The document provides examples of functions in Swift including: 1. A greet function that returns a personalized greeting string. 2. Functions that take closures or callbacks as parameters including examples of passing named closures and trailing closures. 3. Examples of functions that return tuples, optionals, and functions as their return type. The document demonstrates various Swift function features like default parameters, inout parameters, variadic parameters, and functions as first-class citizens.

1. greet(person:)
String person String
1 func greet(person: String) -> String {
2 let greeting = "Hello, " + person + "!"
3 return greeting
4 }
func
->
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2. 1 print(greet(person: "Anna"))
2 // Prints "Hello, Anna!"
3 print(greet(person: "Brian"))
4 // Prints "Hello, Brian!"
greet(person:) String person
greet(person: "Anna") String greet(person:)
print(_:separator:terminator:)
print(_:separator:terminator:)
greet(person:) String greeting
return return greeting
greeting
greet(person:)
"Anna" "Brian"
1 func greetAgain(person: String) -> String {
2 return "Hello again, " + person + "!"
3 }
4 print(greetAgain(person: "Anna"))
5 // Prints "Hello again, Anna!"
String
1 func sayHelloWorld() -> String {
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3. 2 return "hello, world"
3 }
4 print(sayHelloWorld())
5 // Prints "hello, world"
1 func greet(person: String, alreadyGreeted: Bool) -> String {
2 if alreadyGreeted {
3 return greetAgain(person: person)
4 } else {
5 return greet(person: person)
6 }
7 }
8 print(greet(person: "Tim", alreadyGreeted: true))
9 // Prints "Hello again, Tim!"
greet(person:alreadyGreeted:) String
person Bool alreadyGreeted
greet(person:)
greet
greet(person:alreadyGreeted:) greet(person:)
greet(person:)
String
1 func greet(person: String) {
2 print("Hello, (person)!")
3 }
4 greet(person: "Dave")
5 // Prints "Hello, Dave!"
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4. ->
greet(person:)
Void
()
1 func printAndCount(string: String) -> Int {
2 print(string)
3 return string.count
4 }
5 func printWithoutCounting(string: String) {
6 let _ = printAndCount(string: string)
7 }
8 printAndCount(string: "hello, world")
9 // prints "hello, world" and returns a value of 12
10 printWithoutCounting(string: "hello, world")
11 // prints "hello, world" but does not return a value
printAndCount(string:)
Int printWithoutCounting(string:)
minMax(array:)
Int
1 func minMax(array: [Int]) -> (min: Int, max: Int) {
2 var currentMin = array[0]
3 var currentMax = array[0]
4 for value in array[1..<array.count] {
5 if value < currentMin {
6 currentMin = value
7 } else if value > currentMax {
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5. 8 currentMax = value
9 }
10 }
11 return (currentMin, currentMax)
12 }
minMax(array:) Int
min max
minMax(array:) currentMin
currentMax
currentMin currentMax
Int
1 let bounds = minMax(array: [8, -6, 2, 109, 3, 71])
2 print("min is (bounds.min) and max is (bounds.max)")
3 // Prints "min is -6 and max is 109"
nil
(Int, Int)? (String, Int, Bool)?
(Int, Int)?
(Int?, Int?)
minMax(array:) Int
array
minMax(array:)
array[0]
minMax(array:)
nil
1 func minMax(array: [Int]) -> (min: Int, max: Int)? {
2 if array.isEmpty { return nil }
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6. 3 var currentMin = array[0]
4 var currentMax = array[0]
5 for value in array[1..<array.count] {
6 if value < currentMin {
7 currentMin = value
8 } else if value > currentMax {
9 currentMax = value
10 }
11 }
12 return (currentMin, currentMax)
13 }
minMax(array:)
nil
1 if let bounds = minMax(array: [8, -6, 2, 109, 3, 71]) {
2 print("min is (bounds.min) and max is (bounds.max)")
3 }
4 // Prints "min is -6 and max is 109"
1 func greeting(for person: String) -> String {
2 "Hello, " + person + "!"
3 }
4 print(greeting(for: "Dave"))
5 // Prints "Hello, Dave!"
6
7 func anotherGreeting(for person: String) -> String {
8 return "Hello, " + person + "!"
9 }
10 print(anotherGreeting(for: "Dave"))
11 // Prints "Hello, Dave!"
greeting(for:)
anotherGreeting(for:)
return
return return
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7. 1 func someFunction(firstParameterName: Int, secondParameterName: Int) {
2 // In the function body, firstParameterName and secondParameterName
3 // refer to the argument values for the first and second parameters.
4 }
5 someFunction(firstParameterName: 1, secondParameterName: 2)
1 func someFunction(argumentLabel parameterName: Int) {
2 // In the function body, parameterName refers to the argument value
3 // for that parameter.
4 }
greet(person:)
1 func greet(person: String, from hometown: String) -> String {
2 return "Hello (person)! Glad you could visit from (hometown)."
3 }
4 print(greet(person: "Bill", from: "Cupertino"))
5 // Prints "Hello Bill! Glad you could visit from Cupertino."
_
1 func someFunction(_ firstParameterName: Int, secondParameterName: Int) {
2 // In the function body, firstParameterName and secondParameterName
3 // refer to the argument values for the first and second parameters.
4 }
5 someFunction(1, secondParameterName: 2)
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8. 1 func someFunction(parameterWithoutDefault: Int, parameterWithDefault: Int
= 12) {
2 // If you omit the second argument when calling this function, then
3 // the value of parameterWithDefault is 12 inside the function body.
4 }
5 someFunction(parameterWithoutDefault: 3, parameterWithDefault: 6) //
parameterWithDefault is 6
6 someFunction(parameterWithoutDefault: 4) // parameterWithDefault is 12
...
numbers
Double... numbers
[Double]
1 func arithmeticMean(_ numbers: Double...) -> Double {
2 var total: Double = 0
3 for number in numbers {
4 total += number
5 }
6 return total / Double(numbers.count)
7 }
8 arithmeticMean(1, 2, 3, 4, 5)
9 // returns 3.0, which is the arithmetic mean of these five numbers
10 arithmeticMean(3, 8.25, 18.75)
11 // returns 10.0, which is the arithmetic mean of these three numbers
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9. inout
&
inout
swapTwoInts(_:_:)
a b
1 func swapTwoInts(_ a: inout Int, _ b: inout Int) {
2 let temporaryA = a
3 a = b
4 b = temporaryA
5 }
swapTwoInts(_:_:) b a a b
a temporaryA
b a temporaryA b
swapTwoInts(_:_:) Int
someInt anotherInt
swapTwoInts(_:_:)
1 var someInt = 3
2 var anotherInt = 107
3 swapTwoInts(&someInt, &anotherInt)
4 print("someInt is now (someInt), and anotherInt is now (anotherInt)")
5 // Prints "someInt is now 107, and anotherInt is now 3"
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10. someInt anotherInt
swapTwoInts(_:_:)
swapTwoInts
someInt anotherInt
1 func addTwoInts(_ a: Int, _ b: Int) -> Int {
2 return a + b
3 }
4 func multiplyTwoInts(_ a: Int, _ b: Int) -> Int {
5 return a * b
6 }
addTwoInts multiplyTwoInts
Int Int
(Int, Int) -> Int
Int Int
1 func printHelloWorld() {
2 print("hello, world")
3 }
() -> Void Void
var mathFunction: (Int, Int) -> Int = addTwoInts
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11. mathFunction Int
Int addTwoInts
addTwoInts(_:_:) mathFunction
mathFunction
1 print("Result: (mathFunction(2, 3))")
2 // Prints "Result: 5"
1 mathFunction = multiplyTwoInts
2 print("Result: (mathFunction(2, 3))")
3 // Prints "Result: 6"
1 let anotherMathFunction = addTwoInts
2 // anotherMathFunction is inferred to be of type (Int, Int) -> Int
(Int, Int) -> Int
1 func printMathResult(_ mathFunction: (Int, Int) -> Int, _ a: Int, _ b:
Int) {
2 print("Result: (mathFunction(a, b))")
3 }
4 printMathResult(addTwoInts, 3, 5)
5 // Prints "Result: 8"
printMathResult(_:_:_:)
mathFunction (Int, Int) -> Int
a
b Int
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12. printMathResult(_:_:_:) addTwoInts(_:_:)
3 5 3 5 8
printMathResult(_:_:_:)
printMathResult(_:_:_:)
->
stepForward(_:) stepBackward(_:)
stepForward(_:) stepBackward(_:)
(Int) -> Int
1 func stepForward(_ input: Int) -> Int {
2 return input + 1
3 }
4 func stepBackward(_ input: Int) -> Int {
5 return input - 1
6 }
chooseStepFunction(backward:) (Int) -> Int
chooseStepFunction(backward:) stepForward(_:)
stepBackward(_:) backward
1 func chooseStepFunction(backward: Bool) -> (Int) -> Int {
2 return backward ? stepBackward : stepForward
3 }
chooseStepFunction(backward:)
1 var currentValue = 3
2 let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
3 // moveNearerToZero now refers to the stepBackward() function
currentValue currentValue 3
currentValue > 0 true chooseStepFunction(backward:)
stepBackward(_:)
moveNearerToZero
moveNearerToZero
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13. 1 print("Counting to zero:")
2 // Counting to zero:
3 while currentValue != 0 {
4 print("(currentValue)... ")
5 currentValue = moveNearerToZero(currentValue)
6 }
7 print("zero!")
8 // 3...
9 // 2...
10 // 1...
11 // zero!
chooseStepFunction(backward:)
1 func chooseStepFunction(backward: Bool) -> (Int) -> Int {
2 func stepForward(input: Int) -> Int { return input + 1 }
3 func stepBackward(input: Int) -> Int { return input - 1 }
4 return backward ? stepBackward : stepForward
5 }
6 var currentValue = -4
7 let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
8 // moveNearerToZero now refers to the nested stepForward() function
9 while currentValue != 0 {
10 print("(currentValue)... ")
11 currentValue = moveNearerToZero(currentValue)
12 }
13 print("zero!")
14 // -4...
15 // -3...
16 // -2...
17 // -1...
18 // zero!
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15. ON THIS PAGE

16. sorted(by:)
sorted(by:)
sorted(by:)
sorted(by:)
sorted(by:)
String
let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
sorted(by:)
Bool
true false
String
(String, String) -> Bool
sorted(by:)
1 func backward(_ s1: String, _ s2: String) -> Bool {
2 return s1 > s2
3 }
4 var reversedNames = names.sorted(by: backward)
5 // reversedNames is equal to ["Ewa", "Daniella", "Chris",
"Barry", "Alex"]
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17. s1 s2 backward(_:_:)
true s1 s2
"B" "A" "Tom"
"Tim" "Barry"
"Alex"
a > b
{ ( parameters ) -> return type in
statements
}
backward(_:_:)
1 reversedNames = names.sorted(by: { (s1: String, s2: String) ->
Bool in
2 return s1 > s2
3 })
backward(_:_:)
(s1: String, s2: String) -> Bool
in
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18. reversedNames = names.sorted(by: { (s1: String, s2: String) ->
Bool in return s1 > s2 } )
sorted(by:)
sorted(by:)
(String, String) -> Bool (String, String) Bool
->
reversedNames = names.sorted(by: { s1, s2 in return s1 > s2 } )
sorted(by:)
String
return
reversedNames = names.sorted(by: { s1, s2 in s1 > s2 } )
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19. sorted(by:) Bool
s1 > s2 Bool return
$0 $1 $2
in
reversedNames = names.sorted(by: { $0 > $1 } )
$0 $1 String
String
>
String Bool
sorted(by:)
reversedNames = names.sorted(by: >)
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20. 1 func someFunctionThatTakesAClosure(closure: () -> Void) {
2 // function body goes here
3 }
4
5 // Here's how you call this function without using a trailing
closure:
6
7 someFunctionThatTakesAClosure(closure: {
8 // closure's body goes here
9 })
10
11 // Here's how you call this function with a trailing closure
instead:
12
13 someFunctionThatTakesAClosure() {
14 // trailing closure's body goes here
15 }
sorted(by:)
reversedNames = names.sorted() { $0 > $1 }
()
reversedNames = names.sorted { $0 > $1 }
Array map(_:)
map(_:)
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21. map(_:)
Int String [16, 58, 510]
["OneSix", "FiveEight", "FiveOneZero"]
1 let digitNames = [
2 0: "Zero", 1: "One", 2: "Two", 3: "Three", 4: "Four",
3 5: "Five", 6: "Six", 7: "Seven", 8: "Eight", 9: "Nine"
4 ]
5 let numbers = [16, 58, 510]
numbers String
map(_:)
1 let strings = numbers.map { (number) -> String in
2 var number = number
3 var output = ""
4 repeat {
5 output = digitNames[number % 10]! + output
6 number /= 10
7 } while number > 0
8 return output
9 }
10 // strings is inferred to be of type [String]
11 // its value is ["OneSix", "FiveEight", "FiveOneZero"]
map(_:)
number
number number
String
output
number number % 10
digitNames
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22. digitNames !
number % 10
digitNames
String
digitNames output
number % 10 6 16 8 58 0 510
number 10
16 1 58 5 510 51
number 0 output
map(_:)
map(_:)
makeIncrementer
incrementer incrementer()
runningTotal amount
incrementer makeIncrementer runningTotal
amount
1 func makeIncrementer(forIncrement amount: Int) -> () -> Int {
2 var runningTotal = 0
3 func incrementer() -> Int {
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23. 4 runningTotal += amount
5 return runningTotal
6 }
7 return incrementer
8 }
makeIncrementer () -> Int
Int
makeIncrementer(forIncrement:)
runningTotal
0
makeIncrementer(forIncrement:) Int
forIncrement amount
runningTotal
makeIncrementer
incrementer
amount runningTotal
incrementer()
1 func incrementer() -> Int {
2 runningTotal += amount
3 return runningTotal
4 }
incrementer()
runningTotal amount
runningTotal amount
runningTotal
amount makeIncrementer
runningTotal incrementer
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24. makeIncrementer
let incrementByTen = makeIncrementer(forIncrement: 10)
incrementByTen
10 runningTotal
1 incrementByTen()
2 // returns a value of 10
3 incrementByTen()
4 // returns a value of 20
5 incrementByTen()
6 // returns a value of 30
runningTotal
1 let incrementBySeven = makeIncrementer(forIncrement: 7)
2 incrementBySeven()
3 // returns a value of 7
incrementByTen
runningTotal incrementBySeven
1 incrementByTen()
2 // returns a value of 40
incrementBySeven incrementByTen
runningTotal
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25. incrementByTen
1 let alsoIncrementByTen = incrementByTen
2 alsoIncrementByTen()
3 // returns a value of 50
4
5 incrementByTen()
6 // returns a value of 60
alsoIncrementByTen
incrementByTen
@escaping
1 var completionHandlers: [() -> Void] = []
2 func someFunctionWithEscapingClosure(completionHandler: @escaping
() -> Void) {
3 completionHandlers.append(completionHandler)
4 }
someFunctionWithEscapingClosure(_:)
@escaping
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26. @escaping self
someFunctionWithEscapingClosure(_:)
self
someFunctionWithNonescapingClosure(_:)
self
1 func someFunctionWithNonescapingClosure(closure: () -> Void) {
2 closure()
3 }
4
5 class SomeClass {
6 var x = 10
7 func doSomething() {
8 someFunctionWithEscapingClosure { self.x = 100 }
9 someFunctionWithNonescapingClosure { x = 200 }
10 }
11 }
12
13 let instance = SomeClass()
14 instance.doSomething()
15 print(instance.x)
16 // Prints "200"
17
18 completionHandlers.first?()
19 print(instance.x)
20 // Prints "100"
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27. assert(condition:message:file:line:)
condition message condition
message
condition false
1 var customersInLine = ["Chris", "Alex", "Ewa", "Barry",
"Daniella"]
2 print(customersInLine.count)
3 // Prints "5"
4
5 let customerProvider = { customersInLine.remove(at: 0) }
6 print(customersInLine.count)
7 // Prints "5"
8
9 print("Now serving (customerProvider())!")
10 // Prints "Now serving Chris!"
11 print(customersInLine.count)
12 // Prints "4"
customersInLine
customerProvider
String () -> String
1 // customersInLine is ["Alex", "Ewa", "Barry", "Daniella"]
2 func serve(customer customerProvider: () -> String) {
3 print("Now serving (customerProvider())!")
4 }
5 serve(customer: { customersInLine.remove(at: 0) } )
6 // Prints "Now serving Alex!"
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28. serve(customer:)
serve(customer:)
@autoclosure
String
customerProvider
@autoclosure
1 // customersInLine is ["Ewa", "Barry", "Daniella"]
2 func serve(customer customerProvider: @autoclosure () -> String)
{
3 print("Now serving (customerProvider())!")
4 }
5 serve(customer: customersInLine.remove(at: 0))
6 // Prints "Now serving Ewa!"
@autoclosure
@escaping @escaping
1 // customersInLine is ["Barry", "Daniella"]
2 var customerProviders: [() -> String] = []
3 func collectCustomerProviders(_ customerProvider: @autoclosure
@escaping () -> String) {
4 customerProviders.append(customerProvider)
5 }
6 collectCustomerProviders(customersInLine.remove(at: 0))
7 collectCustomerProviders(customersInLine.remove(at: 0))
8
9 print("Collected (customerProviders.count) closures.")
10 // Prints "Collected 2 closures."
11 for customerProvider in customerProviders {
12 print("Now serving (customerProvider())!")
13 }
14 // Prints "Now serving Barry!"
15 // Prints "Now serving Daniella!"
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29. customerProvider
collectCustomerProviders(_:)
customerProviders
customerProvider
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