You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tee.rs
    path of file: ./repos/itertools/src
    
    the code of the file until where you have to start completion: use super::size_hint;

use alloc::collections::
    
    fn next(&mut self) -> Option<Self::Item> {
        // .borrow_mut may fail here -- but only if the user has tied some kind of weird
        // knot where the iterator refers back to itself.
        let mut buffer = self.rcbuffer.borrow_mut();
        if buffer.owner == self.id {
            match buffer.backlog.pop_front() {
                None => {}
                some_elt => return some_elt,
            }
        }
        match buffer.iter.next() {
            None => None,
            Some(elt) => {
                buffer.backlog.push_back(elt.clone());
                buffer.owner = !self.id;
                Some(elt)
            }
        }
    }