defer.swift

var numbers = [Int]()

func appendNumbers() {
    numbers.append(3)
    //: defer{} is executed in the final on the function
    //: use defer{} when you want that any code run it always whatever the function result
    defer {numbers.append(4)}
    numbers.append(5)
}
numbers.append(1)
numbers.append(2)
appendNumbers()
numbers.append(6)

//OUTPUT
numbers -> [1, 2, 3, 5, 4, 6]