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: scoped_map.rs
    path of file: ./repos/gluon/base/src
    
    the code of the file until where you have to start completion: //! A map data type which allows the same key to exist at multiple scope levels
use std::borrow::Borrow;
use std::collections::hash_map::{
    
    fn next(&mut self) -> Option<(&'a K, &'a V)> {
        loop {
            match self.iter.next() {
                Some((k, vs)) => {
                    if let Some(v) = vs.last() {
                        return Some((k, v));
                    }
                }
                None => return None,
            }
        }
    }