new-api-support

Add introspection support for a SwiftUI API (view type, modifier, or View extension function).

Usage

/new-api-support <entity_name>

Where <entity_name> is:

A SwiftUI struct name (e.g., ContentUnavailableView, ProgressView)
A View extension function name (e.g., onAppear, disabled, opacity)
A modifier struct name (e.g., ScaledMetric)

Workflow

Step 1: Locate and Catalog the API

Find the API in the local iOS SDK (prefer local over network):

# Find SwiftUI interface files in Xcode SDK
find /Applications/Xcode.app/Contents/Developer/Platforms -name "SwiftUI.swiftmodule" -type d 2>/dev/null | head -5

# Search for the entity in SwiftUI interfaces
grep -r "<entity_name>" /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks/SwiftUI.framework/Modules/SwiftUI.swiftmodule/*.swiftinterface 2>/dev/null | head -50

# For macOS SDK
grep -r "<entity_name>" /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/SwiftUI.framework/Modules/SwiftUI.swiftmodule/*.swiftinterface 2>/dev/null | head -50

Catalog ALL related APIs:

For functions: Find all overloads (same name, different parameters)
For structs: Find the struct definition AND any View extension functions that return this type
Note ALL @available attributes for each API variant

Example catalog format:

Entity: .buttonStyle(_:)
Type: View extension function
Related APIs:
  1. func buttonStyle<S>(_ style: S) -> some View where S : ButtonStyle
     @available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.0, *)
  2. func buttonStyle<S>(_ style: S) -> some View where S : PrimitiveButtonStyle
     @available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.0, *)

Step 2: Research Usage Context

Understand HOW the API is meant to be used by researching its typical context:

Search for documentation and usage patterns:
- Use web search to find Apple documentation and WWDC sessions
- Look for common usage patterns in tutorials and Stack Overflow
- Identify which parent views/containers the API is typically used with

Identify related parent/child relationships:

Entity Type	Find Related Context
View inside container	Which container views typically hold this view? (e.g., `Tab` goes inside `TabView`)
View modifier	Which views is this modifier typically applied to? (e.g., `subscriptionStoreButtonLabel` applies to `SubscriptionStoreView`)
Container-specific modifier	Which container makes this modifier meaningful? (e.g., `listRowBackground` on views inside `List`)
Style modifier	Which view type does this style affect? (e.g., `buttonStyle` on `Button`)

Document the context for test design:

Example context analysis:

Entity: Tab
Type: View
Typical Context: Used as direct child of TabView
Related APIs: TabView, tabItem (deprecated predecessor)
Test Structure: Tab should be tested INSIDE TabView hierarchy

Entity: subscriptionStoreButtonLabel
Type: View modifier
Typical Context: Applied to SubscriptionStoreView
Related APIs: SubscriptionStoreView, SubscriptionStoreButton
Test Structure: Apply modifier to SubscriptionStoreView, not EmptyView

Check for container-dependent behavior:
- Some modifiers only work in specific contexts (e.g., listRowInsets only meaningful in List)
- Some views only function inside specific parents (e.g., Section in List or Form)
- Test in the correct context to ensure real-world usability

Step 3: Determine File Placement

For new View types (structs like ProgressView, ContentUnavailableView):

Create new file: Sources/ViewInspector/SwiftUI/<ViewName>.swift
Create test file: Tests/ViewInspectorTests/SwiftUI/<ViewName>Tests.swift

For View modifiers/functions, find the appropriate existing file by category:

Category	Source File	Test File
Animation (.animation, .transition)	`Modifiers/AnimationModifiers.swift`	`ViewModifiers/AnimationModifiersTests.swift`
Configuration (.disabled, .labelsHidden)	`Modifiers/ConfigurationModifiers.swift`	`ViewModifiers/ConfigurationModifiersTests.swift`
Environment (.environment, .environmentObject)	`Modifiers/EnvironmentModifiers.swift`	`ViewModifiers/EnvironmentModifiersTests.swift`
Interaction (.onTapGesture, .onAppear)	`Modifiers/InteractionModifiers.swift`	`ViewModifiers/InteractionModifiersTests.swift`
Positioning (.offset, .position)	`Modifiers/PositioningModifiers.swift`	`ViewModifiers/PositioningModifiersTests.swift`
Sizing (.frame, .fixedSize)	`Modifiers/SizingModifiers.swift`	`ViewModifiers/SizingModifiersTests.swift`
Text input (.keyboardType, .textContentType)	`Modifiers/TextInputModifiers.swift`	`ViewModifiers/TextInputModifiersTests.swift`
Transform (.rotationEffect, .scaleEffect)	`Modifiers/TransformingModifiers.swift`	`ViewModifiers/TransformingModifiersTests.swift`
Navigation bar (.navigationTitle)	`Modifiers/NavigationBarModifiers.swift`	-
Custom styles (.buttonStyle, .pickerStyle)	`Modifiers/CustomStyleModifiers.swift`	-

Check existing files to confirm the pattern:

grep -l "similar_modifier" Sources/ViewInspector/Modifiers/*.swift

Step 4: Reverse Engineering Investigation

Create a reverse engineering test to understand the internal structure:

import XCTest
import SwiftUI
@testable import ViewInspector

final class ReverseEngineeringTests: XCTestCase {

    func testInvestigate_<EntityName>() throws {
        // Create a simple view using the target API
        let sut = EmptyView().<targetAPI>()

        // Print the internal structure
        print("\(Inspector.print(sut) as AnyObject)")
    }
}

Run the investigation test:

swift test --filter "testInvestigate_"

Analyze the output to identify:

The internal modifier/view type name (e.g., _AppearanceActionModifier)
Property names and their paths (e.g., appear, disappear)
Nested structure for complex types
Whether it uses ModifiedContent wrapper

Example Inspector.print output:

EmptyView
  → _AppearanceActionModifier
      modifier: _AppearanceActionModifier
        appear: Optional<() -> ()>
          some: (Function)
        disappear: Optional<() -> ()>
          none

Iterate investigation for each API variant and parameter combination to understand all internal structures.

Step 5: Implement Introspection Support

For View modifiers, add to the appropriate Modifiers file:

@available(iOS 13.0, macOS 10.15, tvOS 13.0, *)
public extension InspectableView {

    // For simple value extraction
    func <modifierName>() throws -> <ReturnType> {
        return try modifierAttribute(
            modifierName: "<InternalModifierName>",  // From Inspector.print
            path: "modifier|<propertyPath>",         // Path to the value
            type: <ReturnType>.self,
            call: "<modifierName>")
    }

    // For callback invocation
    func call<CallbackName>() throws {
        let callback = try modifierAttribute(
            modifierName: "<InternalModifierName>",
            path: "modifier|<callbackPath>",
            type: (() -> Void).self,
            call: "call<CallbackName>")
        callback()
    }
}

For new View types, create the full ViewType structure:

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
public extension ViewType {

    struct NewViewType: KnownViewType {
        public static let typePrefix: String = "NewViewType"  // From Inspector.print
        public static var namespacedPrefixes: [String] {
            ["SwiftUI.NewViewType"]
        }
    }
}

// MARK: - Content Extraction

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
extension ViewType.NewViewType: SingleViewContent {  // or MultipleViewContent

    public static func child(_ content: Content) throws -> Content {
        return try Inspector.attribute(path: "content", value: content.view)
    }
}

// MARK: - Extraction from View hierarchy

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
public extension InspectableView where View == ViewType.NewViewType {

    // Add attribute getters based on Inspector.print analysis
    func someAttribute() throws -> SomeType {
        return try Inspector.attribute(
            path: "attributePath",
            value: content.view,
            type: SomeType.self)
    }
}

// MARK: - Global View hierarchy access

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
public extension InspectableView {

    func newViewType(_ index: Int? = nil) throws -> InspectableView<ViewType.NewViewType> {
        return try contentForModifierLookup.newViewType(parent: self, index: index)
    }
}

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
internal extension Content {

    func newViewType(parent: UnwrappedView, index: Int?) throws
        -> InspectableView<ViewType.NewViewType> {
        let call = "newViewType(\(index == nil ? "" : "\(index!)"))"
        return try .init(try Inspector.attribute(path: "content", value: view),
                         parent: parent, call: call, index: index)
    }
}

Step 6: Add Tests

IMPORTANT: Use contextual test structure based on Step 2 research.

Tests should reflect real-world usage patterns, not just technical functionality.

For views that belong inside specific containers:

import XCTest
import SwiftUI
@testable import ViewInspector

// Example: Tab is meant to be used inside TabView
@available(iOS 18.0, macOS 15.0, tvOS 18.0, watchOS 11.0, visionOS 2.0, *)
final class TabTests: XCTestCase {

    // Test extraction in proper context (inside TabView)
    func testTabInsideTabView() throws {
        let sut = TabView {
            Tab("Home", systemImage: "house") {
                Text("Home Content")
            }
            Tab("Settings", systemImage: "gear") {
                Text("Settings Content")
            }
        }
        let tab = try sut.inspect().tabView().tab(0)
        XCTAssertEqual(try tab.labelView().text().string(), "Home")
    }

    // Test searching for content inside Tab inside TabView
    func testSearchForContentInsideTab() throws {
        let sut = TabView {
            Tab("Home", systemImage: "house") {
                Text("Home Content")
            }
        }
        XCTAssertEqual(
            try sut.inspect().find(text: "Home Content").pathToRoot,
            "tabView().tab(0).text()")
    }
}

For modifiers that apply to specific view types:

// Example: subscriptionStoreButtonLabel applies to SubscriptionStoreView
@available(iOS 17.0, macOS 14.0, *)
final class SubscriptionModifiersTests: XCTestCase {

    func testSubscriptionStoreButtonLabel() throws {
        let sut = SubscriptionStoreView(productIDs: ["com.app.subscription"])
            .subscriptionStoreButtonLabel(.multiline)
        let label = try sut.inspect().subscriptionStoreView().subscriptionStoreButtonLabel()
        XCTAssertEqual(label, .multiline)
    }
}

// Example: listRowBackground applies to views inside List
@available(iOS 13.0, macOS 10.15, tvOS 13.0, *)
final class ListModifiersTests: XCTestCase {

    func testListRowBackgroundInsideList() throws {
        let sut = List {
            Text("Row")
                .listRowBackground(Color.red)
        }
        let background = try sut.inspect().list().text(0).listRowBackground()
        // Verify the background color
    }
}

For style modifiers, test with the view type they style:

// Example: buttonStyle applies to Button
@available(iOS 13.0, macOS 10.15, tvOS 13.0, *)
final class ButtonStyleTests: XCTestCase {

    func testButtonStyleOnButton() throws {
        let sut = Button("Tap") { }
            .buttonStyle(.borderedProminent)
        let style = try sut.inspect().button().buttonStyle()
        // Verify style properties
    }
}

Generic test file structure (when no specific context applies):

import XCTest
import SwiftUI
@testable import ViewInspector

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
final class NewViewTypeTests: XCTestCase {

    // Test basic extraction
    func testExtractionFromSingleViewContainer() throws {
        let view = AnyView(NewViewType())
        XCTAssertNoThrow(try view.inspect().anyView().newViewType())
    }

    // Test attribute inspection
    func testSomeAttributeInspection() throws {
        let sut = NewViewType(someParam: .value)
        let value = try sut.inspect().newViewType().someAttribute()
        XCTAssertEqual(value, .value)
    }

    // Test in view hierarchy
    func testSearch() throws {
        let view = HStack { NewViewType() }
        XCTAssertEqual(try view.inspect().find(ViewType.NewViewType.self).pathToRoot,
                       "hStack().newViewType(0)")
    }
}

For generic modifiers (not container-specific):

@available(iOS 13.0, macOS 10.15, tvOS 13.0, *)
final class SomeModifierTests: XCTestCase {

    func testModifierApplication() throws {
        let sut = EmptyView().someModifier(value: 42)
        XCTAssertNoThrow(try sut.inspect().emptyView())
    }

    func testModifierValueInspection() throws {
        let sut = EmptyView().someModifier(value: 42)
        let value = try sut.inspect().emptyView().someModifier()
        XCTAssertEqual(value, 42)
    }
}

Run tests incrementally (headless - fast iteration):

# Run specific test
swift test --filter "NewViewTypeTests/testExtractionFromSingleViewContainer"

# Run all tests for the new type
swift test --filter "NewViewTypeTests"

Final verification on platform simulators:

Headless swift test is fast and suitable for development iteration, but final verification must run on actual platform simulators for all platforms the API supports.

Based on the API's @available attributes, verify tests pass on each supported platform:

# iOS Simulator
xcodebuild test -scheme ViewInspector -destination 'platform=iOS Simulator,name=iPhone 16'

# tvOS Simulator
xcodebuild test -scheme ViewInspector -destination 'platform=tvOS Simulator,name=Apple TV'

# macOS
xcodebuild test -scheme ViewInspector -destination 'platform=macOS'

# visionOS Simulator
xcodebuild test -scheme ViewInspector -destination 'platform=visionOS Simulator,name=Apple Vision Pro'

# watchOS - SPECIAL: Uses separate Xcode project
xcodebuild test -project .watchOS/watchOS.xcodeproj -scheme watchOS -destination 'platform=watchOS Simulator,name=Apple Watch Series 10 (46mm)'

Platform testing requirements:

If API is @available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *) → test on all four platforms
If API is @available(iOS 15.0, *) with @available(macOS, unavailable) → only test iOS
watchOS is peculiar: always use .watchOS/watchOS.xcodeproj instead of the main package

Quick platform matrix check:

# List available simulators
xcrun simctl list devices available

Step 7: Update readiness.md

Add the new API to readiness.md in the appropriate section:

For View types, add to the "View Types" table:

|:white_check_mark:| NewViewType | `attribute1`, `attribute2`, `containedView` |

For Modifiers, add to the "View Modifiers" table:

|:white_check_mark:| `.someModifier(value:)` | `someModifier() -> Type` |

Maintain alphabetical order within each section.

Step 8: Update unsupported_swiftui_apis.md

After adding support for a new API, check if unsupported_swiftui_apis.md exists in the repository root and remove the entry for the newly supported API:

# Check if the file exists
ls unsupported_swiftui_apis.md

# Search for the API entry
grep -n "<entity_name>" unsupported_swiftui_apis.md

Remove the entry from the appropriate section:

For view types: Remove from "View Types - Not Supported" or "View Types - Partial Support"
For modifiers: Remove from "View Modifiers - Not Supported"
For property wrappers: Remove from "Property Wrappers - Not Supported"
For partial support completions: Remove from "View Types - Partial Support" if now fully supported

Also remove from Quick Reference if the API was listed there:

# Remove lines like:
/new-api-support Gauge
/new-api-support "Group(subviews:)"

If the file doesn't exist, skip this step.

Important Notes

Always check @available attributes - Copy them exactly from the SDK and apply to all introspection code and tests
Use XCTAssertThrows instead of XCTAssertThrowsError (enforced by SwiftLint)
Handle platform differences - Some APIs have different availability on iOS/macOS/tvOS/watchOS. Use #if os() when needed
Test all overloads - Each function variant may have different internal structure
Modifier path format - Use | as path separator: "modifier|property|nestedProperty"
Common internal type prefixes:
- _ prefix: Internal SwiftUI types (e.g., _AppearanceActionModifier)
- Modified suffix: Wrapped content (e.g., ModifiedContent)
For callbacks/closures - Store them via try Inspector.attribute() then invoke
Registration in ViewSearchIndex - For new view types, check if registration in ViewSearchIndex.swift is needed for find() to work

Public API Design Principles

Never return Any from public APIs - Consumers need typed values they can work with
Prefer returning SwiftUI types over String, Any, or custom types:
- If a public SwiftUI type exists (like GlassEffectTransition), return it
- When internal types (e.g., _GlassEffectTransition) can't be cast to public types, investigate if you can map string descriptions to public type values
Create wrapper types for complex modifier parameters:
- Instead of multiple methods like glassEffectTintColor() and glassEffectShape(), create a wrapper ViewType.GlassEffect with methods tintColor(), shape(), etc.
- The wrapper holds the internal config and provides typed accessors
- Example pattern:
```
public extension ViewType {
    struct GlassEffect {
        private let config: Any
        public func tintColor() throws -> SwiftUI.Color? { ... }
        public func shape<S>(_ type: S.Type) throws -> S where S: SwiftUI.Shape { ... }
    }
}
```
- Note: When inside ViewType namespace, use fully qualified names like SwiftUI.Color and SwiftUI.Shape to avoid conflicts with other ViewType members
Add BinaryEquatable conformance to the public library API (not just tests) for SwiftUI types that consumers may want to compare in their tests

Investigation Techniques

Inspector.print() returns a String - Must wrap with print() to see output:

print(Inspector.print(someValue))  // Correct
Inspector.print(someValue)         // Wrong - output not visible

Investigate chained method calls to understand behavior:
- Chaining same method (e.g., .tint(.red).tint(.blue)) typically overwrites - last value wins
- Chaining different methods (e.g., .tint(.red).interactive(true)) preserves all values
- There's usually no internal "combined" structure - just single values per property
Check type casting between internal and public types:
- Internal types like _Glass often cannot be cast to public types like Glass
- When casting fails, extract individual properties and map them to public type values

Test Best Practices

Test in proper context - Always test views and modifiers in their intended usage context:
- Child views should be tested inside their parent containers (e.g., Tab inside TabView)
- Container-specific modifiers should be tested on views inside that container (e.g., listRowBackground on views inside List)
- Style modifiers should be tested on the view type they style (e.g., buttonStyle on Button)
- This ensures tests validate real-world usability, not just technical extraction
Platform-unavailable APIs - Wrap entire test file in #if !os(visionOS) (or appropriate platform), not individual tests
Add @MainActor to test class to avoid main actor isolation warnings
Don't test platform-specific default values - They may vary across platforms. Only test explicit parameter values

Compare to exact values instead of XCTAssertNotNil when possible:

// Good
XCTAssertEqual(result.id, AnyHashable("testID"))

// Avoid when exact comparison is possible
XCTAssertNotNil(result.id)

Don't duplicate tests that test the same functionality with different values (e.g., don't need separate tests for Circle, Capsule, RoundedRectangle shapes - one is sufficient)

Test missing modifier errors - Verify error messages are correct:

func testGlassEffectMissingModifierError() throws {
    let sut = EmptyView().padding()
    XCTAssertThrows(
        try sut.inspect().emptyView().glassEffect(),
        "EmptyView does not have 'glassEffect' modifier")
}

Search tests should search for child views inside the container, not just the container itself:

func testSearchForChildInsideContainer() throws {
    let view = VStack {
        NewContainer {
            Text("Child1")
            Text("Child2")
        }
    }
    XCTAssertEqual(
        try view.inspect().find(text: "Child2").pathToRoot,
        "vStack().newContainer(0).text(1)")
}

Some values can't be compared directly - Namespace.ID is recreated during inspection; use XCTAssertNotNil with a comment explaining why

Advanced Introspection Techniques

ViewInspector uses several advanced techniques to access SwiftUI's internal structures. Use these when standard Inspector.attribute() approaches don't work.

1. BinaryEquatable Protocol

Problem: SwiftUI types like Font.Weight, ToolbarItemPlacement, GlassEffectTransition don't conform to Equatable, making test assertions impossible.

Solution: BinaryEquatable compares raw memory bytes instead:

// In BaseTypes.swift
public protocol BinaryEquatable: Equatable { }

extension BinaryEquatable {
    public static func == (lhs: Self, rhs: Self) -> Bool {
        withUnsafeBytes(of: lhs) { lhsBytes -> Bool in
            withUnsafeBytes(of: rhs) { rhsBytes -> Bool in
                lhsBytes.elementsEqual(rhsBytes)
            }
        }
    }
}

// Usage - add conformance to enable comparisons
@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
extension ToolbarItemPlacement: BinaryEquatable { }

@available(iOS 26.0, macOS 26.0, tvOS 26.0, watchOS 26.0, *)
extension GlassEffectTransition: BinaryEquatable { }

When to use: For any SwiftUI type that needs equality comparison in tests but doesn't provide Equatable.

2. unsafeBitCast with Allocator Pattern

Problem: Many SwiftUI types (gesture values, style configurations, proxies) don't have public initializers, but tests need to create instances.

Solution: Create an Allocator struct matching the memory layout, then bitcast:

@available(iOS 13.0, macOS 10.15, tvOS 13.0, *)
private extension GeometryProxy {
    struct Allocator48 {
        let data: (Int64, Int64, Int64, Int64, Int64, Int64) = (0, 0, 0, 0, 0, 0)
    }
    struct Allocator52 {
        let data: (Allocator48, Int32) = (.init(), 0)
    }

    init() {
        switch MemoryLayout<Self>.size {
        case 52:
            self = unsafeBitCast(Allocator52(), to: GeometryProxy.self)
        case 48:
            self = unsafeBitCast(Allocator48(), to: GeometryProxy.self)
        default:
            fatalError(MemoryLayout<Self>.actualSize())
        }
    }
}

Key patterns:

Create multiple Allocator variants for different OS versions (struct sizes change!)
Use MemoryLayout<Self>.size switch to pick the right allocator
Use MemoryLayout<Self>.actualSize() in default case to discover new sizes
Name allocators by size (e.g., Allocator48, Allocator52)

When to use: Creating gesture values, style configurations, proxies, _ViewModifier_Content, _PreferenceValue, etc.

3. Surrogate Pattern for Private Struct Access

Problem: Need to access internal properties of a private SwiftUI type like SignInWithAppleButton.

Solution: Create a Surrogate struct matching the memory layout, then rebind:

// The Surrogate mirrors the internal structure
extension SignInWithAppleButton {
    struct Surrogate {
        let type: ASAuthorizationAppleIDButton.ButtonType
        let onRequest: (ASAuthorizationAppleIDRequest) -> Void
        let onCompletion: (Result<ASAuthorization, Error>) -> Void
    }
}

// Access via unsafeMemoryRebind
private func buttonSurrogate() throws -> Surrogate {
    let button = try Inspector.cast(value: content.view, type: SignInWithAppleButton.self)
    return try Inspector.unsafeMemoryRebind(value: button, type: Surrogate.self)
}

When to use: When you need to access multiple internal properties or invoke internal callbacks.

4. unsafeMemoryRebind for Type Conversion

Problem: Need to convert between types with identical memory layouts (e.g., Swift 6 Sendable closures).

Solution: Use Inspector.unsafeMemoryRebind:

// In Inspector.swift
static func unsafeMemoryRebind<V, T>(value: V, type: T.Type) throws -> T {
    guard MemoryLayout<V>.size == MemoryLayout<T>.size else {
        throw InspectionError.notSupported("Unable to rebind...")
    }
    return withUnsafeBytes(of: value) { bytes in
        return bytes.baseAddress!
            .assumingMemoryBound(to: T.self).pointee
    }
}

When to use: Converting closure types with different Sendable annotations, or accessing surrogate types.

5. withUnsafePointer + withMemoryRebound for Binding Conversion

Problem: Internal enum type is wrapped in Binding but you need a different Binding type (e.g., Toggle's internal ToggleState enum).

Solution: Rebind the pointer:

// Toggle changed from Binding<Bool> to Binding<ToggleState> in iOS 16
private enum ToggleState { case on, off, mixed }

let toggleStateBinding = try Inspector.attribute(label: "_toggleState", value: content.view)
let toggleState = withUnsafePointer(to: toggleStateBinding) {
    $0.withMemoryRebound(to: Binding<ToggleState>.self, capacity: 1) {
        $0.pointee
    }
}
// Now create a Bool binding that wraps the ToggleState
return Binding(
    get: { toggleState.wrappedValue == .on },
    set: { toggleState.wrappedValue = $0 ? .on : .off }
)

When to use: When the internal binding type differs from the public API type.

6. withUnsafeBytes + bindMemory for Closure Invocation

Problem: Need to invoke a closure stored in a generic container with specific type parameters.

Solution: Bind the closure's memory to the expected type:

typealias Closure = (EnvironmentValues) -> ModifiedContent<V, SomeModifier>

guard let typedClosure = withUnsafeBytes(of: closure, {
    $0.bindMemory(to: Closure.self).first
}) else { throw InspectionError.typeMismatch(closure, Closure.self) }

let view = typedClosure(EnvironmentValues())

When to use: Invoking closure-based content builders like GeometryReader, ScrollViewReader, or navigationBarItems.

7. Memory Patching for Environment Injection

Problem: Need to inject environment objects into views that require them for inspection.

Solution: Scan memory for matching patterns and patch:

// In EnvironmentInjection.swift
static func inject<T>(environmentObject: AnyObject, into entity: T) -> T {
    let envObjSize = EnvObject.structSize
    var offset = MemoryLayout<T>.stride - envObjSize

    return withUnsafeBytes(of: EnvObject.Forgery(object: nil)) { reference in
        while offset >= 0 {
            var copy = entity
            withUnsafeMutableBytes(of: &copy) { bytes in
                // Check if memory at offset matches empty env object pattern
                guard bytes[offset..<offset + envObjSize].elementsEqual(reference)
                else { return }
                // Write marker to verify location
                let rawPointer = bytes.baseAddress! + offset + EnvObject.seedOffset
                let pointerToValue = rawPointer.assumingMemoryBound(to: Int.self)
                pointerToValue.pointee = -1
            }
            // Verify via reflection that we found the right location
            if let seed = try? Inspector.attribute(path: label + "|_seed", value: copy, type: Int.self),
               seed == -1 {
                // Patch with actual object
                withUnsafeMutableBytes(of: &copy) { bytes in
                    let rawPointer = bytes.baseAddress! + offset
                    let pointerToValue = rawPointer.assumingMemoryBound(to: EnvObject.Forgery.self)
                    pointerToValue.pointee = .init(object: environmentObject)
                }
                return copy
            }
            offset -= step
        }
        return entity
    }
}

When to use: This technique is already implemented in ViewInspector for environment injection. Reference it when debugging environment-related issues.

8. NSKeyedUnarchiver + setValue for Objective-C Types

Problem: Need to create instances of Objective-C types without public initializers (e.g., ASAuthorizationAppleIDCredential).

Solution: Decode from archived data and mutate with setValue:

public extension ASAuthorizationAppleIDCredential {
    convenience init(user: String, email: String?, fullName: PersonNameComponents?, ...) {
        // Base64-encoded archived empty instance
        let data = Data(base64Encoded: "YnBsaXN0MDD...")
        let decoder = try! NSKeyedUnarchiver(forReadingFrom: data!)
        self.init(coder: decoder)!

        // Mutate with desired values
        setValue(user, forKey: "user")
        setValue(email, forKey: "email")
        setValue(fullName, forKey: "fullName")
        // ... more properties
    }
}

When to use: Creating Objective-C class instances that need custom initialization for testing.

9. MemoryLayout.actualSize() Discovery Helper

Problem: SwiftUI struct sizes change between OS versions, breaking Allocator patterns.

Solution: Use a helper to discover new sizes:

internal extension MemoryLayout {
    static func actualSize() -> String {
        fatalError("New size of \(String(describing: type(of: T.self))) is \(Self.size)")
    }
}

// Usage in switch default case:
init(fractionCompleted: Double?) {
    switch MemoryLayout<Self>.size {
    case 12:
        self = unsafeBitCast(Allocator12(fractionCompleted: fractionCompleted), to: Self.self)
    case 36:
        self = unsafeBitCast(Allocator36(fractionCompleted: fractionCompleted), to: Self.self)
    default:
        fatalError(MemoryLayout<Self>.actualSize())  // "New size of ProgressViewStyleConfiguration is 48"
    }
}

When to use: Always include in Allocator pattern switch statements to detect OS changes.

10. String Description Mapping for Internal Enums

Problem: Internal enums can't be cast to public types, but their string description matches public values.

Solution: Map string descriptions to public enum values:

func glassEffectTransition() throws -> GlassEffectTransition {
    let kind = try modifierAttribute(
        modifierName: "GlassEffectTransitionModifier", path: "modifier|transition|kind",
        type: Any.self, call: "glassEffectTransition")

    // Internal _GlassEffectTransition can't cast to GlassEffectTransition
    // but String(describing:) reveals the case name
    let description = String(describing: kind)
    if description == "materialize" {
        return .materialize
    } else if description.hasPrefix("matchedGeometry") {
        return .matchedGeometry
    } else {
        return .identity
    }
}

When to use: When internal enums have public equivalents but casting fails.

Quick Reference: Choosing the Right Technique

Problem	Technique
Compare non-Equatable types	BinaryEquatable
Create type without public init	Allocator + unsafeBitCast
Access private struct properties	Surrogate + unsafeMemoryRebind
Convert closure types	withUnsafeBytes + bindMemory
Convert binding types	withUnsafePointer + withMemoryRebound
Create Obj-C types	NSKeyedUnarchiver + setValue
Handle OS version changes	MemoryLayout switch + actualSize()
Map internal to public enum	String(describing:) mapping