rust 可变变量

变量绑定默认是不可变的，但加上 mut 修饰语后变量就可以改变。

fn main() {
    let _immutable_binding = 1;
    let mut mutable_binding = 1;

    println!("Before mutation: {}", mutable_binding);

    // 正确代码
    mutable_binding += 1;

    println!("After mutation: {}", mutable_binding);

    // 错误！
    _immutable_binding += 1;
    // 改正 ^ 将此行注释掉
}

cargo build
   Compiling own v0.1.0 (/data2/rust/mut)
error[E0384]: cannot assign twice to immutable variable `_immutable_binding`
  --> src/main.rs:13:5
   |
2  |     let _immutable_binding = 1;
   |         ------------------
   |         |
   |         first assignment to `_immutable_binding`
   |         help: make this binding mutable: `mut _immutable_binding`
...
13 |     _immutable_binding += 1;
   |     ^^^^^^^^^^^^^^^^^^^^^^^ cannot assign twice to immutable variable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0384`.
error: could not compile `own`.

To learn more, run the command again with --verbose.