Mastering Rust - Second Edition

Exercise – fixing the word counter

Armed with the basics, it's time to put our knowledge to use! Here, we have a program that counts instances of words in a text file, which is passed to it as an argument. It's almost complete, but has a few bugs that the compiler catches and a couple of subtle ones. Here's our incomplete program:

// word_counter.rsuse std::env;use std::fs::File;use std::io::prelude::BufRead;use std::io::BufReader;#[derive(Debug)]struct WordCounter(HashMap<String, u64>);impl WordCounter {    fn new() -> WordCounter {        WordCounter(HashMap::new());    }    fn increment(word: &str) {        let key = word.to_string();        let count = self.0.entry(key).or_insert(0);        *count += 1;    }    fn display(self) {        for (key, value) in self.0.iter() { println!("{}: ...