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: tokens.rs
    path of file: ./repos/pest/pest/src/iterators
    
    the code of the file until where you have to start completion: // pest. The Elegant Parser
// Copyright (c) 2018 DragoÈ™ Tiselice
//
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or http://www.apache.org/licens
    
    fn next(&mut self) -> Option<Self::Item> {
        if self.start >= self.end {
            return None;
        }

        let token = self.create_token(self.start);

        self.start += 1;

        Some(token)
    }