Our January project was ambitious: a 2D puzzle game, a-la lemmings with a twist, with big and numerous levels. And of course, all using our homegrown tools, from the compiler to the level editor to the UI system and game framework.

However, January ended too soon, and, sleepless nights notwithstanding, I had to resolve to publish something completely different. It was a good occasion to get to know Twine.

Day 2, Day 2! Woo!

The Advent of Code 2020, Day 2 problem talks about passwords. Sounds familiar.

Basically, our input looks like this:

1-3 a: abcde 1-3 b: cdefg 2-9 c: ccccccccc

Each line contains a “password policy” and a “password”. For the first line, the policy is that the password must contain between 1 and 3 (inclusive) times the letter “a”.

And we’re back!

In the last article, we thanked our old code and bade it adieu, for it did not spark joy. And then we made a new, solid foundation, on which we planned to actually make an executable packer.

As part of this endeavor, we’ve made a crate called encore, which only depends on libcore, and provides some of the things libstd would give us, but which we cannot have, because we do not want to rely on a libc.

Remember the snapshot we made allll the way back in Part 1? Now’s the time to use it.

Well, make sure you’ve committed and pushed all your changes, but when you’re ready, let’s go back in time to before we installed anything catscii-specific in our VM.

This should emulate the experience of a colleague onboarding onto the project well enough!

(I didn’t actually use VirtualBox’s snapshot feature for this, I actually set up a Ubuntu 22.10 VM on another computer entirely, but the effect should be much the same).

Welcome back to the “Making our own executable packer” series, where digressions are our bread and butter.

Last time, we implemented indirect functions in a no-libc C program. Of course, we got lost on the way and accidentally implemented a couple of useful elk-powered GDB functions - with only the minimal required amount of Python code.

The article got pretty long, and we could use a nice distraction. And I have just the thing! A little while ago, a member of the Rust compiler team stumbled upon this series and gave me some feedback.

Let’s tackle the day 16 puzzle!

Parsing

The input looks like this:

Valve AA has flow rate=0; tunnels lead to valves DD, II, BB Valve BB has flow rate=13; tunnels lead to valves CC, AA Valve CC has flow rate=2; tunnels lead to valves DD, BB Valve DD has flow rate=20; tunnels lead to valves CC, AA, EE Valve EE has flow rate=3; tunnels lead to valves FF, DD Valve FF has flow rate=0; tunnels lead to valves EE, GG Valve GG has flow rate=0; tunnels lead to valves FF, HH Valve HH has flow rate=22; tunnel leads to valve GG Valve II has flow rate=0; tunnels lead to valves AA, JJ Valve JJ has flow rate=21; tunnel leads to valve II

It’s time for the Day 14 problem!

After the hassle that was Day 13, I hope this time we’ll have a relatively chill time. And, at least for Part 1, that is true.

Our input looks something like this:

mask = XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X mem[8] = 11 mem[7] = 101 mem[8] = 0

mem is our memory. Our addresses are 36-bit wide, but as you’ll see, that doesn’t matter much.

I do not come to you with answers today, but rather some observations and a lot of questions.

The weird glitch

Recently I was editing some video and I noticed this:

Not what the finger is pointing at — the dots.

Here are the separate layers this image is made up of: the background is a stock image I’ve licensed from Envato Elements:

Because I use it as a background image, I’ve cranked down the exposition in the Color tab:

There are several Rust quizzes online, including one that’s literally called the “Unfair Rust Quiz” at https://this.quiz.is.fckn.gay/, but when I was given the opportunity to record an episode of the Self-Directed Research podcast live on the main stage of EuroRust 2025, I thought I’d come up with something special.

async_trait’s one weird type ascription trick

Now that I got the Log in with GitHub feature working, let’s explore what this would’ve looked like with the async_trait crate.

First up, the trait definition:

/// Something that can refresh credentials #[async_trait::async_trait] pub trait CredentialsRefresher { async fn refresh(&self, creds -> eyre