This article was written using Rust 1.40 nightly (518deda77) with unstable features. Certain unstable features may have been changed or removed since.

Emulators are cool! They help preserve games, improve games, and help make games more accessible. On top of that, making an emulator is a cathartic and satisfying technical challenge!

So, I took this challenge myself and came out the other end with a pretty limited NES emulator, which I call Lochnes. It’s not very good at actually emulating most games, but I’m pretty happy with the guts of the thing and I learned a lot a long the way. I figured it might be worthwhile to share my approach, which might help or inspire others on their own emulation venture!

But before we get to that, let’s talk some emulator theory…

This article was written using Rust 1.13 nightly (the latest as of September 2016) with unstable features. Certain unstable features may have been changed or removed since.

Have you ever noticed how similar Rust and Swift are? I don’t mean just syntactically either– the languages have a lot of similar design philosophies:

• Both languages have pretty good static type systems that prevent many errors at compile time, like NULL reference errors
• Both languages often encourage using simple struct and enum values with traits/protocols where possible, over using object-oriented class hierarchies
• Both languages provide very nice high-level constructs (things like map, or pattern matching) that get compiled and optimized into a static, native (and fast!) binary

Really, you can’t go wrong with using either language: both are really compelling for building things in a wide range of different domains!

That said, I personally prefer Rust, so learning about Swift inspired me to sit down and think, “what can Swift do that Rust can’t, and why?” To me, the most glaring thing was that Swift is really good for app development, while Rust in this regard is… lacking.

For now, let’s just talk about building Cocoa apps for macOS. Sure, you can build a native Cocoa app in Rust right now using the cocoa crate, but it’s very far removed from writing a Cocoa app in Swift: notice the very procedural nature of their “hello world” example app.

So, how can we improve on the ergonomics of the cocoa crate?