swift-patterns

Swift / iOS Patterns

Project Structure

Swift Package (SPM)

MyPackage/
├── Package.swift
├── Sources/
│   ├── MyLibrary/
│   └── MyExecutable/
├── Tests/
│   └── MyLibraryTests/
└── Plugins/

// swift-tools-version: 5.10
import PackageDescription

let package = Package(
    name: "MyPackage",
    platforms: [.iOS(.v17), .macOS(.v14)],
    products: [
        .library(name: "MyLibrary", targets: ["MyLibrary"]),
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-algorithms", from: "1.2.0"),
    ],
    targets: [
        .target(name: "MyLibrary",
                dependencies: [.product(name: "Algorithms", package: "swift-algorithms")]),
        .testTarget(name: "MyLibraryTests", dependencies: ["MyLibrary"]),
    ]
)

Xcode Project Layout

MyApp/
├── MyApp/
│   ├── App/             # Entry point, ContentView
│   ├── Features/        # Feature modules (Views, ViewModels, Models)
│   ├── Core/            # Networking, Storage, Extensions
│   └── Resources/       # Assets.xcassets, Info.plist
├── MyAppTests/
└── MyAppUITests/

Idioms / Code Style

Optionals

// guard-let for early exit
func process(user: User?) {
    guard let user else { return }
    print(user.name)
}

// Optional chaining + nil coalescing
let name = user?.profile?.displayName ?? "Anonymous"

// map/flatMap on optionals
let length: Int? = optionalString.map { $0.count }
// Never force-unwrap in production: user!.name

Protocol-Oriented Programming

protocol Cacheable: Identifiable where ID: Hashable {
    var cacheKey: String { get }
}

extension Cacheable where ID == String {
    var cacheKey: String { id }
}

Value Types vs Reference Types

Use structs by default (value semantics, thread-safe). Use classes when identity matters, shared mutable state is intentional, inheritance is needed, or ObjC interop is required.

Property Wrappers

@propertyWrapper
struct Clamped<Value: Comparable> {
    var wrappedValue: Value {
        didSet { wrappedValue = min(max(wrappedValue, range.lowerBound), range.upperBound) }
    }
    let range: ClosedRange<Value>

    init(wrappedValue: Value, _ range: ClosedRange<Value>) {
        self.range = range
        self.wrappedValue = min(max(wrappedValue, range.lowerBound), range.upperBound)
    }
}

struct Volume {
    @Clamped(0...100) var level: Int = 50
}