I massively overdo the bit where I trademark something with ™ and now autocomplete knows me

The App Launch instrument is your best friend when troubleshooting launch times locally:  Don’t forget to check the Xcode Organiser and your analytics SDKs for launch performance measurements in the wild. Your shiny new iPhone 17 Pro Max does not represent your median users' iPhone 12.

Swift Regex is cool and all, but honestly I can't be bothered to learn another bloody DSL, especially one that isn't portable (or, honestly, ChatGPT-able). I prefer the good old-fashioned NSRegularExpression. This is also the only time I ever use `infix operator` in production!

Pro tip for people just trying to make money on Substack: You you can just ask your readers what they want you to write, and the thing with the most votes makes the most money.

You wouldn't believe how long it used to take to ship apps before Claude Code. With some ruthless prioritisation and scope cutting, we released the Carbn MVP in late 2020 after 3 months of work, complete with: * The world’s most accurate™ Carbon footprint calculator

Swift was primed to be a great language, but it has fallen far from its original vision. Today, we’re going to learn how modern programming languages are governed, then I’ll explain how Swift’s structure is uniquely dictatorial. Is there hope for Swift's future?

I’ll warn you, the runtime implementation of the default actor is complicated. 3,000 lines of C++ complicated. I’ll do my best to keep it short. On first glance at the protocol in Actor.swift, you might convince yourself that an actor is a quaint wrapper over a serial executor. To look at the SIL,

Worst deprecation ever? Don’t you warn me to update then suddenly change the whole signature from sync to be `async throws`…

We did it lads, top #100, no more desperate sales 💸

Wi-Fi on train deteriorated substantially: quality of life significantly reduced.

The AI gold-rush is in full swing. And in a gold rush, you steal shovels 🪏🦹‍♂️ One deadly mistake is commonplace: bundling ChatGPT API keys directly into your shiny new AI app. This makes it trivial to steal your keys, burn through your credits, and rack up painful bills.

After parallelising my app launch sequence, now my app is crashing on launch! 🤪 Subscribe to my newsletter to accelerate your iOS career with new posts every week! 🚀 blog.jacobstechtavern.com/subscribe

Actors set up A LOT of behaviour under the hood at compile-time to enforce isolation. We can see the underlying machinery set up when we compile our Swift code into Swift Intermediate Language. There are two interesting pieces to look at here. First, let’s check out MyActor’s init (screenshot #1)

We've all heard of Static and Dynamic dispatch, but how much do you really understand these concepts? - What is the true performance cost of dynamic dispatch? - How does the compiler know when to make something static? - What do static and dynamic functions work like under the hood?

With my right hand I write a sick article that brings in $12 and with my left hand I immediately spend it on a beer in London

Due to a chance encounter in the Swift developers Slack group, the mystery of the subscriber coming from AI has been solved! Nice to see I'm finally showing up in the training data 😄

Launch time is rarely the top priority when shipping an MVP, but can slowly morph into a serious headwind for your product if you leave it unchecked. We took a disastrous 6.5-second launch and reduced it 4x with my battle-tested techniques:

Actors are a lot more complex than we give them credit for. We can write a dead-simple actor in a few lines of code. The compiler does a lot of work setting up the executor, associating it with the actor, and enforcing async boundaries wherever the actor is accessed. To see this compile-time

I was watching an old, old WWDC talk and it was very quaint how all the attendees got handed a CD-ROM with the MacOS and Xcode betas on it

Advanced Swift Concurrency: Launch Speed Optimisation You can parallelise app launch work in didFinishLaunchingWithOptions using a GCD DispatchGroup to wait and Swift's taskGroup to parallelise steps

When it’s Tuesday so there’s no more Jacob’s Tech Tavern for 6 whole days

🚨 NEW ARTICLE ALERT: HOW ARE ACTORS IMPLEMENTED? 🍺 Actors do a ton of work under the hood to enforce data isolation. Read my blog post know to plumb the forbidden depths and learn how actors are implemented under the hood 🛠️ blog.jacobstechtavern.com/p/how-are-sw...

Anyone who’s built a complex system on early platform-as-a-service tools will run into limitations, hard. AWS Amplify is magic when shipping an MVP, but it has myriad invisible guardrails that smack you in the face as soon as reach out for flexibility.

Advanced Swift Concurrency: Task Groups If async let allows you to run a specific number of arbitrary tasks, task groups run an arbitrary number of specific tasks. They’re a more advanced parallelisation mechanism that doesn’t require you to know the number of jobs at compile-time. You can

Order files are an obscure but critical launch-time optimisation tool.

FREE ARTICLE UNLOCKED 🔓 If you were ever curious about Swift reference counting internals, the most comprehensive deep-dive ever written is now free for everyone to read. Catch it here: blog.jacobstechtavern.com/p/swift-refe...

In Swift Concurrency, Tasks may be initialised with a priority, so we can give the executor guidance about which concurrent code to execute first. This `warmModelCache()` method runs a high-priority task to set up a heavy machine learning model from the file system and caches it in memory.

Those are my emotional support print statements. I need them.

Advanced Swift Concurrency: Pausing a Thread vs Task The APIs for suspending execution are very similar between a thread and a task. The Thread calls sleep, which blocks the thread for the time, meaning it can’t execute any work.

Advanced iOS internals: Mergeable Libraries Mergeable libraries are the hot new approach to linking strategies introduced Xcode 15. They are actually very straightforward, since we now understand the problems they’re trying to solve. Mergeable libraries are designed to link dynamically in debug

Advanced Swift tips: Easily Debug Performance While Instruments are very comprehensive, sometimes you just need timestamps for, e.g., a view first appearing and its data loading up. This helps you locate performance bottlenecks in your code.

Did you know you can use Metal directly in SwiftUI? Code along with my tutorial that assumes ZERO C++ knowledge! Check it out here 🚀 blog.jacobstechtavern.com/p/metal-in-s...

I'm from South London so I have to fight my instinct to write initialisers like this every time

The Swift Apple doesn’t want you to know about: malloc, free, and withUnsafeTemporaryAlloation In order to provide the high level memory-safe interface that we work with every day, Swift requires some amount of low-level unsafety. For example, Data relies on the UnsafeRawPointer and Array uses

AI coding negates 100% of the productivity boost from SwiftUI. You have my permission to migrate back to UIKit.

The UX for installing a Swift Package kinda sucks. I just spent 10 mins debugging a build error because I was meant to install SnapKit target but *not* SnapKit-Dynamic. Why cant there be a tiny little explainer or doc comment showing which targets you might want?

How to use AUTORELEASEPOOL in the real world to reduce your peak memory footprint With an autoreleasepool block, each UIImage and file data in our loop are released upon leaving the scope of the pool. Therefore the loop iterations don’t add up, and peak memory use stays nice and level.

Vibe-coded a prototype in UIKit + MVVM + Combine last night. Retro AF but felt great 🕹️

Far be it from me to pick nits, but were they drunk when they decided on the distribution of line breaks in the base app delegate file?

I built a SwiftUI view modifier with Metal that turns any app into an 8-bit videogame! blog.jacobstechtavern.com/p/8-bit-retr...

Advanced Swift Concurrency: Jumping to the Main Thread vs Main Actor It’s critical to move work between background threads and the main thread, in order to update any UI. The Thread API doesn’t give any natural control over this, so we should really just rely on GCD in this instance.

Increasing Headcount at my first startup: Fresh off a funding round, we had a cool £200k in the bank. I took a cheeky 3-week break to hang out with my new baby, because it’s not like we were going to get any more time together for the next 12 months.  We wanted to run cool, so just had 2 key

Advanced Swift Concurrency: Pausing a Thread vs Task The APIs for suspending execution are very similar between a thread and a task. The Thread calls sleep, which blocks the thread for the time, meaning it can’t execute any work. The OS will be able to switch threads and schedule other work while

maturity is realising "legacy code" is a good thing

It’s common to focus on post-main launch time, including all the code you wrote that runs after Swift’s main()function is called in your app. But pre-main launch time can also be a factor, and depends on your modular architecture. Dynamic frameworks in particular are really important to understand:

The terrible architecture of my first startup: Subscribe to my newsletter to accelerate your iOS career with new posts every week! 🚀 blog.jacobstechtavern.com/subscribe

If he was dictator for life why didn’t he just make everyone upgrade to Python 3? 🤔

Advanced Accessibility in SwiftUI: Using accessibilityRepresentation to help the screenreader Learn how to speed run accessibility in your SwiftUI app in the full (free) article: blog.jacobstechtavern.com/p/oh-sht-my-...

They should declare a bank holiday the day we all update our MacOS versions, the same amount of work would get done

Caught a SQL injection attack in the wild! 🤪