From https://thesquareplanet.com/blog/the-path-to-rust/

rust_reg.rs

// From https://thesquareplanet.com/blog/the-path-to-rust/
// Example 2: non-functional
let mut idx = HashMap::new(); 
for fname in &args {
  let f = match fs::File::open(fname) { 
    Ok(f) => io::BufReader::new(f), 
    Err(e) => panic!("input file {} could not be opened: {}", fname, e), 
  }; 
  let mut words = HashSet::new(); 
  for line in f.lines() { 
    for w in line.unwrap().split_whitespace() { 
      if words.insert(w.to_string()) { 
        // new word seen 
        idx.entry(w.to_string()).or_insert(Vec::new()).push(fname); 
      } 
    } 
  } 
}