Hmm, I see the author liberally using _filename as a variable name saying "I just use names with underscores as functions arguments names".

However: In Rust, variables starting with underscores are usually indicating unused ids and if you actually forget to use it - you will not get a warning. As a tutorial material this sets very wrong mindset for the beginners. ONLY start variable with an underscore if you mean to not use it.

@jesselawson - please update this.