读 Rust入坑指南：核心概念 之测试，因该文中涉及一些代码不知道是什么效果，所以就做了如下的测试：

Ownership的移动 — 在String之间转移

  1. let s1 = String::from("hello");
  2. let s2 = s1;
  3. println!("s1: {}", s1);

执行上面的代码会报如下错误：

  1. warning: unused variable: `s2`
  2.  --> src\main.rs:7:7
  3.   |
  4. 7 |   let s2 = s1;
  5.   |       ^^ help: if this is intentional, prefix it with an underscore: `_s2`
  6.   |
  7.   = note: `#[warn(unused_variables)]` on by default
  10. error[E0382]: borrow of moved value: `s1`
  11.  --> src\main.rs:8:22
  12.   |
  13. 6 |     let s1 = String::from("hello");
  14.   |         -- move occurs because `s1` has type `String`, which does not implement the `Copy` trait
  15. 7 |   let s2 = s1;
  16.   |            -- value moved here
  17. 8 |   println!("s1: {}", s1);
  18.   |                      ^^ value borrowed here after move
  21. error: aborting due to previous error; 1 warning emitted
  24. For more information about this error, try `rustc --explain E0382`.
  26. error: could not compile `hello_cargo`
  28. To learn more, run the command again with --verbose.