swift-patterns

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SKILL.md (first lines)

# Swift Patterns

Modern Swift patterns for iOS/macOS application development.

## SwiftUI View Composition

```swift
// Small, focused views composed together
struct ProductCard: View {
    let product: Product

    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            ProductImage(url: product.imageURL)
            ProductInfo(name: product.name, price: product.price)
            RatingStars(rating: product.rating, count: product.reviewCount)
        }
        .padding()
        .background(.regularMaterial)
        .clipShape(RoundedRectangle(cornerRadius: 12))
    }
}

// Extract subviews for readability and reusability
struct ProductImage: View {
    let url: URL

    var body: some View {
        AsyncImage(url: url) { phase in
            switch phase {
            case .success(let image):
                image.resizable().aspectRatio(contentMode: .fill)
            case .failure:
                Image(systemName: "photo").foregroundStyle(.secondary)
            case .empty:
                ProgressView()
            @unknown default:
                EmptyView()
            }
        }
        .frame(height: 200)
        .clipped()
    }
}

// ViewModifier for reusable styling
struct CardModifier: ViewModifier {
    func body(content: Content) -> some View {
        content
            .padding()
            .background(.regularMaterial)
            .clipShape(RoundedRectangle(cornerRadius: 12))
            .shadow(radius: 2)
    }
}

extension View {
    func cardStyle() -> some View {
        modifier(CardModifier())
    }
}
```

## @Observable Pattern (iOS 17+)

```swift
import Observation

@Observable
final class ProductStore {
    var products: [Product] = []
    var isLoading = false
    var errorMessage: String?

    private let apiClient: APIClient

    init(apiClient: APIClient = .shared) {
        self.apiClient = apiClient
    }

    func loadProducts() async {
        isLoading = true
        errorMessage = nil

        do {
            products = try await apiClient.fetchProducts()
        } catch {
            errorMessage = error.localizedDescription
        }

        isLoading = false
    }

    func deleteProduct(_ product: Product) async throws {
        try await apiClient.deleteProduct(id: product.id)
        products.removeAll { $0.id == product.id }
    }
}

// Usage in SwiftUI (automatic tracking, no @Published needed)
struct ProductListView: View {
    @State private var store = ProductStore()

    var body: some View {
        List(store.products) { product in
            ProductCard(product: product)
        }
        .overlay {
            if store.isLoading { ProgressView() }
            if let error = store.errorMessage {
                ContentUnavailableView("Error", systemImage: "exclamationmark.triangle",
                                       description: Text(error))
            }
        }
        .task { await store.loadProducts() }
    }
}
```

From vibeeval/vibecosystem, MIT.

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