Switch 语句

switch 语句会尝试把某个值与若干个模式（pattern）进行匹配。根据第一个匹配成功的模式，switch 语句会执行对应的代码块。

基本用法

switch 语句最简单的形式就是把一个值与一个或多个相同类型的值进行比较：

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")
}
// 输出 "The last letter of the alphabet"

区间匹配

switch 语句的 case 中可以匹配一个数值区间：

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).")
// 输出 "There are dozens of moons orbiting Saturn."