[Swift 공식 문서] 1. The Basics

let maximumNumberOfLoginAttempts = 10 var currentLoginAttempt = 0

var x = 0.0, y = 0.0, z = 0.0

var welcomeMessage: String

var red, green, blue: Double

let π = 3.141592 let 你好 = "你好世界" let 🐶🐮 = "dogcow"

var friendlyWelcome = "Hello!" friendlyWelcome = "Bonjour!" // friendlyWelcome is now "Bonjour!"

let languageName = "Swift" languageName = "Swift++" // This is a compile-time error: languageName cannot be changed.

print(friendlyWelcome) // Prints "Bonjour!"

print("The current value of friendlyWelcome is \(friendlyWelcome)") // Prints "The current value of friendlyWelcome is Bonjour!"

let cat = "🐱"; print(cat) // Prints "🐱"

let minValue = UInt8.min // minValue is equal to 0, and is of type UInt8 let maxValue = UInt8.max // maxValue is equal to 255, and is of type UInt8

let meaningOfLife = 42 // meaningOfLife is inferred to be of type Int

let anotherPi = 3 + 0.14159 // anotherPi is also inferred to be of type Double

let decimalInteger = 17 let binaryInteger = 0b10001 // 17 in binary notation let octalInteger = 0o21 // 17 in octal notation let hexadecimalInteger = 0x11 // 17 in hexadecimal notation

let decimalDouble = 12.1875 let exponentDouble = 1.21875e1 let hexadecimalDouble = 0xC.3p0

let paddedDouble = 000123.456 let oneMillion = 1_000_000 let justOverOneMillion = 1_000_000.000_000_1

let cannotBeNegative: UInt8 = -1 // UInt8 can't store negative numbers, and so this will report an error let tooBig: Int8 = Int8.max + 1 // Int8 can't store a number larger than its maximum value, // and so this will also report an error

let twoThousand: UInt16 = 2_000 let one: UInt8 = 1 let twoThousandAndOne = twoThousand + UInt16(one)

let three = 3 let pointOneFourOneFiveNine = 0.14159 let pi = Double(three) + pointOneFourOneFiveNine // pi equals 3.14159, and is inferred to be of type Double

let integerPi = Int(pi) // integerPi equals 3, and is inferred to be of type Int

typealias AudioSample = UInt16

var maxAmplitudeFound = AudioSample.min // maxAmplitudeFound is now 0

let orangesAreOrange = true let turnipsAreDelicious = false

if turnipsAreDelicious { print("Mmm, tasty turnips!") } else { print("Eww, turnips are horrible.") } // Prints "Eww, turnips are horrible."

let i = 1 if i { // this example will not compile, and will report an error }

let i = 1 if i == 1 { // this example will compile successfully }

let http404Error = (404, "Not Found") // http404Error is of type (Int, String), and equals (404, "Not Found")

let (statusCode, statusMessage) = http404Error print("The status code is \(statusCode)") // Prints "The status code is 404" print("The status message is \(statusMessage)") // Prints "The status message is Not Found"

let (justTheStatusCode, _) = http404Error print("The status code is \(justTheStatusCode)") // Prints "The status code is 404"

print("The status code is \(http404Error.0)") // Prints "The status code is 404" print("The status message is \(http404Error.1)") // Prints "The status message is Not Found"

let http200Status = (statusCode: 200, description: "OK")

print("The status code is \(http200Status.statusCode)") // Prints "The status code is 200" print("The status message is \(http200Status.description)") // Prints "The status message is OK"

let possibleNumber = "123" let convertedNumber = Int(possibleNumber) // convertedNumber is inferred to be of type "Int?", or "optional Int"

var serverResponseCode: Int? = 404 // serverResponseCode contains an actual Int value of 404 serverResponseCode = nil // serverResponseCode now contains no value

var surveyAnswer: String? // surveyAnswer is automatically set to nil

if convertedNumber != nil { print("convertedNumber contains some integer value.") } // Prints "convertedNumber contains some integer value."

if convertedNumber != nil { print("convertedNumber has an integer value of \(convertedNumber!).") } // Prints "convertedNumber has an integer value of 123.

if let constantName = someOptional { statements }

if let actualNumber = Int(possibleNumber) { print("The string \"\(possibleNumber)\" has an integer value of \(actualNumber)") } else { print("The string \"\(possibleNumber)\" couldn't be converted to an integer") } // Prints "The string "123" has an integer value of 123"

if let firstNumber = Int("4"), let secondNumber = Int("42"), firstNumber < secondNumber && secondNumber < 100 { print("\(firstNumber) < \(secondNumber) < 100") } // Prints "4 < 42 < 100" if let firstNumber = Int("4") { if let secondNumber = Int("42") { if firstNumber < secondNumber && secondNumber < 100 { print("\(firstNumber) < \(secondNumber) < 100") } } } // Prints "4 < 42 < 100"

let possibleString: String? = "An optional string." let forcedString: String = possibleString! // requires an exclamation point let assumedString: String! = "An implicitly unwrapped optional string." let implicitString: String = assumedString // no need for an exclamation point

if assumedString != nil { print(assumedString!) } // Prints "An implicitly unwrapped optional string."

let optionalString = assumedString // The type of optionalString is "String?" and assumedString isn't force-unwrapped.

func canThrowAnError() throws { // this function may or may not throw an error }

// 에러에 대한 케이스를 enum 타입으로 정리해야함 enum VendingMachineError: Error { case invalidSelection case insufficientFunds(coinsNeeded: Int) case outOfStock } struct Item { var price: Int var count: Int } class VendingMachine { var inventory = [ "Candy Bar": Item(price: 12, count: 7), "Chips": Item(price: 10, count: 4), "Pretzels": Item(price: 7, count: 11) ] var coinsDeposited = 0 // 가드 문과 함께 throw 키워드 사용. func vend(itemNamed name: String) throws { guard let item = inventory[name] else { throw VendingMachineError.invalidSelection } guard item.count > 0 else { throw VendingMachineError.outOfStock } guard item.price <= coinsDeposited else { throw VendingMachineError.insufficientFunds(coinsNeeded: item.price - coinsDeposited) } coinsDeposited -= item.price var newItem = item newItem.count -= 1 inventory[name] = newItem print("Dispensing \(name)") } } var vendingMachine = VendingMachine() vendingMachine.coinsDeposited = 8 //이렇게 던져진 에러 case 는 do catch 문으로 처리가능. do { try vendingMachine.vend(itemNamed: "Pretzels") } catch VendingMachineError.invalidSelection { // } catch VendingMachineError.insufficientFunds(_) { // } catch VendingMachineError.outOfStock { // }

let age = -3 assert(age >= 0, "A person's age can't be less than zero.") // This assertion fails because -3 isn't >= 0.

if age > 10 { print("You can ride the roller-coaster or the ferris wheel.") } else if age >= 0 { print("You can ride the ferris wheel.") } else { assertionFailure("A person's age can't be less than zero.") }

// In the implementation of a subscript... precondition(index > 0, "Index must be greater than zero.")