Swift 6 cheatsheet

Swift 6: Types and protocols

6 common Swift 6 tasks.

Structs

Structs are value types with memberwise initializers. Mark mutating methods with mutating.

struct Point {
    var x: Double
    var y: Double

    mutating func move(by dx: Double) { x += dx }
}

var p = Point(x: 1, y: 2)
p.move(by: 3)

Classes

Classes are reference types and support inheritance.

class Vehicle {
    var wheels = 4
    func describe() -> String { "\(wheels) wheels" }
}

class Bike: Vehicle {
    override init() { super.init(); wheels = 2 }
}

Enums with associated values

Each case can carry its own data, and switch extracts it.

enum Result {
    case success(Int)
    case failure(String)
}

switch result {
case .success(let value): print(value)
case .failure(let message): print(message)
}

Protocols and extensions

A protocol describes requirements, and an extension adds default behavior.

protocol Describable {
    var name: String { get }
}

extension Describable {
    func describe() -> String { "I am \(name)" }
}

struct Dog: Describable { let name: String }

Generics

Write a function once for any type that meets a constraint.

func largest<T: Comparable>(_ items: [T]) -> T? {
    items.max()
}

Encode and decode JSON

Conform to Codable and use JSONEncoder and JSONDecoder.

struct User: Codable {
    let id: Int
    let name: String
}

let data = try JSONEncoder().encode(User(id: 1, name: "Ada"))
let user = try JSONDecoder().decode(User.self, from: data)