คลอเชอร์ที่หลุดออกนอกขอบเขต

func run(_ work: () -> Void) {
    work()
}
run { print("done now") }  // "done now"

var handlers: [() -> Void] = []
func register(_ handler: @escaping () -> Void) {
    handlers.append(handler)  // escapes the function
}
register { print("later") }
handlers[0]()  // "later"

func load(then completion: @escaping (String) -> Void) {
    // imagine async work
    completion("data")
}
load { result in print(result) }  // "data"

class Loader {
    var name = "L"
    func start(_ done: @escaping () -> Void) {
        let cb = { print(self.name); done() }
        cb()
    }
}
Loader().start { print("finished") }  // "L" then "finished"

class Emitter {
    private var listeners: [(Int) -> Void] = []
    func on(_ l: @escaping (Int) -> Void) { listeners.append(l) }
    func fire(_ v: Int) { listeners.forEach { $0(v) } }
}
let e = Emitter()
e.on { print("got \($0)") }
e.fire(7)  // "got 7"

class Button {
    var action: (() -> Void)?
    func setAction(_ a: @escaping () -> Void) { action = a }
}
let b = Button()
b.setAction { print("tapped") }
b.action?()  // "tapped"

func maybe(_ f: (() -> Void)?) {
    f?()
}
maybe { print("ran") }  // "ran"

var tasks: [() -> Int] = []
func schedule(_ task: @escaping () -> Int) {
    tasks.append(task)
}
schedule { 1 + 1 }
schedule { 10 * 2 }
print(tasks.map { $0() })  // [2, 20]

func sum(_ xs: [Int], _ f: (Int) -> Int) -> Int {
    xs.reduce(0) { $0 + f($1) }   // non-escaping, fast
}
print(sum([1, 2, 3]) { $0 * $0 })  // 14