lazy & observer properti

struct DataLoader {
    lazy var data: [Int] = {
        print("Loading data...")
        return [1, 2, 3]
    }()
}
var loader = DataLoader()
print("before access")
print(loader.data)   // triggers initialization only now

class CacheOwner {
    let name: String
    lazy var hello: String = "Hi, " + name  // uses self safely after init
    init(name: String) { self.name = name }
}
let co = CacheOwner(name: "Ada")
print(co.hello)

struct Counter {
    var value: Int = 0 {
        willSet { print("will set to", newValue) }
        didSet  { print("did set from", oldValue) }
    }
}
var c = Counter()
c.value = 5
c.value = 9

struct Score {
    var raw: Int = 0 {
        didSet {
            if raw < 0 { raw = 0 }
            if raw > 100 { raw = 100 }
        }
    }
}
var s = Score()
s.raw = 120     // clamped to 100
print(s.raw)
s.raw = -5      // clamped to 0
print(s.raw)