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