Give your simulator superpowers

RocketSim: An Essential Developer Tool
as recommended by Apple

Issue 321
Apr 28, 2026

This week's SwiftLee Weekly covers:

  • SwiftUI Animations
  • SwiftUI Performance Tuning
  • Column breakpoints in Xcode

Enjoy this week's SwiftLee Weekly!

THIS WEEK'S BLOG POST

​Immediate tasks in Swift Concurrency explained​

Immediate tasks are new in Swift 6.2 and a useful tool when working with Swift Concurrency. You really only should use it when you truly know what it's doing, which is why I wrote this week's article in detail.

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CURATED FROM THE COMMUNITY

​An Odometer-Style Number Animation in SwiftUI​

If you love animations and you’re using SwiftUI, you’ll definitely enjoy this animation example by Artem Mirzabekian.
​livsycode.com​

​Optional has a take() function​

Some Swift features take you years to discover, like this take method on optionals explained by Scott Berrevoets.
​scottberrevoets.com​

​Recording & Analyzing SwiftUI Instruments Traces​

SwiftUI Performance Tuning just got easier: let your agents do it using this Agent Skill update by Pol Piella.
​github.com​

​Making breakpoints work with single-line code blocks​

Ever heard about Column Breakpoints in Xcode? If not, this article by Peter Ringset is a must-read.
​peterringset.dev​

​SwiftUI: Refreshable Task Cancellation​

I’ve used the refreshable modifier in SwiftUI plenty of times, but I wasn’t aware of the risk Anton Gubarenko explained.
​antongubarenko.substack.com​

SWIFT EVOLUTION

An overview of last week's Swift Proposal state changes. Check them out when they're in review, as it's your opportunity to influence the direction of Swift's future.

WHAT I'M WORKING ON

An agent-first protocol (rs/1) for Simulator Navigation

As you might know from previous newsletter issues: I'm working on a bundled RocketSim CLI. I want to reinvent how agents navigate through Simulators, and reduce token costs & time spent. RocketSim has the unique advantage of running in the background, allowing for optimizations other popular tools can't do.

I created 5 testing scenarios using the system settings app installed on every Simulator. Comparing the latest RocketSim CLI version to popular open-source alternatives, the results are quite impressive:

  • ~12x fewer tokens
  • 1.6x faster execution
  • 4x fewer wrong taps

RocketSim is able to do this due to its unique agent-first protocol (called rs/1) instead of relying on raw AX dumps. It also has a live snapshot store which allows the agent to reuse state instead of paying to rediscover the UI on every turn. Combined with semantic actions, waits, and typed errors, the agent models have to guess less and get faster to their end destination.

I've also spent a lot of time improving the discoverability of elements on screen. In my experience, elements like tab bars and navigation bars weren't always discovered by other tools.

Finally, installation will be easy due to a bundled CLI & Agent Skill, that will be symlinked from the settings screen commands:

I'm working hard this week and I hope to get it out of the door before next week, so stay tuned!

UNTIL NEXT TIME

Continue your Swift development journey

I hope you've enjoyed this week's content. You don't have to wait till next Tuesday for more insights, I share every day on these channels:

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Thank you so much for your support, and until next Tuesday,

Antoine

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