functions

Function Format

func functionName(parameterName: Type...) -> returnType {

}

func favoriteNumber(person: String, number: Int) -> String {

    let returnString = person + " likes number " + String(number) + "."

    return returnString

}

println(favoriteNumber("Jeremy", 7))

//Console output: Jeremy likes number 7.

//The above function may be shorten by removing "returnString" as below:

func favoriteNumber(person: String, number: Int) -> String {

    return person + " likes number " + String(number) + "."

}

Ignored return value

//if the function is called as below (the above println is now removed):

favoriteNumber("Jeremy", 7)

//The playground prints the return value of "Jeremy likes number 7."

//However, the return value is not used and hence is ignored.

Function without parameters and return values

//Empty () and no ->

func sayHello() {

    println("Hello!!")

}

sayHello()

//Console output: Hello!!

Function with multiple return values

//Use ( ) to include multiple return types

func multipleReturnValues () -> (the1st: String, the2nd: String, the3rd: String) {

    return ("M", "I", "T")

}

let result = multipleReturnValues()

println("\(result.the1st)\(result.the2nd)\(result.the3rd)")

//Console output: MIT

Function with external parameter names

//External parameter names are used to clearly show the parameter name while calling a functions.

func extParaNameFunc(ext1 para1: Int, ext2 para2: Int) {

    println("ext1 = \(para1), ext2 = \(para2)")

}

extParaNameFunc(ext1: 3, ext2: 5)

//Console output: ext1 = 3, ext2 = 5

Shorthand external parameter names

//Simply put a # sign before the parameter name.

//Then a sharing external and internal parameter name is used.

func extParaNameFunc2(#para1: Int, #para2: Int) {

    println("para1 = \(para1), para2 = \(para2)")

}

extParaNameFunc2(para1: 4, para2: 6)

//Console output: para1 = 4, para2 = 6

Function with a default value

func extParaNameFunc3(input1: Int, input2: Int, input3: String = "default") {

    println("\(input1) \(input2) \(input3)")

}

extParaNameFunc3(1, 2)

extParaNameFunc3(1, 2, input3: "yes")

//Input3 is the automatic external name

//Console output: 

1 2 default

1 2 yes

Variadic parameters (zero to multiple input values)
//Use ...

func sumParameters(numbers: Int...) {

    var mySum = 0;

    for number in numbers {

        mySum += number

    }

    println("Sum is \(mySum).")

}

sumParameters(1, 2, 3, 4)

sumParameters(10, 20, 30)

//Console output: 

Sum is 10.

Sum is 60.

Variable parameters
Parameters by default are constant parameter and hence can not be changed.
To declare variable parameters, use var.

func alignCenter(var myString: String, number: Int) {

    for _ in 1...number {

        myString = "-" + myString + "-"

    }

    println("\(myString)")

}

alignCenter("Hi",5)

//Console output: 

-----Hi-----

In-out Parameters
//Use inout

func multiplyBy2(inout var1: Int, inout var2: Int) {

    var1 *= 2

    var2 *= 2

}

var i = 3

var j = 5

multiplyBy2(&i, &j) //Use & sign

println("i = \(i), j = \(j)")

//Console output: 

i = 6, j = 10

Function types

func addInts(a: Int, b: Int) -> Int {

    return a + b

}

var calculation: (Int, Int) -> Int = addInts 

//(Int, Int) -> Int is the function type

println("Result: \(calculation(1, 3))")

//Console output: 

Result: 4