Swift3.0P1 语法指南——控制流

1 for index in 1...5 {
2     print("\(index) times 5 is \(index * 5)")
3 }
4 // 1 times 5 is 5
5 // 2 times 5 is 10
6 // 3 times 5 is 15
7 // 4 times 5 is 20
8 // 5 times 5 is 25

1 let base = 3
2 let power = 10
3 var answer = 1
4 for _ in 1...power {
5     answer *= base
6 }
7 print("\(base) to the power of \(power) is \(answer)")
8 // prints "3 to the power of 10 is 59049"

1 let names = ["Anna", "Alex", "Brian", "Jack"]
2 for name in names {
3     print("Hello, \(name)!")
4 }
5 // Hello, Anna!
6 // Hello, Alex!
7 // Hello, Brian!
8 // Hello, Jack!

1 let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
2 for (animalName, legCount) in numberOfLegs {
3     print("\(animalName)s have \(legCount) legs")
4 }
5 // ants have 6 legs
6 // cats have 4 legs
7 // spiders have 8 legs

1 for var index = 0; index < 3; ++index {
2     print("index is \(index)")
3 }
4 // index is 0
5 // index is 1
6 // index is 2

1 var index: Int
2 for index = 0; index < 3; ++index {
3     print("index is \(index)")
4 }
5 // index is 0
6 // index is 1
7 // index is 2
8 print("The loop statements were executed \(index) times")
9 // prints "The loop statements were executed 3 times"

 1 var square = 0
 2 var diceRoll = 0
 3 while square < finalSquare {
 4     // 掷骰子
 5     if ++diceRoll == 7 { diceRoll = 1 }
 6     // 根据点数移动
 7     square += diceRoll
 8     if square < board.count {
 9         // 如果玩家还在棋盘上，顺着梯子爬上去或者顺着蛇滑下去
10         square += board[square]
11     }
12 }
13 print("Game over!")

1 repeat {
2     // move up or down for a snake or ladder
3     square += board[square]
4     // roll the dice
5     if ++diceRoll == 7 { diceRoll = 1 }
6     // move by the rolled amount
7     square += diceRoll
8 } while square < finalSquare
9 print("Game over!")

1 temperatureInFahrenheit = 90
2 if temperatureInFahrenheit <= 32 {
3     print("It‘s very cold. Consider wearing a scarf.")
4 } else if temperatureInFahrenheit >= 86 {
5     print("It‘s really warm. Don‘t forget to wear sunscreen.")
6 } else {
7     print("It‘s not that cold. Wear a t-shirt.")
8 }
9 // prints "It‘s really warm. Don‘t forget to wear sunscreen."

 1 let someCharacter: Character = "e"
 2 switch someCharacter {
 3 case "a", "e", "i", "o", "u":
 4     print("\(someCharacter) is a vowel")
 5 case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m",
 6 "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
 7     print("\(someCharacter) is a consonant")
 8 default:
 9     print("\(someCharacter) is not a vowel or a consonant")
10 }
11 // prints "e is a vowel"

1 let anotherCharacter: Character = "a"
2 switch anotherCharacter {
3 case "a":
4 case "A":
5     print("The letter A")
6 default:
7     print("Not the letter A")
8 }
9 // this will report a compile-time error

1 switch some value to consider {
2 case value 1,
3 value 2:
4     statements
5 }

 1 let approximateCount = 62
 2 let countedThings = "moons orbiting Saturn"
 3 var naturalCount: String
 4 switch approximateCount {
 5 case 0:
 6     naturalCount = "no"
 7 case 1..<5:
 8     naturalCount = "a few"
 9 case 5..<12:
10     naturalCount = "several"
11 case 12..<100:
12     naturalCount = "dozens of"
13 case 100..<1000:
14     naturalCount = "hundreds of"
15 default:
16     naturalCount = "many"
17 }
18 print("There are \(naturalCount) \(countedThings).")
19 // prints "There are dozens of moons orbiting Saturn."

 1 let somePoint = (1, 1)
 2 switch somePoint {
 3 case (0, 0):
 4     print("(0, 0) is at the origin")
 5 case (_, 0):
 6     print("(\(somePoint.0), 0) is on the x-axis")
 7 case (0, _):
 8     print("(0, \(somePoint.1)) is on the y-axis")
 9 case (-2...2, -2...2):
10     print("(\(somePoint.0), \(somePoint.1)) is inside the box")
11 default:
12     print("(\(somePoint.0), \(somePoint.1)) is outside of the box")
13 }
14 // prints "(1, 1) is inside the box"

 1 let anotherPoint = (2, 0)
 2 switch anotherPoint {
 3 case (let x, 0):
 4     print("on the x-axis with an x value of \(x)")
 5 case (0, let y):
 6     print("on the y-axis with a y value of \(y)")
 7 case let (x, y):
 8     print("somewhere else at (\(x), \(y))")
 9 }
10 // prints "on the x-axis with an x value of 2"

 1 let yetAnotherPoint = (1, -1)
 2 switch yetAnotherPoint {
 3 case let (x, y) where x == y:
 4     print("(\(x), \(y)) is on the line x == y")
 5 case let (x, y) where x == -y:
 6     print("(\(x), \(y)) is on the line x == -y")
 7 case let (x, y):
 8     print("(\(x), \(y)) is just some arbitrary point")
 9 }
10 // prints "(1, -1) is on the line x == -y"

 1             let someCharacter: Character = "e"
 2             switch someCharacter {
 3                 case "a", "e", "i", "o", "u":
 4                     print("\(someCharacter) is a vowel")
 5                 case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m",
 6                     "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
 7                     print("\(someCharacter) is a consonant")
 8                 default:
 9                     print("\(someCharacter) is not a vowel or a consonant")
10             }
11             // Prints "e is a vowel"

1             let stillAnotherPoint = (9, 0)
2             switch stillAnotherPoint {
3                 case (let distance, 0), (0, let distance):
4                     print("On an axis, \(distance) from the origin")
5                 default:
6                     print("Not on an axis")
7             }
8             // Prints "On an axis, 9 from the origin"

 1 let puzzleInput = "great minds think alike"
 2 var puzzleOutput = ""
 3 for character in puzzleInput.characters {
 4     switch character {
 5     case "a", "e", "i", "o", "u", " ":
 6         continue
 7     default:
 8         puzzleOutput.append(character)
 9     }
10 }
11 print(puzzleOutput)
12     // 输出 "grtmndsthnklk"

 1 let numberSymbol: Character = "三"  // Simplified Chinese for the number 3
 2 var possibleIntegerValue: Int?
 3 switch numberSymbol {
 4 case "1", "?", "一", "?":
 5     possibleIntegerValue = 1
 6 case "2", "?", "二", "?":
 7     possibleIntegerValue = 2
 8 case "3", "?", "三", "?":
 9     possibleIntegerValue = 3
10 case "4", "?", "四", "?":
11     possibleIntegerValue = 4
12 default:
13     break
14 }
15 if let integerValue = possibleIntegerValue {
16     print("The integer value of \(numberSymbol) is \(integerValue).")
17 } else {
18     print("An integer value could not be found for \(numberSymbol).")
19 }
20 // prints "The integer value of 三 is 3."

 1 let integerToDescribe = 5
 2 var description = "The number \(integerToDescribe) is"
 3 switch integerToDescribe {
 4 case 2, 3, 5, 7, 11, 13, 17, 19:
 5     description += " a prime number, and also"
 6     fallthrough
 7 default:
 8     description += " an integer."
 9 }
10 print(description)
11 // prints "The number 5 is a prime number, and also an integer."

 1 gameLoop: while square != finalSquare {
 2     if ++diceRoll == 7 { diceRoll = 1 }
 3     switch square + diceRoll {
 4     case finalSquare:
 5         // 到达最后一个方块，游戏结束
 6         break gameLoop
 7     case let newSquare where newSquare > finalSquare:
 8         // 超出最后一个方块，再掷一次骰子
 9         continue gameLoop
10     default:
11         // 本次移动有效
12         square += diceRoll
13         square += board[square]
14     }
15 }
16 print("Game over!")

 1 func greet(person: [String: String]) {
 2     guard let name = person["name"] else {
 3         return
 4     }
 5     
 6     print("Hello \(name)!")
 7     
 8     guard let location = person["location"] else {
 9         print("I hope the weather is nice near you.")
10         return
11     }
12     
13     print("I hope the weather is nice in \(location).")
14 }
15  
16 greet(["name": "John"])
17 // prints "Hello John!"
18 // prints "I hope the weather is nice near you."
19 greet(["name": "Jane", "location": "Cupertino"])
20 // prints "Hello Jane!"
21 // prints "I hope the weather is nice in Cupertino."

1 if #available(iOS 9, OSX 10.10, *) {
2     // Use iOS 9 APIs on iOS, and use OS X v10.10 APIs on OS X
3 } else {
4     // Fall back to earlier iOS and OS X APIs
5 }

1 if #available(platform name version, ..., *) {
2     statements to execute if the APIs are available
3 } else {
4     fallback statements to execute if the APIs are unavailable
5 }