src/doc/rust-by-example/src/variable_bindings/mut.md

   1 # Mutability
   2
   3 Variable bindings are immutable by default, but this can be overridden using
   4 the `mut` modifier.
   5
   6 ```rust,editable,ignore,mdbook-runnable
   7 fn main() {
   8     let _immutable_binding = 1;
   9     let mut mutable_binding = 1;
  10
  11     println!("Before mutation: {}", mutable_binding);
  12
  13     // Ok
  14     mutable_binding += 1;
  15
  16     println!("After mutation: {}", mutable_binding);
  17
  18     // Error! Cannot assign a new value to an immutable variable
  19     _immutable_binding += 1;
  20 }
  21 ```
  22
  23 The compiler will throw a detailed diagnostic about mutability errors.