// 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.

enum Either<T, U> { Left(T), Right(U) }

struct X(Either<(uint,uint),extern fn()>);

impl X {
    pub fn with(&self, blk: |x: &Either<(uint,uint),extern fn()>|) {
        let X(ref e) = *self;
        blk(e)
    }
}

fn main() {
    let mut x = X(Right(main));
    (&mut x).with(|opt| {
        match opt {
            &Right(ref f) => {
                x = X(Left((0,0))); //~ ERROR cannot assign to `x`
                (*f)()
            },
            _ => fail!()
        }
    })
}