rust - 使用 as_slice() 时为 "borrowed value does not live long enough"

Question

我遇到了一个错误:

extern crate rustc_serialize; // 0.3.24

use rustc_serialize::base64::{self, FromBase64, ToBase64};

fn main() {
    let a: [u8; 30] = [0; 30];
    let b = a.from_base64().unwrap().as_slice();
    println!("{:?}", b);
}

错误:

error[E0597]: borrowed value does not live long enough
 --> src/main.rs:7:13
  |
7 |     let b = a.from_base64().unwrap().as_slice();
  |             ^^^^^^^^^^^^^^^^^^^^^^^^           - temporary value dropped here while still borrowed
  |             |
  |             temporary value does not live long enough
8 |     println!("{:?}", b);
9 | }
  | - temporary value needs to live until here
  |
  = note: consider using a `let` binding to increase its lifetime

不过，对我而言，代码不会出错。为什么会出现该错误？

Answer 1

这里的问题是您没有将 from_base64 的结果存储在任何地方，然后通过调用 as_slice 引用它。像这样的链接调用会导致 from_base64 的结果在行尾超出范围，并且引用不再有效。

extern crate rustc_serialize; // 0.3.24

use rustc_serialize::base64::FromBase64;

fn main() {
    let a: [u8; 30] = [0; 30];
    let b = a.from_base64().unwrap();
    println!("{:?}", b.as_slice());
}