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Help Understanding Concurrency Error with Protocol Listener and Actor
Hi all, I'm running into a Swift Concurrency issue and would appreciate some help understanding what's going on. I have a protocol and an actor set up like this: protocol PersistenceListener: AnyObject { func persistenceDidUpdate(key: String, newValue: Any?) } actor Persistence { func addListener(_ listener: PersistenceListener) { listeners.add(listener) } /// Removes a listener. func removeListener(_ listener: PersistenceListener) { listeners.remove(listener) } // MARK: - Private Properties private var listeners = NSHashTable<AnyObject>.weakObjects() // MARK: - Private Methods /// Notifies all registered listeners on the main actor. private func notifyListeners(key: String, value: Any?) async { let currentListeners = listeners.allObjects.compactMap { $0 as? PersistenceListener } for listener in currentListeners { await MainActor.run { listener.persistenceDidUpdate(key: key, newValue: value) } } } } When I compile this code, I get a concurrency error: "Sending 'listener' risks causing data races"
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98
Apr ’25
Issue with Swift 6 migration issues
We are migrating to swift 6 from swift 5 using Xcode 16.2. we are getting below errors in almost each of our source code files : Call to main actor-isolated initializer 'init(storyboard:bundle:)' in a synchronous non isolated context Main actor-isolated property 'delegate' can not be mutated from a nonisolated context Call to main actor-isolated instance method 'register(cell:)' in a synchronous nonisolated context Call to main actor-isolated instance method 'setup()' in a synchronous nonisolated context Few questions related to these compile errors. Some of our functions arguments have default value set but swift 6 does not allow to set any default values. This requires a lot of code changes throughout the project. This would be lot of source code re-write. Using annotations like @uncheck sendable , @Sendable on the class (Main actor) name, lot of functions within those classes , having inside some code which coming from other classes which also showing main thread issue even we using @uncheck sendable. There are so many compile errors, we are still seeing other than what we have listed here. Fixing these compile errors throughout our project, would be like a re-write of our whole application, which would take lot of time. In order for us to migrate efficiently, we have few questions where we need your help with. Below are the questions. Are there any ways we can bypass these errors using any keywords or any other way possible? Can Swift 5 and Swift 6 co-exist? so, we can slowly migrate over a period of time.
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149
Jun ’25
Do i need to put any OS Error handling for Unmanaged.passRetain (obj) or Unmanaged.takeRetain (objptr)
In below Swift code , is there any possiblities of failure of Unmanaged.passRetain and Unmanaged.takeRetain calls ? // can below call fail (constructor returns nil due to OS or language error) and do i need to do explicit error handling here? let str = TWSwiftString(pnew) // Increasing RC by 1 // can below call fail (assuming str is valid) and do i need to do explicit error handling for the same ? let ptr:UnsafeMutableRawPointer? = Unmanaged.passRetained(str).toOpaque() // decrease RC by 1 // can below call fail (assuming ptr is valid) ? and do i need to do explicit error handling Unmanaged<TWSwiftString>.fromOpaque(pStringptr).release()
1
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533
Nov ’24
XCode not making bridging header file?
Hi, I'm trying to add Swift code to my Obj-C project. I've gone through all the tutorials and troubleshooting advice I can find online, no dice. I would appreciate any help, thank you so much in advance. I add a new swift file to my Obj-C project XCode offers to create a bridging header file for me, yes please New .swift file and .h file are added to my project no problem Header file shows up in build settings no problem I add a new class to my new swift file ("@objc class HelloPrinter: NSObject") When I build the app, nothing is generated in the bridging header file and the class is obviously inaccessible to my obj-c code Is this supposed to work? My understanding is that it's supposed to work. Somewhat concerning is the text that XCode puts in the bridging header file when it's created: "Use this file to import your target's public headers that you would like to expose to Swift." I don't want to use this bridging header file for anything. I want XCode to GENERATE STUFF in the bridging file. I also don't want to expose anything to Swift. I want the opposite to happen. So I don't get this text at all. Thanks in advance again.
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79
Apr ’25
Crash when Mutating Array of Tuples with String Property from Multiple Threads
Hi Apple Developer Community, I'm facing a crash when updating an array of tuples from both a background thread and the main thread simultaneously. Here's a simplified version of the code in a macOS app using AppKit: class ViewController: NSViewController { var mainthreadButton = NSButton(title: "test", target: self, action: nil) var numbers = Array(repeating: (dim: Int, key: String)(0, "default"), count: 1000) override func viewDidLoad() { super.viewDidLoad() view.addSubview(mainthreadButton) mainthreadButton.translatesAutoresizingMaskIntoConstraints = false mainthreadButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true mainthreadButton.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true mainthreadButton.widthAnchor.constraint(equalToConstant: 100).isActive = true mainthreadButton.heightAnchor.constraint(equalToConstant: 100).isActive = true mainthreadButton.target = self mainthreadButton.action = #selector(arraytest(_:)) } @objc func arraytest(_ sender: NSButton) { print("array update started") // Background update DispatchQueue.global().async { for i in 0..&lt;1000 { self.numbers[i].dim = i } } // Main thread update var sum = 0 for i in 0..&lt;1000 { numbers[i].dim = i + 1 sum += numbers[i].dim print("test \(sum)") } mainthreadButton.title = "test = \(sum)" } } This results in a crash with the following message: malloc: double free for ptr 0x136040c00 malloc: *** set a breakpoint in malloc_error_break to debug What's interesting: This crash only happens when the tuple contains a String ((dim: Int, key: String)) If I change the tuple type to use two Int values ((dim: Int, key: Int)), the crash does not occur My Questions: Why does mutating an array of tuples containing a String crash when accessed from multiple threads? Why is the crash avoided when the tuple contains only primitive types like Int? Is there an underlying memory management issue with value types containing reference types like String? Any explanation about this behavior and best practices for thread-safe mutation of such arrays would be much appreciated. Thanks in advance!
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92
Apr ’25
Command SwiftCompile failed with a nonzero exit code. in xocde 16 and 15 where as it was working fine in xcode 14.3
My project’s source code was building, running, and archiving successfully in Xcode 14.3. However, after upgrading to Xcode 15, I began encountering the error: “Command SwiftCompile failed with a nonzero exit code.” I couldn't resolve the issue, so I decided to continue using Xcode 14.3. Recently, I upgraded to macOS Sequoia and also updated to Xcode 16. Unfortunately, the same error persists in the latest Xcode: “Command SwiftCompile failed with a nonzero exit code.” The unfortunate part is that Xcode 14.3 no longer works after the macOS upgrade. Whenever I try to run the code, I get the following popup.
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3k
Oct ’24
SwiftUI Entry Point - Proper Location In Project
Hi In C#, one can define associated functions by the following. Notice that "Declarations DE" is a reference to a function in another C# project file. This lets the compiler know that there are other references in the project. Likewise, "Form_Load" is the entry point of the code, similar to "main" in C. Any calls to related functions can be made in this section, to the functions that have been previously defined above. So I set out trying to find similar information about SwiftUI, and found several, but only offer partial answers to my questions. The YouTube video... Extracting functions and subviews in SwiftUI | Bootcamp #20 - YouTube ... goes into some of the details, but still leaves me hanging. Likewise... SOLVED: Swift Functions In Swift UI – SwiftUI – Hacking with Swift forums ... has further information, but nothing concrete that I am looking for. Now in the SwiftUI project, I tried this... The most confusing thing for me, is where is "main"? I found several examples that call functions from the structure shown above, BUT I have no reason as to why. So one web example on StackOverFlow called the function from position 1. That did not work. Position 2 worked to call the function at position 3, but really, why? All this activity brings up a lot of questions for me, such as: Does SwiftUI need function callouts similar to C#, and they are called out even before running "main". I seem to recall Borland Delphi being this way as well. How does SwiftUI make references to other classes (places where other functions are stored in separate files)? Does SwiftUI actually make use of "main" in the normal sense, i.e. similar to C, C#, Rust and so on? I did notice that once a SwiftUI function is called, it makes reference to data being passed very similar to other languages, at least for the examples I found. Note that I looked at official SwiftUI documentation, but did not come across information that answers the above.
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523
Dec ’24
Can I use @_implementationOnly import in my Framework
We have FrameworkA which needs to use another FrameworkB internally to fetch a token. Now when I try to use this FrameworkA, we are seeing an issue with internal framework i.e. No such module 'FrameworkB'. But when I use @_implementationOnly import for the internal FrameworkB, I didn't see any issues. So just wanted to check If I can go ahead and use this @_implementationOnly import flag in Production?
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99
May ’25
Applescript text item delimiters not working
I have a string of the form “Mon 22nd April”. I’m trying to extract the day (i.e. Mon), the date (i.e. 22nd) and the month (i.e. April) using this Applescript: set originalDateString to “Mon 22nd April” -- Extract the components by splitting the string set AppleScript's text item delimiters to " " set dayOfWeekAbbrev to text item 1 of originalDateString set dayOfMonth to text item 2 of originalDateString set monthName to text item 3 of originalDateString When I run this on its own it works as expected: dayOfWeekAbbrev is set to “Mon” dayOfMonth is set to “22nd” monthName is set to “April” When I run this inside a bigger script involving Numbers, the text item delimiters fails to work, no compile or run time errors occur and I end up with: dayOfWeekAbbrev is set to “M” dayOfMonth is set to “o” monthName is set to “n” I.e the first three characters of the string. If I replace originalDateString with the literal string “Mon 22nd April” I get the same result. In other words, text items and being recognized as individual characters, no delimiter (or delimiter is null). Totally confused.
5
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972
Oct ’24
Trailing closure passed to parameter of type 'String' that does not accept a closure
import Foundation import FirebaseAuth import GoogleSignIn import FBSDKLoginKit class AuthController { // Assuming these variables exist in your class var showCustomAlertLoading = false var signUpResultText = "" var isSignUpSucces = false var navigateHome = false // Google Sign-In func googleSign() { guard let presentingVC = (UIApplication.shared.connectedScenes.first as? UIWindowScene)?.windows.first?.rootViewController else { print("No root view controller found.") return } GIDSignIn.sharedInstance.signIn(withPresenting: presentingVC) { authentication, error in if let error = error { print("Error: \(error.localizedDescription)") return } guard let authentication = authentication else { print("Authentication is nil") return } guard let idToken = authentication.idToken else { print("ID Token is missing") return } guard let accessToken = authentication.accessToken else { print("Access Token is missing") return } let credential = GoogleAuthProvider.credential(withIDToken: idToken.tokenString, accessToken: accessToken.tokenString) self.showCustomAlertLoading = true Auth.auth().signIn(with: credential) { authResult, error in guard let user = authResult?.user, error == nil else { self.signUpResultText = error?.localizedDescription ?? "Error occurred" DispatchQueue.main.asyncAfter(deadline: .now() + 2) { self.showCustomAlertLoading = false } return } self.signUpResultText = "\(user.email ?? "No email")\nSigned in successfully" self.isSignUpSucces = true DispatchQueue.main.asyncAfter(deadline: .now() + 3) { self.showCustomAlertLoading = false DispatchQueue.main.asyncAfter(deadline: .now() + 1) { self.navigateHome = true } } print("\(user.email ?? "No email") signed in successfully") } } } // Facebook Sign-In func signInWithFacebook(presentingViewController: UIViewController, completion: @escaping (Bool, Error?) -> Void) { let manager = LoginManager() manager.logIn(permissions: ["public_profile", "email"], from: presentingViewController) { result, error in if let error = error { completion(false, error) return } guard let result = result, !result.isCancelled else { completion(false, NSError(domain: "Facebook Login Error", code: 400, userInfo: nil)) return } if let token = result.token { let credential = FacebookAuthProvider.credential(withAccessToken: token.tokenString) Auth.auth().signIn(with: credential) { (authResult, error) in if let error = error { completion(false, error) return } completion(true, nil) } } } } // Email Sign-In func signInWithEmail(email: String, password: String, completion: @escaping (Bool, Error?) -> Void) { Auth.auth().signIn(withEmail: email, password: password) { (authResult, error) in if let error = error { completion(false, error) return } completion(true, nil) } } }
1
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410
Nov ’24
In app purchase goes to Entered Billing Retry after free trail
I have a VPN application published in the app store. Used Ikev2 for this personal VPN. There are two in-app purchases. One is 'Monthly' and another is 'Yearly' with 3 days free trial. We have seen something strange for the yearly subscriptions which has free trail, the cancellation reason through the billing issue is too high like 70-80% due to billing retry state. Some other apps which have billing issues under 10% always. We have done some research and found that if the user doesn't cancel and Apple is unable to charge then it goes to a billing retry state. If users don't like the app, they could cancel their subscription/free trail easily but they are not doing this and why Apple unable to charge the bill after the trial ends. Am i missing something in the developer end?
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1.1k
Dec ’24
Swift Concurrency: Calling @MainActor Function from Protocol Implementation in Swift 6
I have a Settings class that conform to the TestProtocol. From the function of the protocol I need to call the setString function and this function needs to be on the MainActor. Is there a way of make this work in Swift6, without making the protocol functions running on @MainActor The calls are as follows: class Settings: TestProtocol{ var value:String = "" @MainActor func setString( _ string:String ){ value = string } func passString(string: String) { Task{ await setString(string) } } } protocol TestProtocol{ func passString( string:String ) }
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144
May ’25
Working correctly with actor annotated class
Hi, I have a complex structure of classes, and I'm trying to migrate to swift6 For this classes I've a facade that creates the classes for me without disclosing their internals, only conforming to a known protocol I think I've hit a hard wall in my knowledge of how the actors can exchange data between themselves. I've created a small piece of code that can trigger the error I've hit import SwiftUI import Observation @globalActor actor MyActor { static let shared: some Actor = MyActor() init() { } } @MyActor protocol ProtocolMyActor { var value: String { get } func set(value: String) } @MyActor func make(value: String) -> ProtocolMyActor { return ImplementationMyActor(value: value) } class ImplementationMyActor: ProtocolMyActor { private(set) var value: String init(value: String) { self.value = value } func set(value: String) { self.value = value } } @MainActor @Observable class ViewObserver { let implementation: ProtocolMyActor var value: String init() async { let implementation = await make(value: "Ciao") self.implementation = implementation self.value = await implementation.value } func set(value: String) { Task { await implementation.set(value: value) self.value = value } } } struct MyObservedView: View { @State var model: ViewObserver? var body: some View { if let model { Button("Loaded \(model.value)") { model.set(value: ["A", "B", "C"].randomElement()!) } } else { Text("Loading") .task { self.model = await ViewObserver() } } } } The error Non-sendable type 'any ProtocolMyActor' passed in implicitly asynchronous call to global actor 'MyActor'-isolated property 'value' cannot cross actor boundary Occurs in the init on the line "self.value = await implementation.value" I don't know which concurrency error happens... Yes the init is in the MainActor , but the ProtocolMyActor data can only be accessed in a MyActor queue, so no data races can happen... and each access in my ImplementationMyActor uses await, so I'm not reading or writing the object from a different actor, I just pass sendable values as parameter to a function of the object.. can anybody help me understand better this piece of concurrency problem? Thanks
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578
Nov ’24
Best practice: Use of enum without cases for static helper functions?
Hi all, In Swift, I often see static helper functions grouped in an enum without any cases, like this: enum StringUtils { static func camelCaseToSnakeCase(_ input: String) -> String { // implementation } } Since this enum has no cases, it cannot be instantiated – which is exactly the point. It’s meant to group related functionality without any stored state, and without the need for instantiation. This pattern avoids writing a struct with a private init() and makes the intent clearer: "This is just a static utility, not an object." You’ll often see this used for things like: AnalyticsEvents.track(_:) My question: Is this use of a case-less enum considered good practice in Swift when building static-only helpers? Or is there a better alternative for expressing intent and preventing instantiation? I’d appreciate any insight – especially if there’s official guidance or references from the Swift core team. Thanks!
2
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158
May ’25
Is there any way to write a screensaver for macOS using Python Pygame?
I want to be able to write a cross-platform screensaver that works on both Windows and macOS using the Pygame 2D graphics library in Python. On Windows, this is super easy - you just write your program with three possible command line arguments: /p for preview mode, /c for the configuration dialog mode, and /s for the actual full-screen screensaver mode. Then you just use pyinstaller to build an .exe file and rename the extension to .scr, and you're good to go. However, it seems that making a screensaver on macOS is a pretty convoluted process, and there was stuff about specific Objective-C functions that you had to write, and I didn't really understand the documentation. Could you please tell me if there is any way to simply get my Python Pygame program to build as a proper .saver file? Thanks!
2
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710
Oct ’24
How to Create Applications with Objective-C Without ARC
I've been teaching myself Objective-C and I wanted to start creating projects that don't use ARC to become better at memory management and learn how it all works. I've been attempting to build and run applications, but I'm not really sure where to start as modern iOS development is used with Swift and memory management is handled. Is there any way to create modern applications that use Objective-C, UIKit, and not use ARC?
3
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151
May ’25
Potential of race condition in ARC?
I ran into a memory issue that I don't understand why this could happen. For me, It seems like ARC doesn't guarantee thread-safety. Let see the code below @propertyWrapper public struct AtomicCollection&lt;T&gt; { private var value: [T] private var lock = NSLock() public var wrappedValue: [T] { set { lock.lock() defer { lock.unlock() } value = newValue } get { lock.lock() defer { lock.unlock() } return value } } public init(wrappedValue: [T]) { self.value = wrappedValue } } final class CollectionTest: XCTestCase { func testExample() throws { let rounds = 10000 let exp = expectation(description: "test") exp.expectedFulfillmentCount = rounds @AtomicCollection var array: [Int] = [] for i in 0..&lt;rounds { DispatchQueue.global().async { array.append(i) exp.fulfill() } } wait(for: [exp]) } } It will crash for various reasons (see screenshots below) I know that the test doesn't reflect typical application usage. My app is quite different from traditional app so the code above is just the simplest form for proof of the issue. One more thing to mention here is that array.count won't be equal to 10,000 as expected (probably because of copy-on-write snapshot) So my questions are Is this a bug/undefined behavior/expected behavior of Swift/Obj-c ARC? Why this could happen? Any solutions suggest? How do you usually deal with thread-safe collection (array, dict, set)?
2
0
562
Nov ’24