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Capturing self instead of using self. in switch case in DispatchQueue causes compiler error
I have an @objC used for notification. kTag is an Int constant, fieldBeingEdited is an Int variable. The following code fails at compilation with error: Command CompileSwift failed with a nonzero exit code if I capture self (I edited code, to have minimal case) @objc func keyboardDone(_ sender : UIButton) { DispatchQueue.main.async { [self] () -> Void in switch fieldBeingEdited { case kTag : break default : break } } } If I explicitly use self, it compiles, even with self captured: @objc func keyboardDone(_ sender : UIButton) { DispatchQueue.main.async { [self] () -> Void in switch fieldBeingEdited { // <<-- no need for self here case self.kTag : break // <<-- self here default : break } } } This compiles as well: @objc func keyboardDone(_ sender : UIButton) { DispatchQueue.main.async { () -> Void in switch self.fieldBeingEdited { // <<-- no need for self here case self.kTag : break // <<-- self here default : break } } } Is it a compiler bug or am I missing something ?
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425
Jun ’25
Type ReferenceWritableKeyPath does not conform to the 'Sendable' protocol
This is not a question but more of a hint where I was having trouble with. In my SwiftData App I wanted to move from Swift 5 to Swift 6, for that, as recommended, I stayed in Swift 5 language mode and set 'Strict Concurrency Checking' to 'Complete' within my build settings. It marked all the places where I was using predicates with the following warning: Type '' does not conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode I had the same warnings for SortDescriptors. I spend quite some time searching the web and wrapping my head around how to solve that issue to be able to move to Swift 6. In the end I found this existing issue in the repository of the Swift Language https://github.com/swiftlang/swift/issues/68943. It says that this is not a warning that should be seen by the developer and in fact when turning Swift 6 language mode on those issues are not marked as errors. So if anyone is encountering this when trying to fix all issues while staying in Swift 5 language mode, ignore those, fix the other issues and turn on Swift 6 language mode and hopefully they are gone.
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1.1k
Jun ’25
Bridging Headers is unsupported or Module compiled with Swift 5.5.1 cannot be imported by the Swift 5.6 complier
Hello guys! I faced a problem with building... My device suddenly updated to iOS 15.4.1, my Xcode was 13.2 and I had to update it to the latest version (13.3.1) to build the app. After the update, I had a few problems which were successfully solved but one of them stopped me for a few hours. The problem is with Bridging Headers or Swift Compiler, I really don't know what I did badly, and what causes problems. On several forums I often read that is important to set: Build Settings &gt; Build Options &gt; Build Libraries for Distribution But in any case it doesn't work, on yes: error: using bridging headers with module interfaces is unsupported on no: (line with import framework SWXMLHash) /Users/blablabla/SSLModel.swift:9:8: error: module compiled with Swift 5.5.1 cannot be imported by the Swift 5.6 compiler: /Users/blablabla2/Build/Products/Debug-iphoneos/SWXMLHash.framework/Modules/SWXMLHash.swiftmodule/arm64-apple-ios.swiftmodule import SWXMLHash It will be important that I use Carthage. What should I do? Clone all 10 frameworks that I use and re-build them with a new Xcode which includes compiler 5.6? That may be a bad solution... Any answers on similar topics don't help..
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3.0k
Jul ’25
Passing string between Swift and C++
I want to understand what the recommended way is for string interoperability between swift and c++. Below are the 3 ways to achieve it. Approach 2 is not allowed at work due to restrictions with using std libraries. Approach 1: In C++: char arr[] = "C++ String"; void * cppstring = arr; std::cout<<"before:"<<(char*)cppstring<<std::endl;           // C++ String // calling swift function and passing the void buffer to it, so that swift can update the buffer content Module1::SwiftClass:: ReceiveString (cppstring, length);   std::cout<<"after:"<<(char*)cppstring<<std::endl;             // SwiftStr      In Swift: func ReceiveString (pBuffer : UnsafeMutableRawPointer , pSize : UInt ) -> Void { // to convert cpp-str to swift-str: let swiftStr = String (cString: pBuffer.assumingMemoryBound(to: Int8.self)); print("pBuffer content: \(bufferAsString)"); // to modify cpp-str without converting: let swiftstr:String = "SwiftStr"      _ =  swiftstr.withCString { (cString: UnsafePointer<Int8>) in pBuffer.initializeMemory(as: Int8.self, from: cString, count: swiftstr.count+1) } }  Approach 2:  The ‘String’ type returned from a swift function is received as ‘swift::String’ type in cpp. This is implicitly casted to std::string type. The std::string has the method available to convert it to char *. void TWCppClass::StringConversion () {     // GetSwiftString() is a swift call that returns swift::String which can be received in std::string type     std::string stdstr = Module1::SwiftClass::GetSwiftString ();     char * cstr = stdstr.data ();     const char * conststr= stdstr.c_str (); }    Approach 3: The swift::String type that is obtained from a swift function can be received in char * by directly casting the address of the swift::String. We cannot directly receive a swift::String into a char *. void TWCppClass::StringConversion () {    // GetSwiftString() is a swift call that returns swift::String    swift::String swiftstr = Module1::SwiftClass::GetSwiftString ();    // obtaining the address of swift string and casting it into char *    char * cstr = (char*)&swiftstr; }
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486
Jul ’25
C++ and Swift in Xcode 16 broke my audio unit
I'm developing an audio unit for use on iOS. The AUv3 worked fine with xcode 15.X and swift 5.X. I recently tried to submit an update to my plug-in but Apple refused submission because my Xcode was not the latest. Now that I'm on Xcode 16.4 I can't get my project to compile, even when following all of the same previous steps. As one example of a change, Xcode doesn't appear to include the “C++ and Objective-C interoperability” build setting that it used to. This setting is noted in the Swift documentation and I used to need it, https://www.swift.org/documentation/cxx-interop/project-build-setup/#mixing-swift-and-c-using-xcode Currently my C++ code can't see anything from Swift, and I get a "Use of undeclared identifier 'project_name'". I've selected Switch support for version 5.0 in an attempt to minimize changes from Apple. My process is I generate an Xcode project file from my audio plugin support, JUCE. Then I add in the swift files, click yes to create bridging headers, but c++ doesn't see swift anymore. I'd greatly appreciate any suggestions.
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368
Aug ’25
Function types as return types
Greetings, func stepForward(_ input: Int) -> Int { return input + 1 } func stepBackward(_ input: Int) -> Int { return input - 1 } func chooseStepFunction(backward: Bool) -> (Int) -> Int { return backward ? stepBackward : stepForward /* Error type of expression is ambiguous without a type annotation */ } Why am I getting this error. If I change the function to func chooseStepFunction(backward: Bool) -> (Int) -> Int { if backward { return stepBackward else { return stepForward } } Why is the previous chooseStepFunction giving me an error ? Thx in advance
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223
Aug ’25
Equatable with default actor isolation of MainActor
I filed the following issue on swiftlang/swift on GitHub (Aug 8th), and a followup the swift.org forums, but not getting any replies. As we near the release of Swift 6.2, I want to know if what I'm seeing below is expected, or if it's another case where the compiler needs a fix. protocol P1: Equatable { } struct S1: P1 { } // Error: Conformance of 'S1' to protocol 'P1' crosses into main actor-isolated code an can cause data races struct S1Workaround: @MainActor P1 { } // OK // Another potential workaround if `Equatable` conformance can be moved to the conforming type. protocol P2 { } struct S2: Equatable, P2 { } // OK There was a prior compiler bug fix which addressed inhereted protocols regarding @MainActor. For Equatable, one still has to use @MainActoreven when the default actor isolation is MainActor. Also affects Hashable and any other protocol inheriting from Equatable.
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1.2k
Aug ’25
NSDictionary.isEqual(to:) with Swift dictionary compiles on macOS but not on iOS
The following code works when compiling for macOS: print(NSMutableDictionary().isEqual(to: NSMutableDictionary())) but produces a compiler error when compiling for iOS: 'NSMutableDictionary' is not convertible to '[AnyHashable : Any]' NSDictionary.isEqual(to:) has the same signature on macOS and iOS. Why does this happen? Can I use NSDictionary.isEqual(_:) instead?
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537
Feb ’25
cell.textLabel?.text breaking if a number value is in an array
Hi the below array and code to output a list item works fine: var quotes = [ [ "quote": "I live you the more ...", "order": "1" ], [ "quote": "There is nothing permanent ...", "order": "2" ], [ "quote": "You cannot shake hands ...", "order": "3" ], [ "quote": "Lord, make me an instrument...", "order": "4" ] ] cell.textLabel?.text = quotes[indexPath.row]["quote"] However if I change the "order" values to be numbers rather than text like below then for the above line I get an error message in Xcode "No exact matches in call to subscript". Please could someone tell me how to make it work with the numbers stored as numbers? (I'm wondering if creating an any array type and using the .text function has caused a conflict but I can't find how to resolve) [ "quote": "I live you the more ...", "order": 1 ], [ "quote": "There is nothing permanent ...", "order": 2 ], [ "quote": "You cannot shake hands ...", "order": 3 ], [ "quote": "Lord, make me an instrument...", "order": 4 ] ] Thank you for any pointers :-)
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487
Feb ’25
Swift 6 crash calling requestAutomaticPassPresentationSuppression
I found a similar problem here https://developer.apple.com/forums/thread/764777 and I could solve my problem by wrapping the call to requestAutomaticPassPresentationSuppression in a call to DispatchQueue.global().async. But my question is if this is really how things should work. Even with strict concurrency warnings in Swift 6 I don't get any warnings. Just a runtime crash. How are we supposed to find these problems? Couldn't the compiler assist with a warning/error. Why does the compiler make the assumptions it does about the method that is declared like this: @available(iOS 9.0, *) open class func requestAutomaticPassPresentationSuppression(responseHandler: @escaping (PKAutomaticPassPresentationSuppressionResult) -> Void) -> PKSuppressionRequestToken Now that we have migrated to Swift 6 our code base contains a bunch of unknown places where it will crash as above.
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519
Feb ’25
DebugDescription macro causing “String Interpolation” warnings
Using the DebugDescription macro to display an optional value produces a “String interpolation produces a debug description for an optional value” build warning. For example: @DebugDescription struct MyType: CustomDebugStringConvertible { let optionalValue: String? public var debugDescription: String { "Value: \(optionalValue)" } } The DebugDescription macro does not allow (it is an error) "Value: \(String(describing: optionalValue))" or "Value: \(optionalValue ?? "nil")" because “Only references to stored properties are allowed.” Is there a way to reconcile these? I have a build log full of these warnings, obscuring real issues.
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527
Feb ’25
NSPredicate return wrong result
NSPredicate(format: "SELF MATCHES %@", "^[0-9A-Z]+$").evaluate(with: "126𝒥ℰℬℬ𝒢𝒦𝒮33") Returns true, and I don't know why. 𝒥ℰℬℬ𝒢𝒦𝒮 is not between 0-9 and A-Z, and why it returns true? How to avoid similar problem like this when using NSPredicate?
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578
Feb ’25
How to create an array using a loop
Hello, Please can you tell me how to create an array of dictionaries? This code below should create 4 dictionaries in an array, but I'm getting these errors: For line "var output = [id: "testID", name: "testName"]": cannot find 'name' in scope Type '(any AnyObject).Type' cannot conform to 'Hashable' For line "return output": Type '(any AnyObject).Type' cannot conform to 'Hashable' var quotes: [(id: String, name: String)] { var output = [[(id: String, name: String)]] () for i in 1...4 { var output = [id: "testID", name: "testName"] } return output }
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400
Mar ’25
iOS Share Extension Warning: Passing argument of non-sendable type outside of main actor-isolated context may introduce data races
Consider this simple miniature of my iOS Share Extension: import SwiftUI import Photos class ShareViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() if let itemProviders = (extensionContext?.inputItems.first as? NSExtensionItem)?.attachments { let hostingView = UIHostingController(rootView: ShareView(extensionContext: extensionContext, itemProviders: itemProviders)) hostingView.view.frame = view.frame view.addSubview(hostingView.view) } } } struct ShareView: View { var extensionContext: NSExtensionContext? var itemProviders: [NSItemProvider] var body: some View { VStack{} .task{ await extractItems() } } func extractItems() async { guard let itemProvider = itemProviders.first else { return } guard itemProvider.hasItemConformingToTypeIdentifier(UTType.url.identifier) else { return } do { guard let url = try await itemProvider.loadItem(forTypeIdentifier: UTType.url.identifier) as? URL else { return } try await downloadAndSaveMedia(reelURL: url.absoluteString) extensionContext?.completeRequest(returningItems: []) } catch {} } } On the line 34 guard let url = try await itemProvider.loadItem ... I get these warnings: Passing argument of non-sendable type '[AnyHashable : Any]?' outside of main actor-isolated context may introduce data races; this is an error in the Swift 6 language mode 1.1. Generic enum 'Optional' does not conform to the 'Sendable' protocol (Swift.Optional) Passing argument of non-sendable type 'NSItemProvider' outside of main actor-isolated context may introduce data races; this is an error in the Swift 6 language mode 2.2. Class 'NSItemProvider' does not conform to the 'Sendable' protocol (Foundation.NSItemProvider) How to fix them in Xcode 16? Please provide a solution which works, and not the one which might (meaning you run the same code in Xcode, add your solution and see no warnings). I tried Decorating everything with @MainActors Using @MainActor in the .task @preconcurrency import Decorating everything with @preconcurrency Playing around with nonisolated
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587
Mar ’25
Use FormatStyle to print formatted values from a Vector structure
I'm trying to use FormatStyle from Foundation to format numbers when printing a vector structure. See code below. import Foundation struct Vector<T> { var values: [T] subscript(item: Int) -> T { get { values[item] } set { values[item] = newValue } } } extension Vector: CustomStringConvertible { var description: String { var desc = "( " desc += values.map { "\($0)" }.joined(separator: " ") desc += " )" return desc } } extension Vector { func formatted<F: FormatStyle>(_ style: F) -> String where F.FormatInput == T, F.FormatOutput == String { var desc = "( " desc += values.map { style.format($0) }.joined(separator: " ") desc += " )" return desc } } In the example below, the vector contains a mix of integer and float literals. The result is a vector with a type of Vector<Double>. Since the values of the vector are inferred as Double then I expect the print output to display as decimal numbers. However, the .number formatted output seems to ignore the vector type and print the values as a mix of integers and decimals. This is fixed by explicitly providing a format style with a fraction length. So why is the .formatted(.number) method ignoring the vector type T which is Double in this example? let vec = Vector(values: [-2, 5.5, 100, 19, 4, 8.37]) print(vec) print(vec.formatted(.number)) print(vec.formatted(.number.precision(.fractionLength(1...)))) ( -2.0 5.5 100.0 19.0 4.0 8.37 ) // correct output that uses all Double types ( -2 5.5 100 19 4 8.37 ) // wrong output that uses Int and Double types ( -2.0 5.5 100.0 19.0 4.0 8.37 ) // correct output that uses all Double types
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324
Mar ’25
Use of `for await` with `AyncStream`, and yielding async closures to its continuation
Hello, I was hoping to clarify my understanding of the use of for await with an AsyncStream. My use case is, I'd like to yield async closures to the stream's continuation, with the idea that, when I use for await with the stream to process and execute the closures, it would only continue on to the following closure once the current closure has been run to completion. At a high level, I am trying to implement in-order execution of async closures in the context of re-entrancy. An example of asynchronous work I want to execute is a network call that should write to a database: func syncWithRemote() async -> Void { let data = await fetchDataFromNetwork() await writeToLocalDatabase(data) } For the sake of example, I'll call the intended manager of closure submission SingleOperationRunner. where, at a use site such as this, my desired outcome is that call 1 of syncWithRemote() is always completed before call 2 of it: let singleOperationRunner = SingleOperationRunner(priority: nil) singleOperationRunner.run { syncWithRemote() } singleOperationRunner.run { syncWithRemote() } My sketch implementation looks like this: public final class SingleOperationRunner { private let continuation: AsyncStream<() async -> Void>.Continuation public init(priority: TaskPriority?) { let (stream, continuation) = AsyncStream.makeStream(of: (() async -> Void).self) self.continuation = continuation Task.detached(priority: priority) { // Will this loop only continue when the `await operation()` completes? for await operation in stream { await operation() } } } public func run(operation: @escaping () async -> Void) { continuation.yield(operation) } deinit { continuation.finish() } } The resources I've found are https://developer.apple.com/videos/play/wwdc2022-110351/?time=1445 and https://forums.swift.org/t/swift-async-func-to-run-sequentially/60939/2 but do not think I have fully put the pieces together, so would appreciate any help!
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324
Mar ’25