Higher Order Functions

Higher Order Functions.swift

func printString(aString: String) {
    print("Printing the string passed in: \(aString)")
}

printString("Hi, my name is Thanh")
let someFunction: String -> Void = printString

someFunction("Hi, look at me!")

/*****************/

func sum(a: Int, b: Int) -> Int {
    return a + b
}

let addTwoNumbers = sum

addTwoNumbers(1,b: 2)

/*****************/

func displayString(a: String -> Void) {
    a("I'm a function inside a function!")
}

displayString(printString)

/*****************/

extension Int {
    func apply(operaton: Int -> Int) -> Int {
        return operaton(self)
    }
}

func double(value: Int) -> Int {
    return value * 2
}

10.apply(double)

func closestMultibleOfSix(value: Int) -> Int {
    for x in 1...1000 {
        let multiple = x * 6
        if multiple - value < 6 && multiple > value {
            return multiple
        } else if multiple == value {
            return value
        }
    }
    
    return 0
}

32.apply(closestMultibleOfSix)
12.apply(closestMultibleOfSix)
200.apply(closestMultibleOfSix)

/*****************/

typealias IntegerFunction = Int -> ()

func gameCounter() -> IntegerFunction {
    var counter = 0
    func increment(i: Int) {
        counter += i
        print("Counter value: \(counter)")
    }
    
    return increment
}

let aCounter = gameCounter()
aCounter(1)
aCounter(1)
aCounter(45)

let anotherCounter = gameCounter()
anotherCounter(1)
anotherCounter(10)
anotherCounter(150)

print("aCounter Below")
aCounter(4)


// Bai Tap
extension String {
    func modify(a: String -> String) -> String {
        return a(self)
    }
}

func firstLetter(b: String) -> String {
    return "\(b[b.startIndex])"
}

let value = "Swift".modify(firstLetter)