You have to hold on to the cancellable as long as you want to receive the published values. In your code the cancellable is released as soon as the func applicationDidFinishLaunching finishes and no updates are send any more.

swiftpm file is the default format used by Playgrounds 4 app for iPad when choosing the "app" template when starting a new playground.

Perhaps I don't understand your problem, but where do you see a memory leak? The SwiftUI „runtime“ is keeping the StateObject alive. That's an intended function.

SwiftUI's ViewBuilder is currently still limited to 10 views inside another view. If you want to put more views inside you have to group them using Group: View1{ Group{ Subview1() ... SubView10() } Group{ Subview11() ... Subview20() } }

Mixing C++ and Swift or SwiftUI code in the same file is not yet supported. You can probably mix them in the same project by using C oder Objective-C files for bridging but I am not expert on this topic.

This seems to be the same problem I encountered early in the iOS 15 betas: https://developer.apple.com/forums/thread/689117 but the code where you use the scale value is missing from your example so I could not really say. Apple has changed the documentation since then, so changing the frame inside the scale gesture seems not to be allowed any more.

You have to create an instance of class Root in our preview like this: RootView(rootToView: Root())

How is your ObservableObject imported inside the view? You have to use @ObservedObject oder @StateObject for @Published to work. https://www.hackingwithswift.com/quick-start/swiftui/all-swiftui-property-wrappers-explained-and-compared

Ich bin gerade über eine der seltenen deutschen Seiten mit Swift-Artikeln gestolpert: https://www.ralfebert.de/blog/ Das ist aber bereits für Fortgeschrittene. (I just stumbled across one of the rare pages with articles about Swift: https://www.ralfebert.de/blog/ It is for advanced users though.)

Unfortunately Swift Playgrounds App for iPad does NOT yet support import of password protected packages. I hope they include this feature soon! Perhaps file a bug report with https://feedbackassistant.apple.com to give the development team at Apple more incentive to do so?

Filed FB9333346 on Jul 15, 2021 and FB9684083 on Oct 7, 2021 but unfortunately the problem still persists. The documentation has been changed though, the old way seems to be discouraged though the .scaleEffect(magnifyBy) does not yield the same result.

I found the following workaround: If you separate the two conflicting methods into two different files as extensions on BTDelegate Playgrounds App compiles the code without an error. Unfortunately I could not yet test if in this case both delegate methods are still being called by CoreBluetooth.

Could be a „Known Issue“: In Xcode's 13.3 release notes it says: The Swift compiler may produce spurious Sendable warnings about classes that inherit from a @MainActor class. (85223889)

Have you tried it using the 4.0.1 update of Swift Playgrounds which came out yesterday? It seems to work for me.

You could try if .font(.system(size: 50, weight: .ultraLight, design: .default)).monospacedDigit() gives the intended result.