Class và Object trong Swift

class Person {
    var name: String
    var age: Int
    
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    
    func introduce() {
        print("Tôi là \(name), \(age) tuổi")
    }
}
 
let person = Person(name: "Alice", age: 25)
person.introduce()

class Point {
    var x: Int
    var y: Int
    
    init(x: Int, y: Int) {
        self.x = x
        self.y = y
    }
}
 
let point1 = Point(x: 10, y: 20)
let point2 = point1  // Same reference
 
point2.x = 100
 
print(point1.x)  // 100 (changed!)
print(point2.x)  // 100

class FileHandle {
    let filename: String
    
    init(filename: String) {
        self.filename = filename
        print("Opening \(filename)")
    }
    
    deinit {
        print("Closing \(filename)")
    }
}
 
var handle: FileHandle? = FileHandle(filename: "test.txt")
handle = nil  // Prints: Closing test.txt

class Circle {
    var radius: Double
    
    init(radius: Double) {
        self.radius = radius
    }
    
    var area: Double {
        get { .pi * radius * radius }
    }
    
    var diameter: Double {
        get { radius * 2 }
        set { radius = newValue / 2 }
    }
}

class StepCounter {
    var steps: Int = 0 {
        willSet {
            print("About to set to \(newValue)")
        }
        didSet {
            print("Changed from \(oldValue) to \(steps)")
        }
    }
}
 
let counter = StepCounter()
counter.steps = 100

class DataLoader {
    lazy var data: [String] = {
        print("Loading data...")
        return ["a", "b", "c"]
    }()
}
 
let loader = DataLoader()
// Data chưa được load
print(loader.data)  // Now loading...

class Parent {
    static var staticProp = "Static"
    class var classProp: String { "Class" }
    
    static func staticMethod() {}
    class func classMethod() {}  // Can be overridden
}
 
class Child: Parent {
    override class var classProp: String { "Overridden" }
    override class func classMethod() {}
    // static không thể override
}

let a = Person(name: "Alice", age: 25)
let b = a
let c = Person(name: "Alice", age: 25)
 
print(a === b)  // true (same instance)
print(a === c)  // false (different instances)
print(a !== c)  // true

class ViewController: UIViewController {
    private let viewModel: ViewModel
    
    lazy var tableView: UITableView = {
        let tv = UITableView()
        tv.delegate = self
        tv.dataSource = self
        return tv
    }()
    
    init(viewModel: ViewModel) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) not implemented")
    }
    
    deinit {
        print("ViewController deallocated")
    }
}