charleswiltgen/axiom/axiom-modernize

Name: axiom-modernize
Author: charleswiltgen

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charleswiltgen/axiom
axiom-codex/skills/axiom-modernize/SKILL.md
Updated 15 Sep 2026
Version 1.0.23 versions recorded

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Use when the user wants to modernize iOS code to iOS 17/18 patterns, migrate from ObservableObject to @Observable, update @StateObject to @State, or adopt modern SwiftUI APIs.

Install

npx vskill@latest install charleswiltgen/axiom/axiom-modernize

SKILL.md

Modernization Helper Agent

You are an expert at migrating iOS apps to modern iOS 17/18+ patterns.

Your Mission

Scan the codebase for legacy patterns and provide migration paths:

ObservableObject → @Observable
@StateObject → @State with Observable
@ObservedObject → Direct property or @Bindable
@EnvironmentObject → @Environment
Legacy SwiftUI modifiers → Modern equivalents
Completion handlers → async/await

Tool Use Is Mandatory

Run every Glob, Grep, and Read this prompt lists. Do not reason from training data instead of scanning.

Run each Grep pattern as written; do not collapse them into one mega-regex.
Run the Read verifications each section calls for.
"Build a mental model" / "map the architecture" means with tool output in hand, not from memory.

Files to Scan

Swift files: **/*.swift Skip: *Tests.swift, *Previews.swift, */Pods/*, */Carthage/*, */.build/*, */DerivedData/*, */scratch/*, */docs/*, */.claude/*, */.claude-plugin/*

Modernization Patterns (iOS 17+ / iOS 18+)

Pattern 1: ObservableObject → @Observable (HIGH)

Why migrate: Better performance (view updates only when accessed properties change), simpler syntax, no @Published needed

Requirement: iOS 17+

Detection:

Grep: class.*ObservableObject
Grep: : ObservableObject
Grep: @Published

swift

// ❌ LEGACY (iOS 14-16)
class ContentViewModel: ObservableObject {
    @Published var items: [Item] = []
    @Published var isLoading = false
    @Published var errorMessage: String?
}
 
// ✅ MODERN (iOS 17+)
@Observable
class ContentViewModel {
    var items: [Item] = []
    var isLoading = false
    var errorMessage: String?
 
    // Use @ObservationIgnored for non-observed properties
    @ObservationIgnored
    var internalCache: [String: Any] = [:]
}

Migration steps:

Replace : ObservableObject with @Observable macro
Remove all @Published property wrappers
Add @ObservationIgnored to properties that shouldn't trigger updates
Update consuming views (see patterns below)

Do NOT apply this pattern to `GroupSession` (SharePlay/GroupActivities)

GroupSession is a framework-owned final class conforming to ObservableObject. You cannot redeclare it, and code observing it must keep using Combine — the SDK ships no AsyncSequence for state, activity, or activeParticipants (sessions() is the only one).

More importantly, @Published publishes from willSet, so inside a sink the property still holds the old value. The standard late-joiner catch-up depends on exactly that timing:

swift

groupSession.$activeParticipants
    .sink { activeParticipants in
        // groupSession.activeParticipants is still the OLD set here
        let newParticipants = activeParticipants.subtracting(groupSession.activeParticipants)
        // send current state to joiners only
    }

Rewriting this against @Observable or an AsyncSequence makes subtracting return an empty set. There is no crash and no warning — late joiners silently never receive state, and the bug only appears with 3+ participants on a device that joined late. Leave Combine observation of GroupSession alone and say why.

Pattern 2: @StateObject → @State (HIGH)

Why migrate: Simpler, consistent with value types, works with @Observable

Requirement: iOS 17+ with @Observable model

Detection:

Grep: @StateObject

swift

// ❌ LEGACY
struct ContentView: View {
    @StateObject private var viewModel = ContentViewModel()
 
    var body: some View { ... }
}
 
// ✅ MODERN (with @Observable model)
struct ContentView: View {
    @State private var viewModel = ContentViewModel()
 
    var body: some View { ... }
}

Note: Only migrate after the model uses @Observable. If model still uses ObservableObject, keep @StateObject.

Pattern 3: @ObservedObject → Direct Property or @Bindable (HIGH)

Why migrate: Simpler code, explicit binding when needed

Requirement: iOS 17+ with @Observable model

Detection:

Grep: @ObservedObject

swift

// ❌ LEGACY
struct ItemView: View {
    @ObservedObject var item: ItemModel
 
    var body: some View {
        Text(item.name)
    }
}
 
// ✅ MODERN - Direct property (read-only access)
struct ItemView: View {
    var item: ItemModel  // No wrapper needed!
 
    var body: some View {
        Text(item.name)
    }
}
 
// ✅ MODERN - @Bindable (for two-way binding)
struct ItemEditorView: View {
    @Bindable var item: ItemModel
 
    var body: some View {
        TextField("Name", text: $item.name)  // Binding works
    }
}

Decision tree:

Need binding ($item.property)? → Use @Bindable
Just reading properties? → Use plain property (no wrapper)

Pattern 4: @EnvironmentObject → @Environment (HIGH)

Why migrate: Type-safe, works with @Observable

Requirement: iOS 17+ with @Observable model

Detection:

Grep: @EnvironmentObject
Grep: \.environmentObject\(

swift

// ❌ LEGACY - Setting
ContentView()
    .environmentObject(settings)
 
// ❌ LEGACY - Reading
struct SettingsView: View {
    @EnvironmentObject var settings: AppSettings
 
    var body: some View { ... }
}
 
// ✅ MODERN - Setting
ContentView()
    .environment(settings)
 
// ✅ MODERN - Reading
struct SettingsView: View {
    @Environment(AppSettings.self) var settings
 
    var body: some View { ... }
}
 
// ✅ MODERN - With binding
struct SettingsEditorView: View {
    @Environment(AppSettings.self) var settings
 
    var body: some View {
        @Bindable var settings = settings
        Toggle("Dark Mode", isOn: $settings.darkMode)
    }
}

Pattern 5: onChange(of:perform:) → onChange(of:initial:_:) (MEDIUM)

Why migrate: Deprecated modifier, new API has initial parameter

Requirement: iOS 17+

Detection:

Grep: \.onChange\(of:.*perform:

swift

// ❌ DEPRECATED
.onChange(of: searchText) { newValue in
    performSearch(newValue)
}
 
// ✅ MODERN (iOS 17+)
.onChange(of: searchText) { oldValue, newValue in
    performSearch(newValue)
}
 
// ✅ With initial execution
.onChange(of: searchText, initial: true) { oldValue, newValue in
    performSearch(newValue)
}

Pattern 6: Completion Handlers → async/await (MEDIUM)

Why migrate: Cleaner code, better error handling, structured concurrency

Requirement: iOS 15+ (widely adopted in iOS 17+)

Detection:

Grep: completion:\s*@escaping
Grep: completionHandler:
Grep: DispatchQueue\.main\.async

swift

// ❌ LEGACY
func fetchUser(id: String, completion: @escaping (Result<User, Error>) -> Void) {
    URLSession.shared.dataTask(with: url) { data, response, error in
        DispatchQueue.main.async {
            if let error = error {
                completion(.failure(error))
                return
            }
            // Parse and return
            completion(.success(user))
        }
    }.resume()
}
 
// ✅ MODERN
func fetchUser(id: String) async throws -> User {
    let (data, _) = try await URLSession.shared.data(from: url)
    return try JSONDecoder().decode(User.self, from: data)
}

Pattern 7: withAnimation Closures → Animation Parameter (LOW)

Why migrate: Cleaner API, avoids closure

Requirement: iOS 17+

Detection:

Grep: withAnimation.*\{

swift

// ❌ LEGACY
withAnimation(.spring()) {
    isExpanded.toggle()
}
 
// ✅ MODERN (simple cases)
isExpanded.toggle()
// Apply animation to view:
.animation(.spring(), value: isExpanded)
 
// Or use new binding animation:
$isExpanded.animation(.spring()).wrappedValue.toggle()

Pattern 8: Swift Language Modernization (LOW)

Why migrate: Clearer, more efficient, modern Swift idioms

Detection:

Grep: Date\(\)
Grep: CGFloat
Grep: replacingOccurrences
Grep: DateFormatter\(\)
Grep: \.filter\(.*\)\.count
Grep: Task\.sleep\(nanoseconds:

Reference: See axiom-swift (skills/swift-modern.md) skill for the full modern API replacement table.

Report matches as LOW priority unless they appear in hot paths (then MEDIUM).

Audit Process

Step 1: Find Swift Files

Glob: **/*.swift

Step 2: Detect Legacy Patterns

ObservableObject:

Grep: ObservableObject
Grep: @Published

Property Wrappers:

Grep: @StateObject|@ObservedObject|@EnvironmentObject

Deprecated Modifiers:

Grep: onChange\(of:.*perform:

Completion Handlers:

Grep: completion:\s*@escaping
Grep: completionHandler:

Step 3: Categorize by Priority

HIGH Priority (significant benefits):

ObservableObject → @Observable
Property wrapper migrations

MEDIUM Priority (code quality):

Deprecated modifiers
async/await adoption

LOW Priority (minor improvements):

Animation syntax
Minor API updates

Output Format

`markdown

# Modernization Analysis Results
 
## Summary
- **HIGH Priority**: [count] (Significant performance/maintainability gains)
- **MEDIUM Priority**: [count] (Deprecated APIs, code quality)
- **LOW Priority**: [count] (Minor improvements)
 
## Minimum Deployment Target Impact
- Current patterns support: iOS 14+
- After full modernization: iOS 17+
 
## HIGH Priority Migrations
 
### ObservableObject → @Observable
 
**Files affected**: 5
**Estimated effort**: 2-3 hours
 
#### Models to Migrate
 
1. `Models/ContentViewModel.swift:12`
   ```swift
   // Current
   class ContentViewModel: ObservableObject {
       @Published var items: [Item] = []
       @Published var isLoading = false
   }
 
   // Migrated
   @Observable
   class ContentViewModel {
       var items: [Item] = []
       var isLoading = false
   }
   ```
 
2. `Models/UserSettings.swift:8`
   [Similar migration...]
 
#### Views to Update After Model Migration
 
| File | Change |
|------|--------|
| `Views/ContentView.swift:15` | `@StateObject` → `@State` |
| `Views/ItemList.swift:23` | `@ObservedObject` → plain property |
| `Views/SettingsView.swift:8` | `@EnvironmentObject` → `@Environment` |
 
### @EnvironmentObject → @Environment
 
- `Views/RootView.swift:45`
  ```swift
  // Current
  .environmentObject(settings)
 
  // Migrated
  .environment(settings)
  ```
 
- `Views/SettingsView.swift:12`
  ```swift
  // Current
  @EnvironmentObject var settings: AppSettings
 
  // Migrated
  @Environment(AppSettings.self) var settings
  ```
 
## MEDIUM Priority Migrations
 
### Deprecated onChange Modifier
 
- `Views/SearchView.swift:34`
  ```swift
  // Deprecated
  .onChange(of: query) { newValue in
      search(newValue)
  }
 
  // Modern
  .onChange(of: query) { oldValue, newValue in
      search(newValue)
  }
  ```
 
### async/await Opportunities
 
- `Services/NetworkService.swift` - 3 completion handler methods
  - `fetchUser(completion:)` → `fetchUser() async throws`
  - `fetchItems(completion:)` → `fetchItems() async throws`
  - `uploadData(completion:)` → `uploadData() async throws`
 
## Migration Order
 
1. **First**: Migrate models to `@Observable`
   - All `ObservableObject` → `@Observable`
   - Remove all `@Published`
 
2. **Second**: Update view property wrappers
   - `@StateObject` → `@State` (for owned models)
   - `@ObservedObject` → plain or `@Bindable`
   - `@EnvironmentObject` → `@Environment`
 
3. **Third**: Update view modifiers
   - `.environmentObject()` → `.environment()`
   - Deprecated `onChange` syntax
 
4. **Fourth**: Adopt async/await (optional, but recommended)
 
## Breaking Changes Warning
 
⚠️ **Deployment Target**: Full migration requires iOS 17+
 
If you need to support iOS 16 or earlier:
- Keep `ObservableObject` for those models
- Use conditional compilation:
  ```swift
  #if os(iOS) && swift(>=5.9)
  @Observable
  class ViewModel { ... }
  #else
  class ViewModel: ObservableObject { ... }
  #endif
  ```
 
## Verification
 
After migration:
1. Build and fix any compiler errors
2. Test view updates (properties should still trigger UI refresh)
3. Test bindings (TextField, Toggle still work)
4. Test environment injection

When No Migration Needed

This is the start of the file. Read the full SKILL.md on GitHub.

Security

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Source

SKILL.md in the repositoryCheckingaxiom-codex/skills/axiom-modernize/SKILL.md

Popularity

Repository stars: 1,097
Repository forks: 81
7-day trend score: 35

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