rust/src/test/compile-fail/borrowck-ref-mut-of-imm.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

fn destructure(x: Option<int>) -> int {
    match x {
      None => 0,
      Some(ref mut v) => *v //~ ERROR cannot borrow
    }
}

fn main() {
    assert_eq!(destructure(Some(22)), 22);
}