My Reasons For Using Rust (as a Ruby developer)

By now, there are thousands of articles explaining why Rust is a good option/the fastest/cleanest/nicest/whateverest. While reading about objective attributes that speak for- or against a programming language, a talk by Owen Synge stuck with me.

He explains why he likes Rust. Why he chose it. And what he values in a language. I took this idea for my rust presentation. And now wanted to explain it in some more detail.

I like this perspective, because it shows whether the person promoting Rust, values the same attributes; it shows why someone chose a language, framework or architecture with relevant context.

For me, the three most important attributes of a framework or language are that:

  • Software should work for decades.
  • A system has Good Defaults™: Being Lazy leads to good software; To make "bad" software you must employ extra effort.
  • It is Simpler (not necessarily easier) to maintain, host, test, and deliver.

I am, primarily, web-developer. Lot's of backend work, with DevOps and infrastructure automation and occasionally frontend development. But all the software that I write is to support mobile- and web-apps. This means that attributes like being able to run on this 20 years old ACME controller or even the performance, are less important or even irrelevant. For me.

I've been developing in Ruby and Rails since 2005 and full-time since 2013.

I try not to advertise myself as an "X developer", but use the language that fits the use-case best. On a typical day, I'll write some Ruby, some Python, kludge around with JavaScript, do some Typescript and write some Rust.

While I think it's important to train myself to be a Polyglot programmer, I'll always have one Go-to language. One language that I know much deeper, for which my environment is tuned, which I have much more experience in, and so on. Currently that is Ruby, but I'm quickly shifting that to Rust.

Because Rust ticks those boxes.

Software should work for decades

Most of my software, over 90%, is archived, obsolete, unused, dead. But in the rare 10%, I want to be sure that it can be maintained over longer time. Yet it is impossible to guess up-front what this 10% is. There is software running, which I quickly hacked up late-night in an emergency. Which has been provisioning thousands of WordPress servers for almost 10 years now, it got improved later, though. Yet a very cleanly architectured ORM for a REST backend, with all sorts of Design Patterns, has ran for a few months in a staging environment, and then threw out because we decided PHP/Drupal really wasn't going to cut that project.

Which is why I at least try to architecture all code in a way that it can be improved upon. It doesn't have to be good at the start, but must be possible to be made good later.

The programming language, a framework and its ecosystem solidify a lot of options early on. More then The Architecture, in my experience. It's relative easy to re-architecture something: incremental refactoring. But it's not easy to swap out a framework or language for another. That almost always requires big rewrite, which, as we all probably know, is a company-killer. A wrong choice of language or framework leads almost inevitably to a painted yourself into a corner problem.

And those solidified options should support maintenance over long time. This is where software architecture plays the biggest role, but language has an important say in this. As does the culture of the ecosystem.

In Rails, for example, it is made explicitly clear that doing "stupid things" is OK. While I applaud the idea that it is possible, I have seen this lead to problems in every Rails project that I worked on. Where maintaining some "smart" hack, fancy DSL or full-featured library over time required recurring, and significant cost. Even grinded entire teams to a halt. Not even able to react to market. But even when, with great discipline, you manage to keep your application clean and maintainable, there are technical fundamentals, of the language that make maintenance harder or easier.

Ruby, like Python, for example, requires complex runtime environments and versioning. Rbenv, Gems, Bundler, whatnot. All of these move all the time. Every week at least one of my "shelved" Ruby projects, or JavaScript dependencies needs some critical security update. Any Ruby project that I haven't touched for months, requires significant effort to just get running locally. If at all. I have a tiny rust plaything which I wrote, is finished, and keeps running without me ever looking at it [for months](. As a Ruby developer, this is a new experience!

This is less visible when you have a team working on one project day in day out. But I can assure you, the total time spent on upgrading gems, pips, npm, linter, CI, tests just to keep it running month-to-month is significant. All this is effort I cannot spend on writing the software (that makes me money).

It is more visible in agencies that have many PHP, WordPress, Drupal, Rails or Django projects. Where a client comes back after 20 months to ask for that X integration, which then, most often turns into a full-blown rewrite of the entire project[1].

Rust was built with stability in mind. It's one of the core principles is to be fully backwards compatible and support versions forever.

The release of Rust 1.0 established "stability without stagnation" as a core Rust deliverable. Ever since the 1.0 release, the rule for Rust has been that once a feature has been released on stable, we are committed to supporting that feature for all future releases.

Rust invented a smart combination of versions, editions and releases, in which it can continue rapid improvement to avoid stagnation, but to ensure the project you write today, will compile and run in ten years. And to help you upgrade, if you want, but never force you to.

The crates system: libraries, with dependency management, support this idea too. You'll continue to have access to old libraries, can easily keep them locally, or even on a self-hosted library-server. But where all ruby-gems, pips, or npm-packages must run on the same environment, with Rust you can mix and mash old and new libraries just fine.

Any future compiler will compile your old rust code, so you can pick up an old project work on that, alongside any now modern rust projects. You'll miss features, you might be confused by how stuff was done back then, but it will compile. It will compile any old dependencies alongside any newer. And it will run.

A system has Good Defaults™

I'm a lazy programmer, or at least try to be. And working test driven (TDD), this means cutting corners, writing the quickest hack that works, before refactoring and cleaning up. But often a rough, hard-coded or duplicated piece of code will make it to production: I also don't like to waste time on cleaning up stuff that the customers don't need. And even if I, and my team, were always diligent, and industrious, there will be a deadline, or emergency, where corners must be cut. Where code is rushed out.

I want my frameworks and programming languages to acknowledge this.

To make Doing the Proper Thing easy, and doing the bad thing possible, but harder. That way, I, the lazy programmer, build secure, clean, maintainable software when I'm being lazy. Will forget a private marker. I will forget to make a variable immutable. I will make a typo in a filename of a source file. I will forget to mark a dependency as requirement for this one module.

Rust was built with this in mind. And it trickles down into many of the frameworks, libraries and working-groups.

The most visible is how all variables are immutable, unless you explicitly make them mutable. How definitions, attributes and variables are private, unless you mark them public. How no dependencies are available until explicitly included. How all code is memory safe unless you explicitly mark a chunk as unsafe. And so on.

You'll have to write extra keywords, insert deliberate markers and keywords to "do the worse thing". Not that mutable variables are always bad, but immutable, if possible, is better. So when the software makes me think hmm, do I really need this to be mutable? What if instead I just....

Slightly less visible is how the Rust compiler forces you to handle all exceptions and errors explicitly. You'll never see your Rust program crash because some file could not be read, without first explicitly allowing that crash in the code. And therefore think about that case. This goes for anything that could go wrong. From parsing a CSV, to missing commandline arguments, to form-fields being empty: if it crashes, you explicitly allowed that crash (which is as simple as a .expect("Reticulating Splines")-call though).

Cargo, the default Rust toolkit, comes with a formatter that will format my code according to Community Best Practices. It comes with a test framework and runner. No need to set that up one day. It's there, at the first commit. It comes with a linter. The rust compiler, famously won't compile if it sees errors. All that is available on my laptop, CI, build system, without any configuration, or set-up.

Cargo assumes a well-documented layout of the code, that makes any rust project recognisable, but mostly avoids me having to spend time on decisions on my directory and file-layout: it follows the code-layout. It's clear where tests go, it's clear how modules are split, how to name directories.

I can configure or override all this. I can change the linting and formatting rules (I know at least two former co-workers who would immediately spend days tuning all this....). But being lazy, I'd rather leave them at the defaults. And those happen to be extremely well thought out.

It is Simpler to maintain, host, test, and deliver.

Rust -by default- statically compiles its runtime and dependencies in the resulting binary. This comes at the cost of rather big binaries, but it means that I can just plonk the compiled binary for Linux, onto a Linux machine and run it.

All dependency management is done compile time. This makes deployment as easy as an rsync or scp and a restart.

It makes a CI workflow ridiculous simply: a mere cargo check or cargo build --release. No need to setup rbenv, or compile the right version of node or python. No need to add test frameworks or set up linters. It's all there.

The built-in test-runner will parallelize your builds, will find the tests based on naming conventions. Will build the project in test-mode, will report in one of many popular test-report formats. And so on. All without configuration or set-up.

In a typical Ruby project, almost half my tests are to catch cases that a proper type system would catch. Things like what if the email is null or what to do when the file cannot be read. With Rust, I trust the compiler for all this. My tests can then focus only on business-logic. I write and run a lot less tests.

Delivering the software is about as easy as deployment. Just email someone the binary, or .exe and have them run it. No need to unzip jars, install runtimes, check for versions, DLLs or .so files. The binary for your architecture will most likely just run.

And when maintaining software, complexity is the enemy. Simple the antidote, but getting there, is not easy.

Rust doesn't offer direct tools to help make software simpler. I'm afraid that's more of an art. But it does offer a well-designed, large standard library. Every week I find a chunk of code that I can replace with a single call to something Rust offers out of the box. Often removing tens or even hundreds of lines of code. And more often than not, you don't need third party libraries or even frameworks to build a feature.

Rust promotes commandline tools in it's tutorials and books. Rather than desktop, HTML or GUI applications. It makes it easy to rapidly crank out a new project, rather than shoehorning a feature into the existing project (make the "good option" the "easy option"!).

Any downsides?

Rust is certainly not perfect for me, though.

The lazy trait, has another perspective, for example. I don't always want to think about a potential error like, say "the CSV file not being UTF8", but Rust forces me to deal with that edge-case. Even if this is a tool to run over a single CSV file and then get archived. Developing in Rust is certainly slower for me, than in Ruby. Part of that to experience. But a large part to how rust forces me to deal with all sorts of use-cases always, all the time.

While I appreciate that Rust has no class inheritance, and relies only on composition, Its lack of classes and objects are unfamiliar to me. And require me to re-learn a lot of design-patterns. To design setups that I commonly write without even thinking about. I expect this to fade over time, as I gain experience with traits and structs, but I do miss it often.

I typically try out ideas outside of my codebase. A quick, isolated proof of concept or mock. Isolation being the key. With python, JavaScript or Ruby that is a mere python3, node or irb away. Rust has an online playground but I miss being able to do this locally. A quick cargo init trial works, but I find it to still be a too big hurdle often, and continue hacking in my actual project. And inevitably get distracted by some incompatibility or unrelated error, and then fail the PoC. It doesn't have to be a REPL, just a really fast scratchpad or temporary workspace.

But even when I work in Python, or Ruby, Bash, JavaScript, I apply the lessons that my newest senior peer-programmer has taught me. The lessons that the Rust-compiler taught me. So even when I don't write Rust, Rust has made me a better programmer. Or less-bad, maybe?


  • [1] I consider this a terrible business model; I know from own experience that rewrite or upgrades to newer versions are a significant source of Revenue for Drupal agencies. I dislike this very much.

  • [ ] It is perfectly possible, though to compile a binary that dynamically links, or requires external runtimes or other dependencies. But that requires extra flags, config and work. Another example of the "good defaults".

Woodcut from Doré. Purely illustrative
Doré Woodcut. Its only function is to make the layout look better. And these images are really nice themselves

About the author: Bèr Kessels is an experienced webdeveloper with a great passion for technology and Open Source. A golden combination to implement that technology in a good and efficient way. Follow @berkes on Mastodon. Or read more about Bèr.