结论就是 swift 里 switch-case 不需要加大括号，也不用 break，case 和 case 之间会自动间隔。

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