rust

fn main() {
  let mut a = 10;
  let r = &mut a;
  dbg!(a);
  *r += 2;
  dbg!(a);
}

error[E0503]: cannot use `a` because it was mutably borrowed
 --> 228605438/source.rs:4:3
  |
3 |   let r = &mut a;
  |           ------ borrow of `a` occurs here
4 |   dbg!(a);
  |   ^^^^^^^^ use of borrowed `a`
5 |   *r += 2;
  |   ------- borrow later used here
  |
  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error: aborting due to previous error

For more information about this error, try `rustc --explain E0503`.

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