标签：style http io ar color os 使用 sp for
控制流基本上大同小异，在此列举几个比较有趣的地方。
文档原文是 No Implicit Fallthrough ，粗暴的翻译一下就是：不存在隐式贯穿。其中 Implicit 是一个经常出现的词，中文原意是：“含蓄的，暗示的，隐蓄的”。在 Swift 中通常表示默认处理。比如这里的隐式贯穿，就是指传统的多个case 如果没有 break 就会从上穿到底的情况。再例如 implicitly unwrapped optionals ，隐式解析可选类型，则是默认会进行解包操作不用手动通过 ! 进行解包。
回到 switch 的问题，看下下面这段代码：
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a":
println("The letter a")
case "A":
println("The letter A")
default:
println("Not the letter A")
}
可以看到虽然匹配到了 case "a" 的情况，但是在当前 case 结束之后便直接跳出，没有继续往下执行。如果想继续贯穿到下面的 case 可以通过 fallthrough 实现。
我们可以在 switch 中使用元祖 (tuple) 进行匹配。用 _ 表示所有值。比如下面这个例子，判断坐标属于什么区域：
let somePoint = (1, 1)
switch somePoint {
case (0, 0): // 位于远点
println("(0, 0) is at the origin")
case (_, 0): // x为任意值，y为0，即在 X 轴上
println("(\(somePoint.0), 0) is on the x-axis")
case (0, _): // y为任意值，x为0，即在 Y 轴上
println("(0, \(somePoint.1)) is on the y-axis")
case (-2...2, -2...2): // 在以原点为中心，边长为4的正方形内。
println("(\(somePoint.0), \(somePoint.1)) is inside the box")
default:
println("(\(somePoint.0), \(somePoint.1)) is outside of the box")
}
// "(1, 1) is inside the box"
如果想在 case 中用这个值，那么可以用过值绑定 (value bindings) 解决：
let somePoint = (0, 1)
switch somePoint {
case (0, 0):
println("(0, 0) is at the origin")
case (let x, 0):
println("x is \(x)")
case (0, let y):
println("y is \(y)")
default:
println("default")
}
case 中可以通过 where 对参数进行匹配。比如我们想打印 y=x 或者 y=-x这种45度仰望的情况，以前是通过 if 解决，现在可以用 switch 搞起：
let yetAnotherPoint = (1, -1)
switch yetAnotherPoint {
case let (x, y) where x == y:
println("(\(x), \(y)) is on the line x == y")
case let (x, y) where x == -y:
println("(\(x), \(y)) is on the line x == -y")
case let (x, y):
println("(\(x), \(y)) is just some arbitrary point")
}
// "(1, -1) is on the line x == -y”
Swift 有四个控制转移状态：
看到一个有趣的东西：Swift Cheat Sheet，里面是纯粹的代码片段，如果突然短路忘了语法可以来看看。
比如 Control Flow 部分，有如下代码，基本覆盖了所有的点：
// for loop (array)
let myArray = [1, 1, 2, 3, 5]
for value in myArray {
if value == 1 {
println("One!")
} else {
println("Not one!")
}
}
// for loop (dictionary)
var dict = [
"name": "Steve Jobs",
"title": "CEO",
"company": "Apple"
]
for (key, value) in dict {
println("\(key): \(value)")
}
// for loop (range)
for i in -1...1 { // [-1, 0, 1]
println(i)
}
// use .. to exclude the last number
// for loop (ignoring the current value of the range on each iteration of the loop)
for _ in 1...3 {
// Do something three times.
}
// while loop
var i = 1
while i < 1000 {
i *= 2
}
// do-while loop
do {
println("hello")
} while 1 == 2
// Switch
let vegetable = "red pepper"
switch vegetable {
case "celery":
let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
let vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
let vegetableComment = "Is it a spicy \(x)?"
default: // required (in order to cover all possible input)
let vegetableComment = "Everything tastes good in soup."
}
// Switch to validate plist content
let city:Dictionary<String, AnyObject> = [
"name" : "Qingdao",
"population" : 2_721_000,
"abbr" : "QD"
]
switch (city["name"], city["population"], city["abbr"]) {
case (.Some(let cityName as NSString),
.Some(let pop as NSNumber),
.Some(let abbr as NSString))
where abbr.length == 2:
println("City Name: \(cityName) | Abbr.:\(abbr) Population: \(pop)")
default:
println("Not a valid city")
}
标签：style http io ar color os 使用 sp for
原文地址：http://blog.csdn.net/pleasecallmewhy/article/details/41347391
