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Forays from Node to Rust

Why Rust?

A couple of years ago I picked up the excellent Programming Rust book.

Reading how the Rust compiler enforces memory safety and avoids data-races reminded me of the AHA! moment, when I learned how Node.js makes concurrency accessible to JavaScript developers, without the synchronization headaches of multi-threaded servers.

But there's more. Rust programs have a very minimal runtime - no garbage collector or class loader. This makes Rust ideal for constrained environments like embedded systems or edge compute platforms - so watch this space.

First impressions

This article covers the experience of buiding my first Rust crate.

The shortscale-rs library tries to replicate shortscale, a small JavaScript module with just one function which converts numbers to English words.

The Rust ecosystem has produced an absolutely awesome array of tools and documentation.

To get started:

Those steps also take care of cargo, the Rust build tool.

Image showing cargo commands

VS Code

I followed the recommendations of Jason Williams to install Rust Analyzer for VS Code instead of the default Rust extension. You'll also need CodeLLDB for debugging.

VS Code showing Rust program

I particularly like the ability to run doctests directly in the VS Code terminal.

Rust String and str

In JavaScript building strings is straightforward. Simply use + to concatenate any string to any other string. Empty strings being falsy helps to write very compact logic.

The example below from shortscale.js behaves like the built-in Array.join, except that it avoids repeating separators by ignoring empty strings.

// concatenate array of strings, separated by sep, ignoring '' values
function concat(strings, sep) {
  return strings.reduce((s1, s2) => s1 + (s1 && s2 ? sep : '') + s2, '')
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Here's my first attempt to do something similar in Rust.

type Strvec = Vec<&'static str>;

// concatenate 2 Strvec's, separated with "and" if both have length
fn concat_and(v1: Strvec, v2: Strvec) -> Strvec {
    match (v1.len(), v2.len()) {
        (_, 0) => v1,
        (0, _) => v2,
        (_, _) => [v1, vec!["and"], v2].concat(),
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'Why Strvec?', you might ask. In Rust, the primitive string type, used for string literals, is a str. My first thought was that shortscale-rs should manipulate collections of str's. So, instead of using String concatenation, I put str's into Vec's.

Notice the elegant match syntax - one of my favorite Rust language features. The compiler ensures that the 'arms' of the match cover all possible inputs. The result is both readable and concise. The '_' is shorthand for any value.

Performance does not matter,
until it absolutely does.


The measured performance was, well, an eye-opener! ~4459ns per shortscale_vec_concat call in Rust, compared to ~1342ns for the equivalent in Node.js.

cargo bench

shortscale                          251 ns/iter (+/- 18)
shortscale_string_writer_no_alloc   191 ns/iter (+/- 11)
shortscale_str_push                 247 ns/iter (+/- 22)
shortscale_vec_push                 363 ns/iter (+/- 26)
shortscale_display_no_alloc         498 ns/iter (+/- 21)
shortscale_vec_concat              4459 ns/iter (+/- 344)
shortscale_string_join             5549 ns/iter (+/- 378)
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npm run bench

shortscale                         1342 ns/iter
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Clearly the v8 JavaScript engine in Node.js is working very hard to make string manipulation efficient.

Learn & Iterate

The next thing I tried was to replace the Vec collections with simple Strings, creating and returning those from each function in the Rust program. This is shortscale_string_join. You should see from the benchmark, that its performance was even worse. Clearly I was doing something wrong.

Fast forward to the current implementation, which mutates a pre-allocated String rather than calling functions which create and return new Strings.

The result is significantly faster than JavaScript.

I still have a lot to learn, but this exercise was a great way to start building an intuition for Rust development and the performance of Rust primitives.

Top comments (1)

rishitkhandelwal profile image
Rishit Khandelwal

Did you know we could use JavaScript in rust?
It is amazing.