Matches on &mut[] move the .. match & don't consider disjointness #8636
Description
I believe the following should work, since head and tail are disjoint, and tail is just taking a slice into v (this would mean that v is inaccessible while the result of mut_head_tail is kept around):
fn mut_head_tail<'a, A>(v: &'a mut [A]) -> Option<(&'a mut A, &'a mut [A])> {
match v {
[ref mut head, .. tail] => {
Some((head, tail))
}
[] => None
}
/* // this works currently:
if v.is_empty() {
None
} else {
let (low, hi) = v.mut_split(1);
Some((&mut low[0], hi))
}
*/
}
fn main() {
let mut v = ~[1,2,3,4];
match mut_head_tail(v) {
None => {},
Some((h,t)) => {
*h = 1000;
t.reverse();
}
}
println!("{:?}", v);
}mut-vec-match.rs:3:26: 3:30 error: cannot bind by-move and by-ref in the same pattern
mut-vec-match.rs:3 [ref mut head, .. tail] => {
^~~~
mut-vec-match.rs:3:9: 3:21 note: by-ref binding occurs here
mut-vec-match.rs:3 [ref mut head, .. tail] => {
^~~~~~~~~~~~
error: aborting due to previous error
Changing it to (and removing the t.reverse()):
fn mut_head_tail<'a, A>(v: &'a mut [A]) -> Option<(&'a mut A, ())> {
match v {
[ref mut head, .. ref mut _tail] => {
Some((head, ()))
}
[] => None
}
}mut-vec-match.rs:21:9: 21:21 error: cannot borrow `(*v)[]` as mutable more than once at a time
mut-vec-match.rs:21 [ref mut head, .. ref mut _tail] => {
^~~~~~~~~~~~
mut-vec-match.rs:21:8: 21:40 note: second borrow of `(*v)[]` as mutable occurs here
mut-vec-match.rs:21 [ref mut head, .. ref mut _tail] => {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error