Hands-on Challenge: Port a Program

We've covered the bulk of Rust's most important syntax and features. While you're likely not comfortable with Rust yet, you now know the basics.

One great way to learn a new language, including its idioms and quirks, is to port an existing program written in a language you're already familiar with. That's the goal of this challenge.

Now we're not advocates of the "Rewrite-It-In-Rust" (RIIR) trend, although there are some great Rust alternatives to existing tools out there¹. Rewriting a large piece of software is a risky proposition that, in many contexts, has questionable payoff.

It's typically wiser to write new features, new services, or hardened components in Rust - such that they can interoperate with existing code. Chapter 13 will cover integrating Rust into non-Rust codebases.

Our motivation for this challenge is gaining a deeper understanding of Rust via contrast. Not all idioms and patterns of other languages readily translate, so experiencing those differences first-hand can be enlightening.

"Failing" is OK

You might get stuck somewhere in your port attempt. Depending on the program you choose. That's fine!

If that happens, use this challenge as a "personal watermark" - note how far you've come and what the error was. You can return to the challenge later, after you've had more Rust experience. Whenever you're up for it.

Port a Program of Your Choice To Rust

• Choose a small program (maybe less than 1,000 lines) written in a language you know, and rewrite it from scratch in Rust. We recommend you pick a program you've personally written, especially if you ran into performance limitations. But any program you're deeply interested in is a good choice.

  • Before starting your rewrite, review your program's dependencies. If it uses one or more libraries that have no counterpart on Rust's crates.io, you will either need to choose a different program or also write the dependency yourself. Don't over-scope this challenge!

Semi-automate a C to Rust Port

• If you're already an experienced C developer, you can try porting an existing C program using the c2rust² tool. It's an unofficial, open-source, best-effort transpiler that ingests C source code and outputs Rust source code.

  • The output Rust is, however, both unidiomatic and as unsafe as the input C. Translating C to safe Rust is an open research problem³ that involves inferring program semantics. So you will still need to do extensive refactoring.

  • Some readers may prefer to return to this challenge after Chapter 13, which covers CFFI and unsafe.

  • If you've never written C before but you're incredibly brave and want or need to learn it, you can still do this challenge! We recommend picking up a copy of Effective C⁴ to get started.