How do I pass an iterator I am iterating on to a function?

I'm iterating through an array, and depending on the current value, I'd like to pass the iterator to a sub function and have it deal with a number of values, and upon exiting the sub function, carry on iterating through the array. Below is the closest I've managed to get so far, but I keep getting error: use of moved value: 'iter'.

I've tried looking into lifetimes, but that hasn't worked for me either. I've spent most of a day on this now, and can't seem to get anywhere with it. Any help would be greatly appreciated. Thanks.

enum Thing { Three(char, char, char), Four(char, char, char, char), } fn take_three <'a>(iter: &mut std::slice::Iter<'a, char>) -> Thing { let a = iter.next().unwrap(); let b = iter.next().unwrap(); let c = iter.next().unwrap(); Thing::Three(*a,*b,*c) } fn take_four <'a>(iter: &mut std::slice::Iter<'a, char>) -> Thing { let a = iter.next().unwrap(); let b = iter.next().unwrap(); let c = iter.next().unwrap(); let d = iter.next().unwrap(); Thing::Four(*a,*b,*c,*d) } fn parse_tokens (tokens: &Vec<char>) { let mut iter = tokens.iter(); let mut things: Vec<Thing> = vec![]; for token in iter { match token { &'a' => things.push(take_three(&mut iter)), &'b' => things.push(take_four(&mut iter)), _ => {}, } } } fn main() { let tokens = vec!['a', '1', '2', '3', 'b', '1', '2', '3', '4', 'a', '4', '5', '6']; parse_tokens(&tokens); }