defer ทำงานอย่างไร

func demo() {
    defer { print("cleanup") }
    print("work")
}
demo()

func greet() {
    defer { print("goodbye") }
    print("hello")
}
greet()

func process() {
    defer { print("3 deferred") }
    print("1 start")
    print("2 middle")
}
process()

for i in 1...3 {
    defer { print("end of iteration", i) }
    print("start of iteration", i)
}

func check(_ flag: Bool) {
    if flag {
        defer { print("leaving if block") }
        print("inside if")
    }
    print("after if")
}
check(true)

func counterDemo() {
    var count = 0
    defer { print("final count:", count) }
    count = 5
}
counterDemo()

func order() {
    defer { print("B") }
    print("A")
}
order()
print("C")

func session() {
    print("open session")
    defer { print("close session") }
    print("do work")
}
session()

func run() {
    do {
        defer { print("do block cleanup") }
        print("inside do")
    }
    print("after do")
}
run()

func multi() {
    defer {
        print("step 1 of cleanup")
        print("step 2 of cleanup")
    }
    print("main work")
}
multi()

func guaranteed() {
    defer { print("always runs") }
    print("body")
}
guaranteed()

func demo() {
    defer { print("last") }
    print("first")
}
demo()