Variables are immutable

---

• Variables in Rust are immutable by default.

examples/variables/immutable-number/src/main.rs

fn main() {
    let x = 2;
    println!("{}", x);

    x = 3;
    println!("{}", x);
}

error[E0384]: cannot assign twice to immutable variable `x`
 --> examples/variables/number_immutable.rs:5:5
  |
2 |     let x = 2;
  |         -
  |         |
  |         first assignment to `x`
  |         help: consider making this binding mutable: `mut x`
...
5 |     x = 3;
  |     ^^^^^ cannot assign twice to immutable variable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0384`.