gistfile1.rs

#[allow(dead_code)];

use std::util;

enum List<T> {
    Cons(T, ~List<T>),
    Nil
}

fn pop<T>(prev: &mut ~List<T>) -> Option<~List<T>> {
    let xs = util::replace(match prev {
        &~Cons(_, ref mut rs) => rs,
        &~Nil => return None
    }, ~Nil);
    Some(util::replace(prev, xs))
}

/* NB: xs cannot be inlined, see below:
fn pop<T>(prev: &mut ~List<T>) -> Option<~List<T>> {
    Some(util::replace(prev, util::replace(match prev {
        &~Cons(_, ref mut rs) => rs,
        &~Nil => return None // NB: the first replace was a no-op
    }, ~Nil)))
}
del.rs|21 col 18 error| cannot borrow `(**prev)#1` as mutable more than once at a time
del.rs|20 col 23 n| second borrow of `(**prev)#1` as mutable occurs here
*/