The borrow checker maaaan

I can only speak out of my own experience, which is mostly C++, C#, C and Rust, but I also know a bit of Haskell, Java, Fortran, PHP, Visual Basic, and, to my deepest regret, also JavaScript.

For additional context: I have been working in game development for the last 7 years, my main language is C++ for Unreal, but I’ve also worked on some Unity projects with C# as main language. Before I switched to game dev I worked in material science, and used C, mostly. I use Rust for my spare time projects, and the game company I work at is planning to introduce it into our Unreal projects some point later this year.

Of all the languages I mentioned above, (Safe) Rust and Haskell are the only ones that have not yet made me scream at my PC, or hit my head against the desk.

So, some of the reasons why I personally love Rust:

• Rust is extremely simple compared to the other languages I mentioned above. If you read the official introduction you know all you need to write Safe Rust code.
• Rust’s syntax is elegant. It’s not as elegant as Haskell, but it’s a lot more elegant than any C-based language.
• Rust is (mostly) type safe. There are (nearly) no implicit conversions.
• Rust is memory-safe, without the runtime overhead that garbage collected languages incur.
  • This is a bit of a neutral point though. The Rust compiler will complain if you make mistakes in memory management. Unlike in managed languages, you still need to do the memory management by hand, and find a working solution for it.
• The memory management model of Rust (“borrow checker”) makes data dependencies explicit. This automatically leads to better architecture that reflects dependencies, because if the architecture doesn’t match them, development will become an uphill battle against the borrow checker.
• Due to the borrow checker, you can use references extensively, and rely on the referenced object to valid, and also that it is up-to-date (because it cannot be muted or go out of scope as long as you hold the reference).
• Traits are an amazing way to abstract over types. Either at zero-cost (static dispatch), or, in the rare cases where it’s needed, using virtual function tables.
• Rust aims to have no undefined behaviour. If it compiles the behaviour of the code is well defined.
  • This, together with the borrow checker, ensures that there are (nearly) no “weird bugs”. Where in C++ one quite regularly hits issues that at first glimpse seem impossible, and only can be explained after several days of research on cppreference (“oh, so the C++ standard says that if this piece of code gets compiled on a full moon on a computer with a blue power LED, it’s undefined behaviour”), that almost never happens in Rust.
• Macros in Rust are amazing. There are macros-by-example that work by pattern-matching, but there are also procedural macros, which are Rust functions that take Rust code as input, and generate Rust code as output. This gives you amazing power, and one of the most impressive examples is the Serde serialization framework, that allows you to add serialization to your data types simply by adding an attribute.
• Tooling for Rust is pretty good. The Rust compiler is well known for its helpful error messages. The rust-analyzer plugin for Visual Studio Code is great too. (It also works with vim, Qt Creator and others, but the but Visual Studio Code works best imho.)

The points mentioned above mostly apply to Safe Rust though. Unsafe Rust is a different story.

This brings us to the downsides. Rust isn’t perfect. Far from it, actually. Here are some of the things that aren’t great about Rust.

• No Higher Kinded Types. This is my main issue with Rust. Even C++ has them (as usual for C++ in a horrible un-ergonomic and utterly confusing way). If Rust had Higher Kinded Types, the language could have been simpler still. For instance, there would have been no need for the async keyword in the language itself.
• Unsafe Rust is hard. In my opinion even harder than C++, because of Rust’s aliasing rules. Unlike C++, Rust doesn’t allow mutable memory aliasing. That’s because mutable aliasing can never happen in Safe Rust, and not supporting it improves performance. This means that when writing Unsafe Rust, one has to be careful about aliasing.
  • Luckily one only rarely needs Unsafe Rust, usually only in order to call functions from other languages. Still, it’s hard, and I’d generally suggest to use an automated code generator like cxx.rs for interfacing with other languages.
• Interior Mutability. I understand why it exists, but it breaks a lot of the guarantees that make Rust a great language. So, my conclusion is that one should avoid it as much as possible.

However, the upsides clearly outweigh the downsides imho.

tl;dr If a (Safe) Rust program compiles, chances are pretty high that it also works. This makes programming with it quite enjoyable.

It’s a cult. A vocal minority doesn’t speak for an entire industry.