// 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 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. struct X(Either<(uint,uint),extern fn()>); impl X { pub fn with(&self, blk: &fn(x: &Either<(uint,uint),extern fn()>)) { blk(&**self) } } fn main() { let mut x = X(Right(main)); do (&mut x).with |opt| { match opt { &Right(ref f) => { x = X(Left((0,0))); //~ ERROR cannot assign to `x` (*f)() }, _ => fail2!() } } }