A Rust To-Do List CLI App (Part 1): Clap, TDD, and a HashMap That Behaves

I like small tools that disappear into your workflow. Not “disappear” as in crash silently — disappear as in you stop noticing they exist because they just work. A tiny CLI you can run 30 times a day without thinking. Fast. Predictable. Boring in the best way. So for my first “real” Rust project, I followed a classic learning move: rebuild something simple, but treat it like it’s going to ship. This post is a guided walkthrough inspired by (and crediting) Claudio Restifo’s to-do CLI tutorial. I’m using his approach as a reference point while adding my own beginner-friendly notes and a more TDD-ish mindset. Any code snippets shown below are either directly from, or adapted from, that tutorial and the Rust Book examples — this is not presented as original code. (Mistakes in the explanations, if any, are mine.) Production Grade Rust CLI: https://tobiweissmann.gumroad.com/l/vxlefy What we’re building (and why it’s worth it) A tiny CLI called todo that can: Manage a list of entries: each it