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
