Tuesday, 29 May 2018

Evolving Rust

At the start of the year I talked about using Rust as a tool to write code that was safe, easy to understand, and fast (particularly when working on code with a lot of threads, which is important in the new era of mainstream desktops with up to 16 hardware threads).

Since then I've been working on a few things with Rust and enjoying my time - especially in some cases where I just wanted to check basic parallelism performance (taking advantage of a language where you can go in and do detailed work but also just call to high-level conceptual stuff for a fast test). If you're looping through something and want to know the minimum benefit of threading it, just call to Rayon and you'll get a basic idea. In practice, that usually means changing the iterator from an .into_iter() to .into_par_iter() and that's it.

I finally upgraded my old i5-2500K desktop (on a failing motherboard from 2011) to a new Ryzen 7 so it's been very useful to quickly flip slow blocks of code to parallel computation. When you're just building some very basic tool programs, I'd probably not even think about threading in C, but here it is so easy that I've been quick to drop a (for example, typically) 30ms loop down to 3.5ms. One of the things I've been somewhat missing is easy access to SIMD intrinsics, but this brings me to something else I've been enjoying this year: Rust is evolving.

I'm used to slowly iterating standards with only slight upgrades between them as tools like compilers improve and the std lib slowly grows. Clang warnings and errors were a massive step forward that didn't rely on a new C standard and libraries can offer great features (you'd otherwise not have time to code yourself) but when I think of C features then I generally think of language features that are fixed for quite some time (about a decade).

Rust is currently working on the next big iteration (we're in the Rust-2015 era, which is what Mozilla now calls 1.0 onwards, with Rust-2018 planned before the end of the year) but that's via continuous updates. Features are developed in the nightly branch (or even in a crate that keeps it in a library until the design is agreed as a good fit for integration into the std lib) and only once they're ready are they deployed into stable. But that's happening all the time, even if a lot of people working with Rust swear on nightly as the only way to fly (where you can enable anything in development via its associated feature gate rather than waiting for it to hit stable).

For an example of that, SIMD intrinsics are currently getting ready to hit stable (probably next release). That's something I'm extremely eager to see stabilised, even if I'm going to say the more exciting step is when a Rayon-style library for it exists to make it easier for everyone to build for, maybe even an ispc-style transformation library.

The recent Rust 1.26 update is a great example of how the language is always evolving (without breaking compatibility). 128-bit integers are now in the core types; inclusive ranges mean you can easily create a range that spans the entire underlying type (without overflow leading to unexpected behaviour); main can return an error with an exit code; match has elided some more boilerplate and works with slices; and the trait system now includes existential types.

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