The hottest Runtime Substack posts right now

And their main takeaways
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Ancient Secrets of the Objective-C Runtime

Jacobā€™s Tech Tavern ā€¢ 2842 implied HN points ā€¢ 09 Dec 25
šŸ•¹ Technology Runtime
  1. The Objective-C runtime has powerful internals that go well beyond @objc and selectors, and those capabilities can be leveraged in modern Swift apps today.
  2. Learning how message dispatch, objc_msgSend, and the runtimeā€™s class/method structures work lets you apply practical techniques to simplify and extend UIKit and Swift codebases.
  3. Studying Objectiveā€‘Cā€™s design and runtime is both interesting and immediately useful, giving you new tools and insights to improve current app development.

Copy-on-write teaches you EVERYTHING about Swift Internals šŸ®

Jacobā€™s Tech Tavern ā€¢ 2405 implied HN points ā€¢ 15 Dec 25
šŸ•¹ Technology Runtime
  1. isKnownUniquelyReferenced is the tiny runtime check Swift uses to tell if a heap-backed value has only one owner. Itā€™s the key mechanism that makes copy-on-write work under the hood.
  2. Copy-on-write lets structs behave like independent value types while sharing heap storage until you mutate them, at which point a uniqueness check triggers a deep copy. This gives easy-to-reason-about value semantics with low memory overhead.
  3. Many core Swift types (Array, Set, Dictionary, String, Data) use copy-on-write, and you can implement it yourself by wrapping your value in a reference box and using isKnownUniquelyReferenced to decide when to copy.

ā›·ļøSlalom: Designing a runtime for AI-generated code

Slalom dev blog ā€¢ 8 HN points ā€¢ 10 Feb 24
šŸ•¹ Technology Runtime
  1. The development of a custom runtime is crucial for safely running AI-generated code, focusing on simplicity and user control.
  2. Key features like pausing processes, green threads with backtracking, syntactic continuations, and fair resource management are essential for efficient operation.
  3. Building a reliable runtime for AI-generated code involves creating APIs that prevent potential user errors, allowing for undoable actions and permission-seeking processes.

Realtime UIAppearance refresh

Damiaanā€™s Substack ā€¢ 2 HN points ā€¢ 24 May 23
šŸ•¹ Technology Runtime
  1. UIAppearance in iOS is a feature that allows applying consistent theme changes to user interface elements but has limitations.
  2. By using method swizzling and custom appearance proxy, it is possible to achieve real-time theme switching behavior without private APIs.
  3. Implementing a custom appearance proxy for UIViews can help record and replay appearance styling invocations for seamless user experience.
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