Type erasure is a method to abstract and encapsulate heterogenous generic types inside a single non-generic concrete type. In programming languages with generic types, this is a mechanism for runtime polymorphism which allows you circumvent the constraints of generics at compile time. In the early days of Swift, generics were more challenging to work with — in particular, protocols with associated types. As of Swift 5.7 (and SE-0309: Unlock existentials for all protocols), type erasure is now a feature of the Swift compiler. However, there are still situations where you may need to manually write your own type-erased wrappers.

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Welcome to the next post in my series about ReactiveCollectionsKit. Today I want to discuss diffing. Understanding diffing requires understanding two core concepts: identity and equality. These are two ideas that are also relevant and applicable to programming in general, and can often be confusing for newcomers.

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I recently released a new open source project called ReactiveCollectionsKit. It is a modern, fast, and flexible library for building data-driven, declarative, reactive, and diffable collections and lists for iOS. This library is the culmination of everything I learned from building and maintaining IGListKit, ReactiveLists, and JSQDataSourcesKit. The 4th time’s a charm! 😅 🍀 I truly hope this is the last UICollectionView library I ever write and maintain. I think it will be. You can find the documentation here.

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I was recently working on a project that uses modern collection views on iOS — that is, using diffable data sources, snapshots, and cell providers. I hooked up all the components and my collection view was working, or so I thought. I started to notice some very odd, unpredictable behavior when the collection view was updated. Some of the time, the cells were updated correctly. Other times, I would see duplicates and missing data. Here’s what went wrong.

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This year at WWDC, some significant improvements and changes were announced for UICollectionView and UITableView. You can watch 10252: Make blazing fast lists and collection views for all the details, but I want to highlight some of them here.

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