Agent skill
Swift Ecosystem
This skill should be used when working with Swift projects, "Package.swift", "swift build/test/run", "swiftc", SwiftLint, SwiftFormat, or Swift language patterns. Provides comprehensive Swift ecosystem patterns and best practices for cross-platform CLI and library development.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/swift-ecosystem-motoki317-dotfiles-2
SKILL.md
Swift Language
Type System
Value vs Reference:
- Structs/enums are value types (copied) - prefer for data models
- Classes are reference types (shared) - use when reference semantics or inheritance required
- Enums with associated values for algebraic data types
Optionals: Swift's nil-safety through Optional type.
if let value = optionalValue { use(value) }
guard let value = optionalValue else { return }
let value = optionalValue ?? defaultValue
let result = object?.property?.method()
Avoid force unwrap (!) - use safe unwrapping patterns.
Protocols: Define behavior contracts, prefer composition over inheritance.
protocol Identifiable { var id: String { get } }
protocol Timestamped { var createdAt: Date { get } }
struct User: Identifiable, Timestamped { ... }
Generics: Type parameters with constraints.
func process<T: Codable & Sendable>(_ item: T) -> Data { ... }
func compare<T>(_ a: T, _ b: T) -> Bool where T: Comparable { a < b }
Noncopyable (~Copyable, Swift 6+): Types with unique ownership.
struct UniqueResource: ~Copyable {
consuming func release() { /* takes ownership */ }
}
Error Handling
Throwing functions:
enum ParseError: Error { case invalidFormat, missingField(String) }
func parse(_ input: String) throws -> Config { ... }
do { let config = try parse(input) }
catch ParseError.invalidFormat { ... }
Result type: For async error handling or when throws is inconvenient.
Typed throws (Swift 6+): func parse(_ input: String) throws(ParseError) -> Config
Concurrency (Swift 5.5+)
async/await:
func fetchData() async throws -> Data {
let (data, _) = try await URLSession.shared.data(from: url)
return data
}
Actors: Thread-safe mutable state.
actor Counter {
private var value = 0
func increment() { value += 1 }
func getValue() -> Int { value }
}
Sendable: Mark types safe for concurrent access.
Task groups: Parallel execution with structured concurrency.
try await withThrowingTaskGroup(of: Result.self) { group in
for item in items { group.addTask { try await process(item) } }
return try await group.reduce(into: []) { $0.append($1) }
}
Rules: Use async/await over completion handlers, actors over locks, mark types Sendable when crossing concurrency boundaries.
Memory Management
Weak references: Prevent retain cycles in closures/delegates.
service.fetch { [weak self] result in self?.handleResult(result) }
Unowned: Non-optional weak when lifetime is guaranteed.
Common Patterns
- Builder: Fluent API for complex object construction
- Result Builder (
@resultBuilder): DSL construction - Property Wrappers (
@propertyWrapper): Encapsulate property access patterns
Anti-patterns
- Force unwrap (
!) - Use safe unwrapping - Force try (
try!) - Use do-catch or propagate - Classes for data - Use structs for value semantics
Any/AnyObjectabuse - Use generics or protocols- Retain cycles - Use
[weak self]or[unowned self]
Swift Package Manager
Project Structure
├── Package.swift
├── Sources/
│ ├── MyLibrary/
│ └── MyCLI/main.swift
├── Tests/MyLibraryTests/
└── Plugins/
Package.swift
// swift-tools-version: 6.0
import PackageDescription
let package = Package(
name: "MyPackage",
products: [
.library(name: "MyLibrary", targets: ["MyLibrary"]),
.executable(name: "my-cli", targets: ["MyCLI"])
],
dependencies: [
.package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
],
targets: [
.target(name: "MyLibrary"),
.executableTarget(name: "MyCLI", dependencies: ["MyLibrary", .product(name: "ArgumentParser", package: "swift-argument-parser")]),
.testTarget(name: "MyLibraryTests", dependencies: ["MyLibrary"])
]
)
Commands
swift build # Compile
swift build -c release # Release build
swift run # Build and run executable
swift test # Run all tests
swift test --filter MyTest # Run specific test
swift package resolve # Resolve dependencies
swift package update # Update dependencies
swift package init --type library # Create new package
Toolchain
SwiftLint
# .swiftlint.yml
disabled_rules: [trailing_whitespace, line_length]
opt_in_rules: [empty_count, closure_spacing, force_unwrapping]
included: [Sources, Tests]
excluded: [.build, Packages]
line_length: { warning: 120, error: 200 }
SwiftFormat (nicklockwood)
# .swiftformat
--swiftversion 6.0
--indent 4
--maxwidth 120
--self remove
--wraparguments before-first
SourceKit-LSP
Bundled with Swift toolchain. Install Swift extension in VS Code for IDE integration.
swift-testing (Swift 6+)
import Testing
@Test func addition() { #expect(1 + 1 == 2) }
@Test("Descriptive name") func subtraction() throws { #expect(try compute() > 0) }
@Test(arguments: [1, 2, 3]) func parameterized(value: Int) { #expect(value > 0) }
@Suite("Calculator") struct CalculatorTests { ... }
swift-docc
swift package generate-documentation
Context7 Integration
- Swift Language:
/swiftlang/swift - Argument Parser:
/apple/swift-argument-parser - Swift Log:
/apple/swift-log - SwiftFormat:
/nicklockwood/swiftformat - Vapor:
/vapor/vapor - Alamofire:
/alamofire/alamofire
Best Practices
- Use
swift buildfor compilation;swift testfor testing - Run swiftlint before committing
- Format with swiftformat for consistent style
- Prefer value types (structs) over reference types (classes)
- Use async/await for asynchronous code
- Mark types as Sendable for concurrency safety
- Document public API with
///doc comments - Write tests alongside implementation
- Use Swift Testing framework for new test code
- Never use force unwrap (
!) in library code - Use guard for early exit patterns
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