rust/src/test/compile-fail/borrowck-binding-mutbl.rs

fn impure(_v: [int]/~) {
}

fn main() {
    let x = {mut f: [3]/~};

    alt x {
      {f: v} => {
        impure(v); //! ERROR illegal borrow unless pure: unique value in aliasable, mutable location
        //!^ NOTE impure due to access to impure function
      }
    }
}