borrowenum.rs

extern mod std;

use std::map::HashMap;
use std::map::Set;
use std::map::vec_from_set;

enum Choice {
    Many(Set<int>),
    One(int),
}

fn main(++_argv: ~[~str]) {
    let mut choices: ~[Choice] = ~[Many(HashMap())];

    for vec::each_mut(choices) |choice| {
        match *choice {
            Many(opts) => {
                if opts.size() == 1 {
                    *choice = One(vec_from_set(opts)[0]);
                }
            }
            One(_) => {}
        }
    }

    log(error, choices);
}

stderr

borrowenum.rs:17:17: 17:22 error: illegal borrow unless pure: enum variant in aliasable, mutable location
borrowenum.rs:17             Many(opts) => {
                                  ^~~~~
borrowenum.rs:19:20: 19:27 note: impure due to assigning to dereference of mutable & pointer
borrowenum.rs:19                     *choice = One(vec_from_set(opts)[0]);
                                     ^~~~~~~
error: aborting due to previous error