A Swift Tour
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print("Hello, world!")
// Prints "Hello, world!"
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println("Hello, world!")
// Prints "Hello, world!"
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Simple Values
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var myVariable = 42
myVariable = 50
let myConstant = 42
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var myVariable = 42
myVariable = 50
val myConstant = 42
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let implicitInteger = 70
let implicitDouble = 70.0
let explicitDouble: Double = 70
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val implicitInteger = 70
val implicitDouble = 70.0
val explicitDouble: Double = 70
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let label = "The width is "
let width = 94
let widthLabel = label + String(width)
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val label = "The width is "
val width = 94
val widthLabel = label + width.toString()
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let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."
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let quotation = """
I said "I have \(apples) apples."
And then I said "I have \(apples + oranges) pieces of fruit."
"""
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var shoppingList = ["catfish", "water", "tulips"]
shoppingList[1] = "bottle of water"
var occupations = [
"Malcolm": "Captain",
"Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"
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shoppingList.append("blue paint")
print(shoppingList)
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let emptyArray = [String]()
let emptyDictionary = [String: Float]()
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shoppingList = []
occupations = [:]
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Control Flow
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let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
if score > 50 {
teamScore += 3
} else {
teamScore += 1
}
}
print(teamScore)
// Prints "11"
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var optionalString: String? = "Hello"
print(optionalString == nil)
// Prints "false"
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
greeting = "Hello, \(name)"
}
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let nickname: String? = nil
let fullName: String = "John Appleseed"
let informalGreeting = "Hi \(nickname ?? fullName)"
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let vegetable = "red pepper"
switch vegetable {
case "celery":
print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
print("Is it a spicy \(x)?")
default:
print("Everything tastes good in soup.")
}
// Prints "Is it a spicy red pepper?"
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let interestingNumbers = [
"Prime": [2, 3, 5, 7, 11, 13],
"Fibonacci": [1, 1, 2, 3, 5, 8],
"Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (kind, numbers) in interestingNumbers {
for number in numbers {
if number > largest {
largest = number
}
}
}
print(largest)
// Prints "25"
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var n = 2
while n < 100 {
n *= 2
}
print(n)
// Prints "128"
var m = 2
repeat {
m *= 2
} while m < 100
print(m)
// Prints "128"
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var total = 0
for i in 0..<4 {
total += i
}
print(total)
// Prints "6"
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Functions and Closures
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func greet(person: String, day: String) -> String {
return "Hello \(person), today is \(day)."
}
greet(person: "Bob", day: "Tuesday")
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func greet(_ person: String, on day: String) -> String {
return "Hello \(person), today is \(day)."
}
greet("John", on: "Wednesday")
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func calculateStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) {
var min = scores[0]
var max = scores[0]
var sum = 0
for score in scores {
if score > max {
max = score
} else if score < min {
min = score
}
sum += score
}
return (min, max, sum)
}
let statistics = calculateStatistics(scores: [5, 3, 100, 3, 9])
print(statistics.sum)
// Prints "120"
print(statistics.2)
// Prints "120"
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func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()
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func makeIncrementer() -> ((Int) -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
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func hasAnyMatches(list: [Int], condition: (Int) -> Bool) -> Bool {
for item in list {
if condition(item) {
return true
}
}
return false
}
func lessThanTen(number: Int) -> Bool {
return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(list: numbers, condition: lessThanTen)
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numbers.map({ (number: Int) -> Int in
let result = 3 * number
return result
})
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let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)
// Prints "[60, 57, 21, 36]"
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let sortedNumbers = numbers.sorted { $0 > $1 }
print(sortedNumbers)
// Prints "[20, 19, 12, 7]"
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Objects and Classes
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class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
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var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
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class NamedShape {
var numberOfSides: Int = 0
var name: String
init(name: String) {
self.name = name
}
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
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class Square: NamedShape {
var sideLength: Double
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 4
}
func area() -> Double {
return sideLength * sideLength
}
override func simpleDescription() -> String {
return "A square with sides of length \(sideLength)."
}
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()
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class EquilateralTriangle: NamedShape {
var sideLength: Double = 0.0
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 3
}
var perimeter: Double {
get {
return 3.0 * sideLength
}
set {
sideLength = newValue / 3.0
}
}
override func simpleDescription() -> String {
return "An equilateral triangle with sides of length \(sideLength)."
}
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
print(triangle.perimeter)
// Prints "9.3"
triangle.perimeter = 9.9
print(triangle.sideLength)
// Prints "3.3000000000000003"
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class TriangleAndSquare {
var triangle: EquilateralTriangle {
willSet {
square.sideLength = newValue.sideLength
}
}
var square: Square {
willSet {
triangle.sideLength = newValue.sideLength
}
}
init(size: Double, name: String) {
square = Square(sideLength: size, name: name)
triangle = EquilateralTriangle(sideLength: size, name: name)
}
}
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
print(triangleAndSquare.square.sideLength)
// Prints "10.0"
print(triangleAndSquare.triangle.sideLength)
// Prints "10.0"
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.triangle.sideLength)
// Prints "50.0"
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let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square")
let sideLength = optionalSquare?.sideLength
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Enumerations and Structures
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enum Rank: Int {
case ace = 1
case two, three, four, five, six, seven, eight, nine, ten
case jack, queen, king
func simpleDescription() -> String {
switch self {
case .ace:
return "ace"
case .jack:
return "jack"
case .queen:
return "queen"
case .king:
return "king"
default:
return String(self.rawValue)
}
}
}
let ace = Rank.ace
let aceRawValue = ace.rawValue
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if let convertedRank = Rank(rawValue: 3) {
let threeDescription = convertedRank.simpleDescription()
}
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enum Suit {
case spades, hearts, diamonds, clubs
func simpleDescription() -> String {
switch self {
case .spades:
return "spades"
case .hearts:
return "hearts"
case .diamonds:
return "diamonds"
case .clubs:
return "clubs"
}
}
}
let hearts = Suit.hearts
let heartsDescription = hearts.simpleDescription()
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enum ServerResponse {
case result(String, String)
case failure(String)
}
let success = ServerResponse.result("6:00 am", "8:09 pm")
let failure = ServerResponse.failure("Out of cheese.")
switch success {
case let .result(sunrise, sunset):
print("Sunrise is at \(sunrise) and sunset is at \(sunset).")
case let .failure(message):
print("Failure... \(message)")
}
// Prints "Sunrise is at 6:00 am and sunset is at 8:09 pm."
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struct Card {
var rank: Rank
var suit: Suit
func simpleDescription() -> String {
return "The \(rank.simpleDescription()) of \(suit.simpleDescription())"
}
}
let threeOfSpades = Card(rank: .three, suit: .spades)
let threeOfSpadesDescription = threeOfSpades.simpleDescription()
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Protocols and Extensions
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protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}
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class SimpleClass: ExampleProtocol {
var simpleDescription: String = "A very simple class."
var anotherProperty: Int = 69105
func adjust() {
simpleDescription += " Now 100% adjusted."
}
}
var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription
struct SimpleStructure: ExampleProtocol {
var simpleDescription: String = "A simple structure"
mutating func adjust() {
simpleDescription += " (adjusted)"
}
}
var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription
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extension Int: ExampleProtocol {
var simpleDescription: String {
return "The number \(self)"
}
mutating func adjust() {
self += 42
}
}
print(7.simpleDescription)
// Prints "The number 7"
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let protocolValue: ExampleProtocol = a
print(protocolValue.simpleDescription)
// Prints "A very simple class. Now 100% adjusted."
// print(protocolValue.anotherProperty) // Uncomment to see the error
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Error Handling
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enum PrinterError: Error {
case outOfPaper
case noToner
case onFire
}
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func send(job: Int, toPrinter printerName: String) throws -> String {
if printerName == "Never Has Toner" {
throw PrinterError.noToner
}
return "Job sent"
}
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do {
let printerResponse = try send(job: 1040, toPrinter: "Bi Sheng")
print(printerResponse)
} catch {
print(error)
}
// Prints "Job sent"
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do {
let printerResponse = try send(job: 1440, toPrinter: "Gutenberg")
print(printerResponse)
} catch PrinterError.onFire {
print("I'll just put this over here, with the rest of the fire.")
} catch let printerError as PrinterError {
print("Printer error: \(printerError).")
} catch {
print(error)
}
// Prints "Job sent"
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let printerSuccess = try? send(job: 1884, toPrinter: "Mergenthaler")
let printerFailure = try? send(job: 1885, toPrinter: "Never Has Toner")
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var fridgeIsOpen = false
let fridgeContent = ["milk", "eggs", "leftovers"]
func fridgeContains(_ food: String) -> Bool {
fridgeIsOpen = true
defer {
fridgeIsOpen = false
}
let result = fridgeContent.contains(food)
return result
}
fridgeContains("banana")
print(fridgeIsOpen)
// Prints "false"
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Generics
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func makeArray<Item>(repeating item: Item, numberOfTimes: Int) -> [Item] {
var result = [Item]()
for _ in 0..<numberOfTimes {
result.append(item)
}
return result
}
makeArray(repeating: "knock", numberOfTimes: 4)
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// Reimplement the Swift standard library's optional type
enum OptionalValue<Wrapped> {
case none
case some(Wrapped)
}
var possibleInteger: OptionalValue<Int> = .none
possibleInteger = .some(100)
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func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
where T.Element: Equatable, T.Element == U.Element
{
for lhsItem in lhs {
for rhsItem in rhs {
if lhsItem == rhsItem {
return true
}
}
}
return false
}
anyCommonElements([1, 2, 3], [3])
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