A while back, I asked on Twitter what people found confusing in Rust, and one of the top topics was “how the module system maps to files”.

I remember struggling with that a lot when I first started Rust, so I’ll try to explain it in a way that makes sense to me.

Important note

All that follows is written for Rust 2021 edition. I have no interest in learning (or teaching) the ins and outs of the previous version, especially because it was a lot more confusing to me.

In my previous article, I said I needed to stop thinking of Rust generics as Java generics, because in Rust, generic types are erased.

Someone gently pointed out that they are also erased in Java, the difference was elsewhere. And so, let’s learn the difference together.

Java generics

I learned Java first (a long, long time ago), and their approach to generics made sense to me at the time.

I’ve been looking for this blog post everywhere, but it doesn’t exist, so I guess it’s my turn to write about Some Fun with Rust.

The task at hand

Let’s say you have a recursive, acyclic data structure, like so:

struct Node { values: Vec<i32>, children: Vec<Node>, }

This allows you to represent a tree-like structure:

[1, 2, 3] /\ / \ / \ / \ / \ [4, 5] [6, 7]