Cursor rule

1---
2description: "Swift patterns extending common rules"
3globs: ["**/*.swift", "**/Package.swift"]
4alwaysApply: false
5---
6# Swift Patterns
7 
8> This file extends the common patterns rule with Swift specific content.
9 
10## Protocol-Oriented Design
11 
12Define small, focused protocols. Use protocol extensions for shared defaults:
13 
14```swift
15protocol Repository: Sendable {
16    associatedtype Item: Identifiable & Sendable
17    func find(by id: Item.ID) async throws -> Item?
18    func save(_ item: Item) async throws
19}
20```
21 
22## Value Types
23 
24- Use structs for data transfer objects and models
25- Use enums with associated values to model distinct states:
26 
27```swift
28enum LoadState<T: Sendable>: Sendable {
29    case idle
30    case loading
31    case loaded(T)
32    case failed(Error)
33}
34```
35 
36## Actor Pattern
37 
38Use actors for shared mutable state instead of locks or dispatch queues:
39 
40```swift
41actor Cache<Key: Hashable & Sendable, Value: Sendable> {
42    private var storage: [Key: Value] = [:]
43 
44    func get(_ key: Key) -> Value? { storage[key] }
45    func set(_ key: Key, value: Value) { storage[key] = value }
46}
47```
48 
49## Dependency Injection
50 
51Inject protocols with default parameters -- production uses defaults, tests inject mocks:
52 
53```swift
54struct UserService {
55    private let repository: any UserRepository
56 
57    init(repository: any UserRepository = DefaultUserRepository()) {
58        self.repository = repository
59    }
60}
61```
62 
63## References
64 
65See skill: `swift-actor-persistence` for actor-based persistence patterns.
66See skill: `swift-protocol-di-testing` for protocol-based DI and testing.
67