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SwiftUI isn't tied to the OS version.

It has a runtime API that should work with different versions of the OS. There were changes to the compiler that they didn't talk about until after the fact though. After SwiftUI was announced they did run those through swift-evolution.

SwiftUI for the most part is just a runtime library, the compiler changes made things a bit nicer, but most of it could be achieved without compiler changes.

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Just curious, why can’t SwiftUI apps run on any iOS version prior to 13?

My clients app requires supporting iOS 11, but I’d love to start mixing in sone SwiftUI.

They didn't release the frameworks for those OSs.

That's like how Catalysts runtime wasn't backported to older versions of macOS.

They could decouple those frameworks from the OS, but that adds other headaches and you eventually gotta draw the line somewhere so they tend to only add new frameworks with major OS updates.

And given their swift (pun intended) release schedule and fast user uptake of major releases, this is usually not too much of a hassle.

Thanks!

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