Actor dan isolasi data, nonisolated

actor Counter {
    private var value: Int = 0   // isolated state

    func increment() { value += 1 }      // isolated method (async to outsiders)
    func get() -> Int { value }          // read isolated state
}

let c = Counter()
Task {
    await c.increment()
    print(await c.get())  // 1
}

actor BankAccount {
    private var balance: Int = 0
    func deposit(_ amount: Int) { balance += amount }
    func withdraw(_ amount: Int) -> Bool {
        if balance >= amount { balance -= amount; return true }
        return false
    }
    func current() -> Int { balance }
}

let acc = BankAccount()
Task {
    async let a = acc.deposit(50)
    async let b = acc.withdraw(20)
    _ = await (a, b)                 // operations are serialized inside the actor
    print(await acc.current())       // deterministic balance
}

actor Clock {
    private var ticks: Int = 0
    func tick() { ticks += 1 }
    func read() -> Int { ticks }

    // Nonisolated: safe without awaiting (pure computation / constant)
    nonisolated static let format = "HH:mm:ss"

    nonisolated func describeFormat() -> String {
        // Cannot touch isolated state here; this is pure
        return "Format: " + Self.format
    }
}

let cl = Clock()
Task {
    await cl.tick()
    print(await cl.read())           // 1
    // Nonisolated members don't require await:
    print(Clock.format)              // "HH:mm:ss"
    print(cl.describeFormat())       // sync call
}

actor Logger {
    private var lines: [String] = []
    func log(_ s: String) async {
        lines.append(s)
        // Simulate an await point; actor may process other messages here (reentrant)
        try? await Task.sleep(nanoseconds: 10_000_000)
        lines.append("done")
    }
    func snapshot() -> [String] { lines }
}

let logger = Logger()
Task {
    async let a = logger.log("A")
    async let b = logger.log("B")
    _ = await (a, b)
    print(await logger.snapshot())   // order shows possible interleaving
}