Swift--控制流与oc不同的地方

1.For-in循环中...

for index in 1...5 {

print("\(index) times 5 is \(index * 5)")

}

for _ in 1...5 {

可以用下划线忽略当前值

}

2.字典通过元祖返回

3.do while循环变成repeat

repeat {

statements

} while condition

4.switch不需要break

let someCharacter: Character = "z"

switch someCharacter {

case "a":

print("The first letter of the alphabet")

case "z":

print("The last letter of the alphabet")

default:

print("Some other character")

}

5.switch case的body不能为空

6.case可以带区间

let approximateCount = 62

let countedThings = "moons orbiting Saturn"

var naturalCount: String

switch approximateCount {

case 0:

naturalCount = "no"

case 1..<5:

naturalCount = "a few"

case 5..<12:

naturalCount = "several"

case 12..<100:

naturalCount = "dozens of"

case 100..<1000:

naturalCount = "hundreds of"

default:

naturalCount = "many"

}

print("There are \(naturalCount) \(countedThings).")

7.case的元祖表示

let somePoint = (1, 1)

switch somePoint {

case (0, 0):

print("(0, 0) is at the origin")

case (_, 0):

print("(\(somePoint.0), 0) is on the x-axis")

case (0, _):

print("(0, \(somePoint.1)) is on the y-axis")

case (-2...2, -2...2):

print("(\(somePoint.0), \(somePoint.1)) is inside the box")

default:

print("(\(somePoint.0), \(somePoint.1)) is outside of the box")

}

8.case加额外条件

let yetAnotherPoint = (1, -1)

switch yetAnotherPoint {

case let (x, y) where x == y:

print("(\(x), \(y)) is on the line x == y")

case let (x, y) where x == -y:

print("(\(x), \(y)) is on the line x == -y")

case let (x, y):

print("(\(x), \(y)) is just some arbitrary point")

}

9.case  fallthrough贯穿

fallthrough关键字不会检查它下一个将会落入执行的 case 中的匹配条件。fallthrough简单地使代码继续连接到下一个 case 中的代码

10.while加标签

gameLoop: while square != finalSquare {

diceRoll += 1

if diceRoll == 7 { diceRoll = 1 }

switch square + diceRoll {

case finalSquare:

// diceRoll will move us to the final square, so the game is over

break gameLoop

case let newSquare where newSquare > finalSquare:

// diceRoll will move us beyond the final square, so roll again

continue gameLoop

default:

// this is a valid move, so find out its effect

square += diceRoll

square += board[square]

}

}

print("Game over!")

11.guard与if的区别

像if语句一样，guard的执行取决于一个表达式的布尔值。我们可以使用guard语句来要求条件必须为真时，以执行guard语句后的代码。不同于if语句，一个guard语句总是有一个else从句，如果条件不为真则执行else从句中的代码。

guard let name = person["name"] else {

return

}

12.检测 API 可用性

Swift内置支持检查 API 可用性，这可以确保我们不会在当前部署机器上，不小心地使用了不可用的API。

if #available(iOS 10, macOS 10.12, *) {

// 在 iOS 使用 iOS 10 的 API, 在 macOS 使用 macOS 10.12 的 API

} else {

// 使用先前版本的 iOS 和 macOS 的 API

}

在它一般的形式中，可用性条件使用了一个平台名字和版本的列表。平台名字可以是iOS，macOS，watchOS和tvOS——请访问声明属性来获取完整列表。除了指定像 iOS 8的主板本号，我们可以指定像iOS 8.3 以及 macOS 10.10.3的子版本号。