borrowed
   |                  |
   |                  temporary value does not live long enough
...
10 |     }
   |     - temporary value needs to live until here
   |
   = note: consider using a `let` binding to increase its lifetime

这让我困惑.是line岁还是ss岁还不够长寿？我如何使用let绑定来延长它们的生命周期 ？我以为我已经在用let了？

我已经通读了lifetime guide本书，但还是不太明白.谁能给我一个提示吗？