Updating an app to use strict concurrency

At a glance

Project structure

Source bundle/
├── Original/
│   └── Coffee Tracker WatchKit Extension/
│       ├── CoffeeTrackerApp.swift
│       ├── ExtensionDelegate.swift
│       ├── ContentView.swift
│       ├── CoffeeTrackerView.swift
│       ├── DrinkListView.swift
│       ├── ComplicationController.swift
│       └── HostingController.swift
└── Updated/
    └── Coffee Tracker WatchKit Extension/
        ├── CoffeeTrackerApp.swift
        ├── ExtensionDelegate.swift
        ├── ContentView.swift
        ├── CoffeeTrackerView.swift
        └── DrinkListView.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 11 project/configuration file(s) and 29 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["Original"]
    V2["Updated"]
    Boundary["SwiftUI APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

Original/Coffee Tracker WatchKit Extension/CoffeeTrackerApp.swift:10 — architecture anchor

@main
struct CoffeeTrackerApp: App {

    @WKApplicationDelegateAdaptor private var appDelegate: ExtensionDelegate

    @SceneBuilder var body: some Scene {
        WindowGroup {
            NavigationView {
                ContentView()
            }
        }
    }
}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    CoffeeTrackerApp o-- ExtensionDelegate : appDelegate
    ExtensionDelegate *-- Logger : logger
    ExtensionDelegate *-- Logger : scheduleLogger
    ContentView *-- Logger : logger

Ownership evidence

Original/Coffee Tracker WatchKit Extension/CoffeeTrackerApp.swift:13 — stored dependency or nearest verified ownership anchor

@main
struct CoffeeTrackerApp: App {
    // ...
    @WKApplicationDelegateAdaptor private var appDelegate: ExtensionDelegate
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

Original/Coffee Tracker WatchKit Extension/ComplicationController.swift:19 — representative execution boundary

    func timelineEndDate(for complication: CLKComplication) async -> Date? {
        // Indicate that the app can provide timeline entries for the next 24 hours.
        Date().addingTimeInterval(24.0 * 60.0 * 60.0)
    }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

Updated/CoffeeKit/CoffeeData.swift:310 — representative type boundary

@MainActor
public protocol CaffeineThresholdDelegate: AnyObject {
    func caffeineLevel(at level: Double)
}

The source explicitly defines local protocol relationships: Recaffeinater → CaffeineThresholdDelegate, Recaffeinater → CaffeineThresholdDelegate.

Access control

Reference code

Original/Coffee Tracker WatchKit Extension/CoffeeTrackerApp.swift:13 — representative boundary

@main
struct CoffeeTrackerApp: App {
    // ...
    @WKApplicationDelegateAdaptor private var appDelegate: ExtensionDelegate
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Main application flow

sequenceDiagram
    participant CoffeeData
    participant store
    participant healthKitController
    CoffeeData->>store: load()
    CoffeeData->>CoffeeData: drinksUpdated()
    CoffeeData->>healthKitController: requestAuthorization()
    CoffeeData->>CoffeeData: loadNewDataFromHealthKit()

Reference code

Updated/CoffeeKit/CoffeeData.swift:281 — load()

    func load() async {
        var drinks = await store.load()

        // Remove old drinks.
        drinks.removeOutdatedDrinks()

        // Assign loaded drinks to the model.
        currentDrinks = drinks
        await drinksUpdated()

        // Load new data from HealthKit.
        guard await healthKitController.requestAuthorization() else {
            logger.debug("Unable to authorize HealthKit.")
            return
        }

        await self.healthKitController.loadNewDataFromHealthKit()
    }

Naming conventions

• Types: App: CoffeeTrackerApp; Controller: ComplicationController, HealthKitController, HostingController; Delegate: CaffeineThresholdDelegate, CoffeeLocationDelegate, ExtensionDelegate; Store: CoffeeDataStore; View: CoffeeTrackerView, ContentView, DrinkListView.
• Protocols: CaffeineThresholdDelegate, CaffeineThresholdDelegate.
• Methods: handle, scheduleBackgroundRefreshTasks, caffeineLevel, colorForCaffeineDose, colorForDailyDrinkCount, addDrink.
• Files: Original/Coffee Tracker WatchKit Extension/CoffeeTrackerApp.swift, Updated/Coffee Tracker WatchKit Extension/CoffeeTrackerApp.swift, Original/Coffee Tracker WatchKit Extension/ExtensionDelegate.swift, Updated/Coffee Tracker WatchKit Extension/ExtensionDelegate.swift, Original/Coffee Tracker WatchKit Extension/ContentView.swift, Updated/Coffee Tracker WatchKit Extension/ContentView.swift.

Architecture takeaways

• CoffeeTrackerApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, CoffeeKit, ClockKit, HealthKit through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation