fn main() {
    // Note: explicit type annot is required here
    // because otherwise the inference gets smart
    // and assigns a type of ~[mut ~[const int]].
    let v: ~[mut ~[int]] = ~[mut ~[0]];

    fn f(&&v: ~[mut ~[const int]]) {
        v[0] = ~[mut 3]
    }

    f(v); //~ ERROR (values differ in mutability)
}